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Sample records for motion artifacts caused

  1. Motion artifacts in computed tomography

    International Nuclear Information System (INIS)

    Yang, C.K.

    1979-01-01

    In the year 1972, the first Computed Tomography Scanner (or CT) was introduced and caused a revolution in the field of Diagnostic Radiology. A tomogram is a cross-sectional image of a three-dimensional object obtained through non-invasive measurements. The image that is presented is very similar to what would be seen if a thin cross-sectional slice of the patient was examined. In Computed Tomography, x-rays are passed through the body of a patient in many different directions and their attenuation is detected. By using some mathematical theorems, the attenuation information can be converted into the density of the patient along the x-ray path. Combined with modern sophisticated computer signal processing technology, a cross-sectional image can be generated and displayed on a TV monitor. Usually a good CT image relies on the patient not moving during the x-ray scanning. However, for some unconscious or severely ill patients, this is very difficult to achieve. Thus, the motion during the scan causes the so-called motion artifacts which distort the displayed image and sometimes these motion artifacts make diagnosis impossible. Today, to remove or avoid motion artifacts is one of the major efforts in developing new scanner systems. In this thesis, a better understanding of the motion artifacts problem in CT scaning is gained through computer simulations, real scanner experiments and theoretical analyses. The methods by which the distorted image can be improved are simulated also. In particular, it is assumed that perfect knowledge of the patient motion is known since this represents the theoretical limit on how well the distorted image can be improved

  2. Evaluation of scatter limitation correction: a new method of correcting photopenic artifacts caused by patient motion during whole-body PET/CT imaging.

    Science.gov (United States)

    Miwa, Kenta; Umeda, Takuro; Murata, Taisuke; Wagatsuma, Kei; Miyaji, Noriaki; Terauchi, Takashi; Koizumi, Mitsuru; Sasaki, Masayuki

    2016-02-01

    Overcorrection of scatter caused by patient motion during whole-body PET/computed tomography (CT) imaging can induce the appearance of photopenic artifacts in the PET images. The present study aimed to quantify the accuracy of scatter limitation correction (SLC) for eliminating photopenic artifacts. This study analyzed photopenic artifacts in (18)F-fluorodeoxyglucose ((18)F-FDG) PET/CT images acquired from 12 patients and from a National Electrical Manufacturers Association phantom with two peripheral plastic bottles that simulated the human body and arms, respectively. The phantom comprised a sphere (diameter, 10 or 37 mm) containing fluorine-18 solutions with target-to-background ratios of 2, 4, and 8. The plastic bottles were moved 10 cm posteriorly between CT and PET acquisitions. All PET data were reconstructed using model-based scatter correction (SC), no scatter correction (NSC), and SLC, and the presence or absence of artifacts on the PET images was visually evaluated. The SC and SLC images were also semiquantitatively evaluated using standardized uptake values (SUVs). Photopenic artifacts were not recognizable in any NSC and SLC image from all 12 patients in the clinical study. The SUVmax of mismatched SLC PET/CT images were almost equal to those of matched SC and SLC PET/CT images. Applying NSC and SLC substantially eliminated the photopenic artifacts on SC PET images in the phantom study. SLC improved the activity concentration of the sphere for all target-to-background ratios. The highest %errors of the 10 and 37-mm spheres were 93.3 and 58.3%, respectively, for mismatched SC, and 73.2 and 22.0%, respectively, for mismatched SLC. Photopenic artifacts caused by SC error induced by CT and PET image misalignment were corrected using SLC, indicating that this method is useful and practical for clinical qualitative and quantitative PET/CT assessment.

  3. Motion-induced dose artifacts in helical tomotherapy

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    Kim, Bryan; Chen, Jeff; Battista, Jerry [London Regional Cancer Program, London Health Sciences Centre, London, ON (Canada); Kron, Tomas [Peter MacCallum Cancer Center, Melbourne (Australia)], E-mail: bryan.kim@lhsc.on.ca

    2009-10-07

    Tumor motion is a particular concern for a complex treatment modality such as helical tomotherapy, where couch position, gantry rotation and MLC leaf opening all change with time. In the present study, we have investigated the impact of tumor motion for helical tomotherapy, which could result in three distinct motion-induced dose artifacts, namely (1) dose rounding, (2) dose rippling and (3) IMRT leaf opening asynchronization effect. Dose rounding and dose rippling effects have been previously described, while the IMRT leaf opening asynchronization effect is a newly discovered motion-induced dose artifact. Dose rounding is the penumbral widening of a delivered dose distribution near the edges of a target volume along the direction of tumor motion. Dose rippling is a series of periodic dose peaks and valleys observed within the target region along the direction of couch motion, due to an asynchronous interplay between the couch motion and the longitudinal component of tumor motion. The IMRT leaf opening asynchronization effect is caused by an asynchronous interplay between the temporal patterns of leaf openings and tumor motion. The characteristics of each dose artifact were investigated individually as functions of target motion amplitude and period for both non-IMRT and IMRT helical tomotherapy cases, through computer simulation modeling and experimental verification. The longitudinal dose profiles generated by the simulation program agreed with the experimental data within {+-}0.5% and {+-}1.5% inside the PTV region for the non-IMRT and IMRT cases, respectively. The dose rounding effect produced a penumbral increase up to 20.5 mm for peak-to-peak target motion amplitudes ranging from 1.0 cm to 5.0 cm. Maximum dose rippling magnitude of 25% was calculated, when the target motion period approached an unusually high value of 10 s. The IMRT leaf opening asynchronization effect produced dose differences ranging from -29% to 7% inside the PTV region. This information

  4. Investigating the possible effect of electrode support structure on motion artifact in wearable bioelectric signal monitoring.

    Science.gov (United States)

    Cömert, Alper; Hyttinen, Jari

    2015-05-15

    impedance change were caused by the electrode motion and contained the same frequency components as the applied electrode motion pattern. We found that stabilizing the skin around the electrode using an electrode structure that manages to successfully distribute the force and movement to an area beyond the borders of the electrical contact area reduces the motion artifact when compared to structures that are the same size as the electrode area.

  5. Adaptive cancellation of motion artifact in wearable biosensors.

    Science.gov (United States)

    Yousefi, Rasoul; Nourani, Mehrdad; Panahi, Issa

    2012-01-01

    The performance of wearable biosensors is highly influenced by motion artifact. In this paper, a model is proposed for analysis of motion artifact in wearable photoplethysmography (PPG) sensors. Using this model, we proposed a robust real-time technique to estimate fundamental frequency and generate a noise reference signal. A Least Mean Square (LMS) adaptive noise canceler is then designed and validated using our synthetic noise generator. The analysis and results on proposed technique for noise cancellation shows promising performance.

  6. Correction of computed tomography motion artifacts using pixel-specific back-projection

    International Nuclear Information System (INIS)

    Ritchie, C.J.; Crawford, C.R.; Godwin, J.D.; Kim, Y. King, K.F.

    1996-01-01

    Cardiac and respiratory motion can cause artifacts in computed tomography scans of the chest. The authors describe a new method for reducing these artifacts called pixel-specific back-projection (PSBP). PSBP reduces artifacts caused by in-plane motion by reconstructing each pixel in a frame of reference that moves with the in-plane motion in the volume being scanned. The motion of the frame of reference is specified by constructing maps that describe the motion of each pixel in the image at the time each projection was measured; these maps are based on measurements of the in-plane motion. PSBP has been tested in computer simulations and with volunteer data. In computer simulations, PSBP removed the structured artifacts caused by motion. In scans of two volunteers, PSBP reduced doubling and streaking in chest scans to a level that made the images clinically useful. PSBP corrections of liver scans were less satisfactory because the motion of the liver is predominantly superior-inferior (S-I). PSBP uses a unique set of motion parameters to describe the motion at each point in the chest as opposed to requiring that the motion be described by a single set of parameters. Therefore, PSBP may be more useful in correcting clinical scans than are other correction techniques previously described

  7. A systematic comparison of motion artifact correction techniques for functional near-infrared spectroscopy.

    Science.gov (United States)

    Cooper, Robert J; Selb, Juliette; Gagnon, Louis; Phillip, Dorte; Schytz, Henrik W; Iversen, Helle K; Ashina, Messoud; Boas, David A

    2012-01-01

    Near-infrared spectroscopy (NIRS) is susceptible to signal artifacts caused by relative motion between NIRS optical fibers and the scalp. These artifacts can be very damaging to the utility of functional NIRS, particularly in challenging subject groups where motion can be unavoidable. A number of approaches to the removal of motion artifacts from NIRS data have been suggested. In this paper we systematically compare the utility of a variety of published NIRS motion correction techniques using a simulated functional activation signal added to 20 real NIRS datasets which contain motion artifacts. Principle component analysis, spline interpolation, wavelet analysis, and Kalman filtering approaches are compared to one another and to standard approaches using the accuracy of the recovered, simulated hemodynamic response function (HRF). Each of the four motion correction techniques we tested yields a significant reduction in the mean-squared error (MSE) and significant increase in the contrast-to-noise ratio (CNR) of the recovered HRF when compared to no correction and compared to a process of rejecting motion-contaminated trials. Spline interpolation produces the largest average reduction in MSE (55%) while wavelet analysis produces the highest average increase in CNR (39%). On the basis of this analysis, we recommend the routine application of motion correction techniques (particularly spline interpolation or wavelet analysis) to minimize the impact of motion artifacts on functional NIRS data.

  8. Motion Artifact in the MR imaging of temporomandibular disorders

    International Nuclear Information System (INIS)

    Tamamura, Kiyoharu; Miyajima, Hisashi; Nihei, Yoshinobu; Nemoto, Ryuichi; Ohno, Tomoya

    1997-01-01

    Recently, magnetic resonance imaging (MRI) is indispensable for the diagnosis of temporomandibular disorders (TMD). Motion Artifacts of MRI occur more frequently than in other conventional methods, because it takes a long time to obtain the images. This paper reported on Motion Artifacts on MRI. MRI studies of 232 temporomandibular joints were performed in 116 patients with TMD by using a 0.5-T magnetic resonance (MR) scanner, with spin echo sequence: protondensity-weighted. And we took MRI slices at opening phase and closing phase. So 232 slices were gathered and we evaluated clinically the incidence of Motion Artifacts, that is to say, double and multiple images and other factors. The 103 slices in 56 patients showed Motion Artifacts. There is no significant difference between sexes. By age group, those in their teens were most frequent, followed by those in their fifties, forties, thirties and twenties. Also the same results were obtained for double image and multiple image. Incidence of Motion Artifact was most frequent at the opening phase. There is no significant difference between double and multiple image. (author)

  9. Two-dimensional analysis of motion artifacts, including flow effects

    International Nuclear Information System (INIS)

    Litt, A.M.; Brody, A.S.; Spangler, R.A.; Scott, P.D.

    1990-01-01

    The effects of motion on magnetic resonance images have been theoretically analyzed for the case of a point-like object in simple harmonic motion and for other one-dimensional trajectories. The authors of this paper extend this analysis to a generalized two-dimensional magnetization with an arbitrary motion trajectory. The authors provide specific solutions for the clinically relevant cases of the cross-sections of cylindrical objects in the body, such as the aorta, which has a roughly one-dimensional, simple harmonic motion during respiration. By extending the solution to include inhomogeneous magnetizations, the authors present a model which allows the effects of motion artifacts and flow artifacts to be analyzed simultaneously

  10. Temporal interpolation alters motion in fMRI scans: Magnitudes and consequences for artifact detection.

    Directory of Open Access Journals (Sweden)

    Jonathan D Power

    Full Text Available Head motion can be estimated at any point of fMRI image processing. Processing steps involving temporal interpolation (e.g., slice time correction or outlier replacement often precede motion estimation in the literature. From first principles it can be anticipated that temporal interpolation will alter head motion in a scan. Here we demonstrate this effect and its consequences in five large fMRI datasets. Estimated head motion was reduced by 10-50% or more following temporal interpolation, and reductions were often visible to the naked eye. Such reductions make the data seem to be of improved quality. Such reductions also degrade the sensitivity of analyses aimed at detecting motion-related artifact and can cause a dataset with artifact to falsely appear artifact-free. These reduced motion estimates will be particularly problematic for studies needing estimates of motion in time, such as studies of dynamics. Based on these findings, it is sensible to obtain motion estimates prior to any image processing (regardless of subsequent processing steps and the actual timing of motion correction procedures, which need not be changed. We also find that outlier replacement procedures change signals almost entirely during times of motion and therefore have notable similarities to motion-targeting censoring strategies (which withhold or replace signals entirely during times of motion.

  11. Negligible motion artifacts in scalp electroencephalography (EEG during treadmill walking

    Directory of Open Access Journals (Sweden)

    Kevin eNathan

    2016-01-01

    Full Text Available Recent Mobile Brain/Body Imaging (MoBI techniques based on active electrode scalp electroencephalogram (EEG allow the acquisition and real-time analysis of brain dynamics during active unrestrained motor behavior involving whole body movements such as treadmill walking, over-ground walking and other locomotive and non-locomotive tasks. Unfortunately, MoBI protocols are prone to physiological and non-physiological artifacts, including motion artifacts that may contaminate the EEG recordings. A few attempts have been made to quantify these artifacts during locomotion tasks but with inconclusive results due in part to methodological pitfalls. In this paper, we investigate the potential contributions of motion artifacts in scalp EEG during treadmill walking at three different speeds (1.5, 3.0, and 4.5 km/h using a wireless 64 channel active EEG system and a wireless inertial sensor attached to the subject’s head. The experimental setup was designed according to good measurement practices using state-of-the-art commercially-available instruments, and the measurements were analyzed using Fourier analysis and wavelet coherence approaches. Contrary to prior claims, the subjects’ motion did not significantly affect their EEG during treadmill walking although precaution should be taken when gait speeds approach 4.5 km/h. Overall, these findings suggest how MoBI methods may be safely deployed in neural, cognitive, and rehabilitation engineering applications.

  12. Motion Artifact Quantification and Sensor Fusion for Unobtrusive Health Monitoring

    Directory of Open Access Journals (Sweden)

    Christoph Hoog Antink

    2017-12-01

    Full Text Available Sensors integrated into objects of everyday life potentially allow unobtrusive health monitoring at home. However, since the coupling of sensors and subject is not as well-defined as compared to a clinical setting, the signal quality is much more variable and can be disturbed significantly by motion artifacts. One way of tackling this challenge is the combined evaluation of multiple channels via sensor fusion. For robust and accurate sensor fusion, analyzing the influence of motion on different modalities is crucial. In this work, a multimodal sensor setup integrated into an armchair is presented that combines capacitively coupled electrocardiography, reflective photoplethysmography, two high-frequency impedance sensors and two types of ballistocardiography sensors. To quantify motion artifacts, a motion protocol performed by healthy volunteers is recorded with a motion capture system, and reference sensors perform cardiorespiratory monitoring. The shape-based signal-to-noise ratio SNR S is introduced and used to quantify the effect on motion on different sensing modalities. Based on this analysis, an optimal combination of sensors and fusion methodology is developed and evaluated. Using the proposed approach, beat-to-beat heart-rate is estimated with a coverage of 99.5% and a mean absolute error of 7.9 ms on 425 min of data from seven volunteers in a proof-of-concept measurement scenario.

  13. Motion Artifact Quantification and Sensor Fusion for Unobtrusive Health Monitoring

    Science.gov (United States)

    Hoog Antink, Christoph; Schulz, Florian; Walter, Marian

    2017-01-01

    Sensors integrated into objects of everyday life potentially allow unobtrusive health monitoring at home. However, since the coupling of sensors and subject is not as well-defined as compared to a clinical setting, the signal quality is much more variable and can be disturbed significantly by motion artifacts. One way of tackling this challenge is the combined evaluation of multiple channels via sensor fusion. For robust and accurate sensor fusion, analyzing the influence of motion on different modalities is crucial. In this work, a multimodal sensor setup integrated into an armchair is presented that combines capacitively coupled electrocardiography, reflective photoplethysmography, two high-frequency impedance sensors and two types of ballistocardiography sensors. To quantify motion artifacts, a motion protocol performed by healthy volunteers is recorded with a motion capture system, and reference sensors perform cardiorespiratory monitoring. The shape-based signal-to-noise ratio SNRS is introduced and used to quantify the effect on motion on different sensing modalities. Based on this analysis, an optimal combination of sensors and fusion methodology is developed and evaluated. Using the proposed approach, beat-to-beat heart-rate is estimated with a coverage of 99.5% and a mean absolute error of 7.9 ms on 425 min of data from seven volunteers in a proof-of-concept measurement scenario. PMID:29295594

  14. Motion Artifact Quantification and Sensor Fusion for Unobtrusive Health Monitoring.

    Science.gov (United States)

    Hoog Antink, Christoph; Schulz, Florian; Leonhardt, Steffen; Walter, Marian

    2017-12-25

    Sensors integrated into objects of everyday life potentially allow unobtrusive health monitoring at home. However, since the coupling of sensors and subject is not as well-defined as compared to a clinical setting, the signal quality is much more variable and can be disturbed significantly by motion artifacts. One way of tackling this challenge is the combined evaluation of multiple channels via sensor fusion. For robust and accurate sensor fusion, analyzing the influence of motion on different modalities is crucial. In this work, a multimodal sensor setup integrated into an armchair is presented that combines capacitively coupled electrocardiography, reflective photoplethysmography, two high-frequency impedance sensors and two types of ballistocardiography sensors. To quantify motion artifacts, a motion protocol performed by healthy volunteers is recorded with a motion capture system, and reference sensors perform cardiorespiratory monitoring. The shape-based signal-to-noise ratio SNR S is introduced and used to quantify the effect on motion on different sensing modalities. Based on this analysis, an optimal combination of sensors and fusion methodology is developed and evaluated. Using the proposed approach, beat-to-beat heart-rate is estimated with a coverage of 99.5% and a mean absolute error of 7.9 ms on 425 min of data from seven volunteers in a proof-of-concept measurement scenario.

  15. Correcting for motion artifact in handheld laser speckle images

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    Lertsakdadet, Ben; Yang, Bruce Y.; Dunn, Cody E.; Ponticorvo, Adrien; Crouzet, Christian; Bernal, Nicole; Durkin, Anthony J.; Choi, Bernard

    2018-03-01

    Laser speckle imaging (LSI) is a wide-field optical technique that enables superficial blood flow quantification. LSI is normally performed in a mounted configuration to decrease the likelihood of motion artifact. However, mounted LSI systems are cumbersome and difficult to transport quickly in a clinical setting for which portability is essential in providing bedside patient care. To address this issue, we created a handheld LSI device using scientific grade components. To account for motion artifact of the LSI device used in a handheld setup, we incorporated a fiducial marker (FM) into our imaging protocol and determined the difference between highest and lowest speckle contrast values for the FM within each data set (Kbest and Kworst). The difference between Kbest and Kworst in mounted and handheld setups was 8% and 52%, respectively, thereby reinforcing the need for motion artifact quantification. When using a threshold FM speckle contrast value (KFM) to identify a subset of images with an acceptable level of motion artifact, mounted and handheld LSI measurements of speckle contrast of a flow region (KFLOW) in in vitro flow phantom experiments differed by 8%. Without the use of the FM, mounted and handheld KFLOW values differed by 20%. To further validate our handheld LSI device, we compared mounted and handheld data from an in vivo porcine burn model of superficial and full thickness burns. The speckle contrast within the burn region (KBURN) of the mounted and handheld LSI data differed by burns. Collectively, our results suggest the potential of handheld LSI with an FM as a suitable alternative to mounted LSI, especially in challenging clinical settings with space limitations such as the intensive care unit.

  16. MuSeSe - A multisensor armchair for unobtrusive vital sign estimation and motion artifact analysis.

    Science.gov (United States)

    Antink, Christoph Hoog; Leonhardt, Steffen; Schulz, Florian; Walter, Marian

    2017-07-01

    Unobtrusive vital sign estimation with sensors integrated into objects of everyday living can substantially advance the field of remote monitoring. At the same time, motion artifacts cause severe problems and have to be dealt with. Here, the fusion of multimodal sensor data is a promising approach. In this paper, we present an armchair equipped with capacitively coupled electrocardiogram, two types of ballistocardiographic sensors, photoplethysmographic and two high-frequency impedance sensors. In addition, a video-based sensor for motion analysis is integrated. Using a defined motion protocol, the feasibility of the system is demonstrated in a self-experimentation. Moreover, the influence of different movements on different modalities is analyzed. Finally, robust beat-to-beat interval estimation demonstrates the benefits of multimodal sensor fusion for vital sign estimation in the presence of motion artifacts.

  17. Aggregated particles caused by instrument artifact

    Science.gov (United States)

    Pierce, Ashley M.; Loría-Salazar, S. Marcela; Arnott, W. Patrick; Edwards, Grant C.; Miller, Matthieu B.; Gustin, Mae S.

    2018-04-01

    Previous studies have indicated that superaggregates, clusters of aggregates of soot primary particles, can be formed in large-scale turbulent fires. Due to lower effective densities, higher porosity, and lower aerodynamic diameters, superaggregates may pass through inlets designed to remove particles 2.5 µm in aerodynamic diameter were collected on 36 out of 158 sample days. On preliminary analysis, it was thought that these aggregated particles were superaggregates, depositing past PM10 (particles wind speeds, as well as the use of generators on site. Samples with aggregated particles, referred to as aggregates, were analyzed using a scanning electron microscope for size and shape and energy dispersive X-ray spectroscopy was used for elemental analysis. It was determined, based on the high amounts of aluminum present in the aggregate samples, that a sampling artifact associated with the sample inlet and prolonged, high wind events was the probable reason for the observed aggregates.

  18. Aggregated particles caused by instrument artifact

    Directory of Open Access Journals (Sweden)

    A. M. Pierce

    2018-04-01

    Full Text Available Previous studies have indicated that superaggregates, clusters of aggregates of soot primary particles, can be formed in large-scale turbulent fires. Due to lower effective densities, higher porosity, and lower aerodynamic diameters, superaggregates may pass through inlets designed to remove particles  <  2.5 µm in aerodynamic diameter (PM2.5. Ambient particulate matter samples were collected at Peavine Peak, NV, USA (2515 m northwest of Reno, NV, USA from June to November 2014. The Teledyne Advanced Pollution Instrumentation (TAPI 602 BetaPlus particulate monitor was used to collect PM2.5 on two filter types. During this time, aggregated particles  >  2.5 µm in aerodynamic diameter were collected on 36 out of 158 sample days. On preliminary analysis, it was thought that these aggregated particles were superaggregates, depositing past PM10 (particles  <  10 µm in aerodynamic diameter pre-impactors and PM2.5 cyclones. However, further analysis revealed that these aggregated particles were dissimilar to superaggregates observed in previous studies, both in morphology and in elemental composition. To determine if the aggregated particles were superaggregates or an instrument artifact, samples were investigated for the presence of certain elements, the occurrence of fires, high relative humidity and wind speeds, as well as the use of generators on site. Samples with aggregated particles, referred to as aggregates, were analyzed using a scanning electron microscope for size and shape and energy dispersive X-ray spectroscopy was used for elemental analysis. It was determined, based on the high amounts of aluminum present in the aggregate samples, that a sampling artifact associated with the sample inlet and prolonged, high wind events was the probable reason for the observed aggregates.

  19. The relation between respiratory motion artifact correction and lung standardized uptake value

    International Nuclear Information System (INIS)

    Yin Lijie; Liu Xiaojian; Liu Jie; Xu Rui; Yan Jue

    2014-01-01

    PET/CT is playing an important role in disease diagnosis and therapeutic evaluation. But the respiratory motion artifact may bring trouble in diagnosis and therapy. There are many methods to correct the respiratory motion artifact. Respiratory gated PET/CT is applied most extensively of them. Using respiratory gated PET/CT to correct respiratory motion artifact can increase the maximum standardized uptake value of lung lesion obviously, thereby improving the quality of image and accuracy of diagnosis. (authors)

  20. Nuclear magnetic resonance method and apparatus for reducing motion artifacts

    International Nuclear Information System (INIS)

    Bailes, D.R.

    1988-01-01

    A nuclear magnetic resonance apparatus for imaging a region of a body in which part of the region is moving with a motion such that its displacement with respect to time is a nonmonotonic function during a time period over which a plurality of NMR data signals, which together define an image, are collected. The apparatus is described comprising: excitation means arranged to excite nuclear magnetic spins preferentially in the region; encoding means arranged to encode the magnetic spins; data collection means arranged to collect data signals representative of encoded magnetic spins; display means responsive to collected data signals to display an image of the region; measuring means arranged to produce an output indicative of the displacement of the moving part of the region; and control means for controlling the encoding means during the time period in dependence on the output of the measuring means so that data signals collected during the time period are collected in an order dependent on the motion such that motion artifacts are reduced

  1. Photoplethysmograph signal reconstruction based on a novel motion artifact detection-reduction approach. Part II: Motion and noise artifact removal.

    Science.gov (United States)

    Salehizadeh, S M A; Dao, Duy K; Chong, Jo Woon; McManus, David; Darling, Chad; Mendelson, Yitzhak; Chon, Ki H

    2014-11-01

    We introduce a new method to reconstruct motion and noise artifact (MNA) contaminated photoplethysmogram (PPG) data. A method to detect MNA corrupted data is provided in a companion paper. Our reconstruction algorithm is based on an iterative motion artifact removal (IMAR) approach, which utilizes the singular spectral analysis algorithm to remove MNA artifacts so that the most accurate estimates of uncorrupted heart rates (HRs) and arterial oxygen saturation (SpO2) values recorded by a pulse oximeter can be derived. Using both computer simulations and three different experimental data sets, we show that the proposed IMAR approach can reliably reconstruct MNA corrupted data segments, as the estimated HR and SpO2 values do not significantly deviate from the uncorrupted reference measurements. Comparison of the accuracy of reconstruction of the MNA corrupted data segments between our IMAR approach and the time-domain independent component analysis (TD-ICA) is made for all data sets as the latter method has been shown to provide good performance. For simulated data, there were no significant differences in the reconstructed HR and SpO2 values starting from 10 dB down to -15 dB for both white and colored noise contaminated PPG data using IMAR; for TD-ICA, significant differences were observed starting at 10 dB. Two experimental PPG data sets were created with contrived MNA by having subjects perform random forehead and rapid side-to-side finger movements show that; the performance of the IMAR approach on these data sets was quite accurate as non-significant differences in the reconstructed HR and SpO2 were found compared to non-contaminated reference values, in most subjects. In comparison, the accuracy of the TD-ICA was poor as there were significant differences in reconstructed HR and SpO2 values in most subjects. For non-contrived MNA corrupted PPG data, which were collected with subjects performing walking and stair climbing tasks, the IMAR significantly

  2. Motion artifacts in functional near-infrared spectroscopy: a comparison of motion correction techniques applied to real cognitive data

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    Brigadoi, Sabrina; Ceccherini, Lisa; Cutini, Simone; Scarpa, Fabio; Scatturin, Pietro; Selb, Juliette; Gagnon, Louis; Boas, David A.; Cooper, Robert J.

    2013-01-01

    Motion artifacts are a significant source of noise in many functional near-infrared spectroscopy (fNIRS) experiments. Despite this, there is no well-established method for their removal. Instead, functional trials of fNIRS data containing a motion artifact are often rejected completely. However, in most experimental circumstances the number of trials is limited, and multiple motion artifacts are common, particularly in challenging populations. Many methods have been proposed recently to correct for motion artifacts, including principle component analysis, spline interpolation, Kalman filtering, wavelet filtering and correlation-based signal improvement. The performance of different techniques has been often compared in simulations, but only rarely has it been assessed on real functional data. Here, we compare the performance of these motion correction techniques on real functional data acquired during a cognitive task, which required the participant to speak aloud, leading to a low-frequency, low-amplitude motion artifact that is correlated with the hemodynamic response. To compare the efficacy of these methods, objective metrics related to the physiology of the hemodynamic response have been derived. Our results show that it is always better to correct for motion artifacts than reject trials, and that wavelet filtering is the most effective approach to correcting this type of artifact, reducing the area under the curve where the artifact is present in 93% of the cases. Our results therefore support previous studies that have shown wavelet filtering to be the most promising and powerful technique for the correction of motion artifacts in fNIRS data. The analyses performed here can serve as a guide for others to objectively test the impact of different motion correction algorithms and therefore select the most appropriate for the analysis of their own fNIRS experiment. PMID:23639260

  3. TARGETED PRINCIPLE COMPONENT ANALYSIS: A NEW MOTION ARTIFACT CORRECTION APPROACH FOR NEAR-INFRARED SPECTROSCOPY.

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    Yücel, Meryem A; Selb, Juliette; Cooper, Robert J; Boas, David A

    2014-03-01

    As near-infrared spectroscopy (NIRS) broadens its application area to different age and disease groups, motion artifacts in the NIRS signal due to subject movement is becoming an important challenge. Motion artifacts generally produce signal fluctuations that are larger than physiological NIRS signals, thus it is crucial to correct for them before obtaining an estimate of stimulus evoked hemodynamic responses. There are various methods for correction such as principle component analysis (PCA), wavelet-based filtering and spline interpolation. Here, we introduce a new approach to motion artifact correction, targeted principle component analysis (tPCA), which incorporates a PCA filter only on the segments of data identified as motion artifacts. It is expected that this will overcome the issues of filtering desired signals that plagues standard PCA filtering of entire data sets. We compared the new approach with the most effective motion artifact correction algorithms on a set of data acquired simultaneously with a collodion-fixed probe (low motion artifact content) and a standard Velcro probe (high motion artifact content). Our results show that tPCA gives statistically better results in recovering hemodynamic response function (HRF) as compared to wavelet-based filtering and spline interpolation for the Velcro probe. It results in a significant reduction in mean-squared error (MSE) and significant enhancement in Pearson's correlation coefficient to the true HRF. The collodion-fixed fiber probe with no motion correction performed better than the Velcro probe corrected for motion artifacts in terms of MSE and Pearson's correlation coefficient. Thus, if the experimental study permits, the use of a collodion-fixed fiber probe may be desirable. If the use of a collodion-fixed probe is not feasible, then we suggest the use of tPCA in the processing of motion artifact contaminated data.

  4. TARGETED PRINCIPLE COMPONENT ANALYSIS: A NEW MOTION ARTIFACT CORRECTION APPROACH FOR NEAR-INFRARED SPECTROSCOPY

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    YÜCEL, MERYEM A.; SELB, JULIETTE; COOPER, ROBERT J.; BOAS, DAVID A.

    2014-01-01

    As near-infrared spectroscopy (NIRS) broadens its application area to different age and disease groups, motion artifacts in the NIRS signal due to subject movement is becoming an important challenge. Motion artifacts generally produce signal fluctuations that are larger than physiological NIRS signals, thus it is crucial to correct for them before obtaining an estimate of stimulus evoked hemodynamic responses. There are various methods for correction such as principle component analysis (PCA), wavelet-based filtering and spline interpolation. Here, we introduce a new approach to motion artifact correction, targeted principle component analysis (tPCA), which incorporates a PCA filter only on the segments of data identified as motion artifacts. It is expected that this will overcome the issues of filtering desired signals that plagues standard PCA filtering of entire data sets. We compared the new approach with the most effective motion artifact correction algorithms on a set of data acquired simultaneously with a collodion-fixed probe (low motion artifact content) and a standard Velcro probe (high motion artifact content). Our results show that tPCA gives statistically better results in recovering hemodynamic response function (HRF) as compared to wavelet-based filtering and spline interpolation for the Velcro probe. It results in a significant reduction in mean-squared error (MSE) and significant enhancement in Pearson’s correlation coefficient to the true HRF. The collodion-fixed fiber probe with no motion correction performed better than the Velcro probe corrected for motion artifacts in terms of MSE and Pearson’s correlation coefficient. Thus, if the experimental study permits, the use of a collodion-fixed fiber probe may be desirable. If the use of a collodion-fixed probe is not feasible, then we suggest the use of tPCA in the processing of motion artifact contaminated data. PMID:25360181

  5. Reduction of motion artifacts for PET imaging by respiratory correlated dynamic scanning

    International Nuclear Information System (INIS)

    Chuang, K.-S.; Chen, T.-J.; Chang, C.-C.; Wu, J.; Chen, S.; Wu, L.-C.; Liu, R.-S.

    2006-01-01

    Organ motion caused by respiration is a major challenge in positron emission tomography (PET) imaging. This work proposes a technique to reduce smearing in PET imaging caused by respiratory motion. Dynamic scanning at 1 frame/s is used. A point source, used as a marker, is attached to the object's abdomen during the scan. The source position in the projection view moves with respiratory motion and can be used to represent the respiratory phase within the time interval in which each frame data are acquired. One hundred and twenty frames are obtained for each study. The range of the positions of the marker is divided into four groups, representing different respiratory phases. The frames in which the organ positions (phases) are the same summed to produce a static sub-sinogram. Each sub-sinogram then undergoes regular image reconstruction to yield a motion-free image. The technique is applied to one volunteer under both free and coached breathing conditions. A parameter called the volume reduction factor is adopted to evaluate the effectiveness of this motion-reduction technique. The preliminary results indicate that the proposed technique effectively reduces motion artifacts in the image. Coached breathing yields better results than free breathing condition. The advantages of this method are that (1) the scanning time remains the same; (2) free breathing is allowed during the acquisition of the image; and (3) no user intervention is required

  6. A robust post-processing workflow for datasets with motion artifacts in diffusion kurtosis imaging.

    Science.gov (United States)

    Li, Xianjun; Yang, Jian; Gao, Jie; Luo, Xue; Zhou, Zhenyu; Hu, Yajie; Wu, Ed X; Wan, Mingxi

    2014-01-01

    The aim of this study was to develop a robust post-processing workflow for motion-corrupted datasets in diffusion kurtosis imaging (DKI). The proposed workflow consisted of brain extraction, rigid registration, distortion correction, artifacts rejection, spatial smoothing and tensor estimation. Rigid registration was utilized to correct misalignments. Motion artifacts were rejected by using local Pearson correlation coefficient (LPCC). The performance of LPCC in characterizing relative differences between artifacts and artifact-free images was compared with that of the conventional correlation coefficient in 10 randomly selected DKI datasets. The influence of rejected artifacts with information of gradient directions and b values for the parameter estimation was investigated by using mean square error (MSE). The variance of noise was used as the criterion for MSEs. The clinical practicality of the proposed workflow was evaluated by the image quality and measurements in regions of interest on 36 DKI datasets, including 18 artifact-free (18 pediatric subjects) and 18 motion-corrupted datasets (15 pediatric subjects and 3 essential tremor patients). The relative difference between artifacts and artifact-free images calculated by LPCC was larger than that of the conventional correlation coefficient (pworkflow improved the image quality and reduced the measurement biases significantly on motion-corrupted datasets (pworkflow was reliable to improve the image quality and the measurement precision of the derived parameters on motion-corrupted DKI datasets. The workflow provided an effective post-processing method for clinical applications of DKI in subjects with involuntary movements.

  7. Induction and separation of motion artifacts in EEG data using a mobile phantom head device.

    Science.gov (United States)

    Oliveira, Anderson S; Schlink, Bryan R; Hairston, W David; König, Peter; Ferris, Daniel P

    2016-06-01

    Electroencephalography (EEG) can assess brain activity during whole-body motion in humans but head motion can induce artifacts that obfuscate electrocortical signals. Definitive solutions for removing motion artifact from EEG have yet to be found, so creating methods to assess signal processing routines for removing motion artifact are needed. We present a novel method for investigating the influence of head motion on EEG recordings as well as for assessing the efficacy of signal processing approaches intended to remove motion artifact. We used a phantom head device to mimic electrical properties of the human head with three controlled dipolar sources of electrical activity embedded in the phantom. We induced sinusoidal vertical motions on the phantom head using a custom-built platform and recorded EEG signals with three different acquisition systems while the head was both stationary and in varied motion conditions. Recordings showed up to 80% reductions in signal-to-noise ratio (SNR) and up to 3600% increases in the power spectrum as a function of motion amplitude and frequency. Independent component analysis (ICA) successfully isolated the three dipolar sources across all conditions and systems. There was a high correlation (r > 0.85) and marginal increase in the independent components' (ICs) power spectrum (∼15%) when comparing stationary and motion parameters. The SNR of the IC activation was 400%-700% higher in comparison to the channel data SNR, attenuating the effects of motion on SNR. Our results suggest that the phantom head and motion platform can be used to assess motion artifact removal algorithms and compare different EEG systems for motion artifact sensitivity. In addition, ICA is effective in isolating target electrocortical events and marginally improving SNR in relation to stationary recordings.

  8. Transient severe respiratory motion artifacts after application of gadoxetate disodium. What we currently know

    International Nuclear Information System (INIS)

    Well, Lennart; Weinrich, Julius Matthias; Adam, Gerhard; Bannas, Peter

    2018-01-01

    Gadoxetate disodium is an intracellular contrast agent for magnetic resonance imaging (MRI) of the liver. Recent publications revealed that injection of gadoxetate disodium can lead to imaging artifacts due to transient severe motion (TSM) in the arterial phase of contrast-enhanced liver MRI. In this review we present and discuss published frequencies of TSM, contrast injection and image acquisition protocols, potential risk factors, and proposed strategies to avoid or minimize the effects of TSM. Two reviewers independently searched the PubMed search engine for ''transient severe motion artifact'' and related terms. Reference lists of retrieved articles were also searched. The two reviewers selected in consensus nine studies that reported both frequencies of TSM and potential risk factors. Study data were extracted by both reviewers, and disagreement was resolved by consensus. TSM is caused by impaired breath-hold ability after gadoxetate disodium injection and occurs in 5 -22% of patients. The dose of applied contrast agent, repeated exposure to gadoxetate disodium, high BMI and pulmonary disease have been described as potential risk factors for TSM. However, there are only few concordant results on this topic and the pathophysiology of TSM has not been identified. Proposed strategies for the prevention of TSM are slow injection rates and low doses of diluted gadoxetate disodium. Accelerated and free-breathing MRI sequence protocols and breath-hold training may minimize the effects of TSM. Further prospective studies are needed to confirm these strategies and to identify the underlying mechanism of TSM.

  9. Transient severe respiratory motion artifacts after application of gadoxetate disodium. What we currently know

    Energy Technology Data Exchange (ETDEWEB)

    Well, Lennart; Weinrich, Julius Matthias; Adam, Gerhard; Bannas, Peter [Univ. Medical Center Hamburg-Eppendorf, Hamburg (Germany). Dept. of Diagnostic and Interventional Radiology and Nuclear Medicince

    2018-01-15

    Gadoxetate disodium is an intracellular contrast agent for magnetic resonance imaging (MRI) of the liver. Recent publications revealed that injection of gadoxetate disodium can lead to imaging artifacts due to transient severe motion (TSM) in the arterial phase of contrast-enhanced liver MRI. In this review we present and discuss published frequencies of TSM, contrast injection and image acquisition protocols, potential risk factors, and proposed strategies to avoid or minimize the effects of TSM. Two reviewers independently searched the PubMed search engine for ''transient severe motion artifact'' and related terms. Reference lists of retrieved articles were also searched. The two reviewers selected in consensus nine studies that reported both frequencies of TSM and potential risk factors. Study data were extracted by both reviewers, and disagreement was resolved by consensus. TSM is caused by impaired breath-hold ability after gadoxetate disodium injection and occurs in 5 -22% of patients. The dose of applied contrast agent, repeated exposure to gadoxetate disodium, high BMI and pulmonary disease have been described as potential risk factors for TSM. However, there are only few concordant results on this topic and the pathophysiology of TSM has not been identified. Proposed strategies for the prevention of TSM are slow injection rates and low doses of diluted gadoxetate disodium. Accelerated and free-breathing MRI sequence protocols and breath-hold training may minimize the effects of TSM. Further prospective studies are needed to confirm these strategies and to identify the underlying mechanism of TSM.

  10. Improving pulse oximetry accuracy by removing motion artifacts from photoplethysmograms using relative sensor motion: a preliminary study

    NARCIS (Netherlands)

    Wijshoff, R.W.C.G.R.; Mischi, M.; Woerlee, P.H.; Aarts, R.M.; Van Huffel, S.; Naelaers, G.; Caicedo, A.; Bruley, D.F.; Harrison, D.K.

    2013-01-01

    To expand applicability of pulse oximetry in low-acuity ambulatory settings, the impact of motion on extracted parameters as saturation (SpO2) and pulse rate (PR) needs to be reduced. We hypothesized that sensor motion relative to the skin can be used as an artifact reference in a correlation

  11. Characterization and reduction of motion artifacts in photoplethysmographic signals from a wrist-worn device

    NARCIS (Netherlands)

    Tauţan, A.M.; Young, A.; Wentink, E.; Wieringa, F.P.

    2015-01-01

    Methods for analyzing various motion artifacts in photoplethysmography (PPG) signals, recorded by a wristworn device are reported. The analysis looks both at intrinsic PPG signal properties, through standard deviation, skew and kurtosis, but also at its relationship to five possible motion reference

  12. Real-Time Correction By Optical Tracking with Integrated Geometric Distortion Correction for Reducing Motion Artifacts in fMRI

    Science.gov (United States)

    Rotenberg, David J.

    Artifacts caused by head motion are a substantial source of error in fMRI that limits its use in neuroscience research and clinical settings. Real-time scan-plane correction by optical tracking has been shown to correct slice misalignment and non-linear spin-history artifacts, however residual artifacts due to dynamic magnetic field non-uniformity may remain in the data. A recently developed correction technique, PLACE, can correct for absolute geometric distortion using the complex image data from two EPI images, with slightly shifted k-space trajectories. We present a correction approach that integrates PLACE into a real-time scan-plane update system by optical tracking, applied to a tissue-equivalent phantom undergoing complex motion and an fMRI finger tapping experiment with overt head motion to induce dynamic field non-uniformity. Experiments suggest that including volume by volume geometric distortion correction by PLACE can suppress dynamic geometric distortion artifacts in a phantom and in vivo and provide more robust activation maps.

  13. Identification of a unique cause of ring artifact seen in computed tomography trans-axial images

    International Nuclear Information System (INIS)

    Jha, Ashish Kumar; Purandare, Nilendu C; Shah, Sneha; Agrawal, Archi; Puranik, Ameya D; Rangarajan, Venkatesh

    2013-01-01

    Artifacts present in computed tomography (CT) image often degrade the image quality and ultimately, the diagnostic outcome. Ring artifact in trans-axial image is caused by either miscalibrated or defective detector element of detector row, which is often categorized as scanner based artifact. A ring artifact detected on trans-axial CT image of positron emission tomography/computed tomography (PET/CT), was caused by contamination of CT tube aperture by droplet of injectable contrast medium. This artifact was corrected by removal of contrast droplet from CT tube aperture. The ring artifact is a very common artifact, commonly cited in the literature. Our case puts forward an uncommon cause of this artifact and its method of correction, which also, has no mention in the existing literature

  14. The reduction of motion artifacts in digital subtraction angiography by geometrical image transformation

    International Nuclear Information System (INIS)

    Fitzpatrick, J.M.; Pickens, D.R.; Mandava, V.R.; Grefenstette, J.J.

    1988-01-01

    In the diagnosis of arteriosclerosis, radio-opaque dye is injected into the interior of the arteries to make them visible. Because of its increased contrast sensitivity, digital subtraction angiography has the potential for providing diagnostic images of arteries with reduced dye volumes. In the conventional technique, a mask image, acquired before the introduction of the dye, is subtracted from the contrast image, acquired after the dye is introduced, to produce a difference image in which only the dye in the arteries is visible. The usefulness of this technique has been severely limited by the image degradation caused by patient motion during image acquisition. This motion produces artifacts in the difference image that obscure the arteries. One technique for dealing with the problem is to reduce the degradation by means of image registration. The registration is carried out by means of a geometrical transformation of the mask image before subtraction so that it is in registration with the contrast image. This paper describes a technique for determining an optimal transformation. The authors employ a one-to-one elastic mapping and the Jacobian of that mapping to produce a geometrical image transformation. They choose a parameterized class of such mappings and use a heuristic search algorithm to optimize the parameters to minimize the severity of the motion artifacts. To increase the speed of the optimization process they use a statistical image comparison technique that provides a quick approximate evaluation of each image transformation. They present the experimental results of the application of their registration system to mask-contrast pairs, for images acquired from a specially designed phantom, and for clinical images

  15. A wavelet method for modeling and despiking motion artifacts from resting-state fMRI time series

    Science.gov (United States)

    Patel, Ameera X.; Kundu, Prantik; Rubinov, Mikail; Jones, P. Simon; Vértes, Petra E.; Ersche, Karen D.; Suckling, John; Bullmore, Edward T.

    2014-01-01

    The impact of in-scanner head movement on functional magnetic resonance imaging (fMRI) signals has long been established as undesirable. These effects have been traditionally corrected by methods such as linear regression of head movement parameters. However, a number of recent independent studies have demonstrated that these techniques are insufficient to remove motion confounds, and that even small movements can spuriously bias estimates of functional connectivity. Here we propose a new data-driven, spatially-adaptive, wavelet-based method for identifying, modeling, and removing non-stationary events in fMRI time series, caused by head movement, without the need for data scrubbing. This method involves the addition of just one extra step, the Wavelet Despike, in standard pre-processing pipelines. With this method, we demonstrate robust removal of a range of different motion artifacts and motion-related biases including distance-dependent connectivity artifacts, at a group and single-subject level, using a range of previously published and new diagnostic measures. The Wavelet Despike is able to accommodate the substantial spatial and temporal heterogeneity of motion artifacts and can consequently remove a range of high and low frequency artifacts from fMRI time series, that may be linearly or non-linearly related to physical movements. Our methods are demonstrated by the analysis of three cohorts of resting-state fMRI data, including two high-motion datasets: a previously published dataset on children (N = 22) and a new dataset on adults with stimulant drug dependence (N = 40). We conclude that there is a real risk of motion-related bias in connectivity analysis of fMRI data, but that this risk is generally manageable, by effective time series denoising strategies designed to attenuate synchronized signal transients induced by abrupt head movements. The Wavelet Despiking software described in this article is freely available for download at www

  16. A wavelet method for modeling and despiking motion artifacts from resting-state fMRI time series.

    Science.gov (United States)

    Patel, Ameera X; Kundu, Prantik; Rubinov, Mikail; Jones, P Simon; Vértes, Petra E; Ersche, Karen D; Suckling, John; Bullmore, Edward T

    2014-07-15

    The impact of in-scanner head movement on functional magnetic resonance imaging (fMRI) signals has long been established as undesirable. These effects have been traditionally corrected by methods such as linear regression of head movement parameters. However, a number of recent independent studies have demonstrated that these techniques are insufficient to remove motion confounds, and that even small movements can spuriously bias estimates of functional connectivity. Here we propose a new data-driven, spatially-adaptive, wavelet-based method for identifying, modeling, and removing non-stationary events in fMRI time series, caused by head movement, without the need for data scrubbing. This method involves the addition of just one extra step, the Wavelet Despike, in standard pre-processing pipelines. With this method, we demonstrate robust removal of a range of different motion artifacts and motion-related biases including distance-dependent connectivity artifacts, at a group and single-subject level, using a range of previously published and new diagnostic measures. The Wavelet Despike is able to accommodate the substantial spatial and temporal heterogeneity of motion artifacts and can consequently remove a range of high and low frequency artifacts from fMRI time series, that may be linearly or non-linearly related to physical movements. Our methods are demonstrated by the analysis of three cohorts of resting-state fMRI data, including two high-motion datasets: a previously published dataset on children (N=22) and a new dataset on adults with stimulant drug dependence (N=40). We conclude that there is a real risk of motion-related bias in connectivity analysis of fMRI data, but that this risk is generally manageable, by effective time series denoising strategies designed to attenuate synchronized signal transients induced by abrupt head movements. The Wavelet Despiking software described in this article is freely available for download at www

  17. Biased motion vector interpolation for reduced video artifacts.

    NARCIS (Netherlands)

    2011-01-01

    In a video processing system where motion vectors are estimated for a subset of the blocks of data forming a video frame, and motion vectors are interpolated for the remainder of the blocks of the frame, a method includes determining, for at least at least one block of the current frame for which a

  18. Correction of Motion Artifacts for Real-Time Structured Light

    DEFF Research Database (Denmark)

    Wilm, Jakob; Olesen, Oline Vinter; Paulsen, Rasmus Reinhold

    2015-01-01

    While the problem of motion is often mentioned in conjunction with structured light imaging, few solutions have thus far been proposed. A method is demonstrated to correct for object or camera motion during structured light 3D scene acquisition. The method is based on the combination of a suitabl...

  19. Elimination of motion and pulsation artifacts using BLADE sequences in shoulder MR imaging

    International Nuclear Information System (INIS)

    Lavdas, E.; Zaloni, E.; Vlychou, M.; Vassiou, K.; Fezoulidis, I.; Tsagkalis, A.; Dailiana, Z.

    2015-01-01

    To evaluate the ability of proton-density with fat-suppression BLADE (proprietary name for periodically rotated overlapping parallel lines with enhanced reconstruction in MR systems from Siemens Healthcare, PDFS BLADE) and turbo inversion recovery magnitude-BLADE (TIRM BLADE) sequences to reduce motion and pulsation artifacts in shoulder magnetic resonance examinations. Forty-one consecutive patients who had been routinely scanned for shoulder examination participated in the study. The following pairs of sequences with and without BLADE were compared: (a) Oblique coronal proton-density sequence with fat saturation of 25 patients and (b) oblique sagittal T2 TIRM-weighed sequence of 20 patients. Qualitative analysis was performed by two experienced radiologists. Image motion and pulsation artifacts were also evaluated. In oblique coronal PDFS BLADE sequences, motion artifacts have been significantly eliminated, even in five cases of non-diagnostic value with conventional imaging. Similarly, in oblique sagittal T2 TIRM BLADE sequences, image quality has been improved, even in six cases of non-diagnostic value with conventional imaging. Furthermore, flow artifacts have been improved in more than 80% of all the cases. The use of BLADE sequences is recommended in shoulder imaging, especially in uncooperative patients because it effectively eliminates motion and pulsation artifacts. (orig.)

  20. Reference geometry-based detection of (4D-)CT motion artifacts: a feasibility study

    Science.gov (United States)

    Werner, René; Gauer, Tobias

    2015-03-01

    Respiration-correlated computed tomography (4D or 3D+t CT) can be considered as standard of care in radiation therapy treatment planning for lung and liver lesions. The decision about an application of motion management devices and the estimation of patient-specific motion effects on the dose distribution relies on precise motion assessment in the planning 4D CT data { which is impeded in case of CT motion artifacts. The development of image-based/post-processing approaches to reduce motion artifacts would benefit from precise detection and localization of the artifacts. Simple slice-by-slice comparison of intensity values and threshold-based analysis of related metrics suffer from- depending on the threshold- high false-positive or -negative rates. In this work, we propose exploiting prior knowledge about `ideal' (= artifact free) reference geometries to stabilize metric-based artifact detection by transferring (multi-)atlas-based concepts to this specific task. Two variants are introduced and evaluated: (S1) analysis and comparison of warped atlas data obtained by repeated non-linear atlas-to-patient registration with different levels of regularization; (S2) direct analysis of vector field properties (divergence, curl magnitude) of the atlas-to-patient transformation. Feasibility of approaches (S1) and (S2) is evaluated by motion-phantom data and intra-subject experiments (four patients) as well as - adopting a multi-atlas strategy- inter-subject investigations (twelve patients involved). It is demonstrated that especially sorting/double structure artifacts can be precisely detected and localized by (S1). In contrast, (S2) suffers from high false positive rates.

  1. Artifacts

    Science.gov (United States)

    Harris, Samantha

    2009-01-01

    NASA Headquarters sent a list of items to KSC that were deemed potential artifacts. These items played arole in the Shuttle Program's development and maintenance. Because these items are national assets, many are of interest to museums, schools, other government entities, etc. upon the Space Shuttle's retirement. The list contains over 500 items. All of these items need to be located, photographed, and catalogued with accompanying specific data that needs to be gathered. Initial research suggests that this is a time, labor, and cost intensive project. The purpose of my project was to focus on 20-60 of these 500 items, gather the necessary data, and compile them in a way that can be added to by other users when/if the project goes into full effect.

  2. Transient Severe Motion Artifact Related to Gadoxetate Disodium-Enhanced Liver MRI: Frequency and Risk Evaluation at a German Institution.

    Science.gov (United States)

    Well, Lennart; Rausch, Vanessa Hanna; Adam, Gerhard; Henes, Frank Oliver; Bannas, Peter

    2017-07-01

    Purpose  Varying frequencies (5 - 18 %) of contrast-related transient severe motion (TSM) imaging artifacts during gadoxetate disodium-enhanced arterial phase liver MRI have been reported. Since previous reports originated from the United States and Japan, we aimed to determine the frequency of TSM at a German institution and to correlate it with potential risk factors and previously published results. Materials and Methods  Two age- and sex-matched groups were retrospectively selected (gadoxetate disodium n = 89; gadobenate dimeglumine n = 89) from dynamic contrast-enhanced MRI examinations in a single center. Respiratory motion-related artifacts in non-enhanced and dynamic phases were assessed independently by two readers blinded to contrast agents on a 4-point scale. Scores of ≥ 3 were considered as severe motion artifacts. Severe motion artifacts in arterial phases were considered as TSM if scores in all other phases were risk factors for TSM were evaluated via logistic regression analysis. Results  For gadoxetate disodium, the mean score for respiratory motion artifacts was significantly higher in the arterial phase (2.2 ± 0.9) compared to all other phases (1.6 ± 0.7) (p risk factors (all p > 0.05). Conclusion  We revealed a high frequency of TSM after injection of gadoxetate disodium at a German institution, substantiating the importance of a diagnosis-limiting phenomenon that so far has only been reported from the United States and Japan. In accordance with previous studies, we did not identify associated risk factors for TSM. Key Points:   · Gadoxetate disodium causes TSM in a relevant number of patients.. · The frequency of TSM is similar between the USA, Japan and Germany.. · To date, no validated risk factors for TSM could be identified.. Citation Format · Well L, Rausch VH, Adam G et al. Transient Severe Motion Artifact Related to Gadoxetate Disodium-Enhanced Liver MRI: Frequency and Risk Evaluation at a

  3. Experimental analysis of motion artifacts in chest radiographs with the AMBER system

    International Nuclear Information System (INIS)

    Boetticher, H. von; Hofmann, K.; Luska, G.

    1999-01-01

    The prerequisites, mechanisms and principles of motion artifacts in AMBER radiographs were analysed. The experiments were performed using metronomes, a moving conventional mammography phantom, and arrangements of oscillating coil spring, spheroid and grid elements. A diagnostic dosimeter and TLDs, respectively, were used to measure exposure times and doses. The deree of distortion in AMBER radiographs depends on the direction of the object movement relative to the AMBER fan beam in a complex manner. The size of the motion artifacts depends on the local exposure time. The maximum value of this time is 75 ms and thus 1.5 times higher than specified by the manufacturer. To interpret AMBER radiographs possible system specific artifacts have to be considered to avoid misinterpretations of potentially significant details. (orig.) [de

  4. Effect of motion artifacts and their correction on near-infrared spectroscopy oscillation data

    DEFF Research Database (Denmark)

    Selb, Juliette; Yücel, Meryem A; Phillip, Dorte

    2015-01-01

    Functional near-infrared spectroscopy is prone to contamination by motion artifacts (MAs). Motion correction algorithms have previously been proposed and their respective performance compared for evoked rain activation studies. We study instead the effect of MAs on "oscillation" data which...... in the frequency band around 0.1 and 0.04 Hz, suggesting a physiological origin for the difference. We emphasize the importance of considering MAs as a confounding factor in oscillation-based functional near-infrared spectroscopy studies....

  5. sEMG during Whole-Body Vibration Contains Motion Artifacts and Reflex Activity

    Directory of Open Access Journals (Sweden)

    Karin Lienhard

    2015-01-01

    Full Text Available The purpose of this study was to determine whether the excessive spikes observed in the surface electromyography (sEMG spectrum recorded during whole-body vibration (WBV exercises contain motion artifacts and/or reflex activity. The occurrence of motion artifacts was tested by electrical recordings of the patella. The involvement of reflex activity was investigated by analyzing the magnitude of the isolated spikes during changes in voluntary background muscle activity. Eighteen physically active volunteers performed static squats while the sEMG was measured of five lower limb muscles during vertical WBV using no load and an additional load of 33 kg. In order to record motion artifacts during WBV, a pair of electrodes was positioned on the patella with several layers of tape between skin and electrodes. Spectral analysis of the patella signal revealed recordings of motion artifacts as high peaks at the vibration frequency (fundamental and marginal peaks at the multiple harmonics were observed. For the sEMG recordings, the root mean square of the spikes increased with increasing additional loads (p < 0.05, and was significantly correlated to the sEMG signal without the spikes of the respective muscle (r range: 0.54 - 0.92, p < 0.05. This finding indicates that reflex activity might be contained in the isolated spikes, as identical behavior has been found for stretch reflex responses evoked during direct vibration. In conclusion, the spikes visible in the sEMG spectrum during WBV exercises contain motion artifacts and possibly reflex activity.

  6. Epstein–Barr Virus in Gliomas: Cause, Association, or Artifact?

    Directory of Open Access Journals (Sweden)

    Saghir Akhtar

    2018-04-01

    Full Text Available Gliomas are the most common malignant brain tumors and account for around 60% of all primary central nervous system cancers. Glioblastoma multiforme (GBM is a grade IV glioma associated with a poor outcome despite recent advances in chemotherapy. The etiology of gliomas is unknown, but neurotropic viruses including the Epstein–Barr virus (EBV that is transmitted via salivary and genital fluids have been implicated recently. EBV is a member of the gamma herpes simplex family of DNA viruses that is known to cause infectious mononucleosis (glandular fever and is strongly linked with the oncogenesis of several cancers, including B-cell lymphomas, nasopharyngeal, and gastric carcinomas. The fact that EBV is thought to be the causative agent for primary central nervous system (CNS lymphomas in immune-deficient patients has led to its investigations in other brain tumors including gliomas. Here, we provide a review of the clinical literature pertaining to EBV in gliomas and discuss the possibilities of this virus being simply associative, causative, or even an experimental artifact. We searched the PubMed/MEDLINE databases using the following key words such as: glioma(s, glioblastoma multiforme, brain tumors/cancers, EBV, and neurotropic viruses. Our literature analysis indicates conflicting results on the presence and role of EBV in gliomas. Further comprehensive studies are needed to fully implicate EBV in gliomagenesis and oncomodulation. Understanding the role of EBV and other oncoviruses in the etiology of gliomas, would likely open up new avenues for the treatment and management of these, often fatal, CNS tumors.

  7. Reduction of motion artifact in pulse oximetry by smoothed pseudo Wigner-Ville distribution

    Directory of Open Access Journals (Sweden)

    Zhang Yuan-ting

    2005-03-01

    Full Text Available Abstract Background The pulse oximeter, a medical device capable of measuring blood oxygen saturation (SpO2, has been shown to be a valuable device for monitoring patients in critical conditions. In order to incorporate the technique into a wearable device which can be used in ambulatory settings, the influence of motion artifacts on the estimated SpO2 must be reduced. This study investigates the use of the smoothed psuedo Wigner-Ville distribution (SPWVD for the reduction of motion artifacts affecting pulse oximetry. Methods The SPWVD approach is compared with two techniques currently used in this field, i.e. the weighted moving average (WMA and the fast Fourier transform (FFT approaches. SpO2 and pulse rate were estimated from a photoplethysmographic (PPG signal recorded when subject is in a resting position as well as in the act of performing four types of motions: horizontal and vertical movements of the hand, and bending and pressing motions of the finger. For each condition, 24 sets of PPG signals collected from 6 subjects, each of 30 seconds, were studied with reference to the PPG signal recorded simultaneously from the subject's other hand, which was stationary at all times. Results and Discussion The SPWVD approach shows significant improvement (p Conclusion The results suggested that the SPWVD approach could potentially be used to reduce motion artifact on wearable pulse oximeters.

  8. A novel algorithm to separate motion artifacts from photoplethysmographic signals obtained with a reflectance pulse oximeter.

    Science.gov (United States)

    Yao, Jianchu; Warren, Steve

    2004-01-01

    Pulse oximeters are mainstays for acquiring blood oxygen saturation in static environments such as hospital rooms. However, motion artifacts prevent their broad in wearable, ambulatory environments. To this end, we present a novel algorithm to separate the motion artifacts from plethysmographic data gathered by pulse oximeters. This algorithm, based on the Beer-Lambert law, requires photoplethysmographic data acquired at three excitation wavelengths. The algorithm can calculate venous blood oxygen saturation (SvO2) as well as arterial blood oxygen saturation (SaO2). Preliminary results indicate that the extraction of the venous signal, which is assumed to be most affected by motions, is successful with data acquired from a reflectance-mode sensor.

  9. A trial to reduce cardiac motion artifact on HR-CT images of the lung with the use of subsecond scan and special cine reconstruction algorithm

    Energy Technology Data Exchange (ETDEWEB)

    Sakai, Fumikazu; Tsuuchi, Yasuhiko; Suzuki, Keiko; Ueno, Keiko; Yamada, Takayuki; Okawa, Tomohiko [Tokyo Women`s Medical Coll. (Japan); Yun, Shen; Horiuchi, Tetsuya; Kimura, Fumiko

    1998-05-01

    We describe our trial to reduce cardiac motion artifacts on HR-CT images caused by cardiac pulsation by combining use of subsecond CT (scan time 0.8 s) and a special cine reconstruction algorithm (cine reconstruction algorithm with 180-degree helical interpolation). Eleven to 51 HR-CT images were reconstructed with the special cine reconstruction algorithm at the pitch of 0.1 (0.08 s) from the data obtained by two to six contigious rotation scans at the same level. Images with the fewest cardiac motion artifacts were selected for evaluation. These images were compared with those reconstructed with a conventional cine reconstruction algorithm and step-by-step scan. In spite of its increased radiation exposure, technical complexity and slight degradation of spatial resolution, our method was useful in reducing cardiac motion artifacts on HR-CT images in regions adjacent to the heart. (author)

  10. Automatic identification of motion artifacts in EHG recording for robust analysis of uterine contractions.

    Science.gov (United States)

    Ye-Lin, Yiyao; Garcia-Casado, Javier; Prats-Boluda, Gema; Alberola-Rubio, José; Perales, Alfredo

    2014-01-01

    Electrohysterography (EHG) is a noninvasive technique for monitoring uterine electrical activity. However, the presence of artifacts in the EHG signal may give rise to erroneous interpretations and make it difficult to extract useful information from these recordings. The aim of this work was to develop an automatic system of segmenting EHG recordings that distinguishes between uterine contractions and artifacts. Firstly, the segmentation is performed using an algorithm that generates the TOCO-like signal derived from the EHG and detects windows with significant changes in amplitude. After that, these segments are classified in two groups: artifacted and nonartifacted signals. To develop a classifier, a total of eleven spectral, temporal, and nonlinear features were calculated from EHG signal windows from 12 women in the first stage of labor that had previously been classified by experts. The combination of characteristics that led to the highest degree of accuracy in detecting artifacts was then determined. The results showed that it is possible to obtain automatic detection of motion artifacts in segmented EHG recordings with a precision of 92.2% using only seven features. The proposed algorithm and classifier together compose a useful tool for analyzing EHG signals and would help to promote clinical applications of this technique.

  11. Automatic Identification of Motion Artifacts in EHG Recording for Robust Analysis of Uterine Contractions

    Directory of Open Access Journals (Sweden)

    Yiyao Ye-Lin

    2014-01-01

    Full Text Available Electrohysterography (EHG is a noninvasive technique for monitoring uterine electrical activity. However, the presence of artifacts in the EHG signal may give rise to erroneous interpretations and make it difficult to extract useful information from these recordings. The aim of this work was to develop an automatic system of segmenting EHG recordings that distinguishes between uterine contractions and artifacts. Firstly, the segmentation is performed using an algorithm that generates the TOCO-like signal derived from the EHG and detects windows with significant changes in amplitude. After that, these segments are classified in two groups: artifacted and nonartifacted signals. To develop a classifier, a total of eleven spectral, temporal, and nonlinear features were calculated from EHG signal windows from 12 women in the first stage of labor that had previously been classified by experts. The combination of characteristics that led to the highest degree of accuracy in detecting artifacts was then determined. The results showed that it is possible to obtain automatic detection of motion artifacts in segmented EHG recordings with a precision of 92.2% using only seven features. The proposed algorithm and classifier together compose a useful tool for analyzing EHG signals and would help to promote clinical applications of this technique.

  12. A systematic comparison of motion artifact correction techniques for functional near-infrared spectroscopy

    DEFF Research Database (Denmark)

    Cooper, Robert J; Selb, Juliette; Gagnon, Louis

    2012-01-01

    a significant reduction in the mean-squared error (MSE) and significant increase in the contrast-to-noise ratio (CNR) of the recovered HRF when compared to no correction and compared to a process of rejecting motion-contaminated trials. Spline interpolation produces the largest average reduction in MSE (55....... Principle component analysis, spline interpolation, wavelet analysis, and Kalman filtering approaches are compared to one another and to standard approaches using the accuracy of the recovered, simulated hemodynamic response function (HRF). Each of the four motion correction techniques we tested yields......%) while wavelet analysis produces the highest average increase in CNR (39%). On the basis of this analysis, we recommend the routine application of motion correction techniques (particularly spline interpolation or wavelet analysis) to minimize the impact of motion artifacts on functional NIRS data....

  13. WE-G-209-00: Identifying Image Artifacts, Their Causes, and How to Fix Them

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2016-06-15

    Digital radiography, CT, PET, and MR are complicated imaging modalities which are composed of many hardware and software components. These components work together in a highly coordinated chain of events with the intent to produce high quality images. Acquisition, processing and reconstruction of data must occur in a precise way for optimum image quality to be achieved. Any error or unexpected event in the entire process can produce unwanted pixel intensities in the final images which may contribute to visible image artifacts. The diagnostic imaging physicist is uniquely qualified to investigate and contribute to resolution of image artifacts. This course will teach the participant to identify common artifacts found clinically in digital radiography, CT, PET, and MR, to determine the causes of artifacts, and to make recommendations for how to resolve artifacts. Learning Objectives: Identify common artifacts found clinically in digital radiography, CT, PET and MR. Determine causes of various clinical artifacts from digital radiography, CT, PET and MR. Describe how to resolve various clinical artifacts from digital radiography, CT, PET and MR.

  14. WE-G-209-00: Identifying Image Artifacts, Their Causes, and How to Fix Them

    International Nuclear Information System (INIS)

    2016-01-01

    Digital radiography, CT, PET, and MR are complicated imaging modalities which are composed of many hardware and software components. These components work together in a highly coordinated chain of events with the intent to produce high quality images. Acquisition, processing and reconstruction of data must occur in a precise way for optimum image quality to be achieved. Any error or unexpected event in the entire process can produce unwanted pixel intensities in the final images which may contribute to visible image artifacts. The diagnostic imaging physicist is uniquely qualified to investigate and contribute to resolution of image artifacts. This course will teach the participant to identify common artifacts found clinically in digital radiography, CT, PET, and MR, to determine the causes of artifacts, and to make recommendations for how to resolve artifacts. Learning Objectives: Identify common artifacts found clinically in digital radiography, CT, PET and MR. Determine causes of various clinical artifacts from digital radiography, CT, PET and MR. Describe how to resolve various clinical artifacts from digital radiography, CT, PET and MR.

  15. Effect of high-pitch dual-source CT to compensate motion artifacts: a phantom study.

    Science.gov (United States)

    Farshad-Amacker, Nadja A; Alkadhi, Hatem; Leschka, Sebastian; Frauenfelder, Thomas

    2013-10-01

    To evaluate the potential of high-pitch, dual-source computed tomography (DSCT) for compensation of motion artifacts. Motion artifacts were created using a moving chest/cardiac phantom with integrated stents at different velocities (from 0 to 4-6 cm/s) parallel (z direction), transverse (x direction), and diagonal (x and z direction combined) to the scanning direction using standard-pitch (SP) (pitch = 1) and high-pitch (HP) (pitch = 3.2) 128-detector DSCT (Siemens, Healthcare, Forchheim, Germany). The scanning parameters were (SP/HP): tube voltage, 120 kV/120 kV; effective tube current time product, 300 mAs/500 mAs; and a pitch of 1/3.2. Motion artifacts were analyzed in terms of subjective image quality and object distortion. Image quality was rated by two blinded, independent observers using a 4-point scoring system (1, excellent; 2, good with minor object distortion or blurring; 3, diagnostically partially not acceptable; and 4, diagnostically not acceptable image quality). Object distortion was assessed by the measured changes of the object's outer diameter (x) and length (z) and a corresponding calculated distortion vector (d) (d = √(x(2) + z(2))). The interobserver agreement was excellent (k = 0.91). Image quality using SP was diagnostically not acceptable with any motion in x direction (scores 3 and 4), in contrast to HP DSCT where it remained diagnostic up to 2 cm/s (scores 1 and 2). For motion in the z direction only, image quality remained diagnostic for SP and HP DSCT (scores 1 and 2). Changes of the object's diameter (x), length (z), and distortion vectors (d) were significantly greater with SP (overall: x = 1.9 cm ± 1.7 cm, z = 0.6 cm ± 0.8 cm, and d = 1.4 cm ± 1.5 cm) compared to HP DSCT (overall: x = 0.1 cm ± 0.1 cm, z = 0.0 cm ± 0.1 cm, and d = 0.1 cm ± 0.1 cm; each P pitch DSCT significantly decreases motion artifacts in various directions and improves image quality. Copyright © 2013 AUR. Published by Elsevier Inc. All rights reserved.

  16. A short study to assess the potential of independent component analysis for motion artifact separation in wearable pulse oximeter signals.

    Science.gov (United States)

    Yao, Jianchu; Warren, Steve

    2005-01-01

    Motion artifact reduction and separation become critical when medical sensors are used in wearable monitoring scenarios. Previous research has demonstrated that independent component analysis (ICA) can be applied to pulse oximeter signals to separate photoplethysmographic (PPG) data from motion artifacts, ambient light, and other interference in low-motion environments. However, ICA assumes that all source signal component pairs are mutually independent. It is important to assess the statistical independence of the source components in PPG data, especially if ICA is to be applied in ambulatory monitoring environments, where motion artifacts can have a substantial effect on the quality of data received from light-based sensors. This paper addresses the statistical relationship between motion artifacts and PPG data by calculating the correlation coefficients between arterial volume variations and motion over a range of stationary to high-motion conditions. Analyses indicate that motion significantly affects arterial flow, so care must be taken when applying ICA to light-based sensor data acquired from wearable platforms.

  17. Correction of head motion artifacts in SPECT with fully 3-D OS-EM reconstruction

    International Nuclear Information System (INIS)

    Fulton, R.R.

    1998-01-01

    Full text: A method which relies on continuous monitoring of head position has been developed to correct for head motion in SPECT studies of the brain. Head position and orientation are monitored during data acquisition by an inexpensive head tracking system (ADL-1, Shooting Star Technology, Rosedale, British Colombia). Motion correction involves changing the projection geometry to compensate for motion (using data from the head tracker), and reconstructing with a fully 3-D OS-EM algorithm. The reconstruction algorithm can accommodate any number of movements and any projection geometry. A single iteration of 3-D OS-EM using all available projections provides a satisfactory 3-D reconstruction, essentially free of motion artifacts. The method has been validated in studies of the 3-D Hoffman brain phantom. Multiple 36- degree acquisitions, each with the phantom in a different position, were performed on a Trionix triple head camera. Movements were simulated by combining projections from the different acquisitions. Accuracy was assessed by comparison with a motion-free reconstruction, visually and by calculating mean squared error (MSE). Motion correction reduced distortion perceptibly and, depending on the motions applied, improved MSE by up to an order of magnitude. Three-dimensional reconstruction of the 128 x 128 x 128 data set took 2- minutes on a SUN Ultra 1 workstation. This motion correction technique can be retro-fitted to existing SPECT systems and could be incorporated in future SPECT camera designs. It appears to be applicable in PET as well as SPECT, to be able to correct for any head movements, and to have the potential to improve the accuracy of tomographic brain studies under clinical imaging conditions

  18. Electrocardiogram artifact caused by rigors mimicking narrow complex tachycardia: a case report.

    Science.gov (United States)

    Matthias, Anne Thushara; Indrakumar, Jegarajah

    2014-02-04

    The electrocardiogram (ECG) is useful in the diagnosis of cardiac and non-cardiac conditions. Rigors due to shivering can cause electrocardiogram artifacts mimicking various cardiac rhythm abnormalities. We describe an 80-year-old Sri Lankan man with an abnormal electrocardiogram mimicking narrow complex tachycardia during the immediate post-operative period. Electrocardiogram changes caused by muscle tremor during rigors could mimic a narrow complex tachycardia. Identification of muscle tremor as a cause of electrocardiogram artifact can avoid unnecessary pharmacological and non-pharmacological intervention to prevent arrhythmias.

  19. Quality control of structural MRI images applied using FreeSurfer - a hands-on workflow to rate motion artifacts

    Directory of Open Access Journals (Sweden)

    Lea Luise Backhausen

    2016-12-01

    Full Text Available In structural magnetic resonance imaging motion artifacts are common, especially when not scanning healthy young adults. It has been shown that motion affects the analysis with automated image-processing techniques (e.g. FreeSurfer. This can bias results. Several developmental and adult studies have found reduced volume and thickness of gray matter due to motion artifacts. Thus, quality control is necessary in order to ensure an acceptable level of quality and to define exclusion criteria of images (i.e. determine participants with most severe artifacts. However, information about the quality control workflow and image exclusion procedure is largely lacking in the current literature and the existing rating systems differ. Here we propose a stringent workflow of quality control steps during and after acquisition of T1-weighted images, which enables researchers dealing with populations that are typically affected by motion artifacts to enhance data quality and maximize sample sizes. As an underlying aim we established a thorough quality control rating system for T1-weighted images and applied it to the analysis of developmental clinical data using the automated processing pipeline FreeSurfer. This hands-on workflow and quality control rating system will aid researchers in minimizing motion artifacts in the final data set, and therefore enhance the quality of structural magnetic resonance imaging studies.

  20. Mitigation of motion artifacts in CBCT of lung tumors based on tracked tumor motion during CBCT acquisition

    International Nuclear Information System (INIS)

    Lewis, John H; Li Ruijiang; Jia Xun; Watkins, W Tyler; Song, William Y; Jiang, Steve B; Lou, Yifei

    2011-01-01

    An algorithm capable of mitigating respiratory motion blurring artifacts in cone-beam computed tomography (CBCT) lung tumor images based on the motion of the tumor during the CBCT scan is developed. The tumor motion trajectory and probability density function (PDF) are reconstructed from the acquired CBCT projection images using a recently developed algorithm Lewis et al (2010 Phys. Med. Biol. 55 2505-22). Assuming that the effects of motion blurring can be represented by convolution of the static lung (or tumor) anatomy with the motion PDF, a cost function is defined, consisting of a data fidelity term and a total variation regularization term. Deconvolution is performed through iterative minimization of this cost function. The algorithm was tested on digital respiratory phantom, physical respiratory phantom and patient data. A clear qualitative improvement is evident in the deblurred images as compared to the motion-blurred images for all cases. Line profiles show that the tumor boundaries are more accurately and clearly represented in the deblurred images. The normalized root-mean-squared error between the images used as ground truth and the motion-blurred images are 0.29, 0.12 and 0.30 in the digital phantom, physical phantom and patient data, respectively. Deblurring reduces the corresponding values to 0.13, 0.07 and 0.19. Application of a -700 HU threshold to the digital phantom results in tumor dimension measurements along the superior-inferior axis of 2.8, 1.8 and 1.9 cm in the motion-blurred, ground truth and deblurred images, respectively. Corresponding values for the physical phantom are 3.4, 2.7 and 2.7 cm. A threshold of -500 HU applied to the patient case gives measurements of 3.1, 1.6 and 1.7 cm along the SI axis in the CBCT, 4DCT and deblurred images, respectively. This technique could provide more accurate information about a lung tumor's size and shape on the day of treatment.

  1. Please Don't Move-Evaluating Motion Artifact From Peripheral Quantitative Computed Tomography Scans Using Textural Features.

    Science.gov (United States)

    Rantalainen, Timo; Chivers, Paola; Beck, Belinda R; Robertson, Sam; Hart, Nicolas H; Nimphius, Sophia; Weeks, Benjamin K; McIntyre, Fleur; Hands, Beth; Siafarikas, Aris

    Most imaging methods, including peripheral quantitative computed tomography (pQCT), are susceptible to motion artifacts particularly in fidgety pediatric populations. Methods currently used to address motion artifact include manual screening (visual inspection) and objective assessments of the scans. However, previously reported objective methods either cannot be applied on the reconstructed image or have not been tested for distal bone sites. Therefore, the purpose of the present study was to develop and validate motion artifact classifiers to quantify motion artifact in pQCT scans. Whether textural features could provide adequate motion artifact classification performance in 2 adolescent datasets with pQCT scans from tibial and radial diaphyses and epiphyses was tested. The first dataset was split into training (66% of sample) and validation (33% of sample) datasets. Visual classification was used as the ground truth. Moderate to substantial classification performance (J48 classifier, kappa coefficients from 0.57 to 0.80) was observed in the validation dataset with the novel texture-based classifier. In applying the same classifier to the second cross-sectional dataset, a slight-to-fair (κ = 0.01-0.39) classification performance was observed. Overall, this novel textural analysis-based classifier provided a moderate-to-substantial classification of motion artifact when the classifier was specifically trained for the measurement device and population. Classification based on textural features may be used to prescreen obviously acceptable and unacceptable scans, with a subsequent human-operated visual classification of any remaining scans. Copyright © 2017 The International Society for Clinical Densitometry. Published by Elsevier Inc. All rights reserved.

  2. Optimized statistical parametric mapping procedure for NIRS data contaminated by motion artifacts : Neurometric analysis of body schema extension.

    Science.gov (United States)

    Suzuki, Satoshi

    2017-09-01

    This study investigated the spatial distribution of brain activity on body schema (BS) modification induced by natural body motion using two versions of a hand-tracing task. In Task 1, participants traced Japanese Hiragana characters using the right forefinger, requiring no BS expansion. In Task 2, participants performed the tracing task with a long stick, requiring BS expansion. Spatial distribution was analyzed using general linear model (GLM)-based statistical parametric mapping of near-infrared spectroscopy data contaminated with motion artifacts caused by the hand-tracing task. Three methods were utilized in series to counter the artifacts, and optimal conditions and modifications were investigated: a model-free method (Step 1), a convolution matrix method (Step 2), and a boxcar-function-based Gaussian convolution method (Step 3). The results revealed four methodological findings: (1) Deoxyhemoglobin was suitable for the GLM because both Akaike information criterion and the variance against the averaged hemodynamic response function were smaller than for other signals, (2) a high-pass filter with a cutoff frequency of .014 Hz was effective, (3) the hemodynamic response function computed from a Gaussian kernel function and its first- and second-derivative terms should be included in the GLM model, and (4) correction of non-autocorrelation and use of effective degrees of freedom were critical. Investigating z-maps computed according to these guidelines revealed that contiguous areas of BA7-BA40-BA21 in the right hemisphere became significantly activated ([Formula: see text], [Formula: see text], and [Formula: see text], respectively) during BS modification while performing the hand-tracing task.

  3. Transient severe motion artifact related to gadoxetate disodium-enhanced liver MRI. Frequency and risk evaluation at a German institution

    Energy Technology Data Exchange (ETDEWEB)

    Well, Lennart; Rausch, Vanessa Hanna; Adam, Gerhard; Henes, Frank Oliver; Bannas, Peter [Univ. Medical Center Hamburg-Eppendorf, Hamburg (Germany). Dept. for Diagnostic and Interventional Radiology and Nuclear Medicine

    2017-07-15

    Varying frequencies (5 - 18%) of contrast-related transient severe motion (TSM) imaging artifacts during gadoxetate disodium-enhanced arterial phase liver MRI have been reported. Since previous reports originated from the United States and Japan, we aimed to determine the frequency of TSM at a German institution and to correlate it with potential risk factors and previously published results. Two age- and sex-matched groups were retrospectively selected (gadoxetate disodium n = 89; gadobenate dimeglumine n = 89) from dynamic contrast-enhanced MRI examinations in a single center. Respiratory motion-related artifacts in non-enhanced and dynamic phases were assessed independently by two readers blinded to contrast agents on a 4-point scale. Scores of ≥3 were considered as severe motion artifacts. Severe motion artifacts in arterial phases were considered as TSM if scores in all other phases were < 3. Potential risk factors for TSM were evaluated via logistic regression analysis. For gadoxetate disodium, the mean score for respiratory motion artifacts was significantly higher in the arterial phase (2.2 ± 0.9) compared to all other phases (1.6 ± 0.7) (p < 0.05). The frequency of TSM was significantly higher with gadoxetate disodium (n = 19; 21.1 %) than with gadobenate dimeglumine (n = 1; 1.1%) (p < 0.001). The frequency of TSM at our institution is similar to some, but not all previously published findings. Logistic regression analysis did not show any significant correlation between TSM and risk factors (all p>0.05). We revealed a high frequency of TSM after injection of gadoxetate disodium at a German institution, substantiating the importance of a diagnosis-limiting phenomenon that so far has only been reported from the United States and Japan. In accordance with previous studies, we did not identify associated risk factors for TSM.

  4. Rapid estimation of 4DCT motion-artifact severity based on 1D breathing-surrogate periodicity

    Energy Technology Data Exchange (ETDEWEB)

    Li, Guang, E-mail: lig2@mskcc.org; Caraveo, Marshall [Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York 10065 (United States); Wei, Jie [Department of Computer Science, City College of New York, New York, New York 10031 (United States); Rimner, Andreas; Wu, Abraham J.; Goodman, Karyn A. [Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York 10065 (United States); Yorke, Ellen [Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10065 (United States)

    2014-11-01

    Purpose: Motion artifacts are common in patient four-dimensional computed tomography (4DCT) images, leading to an ill-defined tumor volume with large variations for radiotherapy treatment and a poor foundation with low imaging fidelity for studying respiratory motion. The authors developed a method to estimate 4DCT image quality by establishing a correlation between the severity of motion artifacts in 4DCT images and the periodicity of the corresponding 1D respiratory waveform (1DRW) used for phase binning in 4DCT reconstruction. Methods: Discrete Fourier transformation (DFT) was applied to analyze 1DRW periodicity. The breathing periodicity index (BPI) was defined as the sum of the largest five Fourier coefficients, ranging from 0 to 1. Distortional motion artifacts (excluding blurring) of cine-scan 4DCT at the junctions of adjacent couch positions around the diaphragm were classified in three categories: incomplete, overlapping, and duplicate anatomies. To quantify these artifacts, discontinuity of the diaphragm at the junctions was measured in distance and averaged along six directions in three orthogonal views. Artifacts per junction (APJ) across the entire diaphragm were calculated in each breathing phase and phase-averaged APJ{sup ¯}, defined as motion-artifact severity (MAS), was obtained for each patient. To make MAS independent of patient-specific motion amplitude, two new MAS quantities were defined: MAS{sup D} is normalized to the maximum diaphragmatic displacement and MAS{sup V} is normalized to the mean diaphragmatic velocity (the breathing period was obtained from DFT analysis of 1DRW). Twenty-six patients’ free-breathing 4DCT images and corresponding 1DRW data were studied. Results: Higher APJ values were found around midventilation and full inhalation while the lowest APJ values were around full exhalation. The distribution of MAS is close to Poisson distribution with a mean of 2.2 mm. The BPI among the 26 patients was calculated with a value

  5. Rapid estimation of 4DCT motion-artifact severity based on 1D breathing-surrogate periodicity

    International Nuclear Information System (INIS)

    Li, Guang; Caraveo, Marshall; Wei, Jie; Rimner, Andreas; Wu, Abraham J.; Goodman, Karyn A.; Yorke, Ellen

    2014-01-01

    Purpose: Motion artifacts are common in patient four-dimensional computed tomography (4DCT) images, leading to an ill-defined tumor volume with large variations for radiotherapy treatment and a poor foundation with low imaging fidelity for studying respiratory motion. The authors developed a method to estimate 4DCT image quality by establishing a correlation between the severity of motion artifacts in 4DCT images and the periodicity of the corresponding 1D respiratory waveform (1DRW) used for phase binning in 4DCT reconstruction. Methods: Discrete Fourier transformation (DFT) was applied to analyze 1DRW periodicity. The breathing periodicity index (BPI) was defined as the sum of the largest five Fourier coefficients, ranging from 0 to 1. Distortional motion artifacts (excluding blurring) of cine-scan 4DCT at the junctions of adjacent couch positions around the diaphragm were classified in three categories: incomplete, overlapping, and duplicate anatomies. To quantify these artifacts, discontinuity of the diaphragm at the junctions was measured in distance and averaged along six directions in three orthogonal views. Artifacts per junction (APJ) across the entire diaphragm were calculated in each breathing phase and phase-averaged APJ ¯ , defined as motion-artifact severity (MAS), was obtained for each patient. To make MAS independent of patient-specific motion amplitude, two new MAS quantities were defined: MAS D is normalized to the maximum diaphragmatic displacement and MAS V is normalized to the mean diaphragmatic velocity (the breathing period was obtained from DFT analysis of 1DRW). Twenty-six patients’ free-breathing 4DCT images and corresponding 1DRW data were studied. Results: Higher APJ values were found around midventilation and full inhalation while the lowest APJ values were around full exhalation. The distribution of MAS is close to Poisson distribution with a mean of 2.2 mm. The BPI among the 26 patients was calculated with a value ranging from 0

  6. The cause of the artifact in 4-slice helical computed tomography

    International Nuclear Information System (INIS)

    Taguchi, Katsuyuki; Aradate, Hiroshi; Saito, Yasuo; Zmora, Ilan; Han, Kyung S.; Silver, Michael D.

    2004-01-01

    The causes of the image artifacts in a 4-slice helical computed tomography have been discussed as follows: (1) changeover in pairs of data used in z interpolation, (2) sampling interval in z, and (3) the cone angle. This study analyzes the first two causes of the artifact and describes how the current algorithm [K. Taguchi and H. Aradate, Radiology 205P, 390 (1997); 205P, 618 (1997); Med. Phys. 25, 550-561 (1998); H. Hu, ibid. 26, 5-18 (1999); S. Schaller et al., IEEE Trans. Med. Imaging 19, 822-834 (2000); K. Taguchi, Ph.D. thesis, University of Tsukuba, 2002] solves the problem. An interpolated sinogram for a slice at the edge of a ball phantom shows discontinuity caused by the changeover. If we extend the streak artifact in the reconstructed image, it crosses the focus orbit at the corresponding projection angle. Applying z filtering can reduce such causes by its feathering effect and mixing data obtained by different cone angles; the best results are provided when z filtering is applied to densely sampled helical data

  7. Temporal resolution and motion artifacts in single-source and dual-source cardiac CT

    International Nuclear Information System (INIS)

    Schöndube, Harald; Allmendinger, Thomas; Stierstorfer, Karl; Bruder, Herbert; Flohr, Thomas

    2013-01-01

    Purpose: The temporal resolution of a given image in cardiac computed tomography (CT) has so far mostly been determined from the amount of CT data employed for the reconstruction of that image. The purpose of this paper is to examine the applicability of such measures to the newly introduced modality of dual-source CT as well as to methods aiming to provide improved temporal resolution by means of an advanced image reconstruction algorithm. Methods: To provide a solid base for the examinations described in this paper, an extensive review of temporal resolution in conventional single-source CT is given first. Two different measures for assessing temporal resolution with respect to the amount of data involved are introduced, namely, either taking the full width at half maximum of the respective data weighting function (FWHM-TR) or the total width of the weighting function (total TR) as a base of the assessment. Image reconstruction using both a direct fan-beam filtered backprojection with Parker weighting as well as using a parallel-beam rebinning step are considered. The theory of assessing temporal resolution by means of the data involved is then extended to dual-source CT. Finally, three different advanced iterative reconstruction methods that all use the same input data are compared with respect to the resulting motion artifact level. For brevity and simplicity, the examinations are limited to two-dimensional data acquisition and reconstruction. However, all results and conclusions presented in this paper are also directly applicable to both circular and helical cone-beam CT. Results: While the concept of total TR can directly be applied to dual-source CT, the definition of the FWHM of a weighting function needs to be slightly extended to be applicable to this modality. The three different advanced iterative reconstruction methods examined in this paper result in significantly different images with respect to their motion artifact level, despite exactly the same

  8. Temporal resolution and motion artifacts in single-source and dual-source cardiac CT.

    Science.gov (United States)

    Schöndube, Harald; Allmendinger, Thomas; Stierstorfer, Karl; Bruder, Herbert; Flohr, Thomas

    2013-03-01

    The temporal resolution of a given image in cardiac computed tomography (CT) has so far mostly been determined from the amount of CT data employed for the reconstruction of that image. The purpose of this paper is to examine the applicability of such measures to the newly introduced modality of dual-source CT as well as to methods aiming to provide improved temporal resolution by means of an advanced image reconstruction algorithm. To provide a solid base for the examinations described in this paper, an extensive review of temporal resolution in conventional single-source CT is given first. Two different measures for assessing temporal resolution with respect to the amount of data involved are introduced, namely, either taking the full width at half maximum of the respective data weighting function (FWHM-TR) or the total width of the weighting function (total TR) as a base of the assessment. Image reconstruction using both a direct fan-beam filtered backprojection with Parker weighting as well as using a parallel-beam rebinning step are considered. The theory of assessing temporal resolution by means of the data involved is then extended to dual-source CT. Finally, three different advanced iterative reconstruction methods that all use the same input data are compared with respect to the resulting motion artifact level. For brevity and simplicity, the examinations are limited to two-dimensional data acquisition and reconstruction. However, all results and conclusions presented in this paper are also directly applicable to both circular and helical cone-beam CT. While the concept of total TR can directly be applied to dual-source CT, the definition of the FWHM of a weighting function needs to be slightly extended to be applicable to this modality. The three different advanced iterative reconstruction methods examined in this paper result in significantly different images with respect to their motion artifact level, despite exactly the same amount of data being used

  9. Detection of motion artifacts in optical coherence tomography using the fundus enhancement system

    International Nuclear Information System (INIS)

    Schaudig, U.; Skevas, C.; Scholz, F.

    2007-01-01

    Extensive artefacts due to major eye movements are detectable in optical coherence tomography images (OCT), but frequency and extent of small eye movements have not been studied. To investigate frequency and extent of irregularities in OCT imaging due to eye movements during the scanning process in OCT. A fundus enhancement system (FES) originally designed to improve retinal image quality in a conventional OCT device (Zeiss Stratus OCT) in order to integrate OCT images into fluorescence angiographies was used to record the scanning process and review OCT-scan acquisition in slow motion. A horizontal and a vertical single line scan of 5 mm length through the center of fixation were obtained in 40 eyes of 20 normal healthy subjects, all with a visual acuity of at least 20/20. Scans were investigated for loss of fixation and eye movements during the scanning process. Outcome measures were presence or absence of eye movements during the scanning process and mean deviation from the intended scan position, measured in millimeter. 7 of 20 patients showed no eye movements in both eyes. 4 of the remaining 13 patients showed eye movements only in one eye. In the eyes with detectable movements, the mean deviation from the intended scan position was 0.2 mm in the horizontal and 0.28 mm in the vertical scans. Fundus imaging in conventional systems can be enhanced to detect artifacts due to minimal eye movements during the scanning process. In this first series with normal healthy subjects, minimal eye movements were present in the over half of the investigations. Although the distances from the intended scan positions seem to be small in normal eyes, further investigations of the phenomenon are necessary. OCT is increasingly used as the primary tool for controlling therapy in macular diseases and the extent of motion artefacts is not known. (author) [de

  10. A technique to reduce motion artifact for externally triggered cine-MRI(EC-MRI) based on detecting the onset of the articulated word with spectral analysis

    International Nuclear Information System (INIS)

    Shimada, Yasuhiro; Nishimoto, Hironori; Kochiyama, Takanori; Fujimoto, Ichiro; Mano, Hiroaki; Masaki, Shinobu; Murase, Kenya

    2012-01-01

    One issue in externally triggered cine-magnetic resonance imaging (EC-MRI) for the dynamic observation of speech organs is motion artifact in the phase-encoding direction caused by unstable repetitions of speech during data acquisition. We propose a technique to reduce such artifact by rearranging the k-space data used to reconstruct MR images based on the analysis of recorded speech sounds. We recorded the subject's speech sounds during EC-MRI and used post hoc acoustical processing to reduce scanning noise and detect the onset of each utterance based on analysis of the recorded sounds. We selected each line of k-space from several data acquisition sessions and rearranged them to reconstruct a new series of dynamic MR images according to the analyzed time of utterance onset. Comparative evaluation showed significant reduction in motion artifact signal in the dynamic MR images reconstructed by the proposed method. The quality of the reconstructed images was sufficient to observe the dynamic aspects of speech production mechanisms. (author)

  11. Evaluation and reduction of respiratory motion artifacts in small animal SPECT with GATE

    International Nuclear Information System (INIS)

    Lee, C.-L.; Park, S.-J.; Kim, H.-J.

    2015-01-01

    The degradation of image quality caused by respiration is a major impediment to accurate lesion detection in single photon emission computed tomography (SPECT) imaging. This study was performed to evaluate the effects of lung motion on image quantification. A small animal SPECT system with NaI(Tl) was modeled in the Geant4 application for tomographic emission (GATE) simulation for a lung lesion using a 4D mouse whole-body phantom. SPECT images were obtained using 120 projection views acquired from 0 o to 360 o with a 3 o step. Slices were reconstructed using ordered subsets expectation maximization (OS-EM) without attenuation correction with five iterations and four subsets. Image quality was compared between the static mode without respiratory motion, and dynamic mode with respiratory motion in terms of spatial resolution was measured by the full width at half maximum (FWHM), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). The FWHM of the non-gated image and the respiratory gated image were also compared. Spatial resolution improved as activity increased and lesion diameter decreased in the static and dynamic modes. The SNR and CNR increased significantly as lesion activity increased and lesion diameter decreased. Our results show that respiratory motion leads to reduced contrast and quantitative accuracy and that image quantification depends on both the amplitude and the pattern of the respiratory motion. We verified that respiratory motion can have a major effect on the accuracy of measurement of lung lesions and that respiratory gating can reduce activity smearing on SPECT images

  12. Detection of motion artifact patterns in photoplethysmographic signals based on time and period domain analysis

    International Nuclear Information System (INIS)

    Couceiro, R; Carvalho, P; Paiva, R P; Henriques, J; Muehlsteff, J

    2014-01-01

    The presence of motion artifacts in photoplethysmographic (PPG) signals is one of the major obstacles in the extraction of reliable cardiovascular parameters in continuous monitoring applications. In the current paper we present an algorithm for motion artifact detection based on the analysis of the variations in the time and the period domain characteristics of the PPG signal. The extracted features are ranked using a normalized mutual information feature selection algorithm and the best features are used in a support vector machine classification model to distinguish between clean and corrupted sections of the PPG signal. The proposed method has been tested in healthy and cardiovascular diseased volunteers, considering 11 different motion artifact sources. The results achieved by the current algorithm (sensitivity—SE: 84.3%, specificity—SP: 91.5% and accuracy—ACC: 88.5%) show that the current methodology is able to identify both corrupted and clean PPG sections with high accuracy in both healthy (ACC: 87.5%) and cardiovascular diseases (ACC: 89.5%) context. (paper)

  13. A comparative evaluation of adaptive noise cancellation algorithms for minimizing motion artifacts in a forehead-mounted wearable pulse oximeter.

    Science.gov (United States)

    Comtois, Gary; Mendelson, Yitzhak; Ramuka, Piyush

    2007-01-01

    Wearable physiological monitoring using a pulse oximeter would enable field medics to monitor multiple injuries simultaneously, thereby prioritizing medical intervention when resources are limited. However, a primary factor limiting the accuracy of pulse oximetry is poor signal-to-noise ratio since photoplethysmographic (PPG) signals, from which arterial oxygen saturation (SpO2) and heart rate (HR) measurements are derived, are compromised by movement artifacts. This study was undertaken to quantify SpO2 and HR errors induced by certain motion artifacts utilizing accelerometry-based adaptive noise cancellation (ANC). Since the fingers are generally more vulnerable to motion artifacts, measurements were performed using a custom forehead-mounted wearable pulse oximeter developed for real-time remote physiological monitoring and triage applications. This study revealed that processing motion-corrupted PPG signals by least mean squares (LMS) and recursive least squares (RLS) algorithms can be effective to reduce SpO2 and HR errors during jogging, but the degree of improvement depends on filter order. Although both algorithms produced similar improvements, implementing the adaptive LMS algorithm is advantageous since it requires significantly less operations.

  14. Discrimination of common myocardial tomography artifacts

    International Nuclear Information System (INIS)

    Shi Hongcheng; Chen Shaoliang; Yao Zhifeng; Zhu Weimin; Liu Wenguan

    2002-01-01

    To study the characteristics of common myocardial tomography artifacts so as to increase the diagnosis accuracy, 132 patients with myocardial perfusion were reviewed. With careful recognition of artifacts, the patients were re-diagnosed and compared with previous results. It was found that attenuation artifacts and motion artifacts were found frequently in thallium SPECT images. Artifacts caused by thoracic wall were frequent in female and showed a fixed defect in anterior or lateral wall; attenuation artifacts caused by left hemi diaphragm were always found in male and showed that the inferior wall became thinner gradually from apex to bottom in vertical long axis slices. The coexistence of defects and hot areas was the characteristics of motion artifacts. Artifacts caused by non-target organs, liver and/or gastrointestinal tracts, were frequently seen in 99m Tc-MIBI SPECT image. By recognizing the artifacts, misdiagnosis rate decreased significantly from 13.6% to 6.8%. Authors' studies show that all kinds of artifacts have their prevalence rate and imaging feature, the artifacts could be eliminated effectively by careful analysis and some correction measures

  15. Image artifacts in concurrent transcranial magnetic stimulation (TMS) and fMRI caused by leakage currents: modeling and compensation.

    Science.gov (United States)

    Weiskopf, Nikolaus; Josephs, Oliver; Ruff, Christian C; Blankenburg, Felix; Featherstone, Eric; Thomas, Anthony; Bestmann, Sven; Driver, Jon; Deichmann, Ralf

    2009-05-01

    To characterize and eliminate a new type of image artifact in concurrent transcranial magnetic stimulation and functional MRI (TMS-fMRI) caused by small leakage currents originating from the high-voltage capacitors in the TMS stimulator system. The artifacts in echo-planar images (EPI) caused by leakage currents were characterized and quantified in numerical simulations and phantom studies with different phantom-coil geometries. A relay-diode combination was devised and inserted in the TMS circuit that shorts the leakage current. Its effectiveness for artifact reduction was assessed in a phantom scan resembling a realistic TMS-fMRI experiment. The leakage-current-induced signal changes exhibited a multipolar spatial pattern and the maxima exceeded 1% at realistic coil-cortex distances. The relay-diode combination effectively reduced the artifact to a negligible level. The leakage-current artifacts potentially obscure effects of interest or lead to false-positives. Since the artifact depends on the experimental setup and design (eg, amplitude of the leakage current, coil orientation, paradigm, EPI parameters), we recommend its assessment for each experiment. The relay-diode combination can eliminate the artifacts if necessary.

  16. Image Artifacts in Concurrent Transcranial Magnetic Stimulation (TMS) and fMRI Caused by Leakage Currents: Modeling and Compensation

    Science.gov (United States)

    Weiskopf, Nikolaus; Josephs, Oliver; Ruff, Christian C; Blankenburg, Felix; Featherstone, Eric; Thomas, Anthony; Bestmann, Sven; Driver, Jon; Deichmann, Ralf

    2009-01-01

    Purpose To characterize and eliminate a new type of image artifact in concurrent transcranial magnetic stimulation and functional MRI (TMS-fMRI) caused by small leakage currents originating from the high-voltage capacitors in the TMS stimulator system. Materials and Methods The artifacts in echo-planar images (EPI) caused by leakage currents were characterized and quantified in numerical simulations and phantom studies with different phantom-coil geometries. A relay-diode combination was devised and inserted in the TMS circuit that shorts the leakage current. Its effectiveness for artifact reduction was assessed in a phantom scan resembling a realistic TMS-fMRI experiment. Results The leakage-current-induced signal changes exhibited a multipolar spatial pattern and the maxima exceeded 1% at realistic coil-cortex distances. The relay-diode combination effectively reduced the artifact to a negligible level. Conclusion The leakage-current artifacts potentially obscure effects of interest or lead to false-positives. Since the artifact depends on the experimental setup and design (eg, amplitude of the leakage current, coil orientation, paradigm, EPI parameters), we recommend its assessment for each experiment. The relay-diode combination can eliminate the artifacts if necessary. J. Magn. Reson. Imaging 2009;29:1211–1217. © 2009 Wiley-Liss, Inc. PMID:19388099

  17. Thin-section CT of lung without ECG gating: 64-detector row CT can markedly reduce cardiac motion artifact which can simulate lung lesions

    International Nuclear Information System (INIS)

    Yanagawa, Masahiro; Tomiyama, Noriyuki; Sumikawa, Hiromitsu; Inoue, Atsuo; Daimon, Tadahisa; Honda, Osamu; Mihara, Naoki; Johkoh, Takeshi; Nakamura, Hironobu

    2009-01-01

    Purpose: Motion artifacts, which can mimic thickened bronchial wall and the cystic appearance of bronchiectasis, constitute a potential pitfall in the diagnosis of interstitial or bronchial disease. Therefore, purpose of our study was to evaluate whether 64-detector row CT (64-MDCT) enables a reduction in respiratory or cardiac motion artifacts in the lung area on thin-section CT without ECG gating, and to examine the correlation between cardiac motion artifact and heart rate. Materials and methods: Thirty-two patients with suspected diffuse lung disease, who underwent both 8- and 64-MDCT (gantry rotation time, 0.5 and 0.4 s, respectively), were included. The heart rates of an additional 155 patients were measured (range, 48-126 beats per minute; mean, 76 beats per minute) immediately prior to 64-MDCT, and compared to the degree of cardiac motion artifact. Two independent observers evaluated the following artifacts on a monitor without the knowledge of relevant clinical information: (1) artifacts on 8- and 64-MDCT images with 1.25-mm thickness and those on 64-MDCT images with 0.625-mm thickness in 32 patients; and (2) artifacts on 64-MDCT images with 0.625-mm thickness in 155 patients. Results: Interobserver agreement was good in evaluating artifacts on 8-MDCT images with 1.25-mm thickness (weighted Kappa test, κ = 0.61-0.71), and fair or poor in the other evaluations (κ < 0.31). Two observers stated that cardiac motion artifacts were more significant on 8-MDCT than on 64-MDCT in all 32 patients. Statistically significant differences were found at various checkpoints only in comparing artifacts between 8- and 64-MDCT for 1.25-mm thickness (Wilcoxon's signed-rank test, p < 0.0017). Cardiac motion artifacts on 64-MDCT had no significant correlation with heart rate (Spearman's correlation coefficient by rank test). Conclusion: The high temporal resolution of 64-MDCT appears to reduce cardiac motion artifact that can affect thin-section scans of the lung parenchyma

  18. Thin-section CT of lung without ECG gating: 64-detector row CT can markedly reduce cardiac motion artifact which can simulate lung lesions

    Energy Technology Data Exchange (ETDEWEB)

    Yanagawa, Masahiro [Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871 (Japan)], E-mail: m-yanagawa@radiol.med.osaka-u.ac.jp; Tomiyama, Noriyuki; Sumikawa, Hiromitsu; Inoue, Atsuo [Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871 (Japan); Daimon, Tadahisa [Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871 (Japan); Department of Medicine, Division of Pulmonary Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi 329-0498 (Japan); Honda, Osamu [Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871 (Japan); Mihara, Naoki [Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871 (Japan); Department of Radiology, Osaka Advanced Medical Imaging Center, 5-20-1 Momoyamadai, Suita-city, Osaka 565-0854 (Japan); Johkoh, Takeshi [Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871 (Japan); Department of Medical Physics, Osaka University Graduate School of Medicine, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871 (Japan); Nakamura, Hironobu [Department of Radiology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-city, Osaka 565-0871 (Japan)

    2009-01-15

    Purpose: Motion artifacts, which can mimic thickened bronchial wall and the cystic appearance of bronchiectasis, constitute a potential pitfall in the diagnosis of interstitial or bronchial disease. Therefore, purpose of our study was to evaluate whether 64-detector row CT (64-MDCT) enables a reduction in respiratory or cardiac motion artifacts in the lung area on thin-section CT without ECG gating, and to examine the correlation between cardiac motion artifact and heart rate. Materials and methods: Thirty-two patients with suspected diffuse lung disease, who underwent both 8- and 64-MDCT (gantry rotation time, 0.5 and 0.4 s, respectively), were included. The heart rates of an additional 155 patients were measured (range, 48-126 beats per minute; mean, 76 beats per minute) immediately prior to 64-MDCT, and compared to the degree of cardiac motion artifact. Two independent observers evaluated the following artifacts on a monitor without the knowledge of relevant clinical information: (1) artifacts on 8- and 64-MDCT images with 1.25-mm thickness and those on 64-MDCT images with 0.625-mm thickness in 32 patients; and (2) artifacts on 64-MDCT images with 0.625-mm thickness in 155 patients. Results: Interobserver agreement was good in evaluating artifacts on 8-MDCT images with 1.25-mm thickness (weighted Kappa test, {kappa} = 0.61-0.71), and fair or poor in the other evaluations ({kappa} < 0.31). Two observers stated that cardiac motion artifacts were more significant on 8-MDCT than on 64-MDCT in all 32 patients. Statistically significant differences were found at various checkpoints only in comparing artifacts between 8- and 64-MDCT for 1.25-mm thickness (Wilcoxon's signed-rank test, p < 0.0017). Cardiac motion artifacts on 64-MDCT had no significant correlation with heart rate (Spearman's correlation coefficient by rank test). Conclusion: The high temporal resolution of 64-MDCT appears to reduce cardiac motion artifact that can affect thin-section scans of

  19. SU-E-J-257: Image Artifacts Caused by Implanted Calypso Beacons in MRI Studies

    International Nuclear Information System (INIS)

    Amro, H; Chetty, I; Gordon, J; Wen, N

    2014-01-01

    Purpose: The presence of Calypso Beacon-transponders in patients can cause artifacts during MRI imaging studies. This could be a problem for post-treatment follow up of cancer patients using MRI studies to evaluate metastasis and for functional imaging studies.This work assesses (1) the volume immediately surrounding the transponders that will not be visualized by the MRI due to the beacons, and (2) the dependence of the non-visualized volume on beacon orientation, and scanning techniques. Methods: Two phantoms were used in this study (1) water filled box, (2) and a 2300 cc block of pork meat. Calypso beacons were implanted in the phantoms both in parallel and perpendicular orientations with respect to the MR scanner magnetic field. MR image series of the phantom were obtained with on a 1.0T high field open MR-SIM with multiple pulse sequences, for example, T1-weighted fast field echo and T2-weighted turbo spin echo. Results: On average, a no-signal region with 2 cm radius and 3 cm length was measured. Image artifacts are more significant when beacons are placed parallel to scanner magnetic field; the no-signal area around the beacon was about 0.5 cm larger in orthogonal orientation. The no-signal region surrounding the beacons slightly varies in dimension for the different pulse sequences. Conclusion: The use of Calypso beacons can prohibit the use of MRI studies in post-treatment assessments, especially in the immediate region surrounding the implanted beacon. A characterization of the MR scanner by identifying the no-signal regions due to implanted beacons is essential. This may render the use of Calypso beacons useful for some cases and give the treating physician a chance to identify those patients prior to beacon implantation

  20. SU-E-J-257: Image Artifacts Caused by Implanted Calypso Beacons in MRI Studies

    Energy Technology Data Exchange (ETDEWEB)

    Amro, H; Chetty, I; Gordon, J; Wen, N [Henry Ford Health System, Detroit, MI (United States)

    2014-06-01

    Purpose: The presence of Calypso Beacon-transponders in patients can cause artifacts during MRI imaging studies. This could be a problem for post-treatment follow up of cancer patients using MRI studies to evaluate metastasis and for functional imaging studies.This work assesses (1) the volume immediately surrounding the transponders that will not be visualized by the MRI due to the beacons, and (2) the dependence of the non-visualized volume on beacon orientation, and scanning techniques. Methods: Two phantoms were used in this study (1) water filled box, (2) and a 2300 cc block of pork meat. Calypso beacons were implanted in the phantoms both in parallel and perpendicular orientations with respect to the MR scanner magnetic field. MR image series of the phantom were obtained with on a 1.0T high field open MR-SIM with multiple pulse sequences, for example, T1-weighted fast field echo and T2-weighted turbo spin echo. Results: On average, a no-signal region with 2 cm radius and 3 cm length was measured. Image artifacts are more significant when beacons are placed parallel to scanner magnetic field; the no-signal area around the beacon was about 0.5 cm larger in orthogonal orientation. The no-signal region surrounding the beacons slightly varies in dimension for the different pulse sequences. Conclusion: The use of Calypso beacons can prohibit the use of MRI studies in post-treatment assessments, especially in the immediate region surrounding the implanted beacon. A characterization of the MR scanner by identifying the no-signal regions due to implanted beacons is essential. This may render the use of Calypso beacons useful for some cases and give the treating physician a chance to identify those patients prior to beacon implantation.

  1. Reduction of respiratory ghosting motion artifacts in conventional two-dimensional multi-slice Cartesian turbo spin-echo: which k-space filling order is the best?

    Science.gov (United States)

    Inoue, Yuuji; Yoneyama, Masami; Nakamura, Masanobu; Takemura, Atsushi

    2018-06-01

    The two-dimensional Cartesian turbo spin-echo (TSE) sequence is widely used in routine clinical studies, but it is sensitive to respiratory motion. We investigated the k-space orders in Cartesian TSE that can effectively reduce motion artifacts. The purpose of this study was to demonstrate the relationship between k-space order and degree of motion artifacts using a moving phantom. We compared the degree of motion artifacts between linear and asymmetric k-space orders. The actual spacing of ghost artifacts in the asymmetric order was doubled compared with that in the linear order in the free-breathing situation. The asymmetric order clearly showed less sensitivity to incomplete breath-hold at the latter half of the imaging period. Because of the actual number of partitions of the k-space and the temporal filling order, the asymmetric k-space order of Cartesian TSE was superior to the linear k-space order for reduction of ghosting motion artifacts.

  2. TU-F-BRB-02: Motion Artifacts and Suppression in MRI

    International Nuclear Information System (INIS)

    Zhong, X.

    2015-01-01

    The current clinical standard of organ respiratory imaging, 4D-CT, is fundamentally limited by poor soft-tissue contrast and imaging dose. These limitations are potential barriers to beneficial “4D” radiotherapy methods which optimize the target and OAR dose-volume considering breathing motion but rely on a robust motion characterization. Conversely, MRI imparts no known radiation risk and has excellent soft-tissue contrast. MRI-based motion management is therefore highly desirable and holds great promise to improve radiotherapy of moving cancers, particularly in the abdomen. Over the past decade, MRI techniques have improved significantly, making MR-based motion management clinically feasible. For example, cine MRI has high temporal resolution up to 10 f/s and has been used to track and/or characterize tumor motion, study correlation between external and internal motions. New MR technologies, such as 4D-MRI and MRI hybrid treatment machines (i.e. MR-linac or MR-Co60), have been recently developed. These technologies can lead to more accurate target volume determination and more precise radiation dose delivery via direct tumor gating or tracking. Despite all these promises, great challenges exist and the achievable clinical benefit of MRI-based tumor motion management has yet to be fully explored, much less realized. In this proposal, we will review novel MR-based motion management methods and technologies, the state-of-the-art concerning MRI development and clinical application and the barriers to more widespread adoption. Learning Objectives: Discuss the need of MR-based motion management for improving patient care in radiotherapy. Understand MR techniques for motion imaging and tumor motion characterization. Understand the current state of the art and future steps for clinical integration. Henry Ford Health System holds research agreements with Philips Healthcare. Research sponsored in part by a Henry Ford Health System Internal Mentored Grant

  3. TU-F-BRB-02: Motion Artifacts and Suppression in MRI

    Energy Technology Data Exchange (ETDEWEB)

    Zhong, X. [Siemens (Germany)

    2015-06-15

    The current clinical standard of organ respiratory imaging, 4D-CT, is fundamentally limited by poor soft-tissue contrast and imaging dose. These limitations are potential barriers to beneficial “4D” radiotherapy methods which optimize the target and OAR dose-volume considering breathing motion but rely on a robust motion characterization. Conversely, MRI imparts no known radiation risk and has excellent soft-tissue contrast. MRI-based motion management is therefore highly desirable and holds great promise to improve radiotherapy of moving cancers, particularly in the abdomen. Over the past decade, MRI techniques have improved significantly, making MR-based motion management clinically feasible. For example, cine MRI has high temporal resolution up to 10 f/s and has been used to track and/or characterize tumor motion, study correlation between external and internal motions. New MR technologies, such as 4D-MRI and MRI hybrid treatment machines (i.e. MR-linac or MR-Co60), have been recently developed. These technologies can lead to more accurate target volume determination and more precise radiation dose delivery via direct tumor gating or tracking. Despite all these promises, great challenges exist and the achievable clinical benefit of MRI-based tumor motion management has yet to be fully explored, much less realized. In this proposal, we will review novel MR-based motion management methods and technologies, the state-of-the-art concerning MRI development and clinical application and the barriers to more widespread adoption. Learning Objectives: Discuss the need of MR-based motion management for improving patient care in radiotherapy. Understand MR techniques for motion imaging and tumor motion characterization. Understand the current state of the art and future steps for clinical integration. Henry Ford Health System holds research agreements with Philips Healthcare. Research sponsored in part by a Henry Ford Health System Internal Mentored Grant.

  4. Artifacts in Magnetic Resonance Imaging

    International Nuclear Information System (INIS)

    Krupa, Katarzyna; Bekiesińska-Figatowska, Monika

    2015-01-01

    Artifacts in magnetic resonance imaging and foreign bodies within the patient’s body may be confused with a pathology or may reduce the quality of examinations. Radiologists are frequently not informed about the medical history of patients and face postoperative/other images they are not familiar with. A gallery of such images was presented in this manuscript. A truncation artifact in the spinal cord could be misinterpreted as a syrinx. Motion artifacts caused by breathing, cardiac movement, CSF pulsation/blood flow create a ghost artifact which can be reduced by patient immobilization, or cardiac/respiratory gating. Aliasing artifacts can be eliminated by increasing the field of view. An artificially hyperintense signal on FLAIR images can result from magnetic susceptibility artifacts, CSF/vascular pulsation, motion, but can also be found in patients undergoing MRI examinations while receiving supplemental oxygen. Metallic and other foreign bodies which may be found on and in patients’ bodies are the main group of artifacts and these are the focus of this study: e.g. make-up, tattoos, hairbands, clothes, endovascular embolization, prostheses, surgical clips, intraorbital and other medical implants, etc. Knowledge of different types of artifacts and their origin, and of possible foreign bodies is necessary to eliminate them or to reduce their negative influence on MR images by adjusting acquisition parameters. It is also necessary to take them into consideration when interpreting the images. Some proposals of reducing artifacts have been mentioned. Describing in detail the procedures to avoid or limit the artifacts would go beyond the scope of this paper but technical ways to reduce them can be found in the cited literature

  5. Simple motion correction strategy reduces respiratory-induced motion artifacts for k-t accelerated and compressed-sensing cardiovascular magnetic resonance perfusion imaging.

    Science.gov (United States)

    Zhou, Ruixi; Huang, Wei; Yang, Yang; Chen, Xiao; Weller, Daniel S; Kramer, Christopher M; Kozerke, Sebastian; Salerno, Michael

    2018-02-01

    SSIM (p simple and robust rigid motion compensation strategy greatly reduces motion artifacts and improves image quality for standard k-t PCA and k-t SLR techniques in setting of respiratory motion due to imperfect breath-holding.

  6. Signal processing methods for reducing artifacts in microelectrode brain recordings caused by functional electrical stimulation

    Science.gov (United States)

    Young, D.; Willett, F.; Memberg, W. D.; Murphy, B.; Walter, B.; Sweet, J.; Miller, J.; Hochberg, L. R.; Kirsch, R. F.; Ajiboye, A. B.

    2018-04-01

    Objective. Functional electrical stimulation (FES) is a promising technology for restoring movement to paralyzed limbs. Intracortical brain-computer interfaces (iBCIs) have enabled intuitive control over virtual and robotic movements, and more recently over upper extremity FES neuroprostheses. However, electrical stimulation of muscles creates artifacts in intracortical microelectrode recordings that could degrade iBCI performance. Here, we investigate methods for reducing the cortically recorded artifacts that result from peripheral electrical stimulation. Approach. One participant in the BrainGate2 pilot clinical trial had two intracortical microelectrode arrays placed in the motor cortex, and thirty-six stimulating intramuscular electrodes placed in the muscles of the contralateral limb. We characterized intracortically recorded electrical artifacts during both intramuscular and surface stimulation. We compared the performance of three artifact reduction methods: blanking, common average reference (CAR) and linear regression reference (LRR), which creates channel-specific reference signals, composed of weighted sums of other channels. Main results. Electrical artifacts resulting from surface stimulation were 175  ×  larger than baseline neural recordings (which were 110 µV peak-to-peak), while intramuscular stimulation artifacts were only 4  ×  larger. The artifact waveforms were highly consistent across electrodes within each array. Application of LRR reduced artifact magnitudes to less than 10 µV and largely preserved the original neural feature values used for decoding. Unmitigated stimulation artifacts decreased iBCI decoding performance, but performance was almost completely recovered using LRR, which outperformed CAR and blanking and extracted useful neural information during stimulation artifact periods. Significance. The LRR method was effective at reducing electrical artifacts resulting from both intramuscular and surface FES, and

  7. Reduction of thoracic aorta motion artifact with high-pitch 128-slice dual-source computed tomographic angiography: a historical control study.

    Science.gov (United States)

    Nakagawa, Junichiro; Tasaki, Osamu; Watanabe, Yoshiyuki; Azuma, Takeo; Ohnishi, Mitsuo; Ukai, Isao; Tahara, Kenichi; Ogura, Hiroshi; Kuwagata, Yasuyuki; Hamasaki, Toshimitsu; Shimazu, Takeshi

    2013-01-01

    Electrocardiogram-gated imaging combined with multi-detector row computed tomography (MDCT) has reduced cardiac motion artifacts, but it was not practical in the emergency setting. The purpose of this study was to evaluate the ability of a high-pitch, 128-slice dual-source CT (DSCT) scanner to reduce motion artifacts in patients admitted to the emergency room. This study comprised 100 patients suspected of having thoracic aorta lesions. We examined 47 patients with the 128-slice DSCT scanner (DSCT group), and 53 patients were examined with a 64-slice MDCT scanner (MDCT group). Six anatomic areas in the thoracic aorta were evaluated. Computed tomography images in the DSCT group were distinct, and significant differences were observed in images of all areas between the 2 groups except for the descending aorta. The high-pitch DSCT scanner can reduce motion artifacts of the thoracic aorta and enable radiological diagnosis even in patients with tachycardia and without breath hold.

  8. SU-E-I-51: Use of Blade Sequences in Cervical Spine MR Imaging for Eliminating Motion, Truncation and Flow Artifacts

    Energy Technology Data Exchange (ETDEWEB)

    Mavroidis, P [University of Texas Health Science Center, UTHSCSA, San Antonio, TX (United States); Lavdas, E; Kostopoulos, S; Ninos, C; Strikou, A; Glotsos, D; Vlachopoulou, A; Oikonomou, G [Technological Education Institute of Athens, Athens, Athens (Greece); Economopoulos, N [General University Hospital ATTIKON, Athens, Athens (Greece); Roka, V [Health Center of Farkadona, Trikala (Greece); Sakkas, G [Center for Research and Technology of Thessaly, Trikala (Greece); Tsagkalis, A; Batsikas, G [IASO Thessalias Hospital, Larissa (Greece); Statkahis, S [Cancer Therapy and Research Center, San Antonio, TX (United States); Papanikolaou, N [University of Texas HSC SA, San Antonio, TX (United States)

    2014-06-01

    Purpose: To assess the efficacy of the BLADE technique to eliminate motion, truncation, flow and other artifacts in Cervical Spine MRI compared to the conventional technique. To study the ability of the examined sequences to reduce the indetention and wrap artifacts, which have been reported in BLADE sagittal sequences. Methods: Forty consecutive subjects, who had been routinely scanned for cervical spine examination using four different image acquisition techniques, were analyzed. More specifically, the following pairs of sequences were compared: a) T2 TSE SAG vs. T2 TSE SAG BLADE and b) T2 TIRM SAG vs. T2 TIRM SAG BLADE. A quantitative analysis was performed using the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and relative contrast (ReCon) measures. A qualitative analysis was also performed by two radiologists, who graded seven image characteristics on a 5-point scale (0:non-visualization; 1:poor; 2:average; 3:good; 4:excellent). The observers also evaluated the presence of image artifacts (motion, truncation, flow, indentation). Results: Based on the findings of the quantitative analysis, the ReCON values of the CSF (cerebrospinal fluid)/SC (spinal cord) between TIRM SAG and TIRM SAG BLADE were found to present statistical significant differences (p<0.001). Regarding motion and truncation artifacts, the T2 TSE SAG BLADE was superior compared to the T2 TSE SAG and the T2 TIRM SAG BLADE was superior compared to the T2 TIRM SAG. Regarding flow artifacts, T2 TIRM SAG BLADE eliminated more artifacts compared to the T2 TIRM SAG. Conclusion: The use of BLADE sequences in cervical spine MR examinations appears to be capable of potentially eliminating motion, pulsatile flow and trancation artifacts. Furthermore, BLADE sequences are proposed to be used in the standard examination protocols based on the fact that a significantly improved image quality could be achieved.

  9. SU-E-I-51: Use of Blade Sequences in Cervical Spine MR Imaging for Eliminating Motion, Truncation and Flow Artifacts

    International Nuclear Information System (INIS)

    Mavroidis, P; Lavdas, E; Kostopoulos, S; Ninos, C; Strikou, A; Glotsos, D; Vlachopoulou, A; Oikonomou, G; Economopoulos, N; Roka, V; Sakkas, G; Tsagkalis, A; Batsikas, G; Statkahis, S; Papanikolaou, N

    2014-01-01

    Purpose: To assess the efficacy of the BLADE technique to eliminate motion, truncation, flow and other artifacts in Cervical Spine MRI compared to the conventional technique. To study the ability of the examined sequences to reduce the indetention and wrap artifacts, which have been reported in BLADE sagittal sequences. Methods: Forty consecutive subjects, who had been routinely scanned for cervical spine examination using four different image acquisition techniques, were analyzed. More specifically, the following pairs of sequences were compared: a) T2 TSE SAG vs. T2 TSE SAG BLADE and b) T2 TIRM SAG vs. T2 TIRM SAG BLADE. A quantitative analysis was performed using the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and relative contrast (ReCon) measures. A qualitative analysis was also performed by two radiologists, who graded seven image characteristics on a 5-point scale (0:non-visualization; 1:poor; 2:average; 3:good; 4:excellent). The observers also evaluated the presence of image artifacts (motion, truncation, flow, indentation). Results: Based on the findings of the quantitative analysis, the ReCON values of the CSF (cerebrospinal fluid)/SC (spinal cord) between TIRM SAG and TIRM SAG BLADE were found to present statistical significant differences (p<0.001). Regarding motion and truncation artifacts, the T2 TSE SAG BLADE was superior compared to the T2 TSE SAG and the T2 TIRM SAG BLADE was superior compared to the T2 TIRM SAG. Regarding flow artifacts, T2 TIRM SAG BLADE eliminated more artifacts compared to the T2 TIRM SAG. Conclusion: The use of BLADE sequences in cervical spine MR examinations appears to be capable of potentially eliminating motion, pulsatile flow and trancation artifacts. Furthermore, BLADE sequences are proposed to be used in the standard examination protocols based on the fact that a significantly improved image quality could be achieved

  10. Regularly incremented phase encoding - MR fingerprinting (RIPE-MRF) for enhanced motion artifact suppression in preclinical cartesian MR fingerprinting.

    Science.gov (United States)

    Anderson, Christian E; Wang, Charlie Y; Gu, Yuning; Darrah, Rebecca; Griswold, Mark A; Yu, Xin; Flask, Chris A

    2018-04-01

    The regularly incremented phase encoding-magnetic resonance fingerprinting (RIPE-MRF) method is introduced to limit the sensitivity of preclinical MRF assessments to pulsatile and respiratory motion artifacts. As compared to previously reported standard Cartesian-MRF methods (SC-MRF), the proposed RIPE-MRF method uses a modified Cartesian trajectory that varies the acquired phase-encoding line within each dynamic MRF dataset. Phantoms and mice were scanned without gating or triggering on a 7T preclinical MRI scanner using the RIPE-MRF and SC-MRF methods. In vitro phantom longitudinal relaxation time (T 1 ) and transverse relaxation time (T 2 ) measurements, as well as in vivo liver assessments of artifact-to-noise ratio (ANR) and MRF-based T 1 and T 2 mean and standard deviation, were compared between the two methods (n = 5). RIPE-MRF showed significant ANR reductions in regions of pulsatility (P Reson Med 79:2176-2182, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  11. Artifacts in digital radiography

    Energy Technology Data Exchange (ETDEWEB)

    Min, Jung Whan [Dept. of Radiological Technology, Shin Gu University, Sungnam (Korea, Republic of); Kim, Jung Min [Dept. of Radiological Technology, Korea University, Seoul (Korea, Republic of); Jeong, Hoi Woun [Dept. of Radiological Technology, Beakseok Culture University, Cheonan (Korea, Republic of)

    2015-12-15

    Digital Radiography is a big part of diagnostic radiology. Because uncorrected digital radiography image supported false effect of Patient’s health care. We must be manage the correct digital radiography image. Thus, the artifact images can have effect to make a wrong diagnosis. We report types of occurrence by analyzing the artifacts that occurs in digital radiography system. We had collected the artifacts occurred in digital radiography system of general hospital from 2007 to 2014. The collected data had analyzed and then had categorize as the occurred causes. The artifacts could be categorized by hardware artifacts, software artifacts, operating errors, system artifacts, and others. Hardware artifact from a Ghost artifact that is caused by lag effect occurred most frequently. The others cases are the artifacts caused by RF noise and foreign body in equipments. Software artifacts are many different types of reasons. The uncorrected processing artifacts and the image processing error artifacts occurred most frequently. Exposure data recognize (EDR) error artifacts, the processing error of commissural line, and etc., the software artifacts were caused by various reasons. Operating artifacts were caused when the user did not have the full understanding of the digital medical image system. System artifacts had appeared the error due to DICOM header information and the compression algorithm. The obvious artifacts should be re-examined, and it could result in increasing the exposure dose of the patient. The unclear artifact leads to a wrong diagnosis and added examination. The ability to correctly determine artifact are required. We have to reduce the artifact occurrences by understanding its characteristic and providing sustainable education as well as the maintenance of the equipments.

  12. Artifacts in digital radiography

    International Nuclear Information System (INIS)

    Min, Jung Whan; Kim, Jung Min; Jeong, Hoi Woun

    2015-01-01

    Digital Radiography is a big part of diagnostic radiology. Because uncorrected digital radiography image supported false effect of Patient’s health care. We must be manage the correct digital radiography image. Thus, the artifact images can have effect to make a wrong diagnosis. We report types of occurrence by analyzing the artifacts that occurs in digital radiography system. We had collected the artifacts occurred in digital radiography system of general hospital from 2007 to 2014. The collected data had analyzed and then had categorize as the occurred causes. The artifacts could be categorized by hardware artifacts, software artifacts, operating errors, system artifacts, and others. Hardware artifact from a Ghost artifact that is caused by lag effect occurred most frequently. The others cases are the artifacts caused by RF noise and foreign body in equipments. Software artifacts are many different types of reasons. The uncorrected processing artifacts and the image processing error artifacts occurred most frequently. Exposure data recognize (EDR) error artifacts, the processing error of commissural line, and etc., the software artifacts were caused by various reasons. Operating artifacts were caused when the user did not have the full understanding of the digital medical image system. System artifacts had appeared the error due to DICOM header information and the compression algorithm. The obvious artifacts should be re-examined, and it could result in increasing the exposure dose of the patient. The unclear artifact leads to a wrong diagnosis and added examination. The ability to correctly determine artifact are required. We have to reduce the artifact occurrences by understanding its characteristic and providing sustainable education as well as the maintenance of the equipments

  13. Motion-induced blindness and microsaccades: cause and effect

    NARCIS (Netherlands)

    Bonneh, Y.S.; Donner, T.H.; Sagi, D.; Fried, M.; Heeger, D.J.; Arieli, A.

    2010-01-01

    It has been suggested that subjective disappearance of visual stimuli results from a spontaneous reduction of microsaccade rate causing image stabilization, enhanced adaptation, and a consequent fading. In motion-induced blindness (MIB), salient visual targets disappear intermittently when

  14. Evaluation of soft-tissue artifacts when using anatomical and technical markers to measure mandibular motion

    Directory of Open Access Journals (Sweden)

    Chien-Chih Chen

    2011-06-01

    Conclusions: It appears that markers on the frontal nose bridge are good alternatives to transoral rigid devices for measuring mandibular motion, compared to optical frame markers and other skin markers on the face. The results of the current study will be helpful for establishing guidelines for marker placement when measuring mandibular movements in patients with potential temporomandibular disorders.

  15. Effects of Maternal Valium Administration on Fetal MRI Motion Artifact: A Comparison Study at High Altitude.

    Science.gov (United States)

    Meyers, Mariana L; Mirsky, David M; Dannull, Kimberly A; Tong, Suhong; Crombleholme, Timothy M

    2017-01-01

    Fetal MRI is performed without sedation. In cases of maternal claustrophobia or when reduction of fetal motion is critical, benzodiazepines may help. The purpose of this study was to evaluate the effects of low-dose benzodiazepine on fetal motion MRI and its effect on maternal oxygen levels at higher elevation. A total of 131 fetal MRI scans performed from March 2012 through December 2013 were studied. Nineteen of the cases were performed following Valium administration. Images were graded with a 5-point Likert scale. Using pulse oximetry, maternal oxygen levels were recorded. Results were analyzed for each category combining 3 readers' interpretations. Using a 2-sample t test model, the average imaging scores were better for the control than the Valium group (p = 0.0139). Maternal oxygen levels at different times and positions were compared using independent 2-sample t test between the Valium and control groups showing no change in O2 saturation, except when controlling for altitude and gestational age (p = 0.0326). Administration of low-dose Valium did not decrease fetal motion on MRI. Valium did not pose any risk of maternal hypoxemia, except when controlling for altitude and gestational age on supine position. Thus, caution should be exercised to prevent the risk of fetal hypoxemia. © 2016 S. Karger AG, Basel.

  16. MOTION ARTIFACT REDUCTION IN FUNCTIONAL NEAR INFRARED SPECTROSCOPY SIGNALS BY AUTOREGRESSIVE MOVING AVERAGE MODELING BASED KALMAN FILTERING

    Directory of Open Access Journals (Sweden)

    MEHDI AMIAN

    2013-10-01

    Full Text Available Functional near infrared spectroscopy (fNIRS is a technique that is used for noninvasive measurement of the oxyhemoglobin (HbO2 and deoxyhemoglobin (HHb concentrations in the brain tissue. Since the ratio of the concentration of these two agents is correlated with the neuronal activity, fNIRS can be used for the monitoring and quantifying the cortical activity. The portability of fNIRS makes it a good candidate for studies involving subject's movement. The fNIRS measurements, however, are sensitive to artifacts generated by subject's head motion. This makes fNIRS signals less effective in such applications. In this paper, the autoregressive moving average (ARMA modeling of the fNIRS signal is proposed for state-space representation of the signal which is then fed to the Kalman filter for estimating the motionless signal from motion corrupted signal. Results are compared to the autoregressive model (AR based approach, which has been done previously, and show that the ARMA models outperform AR models. We attribute it to the richer structure, containing more terms indeed, of ARMA than AR. We show that the signal to noise ratio (SNR is about 2 dB higher for ARMA based method.

  17. Combination of fat saturation and variable bandwidth imaging to increase signal-to-noise ratio and decrease motion artifacts for body MR imaging at high field

    International Nuclear Information System (INIS)

    Chew, W.M.

    1989-01-01

    The signal-to-noise ratio (SNR) of the MR imaging examination is a critical component of the quality of the image. Standard methods to increase SNR include signal averaging with multiple excitations, at the expense of imaging time (which on T2-weighted images could be quite significant), or increasing pixel volume by manipulation of field of view, matrix size, and/or section thickness, all at the expense of resolution. Another available method to increase SNR is to reduce the bandwidth of the receiver, which increases SNR by the square root of the amount of the reduction. The penalty imposed on high-field-strength MR examinations of the body is an unacceptable increase in chemical shift artifact. However, presaturating the fat resonance eliminates the chemical shift artifact. Thus, a combination of imaging techniques, fat suppression, and decreased bandwidth imaging can produce images free of chemical shift artifact with increased SNR and no penalty in resolution or imaging time. Early studies also show a reduction in motion artifact when fat saturation is used. This paper reports MR imaging performed with a 1.5-T Signa imager. With this technique, T2-weighted images (2,500/20/80 [repetition time msec/echo time msec/inversion time msec]) illustrating the increase in SNR and T1-weighted images (600/20) demonstrating a decrease in motion artifact are shown

  18. E-Bra system for women ECG measurement with GPRS communication, Nanosensor, and motion artifact remove algorithm

    Science.gov (United States)

    Kwon, Hyeokjun; Oh, Sechang; Kumar, Prashanth S.; Varadan, Vijay K.

    2012-10-01

    with conductive gel. However, the gel can be dried when taking long time monitoring. The gold nanowire structure electrodes without consideration of uncomfortable usage of gel are attached on beneath the chest position of a brassiere, and the electrodes convert the physical ECG signal to voltage potential signal. The voltage potential ECG signal is converted to digital signal by AD converter included in microprocessor. The converted ECG signal by AD converter is saved on every 1 sec period in the internal RAM in microprocessor. For transmission of the saved data in the internal RAM to a server computer locating at remote area, the system uses the GPRS communication technology, which can develop the wide area network(WAP) without any gateway and repeater. In addition, the transmission system is operated on client mode of GPRS communication. The remote server is installed a program including the functions of displaying and analyzing the transmitted ECG. To display the ECG data, the program is operated with TCP/IP server mode and static IP address, and to analyze the ECG data, the paper suggests motion artifact remove algorithm including adaptive filter with LMS(least mean square), baseline detection algorithm using predictability estimation theory, a filter with moving weighted factor, low pass filter, peak to peak detection, and interpolation.

  19. The Cardiac MR Images and Causes of Paradoxical Septal Motion

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Dong Hun [Soonchunhyang University Bucheon Hospital, Bucheon (Korea, Republic of); Choi, Sang Il; Chun, Eun Ju [Seoul National University Bundang Hospital, Seongnam (Korea, Republic of); Choi, Sung Hun [Ulsan University Hospital, Ulsan (Korea, Republic of); Park, Jae Hyung [Seoul National University Hospital, Seoul (Korea, Republic of)

    2010-10-15

    Real-time cine MRI studies using the steady-state free precession (SSFP) technique are very useful for evaluating cardiac and septal motion. During diastole, the septum acts as a compliant membrane between the two ventricles, and its position and geometry respond to even small alterations in the trans-septal pressure gradients. Abnormal septal motion can be caused by an overload of the right ventricle, delayed ventricular filling and abnormal conduction. In this study, we illustrate, based on our experiences, the causes of abnormal septal motion such as corrective surgery for tetralogy of Fallot, an atrial septal defect, pulmonary thromboembolism, mitral stenosis, constrictive pericarditis and left bundle branch block. In addition, we discuss the significance of paradoxical septal motion in the context of cardiac MR imaging.

  20. The Cardiac MR Images and Causes of Paradoxical Septal Motion

    International Nuclear Information System (INIS)

    Kim, Dong Hun; Choi, Sang Il; Chun, Eun Ju; Choi, Sung Hun; Park, Jae Hyung

    2010-01-01

    Real-time cine MRI studies using the steady-state free precession (SSFP) technique are very useful for evaluating cardiac and septal motion. During diastole, the septum acts as a compliant membrane between the two ventricles, and its position and geometry respond to even small alterations in the trans-septal pressure gradients. Abnormal septal motion can be caused by an overload of the right ventricle, delayed ventricular filling and abnormal conduction. In this study, we illustrate, based on our experiences, the causes of abnormal septal motion such as corrective surgery for tetralogy of Fallot, an atrial septal defect, pulmonary thromboembolism, mitral stenosis, constrictive pericarditis and left bundle branch block. In addition, we discuss the significance of paradoxical septal motion in the context of cardiac MR imaging

  1. Estimating actigraphy from motion artifacts in ECG and respiratory effort signals.

    Science.gov (United States)

    Fonseca, Pedro; Aarts, Ronald M; Long, Xi; Rolink, Jérôme; Leonhardt, Steffen

    2016-01-01

    Recent work in unobtrusive sleep/wake classification has shown that cardiac and respiratory features can help improve classification performance. Nevertheless, actigraphy remains the single most discriminative modality for this task. Unfortunately, it requires the use of dedicated devices in addition to the sensors used to measure electrocardiogram (ECG) or respiratory effort. This paper proposes a method to estimate actigraphy from the body movement artifacts present in the ECG and respiratory inductance plethysmography (RIP) based on the time-frequency analysis of those signals. Using a continuous wavelet transform to analyze RIP, and ECG and RIP combined, it provides a surrogate measure of actigraphy with moderate correlation (for ECG+RIP, ρ = 0.74, p  <  0.001) and agreement (mean bias ratio of 0.94 and 95% agreement ratios of 0.11 and 8.45) with reference actigraphy. More important, it can be used as a replacement of actigraphy in sleep/wake classification: after cross-validation with a data set comprising polysomnographic (PSG) recordings of 15 healthy subjects and 25 insomniacs annotated by an external sleep technician, it achieves a statistically non-inferior classification performance when used together with respiratory features (average κ of 0.64 for 15 healthy subjects, and 0.50 for a dataset with 40 healthy and insomniac subjects), and when used together with respiratory and cardiac features (average κ of 0.66 for 15 healthy subjects, and 0.56 for 40 healthy and insomniac subjects). Since this method eliminates the need for a dedicated actigraphy device, it reduces the number of sensors needed for sleep/wake classification to a single sensor when using respiratory features, and to two sensors when using respiratory and cardiac features without any loss in performance. It offers a major benefit in terms of comfort for long-term home monitoring and is immediately applicable for legacy ECG and RIP monitoring devices already used in clinical

  2. Quantitative analysis of magnetic resonance imaging susceptibility artifacts caused by neurosurgical biomaterials. Comparison of 0.5, 1.5, and 3.0 tesla magnetic fields

    International Nuclear Information System (INIS)

    Matsuura, Hideki; Inoue, Takashi; Ogasawara, Kuniaki; Sasaki, Makoto; Konno, Hiromu; Kuzu, Yasutaka; Nishimoto, Hideaki; Ogawa, Akira

    2005-01-01

    Magnetic resonance (MR) imaging is an important diagnostic tool for neurosurgical diseases but susceptibility artifacts caused by biomaterial instrumentation frequently causes difficulty in visualizing postoperative changes. The susceptibility artifacts caused by neurosurgical biomaterials were compared quantitatively by 0.5, 1.5, and 3.0 Tesla MR imaging. MR imaging of uniform size and shape of pieces ceramic (zirconia), pure titanium, titanium alloy, and cobalt-based alloy was performed at 0.5, 1.5, and 3.0 Tesla. A linear region of interest was defined across the center of the biomaterial in the transverse direction, and the susceptibility artifact diameter was calculated. Susceptibility artifacts developed around all biomaterials at all magnetic field strengths. The artifact diameters caused by pure titanium, titanium alloy, and cobalt-based alloy increased in the order of 0.5, 1.5, to 3.0 Tesla magnetic fields. The artifact diameter of ceramic was not influenced by magnetic field strength, and was the smallest of all biomaterials at all magnetic field strengths. The artifacts caused by biomaterials except ceramic increase with the magnetic field strength. Ceramic instrumentation will minimize artifacts in all magnetic fields. (author)

  3. Genesis of multipeaked waves of the esophagus: repetitive contractions or motion artifact?

    Science.gov (United States)

    Sampath, Neha J; Bhargava, Valmik; Mittal, Ravinder K

    2010-06-01

    Multipeaked waves (MPW) in the distal esophagus occur frequently in patients with esophageal spastic motor disorders and diabetes mellitus and are thought to represent repetitive esophageal contractions. We aimed to investigate whether the relative motion between a stationary pressure sensor and contracted peristaltic esophageal segment that moves with respiration leads to the formation of MPW. We mathematically modeled the effect of relative movement between a moving pressure segment and a fixed pressure sensor on the pressure waveform morphology. We conducted retrospective analysis of 100 swallow-induced esophageal contractions in 10 patients, who demonstrated >30% MPW on high-resolution manometry (HRM) during standardized swallows. Finally, using HRM, we determined the effects of suspended breathing and hyperventilation on the waveform morphology in 10 patients prospectively. Modeling revealed that relative movement between a stationary pressure sensor and a moving contracted segment, contraction duration, contraction amplitude, respiratory frequency, and depth of respiration affects the waveform morphology. Retrospective analysis demonstrated a close temporal association with the onset of second and subsequent contractions in MPW with respiratory phase reversals. Numbers of peaks in MPW and respiratory phase reversals were closely related to the duration of contraction. In the prospective study, suspended breathing and hyperventilation resulted in a significant decrease and increase in the MPW frequency as well as the number of peaks within MPW respectively. We conclude that MPW observed during clinical motility studies are not indicative of repetitive esophageal contraction; rather they represent respiration-related movement of the contracted esophageal segment in relation to the stationary pressure sensor.

  4. Free-breathing high-pitch 80kVp dual-source computed tomography of the pediatric chest: Image quality, presence of motion artifacts and radiation dose.

    Science.gov (United States)

    Bodelle, Boris; Fischbach, Constanze; Booz, Christian; Yel, Ibrahim; Frellesen, Claudia; Beeres, Martin; Vogl, Thomas J; Scholtz, Jan-Erik

    2017-04-01

    To investigate image quality, presence of motion artifacts and effects on radiation dose of 80kVp high-pitch dual-source CT (DSCT) in combination with an advanced modeled iterative reconstruction algorithm (ADMIRE) of the pediatric chest compared to single-source CT (SSCT). The study was approved by the institutional review board. Eighty-seven consecutive pediatric patients (mean age 9.1±4.9years) received either free-breathing high-pitch (pitch 3.2) chest 192-slice DSCT (group 1, n=31) or standard-pitch (pitch 1.2) 128-slice SSCT (group 2, n=56) with breathing-instructions by random assignment. Tube settings were similar in both groups with 80 kVp and 74 ref. mAs. Images were reconstructed using FBP for both groups. Additionally, ADMIRE was used in group 1. Effective thorax diameter, image noise, and signal-to-noise ratio (SNR) of the pectoralis major muscle and the thoracic aorta were calculated. Motion artifacts were measured as doubling boarders of the diaphragm and the heart. Images were rated by two blinded readers for overall image quality and presence of motion artifacts on 5-point-scales. Size specific dose estimates (SSDE, mGy) and effective dose (ED, mSv) were calculated. Age and effective thorax diameter showed no statistically significant differences in both groups. Image noise and SNR were comparable (p>0.64) for SSCT and DSCT with ADMIRE, while DSCT with FBP showed inferior results (pchest DSCT in combination with ADMIRE reduces motion artifacts and increases image quality while lowering radiation exposure in free-breathing pediatric patients without sedation. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Motion compensated digital tomosynthesis

    NARCIS (Netherlands)

    van der Reijden, Anneke; van Herk, Marcel; Sonke, Jan-Jakob

    2013-01-01

    Digital tomosynthesis (DTS) is a limited angle image reconstruction method for cone beam projections that offers patient surveillance capabilities during VMAT based SBRT delivery. Motion compensation (MC) has the potential to mitigate motion artifacts caused by respiratory motion, such as blur. The

  6. Free-breathing high-pitch 80 kVp dual-source computed tomography of the pediatric chest: Image quality, presence of motion artifacts and radiation dose

    Energy Technology Data Exchange (ETDEWEB)

    Bodelle, Boris, E-mail: bbodelle@googlemail.com; Fischbach, Constanze; Booz, Christian; Yel, Ibrahim; Frellesen, Claudia; Beeres, Martin; Vogl, Thomas J.; Scholtz, Jan-Erik

    2017-04-15

    Objectives: To investigate image quality, presence of motion artifacts and effects on radiation dose of 80 kVp high-pitch dual-source CT (DSCT) in combination with an advanced modeled iterative reconstruction algorithm (ADMIRE) of the pediatric chest compared to single-source CT (SSCT). Materials and methods: The study was approved by the institutional review board. Eighty-seven consecutive pediatric patients (mean age 9.1 ± 4.9 years) received either free-breathing high-pitch (pitch 3.2) chest 192-slice DSCT (group 1, n = 31) or standard-pitch (pitch 1.2) 128-slice SSCT (group 2, n = 56) with breathing-instructions by random assignment. Tube settings were similar in both groups with 80 kVp and 74 ref. mAs. Images were reconstructed using FBP for both groups. Additionally, ADMIRE was used in group 1. Effective thorax diameter, image noise, and signal-to-noise ratio (SNR) of the pectoralis major muscle and the thoracic aorta were calculated. Motion artifacts were measured as doubling boarders of the diaphragm and the heart. Images were rated by two blinded readers for overall image quality and presence of motion artifacts on 5-point-scales. Size specific dose estimates (SSDE, mGy) and effective dose (ED, mSv) were calculated. Results: Age and effective thorax diameter showed no statistically significant differences in both groups. Image noise and SNR were comparable (p > 0.64) for SSCT and DSCT with ADMIRE, while DSCT with FBP showed inferior results (p < 0.01). Motion artifacts were reduced significantly (p = 0.001) with DSCT. DSCT with ADMIRE showed the highest overall IQ (p < 0.0001). Radiation dose was lower for DSCT compared to SSCT (median SSDE: 0.82 mGy vs. 0.92 mGy, p < 0.02; median ED: 0.4 mSv vs. 0.48 mSv, p = 0.02). Conclusions: High-pitch 80 kVp chest DSCT in combination with ADMIRE reduces motion artifacts and increases image quality while lowering radiation exposure in free-breathing pediatric patients without sedation.

  7. Free-breathing high-pitch 80 kVp dual-source computed tomography of the pediatric chest: Image quality, presence of motion artifacts and radiation dose

    International Nuclear Information System (INIS)

    Bodelle, Boris; Fischbach, Constanze; Booz, Christian; Yel, Ibrahim; Frellesen, Claudia; Beeres, Martin; Vogl, Thomas J.; Scholtz, Jan-Erik

    2017-01-01

    Objectives: To investigate image quality, presence of motion artifacts and effects on radiation dose of 80 kVp high-pitch dual-source CT (DSCT) in combination with an advanced modeled iterative reconstruction algorithm (ADMIRE) of the pediatric chest compared to single-source CT (SSCT). Materials and methods: The study was approved by the institutional review board. Eighty-seven consecutive pediatric patients (mean age 9.1 ± 4.9 years) received either free-breathing high-pitch (pitch 3.2) chest 192-slice DSCT (group 1, n = 31) or standard-pitch (pitch 1.2) 128-slice SSCT (group 2, n = 56) with breathing-instructions by random assignment. Tube settings were similar in both groups with 80 kVp and 74 ref. mAs. Images were reconstructed using FBP for both groups. Additionally, ADMIRE was used in group 1. Effective thorax diameter, image noise, and signal-to-noise ratio (SNR) of the pectoralis major muscle and the thoracic aorta were calculated. Motion artifacts were measured as doubling boarders of the diaphragm and the heart. Images were rated by two blinded readers for overall image quality and presence of motion artifacts on 5-point-scales. Size specific dose estimates (SSDE, mGy) and effective dose (ED, mSv) were calculated. Results: Age and effective thorax diameter showed no statistically significant differences in both groups. Image noise and SNR were comparable (p > 0.64) for SSCT and DSCT with ADMIRE, while DSCT with FBP showed inferior results (p < 0.01). Motion artifacts were reduced significantly (p = 0.001) with DSCT. DSCT with ADMIRE showed the highest overall IQ (p < 0.0001). Radiation dose was lower for DSCT compared to SSCT (median SSDE: 0.82 mGy vs. 0.92 mGy, p < 0.02; median ED: 0.4 mSv vs. 0.48 mSv, p = 0.02). Conclusions: High-pitch 80 kVp chest DSCT in combination with ADMIRE reduces motion artifacts and increases image quality while lowering radiation exposure in free-breathing pediatric patients without sedation.

  8. Reduction of artifacts caused by orthopedic hardware in the spine in spectral detector CT examinations using virtual monoenergetic image reconstructions and metal-artifact-reduction algorithms

    Energy Technology Data Exchange (ETDEWEB)

    Grosse Hokamp, Nils; Neuhaus, V.; Abdullayev, N.; Laukamp, K.; Lennartz, S.; Mpotsaris, A.; Borggrefe, J. [University Hospital Cologne, Department of Diagnostic and Interventional Radiology, Cologne (Germany)

    2018-02-15

    Aim of this study was to assess the artifact reduction in patients with orthopedic hardware in the spine as provided by (1) metal-artifact-reduction algorithms (O-MAR) and (2) virtual monoenergetic images (MonoE) as provided by spectral detector CT (SDCT) compared to conventional iterative reconstruction (CI). In all, 28 consecutive patients with orthopedic hardware in the spine who underwent SDCT-examinations were included. CI, O-MAR and MonoE (40-200 keV) images were reconstructed. Attenuation (HU) and noise (SD) were measured in order to calculate signal-to-noise ratio (SNR) of paravertebral muscle and spinal canal. Subjective image quality was assessed by two radiologists in terms of image quality and extent of artifact reduction. O-MAR and high-keV MonoE showed significant decrease of hypodense artifacts in terms of higher attenuation as compared to CI (CI vs O-MAR, 200 keV MonoE: -396.5HU vs. -115.2HU, -48.1HU; both p ≤ 0.001). Further, artifacts as depicted by noise were reduced in O-MAR and high-keV MonoE as compared to CI in (1) paravertebral muscle and (2) spinal canal - CI vs. O-MAR/200 keV: (1) 34.7 ± 19.0 HU vs. 26.4 ± 14.4 HU, p ≤ 0.05/27.4 ± 16.1, n.s.; (2) 103.4 ± 61.3 HU vs. 72.6 ± 62.6 HU/60.9 ± 40.1 HU, both p ≤ 0.001. Subjectively both O-MAR and high-keV images yielded an artifact reduction in up to 24/28 patients. Both, O-MAR and high-keV MonoE reconstructions as provided by SDCT lead to objective and subjective artifact reduction, thus the combination of O-MAR and MonoE seems promising for further reduction. (orig.)

  9. Lunar ground penetrating radar: Minimizing potential data artifacts caused by signal interaction with a rover body

    Science.gov (United States)

    Angelopoulos, Michael; Redman, David; Pollard, Wayne H.; Haltigin, Timothy W.; Dietrich, Peter

    2014-11-01

    Ground-penetrating radar (GPR) is the leading geophysical candidate technology for future lunar missions aimed at mapping shallow stratigraphy (lunar materials, as well as its small size and lightweight components, make it a very attractive option from both a scientific and engineering perspective. However, the interaction between a GPR signal and the rover body is poorly understood and must be investigated prior to a space mission. In doing so, engineering and survey design strategies should be developed to enhance GPR performance in the context of the scientific question being asked. This paper explores the effects of a rover (simulated with a vertical metal plate) on GPR results for a range of heights above the surface and antenna configurations at two sites: (i) a standard GPR testing site with targets of known position, size, and material properties, and; (ii) a frozen lake for surface reflectivity experiments. Our results demonstrate that the GPR antenna configuration is a key variable dictating instrument design, with the XX polarization considered optimal for minimizing data artifact generation. These findings could thus be used to help guide design requirements for an eventual flight instrument.

  10. Effect of motion artifacts and their correction on near-infrared spectroscopy oscillation data: a study in healthy subjects and stroke patients.

    Science.gov (United States)

    Selb, Juliette; Yücel, Meryem A; Phillip, Dorte; Schytz, Henrik W; Iversen, Helle K; Vangel, Mark; Ashina, Messoud; Boas, David A

    2015-05-01

    Functional near-infrared spectroscopy is prone to contamination by motion artifacts (MAs). Motion correction algorithms have previously been proposed and their respective performance compared for evoked rain activation studies. We study instead the effect of MAs on "oscillation" data which is at the basis of functional connectivity and autoregulation studies. We use as our metric of interest the interhemispheric correlation (IHC), the correlation coefficient between symmetrical time series of oxyhemoglobin oscillations. We show that increased motion content results in a decreased IHC. Using a set of motion-free data on which we add real MAs, we find that the best motion correction approach consists of discarding the segments of MAs following a careful approach to minimize the contamination due to band-pass filtering of data from "bad" segments spreading into adjacent "good" segments. Finally, we compare the IHC in a stroke group and in a healthy group that we artificially contaminated with the MA content of the stroke group, in order to avoid the confounding effect of increased motion incidence in the stroke patients. After motion correction, the IHC remains lower in the stroke group in the frequency band around 0.1 and 0.04 Hz, suggesting a physiological origin for the difference. We emphasize the importance of considering MAs as a confounding factor in oscillation-based functional near-infrared spectroscopy studies.

  11. Comparison of the artifacts caused by metallic implants in breast MRI using dual-echo dixon versus conventional fat-suppression techniques.

    Science.gov (United States)

    Le, Yuan; Kipfer, Hal D; Majidi, Shadie S; Holz, Stephanie; Lin, Chen

    2014-09-01

    The purpose of this article is to evaluate and compare the artifacts caused by metal implants in breast MR images acquired with dual-echo Dixon and two conventional fat-suppression techniques. Two types of biopsy markers were embedded into a uniform fat-water emulsion. T1-weighted gradient-echo images were acquired on a clinical 3-T MRI scanner with three different fat-suppression techniques-conventional or quick fat saturation, spectrally selective adiabatic inversion recovery (SPAIR), and dual-echo Dixon-and the 3D volumes of artifacts were measured. Among the subjects of a clinical breast MRI study using the same scanner, five patients were found to have one or more metal implants. The artifacts in Dixon and SPAIR fat-suppressed images were evaluated by three radiologists, and the results were compared with those of the phantom study. In the phantom study, the artifacts appeared as interleaved bright and dark rings on SPAIR and quick-fat-saturation images, whereas they appeared as dark regions with a thin bright rim on Dixon images. The artifacts imaged with the Dixon technique had the smallest total volume. However, the reviewers found larger artifact diameters on patient images using the Dixon sequence because only the central region was recognized as an artifact on the SPAIR images. Metal implants introduce artifacts of different types and sizes, according to the different fat-suppression techniques used. The dual-echo Dixon technique produces a larger central void, allowing the implant to be easily identified, but presents a smaller overall artifact volume by obscuring less area in the image, according to a quantitative phantom study.

  12. How MRI Compatible is 'MRI Compatible'? A Systematic Comparison of Artifacts Caused by Biopsy Needles at 3.0 and 1.5 T

    Energy Technology Data Exchange (ETDEWEB)

    Penzkofer, Tobias, E-mail: tpenzkofer@ukaachen.de [RWTH Aachen University Hospital, Department of Diagnostic and Interventional Radiology (Germany); Peykan, Nilufar [Klinikum Osnabrueck, Roentgen- und Strahlenklinik (Germany); Schmidt, Katja [RWTH Aachen University Hospital, Department of Diagnostic and Interventional Radiology (Germany); Krombach, Gabriele [Justus-Liebig University Giessen, Department of Radiology (Germany); Kuhl, Christiane K. [RWTH Aachen University Hospital, Department of Diagnostic and Interventional Radiology (Germany)

    2013-12-15

    Purpose: This study was designed to systematically investigate artifacts caused by interventional needles recommended for use in MRI, with focus on field strength, needle/mandrin type, orientation and sequence. Methods: Eight different MRI compatible needles were placed in porcine tissue and examined at 1.5 and 3.0 T with balanced-steady-state-free-precession (B-SSFP) and T1-weighted-spoiled-gradient-echo (T1-SPGR) sequences in different orientations to B{sub 0}. Artifact diameters with regards to the primary, inner, and secondary, outer artifacts were assessed and statistically evaluated. Results: The types and degree of artifacts varied considerably, especially between different mandrin types even for the same needles. Orientation of the needle in the magnetic field was another main contributor to the artifact dimensions. Less important factors were the type of pulse sequence and field strength. Artifacts ranged from 0.7 mm (steel, 0 Degree-Sign , B-SSFP, 3.0 T, inner) to 71.4 mm (nitinol, 90 Degree-Sign , B-SSFP, 1.5 T, outer). Inner artifact diameters in B-SSFP were slightly larger (8.2 {+-} 5.7 mm) than those in T1-SPGR (7.6 {+-} 5.4 mm) and comparable between 1.5 and 3.0 T (e.g., 8.0 vs. 8.4 mm, B-SSFP). Conclusions: Although all were sold as 'MR compatible,' the artifacts differed greatly between needle types, and even more so for different mandrins. The results suggest an empirical approach to the needle choice based on lesion type and approach angle.

  13. How MRI Compatible is “MRI Compatible”? A Systematic Comparison of Artifacts Caused by Biopsy Needles at 3.0 and 1.5 T

    International Nuclear Information System (INIS)

    Penzkofer, Tobias; Peykan, Nilufar; Schmidt, Katja; Krombach, Gabriele; Kuhl, Christiane K.

    2013-01-01

    Purpose: This study was designed to systematically investigate artifacts caused by interventional needles recommended for use in MRI, with focus on field strength, needle/mandrin type, orientation and sequence. Methods: Eight different MRI compatible needles were placed in porcine tissue and examined at 1.5 and 3.0 T with balanced-steady-state-free-precession (B-SSFP) and T1-weighted-spoiled-gradient-echo (T1-SPGR) sequences in different orientations to B 0 . Artifact diameters with regards to the primary, inner, and secondary, outer artifacts were assessed and statistically evaluated. Results: The types and degree of artifacts varied considerably, especially between different mandrin types even for the same needles. Orientation of the needle in the magnetic field was another main contributor to the artifact dimensions. Less important factors were the type of pulse sequence and field strength. Artifacts ranged from 0.7 mm (steel, 0°, B-SSFP, 3.0 T, inner) to 71.4 mm (nitinol, 90°, B-SSFP, 1.5 T, outer). Inner artifact diameters in B-SSFP were slightly larger (8.2 ± 5.7 mm) than those in T1-SPGR (7.6 ± 5.4 mm) and comparable between 1.5 and 3.0 T (e.g., 8.0 vs. 8.4 mm, B-SSFP). Conclusions: Although all were sold as “MR compatible,” the artifacts differed greatly between needle types, and even more so for different mandrins. The results suggest an empirical approach to the needle choice based on lesion type and approach angle

  14. Artifacts in MRI of the temporomandibular joint caused by dental alloys: a phantom study at 1.5 T

    International Nuclear Information System (INIS)

    Fellner, C.; Erlangen-Nuernberg Univ., Erlangen; Behr, M.; Fellner, F.; Held, P.; Handel, G.; Feuerbach, S.

    1997-01-01

    Purpose: The influence of dental alloys on MRI of the temporomandibular joint was studied using a phantom model for this joint. Methods: At 1,5 T, 15 dental alloys and 14 of their most important components were investigated acquiring sagittal (FOV: 150 mm) and transverse (FOV: 250 mm) T 1 -weighted SE additionally. The artifacts were assessed qualitatively as well as quantitatively, and the samples were subdivided into four artifact categories. Results: Ag, Cu, Ga, In, Ti, Sn, Zn, amalgan, the precious alloys, the Au-Pd and Ag-Pd alloys showed no artifacts (category I). Minimal artifacts below 10 mm on transverse images (category II) were found for Cr, Pd, Pt and for the Ni-Cr alloy. Mn and the remaining non-precious alloys induced artifacts up to 30 mm (category III). Significant artifacts - more than 30 mm - (category IV) were to be more susceptible for artifacts than T 1 -weighted SE and FLASH techniques. Conclusions: In contrast to dental alloys for fixed prosthodontics, Ni-Cr- or 18/8 wires used for orthodontic bands can influence not only the image quality, but also the diagnostic reliability of MRI of the temporomandibular joint. (orig.) [de

  15. Motion in images is essential to cause motion sickness symptoms, but not to increase postural sway

    NARCIS (Netherlands)

    Lubeck, A.J.A.; Bos, J.E.; Stins, J.F.

    2015-01-01

    Abstract Objective It is generally assumed that motion in motion images is responsible for increased postural sway as well as for visually induced motion sickness (VIMS). However, this has not yet been tested. To that end, we studied postural sway and VIMS induced by motion and still images. Method

  16. Study on motion artifacts in coronary arteries with an anthropomorphic moving heart phantom on an ECG-gated multidetector computed tomography unit

    International Nuclear Information System (INIS)

    Greuter, Marcel J.W.; Dorgelo, Joost; Tukker, Wim G.J.; Oudkerk, Matthijs

    2005-01-01

    Acquisition time plays a key role in the quality of cardiac multidetector computed tomography (MDCT) and is directly related to the rotation time of the scanner. The purpose of this study is to examine the influence of heart rate and a multisector reconstruction algorithm on the image quality of coronary arteries of an anthropomorphic adjustable moving heart phantom on an ECG-gated MDCT unit. The heart phantom and a coronary artery phantom were used on a MDCT unit with a rotation time of 500 ms. The movement of the heart was determined by analysis of the images taken at different phases. The results indicate that the movement of the coronary arteries on the heart phantom is comparable to that in a clinical setting. The influence of the heart rate on image quality and artifacts was determined by analysis of several heart rates between 40 and 80 bpm where the movement of the heart was synchronized using a retrospective ECG-gated acquisition protocol. The resulting reformatted volume rendering images of the moving heart and the coronary arteries were qualitatively compared as a result of the heart rate. The evaluation was performed on three independent series by two independent radiologists for the image quality of the coronary arteries and the presence of artifacts. The evaluation shows that at heart rates above 50 bpm the influence of motion artifacts in the coronary arteries becomes apparent. In addition the influence of a dedicated multisector reconstruction technique on image quality was determined. The results show that the image quality of the coronary arteries is not only related to the heart rate and that the influence of the multisector reconstruction technique becomes significant above 70 bpm. Therefore, this study proves that from the actual acquisition time per heart cycle one cannot determine an actual acquisition time, but only a mathematical acquisition time. (orig.)

  17. Reduction of Motion Artifacts and Improvement of R Peak Detecting Accuracy Using Adjacent Non-Intrusive ECG Sensors

    Directory of Open Access Journals (Sweden)

    Minho Choi

    2016-05-01

    Full Text Available Non-intrusive electrocardiogram (ECG monitoring has many advantages: easy to measure and apply in daily life. However, motion noise in the measured signal is the major problem of non-intrusive measurement. This paper proposes a method to reduce the noise and to detect the R peaks of ECG in a stable manner in a sitting arrangement using non-intrusive sensors. The method utilizes two capacitive ECG sensors (cECGs to measure ECG, and another two cECGs located adjacent to the sensors for ECG are added to obtain the information on motion. Then, active noise cancellation technique and the motion information are used to reduce motion noise. To verify the proposed method, ECG was measured indoors and during driving, and the accuracy of the detected R peaks was compared. After applying the method, the sum of sensitivity and positive predictivity increased 8.39% on average and 26.26% maximally in the data. Based on the results, it was confirmed that the motion noise was reduced and that more reliable R peak positions could be obtained by the proposed method. The robustness of the new ECG measurement method will elicit benefits to various health care systems that require noninvasive heart rate or heart rate variability measurements.

  18. Electrocardiography-triggered high-resolution CT for reducing cardiac motion artifact. Evaluation of the extent of ground-glass attenuation in patients with idiopathic pulmonary fibrosis

    International Nuclear Information System (INIS)

    Nishiura, Motoko; Johkoh, Takeshi; Yamamoto, Shuji

    2007-01-01

    The aim of this study was to evaluate the decreasing of cardiac motion artifact and whether the extent of ground-glass attenuation of idiopathic pulmonary fibrosis (IPF) was accurately assessed by electrocardiography (ECG)-triggered high-resolution computed tomography (HRCT) by 0.5-s/rotation multidetector-row CT (MDCT). ECG-triggered HRCT were scanned at the end-diastolic phase by a MDCT scanner with the following scan parameters; axial four-slice mode, 0.5 mm collimation, 0.5-s/rotation, 120 kVp, 200 mA/rotation, high-frequency algorithm, and half reconstruction. In 42 patients with IPF, both conventional HRCT (ECG gating (-), full reconstruction) and ECG-triggered HRCT were performed at the same levels (10-mm intervals) with the above scan parameters. The correlation between percent diffusion of carbon monoxide of the lung (%DLCO) and the mean extent of ground-glass attenuation on both conventional HRCT and ECG-triggered HRCT was evaluated with the Spearman rank correlation coefficient test. The correlation between %DLCO and the mean extent of ground-glass attenuation on ECG-triggered HRCT (observer A: r=-0.790, P<0.0001; observer B: r=-0.710, P<0.0001) was superior to that on conventional HRCT (observer A: r=-0.395, P<0.05; observer B: r=-0.577, P=0.002) for both observers. ECG-triggered HRCT by 0.5 s/rotation MDCT can reduce the cardiac motion artifact and is useful for evaluating the extent of ground-glass attenuation of IPF. (author)

  19. Directional bias of illusory stream caused by relative motion adaptation.

    Science.gov (United States)

    Tomimatsu, Erika; Ito, Hiroyuki

    2016-07-01

    Enigma is an op-art painting that elicits an illusion of rotational streaming motion. In the present study, we tested whether adaptation to various motion configurations that included relative motion components could be reflected in the directional bias of the illusory stream. First, participants viewed the center of a rotating Enigma stimulus for adaptation. There was no physical motion on the ring area. During the adaptation period, the illusory stream on the ring was mainly seen in the direction opposite to that of the physical rotation. After the physical rotation stopped, the illusory stream on the ring was mainly seen in the same direction as that of the preceding physical rotation. Moreover, adapting to strong relative motion induced a strong bias in the illusory motion direction in the subsequently presented static Enigma stimulus. The results suggest that relative motion detectors corresponding to the ring area may produce the illusory stream of Enigma. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

  20. From naive to scientific understanding of motion and its causes

    International Nuclear Information System (INIS)

    Ascari, A.; Corni, F.; Ceroni, G.; Fuchs, Hans U.

    2015-01-01

    The difference in the descriptions of motion phenomena made by pupils in the first grades of secondary school and physicists is quite evident. Conceptual metaphors hidden in language suggest that there is continuity between the conceptual structure involved in the description and the interpretation of motion of experts and lay persons. In this paper the presence of such a continuity is shown through a metaphor analysis of linguistic expressions from both groups.

  1. SU-F-J-117: Impact of Motion Artifacts On Image Quality and Accuracy of Tumor Motion Reconstruction in 4D CT-On-Rails and MV-CBCT Scans: A Phantom Study

    Energy Technology Data Exchange (ETDEWEB)

    Lin, T; Ma, C [Fox Chase Cancer Center, Philadelphia, PA (United States)

    2016-06-15

    Purpose: To compare and quantify respiratory motion artifacts in images from free breathing 4D-CT-on-Rails(CTOR) and those from MV-Cone-beam-CT(MVCB) and facilitate respiratory motion guided radiation therapy. Methods: 4D-CTOR: Siemens Somatom CT-on-Rails system with Anzai belt loaded with pressure sensor load cells. 4D scans were performed in helical mode, pitch 0.1, gantry rotation time 0.5s, 1.5mm slice thickness, 120kVp, 400 mAs. Normal and fast breathing (>12rpm) scanning protocols were investigated. Helical scan, AIP(average intensity projection) and MIP(maximum intensity projection) were generated from 4D-CTOR scans with amplitude sorting into 10 phases.MVCB: Siemens Artiste diamond view(1MV)MVCB was performed with 5MU thorax protocol with 60 second of full rotation.Phantom: Anzai AZ-733V respiratory phantom. The settings were set to normal and resp. modes with repetition rates at 15 rpm and 10 rpm. Surgical clips, acrylic, wooden, rubber and lung density, total six mock-ups were scanned and compared in this study.Signal-to-noise ratio(SNR), contrast-to-noise ratio(CNR) and reconstructed motion volume were compared to different respiratory setups for the mock-ups. Results: Reconstructed motion volume was compared to the real object volume for the six test mock-ups. It shows that free breathing helical in all instances underestimates the object excursions largest to −67.4% and least −6.3%. Under normal breathing settings, MIP can predict very precise motion volume with minimum 0.4% and largest −13.9%. MVCB shows underestimate of the motion volume with −1.11% minimum and −18.0% maximum. With fast breathing, AIP provides bad representation of the object motion; however, the MIP can predict the motion volume with −2.0% to −11.4% underestimate. Conclusion: Respiratory motion guided radiation therapy requires good motion recording. This study shows that regular CTOR helical scans provides bad guidance, 4D CTOR AIP cannot represent the fast breathing

  2. Evaluation of MRI artifacts caused by metallic dental implants and classification of the dental materials in use

    Czech Academy of Sciences Publication Activity Database

    Starčuk jr., Zenon; Bartušek, Karel; Hubálková, H.; Bachorec, T.; Starčuková, Jana; Krupa, P.

    2006-01-01

    Roč. 6, č. 2 (2006), s. 24-27 ISSN 1335-8871 R&D Projects: GA MZd NR8110 Institutional research plan: CEZ:AV0Z20650511 Keywords : magnetic resonance imaging * artifacts * metallic implants * dental alloys * magnetic susceptibility Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  3. Lévy meets poisson: a statistical artifact may lead to erroneous recategorization of Lévy walk as Brownian motion.

    Science.gov (United States)

    Gautestad, Arild O

    2013-03-01

    The flow of GPS data on animal space is challenging old paradigms, such as the issue of the scale-free Lévy walk versus scale-specific Brownian motion. Since these movement classes often require different protocols with respect to ecological analyses, further theoretical development in this field is important. I describe central concepts such as scale-specific versus scale-free movement and the difference between mechanistic and statistical-mechanical levels of analysis. Next, I report how a specific sampling scheme may have produced much confusion: a Lévy walk may be wrongly categorized as Brownian motion if the duration of a move, or bout, is used as a proxy for step length and a move is subjectively defined. Hence, the categorization and recategorization of movement class compliance surrounding the Lévy walk controversy may have been based on a statistical artifact. This issue may be avoided by collecting relocations at a fixed rate at a temporal scale that minimizes over- and undersampling.

  4. iPhone 4s photoplethysmography: which light color yields the most accurate heart rate and normalized pulse volume using the iPhysioMeter Application in the presence of motion artifact?

    Directory of Open Access Journals (Sweden)

    Kenta Matsumura

    Full Text Available Recent progress in information and communication technologies has made it possible to measure heart rate (HR and normalized pulse volume (NPV, which are important physiological indices, using only a smartphone. This has been achieved with reflection mode photoplethysmography (PPG, by using a smartphone's embedded flash as a light source and the camera as a light sensor. Despite its widespread use, the method of PPG is susceptible to motion artifacts as physical displacements influence photon propagation phenomena and, thereby, the effective optical path length. Further, it is known that the wavelength of light used for PPG influences the photon penetration depth and we therefore hypothesized that influences of motion artifact could be wavelength-dependant. To test this hypothesis, we made measurements in 12 healthy volunteers of HR and NPV derived from reflection mode plethysmograms recorded simultaneously at three different spectral regions (red, green and blue at the same physical location with a smartphone. We then assessed the accuracy of the HR and NPV measurements under the influence of motion artifacts. The analyses revealed that the accuracy of HR was acceptably high with all three wavelengths (all rs > 0.996, fixed biases: -0.12 to 0.10 beats per minute, proportional biases: r =  -0.29 to 0.03, but that of NPV was the best with green light (r = 0.791, fixed biases: -0.01 arbitrary units, proportional bias: r = 0.11. Moreover, the signal-to-noise ratio obtained with green and blue light PPG was higher than that of red light PPG. These findings suggest that green is the most suitable color for measuring HR and NPV from the reflection mode photoplethysmogram under motion artifact conditions. We conclude that the use of green light PPG could be of particular benefit in ambulatory monitoring where motion artifacts are a significant issue.

  5. Metallic artifacts caused by dental metal prostheses on PET images. A PET/CT phantom study using different PET/CT scanners

    International Nuclear Information System (INIS)

    Shimamoto, Hiroaki; Kakimoto, Naoya; Murakami, Shumei; Furukawa, Souhei; Fujino, Kouichi; Hamada, Seiki; Shimosegawa, Eku; Hatazawa, Jun

    2009-01-01

    The objective of this study was to investigate the effects of computed tomography (CT) artifacts caused by dental metal prostheses on positron emission tomography (PET) images. A dental arch cast was fixed in a cylindrical water-bath phantom. A spherical phantom positioned in the vicinity of the dental arch cast was used to simulate a tumor. To simulate the tumor imaging, the ratio of the 18 F-fluoro-deoxy-glucose radioactivity concentration of the spherical phantom to that of the water-bath phantom was set at 2.5. A dental bridge composed of a gold-silver-palladium alloy on the right mandibular side was prepared. A spherical phantom was set in the white artifact area on the CT images (site A), in a slightly remote area from the white artifact (site B), and in a black artifact area (site C). A PET/CT scan was performed with and without the metal bridge at each simulated tumor site, and the artifactual influence was evaluated on the axial attenuation-corrected (AC) PET images, in which the simulated tumor produced the strongest accumulation. Measurements were performed using three types of PET/CT scanners (scanners 1 and 2 with CT-based attenuation correction, and 3 with Cesium-137 ( 137 Cs)-based attenuation correction). The influence of the metal bridge was evaluated using the change rate of the SUVmean with and without the metal bridge. At site A, an overestimation was shown (scanner 1: +5.0% and scanner 2: +2.5%), while scanner 3 showed an underestimation of -31.8%. At site B, an overestimation was shown (scanner 1: +2.1% and scanner 2: +2.0%), while scanner 3 showed an underestimation of -2.6%. However, at site C, an underestimation was shown (scanner 1: -25.0%, scanner 2: -32.4%, and scanner 3: -8.4%). When CT is used for attenuation correction in patients with dental metal prostheses, an underestimation of radioactivity of accumulated tracer is anticipated in the dark streak artifact area on the CT images. In this study, the dark streak artifacts of the CT

  6. A Robust Motion Artifact Detection Algorithm for Accurate Detection of Heart Rates From Photoplethysmographic Signals Using Time-Frequency Spectral Features.

    Science.gov (United States)

    Dao, Duy; Salehizadeh, S M A; Noh, Yeonsik; Chong, Jo Woon; Cho, Chae Ho; McManus, Dave; Darling, Chad E; Mendelson, Yitzhak; Chon, Ki H

    2017-09-01

    Motion and noise artifacts (MNAs) impose limits on the usability of the photoplethysmogram (PPG), particularly in the context of ambulatory monitoring. MNAs can distort PPG, causing erroneous estimation of physiological parameters such as heart rate (HR) and arterial oxygen saturation (SpO2). In this study, we present a novel approach, "TifMA," based on using the time-frequency spectrum of PPG to first detect the MNA-corrupted data and next discard the nonusable part of the corrupted data. The term "nonusable" refers to segments of PPG data from which the HR signal cannot be recovered accurately. Two sequential classification procedures were included in the TifMA algorithm. The first classifier distinguishes between MNA-corrupted and MNA-free PPG data. Once a segment of data is deemed MNA-corrupted, the next classifier determines whether the HR can be recovered from the corrupted segment or not. A support vector machine (SVM) classifier was used to build a decision boundary for the first classification task using data segments from a training dataset. Features from time-frequency spectra of PPG were extracted to build the detection model. Five datasets were considered for evaluating TifMA performance: (1) and (2) were laboratory-controlled PPG recordings from forehead and finger pulse oximeter sensors with subjects making random movements, (3) and (4) were actual patient PPG recordings from UMass Memorial Medical Center with random free movements and (5) was a laboratory-controlled PPG recording dataset measured at the forehead while the subjects ran on a treadmill. The first dataset was used to analyze the noise sensitivity of the algorithm. Datasets 2-4 were used to evaluate the MNA detection phase of the algorithm. The results from the first phase of the algorithm (MNA detection) were compared to results from three existing MNA detection algorithms: the Hjorth, kurtosis-Shannon entropy, and time-domain variability-SVM approaches. This last is an approach

  7. Orientation tuning of contrast masking caused by motion streaks.

    Science.gov (United States)

    Apthorp, Deborah; Cass, John; Alais, David

    2010-08-01

    We investigated whether the oriented trails of blur left by fast-moving dots (i.e., "motion streaks") effectively mask grating targets. Using a classic overlay masking paradigm, we varied mask contrast and target orientation to reveal underlying tuning. Fast-moving Gaussian blob arrays elevated thresholds for detection of static gratings, both monoptically and dichoptically. Monoptic masking at high mask (i.e., streak) contrasts is tuned for orientation and exhibits a similar bandwidth to masking functions obtained with grating stimuli (∼30 degrees). Dichoptic masking fails to show reliable orientation-tuned masking, but dichoptic masks at very low contrast produce a narrowly tuned facilitation (∼17 degrees). For iso-oriented streak masks and grating targets, we also explored masking as a function of mask contrast. Interestingly, dichoptic masking shows a classic "dipper"-like TVC function, whereas monoptic masking shows no dip and a steeper "handle". There is a very strong unoriented component to the masking, which we attribute to transiently biased temporal frequency masking. Fourier analysis of "motion streak" images shows interesting differences between dichoptic and monoptic functions and the information in the stimulus. Our data add weight to the growing body of evidence that the oriented blur of motion streaks contributes to the processing of fast motion signals.

  8. Artifacts produced during electrical stimulation of the vestibular nerve in cats. [autonomic nervous system components of motion sickness

    Science.gov (United States)

    Tang, P. C.

    1973-01-01

    Evidence is presented to indicate that evoked potentials in the recurrent laryngeal, the cervical sympathetic, and the phrenic nerve, commonly reported as being elicited by vestibular nerve stimulation, may be due to stimulation of structures other than the vestibular nerve. Experiments carried out in decerebrated cats indicated that stimulation of the petrous bone and not that of the vestibular nerve is responsible for the genesis of evoked potentials in the recurrent laryngeal and the cervical sympathetic nerves. The phrenic response to electrical stimulation applied through bipolar straight electrodes appears to be the result of stimulation of the facial nerve in the facial canal by current spread along the petrous bone, since stimulation of the suspended facial nerve evoked potentials only in the phrenic nerve and not in the recurrent laryngeal nerve. These findings indicate that autonomic components of motion sickness represent the secondary reactions and not the primary responses to vestibular stimulation.

  9. Investigation of artifacts caused by deuterium background correction in the determination of phosphorus by electrothermal atomization using high-resolution continuum source atomic absorption spectrometry

    International Nuclear Information System (INIS)

    Dessuy, Morgana B.; Vale, Maria Goreti R.; Lepri, Fabio G.; Borges, Daniel L.G.; Welz, Bernhard; Silva, Marcia M.; Heitmann, Uwe

    2008-01-01

    The artifacts created in the measurement of phosphorus at the 213.6-nm non-resonance line by electrothermal atomic absorption spectrometry using line source atomic absorption spectrometry (LS AAS) and deuterium lamp background correction (D 2 BC) have been investigated using high-resolution continuum source atomic absorption spectrometry (HR-CS AAS). The absorbance signals and the analytical curves obtained by LS AAS without and with D 2 BC, and with HR-CS AAS without and with automatic correction for continuous background absorption, and also with least-squares background correction for molecular absorption with rotational fine structure were compared. The molecular absorption due to the suboxide PO that exhibits pronounced fine structure could not be corrected by the D 2 BC system, causing significant overcorrection. Among the investigated chemical modifiers, NaF, La, Pd and Pd + Ca, the Pd modifier resulted in the best agreement of the results obtained with LS AAS and HR-CS AAS. However, a 15% to 100% higher sensitivity, expressed as slope of the analytical curve, was obtained for LS AAS compared to HR-CS AAS, depending on the modifier. Although no final proof could be found, the most likely explanation is that this artifact is caused by a yet unidentified phosphorus species that causes a spectrally continuous absorption, which is corrected without problems by HR-CS AAS, but which is not recognized and corrected by the D 2 BC system of LS AAS

  10. Quantifying skin motion artifact error of the hindfoot and forefoot marker clusters with the optical tracking of a multi-segment foot model using single-plane fluoroscopy.

    Science.gov (United States)

    Shultz, R; Kedgley, A E; Jenkyn, T R

    2011-05-01

    The trajectories of skin-mounted markers tracked with optical motion capture are assumed to be an adequate representation of the underlying bone motions. However, it is well known that soft tissue artifact (STA) exists between marker and bone. This study quantifies the STA associated with the hindfoot and midfoot marker clusters of a multi-segment foot model. To quantify STA of the hindfoot and midfoot marker clusters with respect to the calcaneus and navicular respectively, fluoroscopic images were collected on 27 subjects during four quasi-static positions, (1) quiet standing (non-weight bearing), (2) at heel strike (weight-bearing), (3) at midstance (weight-bearing) and (4) at toe-off (weight-bearing). The translation and rotation components of STA were calculated in the sagittal plane. Translational STA at the calcaneus varied from 5.9±7.3mm at heel-strike to 12.1±0.3mm at toe-off. For the navicular the translational STA ranged from 7.6±7.6mm at heel strike to 16.4±16.7mm at toe-off. Rotational STA was relatively smaller for both bones at all foot positions. For the calcaneus they varied between 0.1±2.2° at heel-strike to 0.2±0.6° at toe-off. For the navicular, the rotational STA ranged from 0.6±0.9° at heel-strike to 0.7±0.7° at toe-off. The largest translational STA found in this study (16mm for the navicular) was smaller than those reported in the literature for the thigh and the lower leg, but was larger than the STA of individual spherical markers affixed to the foot. The largest errors occurred at toe-off position for all subjects for both the hindfoot and midfoot clusters. Future studies are recommended to quantify true three-dimensional STA of the entire foot during gait. Copyright © 2011. Published by Elsevier B.V.

  11. Reduction of dark-band-like metal artifacts caused by dental implant bodies using hypothetical monoenergetic imaging after dual-energy computed tomography.

    Science.gov (United States)

    Tanaka, Ray; Hayashi, Takafumi; Ike, Makiko; Noto, Yoshiyuki; Goto, Tazuko K

    2013-06-01

    The aim of this study was to evaluate the usefulness of hypothetical monoenergetic images after dual-energy computed tomography (DECT) for assessment of the bone encircling dental implant bodies. Seventy-two axial images of implantation sites clipped out from image data scanned using DECT in dual-energy mode were used. Subjective assessment on reduction of dark-band-like artifacts (R-DBAs) and diagnosability of adjacent bone condition (D-ABC) in 3 sets of DECT images-a fused image set (DE120) and 2 sets of hypothetical monoenergetic images (ME100, ME190)-was performed and the results were statistically analyzed. With regards to R-DBAs and D-ABC, significant differences among DE120, ME100, and ME190 were observed. The ME100 and ME190 images revealed more artifact reduction and diagnosability than those of DE120. DECT imaging followed by hypothetical monoenergetic image construction can cause R-DBAs and increase D-ABC and may be potentially used for the evaluation of postoperative changes in the bone encircling implant bodies. Copyright © 2013 Elsevier Inc. All rights reserved.

  12. Dynamics in artifact ecologies

    DEFF Research Database (Denmark)

    Bødker, Susanne; Klokmose, Clemens Nylandsted

    2012-01-01

    We increasingly interact with multiple interactive artifacts with overlapping capabilities during our daily activities. It has previously been shown that the use of an interactive artifact cannot be understood in isolation, but artifacts must be understood as part of an artifact ecology, where...... artifacts influence the use of others. Understanding this interplay becomes more and more essential for interaction design as our artifact ecologies grow. This paper continues a recent discourse on artifact ecologies. Through interviews with iPhone users, we demonstrate that relationships between artifacts...... in artifact ecologies cannot be understood as static, instead they evolve dynamically over time. We provide activity theory-based concepts to explain these dynamics....

  13. Influence of misonidazole on the radiation response of murine tumors of different size: possible artifacts caused by pentobarbital sodium anesthesia

    International Nuclear Information System (INIS)

    Wondergem, J.; Haveman, J.; van der Schueren, E.; van den Hoeven, H.; Breur, K.

    1981-01-01

    The radiosensitivity of a transplantable murine adenocarcinoma decreased with increasing tumor volume. In unanesthetized mice this phenomenon (based on the effect of the hypoxic cell sensitizer misonidazole), in the range of volumes studied, can largely be explained by the appearance of hypoxic cells in the tumor during growth. The use of pentobarbital sodium during irradiation is confiremd to be a disturbing factor, as it may increase the hypoxic cell fraction in the tumors. No evidence was found for a direct radiochemical protection because of pentobarbital sodium. The radioprotective effect of the anesthetic could only be demonstrated in conditions where there is already a fraction of hypoxic cells; no influence of the anesthesia was found in small tumors in which the fraction of hypoxic cells was relatively small. This may account for the previously conflicting data on the influence of pentobarbital sodium anesthesia. The vascularization of larger tumors is apparently inferior to smaller tumors and this has important repercussions in the case of anesthesia. Changes in blood flow induced by pentobarbital sodium in larger tumors cause an insufficient oxygenation and hence acute hypoxia

  14. Artifacts in magnetic resonance imaging of the head

    Energy Technology Data Exchange (ETDEWEB)

    Iwama, Toru; Andoh, Takashi; Sakai, Noboru; Yamada, Hiromu [Gifu Univ. (Japan). Faculty of Medicine; Funakoshi, Takashi; Akiyama, Shigeru; Yoshida, Kakuro

    1989-08-01

    The results of 505 magnetic resonance (MR) imaging examinations of the head disclosed several different types of artifact. Various artifacts observed with two-dimentional Fourier transformation are described and illustrated. All images were obtained with a 0.5 Tesla superconducting MR imager. About 70% of all images contained artifacts. Phase encoding artifacts due to motion or flow were most frequently observed. Center, 'zipper,' truncation, radiofrequency, and ferromagnetic artifacts and contrast error on inversion recovery (IR) images were noted less frequently. Phase encoding artifacts and contrast errors on IR images totally degraded the images, and 'zipper' artifacts were regional. Center artifacts resembled small infarctions, and ferromagnetic artifacts sometimes mimicked hematmas. It is important to recognize these artifacts and to devise methods to avoid their influence on the region of interest. (author).

  15. On turbulent motion caused by temperature fluctuations - a critical review on the Boussinesq approximation

    International Nuclear Information System (INIS)

    Ruediger, R.

    1977-01-01

    Fluctuating motions which are caused by a given stochastical temperature field acting in a gas with gravitation and T = constant are dealt with. It results that the often used Boussinesq approximation much underestimates the horizontal motions in case wide-spread temperature fluctuations occur. For sufficiently large scales the horizontal motion exceeds the vertical ones even in the case of the temperature field fluctuating completely isotropically. Scales of 1,000 km and 1 day in the Earth atmosphere lead to the observed value u'(horizontal)/u'(vertical) approximately 10. Finally besides the relation between density correlation and pressure correlation the expression for the turbulent mass transport vanishing with the molecular viscosity is determined. (author)

  16. Can origin of the 2400-year cycle of solar activity be caused by solar inertial motion?

    Directory of Open Access Journals (Sweden)

    I. Charvátová

    Full Text Available A solar activity cycle of about 2400 years has until now been of uncertain origin. Recent results indicate it is caused by solar inertial motion. First we describe the 178.7-year basic cycle of solar motion. The longer cycle, over an 8000 year interval, is found to average 2402.2 years. This corresponds to the Jupiter/Heliocentre/Barycentre alignments (9.8855 × 243. Within each cycle an exceptional segment of 370 years has been found characterized by a looping pattern by a trefoil or quasitrefoil geometry. Solar activity, evidenced by 14C tree-ring proxies, shows the same pattern. Solar motion is computable in advance, so this provides a basis for future predictive assessments. The next 370-year segment will occur between AD 2240 and 2610.

    Key words: Solar physics (celestial mechanics

  17. Artifacts in MR angiography of the intracranial vessels using the 3D TOF and 3D PC techniques

    International Nuclear Information System (INIS)

    Park, Dong Woo; Lee, Seung Ro; Hahm, Chang Kok; Kim, Yong Soo; Park, Choong Ki

    1997-01-01

    To classify artifacts and to assess their frequency in magnetic resonance angiography of intracranial vessels using three- dimensional time-of-flight and phase-contrast techniques. One hundred and eleven patients with suspected cerebrovascular disease were imaged on a 1.5T superconducting magnetic resonance machine employing three- dimensional time-of-flight and phase-contrast magnetic resonance angiographic techniques. We retrospectively reviewed the artifacts in three- dimensional time-of-flight and phase-contrast magnetic resonance angiography of the intracranial circulatory system, comparing them with routine spin-echo magnetic resonance images and magnetic resonance angiography source images, and partially with conventional angiography. Artifacts in magnetic resonance angiography were classified as flow-related, and flow-unrealted, by patient, hardware, magnetic resonance angiography acquisition and postprocessing techniques. Type and frequency of flow-related artifacts included saturation artifact (100%), dephasing artifact (100%), phase-encoding ghost artifact (97%), turbulence artifact (14%) and flow displacement artifact (5%) on three- dimensional time-of-flight and phase-contrast magnetic resonance angiography, and phase aliasing artifact (2%) on three-dimensional phase-contrast magnetic resonance angiography. Type and frequency of flow-unrelated artifacts included stair-step artifact (100%) by three- dimensional reconstruction process, magnetic susceptibility artifact by carotid canal (69%) and metal (4%), maximum intensity projection artifact (30%) by maximum intensity projection algorithm, and motion artifact by respiration (20%) and voluntary movement (8%); these were seen on both time-of-flight and phase-contrast magnetic resonance angiography. Paramagnetic substance artifact by fat and paranasal sinus mucosa (100%), hematoma (14%) and gadolinium (5%) were seen on time-of-flight magnetic resonance angiography. In three- dimensional time-of-flight and

  18. Widespread ground motion distribution caused by rupture directivity during the 2015 Gorkha, Nepal earthquake

    Science.gov (United States)

    Koketsu, Kazuki; Miyake, Hiroe; Guo, Yujia; Kobayashi, Hiroaki; Masuda, Tetsu; Davuluri, Srinagesh; Bhattarai, Mukunda; Adhikari, Lok Bijaya; Sapkota, Soma Nath

    2016-06-01

    The ground motion and damage caused by the 2015 Gorkha, Nepal earthquake can be characterized by their widespread distributions to the east. Evidence from strong ground motions, regional acceleration duration, and teleseismic waveforms indicate that rupture directivity contributed significantly to these distributions. This phenomenon has been thought to occur only if a strike-slip or dip-slip rupture propagates to a site in the along-strike or updip direction, respectively. However, even though the earthquake was a dip-slip faulting event and its source fault strike was nearly eastward, evidence for rupture directivity is found in the eastward direction. Here, we explore the reasons for this apparent inconsistency by performing a joint source inversion of seismic and geodetic datasets, and conducting ground motion simulations. The results indicate that the earthquake occurred on the underthrusting Indian lithosphere, with a low dip angle, and that the fault rupture propagated in the along-strike direction at a velocity just slightly below the S-wave velocity. This low dip angle and fast rupture velocity produced rupture directivity in the along-strike direction, which caused widespread ground motion distribution and significant damage extending far eastwards, from central Nepal to Mount Everest.

  19. Mesoscale hybrid calibration artifact

    Science.gov (United States)

    Tran, Hy D.; Claudet, Andre A.; Oliver, Andrew D.

    2010-09-07

    A mesoscale calibration artifact, also called a hybrid artifact, suitable for hybrid dimensional measurement and the method for make the artifact. The hybrid artifact has structural characteristics that make it suitable for dimensional measurement in both vision-based systems and touch-probe-based systems. The hybrid artifact employs the intersection of bulk-micromachined planes to fabricate edges that are sharp to the nanometer level and intersecting planes with crystal-lattice-defined angles.

  20. Reducing artifacts from varying projection truncations

    DEFF Research Database (Denmark)

    Borg, Leise; Jørgensen, Jakob Sauer; Frikel, Jürgen

    We study samples with full and partial occlusion causing streak artifacts, and propose two modifications of filtered backprojection for artifact removal. Data is obtained by the SPring-8 synchrotron using a monochromatic parallel-beam scan [1]. Thresholding in the sinogram segments the metal...

  1. On the motion of dayside auroras caused by a solar wind pressure pulse

    Directory of Open Access Journals (Sweden)

    A. Kozlovsky

    2005-02-01

    Full Text Available Global ultraviolet auroral images from the IMAGE satellite were used to investigate the dynamics of the dayside auroral oval responding to a sudden impulse (SI in the solar wind pressure. At the same time, the TV all-sky camera and the EISCAT radar on Svalbard (in the pre-noon sector allowed for detailed investigation of the auroral forms and the ionospheric plasma flow. After the SI, new discrete auroral forms appeared in the poleward part of the auroral oval so that the middle of the dayside oval moved poleward from about 70° to about 73° of the AACGM latitude. This poleward shift first occurred in the 15 MLT sector, then similar shifts were observed in the MLT sectors located more westerly, and eventually the shift was seen in the 6 MLT sector. Thus, the auroral disturbance "propagated" westward (from 15 MLT to 6 MLT at an apparent speed of the order of 7km/s. This motion of the middle of the auroral oval was caused by the redistribution of the luminosity within the oval and was not associated with the corresponding motion of the poleward boundary of the oval. The SI was followed by an increase in the northward plasma convection velocity. Individual auroral forms showed poleward progressions with velocities close to the velocity of the northward plasma convection. The observations indicate firstly a pressure disturbance propagation through the magnetosphere at a velocity of the order of 200km/s which is essentially slower than the velocity of the fast Alfvén (magnetosonic wave, and secondly a potential (curl-free electric field generation behind the front of the propagating disturbance, causing the motion of the auroras. We suggest a physical explanation for the slow propagation of the disturbance through the magnetosphere and a model for the electric field generation. Predictions of the model are supported by the global convection maps produced by the SuperDARN HF radars. Finally, the interchange instability and the eigenmode toroidal

  2. MADR: metal artifact detection and reduction

    Science.gov (United States)

    Jaiswal, Sunil Prasad; Ha, Sungsoo; Mueller, Klaus

    2016-04-01

    Metal in CT-imaged objects drastically reduces the quality of these images due to the severe artifacts it can cause. Most metal artifacts reduction (MAR) algorithms consider the metal-affected sinogram portions as the corrupted data and replace them via sophisticated interpolation methods. While these schemes are successful in removing the metal artifacts, they fail to recover some of the edge information. To address these problems, the frequency shift metal artifact reduction algorithm (FSMAR) was recently proposed. It exploits the information hidden in the uncorrected image and combines the high frequency (edge) components of the uncorrected image with the low frequency components of the corrected image. Although this can effectively transfer the edge information of the uncorrected image, it also introduces some unwanted artifacts. The essential problem of these algorithms is that they lack the capability of detecting the artifacts and as a result cannot discriminate between desired and undesired edges. We propose a scheme that does better in these respects. Our Metal Artifact Detection and Reduction (MADR) scheme constructs a weight map which stores whether a pixel in the uncorrected image belongs to an artifact region or a non-artifact region. This weight matrix is optimal in the Linear Minimum Mean Square Sense (LMMSE). Our results demonstrate that MADR outperforms the existing algorithms and ensures that the anatomical structures close to metal implants are better preserved.

  3. REDUCTION OF GROUND MOTION INTENSITY CAUSED BY BLASTING ON STONE QUARRIES"HERCEGOVAC" AND "MAX-STOJA"

    Directory of Open Access Journals (Sweden)

    Marin Petrov

    1993-12-01

    Full Text Available Ground motion intensity caused by deep-hole blasting on the stone quarries »Hercegovac« and »Max-Stoja« was determined by measuring of ground vibrations magnitudes and by interpretation of measuring results under world damage criteria for structures. Reduction of ground motion intensity was realized on the basis of calculation of permissible charge quantity per ignition level (the paper is published in Croatian.

  4. Motion in radiotherapy

    DEFF Research Database (Denmark)

    Korreman, Stine Sofia

    2012-01-01

    This review considers the management of motion in photon radiation therapy. An overview is given of magnitudes and variability of motion of various structures and organs, and how the motion affects images by producing artifacts and blurring. Imaging of motion is described, including 4DCT and 4DPE...

  5. Improving the use of principal component analysis to reduce physiological noise and motion artifacts to increase the sensitivity of task-based fMRI.

    Science.gov (United States)

    Soltysik, David A; Thomasson, David; Rajan, Sunder; Biassou, Nadia

    2015-02-15

    Functional magnetic resonance imaging (fMRI) time series are subject to corruption by many noise sources, especially physiological noise and motion. Researchers have developed many methods to reduce physiological noise, including RETROICOR, which retroactively removes cardiac and respiratory waveforms collected during the scan, and CompCor, which applies principal components analysis (PCA) to remove physiological noise components without any physiological monitoring during the scan. We developed four variants of the CompCor method. The optimized CompCor method applies PCA to time series in a noise mask, but orthogonalizes each component to the BOLD response waveform and uses an algorithm to determine a favorable number of components to use as "nuisance regressors." Whole brain component correction (WCompCor) is similar, except that it applies PCA to time-series throughout the whole brain. Low-pass component correction (LCompCor) identifies low-pass filtered components throughout the brain, while high-pass component correction (HCompCor) identifies high-pass filtered components. We compared the new methods with the original CompCor method by examining the resulting functional contrast-to-noise ratio (CNR), sensitivity, and specificity. (1) The optimized CompCor method increased the CNR and sensitivity compared to the original CompCor method and (2) the application of WCompCor yielded the best improvement in the CNR and sensitivity. The sensitivity of the optimized CompCor, WCompCor, and LCompCor methods exceeded that of the original CompCor method. However, regressing noise signals showed a paradoxical consequence of reducing specificity for all noise reduction methods attempted. Published by Elsevier B.V.

  6. Artifacts that mimic ballistic magnetoresistance

    International Nuclear Information System (INIS)

    Egelhoff, W.F. . E-mail : egelhoff@nist.gov; Gan, L.; Ettedgui, H.; Kadmon, Y.; Powell, C.J.; Chen, P.J.; Shapiro, A.J.; McMichael, R.D.; Mallett, J.J.; Moffat, T.P.; Stiles, M.D.; Svedberg, E.B.

    2005-01-01

    We have investigated the circumstances underlying recent reports of very large values of ballistic magnetoresistance (BMR) in nanocontacts between magnetic wires. We find that the geometries used are subject to artifacts due to motion of the wires that distort the nanocontact thereby changing its electrical resistance. Since these nanocontacts are often of atomic scale, reliable experiments would require stability on the atomic scale. No method for achieving such stability in macroscopic wires is apparent. We conclude that macroscopic magnetic wires cannot be used to establish the validity of the BMR effect

  7. Ripple artifact reduction using slice overlap in slice encoding for metal artifact correction.

    Science.gov (United States)

    den Harder, J Chiel; van Yperen, Gert H; Blume, Ulrike A; Bos, Clemens

    2015-01-01

    Multispectral imaging (MSI) significantly reduces metal artifacts. Yet, especially in techniques that use gradient selection, such as slice encoding for metal artifact correction (SEMAC), a residual ripple artifact may be prominent. Here, an analysis is presented of the ripple artifact and of slice overlap as an approach to reduce the artifact. The ripple artifact was analyzed theoretically to clarify its cause. Slice overlap, conceptually similar to spectral bin overlap in multi-acquisition with variable resonances image combination (MAVRIC), was achieved by reducing the selection gradient and, thus, increasing the slice profile width. Time domain simulations and phantom experiments were performed to validate the analyses and proposed solution. Discontinuities between slices are aggravated by signal displacement in the frequency encoding direction in areas with deviating B0. Specifically, it was demonstrated that ripple artifacts appear only where B0 varies both in-plane and through-plane. Simulations and phantom studies of metal implants confirmed the efficacy of slice overlap to reduce the artifact. The ripple artifact is an important limitation of gradient selection based MSI techniques, and can be understood using the presented simulations. At a scan-time penalty, slice overlap effectively addressed the artifact, thereby improving image quality near metal implants. © 2014 Wiley Periodicals, Inc.

  8. Effects of Cable Sway, Electrode Surface Area, and Electrode Mass on Electroencephalography Signal Quality during Motion.

    Science.gov (United States)

    Symeonidou, Evangelia-Regkina; Nordin, Andrew D; Hairston, W David; Ferris, Daniel P

    2018-04-03

    More neuroscience researchers are using scalp electroencephalography (EEG) to measure electrocortical dynamics during human locomotion and other types of movement. Motion artifacts corrupt the EEG and mask underlying neural signals of interest. The cause of motion artifacts in EEG is often attributed to electrode motion relative to the skin, but few studies have examined EEG signals under head motion. In the current study, we tested how motion artifacts are affected by the overall mass and surface area of commercially available electrodes, as well as how cable sway contributes to motion artifacts. To provide a ground-truth signal, we used a gelatin head phantom with embedded antennas broadcasting electrical signals, and recorded EEG with a commercially available electrode system. A robotic platform moved the phantom head through sinusoidal displacements at different frequencies (0-2 Hz). Results showed that a larger electrode surface area can have a small but significant effect on improving EEG signal quality during motion and that cable sway is a major contributor to motion artifacts. These results have implications in the development of future hardware for mobile brain imaging with EEG.

  9. Hotspot motion caused the Hawaiian-Emperor Bend and LLSVPs are not fixed

    Science.gov (United States)

    Tarduno, J. A.; Bono, R. K.

    2017-12-01

    Paleomagnetic study of volcanic rocks remains the gold standard on which to assess hotspot motion, true polar wander and plate motion recorded by oceanic plates. There is remarkable consistency between paleomagnetic results from basaltic lavas recovered by ocean drilling of the Emperor seamounts, and independent predictions of plate circuits. Both reveal greater than 40 mm/yr of southward hotspot motion; thus the dominant reason for the distinct bend morphology the Hawaiian-Emperor track is hotspot motion rather than plate motion. These findings provide the motivation for moving beyond hotspot fixity to understand mantle processes responsible for the observed motions. Global analyses as well as comparisons between the Hawaiian-Emperor and Louisville tracks indicate only a minor (if any) role for true polar wander. Two viable, non-mutually exclusive processes to explain the observed Hawaiian plume motion are: i. plume-ridge and ii plume-LLSVP interaction. Here we further explore these issues by paleomagnetic analyses of basalts from the Cenozoic Hawaiian chain and Late Cretaceous basalts of the southernmost Pacific Plate. The latter yield paleolatitudes consistent with those from the northern Pacific, indicating that long-standing non-dipole fields cannot have been large enough to affect conclusions on hotspot drift. Data from the former suggest some relative motions between the LLSVPs on tens-of-millions of year time scales, which probably record the continual reshaping of these provinces by plume motion in the lower mantle.

  10. Correlation-based motion vector processing with adaptive interpolation scheme for motion-compensated frame interpolation.

    Science.gov (United States)

    Huang, Ai-Mei; Nguyen, Truong

    2009-04-01

    In this paper, we address the problems of unreliable motion vectors that cause visual artifacts but cannot be detected by high residual energy or bidirectional prediction difference in motion-compensated frame interpolation. A correlation-based motion vector processing method is proposed to detect and correct those unreliable motion vectors by explicitly considering motion vector correlation in the motion vector reliability classification, motion vector correction, and frame interpolation stages. Since our method gradually corrects unreliable motion vectors based on their reliability, we can effectively discover the areas where no motion is reliable to be used, such as occlusions and deformed structures. We also propose an adaptive frame interpolation scheme for the occlusion areas based on the analysis of their surrounding motion distribution. As a result, the interpolated frames using the proposed scheme have clearer structure edges and ghost artifacts are also greatly reduced. Experimental results show that our interpolated results have better visual quality than other methods. In addition, the proposed scheme is robust even for those video sequences that contain multiple and fast motions.

  11. Small Artifacts - Big Technologies

    DEFF Research Database (Denmark)

    Kreiner, Kristian

    2005-01-01

    The computer IC is the heart of the information and telecommunication technology. It is a tiny artifact, but with incredible organizing powers. We use this physical artifact as the location for studying central problems of the knowledge economy. First, the paper describes the history of chip design...

  12. Voting strategy for artifact reduction in digital breast tomosynthesis

    International Nuclear Information System (INIS)

    Wu Tao; Moore, Richard H.; Kopans, Daniel B.

    2006-01-01

    Artifacts are observed in digital breast tomosynthesis (DBT) reconstructions due to the small number of projections and the narrow angular range that are typically employed in tomosynthesis imaging. In this work, we investigate the reconstruction artifacts that are caused by high-attenuation features in breast and develop several artifact reduction methods based on a 'voting strategy'. The voting strategy identifies the projection(s) that would introduce artifacts to a voxel and rejects the projection(s) when reconstructing the voxel. Four approaches to the voting strategy were compared, including projection segmentation, maximum contribution deduction, one-step classification, and iterative classification. The projection segmentation method, based on segmentation of high-attenuation features from the projections, effectively reduces artifacts caused by metal and large calcifications that can be reliably detected and segmented from projections. The other three methods are based on the observation that contributions from artifact-inducing projections have higher value than those from normal projections. These methods attempt to identify the projection(s) that would cause artifacts by comparing contributions from different projections. Among the three methods, the iterative classification method provides the best artifact reduction; however, it can generate many false positive classifications that degrade the image quality. The maximum contribution deduction method and one-step classification method both reduce artifacts well from small calcifications, although the performance of artifact reduction is slightly better with the one-step classification. The combination of one-step classification and projection segmentation removes artifacts from both large and small calcifications

  13. Feasibility of Stereo-Infrared Tracking to Monitor Patient Motion During Cardiac SPECT Imaging

    OpenAIRE

    Beach, Richard D.; Pretorius, P. Hendrik; Boening, Guido; Bruyant, Philippe P.; Feng, Bing; Fulton, Roger R.; Gennert, Michael A.; Nadella, Suman; King, Michael A.

    2004-01-01

    Patient motion during cardiac SPECT imaging can cause diagnostic imaging artifacts. We investigated the feasibility of monitoring patient motion using the Polaris motion-tracking system. This system uses passive infrared reflection from small spheres to provide real-time position data with vendor stated 0.35 mm accuracy and 0.2 mm repeatability. In our configuration, the Polaris system views through the SPECT gantry toward the patient's head. List-mode event data was temporally synchronized w...

  14. Dose modulated retrospective ECG-gated versus non-gated 64-row CT angiography of the aorta at the same radiation dose: Comparison of motion artifacts, diagnostic confidence and signal-to-noise-ratios

    International Nuclear Information System (INIS)

    Schernthaner, Ruediger E.; Stadler, Alfred; Beitzke, Dietrich; Homolka, Peter; Weber, Michael; Lammer, Johannes; Czerny, Martin; Loewe, Christian

    2012-01-01

    Purpose: To compare ECG-gated and non-gated CT angiography of the aorta at the same radiation dose, with regard to motion artifacts (MA), diagnostic confidence (DC) and signal-to-noise-ratios (SNRs). Materials and methods: Sixty consecutive patients prospectively randomized into two groups underwent 64-row CT angiography, with or without dose-modulated ECG-gating, of the entire aorta, due to several pathologies of the ascending aorta. MA and DC were both assessed using a four-point scale. SNRs were calculated by dividing the mean enhancement by the standard deviation. The dose-length-product (DLP) of each examination was recorded and the effective dose was estimated. Results: Dose-modulated ECG-gating showed statistically significant advantages over non-gated CT angiography, with regard to MA (p < 0.001) and DC (p < 0.001), at the aortic valve, at the origin of the coronary arteries, and at the dissection membrane, with a significant correlation (p < 0.001) between MA and DC. At the aortic wall, however, ECG-gated CT angiography showed statistically significant fewer MA (p < 0.001), but not a statistically significant higher DC (p = 0.137) compared to non-gated CT angiography. At the supra-aortic vessels and the descending aorta, the ECG-triggering showed no statistically significant differences with regard to MA (p = 0.861 and 0.526, respectively) and DC (p = 1.88 and 0.728, respectively). The effective dose of ECG-gated CT angiography (23.24 mSv; range, 18.43–25.94 mSv) did not differ significantly (p = 0.051) from that of non-gated CT angiography (24.28 mSv; range, 19.37–29.27 mSv). Conclusion: ECG-gated CT angiography of the entire aorta reduces MA and results in a higher DC with the same SNR, compared to non-gated CT angiography at the same radiation dose.

  15. Iterative CT reconstruction with correction for known rigid motion

    Energy Technology Data Exchange (ETDEWEB)

    Nuyts, Johan [Katholieke Univ. Leuven (Belgium). Dept. of Nuclear Medicine; Kim, Jung-Ha; Fulton, Roger [Sydney Univ., NSW (Australia). School of Physics; Westmead Hospital, Sydney (Australia). Medical Physics

    2011-07-01

    In PET/CT brain imaging, correction for motion may be needed, in particular for children and psychiatric patients. Motion is more likely to occur in the lengthy PET measurement, but also during the short CT acquisition patient motion is possible. Rigid motion of the head can be measured independently from the PET/CT system with optical devices. In this paper, we propose a method and some preliminary simulation results for iterative CT reconstruction with correction for known rigid motion. We implemented an iterative algorithm for fully 3D reconstruction from helical CT scans. The motion of the head is incorporated in the system matrix as a view-dependent motion of the CT-system. The first simulation results indicate that some motion patterns may produce loss of essential data. This loss precludes exact reconstruction and results in artifacts in the reconstruction, even when motion is taken into account. However, by reducing the pitch during acquisition, the same motion pattern no longer caused artifacts in the motion corrected image. (orig.)

  16. Human movement analysis using stereophotogrammetry. Part 3. Soft tissue artifact assessment and compensation.

    Science.gov (United States)

    Leardini, Alberto; Chiari, Lorenzo; Della Croce, Ugo; Cappozzo, Aurelio

    2005-02-01

    When using optoelectronic stereophotogrammetry, skin deformation and displacement causes marker movement with respect to the underlying bone. This movement represents an artifact, which affects the estimation of the skeletal system kinematics, and is regarded as the most critical source of error in human movement analysis. A comprehensive review of the state-of-the-art for assessment, minimization and compensation of the soft tissue artifact (STA) is provided. It has been shown that STA is greater than the instrumental error associated with stereophotogrammetry, has a frequency content similar to the actual bone movement, is task dependent and not reproducible among subjects and, of lower limb segments, is greatest at the thigh. It has been shown that in in vivo experiments only motion about the flexion/extension axis of the hip, knees and ankles can be determined reliably. Motion about other axes at those joints should be regarded with much more caution as this artifact produces spurious effects with magnitudes comparable to the amount of motion actually occurring in those joints. Techniques designed to minimize the contribution of and compensate for the effects of this artifact can be divided up into those which model the skin surface and those which include joint motion constraints. Despite the numerous solutions proposed, the objective of reliable estimation of 3D skeletal system kinematics using skin markers has not yet been satisfactorily achieved and greatly limits the contribution of human movement analysis to clinical practice and biomechanical research. For STA to be compensated for effectively, it is here suggested that either its subject-specific pattern is assessed by ad hoc exercises or it is characterized from a large series of measurements on different subject populations. Alternatively, inclusion of joint constraints into a more general STA minimization approach may provide an acceptable solution.

  17. The Role of Viscosity in Causing the Plasma Poloidal Motion in Magnetic Clouds

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Ake; Wang, Yuming; Liu, Jiajia; Zhou, Zhenjun; Shen, Chenglong; Liu, Rui; Zhuang, Bin; Zhang, Quanhao, E-mail: ymwang@ustc.edu.cn [CAS Key Laboratory of Geospace Environment, Department of Geophysics and Planetary Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2017-08-20

    An interesting phenomenon, plasma poloidal motion, has been found in many magnetic clouds (MCs), and viscosity has been proposed as a possible mechanism. However, it is not clear how significant the role of viscosity is in generating such motion. In this paper, we conduct a statistical study of the MCs detected by the Wind spacecraft during 1995–2012. It is found that, for 19% of all the studied MCs (186), the poloidal velocities of the MC plasma near the MC boundaries are well correlated with those of the corresponding ambient solar wind plasma. A non-monotonic increase from inner to outer MCs suggests that the viscosity does play a role, albeit weak, on the poloidal motion in the MC statistically. The possible dependence on the solar wind parameters is then studied in detail for the nine selected crossings, which represent the viscosity characteristic. There is an evident negative correlation between the viscosity and the density, a weak negative correlation between the viscosity and the turbulence strength, and no clear correlation between the viscosity and the temperature.

  18. Capillary Electrophoresis Artifact Due to Eosin

    Science.gov (United States)

    Murphy, Kathleen M.; Berg, Karin D.; Geiger, Tanya; Hafez, Michael; Flickinger, Katie A.; Cooper, Lisa; Pearson, Patrick; Eshleman, James R.

    2005-01-01

    Capillary electrophoresis (CE) is a commonly used tool in the analysis of fluorescently labeled PCR amplification products. We have identified a CE artifact caused by the tissue stain eosin that can complicate the interpretation of CE data. The artifact was detected during routine analysis of a DNA sample isolated from a formalin-fixed, paraffin-embedded tissue sample considered histologically suspicious for a B-cell neoplasm. A standard clinical PCR and CE assay for immunoglobulin heavy chain (IGH) gene rearrangement revealed a weak polyclonal population of rearranged IGH genes and a 71 base peak suspicious for IGH clonality. The spectral properties of the 71 base peak were unusual in that although the dominant fluorescence of the peak was blue, it also fluoresced in green and yellow (blue>green>yellow), raising the suspicion that the peak might represent an artifact. CE analysis of the genomic DNA sample without PCR amplification demonstrated the presence of the 71 base peak, suggesting that the artifact was caused by a contaminant within the DNA sample itself. We demonstrate that eosin, which was used to stain the formalin-fixed tissue during processing, yields a discrete 71 base peak of similar morphology to the contaminant peak on CE analysis. The data suggest that eosin in the fixed tissue was not completely eliminated during nucleic acid extraction, resulting in the artifact peak. We discuss the implications of this potentially common contaminant on the interpretation of CE data and demonstrate that artifacts caused by eosin can be avoided by using more stringent DNA purification steps. Histological dyes may fluoresce, and artifacts from them should be considered when primary peaks contain additional underlying peaks of other colors. PMID:15681487

  19. Probabilistic evaluation of near-field ground motions due to buried-rupture earthquakes caused by undefined faults

    International Nuclear Information System (INIS)

    Shohei Motohashi; Katsumi Ebisawa; Masaharu Sakagmi; Kazuo Dan; Yasuhiro Ohtsuka; Takao Kagawa

    2005-01-01

    The Nuclear Safety Commission of Japan has been reviewing the current Guideline for Earthquake Resistant Design of Nuclear Power Plants since July 2001. According to recent earthquake research, one of the main issues in the review is the design earthquake motion due to close-by earthquakes caused by undefined faults. This paper proposes a probabilistic method for covering variations of earthquake magnitude and location of undefined faults by strong motion simulation technique based on fault models for scenario earthquakes, and describes probabilistic response spectra due to close-by scenario earthquakes caused by undefined faults. Horizontal uniform hazard spectra evaluated by a hybrid technique are compared with those evaluated by an empirical approach. The response spectra with a damping factor of 5% at 0.02 s simulated by the hybrid technique are about 160, 340, 570, and 800 cm/s/s for annual exceedance probabilities of 10 -3 , 10 -4 , 10 -5 , and 10 -6 , respectively, which are in good agreement with the response spectra evaluated by the empirical approach. It is also recognized that the response spectrum proposed by Kato et al. (2004) as the upper level of the strong motion records of buried-rupture earthquakes corresponded to the uniform hazard spectra between 10 -5 and 10 -4 in the period range shorter than 0.4 s. (authors)

  20. Fake signals caused by heavy-mass motions near a sensitive spherical gravitational wave antenna

    International Nuclear Information System (INIS)

    Lobo, Alberto; Cerdonio, Massimo; Montero, Alvaro

    2002-01-01

    In this paper we analyse in quantitative detail the effect of a moving mass on a spherical gravitational wave detector. This applies to situations where heavy traffic or similar disturbances occur near the GW antenna. Such disturbances result in quadrupole tidal stresses in the antenna mass, and they therefore precisely fake a real gravitational signal. The study shows that there are always characteristic frequencies, depending on the motion of the external masses, at which the fake signals are most intense. It however appears that, even at those frequencies, fake signals should be orders of magnitude below the sensitivity curve of an optimized detector, in likely realistic situations

  1. Evaluating correlation between geometrical relationship and dose difference caused by respiratory motion using statistical analysis

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Dong Seok; Kim, Dong Su; Kim, Tae Ho; Kim, Kyeong Hyeon; Yoon, Do Kun; Suh, Tae Suk [The Catholic University of Korea, Seoul (Korea, Republic of); Kang, Seong Hee [Seoul National University Hospital, Seoul (Korea, Republic of); Cho, Min Seok [Asan Medical Center, Seoul (Korea, Republic of); Noh, Yu Yoon [Eulji University Hospital, Daejeon (Korea, Republic of)

    2017-04-15

    Three-dimensional dose (3D dose) can consider coverage of moving target, however it is difficult to provide dosimetric effect which occurs by respiratory motions. Four-dimensional dose (4D dose) which uses deformable image registration (DIR) algorithm from four-dimensional computed tomography (4DCT) images can consider dosimetric effect by respiratory motions. The dose difference between 3D dose and 4D dose can be varied according to the geometrical relationship between a planning target volume (PTV) and an organ at risk (OAR). The purpose of this study is to evaluate the correlation between the overlap volume histogram (OVH), which quantitatively shows the geometrical relationship between the PTV and OAR, and the dose differences. In conclusion, no significant statistical correlation was found between the OVH and dose differences. However, it was confirmed that a higher difference between the 3D and 4D doses could occur in cases that have smaller OVH value. No significant statistical correlation was found between the OVH and dose differences. However, it was confirmed that a higher difference between the 3D and 4D doses could occur in cases that have smaller OVH value.

  2. The Information Systems Artifact

    DEFF Research Database (Denmark)

    Chatterjee, Surtirtha; Xiao, Xiao; Elbanna, Amany

    2017-01-01

    Passionate debates regarding the defining characteristic of the “IT artifact” continue. Such debates, and also the lack of explicit consideration of the “information” element in the IT artifact, motivate us to propose a revised conception, drawing upon concepts from General Systems Theory (GST). ...

  3. Analyses of surface motions caused by the magnitude 9.0 2004 Sumatra earthquake

    DEFF Research Database (Denmark)

    Khan, Shfaqat Abbas; Gudmundsson, Ó.

    The Sumatra, Indonesia, earthquake on December 26th was one of the most devastating earthquakes in history. With a magnitude of Mw = 9.0 it is the forth largest earthquake recorded since 1900. It occurred about one hundred kilometers off the west coast of northern Sumatra, where the relatively thin...... of years. The result was a devastating tsunami hitting coastlines across the Indian Ocean killing more than 225,000 people in Sri Lanka, India, Indonesia, Thailand and Malaysia. An earthquake of this magnitude is expected to involve a displacement on the fault on the order of 10 meters. But, what...... was the actual amplitude of the surface motions that triggered the tsunami? This can be constrained using the amplitudes of elastic waves radiated from the earthquake, or by direct measurements of deformation. Here we present estimates of the deformation based on continuous Global Positioning System (GPS...

  4. Photomultiplier tube artifacts on 67Ga-citrate imaging caused by loss of correction floods due to an off-peak status of one head of a dual-head γ-camera.

    Science.gov (United States)

    Glaser, Joseph E; Song, Na; Jaini, Sridivya; Lorenzo, Ruth; Love, Charito

    2012-12-01

    γ-cameras use flood-field corrections to ensure image uniformity during clinical imaging. A loss or corruption of the correction data of one head of a dual-head camera can result in an off-peak artifactual appearance. We present our experience with the occurrence of such an incident on a (67)Ga scan. A patient was referred for a whole-body (67)Ga scan to evaluate for causes of neutropenic fever. Whole-body planar and static images of the head, chest, abdomen, pelvis, and lower extremities in multiple projections were obtained. Whole-body images showed decreased image quality on the anterior view obtained with detector 1 and an unremarkable posterior image obtained with detector 2. A problem with detector 2 was suspected, and additional static images were obtained after rotation of the detector heads. The posterior images taken with detector 1 showed photomultiplier tube outlines. The anterior images taken with detector 2 showed improved count and image quality. It was later found that the uniformity map for detector 2 had been lost and that this software malfunction led to the resulting imaging problem. When artifacts with an off-peak appearance are seen on scintigraphic images, evaluation of possible causes should include not only isotope window settings but also an incorrect or corrupted uniformity map.

  5. Metallic artifact in MRI after removal of orthopedic implants

    International Nuclear Information System (INIS)

    Bagheri, Mohammad Hadi; Hosseini, Mehrdad Mohammad; Emami, Mohammad Jafar; Foroughi, Amin Aiboulhassani

    2012-01-01

    Objective: The aim of the present study was to evaluate the metallic artifacts in MRI of the orthopedic patients after removal of metallic implants. Subjects and methods: From March to August 2009, 40 orthopedic patients operated for removal of orthopedic metallic implants were studied by post-operative MRI from the site of removal of implants. A grading scale of 0–3 was assigned for artifact in MR images whereby 0 was considered no artifact; and I–III were considered mild, moderate, and severe metallic artifacts, respectively. These grading records were correlated with other variables including the type, size, number, and composition of metallic devices; and the site and duration of orthopedic devices stay in the body. Results: Metallic susceptibly artifacts were detected in MRI of 18 of 40 cases (45%). Screws and pins in removed hardware were the most important factors for causing artifacts in MRI. The artifacts were found more frequently in the patients who had more screws and pins in the removed implants. Gender, age, site of implantation of the device, length of the hardware, composition of the metallic implants (stainless steel versus titanium), and duration of implantation of the hardware exerted no effect in producing metallic artifacts after removal of implants. Short TE sequences of MRI (such as T1 weighted) showed fewer artifacts. Conclusion: Susceptibility of metallic artifacts is a frequent phenomenon in MRI of patients upon removal of metallic orthopedic implants.

  6. Metallic artifact in MRI after removal of orthopedic implants.

    Science.gov (United States)

    Bagheri, Mohammad Hadi; Hosseini, Mehrdad Mohammad; Emami, Mohammad Jafar; Foroughi, Amin Aiboulhassani

    2012-03-01

    The aim of the present study was to evaluate the metallic artifacts in MRI of the orthopedic patients after removal of metallic implants. From March to August 2009, 40 orthopedic patients operated for removal of orthopedic metallic implants were studied by post-operative MRI from the site of removal of implants. A grading scale of 0-3 was assigned for artifact in MR images whereby 0 was considered no artifact; and I-III were considered mild, moderate, and severe metallic artifacts, respectively. These grading records were correlated with other variables including the type, size, number, and composition of metallic devices; and the site and duration of orthopedic devices stay in the body. Metallic susceptibly artifacts were detected in MRI of 18 of 40 cases (45%). Screws and pins in removed hardware were the most important factors for causing artifacts in MRI. The artifacts were found more frequently in the patients who had more screws and pins in the removed implants. Gender, age, site of implantation of the device, length of the hardware, composition of the metallic implants (stainless steel versus titanium), and duration of implantation of the hardware exerted no effect in producing metallic artifacts after removal of implants. Short TE sequences of MRI (such as T1 weighted) showed fewer artifacts. Susceptibility of metallic artifacts is a frequent phenomenon in MRI of patients upon removal of metallic orthopedic implants. Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.

  7. Human-Robot Collaboration Dynamic Impact Testing and Calibration Instrument for Disposable Robot Safety Artifacts.

    Science.gov (United States)

    Dagalakis, Nicholas G; Yoo, Jae Myung; Oeste, Thomas

    2016-01-01

    The Dynamic Impact Testing and Calibration Instrument (DITCI) is a simple instrument with a significant data collection and analysis capability that is used for the testing and calibration of biosimulant human tissue artifacts. These artifacts may be used to measure the severity of injuries caused in the case of a robot impact with a human. In this paper we describe the DITCI adjustable impact and flexible foundation mechanism, which allows the selection of a variety of impact force levels and foundation stiffness. The instrument can accommodate arrays of a variety of sensors and impact tools, simulating both real manufacturing tools and the testing requirements of standards setting organizations. A computer data acquisition system may collect a variety of impact motion, force, and torque data, which are used to develop a variety of mathematical model representations of the artifacts. Finally, we describe the fabrication and testing of human abdomen soft tissue artifacts, used to display the magnitude of impact tissue deformation. Impact tests were performed at various maximum impact force and average pressure levels.

  8. Impact of patient motion on myocardial perfusion SPECT

    International Nuclear Information System (INIS)

    Huang Kemin; Feng Yanlin; He Xiaohong; Wen Guanghua; Yu Fengwen; Liu Shusheng; Liu Dejun; Yuan Jianwei; Yang Ming

    2008-01-01

    Objective: It is well known that patient motion may cause artifacts in myocardial SPECT images and affect clinical diagnosis. The aim of the study was to evaluate the effects of motion on quality and semi-quantitative results of myocardial perfusion images. Methods: Six healthy volunteers un- derwent myocardial perfusion SPECT. The raw data in each case was manually shifted 1-6 frames and 1 4 pixels, respectively by using the motion correction software. The shifted raw data were then reconstructed. A semi-quantitative software was used to assess the myocardial perfusion of left ventricle. The quality and semi-quantitative results of the tomographic images reconstructed from the raw data with and without motion were compared and analyzed. SPSS 12.0 was used for data analysis. Results: There was no visible artifact and semi-quantitative difference on the data with 1 frame and (or) 1 pixel shift when compared with the original data without shift. The image artifacts became significantly deteriorated when the number of flame and (or) pixel shift was increased. In general, the image artifact of inferior and posterior wall was related to the upward shift, and that of anterior and infero-posterior wall was related to the downward shift, that of septal, anterior, infero-postefior wall and apex was related to right-ward shift, and the septal and infero-posterior wall was related to the left-ward shift. The differences along the x-axis shift were more prominent than that of the y-axis (t=2.848, P<0.01), and the differences in the downward and rightward shift were more severe than the upward and leftward shift (t=2.941, 6.598; all P<0.01), respectively. Conclusions: Image artifacts became significant when there was motion induced by manual shift of more than one flame and (or) one pixel. Different motion directions were closely related to different segments of left ventricle. (authors)

  9. Pitfalls and artifacts in magnetic resonance imaging

    International Nuclear Information System (INIS)

    Kulkarni, M.V.; Patton, J.A.

    1986-01-01

    As a new imaging technique, MRI is subject to new and unfamiliar artifacts. Because of the wide range of pulse sequences used in MRI, the technique is prone to some artifacts, such as even echo rephasing, which are not found in other imaging systems. With newer and stronger magnetic fields, artifacts such as those caused by chemical shift will be more pronounced. For the maintenance of high quality images, new techniques controlling quality are essential. These techniques include the development of new phantoms and new procedures. The American Association of Physicists in Medicine is currently developing guidelines for quality assurance programs. As with other imaging modalities, these quality assurance guidelines could be unique to MRI. The daily or weekly evaluation of signal-to-noise ratio, image uniformity, signal linearity, spatial linearity, spatial resolution, frequencies, etc. is essential. Some guidelines are described in the current literature. With further modifications and improvements in MRI techniques, new artifacts may be discovered. Identification of these artifacts will improve the interpretation of the image and patient management

  10. Artifacts Quantification of Metal Implants in MRI

    Science.gov (United States)

    Vrachnis, I. N.; Vlachopoulos, G. F.; Maris, T. G.; Costaridou, L. I.

    2017-11-01

    The presence of materials with different magnetic properties, such as metal implants, causes distortion of the magnetic field locally, resulting in signal voids and pile ups, i.e. susceptibility artifacts in MRI. Quantitative and unbiased measurement of the artifact is prerequisite for optimization of acquisition parameters. In this study an image gradient based segmentation method is proposed for susceptibility artifact quantification. The method captures abrupt signal alterations by calculation of the image gradient. Then the artifact is quantified in terms of its extent by an automated cross entropy thresholding method as image area percentage. The proposed method for artifact quantification was tested in phantoms containing two orthopedic implants with significantly different magnetic permeabilities. The method was compared against a method proposed in the literature, considered as a reference, demonstrating moderate to good correlation (Spearman’s rho = 0.62 and 0.802 in case of titanium and stainless steel implants). The automated character of the proposed quantification method seems promising towards MRI acquisition parameter optimization.

  11. An Additive Manufacturing Test Artifact

    Science.gov (United States)

    Moylan, Shawn; Slotwinski, John; Cooke, April; Jurrens, Kevin; Donmez, M Alkan

    2014-01-01

    A test artifact, intended for standardization, is proposed for the purpose of evaluating the performance of additive manufacturing (AM) systems. A thorough analysis of previously proposed AM test artifacts as well as experience with machining test artifacts have inspired the design of the proposed test artifact. This new artifact is designed to provide a characterization of the capabilities and limitations of an AM system, as well as to allow system improvement by linking specific errors measured in the test artifact to specific sources in the AM system. The proposed test artifact has been built in multiple materials using multiple AM technologies. The results of several of the builds are discussed, demonstrating how the measurement results can be used to characterize and improve a specific AM system. PMID:26601039

  12. The Human-Artifact Model

    DEFF Research Database (Denmark)

    Bødker, Susanne; Klokmose, Clemens Nylandsted

    2011-01-01

    Although devices of all shapes and sizes currently dominate the technological landscape, human–computer interaction (HCI) as a field is not yet theoretically equipped to match this reality. In this article we develop the human–artifact model, which has its roots in activity theoretical HCI....... By reinterpreting the activity theoretical foundation, we present a framework that helps addressing the analysis of individual interactive artifacts while embracing that they are part of a larger ecology of artifacts. We show how the human–artifact model helps structuring the understanding of an artifact's action......-possibilities in relation to the artifact ecology surrounding it. Essential to the model is that it provides four interconnected levels of analysis and addresses the possibilities and problems at these four levels. Artifacts and their use are constantly developing, and we address development in, and of, use. The framework...

  13. Detection of artifacts from high energy bursts in neonatal EEG.

    Science.gov (United States)

    Bhattacharyya, Sourya; Biswas, Arunava; Mukherjee, Jayanta; Majumdar, Arun Kumar; Majumdar, Bandana; Mukherjee, Suchandra; Singh, Arun Kumar

    2013-11-01

    Detection of non-cerebral activities or artifacts, intermixed within the background EEG, is essential to discard them from subsequent pattern analysis. The problem is much harder in neonatal EEG, where the background EEG contains spikes, waves, and rapid fluctuations in amplitude and frequency. Existing artifact detection methods are mostly limited to detect only a subset of artifacts such as ocular, muscle or power line artifacts. Few methods integrate different modules, each for detection of one specific category of artifact. Furthermore, most of the reference approaches are implemented and tested on adult EEG recordings. Direct application of those methods on neonatal EEG causes performance deterioration, due to greater pattern variation and inherent complexity. A method for detection of a wide range of artifact categories in neonatal EEG is thus required. At the same time, the method should be specific enough to preserve the background EEG information. The current study describes a feature based classification approach to detect both repetitive (generated from ECG, EMG, pulse, respiration, etc.) and transient (generated from eye blinking, eye movement, patient movement, etc.) artifacts. It focuses on artifact detection within high energy burst patterns, instead of detecting artifacts within the complete background EEG with wide pattern variation. The objective is to find true burst patterns, which can later be used to identify the Burst-Suppression (BS) pattern, which is commonly observed during newborn seizure. Such selective artifact detection is proven to be more sensitive to artifacts and specific to bursts, compared to the existing artifact detection approaches applied on the complete background EEG. Several time domain, frequency domain, statistical features, and features generated by wavelet decomposition are analyzed to model the proposed bi-classification between burst and artifact segments. A feature selection method is also applied to select the

  14. Metal and calcification artifact reduction for digital breast tomosynthesis

    Science.gov (United States)

    Wicklein, Julia; Jerebko, Anna; Ritschl, Ludwig; Mertelmeier, Thomas

    2017-03-01

    Tomosynthesis images of the breast suffer from artifacts caused by the presence of highly absorbing materials. These can be either induced by metal objects like needles or clips inserted during biopsy devices, or larger calcifications inside the examined breast. Mainly two different kinds of artifacts appear after the filtered backprojection procedure. The first type is undershooting artifacts near edges of high-contrast objects caused by the filtering step. The second type is out-of-plane (ripple) artifacts that appear even in slices where the metal object or macrocalcifications does not exist. Due to the limited angular range of tomosynthesis systems, overlapping structures have high influence on neighboring regions. To overcome these problems, a segmentation of artifact introducing objects is performed on the projection images. Both projection versions, with and without high-contrast objects are filtered independently to avoid undershootings. During backprojection a decision is made for each reconstructed voxel, if it is artifact or high-contrast object. This is based on a mask image, gained from the segmentation of high-contrast objects. This procedure avoids undershooting artifacts and additionally reduces out-of-plane ripple. Results are demonstrated for different kinds of artifact inducing objects and calcifications.

  15. Rolling Shutter Motion Deblurring

    KAUST Repository

    Su, Shuochen

    2015-06-07

    Although motion blur and rolling shutter deformations are closely coupled artifacts in images taken with CMOS image sensors, the two phenomena have so far mostly been treated separately, with deblurring algorithms being unable to handle rolling shutter wobble, and rolling shutter algorithms being incapable of dealing with motion blur. We propose an approach that delivers sharp and undis torted output given a single rolling shutter motion blurred image. The key to achieving this is a global modeling of the camera motion trajectory, which enables each scanline of the image to be deblurred with the corresponding motion segment. We show the results of the proposed framework through experiments on synthetic and real data.

  16. Analysis of aliasing artifacts in 16-slice helical CT

    International Nuclear Information System (INIS)

    Chen Wei; Liu Jingkang; Ou Xiaoguang; Li Wenzheng; Liao Weihua; Yan Ang

    2006-01-01

    Objective: To recognize the features of aliasing artifacts on CT images, and to investigate the effects of imaging parameters on the magnitude of this artifacts. Methods: An adult dry skull was placed in a plastic water-filled container and scanned with a PHILIPS 16-slice helical CT. All the acquired transaxial images by using several different acquisition or reconstruction parameters were examined for comparative assessment of the aliasing artifacts. Results: The aliasing artifacts could be seen in most instances and characterized as the spokewise patterns emanating from the edges of high contrast structure as its radius varies sharply in the longitudinal direction. The images that scanned with pitch of 0.3, 0.6 and 0.9, respectively, showed aliasing artifacts, and its severities increased with pitches escalated (detector combination 16 x 1.5, reconstruction thickness 2 mm); There were more significant aliasing artifacts on the images reconstructed with 0.8 mm slice width compared with 1-mm slice width, and no aliasing artifacts were observed on the images reconstructed with 2-mm slice width (detector combination 16 x 0.75, pitch 0.6); No artifacts were perceived on the images scanned with detector combination 16 x 0.75, while presented evidently with the use of detector combination 16 x 1.5 (pitch 0.6, reconstruction thickness 2 mm); The degrees of aliasing artifacts were unaltered when reconstruction interval and tube current changed. Conclusions: Aliasing artifacts are caused by undersampling. When the operator choose the thinner sampling thickness, lower pitch and a much wider reconstruction thickness judiciously, aliasing artifacts could be effectively mitigated or suppressed. (authors)

  17. From Ecological Sounding Artifacts Towards Sonic Artifact Ecologies

    DEFF Research Database (Denmark)

    Erkut, Cumhur; Serafin, Stefania

    2016-01-01

    The discipline of sonic interaction design has been focused on the interaction between a single user and an artifact. This strongly limits one of the fundamental aspects of music as a social and interactive experience. In this paper we propose sonic artifact ecologies as a mean to examine interac...

  18. PROMO – Real-time Prospective Motion Correction in MRI using Image-based Tracking

    Science.gov (United States)

    White, Nathan; Roddey, Cooper; Shankaranarayanan, Ajit; Han, Eric; Rettmann, Dan; Santos, Juan; Kuperman, Josh; Dale, Anders

    2010-01-01

    Artifacts caused by patient motion during scanning remain a serious problem in most MRI applications. The prospective motion correction technique attempts to address this problem at its source by keeping the measurement coordinate system fixed with respect to the patient throughout the entire scan process. In this study, a new image-based approach for prospective motion correction is described, which utilizes three orthogonal 2D spiral navigator acquisitions (SP-Navs) along with a flexible image-based tracking method based on the Extended Kalman Filter (EKF) algorithm for online motion measurement. The SP-Nav/EKF framework offers the advantages of image-domain tracking within patient-specific regions-of-interest and reduced sensitivity to off-resonance-induced corruption of rigid-body motion estimates. The performance of the method was tested using offline computer simulations and online in vivo head motion experiments. In vivo validation results covering a broad range of staged head motions indicate a steady-state error of the SP-Nav/EKF motion estimates of less than 10 % of the motion magnitude, even for large compound motions that included rotations over 15 degrees. A preliminary in vivo application in 3D inversion recovery spoiled gradient echo (IR-SPGR) and 3D fast spin echo (FSE) sequences demonstrates the effectiveness of the SP-Nav/EKF framework for correcting 3D rigid-body head motion artifacts prospectively in high-resolution 3D MRI scans. PMID:20027635

  19. A particle accelerator probes artifacts

    International Nuclear Information System (INIS)

    Dran, J.C.; Calligaro, Th.; Salomon, J.

    2002-01-01

    The AGLAE system is made up of a 2 mega volts electrostatic accelerator and of 3 irradiation lines: one leads to a vacuum enclosure in which targets are irradiated and the 2 others lines are designed to irradiate targets under an air or helium atmosphere. The AGLAE system is located in the premises of the Louvre museum in Paris and is devoted to the study of cultural objects through ion beam analysis (IBA). 4 techniques are used: -) proton-induced X-ray emission (PIXE) -) proton-induced gamma ray (PIGE) -) Rutherford backscattering spectrometry (NRS) and -) nuclear reaction analysis (NRA). A decisive progress has permitted the direct analysis of artifacts without sampling. The object itself is set just a few millimeters away from the exit window of the beam in an air or helium atmosphere. The exit window must be resistant enough to bear the atmospheric pressure and the damages caused by the proton beam but must be thin enough to not deteriorate the quality of the beam. By using a 10 -7 m thick exit window made of Si 3 N 4 we get a beam whose diameter is 10 -5 m. This new technology presents 4 main advantages: 1) any object of any shape can be studied without sampling, 2) the analysis of very fragile artifacts that might be damaged by the vacuum setting is now possible, 3) a reduction of the thermal side-effects of the beam, and 4) the absence of accumulation of charges in isolating material allows to rid of covering the object with a conducting coating before irradiating it. (A.C.)

  20. Prostate bed motion may cause geographic miss in post-prostatectomy image-guided intensity-modulated radiotherapy

    International Nuclear Information System (INIS)

    Bell, Linda J.; Cox, Jennifer; Eade, Thomas; Rinks, Marianne; Kneebone, Andrew

    2013-01-01

    There is little data to guide radiation oncologists on appropriate margin selection in the post-prostatectomy setting. The aim of this study was to quantify interfraction variation in motion of the prostate bed to determine these margins. The superior and inferior surgical clips in the prostate bed were tracked on pretreatment cone beam CT images (n=377) for 40 patients who had received post-prostatectomy radiotherapy. Prostate bed motion was calculated for the upper and lower segments by measuring the position of surgical clips located close to midline relative to bony anatomy in the axial (translational) and sagittal (tilt) planes. The frequency of potential geographic misses was calculated for either 1cm or 0.5cm posterior planning target volume margins. The mean magnitude of movement of the prostate bed in the anterior–posterior, superior–inferior and left–right planes, respectively, were as follows: upper portion, 0.50cm, 0.28cm, 0.10cm; lower portion, 0.18cm, 0.18cm, 0.08cm. The random and systematic errors, respectively, of the prostate bed motion in the anterior–posterior, superior–inferior and left–right planes, respectively, were as follows: upper portion, 0.47cm and 0.50cm, 0.28cm and 0.27cm, 0.11cm and 0.11cm; lower portion, 0.17cm and 18cm, 0.17cm and 0.19cm, 0.08cm and 0.10cm. Most geographic misses occurred in the upper prostate bed in the anterior–posterior plane. The median prostate bed tilt was 1.8° (range −23.4° to 42.3°). Variability was seen in all planes for the movement of both surgical clips. The greatest movement occurred in the anterior–posterior plane in the upper prostate bed, which could cause geographic miss of treatment delivery. The variability in the movement of the superior and inferior clips indicates a prostate bed tilt that would be difficult to correct with standard online matching techniques. This creates a strong argument for using anisotropic planning target volume margins in post

  1. Data-driven motion correction in brain SPECT

    International Nuclear Information System (INIS)

    Kyme, A.Z.; Hutton, B.F.; Hatton, R.L.; Skerrett, D.W.

    2002-01-01

    Patient motion can cause image artifacts in SPECT despite restraining measures. Data-driven detection and correction of motion can be achieved by comparison of acquired data with the forward-projections. By optimising the orientation of the reconstruction, parameters can be obtained for each misaligned projection and applied to update this volume using a 3D reconstruction algorithm. Digital and physical phantom validation was performed to investigate this approach. Noisy projection data simulating at least one fully 3D patient head movement during acquisition were constructed by projecting the digital Huffman brain phantom at various orientations. Motion correction was applied to the reconstructed studies. The importance of including attenuation effects in the estimation of motion and the need for implementing an iterated correction were assessed in the process. Correction success was assessed visually for artifact reduction, and quantitatively using a mean square difference (MSD) measure. Physical Huffman phantom studies with deliberate movements introduced during the acquisition were also acquired and motion corrected. Effective artifact reduction in the simulated corrupt studies was achieved by motion correction. Typically the MSD ratio between the corrected and reference studies compared to the corrupted and reference studies was > 2. Motion correction could be achieved without inclusion of attenuation effects in the motion estimation stage, providing simpler implementation and greater efficiency. Moreover the additional improvement with multiple iterations of the approach was small. Improvement was also observed in the physical phantom data, though the technique appeared limited here by an object symmetry. Copyright (2002) The Australian and New Zealand Society of Nuclear Medicine Inc

  2. Grain-boundary, glassy-phase identification and possible artifacts

    International Nuclear Information System (INIS)

    Simpson, Y.K.; Carter, C.B.; Sklad, P.; Bentley, J.

    1985-01-01

    Specimen artifacts such as grain boundary grooving, surface damage of the specimen, and Si contamination are shown experimentally to arise from the ion milling used in the preparation of transmission electron microscopy specimens. These artifacts in polycrystalline, ceramic specimens can cause clean grain boundaries to appear to contain a glassy phase when the dark-field diffuse scattering technique, the Fresnel fringe technique, and analytical electron microscopy (energy dispersive spectroscopy) are used to identify glassy phases at a grain boundary. The ambiguity in interpreting each of these techniques due to the ion milling artifacts will be discussed from a theoretical view point and compared to experimental results obtained for alumina

  3. Motion compensation in digital subtraction angiography using graphics hardware.

    Science.gov (United States)

    Deuerling-Zheng, Yu; Lell, Michael; Galant, Adam; Hornegger, Joachim

    2006-07-01

    An inherent disadvantage of digital subtraction angiography (DSA) is its sensitivity to patient motion which causes artifacts in the subtraction images. These artifacts could often reduce the diagnostic value of this technique. Automated, fast and accurate motion compensation is therefore required. To cope with this requirement, we first examine a method explicitly designed to detect local motions in DSA. Then, we implement a motion compensation algorithm by means of block matching on modern graphics hardware. Both methods search for maximal local similarity by evaluating a histogram-based measure. In this context, we are the first who have mapped an optimizing search strategy on graphics hardware while paralleling block matching. Moreover, we provide an innovative method for creating histograms on graphics hardware with vertex texturing and frame buffer blending. It turns out that both methods can effectively correct the artifacts in most case, as the hardware implementation of block matching performs much faster: the displacements of two 1024 x 1024 images can be calculated at 3 frames/s with integer precision or 2 frames/s with sub-pixel precision. Preliminary clinical evaluation indicates that the computation with integer precision could already be sufficient.

  4. Turquoise Artifact from Teotihuacan

    Energy Technology Data Exchange (ETDEWEB)

    Spence, Michael W.; Harbottle, Garman; Weigand, Phil C.

    1999-07-01

    Turquoise artifacts appeared sporadically in Mesoamerica as early as the Formative period (Merry de Morales 1987:100, Figure 8.4; Weigand 1989:43). Most occurrences, however, postdate the collapse of Teotihuacan. In the Late Classic and Postclassic periods increasing quantities are found, often in the form of elaborate mosaics, in a wide variety of contexts in central, west and northwest Mexico. Neutron activation analysis has determined that much of this turquoise derives from sources in the southwestern United States (Weigand et al. 1977; Harbottle and Weigand 1992; Weigand and Harbottle 1993). Teotihuacan played a major role in Mesoamerica during the Terminal Formative and Early-Middle Classic periods. It was the dominant power in central Mexico from about the time of Christ to its collapse at about A.D. 650 (Millon 1988, 1992; Cowgill 1996). Throughout this period goods flowed into Teotihuacan from many parts of the Mesoamerican world. Despite this widespread economic interaction, only two pieces of turquoise have been recovered in the city. In the following pages, the context and implications of one of these finds will be examined.

  5. Successive approximation algorithm for cancellation of artifacts in DSA images

    International Nuclear Information System (INIS)

    Funakami, Raiko; Hiroshima, Kyoichi; Nishino, Junji

    2000-01-01

    In this paper, we propose an algorithm for cancellation of artifacts in DSA images. We have already proposed an automatic registration method based on the detection of local movements. When motion of the object is large, it is difficult to estimate the exact movement, and the cancellation of artifacts may therefore fail. The algorithm we propose here is based on a simple rigid model. We present the results of applying the proposed method to a series of experimental X-ray images, as well as the results of applying the algorithm as preprocessing for a registration method based on local movement. (author)

  6. Investigating media artifacts with children

    DEFF Research Database (Denmark)

    Chimirri, Niklas Alexander

    The dissertation’s aim is to explore the everyday relevance media artifacts have for young children. It discusses and further develops analytical concepts that are committed to taking the children’s perspectives on possibilities and limitations of such artifacts seriously. These conceptual...... developments are rooted in the author’s participation in a daycare practice in Berlin, Germany. The daycare’s situational approach precisely attempted to draw on the children’s everyday life experiences so as to engage in problem-oriented learning projects, on media artifacts and beyond....

  7. A particle accelerator probes artifacts

    CERN Document Server

    Dran, J C; Salomon, J

    2002-01-01

    The AGLAE system is made up of a 2 mega volts electrostatic accelerator and of 3 irradiation lines: one leads to a vacuum enclosure in which targets are irradiated and the 2 others lines are designed to irradiate targets under an air or helium atmosphere. The AGLAE system is located in the premises of the Louvre museum in Paris and is devoted to the study of cultural objects through ion beam analysis (IBA). 4 techniques are used: -) proton-induced X-ray emission (PIXE) -) proton-induced gamma ray (PIGE) -) Rutherford backscattering spectrometry (NRS) and -) nuclear reaction analysis (NRA). A decisive progress has permitted the direct analysis of artifacts without sampling. The object itself is set just a few millimeters away from the exit window of the beam in an air or helium atmosphere. The exit window must be resistant enough to bear the atmospheric pressure and the damages caused by the proton beam but must be thin enough to not deteriorate the quality of the beam. By using a 10 sup - sup 7 m thick exit w...

  8. Archaic artifacts resembling celestial spheres

    Science.gov (United States)

    Dimitrakoudis, S.; Papaspyrou, P.; Petoussis, V.; Moussas, X.

    We present several bronze artifacts from the Archaic Age in Greece (750-480 BC) that resemble celestial spheres or forms of other astronomical significance. They are studied in the context of the Dark Age transition from Mycenaean Age astronomical themes to the philosophical and practical revival of astronomy in the Classical Age with its plethora of astronomical devices. These artifacts, mostly votive in nature are spherical in shape and appear in a variety of forms their most striking characteristic being the depiction of meridians and/or an equator. Most of those artifacts come from Thessaly, and more specifically from the temple of Itonia Athena at Philia, a religious center of pan-Hellenic significance. Celestial spheres, similar in form to the small artifacts presented in this study, could be used to measure latitudes, or estimate the time at a known place, and were thus very useful in navigation.

  9. Ring artifact correction for high-resolution micro CT

    International Nuclear Information System (INIS)

    Kyriakou, Yiannis; Prell, Daniel; Kalender, Willi A

    2009-01-01

    In high-resolution micro CT using flat detectors (FD), imperfect or defect detector elements may cause concentric-ring artifacts due to their continuous over- or underestimation of attenuation values, which often disturb image quality. We here present a dedicated image-based ring artifact correction method for high-resolution micro CT, based on median filtering of the reconstructed image and working on a transformed version of the reconstructed images in polar coordinates. This post-processing method reduced ring artifacts in the reconstructed images and improved image quality for phantom and in in vivo scans. Noise and artifacts were reduced both in transversal and in multi-planar reformations along the longitudinal axis. (note)

  10. Artifact detection in electrodermal activity using sparse recovery

    Science.gov (United States)

    Kelsey, Malia; Palumbo, Richard Vincent; Urbaneja, Alberto; Akcakaya, Murat; Huang, Jeannie; Kleckner, Ian R.; Barrett, Lisa Feldman; Quigley, Karen S.; Sejdic, Ervin; Goodwin, Matthew S.

    2017-05-01

    Electrodermal Activity (EDA) - a peripheral index of sympathetic nervous system activity - is a primary measure used in psychophysiology. EDA is widely accepted as an indicator of physiological arousal, and it has been shown to reveal when psychologically novel events occur. Traditionally, EDA data is collected in controlled laboratory experiments. However, recent developments in wireless biosensing have led to an increase in out-of-lab studies. This transition to ambulatory data collection has introduced challenges. In particular, artifacts such as wearer motion, changes in temperature, and electrical interference can be misidentified as true EDA responses. The inability to distinguish artifact from signal hinders analyses of ambulatory EDA data. Though manual procedures for identifying and removing EDA artifacts exist, they are time consuming - which is problematic for the types of longitudinal data sets represented in modern ambulatory studies. This manuscript presents a novel technique to automatically identify and remove artifacts in EDA data using curve fitting and sparse recovery methods. Our method was evaluated using labeled data to determine the accuracy of artifact identification. Procedures, results, conclusions, and future directions are presented.

  11. Optimizing T2-weighted magnetic resonance sequences for surface coil microimaging of the eye with regard to lid, eyeball and head moving artifacts.

    Science.gov (United States)

    Obata, Takayuki; Uemura, Koji; Nonaka, Hiroi; Tamura, Mitsuru; Tanada, Shuji; Ikehira, Hiroo

    2006-01-01

    To acquire high-resolution magnetic resonance (MR) images, we developed a new blinking artifact reduced pulse (BARP) sequence with a surface coil specialized for microscopic imaging (47 mm in diameter). To reduce eye movement, we ascertained that the subjects' eyes were kept open and fixated to the target in the 1.5-T MR gantry. To reduce motion artifacts from blinking, we inserted rest periods for blinking (1.5 s within every 5 s) during MR scanning (T2-weighted fast spin echo; repetition time, 5 s; echo time, 100 ms; echo train, 11; matrix, 256 x 128; field of view, 5 cm; 1-mm thickness x 30 slices). Three scans (100 s x 3) were performed for each normal subject, and they were added together after automatic adjustment for location to reduce quality loss caused by head motion. T2-weighted MR images were acquired with a high resolution and a high signal-to-noise ratio. Motion artifacts were reduced with BARP, as compared with those with random blinking. Intraocular structures such as the iris and ciliary muscles were clearly visualized. Because the whole eye can be covered with a 1-mm thickness by this method, three-dimensional maps can easily be generated from the obtained images. The application of BARP with a surface coil of the human eye might become a useful and widely adopted procedure for MR microimaging.

  12. Artifact removal from EEG signals using adaptive filters in cascade

    Science.gov (United States)

    Garcés Correa, A.; Laciar, E.; Patiño, H. D.; Valentinuzzi, M. E.

    2007-11-01

    Artifacts in EEG (electroencephalogram) records are caused by various factors, like line interference, EOG (electro-oculogram) and ECG (electrocardiogram). These noise sources increase the difficulty in analyzing the EEG and to obtaining clinical information. For this reason, it is necessary to design specific filters to decrease such artifacts in EEG records. In this paper, a cascade of three adaptive filters based on a least mean squares (LMS) algorithm is proposed. The first one eliminates line interference, the second adaptive filter removes the ECG artifacts and the last one cancels EOG spikes. Each stage uses a finite impulse response (FIR) filter, which adjusts its coefficients to produce an output similar to the artifacts present in the EEG. The proposed cascade adaptive filter was tested in five real EEG records acquired in polysomnographic studies. In all cases, line-frequency, ECG and EOG artifacts were attenuated. It is concluded that the proposed filter reduces the common artifacts present in EEG signals without removing significant information embedded in these records.

  13. Artifact removal from EEG signals using adaptive filters in cascade

    International Nuclear Information System (INIS)

    Garces Correa, A; Laciar, E; Patino, H D; Valentinuzzi, M E

    2007-01-01

    Artifacts in EEG (electroencephalogram) records are caused by various factors, like line interference, EOG (electro-oculogram) and ECG (electrocardiogram). These noise sources increase the difficulty in analyzing the EEG and to obtaining clinical information. For this reason, it is necessary to design specific filters to decrease such artifacts in EEG records. In this paper, a cascade of three adaptive filters based on a least mean squares (LMS) algorithm is proposed. The first one eliminates line interference, the second adaptive filter removes the ECG artifacts and the last one cancels EOG spikes. Each stage uses a finite impulse response (FIR) filter, which adjusts its coefficients to produce an output similar to the artifacts present in the EEG. The proposed cascade adaptive filter was tested in five real EEG records acquired in polysomnographic studies. In all cases, line-frequency, ECG and EOG artifacts were attenuated. It is concluded that the proposed filter reduces the common artifacts present in EEG signals without removing significant information embedded in these records

  14. Artifact removal from EEG signals using adaptive filters in cascade

    Energy Technology Data Exchange (ETDEWEB)

    Garces Correa, A [Gabinete de TecnologIa Medica, Facultad de Ingenieria, Universidad Nacional de San Juan (Argentina); Laciar, E [Gabinete de TecnologIa Medica, Facultad de Ingenieria, Universidad Nacional de San Juan (Argentina); Patino, H D [Instituto de Automatica, Facultad de Ingenieria, Universidad Nacional de San Juan (Argentina); Valentinuzzi, M E [Instituto Superior de Investigaciones Biologicas (INSIBIO), UNT-CONICET, Tucuman (Argentina)

    2007-11-15

    Artifacts in EEG (electroencephalogram) records are caused by various factors, like line interference, EOG (electro-oculogram) and ECG (electrocardiogram). These noise sources increase the difficulty in analyzing the EEG and to obtaining clinical information. For this reason, it is necessary to design specific filters to decrease such artifacts in EEG records. In this paper, a cascade of three adaptive filters based on a least mean squares (LMS) algorithm is proposed. The first one eliminates line interference, the second adaptive filter removes the ECG artifacts and the last one cancels EOG spikes. Each stage uses a finite impulse response (FIR) filter, which adjusts its coefficients to produce an output similar to the artifacts present in the EEG. The proposed cascade adaptive filter was tested in five real EEG records acquired in polysomnographic studies. In all cases, line-frequency, ECG and EOG artifacts were attenuated. It is concluded that the proposed filter reduces the common artifacts present in EEG signals without removing significant information embedded in these records.

  15. Reflection-artifact-free photoacoustic imaging using PAFUSion (photoacoustic-guided focused ultrasound)

    Science.gov (United States)

    Kuniyil Ajith Singh, Mithun; Jaeger, Michael; Frenz, Martin; Steenbergen, Wiendelt

    2016-03-01

    Reflection artifacts caused by acoustic inhomogeneities are a main challenge to deep-tissue photoacoustic imaging. Photoacoustic transients generated by the skin surface and superficial vasculature will propagate into the tissue and reflect back from echogenic structures to generate reflection artifacts. These artifacts can cause problems in image interpretation and limit imaging depth. In its basic version, PAFUSion mimics the inward travelling wave-field from blood vessel-like PA sources by applying focused ultrasound pulses, and thus provides a way to identify reflection artifacts. In this work, we demonstrate reflection artifact correction in addition to identification, towards obtaining an artifact-free photoacoustic image. In view of clinical applications, we implemented an improved version of PAFUSion in which photoacoustic data is backpropagated to imitate the inward travelling wave-field and thus the reflection artifacts of a more arbitrary distribution of PA sources that also includes the skin melanin layer. The backpropagation is performed in a synthetic way based on the pulse-echo acquisitions after transmission on each single element of the transducer array. We present a phantom experiment and initial in vivo measurements on human volunteers where we demonstrate significant reflection artifact reduction using our technique. The results provide a direct confirmation that reflection artifacts are prominent in clinical epi-photoacoustic imaging, and that PAFUSion can reduce these artifacts significantly to improve the deep-tissue photoacoustic imaging.

  16. Analysis of artifact and infrequent physiological uptake in 18F-FDG PET/CT

    International Nuclear Information System (INIS)

    Li Tianran; Zhao Chunlei; Qian Gennian; Chen Ziqian; Wang Kaitang; You Xueyu; Zheng Chunyu

    2006-01-01

    Objective: To explore the artifact and infrequent physiological uptake in PET/CT with its imaging and formation features. Methods: The data of PET/CT imaging were retrospectively analyzed and classified based on their cause. Besides, the infrequent physiological uptakes were also analyzed. Results: Artifacts could be classified into natural and technological causes. In natural causes, respiratory movement and high-density matters artifacts were frequently found, whereas in technological cause, the truncation, radioactive leakage and pollution commonly appeared. Infrequent physiological uptakes included uterine endometrium, breast and fat uptakes. Conclusions: The imaging features of artifact in PET can be divided into 'hot' or 'cold' area while infrequent physiological uptakes mainly are 'hot' area. Among the cause of artifact formation, CT-based attenuation corrected physical factor is the commonest. The infrequent physiological uptake somewhat relates to technological error. (authors)

  17. Reduction of metal artifacts: beam hardening and photon starvation effects

    Science.gov (United States)

    Yadava, Girijesh K.; Pal, Debashish; Hsieh, Jiang

    2014-03-01

    The presence of metal-artifacts in CT imaging can obscure relevant anatomy and interfere with disease diagnosis. The cause and occurrence of metal-artifacts are primarily due to beam hardening, scatter, partial volume and photon starvation; however, the contribution to the artifacts from each of them depends on the type of hardware. A comparison of CT images obtained with different metallic hardware in various applications, along with acquisition and reconstruction parameters, helps understand methods for reducing or overcoming such artifacts. In this work, a metal beam hardening correction (BHC) and a projection-completion based metal artifact reduction (MAR) algorithms were developed, and applied on phantom and clinical CT scans with various metallic implants. Stainless-steel and Titanium were used to model and correct for metal beam hardening effect. In the MAR algorithm, the corrupted projection samples are replaced by the combination of original projections and in-painted data obtained by forward projecting a prior image. The data included spine fixation screws, hip-implants, dental-filling, and body extremity fixations, covering range of clinically used metal implants. Comparison of BHC and MAR on different metallic implants was used to characterize dominant source of the artifacts, and conceivable methods to overcome those. Results of the study indicate that beam hardening could be a dominant source of artifact in many spine and extremity fixations, whereas dental and hip implants could be dominant source of photon starvation. The BHC algorithm could significantly improve image quality in CT scans with metallic screws, whereas MAR algorithm could alleviate artifacts in hip-implants and dentalfillings.

  18. Spring-like motion caused large anisotropic thermal expansion in nonporous M(eim)2 (M = Zn, Cd).

    Science.gov (United States)

    Liu, Zhanning; Liu, Chenxi; Li, Qiang; Chen, Jun; Xing, Xianran

    2017-09-20

    Two nonporous coordination polymers were found to possess large anisotropic thermal expansion, which was derived from the flexible structures. A "spring-like" thermal motion was proposed to illustrate the mechanism. Compound Cd(eim) 2 (eim = 2-ethylimidazole) possesses large linear and reversible thermal expansion properties and the emission intensity shows a linear decrease with temperature, making it a candidate for thermo-responsive materials.

  19. Checking behavioral conformance of artifacts

    NARCIS (Netherlands)

    Fahland, D.; Leoni, de M.; Dongen, van B.F.; Aalst, van der W.M.P.

    2011-01-01

    The usefulness of process models (e.g., for analysis, improvement, or execution) strongly depends on their ability to describe reality. Conformance checking is a technique to validate how good a given process model describes recorded executions of the actual process. Recently, artifacts have been

  20. Toddlers View Artifact Function Normatively

    Science.gov (United States)

    Casler, Krista; Terziyan, Treysi; Greene, Kimberly

    2009-01-01

    When children use objects like adults, are they simply tracking regularities in others' object use, or are they demonstrating a normatively defined awareness that there are right and wrong ways to act? This study provides the first evidence for the latter possibility. Young 2- and 3-year-olds (n = 32) learned functions of 6 artifacts, both…

  1. Artifacts by dental materials on magnetic resonance imaging

    International Nuclear Information System (INIS)

    Hong, Hyun Sook; Choi, Deuk Lin; Kim, Ki Jung; Suh, Won Hyuck

    1992-01-01

    Magnetic resonance imaging (MRI) has proved to be a valuable method for evaluation of the head and neck. Unfortunately, metallic devices associated with certain dental fillings and appliances often cause variable artifacts that can obscure normal or pathologic conditions on MR and computed tomography. In this work, we assessed the MR appearance of dental prosthetic materials in vitro and in vivo including precious alloys, nonprecions alloys, resin, amalgam and titanium alloy. For in vivo studies, these materials were placed in healthy volunteer's mouths and then images were assessed. Analysis of the appearance of shape and extent of artifact, and observed influence of these artifacts on the image interpretation at 0.2 Tesla permanent type MR scanner were valuated. Material used as temporary or permanent filling of crowns such as amalgam, precious alloy and, microfilled resin did not cause artifact on the image. The size of the artifact produced by the nonprecious alloys was influenced by the ferromagnetism of the object and the volume prosthesis, and was related to the scanning sequence. Nonprecious alloys produced minimal local signal distortion, where precious alloys, and dental resin had no effect on the MR images in vivo. These results were mainly from a low field strength MR scanner used in this study

  2. Metal artifact reduction method using metal streaks image subtraction

    International Nuclear Information System (INIS)

    Pua, Rizza D.; Cho, Seung Ryong

    2014-01-01

    Many studies have been dedicated for metal artifact reduction (MAR); however, the methods are successful to varying degrees depending on situations. Sinogram in-painting, filtering, iterative method are some of the major categories of MAR. Each has its own merits and weaknesses. A combination of these methods or hybrid methods have also been developed to make use of the different benefits of two techniques and minimize the unfavorable results. Our method focuses on the in-paitning approach and a hybrid MAR described by Xia et al. Although in-painting scheme is an effective technique in reducing the primary metal artifacts, a major drawback is the reintroduction of new artifacts that can be caused by an inaccurate interpolation process. Furthermore, combining the segmented metal image to the corrected nonmetal image in the final step of a conventional inpainting approach causes an issue of incorrect metal pixel values. Our proposed method begins with a sinogram in-painting approach and ends with an image-based metal artifact reduction scheme. This work provides a simple, yet effective solution for reducing metal artifacts and acquiring the original metal pixel information. The proposed method demonstrated its effectiveness in a simulation setting. The proposed method showed image quality that is comparable to the standard MAR; however, quantitatively more accurate than the standard MAR

  3. A New Approach for Automatic Removal of Movement Artifacts in Near-Infrared Spectroscopy Time Series by Means of Acceleration Data

    Directory of Open Access Journals (Sweden)

    Andreas Jaakko Metz

    2015-11-01

    Full Text Available Near-infrared spectroscopy (NIRS enables the non-invasive measurement of changes in hemodynamics and oxygenation in tissue. Changes in light-coupling due to movement of the subject can cause movement artifacts (MAs in the recorded signals. Several methods have been developed so far that facilitate the detection and reduction of MAs in the data. However, due to fixed parameter values (e.g., global threshold none of these methods are perfectly suitable for long-term (i.e., hours recordings or were not time-effective when applied to large datasets. We aimed to overcome these limitations by automation, i.e., data adaptive thresholding specifically designed for long-term measurements, and by introducing a stable long-term signal reconstruction. Our new technique (“acceleration-based movement artifact reduction algorithm”, AMARA is based on combining two methods: the “movement artifact reduction algorithm” (MARA, Scholkmann et al. Phys. Meas. 2010, 31, 649–662, and the “accelerometer-based motion artifact removal” (ABAMAR, Virtanen et al. J. Biomed. Opt. 2011, 16, 087005. We describe AMARA in detail and report about successful validation of the algorithm using empirical NIRS data, measured over the prefrontal cortex in adolescents during sleep. In addition, we compared the performance of AMARA to that of MARA and ABAMAR based on validation data.

  4. Dealing with noise and physiological artifacts in human EEG recordings: empirical mode methods

    Science.gov (United States)

    Runnova, Anastasiya E.; Grubov, Vadim V.; Khramova, Marina V.; Hramov, Alexander E.

    2017-04-01

    In the paper we propose the new method for removing noise and physiological artifacts in human EEG recordings based on empirical mode decomposition (Hilbert-Huang transform). As physiological artifacts we consider specific oscillatory patterns that cause problems during EEG analysis and can be detected with additional signals recorded simultaneously with EEG (ECG, EMG, EOG, etc.) We introduce the algorithm of the proposed method with steps including empirical mode decomposition of EEG signal, choosing of empirical modes with artifacts, removing these empirical modes and reconstructing of initial EEG signal. We show the efficiency of the method on the example of filtration of human EEG signal from eye-moving artifacts.

  5. Iterative image-domain ring artifact removal in cone-beam CT

    Science.gov (United States)

    Liang, Xiaokun; Zhang, Zhicheng; Niu, Tianye; Yu, Shaode; Wu, Shibin; Li, Zhicheng; Zhang, Huailing; Xie, Yaoqin

    2017-07-01

    Ring artifacts in cone beam computed tomography (CBCT) images are caused by pixel gain variations using flat-panel detectors, and may lead to structured non-uniformities and deterioration of image quality. The purpose of this study is to propose a method of general ring artifact removal in CBCT images. This method is based on the polar coordinate system, where the ring artifacts manifest as stripe artifacts. Using relative total variation, the CBCT images are first smoothed to generate template images with fewer image details and ring artifacts. By subtracting the template images from the CBCT images, residual images with image details and ring artifacts are generated. As the ring artifact manifests as a stripe artifact in a polar coordinate system, the artifact image can be extracted by mean value from the residual image; the image details are generated by subtracting the artifact image from the residual image. Finally, the image details are compensated to the template image to generate the corrected images. The proposed framework is iterated until the differences in the extracted ring artifacts are minimized. We use a 3D Shepp-Logan phantom, Catphan©504 phantom, uniform acrylic cylinder, and images from a head patient to evaluate the proposed method. In the experiments using simulated data, the spatial uniformity is increased by 1.68 times and the structural similarity index is increased from 87.12% to 95.50% using the proposed method. In the experiment using clinical data, our method shows high efficiency in ring artifact removal while preserving the image structure and detail. The iterative approach we propose for ring artifact removal in cone-beam CT is practical and attractive for CBCT guided radiation therapy.

  6. Artifacts as Authoritative Actors in Educational Reform

    Science.gov (United States)

    März, Virginie; Kelchtermans, Geert; Vermeir, Karen

    2017-01-01

    Educational reforms are often translated in and implemented through artifacts. Although research has frequently treated artifacts as merely functional, more recent work acknowledges the complex relationship between material artifacts and human/organizational behavior. This article aims at disentangling this relationship in order to deepen our…

  7. Automated filtering of intrinsic movement artifacts during two-photon intravital microscopy.

    Directory of Open Access Journals (Sweden)

    Denis Soulet

    Full Text Available In vivo imaging using two-photon microscopy is an essential tool to explore the dynamic of physiological events deep within biological tissues for short or extended periods of time. The new capabilities offered by this technology (e.g. high tissue penetrance, low toxicity have opened a whole new era of investigations in modern biomedical research. However, the potential of using this promising technique in tissues of living animals is greatly limited by the intrinsic irregular movements that are caused by cardiac and respiratory cycles and muscular and vascular tone. Here, we show real-time imaging of the brain, spinal cord, sciatic nerve and myenteric plexus of living mice using a new automated program, named Intravital_Microscopy_Toolbox, that removes frames corrupted with motion artifacts from time-lapse videos. Our approach involves generating a dissimilarity score against precalculated reference frames in a specific reference channel, thus allowing the gating of distorted, out-of-focus or translated frames. Since the algorithm detects the uneven peaks of image distortion caused by irregular animal movements, the macro allows a fast and efficient filtering of the image sequence. In addition, extra features have been implemented in the macro, such as XY registration, channel subtraction, extended field of view with maximum intensity projection, noise reduction with average intensity projections, and automated timestamp and scale bar overlay. Thus, the Intravital_Microscopy_Toolbox macro for ImageJ provides convenient tools for biologists who are performing in vivo two-photon imaging in tissues prone to motion artifacts.

  8. Photoacoustic reflection artifact reduction using photoacoustic-guided focused ultrasound : comparison between plane-wave and element-by-element synthetic backpropagation approach

    NARCIS (Netherlands)

    Kuniyil Ajith Singh, M.; Jaeger, M.; Frenz, M.; Steenbergen, Wiendelt

    2017-01-01

    Reflection artifacts caused by acoustic inhomogeneities constitute a major problem in epi-mode biomedical photoacoustic imaging. Photoacoustic transients from the skin and superficial optical absorbers traverse into the tissue and reflect off echogenic structures to generate reflection artifacts.

  9. Understanding the distribution of strong motions and the damage caused during the September 19th, 2017 earthquake

    Science.gov (United States)

    Aguirre, J.; Ramirez-Guzman, L.; Leonardo Suárez, M.; Quintanar, L.

    2017-12-01

    On September 19, 2017, a normal fault earthquake of magnitude Mw 7.1 occurred 120 km from Mexico City. The quake generated large accelerations, more than 200 cm/s*s at least in two stations in Mexico City, where there was extensive damage. The damage pattern, which includes more than 40 building collapses, differs from the one induced by the 1985 Michoacan earthquake. While the observed accelerations in stations located in the Hill and Transition zones are the largest ever recorded, in the Lake zone the intensities were lower than those recorded in 1985. Even though the proximity of the epicenter could partially explain the accelerations, other factors need to be explored to understand the nuances of the ground motion. Unlike 1985, there is a substantially larger number of acceleration records in Mexico City, operated and maintained by different institutions. In this paper, we present the analysis of acceleration records and 3D numerical simulations to understand if effects such as focusing and directionality participate in the amplified motion. Finally, transfer functions between Lake and Hill zones and response and design spectral values are analyzed in regions where the building code requirements were exceeded. Acknowledgments: Records used in this research are obtained, processed and maintained by the National Autonomous University of Mexico through the Seismic Instrumentation Unit of the Institute of Engineering and the National Seismological Service of the Institute of Geophysics. The Centro de Intrumentacion y Registro Sismico A.C. (CIRES) kindly provided their records. This Project was funded in part by the Secretaria de Ciencia, Tecnología e Innovación (SECITI) of Mexico City. Project SECITI/073/2016.

  10. Model-based respiratory motion compensation for emission tomography image reconstruction

    International Nuclear Information System (INIS)

    Reyes, M; Malandain, G; Koulibaly, P M; Gonzalez-Ballester, M A; Darcourt, J

    2007-01-01

    In emission tomography imaging, respiratory motion causes artifacts in lungs and cardiac reconstructed images, which lead to misinterpretations, imprecise diagnosis, impairing of fusion with other modalities, etc. Solutions like respiratory gating, correlated dynamic PET techniques, list-mode data based techniques and others have been tested, which lead to improvements over the spatial activity distribution in lungs lesions, but which have the disadvantages of requiring additional instrumentation or the need of discarding part of the projection data used for reconstruction. The objective of this study is to incorporate respiratory motion compensation directly into the image reconstruction process, without any additional acquisition protocol consideration. To this end, we propose an extension to the maximum likelihood expectation maximization (MLEM) algorithm that includes a respiratory motion model, which takes into account the displacements and volume deformations produced by the respiratory motion during the data acquisition process. We present results from synthetic simulations incorporating real respiratory motion as well as from phantom and patient data

  11. Streak artifacts on Kidney CT: Ionic vs nonionic contrast media

    International Nuclear Information System (INIS)

    Cho, Eun Ok; Kim, Won Hong; Jung, Myung Suk; Kim, Yong Hoon; Hur, Gham

    1993-01-01

    The authors reviewed findings of enhanced abdominal computed tomography (CT) scans to know the difference between a higher dose of conventional ionic contrast media(iothalamate meglumine) and a lower dose of a new, nonionic contrast material(ioversol). One hundred adult patients were divided into two groups. Each group consisted of 50 patients. Iothalamate meglumine and ioversol were intravenously administered in each group. The radio of the male to female in the former was 28:22, and the latter 29:21. We examine the degree of renal streak artifact and measure the Hounsfield number of urine in renal collecting system. There were significant differences of the degree of the streak artifact depending upon the osmolality of contrast media used and that was related with urine CT number(P value<0.005). We authors conclude that nonionic low osmolar contrast media is prone to cause streak artifacts and distortions of renal image than conventional ionic high osmolar contrast media

  12. Artifact

    DEFF Research Database (Denmark)

    2014-01-01

    CONCEPTUAL TYPE: TYPE LED BY IDEAS 26/10/12“Where are the idealistic fonts, the artsy fonts, the non fonts, the political fonts, the funny fonts, the difficult fonts, the fonts that don’t look like fonts, the fonts that are frontiers of new beliefs? We would like to focus on the ideas and concept...

  13. Simulation-based artifact correction (SBAC) for metrological computed tomography

    Science.gov (United States)

    Maier, Joscha; Leinweber, Carsten; Sawall, Stefan; Stoschus, Henning; Ballach, Frederic; Müller, Tobias; Hammer, Michael; Christoph, Ralf; Kachelrieß, Marc

    2017-06-01

    Computed tomography (CT) is a valuable tool for the metrolocical assessment of industrial components. However, the application of CT to the investigation of highly attenuating objects or multi-material components is often restricted by the presence of CT artifacts caused by beam hardening, x-ray scatter, off-focal radiation, partial volume effects or the cone-beam reconstruction itself. In order to overcome this limitation, this paper proposes an approach to calculate a correction term that compensates for the contribution of artifacts and thus enables an appropriate assessment of these components using CT. Therefore, we make use of computer simulations of the CT measurement process. Based on an appropriate model of the object, e.g. an initial reconstruction or a CAD model, two simulations are carried out. One simulation considers all physical effects that cause artifacts using dedicated analytic methods as well as Monte Carlo-based models. The other one represents an ideal CT measurement i.e. a measurement in parallel beam geometry with a monochromatic, point-like x-ray source and no x-ray scattering. Thus, the difference between these simulations is an estimate for the present artifacts and can be used to correct the acquired projection data or the corresponding CT reconstruction, respectively. The performance of the proposed approach is evaluated using simulated as well as measured data of single and multi-material components. Our approach yields CT reconstructions that are nearly free of artifacts and thereby clearly outperforms commonly used artifact reduction algorithms in terms of image quality. A comparison against tactile reference measurements demonstrates the ability of the proposed approach to increase the accuracy of the metrological assessment significantly.

  14. Letters What causes an ice skater to accelerate? Note on the definitions of weight A-level physics is mathematical enough Correction to 'Confusion over the physics of circular motion'

    Science.gov (United States)

    2011-11-01

    What causes an ice skater to accelerate? Hugh Fricker Note on the definitions of weight Nenad Stojilovic A-level physics is mathematical enough Helen Hare Correction to 'Confusion over the physics of circular motion'

  15. Correction of CT artifacts and its influence on Monte Carlo dose calculations

    International Nuclear Information System (INIS)

    Bazalova, Magdalena; Beaulieu, Luc; Palefsky, Steven; Verhaegen, Frank

    2007-01-01

    Computed tomography (CT) images of patients having metallic implants or dental fillings exhibit severe streaking artifacts. These artifacts may disallow tumor and organ delineation and compromise dose calculation outcomes in radiotherapy. We used a sinogram interpolation metal streaking artifact correction algorithm on several phantoms of exact-known compositions and on a prostate patient with two hip prostheses. We compared original CT images and artifact-corrected images of both. To evaluate the effect of the artifact correction on dose calculations, we performed Monte Carlo dose calculation in the EGSnrc/DOSXYZnrc code. For the phantoms, we performed calculations in the exact geometry, in the original CT geometry and in the artifact-corrected geometry for photon and electron beams. The maximum errors in 6 MV photon beam dose calculation were found to exceed 25% in original CT images when the standard DOSXYZnrc/CTCREATE calibration is used but less than 2% in artifact-corrected images when an extended calibration is used. The extended calibration includes an extra calibration point for a metal. The patient dose volume histograms of a hypothetical target irradiated by five 18 MV photon beams in a hypothetical treatment differ significantly in the original CT geometry and in the artifact-corrected geometry. This was found to be mostly due to miss-assignment of tissue voxels to air due to metal artifacts. We also developed a simple Monte Carlo model for a CT scanner and we simulated the contribution of scatter and beam hardening to metal streaking artifacts. We found that whereas beam hardening has a minor effect on metal artifacts, scatter is an important cause of these artifacts

  16. Reducing 4D CT artifacts using optimized sorting based on anatomic similarity.

    Science.gov (United States)

    Johnston, Eric; Diehn, Maximilian; Murphy, James D; Loo, Billy W; Maxim, Peter G

    2011-05-01

    Four-dimensional (4D) computed tomography (CT) has been widely used as a tool to characterize respiratory motion in radiotherapy. The two most commonly used 4D CT algorithms sort images by the associated respiratory phase or displacement into a predefined number of bins, and are prone to image artifacts at transitions between bed positions. The purpose of this work is to demonstrate a method of reducing motion artifacts in 4D CT by incorporating anatomic similarity into phase or displacement based sorting protocols. Ten patient datasets were retrospectively sorted using both the displacement and phase based sorting algorithms. Conventional sorting methods allow selection of only the nearest-neighbor image in time or displacement within each bin. In our method, for each bed position either the displacement or the phase defines the center of a bin range about which several candidate images are selected. The two dimensional correlation coefficients between slices bordering the interface between adjacent couch positions are then calculated for all candidate pairings. Two slices have a high correlation if they are anatomically similar. Candidates from each bin are then selected to maximize the slice correlation over the entire data set using the Dijkstra's shortest path algorithm. To assess the reduction of artifacts, two thoracic radiation oncologists independently compared the resorted 4D datasets pairwise with conventionally sorted datasets, blinded to the sorting method, to choose which had the least motion artifacts. Agreement between reviewers was evaluated using the weighted kappa score. Anatomically based image selection resulted in 4D CT datasets with significantly reduced motion artifacts with both displacement (P = 0.0063) and phase sorting (P = 0.00022). There was good agreement between the two reviewers, with complete agreement 34 times and complete disagreement 6 times. Optimized sorting using anatomic similarity significantly reduces 4D CT motion

  17. Use of cognitive artifacts in chemistry learning

    Science.gov (United States)

    Yengin, Ilker

    In everyday life, we interact with cognitive artifacts to receive and/or manipulate information so as to alter our thinking processes. CHEM/TEAC 869Q is a distance course that includes extensive explicit instruction in the use of a cognitive artifact. This study investigates issues related to the design of that online artifact. In order to understand design implications and how cognitive artifacts contribute to students' thinking and learning, a qualitative research methodology was engaged that utilized think aloud sessions. Participants' described constrained and structured cognitive models while using the artifact. The study also was informed by interviews and researcher's field notes. A purposeful sampling method led to the selection of participants, four males and two females, who had no prior history of using a course from the 869 series but who had experienced the scientific content covered by the CHEM869Q course. Analysis of the results showed both that a cognitive artifact may lead users' minds in decision making, and that problem solving processes were affected by cognitive artifact's design. When there is no design flaw, users generally thought that the cognitive artifact was helpful by simplifying steps, overcoming other limitations, and reducing errors in a reliable, effective, and easy to use way. Moreover, results showed that successful implementation of cognitive artifacts into teaching --learning practices depended on user willingness to transfer a task to the artifact. While users may like the idea of benefiting from a cognitive artifact, nevertheless, they may tend to limit their usage. They sometimes think that delegating a task to a cognitive artifact makes them dependent, and that they may not learn how to perform the tasks by themselves. They appear more willing to use a cognitive artifact after they have done the task by themselves.

  18. Spectral CT metal artifact reduction with an optimization-based reconstruction algorithm

    Science.gov (United States)

    Gilat Schmidt, Taly; Barber, Rina F.; Sidky, Emil Y.

    2017-03-01

    Metal objects cause artifacts in computed tomography (CT) images. This work investigated the feasibility of a spectral CT method to reduce metal artifacts. Spectral CT acquisition combined with optimization-based reconstruction is proposed to reduce artifacts by modeling the physical effects that cause metal artifacts and by providing the flexibility to selectively remove corrupted spectral measurements in the spectral-sinogram space. The proposed Constrained `One-Step' Spectral CT Image Reconstruction (cOSSCIR) algorithm directly estimates the basis material maps while enforcing convex constraints. The incorporation of constraints on the reconstructed basis material maps is expected to mitigate undersampling effects that occur when corrupted data is excluded from reconstruction. The feasibility of the cOSSCIR algorithm to reduce metal artifacts was investigated through simulations of a pelvis phantom. The cOSSCIR algorithm was investigated with and without the use of a third basis material representing metal. The effects of excluding data corrupted by metal were also investigated. The results demonstrated that the proposed cOSSCIR algorithm reduced metal artifacts and improved CT number accuracy. For example, CT number error in a bright shading artifact region was reduced from 403 HU in the reference filtered backprojection reconstruction to 33 HU using the proposed algorithm in simulation. In the dark shading regions, the error was reduced from 1141 HU to 25 HU. Of the investigated approaches, decomposing the data into three basis material maps and excluding the corrupted data demonstrated the greatest reduction in metal artifacts.

  19. Designing a compact MRI motion phantom

    Directory of Open Access Journals (Sweden)

    Schmiedel Max

    2016-09-01

    Full Text Available Even today, dealing with motion artifacts in magnetic resonance imaging (MRI is a challenging task. Image corruption due to spontaneous body motion complicates diagnosis. In this work, an MRI phantom for rigid motion is presented. It is used to generate motion-corrupted data, which can serve for evaluation of blind motion compensation algorithms. In contrast to commercially available MRI motion phantoms, the presented setup works on small animal MRI systems. Furthermore, retrospective gating is performed on the data, which can be used as a reference for novel motion compensation approaches. The motion of the signal source can be reconstructed using motor trigger signals and be utilized as the ground truth for motion estimation. The proposed setup results in motion corrected images. Moreover, the importance of preprocessing the MRI raw data, e.g. phase-drift correction, is demonstrated. The gained knowledge can be used to design an MRI phantom for elastic motion.

  20. TU-F-CAMPUS-J-04: Evaluation of Metal Artifact Reduction Technique for the Radiation Therapy Planning

    International Nuclear Information System (INIS)

    Jeong, K; Kuo, H; Ritter, J; Shen, J; Basavatia, A; Yaparpalvi, R; Kalnicki, S; Tome, W

    2015-01-01

    Purpose: To evaluate the feasibility of using a metal artifact reduction technique in depleting metal artifact and its application in improving dose calculation in External Radiation Therapy Planning. Methods: CIRS electron density phantom was scanned with and without steel drill bits placed in some plug holes. Meta artifact reduction software with Metal Deletion Technique (MDT) was used to remove metal artifacts for scanned image with metal. Hounsfield units of electron density plugs from artifact free reference image and MDT processed images were compared. To test the dose calculation improvement after the MDT processed images, clinically approved head and neck plan with manual dental artifact correction was tested. Patient images were exported and processed with MDT and plan was recalculated with new MDT image without manual correction. Dose profiles near the metal artifacts were compared. Results: The MDT used in this study effectively reduced the metal artifact caused by beam hardening and scatter. The windmill around the metal drill was greatly improved with smooth rounded view. Difference of the mean HU in each density plug between reference and MDT images were less than 10 HU in most of the plugs. Dose difference between original plan and MDT images were minimal. Conclusion: Most metal artifact reduction methods were developed for diagnostic improvement purpose. Hence Hounsfield unit accuracy was not rigorously tested before. In our test, MDT effectively eliminated metal artifacts with good HU reproduciblity. However, it can introduce new mild artifacts so the MDT images should be checked with original images

  1. Filtration of human EEG recordings from physiological artifacts with empirical mode method

    Science.gov (United States)

    Grubov, Vadim V.; Runnova, Anastasiya E.; Khramova, Marina V.

    2017-03-01

    In the paper we propose the new method for dealing with noise and physiological artifacts in experimental human EEG recordings. The method is based on analysis of EEG signals with empirical mode decomposition (Hilbert-Huang transform). We consider noises and physiological artifacts on EEG as specific oscillatory patterns that cause problems during EEG analysis and can be detected with additional signals recorded simultaneously with EEG (ECG, EMG, EOG, etc.) We introduce the algorithm of the method with following steps: empirical mode decomposition of EEG signal, choosing of empirical modes with artifacts, removing empirical modes with artifacts, reconstruction of the initial EEG signal. We test the method on filtration of experimental human EEG signals from eye-moving artifacts and show high efficiency of the method.

  2. Detection of movement artifact in recorded pulse oximeter saturation.

    Science.gov (United States)

    Poets, C F; Stebbens, V A

    1997-10-01

    Movement artifact (MA) must be detected when analysing recordings of pulse oximeter saturation (SpO2). Visual analysis of individual pulse waveforms is the safest, but also the most tedious, method for this purpose. We wanted to test the reliability of a computer algorithm (Edentec Motion Annotation System), based on a comparison between pulse and heart rate, for MA detection. Ten 12-h recordings of SpO2, pulse waveforms and heart rate from ten preterm infants were analysed for the presence of MA on the pulse waveform signal. These data were used to determine the sensitivity and specificity of the computer algorithm, and of the oximeter itself, in detecting MA. Recordings were divided into segments of 2.5 s duration to compare the movement identification methods. Of the segments 31% +/- 6% (mean +/- SD) contained MA. The computer algorithm identified 95% +/- 3% of these segments, the pulse oximeter only 18% +/- 11%. Specificity was 85% +/- 4% and 99% +/- 0%, respectively. SpO2 was signal showed MA during this time, leaving a significant potential for erroneous identification of hypoxaemia. Recordings of SpO2 do not allow a reliable identification of MA. Without additional information about movement artifact, a significant proportion of recording time of pulse oximeter signal may be regarded as demonstrating hypoxaemia which, in fact, simply reflects poor measurement conditions. The computer algorithm used in this study identified periods of movement artifact reliably.

  3. Independent component analysis of gait-related movement artifact recorded using EEG electrodes during treadmill walking.

    Directory of Open Access Journals (Sweden)

    Kristine Lynne Snyder

    2015-12-01

    Full Text Available There has been a recent surge in the use of electroencephalography (EEG as a tool for mobile brain imaging due to its portability and fine time resolution. When EEG is combined with independent component analysis (ICA and source localization techniques, it can model electrocortical activity as arising from temporally independent signals located in spatially distinct cortical areas. However, for mobile tasks, it is not clear how movement artifacts influence ICA and source localization. We devised a novel method to collect pure movement artifact data (devoid of any electrophysiological signals with a 256-channel EEG system. We first blocked true electrocortical activity using a silicone swim cap. Over the silicone layer, we placed a simulated scalp with electrical properties similar to real human scalp. We collected EEG movement artifact signals from ten healthy, young subjects wearing this setup as they walked on a treadmill at speeds from 0.4-1.6 m/s. We performed ICA and dipole fitting on the EEG movement artifact data to quantify how accurately these methods would identify the artifact signals as non-neural. ICA and dipole fitting accurately localized 99% of the independent components in non-neural locations or lacked dipolar characteristics. The remaining 1% of sources had locations within the brain volume and low residual variances, but had topographical maps, power spectra, time courses, and event related spectral perturbations typical of non-neural sources. Caution should be exercised when interpreting ICA for data that includes semi-periodic artifacts including artifact arising from human walking. Alternative methods are needed for the identification and separation of movement artifact in mobile EEG signals, especially methods that can be performed in real time. Separating true brain signals from motion artifact could clear the way for EEG brain computer interfaces for assistance during mobile activities, such as walking.

  4. Image statistics and nonlinear artifacts in composed transmission x-ray tomography

    International Nuclear Information System (INIS)

    Duerinckx, A.J.G.

    1979-01-01

    Knowledge of the image quality and image statistics in Computed Tomography (CT) images obtained with transmission x-ray CT scanners can increase the amount of clinically useful information that can be retrieved. Artifacts caused by nonlinear shadows are strongly object-dependent and are visible over larger areas of the image. No simple technique exists for their complete elimination. One source of artifacts in the first order statistics is the nonlinearities in the measured shadow or projection data used to reconstruct the image. One of the leading causes is the polychromaticity of the x-ray beam used in transmission CT scanners. Ways to improve the resulting image quality and techniques to extract additional information using dual energy scanning are discussed. A unique formalism consisting of a vector representation of the material dependence of the photon-tissue interactions is generalized to allow an in depth analysis. Poly-correction algorithms are compared using this analytic approach. Both quantum and detector electronic noise decrease the quality or information content of first order statistics. Preliminary results are presented using an heuristic adaptive nonlinear noise filter system for projection data. This filter system can be improved and/or modified to remove artifacts in both first and second order image statistics. Artifacts in the second order image statistics arise from the contribution of quantum noise. This can be described with a nonlinear detection equivalent model, similar to the model used to study artifacts in first order statistics. When analyzing these artifacts in second order statistics, one can divide them into linear artifacts, which do not present any problem of interpretation, and nonlinear artifacts, referred to as noise artifacts. A study of noise artifacts is presented together with a discussion of their relative importance in diagnostic radiology

  5. Edge artifact correction for industrial computed tomography images

    International Nuclear Information System (INIS)

    Cai Yufang; Li Dan; Wang Jue

    2013-01-01

    To eliminate the edge artifacts of industrial CT images, and improve the identification ability of the image and the precision of the dimension measurement, a coefficient adjusting method for reducing crosstalk noise is proposed. It is concluded from theoretical analysis that crosstalk generated from adjacent detectors by Compton scattering is the major reason for the edge artifacts. According to the mathematic model of the detector crosstalk, we design a special detector system configuration and stair-step phantom for estimating the quantity of crosstalk noise. The relationship between crosstalk ratio and intensity of the incident X-ray is acquired by regressing experimental data with least square method. The experimental result shows that the first-order crosstalk ratio between detectors is about 9.0%, and the second-order crosstalk ratio is about 1.2%. Thus the first-order crosstalk is the main factor causing edge artifacts. The proposed method can reduce the edge artifacts significantly, and meanwhile maintain the detail and edge of CT images. (authors)

  6. The Many Faces of Computational Artifacts

    DEFF Research Database (Denmark)

    Christensen, Lars Rune; Harper, Richard

    2016-01-01

    Building on data from fieldwork at a medical department, this paper focuses on the varied nature of computational artifacts in practice. It shows that medical practice relies on multiple heterogeneous computational artifacts that form complex constellations. In the hospital studied the computatio...

  7. Conceptual Model of Artifacts for Design Science Research

    DEFF Research Database (Denmark)

    Bækgaard, Lars

    2015-01-01

    We present a conceptual model of design science research artifacts. The model views an artifact at three levels. At the artifact level a selected artifact is viewed as a combination of material and immaterial aspects and a set of representations hereof. At the design level the selected artifact...

  8. Image Quality of the 3 Dimensional Phase-Contrast Technique in an Intracranial Magnetic Resonance Angiography with Artifacts Caused by Orthodontic Devices: A Comparison with 3 Dimensional Time-of-Flight Technique

    International Nuclear Information System (INIS)

    Kang, Seong Jin; Kim, Young Soo; Hong, Hyun Sook; Kim, Dong Hun

    2011-01-01

    To evaluate the degree of image distortion caused by orthodontic devices during a intracranial magnetic resonance angiography (MRA), and to determine the effectiveness of the 3 dimensional phase-contrast (3D PC). Subjects were divided into group A (n = 20) wearing a home-made orthodontic device, and group B (n = 10) with an actual orthodontic device. A 3.0T MR scanner was used, applying 3D time-of-flight (TOF) and 3D PC. Two board-certified radiologists evaluated images independently based on a four point scale classifying segments of the circle of Willis. Magnetic susceptibility variations and contrast-to-noise ratio (CNR) on maximum intensity projection images were measured. In group A, scores of the 3D TOF and 3D PC were 2.84 ± 0.1 vs. 2.88 ± 0.1 (before) and 1.8 ± 0.4 vs 2.83 ± 0.1 (after wearing device), respectively. In group B, the scores of 3D TOF and 3D PC were 1.86 ± 0.43 and 2.81 ± 0.15 (p = 0.005), respectively. Magnetic susceptibility variations showed meaningful results after wearing the device (p = 0.0001). CNRs of the 3D PC before and after wearing device were 142.9 ± 6.6 vs. 140.8 ± 7.2 (p = 0.7507), respectively. In the 3D TOF, CNRs were 324.8 ± 25.4 vs. 466.3 ± 41.7 (p = 0.0001). The 3D PC may be a solution method for distorted images by magnetic susceptibility in the intracranial MRA compared with 3D TOF.

  9. Image Quality of the 3 Dimensional Phase-Contrast Technique in an Intracranial Magnetic Resonance Angiography with Artifacts Caused by Orthodontic Devices: A Comparison with 3 Dimensional Time-of-Flight Technique

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Seong Jin; Kim, Young Soo; Hong, Hyun Sook [Dept. of Radiology, Soonchunhyang University College of Medicine, Bucheon (Korea, Republic of); Kim, Dong Hun [Dept. of Radiology, Chosun University School of Medicine, Kwangju (Korea, Republic of)

    2011-07-15

    To evaluate the degree of image distortion caused by orthodontic devices during a intracranial magnetic resonance angiography (MRA), and to determine the effectiveness of the 3 dimensional phase-contrast (3D PC). Subjects were divided into group A (n = 20) wearing a home-made orthodontic device, and group B (n = 10) with an actual orthodontic device. A 3.0T MR scanner was used, applying 3D time-of-flight (TOF) and 3D PC. Two board-certified radiologists evaluated images independently based on a four point scale classifying segments of the circle of Willis. Magnetic susceptibility variations and contrast-to-noise ratio (CNR) on maximum intensity projection images were measured. In group A, scores of the 3D TOF and 3D PC were 2.84 {+-} 0.1 vs. 2.88 {+-} 0.1 (before) and 1.8 {+-} 0.4 vs 2.83 {+-} 0.1 (after wearing device), respectively. In group B, the scores of 3D TOF and 3D PC were 1.86 {+-} 0.43 and 2.81 {+-} 0.15 (p = 0.005), respectively. Magnetic susceptibility variations showed meaningful results after wearing the device (p = 0.0001). CNRs of the 3D PC before and after wearing device were 142.9 {+-} 6.6 vs. 140.8 {+-} 7.2 (p = 0.7507), respectively. In the 3D TOF, CNRs were 324.8 {+-} 25.4 vs. 466.3 {+-} 41.7 (p = 0.0001). The 3D PC may be a solution method for distorted images by magnetic susceptibility in the intracranial MRA compared with 3D TOF.

  10. Application of basic physics principles to clinical neuroradiology: differentiating artifacts from true pathology on MRI.

    Science.gov (United States)

    Hakky, Michael; Pandey, Shilpa; Kwak, Ellie; Jara, Hernan; Erbay, Sami H

    2013-08-01

    This article outlines artifactual findings commonly encountered in neuroradiologic MRI studies and offers clues to differentiate them from true pathology on the basis of their physical properties. Basic MR physics concepts are used to shed light on the causes of these artifacts. MRI is one of the most commonly used techniques in neuroradiology. Unfortunately, MRI is prone to image distortion and artifacts that can be difficult to identify. Using the provided case illustrations, practical clues, and relevant physical applications, radiologists may devise algorithms to troubleshoot these artifacts.

  11. Survey on the artifacts of magnetic resonance imaging in the maxillo-facial regions

    International Nuclear Information System (INIS)

    Arita, Masahiro; Okayosi, Tetsuo; Sakamoto, Fumihiko; Furuhasi, Kaiji; Wakuta, Kazunari; Ohba, Takeshi; Morikawa, Masao; Han, Dongwei

    2000-01-01

    Magnetic resonance imaging (MRI) is accepted as a valuable method for evaluating and diagnosing various diseases in medical and dental area. On the other hand, dental magnetic attachments have been applied as one of the most suitable retainers of removable prostheses. The dental magnetic attachment is an advanced procedure for the restoration, whereas the dental magnetic attachment is one of the causes of MRI artifacts and/or distortions. In this study the results obtained by a survey in general hospitals on MRI artifacts caused by dental metals, especially dental magnetic attachments, are reported. The results obtained were as follows; MRI artifacts are experienced in most hospitals. Most radiologists did not regard the effect of the magnetic alloy as the cause, although they thought dental metals in oral cavity were the main cause of MRI artifact. Although about a half of radiologist were aware of the presence of the magnetic attachments, few of them had little experience in taking pictures of the patients with magnetic attachment or magnetic keepers by using MRI. Even when dental metals and magnetic keepers in oral cavity were considered to produce the MRI artifacts, none of radiologists asked dentists to remove them. They tried to solve the trouble of MRI artifacts by themselves. Prothodontists should give much more information about the dental magnetic attachment to radiologists and medical doctors in addition to improving the magnetic attachment and investigating materials to minimize the effect on MRI. (author)

  12. Image artifacts and technical limitations

    International Nuclear Information System (INIS)

    Kelly, W.M.

    1987-01-01

    The swift temporal progression of magnetic resonance imaging (MRI) from experimental prototype design to sophisticated instrument production can be sharply contrasted to the more protracted time course that characterized the development of X-ray computed tomography (CT). Most notably, the current generation of CT scanners represents the product of more than a decade of design innovation and technologic improvement, punctuated by the introduction of a whole new ''generation'' of CT scanners at periodic intervals. The more rapid evolutionary changes unique to MRI have been permitted by the greater abundance of sophisticated technologic expertise and necessitated by economic considerations, especially the desire to avoid premature obsolescence. Quite clearly, ''state-of-the-art'' MRI units available today are intended to remain state of the art for many years into the future. In clinical trials, MRI has proved particularly effacacious for evaluation of suspected neurologic disease, prompting neuroradiologists to welcome this new non-invasive diagnostic tool with unprecedented enthusiasm. In early reports, the lack of ionizing radiation, apparent absence of significant biological hazards, and ''elimination'' of artifacts were all acclaimed as major technical advantages. Now, as this diagnostic modality is undergoing widespread dissemination and a large body of clinical experience begins to accumulate, increasing attention is being focused on the limitations of MRI

  13. Reduction of variable-truncation artifacts from beam occlusion during in situ x-ray tomography

    DEFF Research Database (Denmark)

    Borg, Leise; Jørgensen, Jakob Sauer; Frikel, Jürgen

    2017-01-01

    Many in situ x-ray tomography studies require experimental rigs which may partially occlude the beam and cause parts of the projection data to be missing. In a study of fluid flow in porous chalk using a percolation cell with four metal bars drastic streak artifacts arise in the filtered...... and artifact-reduction methods are designed in context of FBP reconstruction motivated by computational efficiency practical for large, real synchrotron data. While a specific variable-truncation case is considered, the proposed methods can be applied to general data cut-offs arising in different in situ x-ray...... backprojection (FBP) reconstruction at certain orientations. Projections with non-trivial variable truncation caused by the metal bars are the source of these variable-truncation artifacts. To understand the artifacts a mathematical model of variable-truncation data as a function of metal bar radius and distance...

  14. Constant flow ventilation as a novel approach to elimination of respiratory artifact in MR imaging

    International Nuclear Information System (INIS)

    Shtern, F.; Kersh, R.; Lee, A.; Venegas, J.; Brady, T.J.

    1988-01-01

    This pilot study was performed to evaluate constant flow ventilation (CFV) as a method of respiratory artifact suppression in magnetic resonance (MR) imaging. In contrast to currently used methods of respiratory artifact suppression, CFV is able to provide adequate ventilation in the absence of any chest wall motion and thus obviates the need for respiratory gating. High-velocity jets of fresh gas delivered through two narrow (2-mm) intrabronchial cannulas promote gas exchange through airway turbulence and enhanced molecular diffusion. One mongrel dog (8.5 kg) was anesthetized with pentobarbital (35 mg/kg). For CFV, endobronchial cannulas were inserted with the aid of bronchoscopy and connected to a flow meter (flow rate, 500 mL/sec). Intrathoracic pressure was monitored via a pressure transducer connected to an air-filled intraesophageal balloon. Conventional ventilation (CV), with a tidal volume of 85 mL and ten breaths per minute, was provided through a cuffed endotracheal tube. After establishment of adequate ventilation (carbon dioxide pressure, 39), muscle paralysis was induced by succinylcholine at 0.1 mg/kg. T2-weighted [1,500/50 (repetition time msec/echo time msec), two excitations] gradient-echo and spin-echo images were obtained at 0.6T with both CV and CFV. MR images with CFV were free of respiratory motion artifact, which was present on all MR images with CV. This pilot study indicates that implementation of CFV results in elimination of respiratory motion artifact

  15. Reduced aliasing artifacts using shaking projection k-space sampling trajectory

    Science.gov (United States)

    Zhu, Yan-Chun; Du, Jiang; Yang, Wen-Chao; Duan, Chai-Jie; Wang, Hao-Yu; Gao, Song; Bao, Shang-Lian

    2014-03-01

    Radial imaging techniques, such as projection-reconstruction (PR), are used in magnetic resonance imaging (MRI) for dynamic imaging, angiography, and short-T2 imaging. They are less sensitive to flow and motion artifacts, and support fast imaging with short echo times. However, aliasing and streaking artifacts are two main sources which degrade radial imaging quality. For a given fixed number of k-space projections, data distributions along radial and angular directions will influence the level of aliasing and streaking artifacts. Conventional radial k-space sampling trajectory introduces an aliasing artifact at the first principal ring of point spread function (PSF). In this paper, a shaking projection (SP) k-space sampling trajectory was proposed to reduce aliasing artifacts in MR images. SP sampling trajectory shifts the projection alternately along the k-space center, which separates k-space data in the azimuthal direction. Simulations based on conventional and SP sampling trajectories were compared with the same number projections. A significant reduction of aliasing artifacts was observed using the SP sampling trajectory. These two trajectories were also compared with different sampling frequencies. A SP trajectory has the same aliasing character when using half sampling frequency (or half data) for reconstruction. SNR comparisons with different white noise levels show that these two trajectories have the same SNR character. In conclusion, the SP trajectory can reduce the aliasing artifact without decreasing SNR and also provide a way for undersampling reconstruction. Furthermore, this method can be applied to three-dimensional (3D) hybrid or spherical radial k-space sampling for a more efficient reduction of aliasing artifacts.

  16. Reduced aliasing artifacts using shaking projection k-space sampling trajectory

    International Nuclear Information System (INIS)

    Zhu Yan-Chun; Yang Wen-Chao; Wang Hao-Yu; Gao Song; Bao Shang-Lian; Du Jiang; Duan Chai-Jie

    2014-01-01

    Radial imaging techniques, such as projection-reconstruction (PR), are used in magnetic resonance imaging (MRI) for dynamic imaging, angiography, and short-T2 imaging. They are less sensitive to flow and motion artifacts, and support fast imaging with short echo times. However, aliasing and streaking artifacts are two main sources which degrade radial imaging quality. For a given fixed number of k-space projections, data distributions along radial and angular directions will influence the level of aliasing and streaking artifacts. Conventional radial k-space sampling trajectory introduces an aliasing artifact at the first principal ring of point spread function (PSF). In this paper, a shaking projection (SP) k-space sampling trajectory was proposed to reduce aliasing artifacts in MR images. SP sampling trajectory shifts the projection alternately along the k-space center, which separates k-space data in the azimuthal direction. Simulations based on conventional and SP sampling trajectories were compared with the same number projections. A significant reduction of aliasing artifacts was observed using the SP sampling trajectory. These two trajectories were also compared with different sampling frequencies. A SP trajectory has the same aliasing character when using half sampling frequency (or half data) for reconstruction. SNR comparisons with different white noise levels show that these two trajectories have the same SNR character. In conclusion, the SP trajectory can reduce the aliasing artifact without decreasing SNR and also provide a way for undersampling reconstruction. Furthermore, this method can be applied to three-dimensional (3D) hybrid or spherical radial k-space sampling for a more efficient reduction of aliasing artifacts

  17. Iterative Covariance-Based Removal of Time-Synchronous Artifacts: Application to Gastrointestinal Electrical Recordings.

    Science.gov (United States)

    Erickson, Jonathan C; Putney, Joy; Hilbert, Douglas; Paskaranandavadivel, Niranchan; Cheng, Leo K; O'Grady, Greg; Angeli, Timothy R

    2016-11-01

    The aim of this study was to develop, validate, and apply a fully automated method for reducing large temporally synchronous artifacts present in electrical recordings made from the gastrointestinal (GI) serosa, which are problematic for properly assessing slow wave dynamics. Such artifacts routinely arise in experimental and clinical settings from motion, switching behavior of medical instruments, or electrode array manipulation. A novel iterative Covariance-Based Reduction of Artifacts (COBRA) algorithm sequentially reduced artifact waveforms using an updating across-channel median as a noise template, scaled and subtracted from each channel based on their covariance. Application of COBRA substantially increased the signal-to-artifact ratio (12.8 ± 2.5 dB), while minimally attenuating the energy of the underlying source signal by 7.9% on average ( -11.1 ± 3.9 dB). COBRA was shown to be highly effective for aiding recovery and accurate marking of slow wave events (sensitivity = 0.90 ± 0.04; positive-predictive value = 0.74 ± 0.08) from large segments of in vivo porcine GI electrical mapping data that would otherwise be lost due to a broad range of contaminating artifact waveforms. Strongly reducing artifacts with COBRA ultimately allowed for rapid production of accurate isochronal activation maps detailing the dynamics of slow wave propagation in the porcine intestine. Such mapping studies can help characterize differences between normal and dysrhythmic events, which have been associated with GI abnormalities, such as intestinal ischemia and gastroparesis. The COBRA method may be generally applicable for removing temporally synchronous artifacts in other biosignal processing domains.

  18. Motion of the esophagus due to cardiac motion.

    Directory of Open Access Journals (Sweden)

    Jacob Palmer

    Full Text Available When imaging studies (e.g. CT are used to quantify morphological changes in an anatomical structure, it is necessary to understand the extent and source of motion which can give imaging artifacts (e.g. blurring or local distortion. The objective of this study was to assess the magnitude of esophageal motion due to cardiac motion. We used retrospective electrocardiogram-gated contrast-enhanced computed tomography angiography images for this study. The anatomic region from the carina to the bottom of the heart was taken at deep-inspiration breath hold with the patients' arms raised above their shoulders, in a position similar to that used for radiation therapy. The esophagus was delineated on the diastolic phase of cardiac motion, and deformable registration was used to sequentially deform the images in nearest-neighbor phases among the 10 cardiac phases, starting from the diastolic phase. Using the 10 deformation fields generated from the deformable registration, the magnitude of the extreme displacements was then calculated for each voxel, and the mean and maximum displacement was calculated for each computed tomography slice for each patient. The average maximum esophageal displacement due to cardiac motion for all patients was 5.8 mm (standard deviation: 1.6 mm, maximum: 10.0 mm in the transverse direction. For 21 of 26 patients, the largest esophageal motion was found in the inferior region of the heart; for the other patients, esophageal motion was approximately independent of superior-inferior position. The esophagus motion was larger at cardiac phases where the electrocardiogram R-wave occurs. In conclusion, the magnitude of esophageal motion near the heart due to cardiac motion is similar to that due to other sources of motion, including respiratory motion and intra-fraction motion. A larger cardiac motion will result into larger esophagus motion in a cardiac cycle.

  19. Colorectal Cancer "Methylator Phenotype": Fact or Artifact?

    Directory of Open Access Journals (Sweden)

    Charles Anacleto

    2005-04-01

    Full Text Available It has been proposed that human colorectal tumors can be classified into two groups: one in which methylation is rare, and another with methylation of several loci associated with a "CpG island methylated phenotype (CIMP," characterized by preferential proximal location in the colon, but otherwise poorly defined. There is considerable overlap between this putative methylator phenotype and the well-known mutator phenotype associated with microsatellite instability (MSI. We have examined hypermethylation of the promoter region of five genes (DAPK, MGMT, hMLH1, p16INK4a, and p14ARF in 106 primary colorectal cancers. A graph depicting the frequency of methylated loci in the series of tumors showed a continuous, monotonically decreasing distribution quite different from the previously claimed discontinuity. We observed a significant association between the presence of three or more methylated loci and the proximal location of the tumors. However, if we remove from analysis the tumors with hMLH1 methylation or those with MSI, the significance vanishes, suggesting that the association between multiple methylations and proximal location was indirect due to the correlation with MSI. Thus, our data do not support the independent existence of the so-called methylator phenotype and suggest that it rather may represent a statistical artifact caused by confounding of associations.

  20. Evaluating an artifact in design science research

    CSIR Research Space (South Africa)

    Herselman, M

    2015-09-01

    Full Text Available In this paper, we describe the iterative evaluation of an artifact developed through the application of Design Science Research (DSR) methodology in a resource constrained environment. In the DSR process the aspect of evaluation is often done...

  1. Influence of physiologic motion on the appearance of tissue in MR images

    International Nuclear Information System (INIS)

    Ehman, R.L.; McNamara, M.T.; Brasch, R.C.; Felmlee, J.P.; Gray, J.E.; Higgins, C.B.

    1986-01-01

    Studies were performed to determine the possible influence of physiologic motion on the parenchymal intensity of organs in magnetic resonance (MR) images. It is known that periodic motion associated with respiration and cardiac function causes characteristic artifacts in spin-warp images. The present study shows that bulk motion can also cause striking intensity changes at velocities equivalent to the craniocaudal respiratory excursion of organs in the upper abdomen. The magnitude of the effect depends on the velocity and direction of motion with respect to the three orthogonal axes of the imager and on the technical details of the imager and pulse sequence. Large systematic errors in calculated tissue relaxation times are possible due to this phenomenon. The findings have important implications for clinical imaging because motion can cause artifactual changes in the gray-scale relationships among tissues. Some pulse sequences are much less sensitive to these effects. These results provide guidance for selecting MR techniques that reduce the detrimental effect of respiratory and other physiologic motion on examinations of the upper abdomen and thorax

  2. Real-time out-of-plane artifact subtraction tomosynthesis imaging using prior CT for scanning beam digital x-ray system

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Meng, E-mail: mengwu@stanford.edu [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Fahrig, Rebecca [Department of Radiology, Stanford University, Stanford, California 94305 (United States)

    2014-11-01

    Purpose: The scanning beam digital x-ray system (SBDX) is an inverse geometry fluoroscopic system with high dose efficiency and the ability to perform continuous real-time tomosynthesis in multiple planes. This system could be used for image guidance during lung nodule biopsy. However, the reconstructed images suffer from strong out-of-plane artifact due to the small tomographic angle of the system. Methods: The authors propose an out-of-plane artifact subtraction tomosynthesis (OPAST) algorithm that utilizes a prior CT volume to augment the run-time image processing. A blur-and-add (BAA) analytical model, derived from the project-to-backproject physical model, permits the generation of tomosynthesis images that are a good approximation to the shift-and-add (SAA) reconstructed image. A computationally practical algorithm is proposed to simulate images and out-of-plane artifacts from patient-specific prior CT volumes using the BAA model. A 3D image registration algorithm to align the simulated and reconstructed images is described. The accuracy of the BAA analytical model and the OPAST algorithm was evaluated using three lung cancer patients’ CT data. The OPAST and image registration algorithms were also tested with added nonrigid respiratory motions. Results: Image similarity measurements, including the correlation coefficient, mean squared error, and structural similarity index, indicated that the BAA model is very accurate in simulating the SAA images from the prior CT for the SBDX system. The shift-variant effect of the BAA model can be ignored when the shifts between SBDX images and CT volumes are within ±10 mm in the x and y directions. The nodule visibility and depth resolution are improved by subtracting simulated artifacts from the reconstructions. The image registration and OPAST are robust in the presence of added respiratory motions. The dominant artifacts in the subtraction images are caused by the mismatches between the real object and the prior CT

  3. Image-based metal artifact reduction in x-ray computed tomography utilizing local anatomical similarity

    Science.gov (United States)

    Dong, Xue; Yang, Xiaofeng; Rosenfield, Jonathan; Elder, Eric; Dhabaan, Anees

    2017-03-01

    X-ray computed tomography (CT) is widely used in radiation therapy treatment planning in recent years. However, metal implants such as dental fillings and hip prostheses can cause severe bright and dark streaking artifacts in reconstructed CT images. These artifacts decrease image contrast and degrade HU accuracy, leading to inaccuracies in target delineation and dose calculation. In this work, a metal artifact reduction method is proposed based on the intrinsic anatomical similarity between neighboring CT slices. Neighboring CT slices from the same patient exhibit similar anatomical features. Exploiting this anatomical similarity, a gamma map is calculated as a weighted summation of relative HU error and distance error for each pixel in an artifact-corrupted CT image relative to a neighboring, artifactfree image. The minimum value in the gamma map for each pixel is used to identify an appropriate pixel from the artifact-free CT slice to replace the corresponding artifact-corrupted pixel. With the proposed method, the mean CT HU error was reduced from 360 HU and 460 HU to 24 HU and 34 HU on head and pelvis CT images, respectively. Dose calculation accuracy also improved, as the dose difference was reduced from greater than 20% to less than 4%. Using 3%/3mm criteria, the gamma analysis failure rate was reduced from 23.25% to 0.02%. An image-based metal artifact reduction method is proposed that replaces corrupted image pixels with pixels from neighboring CT slices free of metal artifacts. This method is shown to be capable of suppressing streaking artifacts, thereby improving HU and dose calculation accuracy.

  4. Study of the Subjective Visibility of Packet Loss Artifacts in Decoded Video Sequences

    DEFF Research Database (Denmark)

    Korhonen, Jari

    2018-01-01

    Packet loss is a significant cause of visual impairments in video broadcasting over packet-switched networks. There are several subjective and objective video quality assessment methods focused on the overall perception of video quality. However, less attention has been paid on the visibility...... of packet loss artifacts appearing in spatially and temporally limited regions of a video sequence. In this paper, we present the results of a subjective study, using a methodology where a video sequence is displayed on a touchscreen and the users tap it in the positions where they observe artifacts. We...... also analyze the objective features derived from those artifacts, and propose different models for combining those features into an objective metric for assessing the noticeability of the artifacts. The practical results show that the proposed metric predicts visibility of packet loss impairments...

  5. ARTiiFACT: a tool for heart rate artifact processing and heart rate variability analysis.

    Science.gov (United States)

    Kaufmann, Tobias; Sütterlin, Stefan; Schulz, Stefan M; Vögele, Claus

    2011-12-01

    The importance of appropriate handling of artifacts in interbeat interval (IBI) data must not be underestimated. Even a single artifact may cause unreliable heart rate variability (HRV) results. Thus, a robust artifact detection algorithm and the option for manual intervention by the researcher form key components for confident HRV analysis. Here, we present ARTiiFACT, a software tool for processing electrocardiogram and IBI data. Both automated and manual artifact detection and correction are available in a graphical user interface. In addition, ARTiiFACT includes time- and frequency-based HRV analyses and descriptive statistics, thus offering the basic tools for HRV analysis. Notably, all program steps can be executed separately and allow for data export, thus offering high flexibility and interoperability with a whole range of applications.

  6. Uncertainties in observational data on organic aerosol: An annual perspective of sampling artifacts in Beijing, China

    International Nuclear Information System (INIS)

    Cheng, Yuan; He, Ke-bin

    2015-01-01

    Current understanding of organic aerosol (OA) is challenged by the large gap between simulation results and observational data. Based on six campaigns conducted in a representative mega city in China, this study provided an annual perspective of the uncertainties in observational OA data caused by sampling artifacts. Our results suggest that for the commonly-used sampling approach that involves collection of particles on a bare quartz filter, the positive artifact could result in a 20–40 % overestimation of OA concentrations. Based on an evaluation framework that includes four criteria, an activated carbon denuder was demonstrated to be able to effectively eliminate the positive artifact with a long useful time of at least one month, and hence it was recommended to be a good choice for routine measurement of carbonaceous aerosol. - Highlights: • Positive artifact can cause an overestimation of OA concentrations by up to 40%. • It remains a challenge to measure semivolatile OA based on filter sampling. • The positive artifact can be effectively removed by an ACM denuder. • The ACM denuder is small in size, easy to use and multi-functional. • The ACM denuder is recommended for routine measurement of OA. - Accounting for sampling artifacts can help to bridge the gap between simulated and observed OA concentrations.

  7. Technical artifacts in chromatographic analysis of Tc-99m radiopharmaceuticals

    International Nuclear Information System (INIS)

    Kowalsky, R.J.; Creekmore, J.R.

    1982-01-01

    Technical artifacts produced during chromatographic analysis of technetium radiopharmaceuticals were investigated. Such artifacts are, we found, caused by improper spotting and drying techniques; these in turn produce spuriously high impurities in Tc-99m complexes of DTPA, MDP, PPi, and GH. The ITLC-SG/acetone system produces considerable streaking of Tc-complex if the applied spot is large and not dried before development. This results in activity in the solvent front portion of the chromatographic strip indicating falsely high levels of pertechnetate impurity. Proper drying of the applied spot eliminates the artifact. The ITLC-SG/saline system yields falsely high, hydrolyzed-reduced technetium impurities if the spot is allowed to enter the solvent during development. Correct spot placement and size eliminate this problem. Strips that are allowed to dry in room air for several minutes may indicate considerable pertechnetate impurity on the chromatogram; yet this may not actually be present in the radiopharmaceutical vial. Drying spots rapidly with hot air or in a nitrogen atmosphere before development eliminates this problem

  8. On removing interpolation and resampling artifacts in rigid image registration.

    Science.gov (United States)

    Aganj, Iman; Yeo, Boon Thye Thomas; Sabuncu, Mert R; Fischl, Bruce

    2013-02-01

    We show that image registration using conventional interpolation and summation approximations of continuous integrals can generally fail because of resampling artifacts. These artifacts negatively affect the accuracy of registration by producing local optima, altering the gradient, shifting the global optimum, and making rigid registration asymmetric. In this paper, after an extensive literature review, we demonstrate the causes of the artifacts by comparing inclusion and avoidance of resampling analytically. We show the sum-of-squared-differences cost function formulated as an integral to be more accurate compared with its traditional sum form in a simple case of image registration. We then discuss aliasing that occurs in rotation, which is due to the fact that an image represented in the Cartesian grid is sampled with different rates in different directions, and propose the use of oscillatory isotropic interpolation kernels, which allow better recovery of true global optima by overcoming this type of aliasing. Through our experiments on brain, fingerprint, and white noise images, we illustrate the superior performance of the integral registration cost function in both the Cartesian and spherical coordinates, and also validate the introduced radial interpolation kernel by demonstrating the improvement in registration.

  9. Blind retrospective motion correction of MR images.

    Science.gov (United States)

    Loktyushin, Alexander; Nickisch, Hannes; Pohmann, Rolf; Schölkopf, Bernhard

    2013-12-01

    Subject motion can severely degrade MR images. A retrospective motion correction algorithm, Gradient-based motion correction, which significantly reduces ghosting and blurring artifacts due to subject motion was proposed. The technique uses the raw data of standard imaging sequences; no sequence modifications or additional equipment such as tracking devices are required. Rigid motion is assumed. The approach iteratively searches for the motion trajectory yielding the sharpest image as measured by the entropy of spatial gradients. The vast space of motion parameters is efficiently explored by gradient-based optimization with a convergence guarantee. The method has been evaluated on both synthetic and real data in two and three dimensions using standard imaging techniques. MR images are consistently improved over different kinds of motion trajectories. Using a graphics processing unit implementation, computation times are in the order of a few minutes for a full three-dimensional volume. The presented technique can be an alternative or a complement to prospective motion correction methods and is able to improve images with strong motion artifacts from standard imaging sequences without requiring additional data. Copyright © 2013 Wiley Periodicals, Inc., a Wiley company.

  10. Reduction of variable-truncation artifacts from beam occlusion during in situ x-ray tomography

    Science.gov (United States)

    Borg, Leise; Jørgensen, Jakob S.; Frikel, Jürgen; Sporring, Jon

    2017-12-01

    Many in situ x-ray tomography studies require experimental rigs which may partially occlude the beam and cause parts of the projection data to be missing. In a study of fluid flow in porous chalk using a percolation cell with four metal bars drastic streak artifacts arise in the filtered backprojection (FBP) reconstruction at certain orientations. Projections with non-trivial variable truncation caused by the metal bars are the source of these variable-truncation artifacts. To understand the artifacts a mathematical model of variable-truncation data as a function of metal bar radius and distance to sample is derived and verified numerically and with experimental data. The model accurately describes the arising variable-truncation artifacts across simulated variations of the experimental setup. Three variable-truncation artifact-reduction methods are proposed, all aimed at addressing sinogram discontinuities that are shown to be the source of the streaks. The ‘reduction to limited angle’ (RLA) method simply keeps only non-truncated projections; the ‘detector-directed smoothing’ (DDS) method smooths the discontinuities; while the ‘reflexive boundary condition’ (RBC) method enforces a zero derivative at the discontinuities. Experimental results using both simulated and real data show that the proposed methods effectively reduce variable-truncation artifacts. The RBC method is found to provide the best artifact reduction and preservation of image features using both visual and quantitative assessment. The analysis and artifact-reduction methods are designed in context of FBP reconstruction motivated by computational efficiency practical for large, real synchrotron data. While a specific variable-truncation case is considered, the proposed methods can be applied to general data cut-offs arising in different in situ x-ray tomography experiments.

  11. Quantification of Artifact Reduction With Real-Time Cine Four-Dimensional Computed Tomography Acquisition Methods

    International Nuclear Information System (INIS)

    Langner, Ulrich W.; Keall, Paul J.

    2010-01-01

    Purpose: To quantify the magnitude and frequency of artifacts in simulated four-dimensional computed tomography (4D CT) images using three real-time acquisition methods- direction-dependent displacement acquisition, simultaneous displacement and phase acquisition, and simultaneous displacement and velocity acquisition- and to compare these methods with commonly used retrospective phase sorting. Methods and Materials: Image acquisition for the four 4D CT methods was simulated with different displacement and velocity tolerances for spheres with radii of 0.5 cm, 1.5 cm, and 2.5 cm, using 58 patient-measured tumors and respiratory motion traces. The magnitude and frequency of artifacts, CT doses, and acquisition times were computed for each method. Results: The mean artifact magnitude was 50% smaller for the three real-time methods than for retrospective phase sorting. The dose was ∼50% lower, but the acquisition time was 20% to 100% longer for the real-time methods than for retrospective phase sorting. Conclusions: Real-time acquisition methods can reduce the frequency and magnitude of artifacts in 4D CT images, as well as the imaging dose, but they increase the image acquisition time. The results suggest that direction-dependent displacement acquisition is the preferred real-time 4D CT acquisition method, because on average, the lowest dose is delivered to the patient and the acquisition time is the shortest for the resulting number and magnitude of artifacts.

  12. Ridding fMRI data of motion-related influences: Removal of signals with distinct spatial and physical bases in multiecho data.

    Science.gov (United States)

    Power, Jonathan D; Plitt, Mark; Gotts, Stephen J; Kundu, Prantik; Voon, Valerie; Bandettini, Peter A; Martin, Alex

    2018-02-27

    "Functional connectivity" techniques are commonplace tools for studying brain organization. A critical element of these analyses is to distinguish variance due to neurobiological signals from variance due to nonneurobiological signals. Multiecho fMRI techniques are a promising means for making such distinctions based on signal decay properties. Here, we report that multiecho fMRI techniques enable excellent removal of certain kinds of artifactual variance, namely, spatially focal artifacts due to motion. By removing these artifacts, multiecho techniques reveal frequent, large-amplitude blood oxygen level-dependent (BOLD) signal changes present across all gray matter that are also linked to motion. These whole-brain BOLD signals could reflect widespread neural processes or other processes, such as alterations in blood partial pressure of carbon dioxide (pCO 2 ) due to ventilation changes. By acquiring multiecho data while monitoring breathing, we demonstrate that whole-brain BOLD signals in the resting state are often caused by changes in breathing that co-occur with head motion. These widespread respiratory fMRI signals cannot be isolated from neurobiological signals by multiecho techniques because they occur via the same BOLD mechanism. Respiratory signals must therefore be removed by some other technique to isolate neurobiological covariance in fMRI time series. Several methods for removing global artifacts are demonstrated and compared, and were found to yield fMRI time series essentially free of motion-related influences. These results identify two kinds of motion-associated fMRI variance, with different physical mechanisms and spatial profiles, each of which strongly and differentially influences functional connectivity patterns. Distance-dependent patterns in covariance are nearly entirely attributable to non-BOLD artifacts.

  13. Metallic artifacts in magnetic resonance imaging

    International Nuclear Information System (INIS)

    Abe, Eiji; Okuyama, Koichiro; Ishikawa, Noriyuki; Hongo, Michio; Sato, Kozo; Sashi, Ryuji; Ishikawa, Eijiro.

    1995-01-01

    Seven metallic implants with different content of magnetic materials were compared in terms of the degree of MRI artifact. The degree of artifact well correlated with the total content of iron and cobalt than the total content of ferromagnets (iron, cobalt, nickel). No significant difference was observed regarding artifact among 4 titanium alloys containing very small amount of ferromagnet (0.058%-2.5%). Pedicle screws were made from different alloys in the same shape. Those screws were inserted into the swine vertebrae and artifact was evaluated by MRI. The degree of artifact was SUS316 (stainless steel)>MP-35N (cobalt alloy)>Ti-6AI-4V (titanium alloy), 1.5 Tesla>0.5 Tesla as for magnetic intensity, and T2 (gradient echo)>T2 (long SE)>proton density>T1 as for exposure condition. The condition of the site screw was inserted in the vertebral canal was detectable by T1-weighted images of titanium alloy and cobalt alloy in 0.5 Tesla and T1-weighted images of titanium alloy in 1.5 Tesla. (S.Y)

  14. A scheme for PET data normalization in event-based motion correction

    International Nuclear Information System (INIS)

    Zhou, Victor W; Kyme, Andre Z; Fulton, Roger; Meikle, Steven R

    2009-01-01

    Line of response (LOR) rebinning is an event-based motion-correction technique for positron emission tomography (PET) imaging that has been shown to compensate effectively for rigid motion. It involves the spatial transformation of LORs to compensate for motion during the scan, as measured by a motion tracking system. Each motion-corrected event is then recorded in the sinogram bin corresponding to the transformed LOR. It has been shown previously that the corrected event must be normalized using a normalization factor derived from the original LOR, that is, based on the pair of detectors involved in the original coincidence event. In general, due to data compression strategies (mashing), sinogram bins record events detected on multiple LORs. The number of LORs associated with a sinogram bin determines the relative contribution of each LOR. This paper provides a thorough treatment of event-based normalization during motion correction of PET data using LOR rebinning. We demonstrate theoretically and experimentally that normalization of the corrected event during LOR rebinning should account for the number of LORs contributing to the sinogram bin into which the motion-corrected event is binned. Failure to account for this factor may cause artifactual slice-to-slice count variations in the transverse slices and visible horizontal stripe artifacts in the coronal and sagittal slices of the reconstructed images. The theory and implementation of normalization in conjunction with the LOR rebinning technique is described in detail, and experimental verification of the proposed normalization method in phantom studies is presented.

  15. A short discussion on artifact creating conditions using multibeam bathymetric systems in a highly reflecting and smooth bottom

    Digital Repository Service at National Institute of Oceanography (India)

    Chakraborty, B.

    Using multibeam system, artifact creating conditions are dominant when functioning in highly reflective and flat bottom areas. This simulation study manifests the causes responsible for creating such conditions which influence seafloor...

  16. Markerless motion estimation for motion-compensated clinical brain imaging

    Science.gov (United States)

    Kyme, Andre Z.; Se, Stephen; Meikle, Steven R.; Fulton, Roger R.

    2018-05-01

    Motion-compensated brain imaging can dramatically reduce the artifacts and quantitative degradation associated with voluntary and involuntary subject head motion during positron emission tomography (PET), single photon emission computed tomography (SPECT) and computed tomography (CT). However, motion-compensated imaging protocols are not in widespread clinical use for these modalities. A key reason for this seems to be the lack of a practical motion tracking technology that allows for smooth and reliable integration of motion-compensated imaging protocols in the clinical setting. We seek to address this problem by investigating the feasibility of a highly versatile optical motion tracking method for PET, SPECT and CT geometries. The method requires no attached markers, relying exclusively on the detection and matching of distinctive facial features. We studied the accuracy of this method in 16 volunteers in a mock imaging scenario by comparing the estimated motion with an accurate marker-based method used in applications such as image guided surgery. A range of techniques to optimize performance of the method were also studied. Our results show that the markerless motion tracking method is highly accurate (brain imaging and holds good promise for a practical implementation in clinical PET, SPECT and CT systems.

  17. Superluminal motion (review)

    Science.gov (United States)

    Malykin, G. B.; Romanets, E. A.

    2012-06-01

    Prior to the development of Special Relativity, no restrictions were imposed on the velocity of the motion of particles and material bodies, as well as on energy transfer and signal propagation. At the end of the 19th century and the beginning of the 20th century, it was shown that a charge that moves at a velocity faster than the speed of light in an optical medium, in particular, in vacuum, gives rise to impact radiation, which later was termed the Vavilov-Cherenkov radiation. Shortly after the development of Special Relativity, some researchers considered the possibility of superluminal motion. In 1923, the Soviet physicist L.Ya. Strum suggested the existence of tachyons, which, however, have not been discovered yet. Superluminal motions can occur only for images, e.g., for so-called "light spots," which were considered in 1972 by V.L. Ginzburg and B.M. Bolotovskii. These spots can move with a superluminal phase velocity but are incapable of transferring energy and information. Nevertheless, these light spots may induce quite real generation of microwave radiation in closed waveguides and create the Vavilov-Cherenkov radiation in vacuum. In this work, we consider various paradoxes, illusions, and artifacts associated with superluminal motion.

  18. Gold-wire artifacts on diagnostic radiographs: A case report

    International Nuclear Information System (INIS)

    Keestra, Johan Anton Jochum; Jacobs, Reinhilde; Quirynen, Marc

    2014-01-01

    This report described a case in which diagnostic radiographs showed irregular dense radiopaque strings and curved lines in the head and neck area. These artifacts could lead to misinterpretation since they may obscure anatomical structures and/or mask critical structures/pathologies. A more detailed history of the patient indicated that these strings originated from a facelift procedure in which a gold-wire technique was used. Considering that such intervention may cause a radiodiagnostic burden, it should be included in the anamnesis prior to radiography.

  19. Gold-wire artifacts on diagnostic radiographs: A case report

    Energy Technology Data Exchange (ETDEWEB)

    Keestra, Johan Anton Jochum; Jacobs, Reinhilde; Quirynen, Marc [Dept. of Oral Health Sciences, KU Leuven and Dentistry, University Hospitals, KU Leuven, Leuven (Belgium)

    2014-03-15

    This report described a case in which diagnostic radiographs showed irregular dense radiopaque strings and curved lines in the head and neck area. These artifacts could lead to misinterpretation since they may obscure anatomical structures and/or mask critical structures/pathologies. A more detailed history of the patient indicated that these strings originated from a facelift procedure in which a gold-wire technique was used. Considering that such intervention may cause a radiodiagnostic burden, it should be included in the anamnesis prior to radiography.

  20. Metal artifact reduction using a patch-based reconstruction for digital breast tomosynthesis

    Science.gov (United States)

    Borges, Lucas R.; Bakic, Predrag R.; Maidment, Andrew D. A.; Vieira, Marcelo A. C.

    2017-03-01

    Digital breast tomosynthesis (DBT) is rapidly emerging as the main clinical tool for breast cancer screening. Although several reconstruction methods for DBT are described by the literature, one common issue is the interplane artifacts caused by out-of-focus features. For breasts containing highly attenuating features, such as surgical clips and large calcifications, the artifacts are even more apparent and can limit the detection and characterization of lesions by the radiologist. In this work, we propose a novel method of combining backprojected data into tomographic slices using a patch-based approach, commonly used in denoising. Preliminary tests were performed on a geometry phantom and on an anthropomorphic phantom containing metal inserts. The reconstructed images were compared to a commercial reconstruction solution. Qualitative assessment of the reconstructed images provides evidence that the proposed method reduces artifacts while maintaining low noise levels. Objective assessment supports the visual findings. The artifact spread function shows that the proposed method is capable of suppressing artifacts generated by highly attenuating features. The signal difference to noise ratio shows that the noise levels of the proposed and commercial methods are comparable, even though the commercial method applies post-processing filtering steps, which were not implemented on the proposed method. Thus, the proposed method can produce tomosynthesis reconstructions with reduced artifacts and low noise levels.

  1. Removal of the ballistocardiographic artifact from EEG-fMRI data: a canonical correlation approach

    International Nuclear Information System (INIS)

    Assecondi, Sara; Hallez, Hans; Staelens, Steven; Lemahieu, Ignace; Bianchi, Anna M; Huiskamp, Geertjan M

    2009-01-01

    The simultaneous recording of electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) can give new insights into how the brain functions. However, the strong electromagnetic field of the MR scanner generates artifacts that obscure the EEG and diminish its readability. Among them, the ballistocardiographic artifact (BCGa) that appears on the EEG is believed to be related to blood flow in scalp arteries leading to electrode movements. Average artifact subtraction (AAS) techniques, used to remove the BCGa, assume a deterministic nature of the artifact. This assumption may be too strong, considering the blood flow related nature of the phenomenon. In this work we propose a new method, based on canonical correlation analysis (CCA) and blind source separation (BSS) techniques, to reduce the BCGa from simultaneously recorded EEG-fMRI. We optimized the method to reduce the user's interaction to a minimum. When tested on six subjects, recorded in 1.5 T or 3 T, the average artifact extracted with BSS-CCA and AAS did not show significant differences, proving the absence of systematic errors. On the other hand, when compared on the basis of intra-subject variability, we found significant differences and better performance of the proposed method with respect to AAS. We demonstrated that our method deals with the intrinsic subject variability specific to the artifact that may cause averaging techniques to fail.

  2. Five-dimensional motion compensation for respiratory and cardiac motion with cone-beam CT of the thorax region

    Science.gov (United States)

    Sauppe, Sebastian; Hahn, Andreas; Brehm, Marcus; Paysan, Pascal; Seghers, Dieter; Kachelrieß, Marc

    2016-03-01

    We propose an adapted method of our previously published five-dimensional (5D) motion compensation (MoCo) algorithm1, developed for micro-CT imaging of small animals, to provide for the first time motion artifact-free 5D cone-beam CT (CBCT) images from a conventional flat detector-based CBCT scan of clinical patients. Image quality of retrospectively respiratory- and cardiac-gated volumes from flat detector CBCT scans is deteriorated by severe sparse projection artifacts. These artifacts further complicate motion estimation, as it is required for MoCo image reconstruction. For high quality 5D CBCT images at the same x-ray dose and the same number of projections as todays 3D CBCT we developed a double MoCo approach based on motion vector fields (MVFs) for respiratory and cardiac motion. In a first step our already published four-dimensional (4D) artifact-specific cyclic motion-compensation (acMoCo) approach is applied to compensate for the respiratory patient motion. With this information a cyclic phase-gated deformable heart registration algorithm is applied to the respiratory motion-compensated 4D CBCT data, thus resulting in cardiac MVFs. We apply these MVFs on double-gated images and thereby respiratory and cardiac motion-compensated 5D CBCT images are obtained. Our 5D MoCo approach processing patient data acquired with the TrueBeam 4D CBCT system (Varian Medical Systems). Our double MoCo approach turned out to be very efficient and removed nearly all streak artifacts due to making use of 100% of the projection data for each reconstructed frame. The 5D MoCo patient data show fine details and no motion blurring, even in regions close to the heart where motion is fastest.

  3. SU-C-206-03: Metal Artifact Reduction in X-Ray Computed Tomography Based On Local Anatomical Similarity

    International Nuclear Information System (INIS)

    Dong, X; Yang, X; Rosenfield, J; Elder, E; Dhabaan, A

    2016-01-01

    Purpose: Metal implants such as orthopedic hardware and dental fillings cause severe bright and dark streaking in reconstructed CT images. These artifacts decrease image contrast and degrade HU accuracy, leading to inaccuracies in target delineation and dose calculation. Additionally, such artifacts negatively impact patient set-up in image guided radiation therapy (IGRT). In this work, we propose a novel method for metal artifact reduction which utilizes the anatomical similarity between neighboring CT slices. Methods: Neighboring CT slices show similar anatomy. Based on this anatomical similarity, the proposed method replaces corrupted CT pixels with pixels from adjacent, artifact-free slices. A gamma map, which is the weighted summation of relative HU error and distance error, is calculated for each pixel in the artifact-corrupted CT image. The minimum value in each pixel’s gamma map is used to identify a pixel from the adjacent CT slice to replace the corresponding artifact-corrupted pixel. This replacement only occurs if the minimum value in a particular pixel’s gamma map is larger than a threshold. The proposed method was evaluated with clinical images. Results: Highly attenuating dental fillings and hip implants cause severe streaking artifacts on CT images. The proposed method eliminates the dark and bright streaking and improves the implant delineation and visibility. In particular, the image non-uniformity in the central region of interest was reduced from 1.88 and 1.01 to 0.28 and 0.35, respectively. Further, the mean CT HU error was reduced from 328 HU and 460 HU to 60 HU and 36 HU, respectively. Conclusions: The proposed metal artifact reduction method replaces corrupted image pixels with pixels from neighboring slices that are free of metal artifacts. This method proved capable of suppressing streaking artifacts, improving HU accuracy and image detectability.

  4. SU-C-206-03: Metal Artifact Reduction in X-Ray Computed Tomography Based On Local Anatomical Similarity

    Energy Technology Data Exchange (ETDEWEB)

    Dong, X; Yang, X; Rosenfield, J; Elder, E; Dhabaan, A [Emory University, Winship Cancer Institute, Atlanta, GA (United States)

    2016-06-15

    Purpose: Metal implants such as orthopedic hardware and dental fillings cause severe bright and dark streaking in reconstructed CT images. These artifacts decrease image contrast and degrade HU accuracy, leading to inaccuracies in target delineation and dose calculation. Additionally, such artifacts negatively impact patient set-up in image guided radiation therapy (IGRT). In this work, we propose a novel method for metal artifact reduction which utilizes the anatomical similarity between neighboring CT slices. Methods: Neighboring CT slices show similar anatomy. Based on this anatomical similarity, the proposed method replaces corrupted CT pixels with pixels from adjacent, artifact-free slices. A gamma map, which is the weighted summation of relative HU error and distance error, is calculated for each pixel in the artifact-corrupted CT image. The minimum value in each pixel’s gamma map is used to identify a pixel from the adjacent CT slice to replace the corresponding artifact-corrupted pixel. This replacement only occurs if the minimum value in a particular pixel’s gamma map is larger than a threshold. The proposed method was evaluated with clinical images. Results: Highly attenuating dental fillings and hip implants cause severe streaking artifacts on CT images. The proposed method eliminates the dark and bright streaking and improves the implant delineation and visibility. In particular, the image non-uniformity in the central region of interest was reduced from 1.88 and 1.01 to 0.28 and 0.35, respectively. Further, the mean CT HU error was reduced from 328 HU and 460 HU to 60 HU and 36 HU, respectively. Conclusions: The proposed metal artifact reduction method replaces corrupted image pixels with pixels from neighboring slices that are free of metal artifacts. This method proved capable of suppressing streaking artifacts, improving HU accuracy and image detectability.

  5. Exercise-Stress Echocardiography Reveals Systolic Anterior Motion of the Mitral Valve as a Cause of Syncopes in a Cardiac Amyloidosis Patient

    DEFF Research Database (Denmark)

    Clemmensen, Tor Skibsted; Mølgaard, Henning; Andersen, Niels Frost

    2016-01-01

    increased left ventricular outflow track (LVOT) velocity. However, bicycle exercise-stress test with simultaneous echocardiography revealed a stepwise decrease in blood pressure, a substantial increase in the LVOT velocity, and severe systolic anterior motion of the mitral valve. The patients' symptoms were...

  6. Moving metal artifact reduction in cone-beam CT scans with implanted cylindrical gold markers

    International Nuclear Information System (INIS)

    Toftegaard, Jakob; Fledelius, Walther; Worm, Esben S.; Poulsen, Per R.; Seghers, Dieter; Huber, Michael; Brehm, Marcus; Elstrøm, Ulrik V.

    2014-01-01

    Purpose: Implanted gold markers for image-guided radiotherapy lead to streaking artifacts in cone-beam CT (CBCT) scans. Several methods for metal artifact reduction (MAR) have been published, but they all fail in scans with large motion. Here the authors propose and investigate a method for automatic moving metal artifact reduction (MMAR) in CBCT scans with cylindrical gold markers. Methods: The MMAR CBCT reconstruction method has six steps. (1) Automatic segmentation of the cylindrical markers in the CBCT projections. (2) Removal of each marker in the projections by replacing the pixels within a masked area with interpolated values. (3) Reconstruction of a marker-free CBCT volume from the manipulated CBCT projections. (4) Reconstruction of a standard CBCT volume with metal artifacts from the original CBCT projections. (5) Estimation of the three-dimensional (3D) trajectory during CBCT acquisition for each marker based on the segmentation in Step 1, and identification of the smallest ellipsoidal volume that encompasses 95% of the visited 3D positions. (6) Generation of the final MMAR CBCT reconstruction from the marker-free CBCT volume of Step 3 by replacing the voxels in the 95% ellipsoid with the corresponding voxels of the standard CBCT volume of Step 4. The MMAR reconstruction was performed retrospectively using a half-fan CBCT scan for 29 consecutive stereotactic body radiation therapy patients with 2–3 gold markers implanted in the liver. The metal artifacts of the MMAR reconstructions were scored and compared with a standard MAR reconstruction by counting the streaks and by calculating the standard deviation of the Hounsfield units in a region around each marker. Results: The markers were found with the same autosegmentation settings in 27 CBCT scans, while two scans needed slightly changed settings to find all markers automatically in Step 1 of the MMAR method. MMAR resulted in 15 scans with no streaking artifacts, 11 scans with 1–4 streaks, and 3 scans

  7. Motion tolerant iterative reconstruction algorithm for cone-beam helical CT imaging

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Hisashi; Goto, Taiga; Hirokawa, Koichi; Miyazaki, Osamu [Hitachi Medical Corporation, Chiba-ken (Japan). CT System Div.

    2011-07-01

    We have developed a new advanced iterative reconstruction algorithm for cone-beam helical CT. The features of this algorithm are: (a) it uses separable paraboloidal surrogate (SPS) technique as a foundation for reconstruction to reduce noise and cone-beam artifact, (b) it uses a view weight in the back-projection process to reduce motion artifact. To confirm the improvement of our proposed algorithm over other existing algorithm, such as Feldkamp-Davis-Kress (FDK) or SPS algorithm, we compared the motion artifact reduction, image noise reduction (standard deviation of CT number), and cone-beam artifact reduction on simulated and clinical data set. Our results demonstrate that the proposed algorithm dramatically reduces motion artifacts compared with the SPS algorithm, and decreases image noise compared with the FDK algorithm. In addition, the proposed algorithm potentially improves time resolution of iterative reconstruction. (orig.)

  8. [E-MTAB-587] PCR_artifacts

    NARCIS (Netherlands)

    Muino Acuna, J.M.

    2011-01-01

    WARNING: This library was yield low amount of material and it was over-amplified by PCR. This libraries are used study the robustness of several statitical methods against PCR artifacts. ChIP experiments were performed on Arabidopsis wildtype inflorescences using an antibody raised against a

  9. Mediating Artifact in Teacher Professional Development

    Science.gov (United States)

    Svendsen, Bodil

    2015-01-01

    This article focuses on teacher professional development (TPD) in natural science through the 5E model as mediating artifact. The study was conducted in an upper secondary school, grounded in a school-based intervention research project. My contribution to the field of research on TPD is founded on the hypothesis that teachers would be best…

  10. Cooperative learning, problem solving and mediating artifacts

    African Journals Online (AJOL)

    PROF.MIREKU

    10, 2012. 39. Cooperative learning, problem solving and mediating artifacts. F. Bahmaei6 & N. ... out cooperative learning in the end, post-test was done and by analyzing the tests it was concluded that ... Johnson et al, 1991 b, Reynolds et al. 1995, Vidakovic .... connection of mental constructs (Hiebert, Carpenter, 1992).

  11. Observer Evaluation of a Metal Artifact Reduction Algorithm Applied to Head and Neck Cone Beam Computed Tomographic Images

    Energy Technology Data Exchange (ETDEWEB)

    Korpics, Mark; Surucu, Murat; Mescioglu, Ibrahim; Alite, Fiori; Block, Alec M.; Choi, Mehee; Emami, Bahman; Harkenrider, Matthew M.; Solanki, Abhishek A.; Roeske, John C., E-mail: jroeske@lumc.edu

    2016-11-15

    Purpose and Objectives: To quantify, through an observer study, the reduction in metal artifacts on cone beam computed tomographic (CBCT) images using a projection-interpolation algorithm, on images containing metal artifacts from dental fillings and implants in patients treated for head and neck (H&N) cancer. Methods and Materials: An interpolation-substitution algorithm was applied to H&N CBCT images containing metal artifacts from dental fillings and implants. Image quality with respect to metal artifacts was evaluated subjectively and objectively. First, 6 independent radiation oncologists were asked to rank randomly sorted blinded images (before and after metal artifact reduction) using a 5-point rating scale (1 = severe artifacts; 5 = no artifacts). Second, the standard deviation of different regions of interest (ROI) within each image was calculated and compared with the mean rating scores. Results: The interpolation-substitution technique successfully reduced metal artifacts in 70% of the cases. From a total of 60 images from 15 H&N cancer patients undergoing image guided radiation therapy, the mean rating score on the uncorrected images was 2.3 ± 1.1, versus 3.3 ± 1.0 for the corrected images. The mean difference in ranking score between uncorrected and corrected images was 1.0 (95% confidence interval: 0.9-1.2, P<.05). The standard deviation of each ROI significantly decreased after artifact reduction (P<.01). Moreover, a negative correlation between the mean rating score for each image and the standard deviation of the oral cavity and bilateral cheeks was observed. Conclusion: The interpolation-substitution algorithm is efficient and effective for reducing metal artifacts caused by dental fillings and implants on CBCT images, as demonstrated by the statistically significant increase in observer image quality ranking and by the decrease in ROI standard deviation between uncorrected and corrected images.

  12. Material-Dependent Implant Artifact Reduction Using SEMAC-VAT and MAVRIC: A Prospective MRI Phantom Study.

    Science.gov (United States)

    Filli, Lukas; Jud, Lukas; Luechinger, Roger; Nanz, Daniel; Andreisek, Gustav; Runge, Val M; Kozerke, Sebastian; Farshad-Amacker, Nadja A

    2017-06-01

    The aim of this study was to compare the degree of artifact reduction in magnetic resonance imaging achieved with slice encoding for metal artifact correction (SEMAC) in combination with view angle tilting (VAT) and multiacquisition variable resonance image combination (MAVRIC) for standard contrast weightings and different metallic materials. Four identically shaped rods made of the most commonly used prosthetic materials (stainless steel, SS; titanium, Ti; cobalt-chromium-molybdenum, CoCr; and oxidized zirconium, oxZi) were scanned at 3 T. In addition to conventional fast spin-echo sequences, metal artifact reduction sequences (SEMAC-VAT and MAVRIC) with varying degrees of artifact suppression were applied at different contrast weightings (T1w, T2w, PDw). Two independent readers measured in-plane and through-plane artifacts in a standardized manner. In addition, theoretical frequency-offset and frequency-offset-gradient maps were calculated. Interobserver agreement was assessed using intraclass correlation coefficient. Interobserver agreement was almost perfect (intraclass correlation coefficient, 0.86-0.99). Stainless steel caused the greatest artifacts, followed by CoCr, Ti, and oxZi regardless of the imaging sequence. While for Ti and oxZi rods scanning with weak SEMAC-VAT showed some advantage, for SS and CoCr, higher modes of SEMAC-VAT or MAVRIC were necessary to achieve artifact reduction. MAVRIC achieved better artifact reduction than SEMAC-VAT at the cost of longer acquisition times. Simulations matched well with the apparent geometry of the frequency-offset maps. For Ti and oxZi implants, weak SEMAC-VAT may be preferred as it is faster and produces less artifact than conventional fast spin-echo. Medium or strong SEMAC-VAT or MAVRIC modes are necessary for significant artifact reduction for SS and CoCr implants.

  13. Interactive inverse kinematics for human motion estimation

    DEFF Research Database (Denmark)

    Engell-Nørregård, Morten Pol; Hauberg, Søren; Lapuyade, Jerome

    2009-01-01

    We present an application of a fast interactive inverse kinematics method as a dimensionality reduction for monocular human motion estimation. The inverse kinematics solver deals efficiently and robustly with box constraints and does not suffer from shaking artifacts. The presented motion...... to significantly speed up the particle filtering. It should be stressed that the observation part of the system has not been our focus, and as such is described only from a sense of completeness. With our approach it is possible to construct a robust and computationally efficient system for human motion estimation....

  14. An image-based approach to understanding the physics of MR artifacts.

    Science.gov (United States)

    Morelli, John N; Runge, Val M; Ai, Fei; Attenberger, Ulrike; Vu, Lan; Schmeets, Stuart H; Nitz, Wolfgang R; Kirsch, John E

    2011-01-01

    As clinical magnetic resonance (MR) imaging becomes more versatile and more complex, it is increasingly difficult to develop and maintain a thorough understanding of the physical principles that govern the changing technology. This is particularly true for practicing radiologists, whose primary obligation is to interpret clinical images and not necessarily to understand complex equations describing the underlying physics. Nevertheless, the physics of MR imaging plays an important role in clinical practice because it determines image quality, and suboptimal image quality may hinder accurate diagnosis. This article provides an image-based explanation of the physics underlying common MR imaging artifacts, offering simple solutions for remedying each type of artifact. Solutions that have emerged from recent technologic advances with which radiologists may not yet be familiar are described in detail. Types of artifacts discussed include those resulting from voluntary and involuntary patient motion, magnetic susceptibility, magnetic field inhomogeneities, gradient nonlinearity, standing waves, aliasing, chemical shift, and signal truncation. With an improved awareness and understanding of these artifacts, radiologists will be better able to modify MR imaging protocols so as to optimize clinical image quality, allowing greater confidence in diagnosis. Copyright © RSNA, 2011.

  15. Teaching and Learning the Nature of Technical Artifacts

    Science.gov (United States)

    Frederik, Ineke; Sonneveld, Wim; de Vries, Marc J.

    2011-01-01

    Artifacts are probably our most obvious everyday encounter with technology. Therefore, a good understanding of the nature of technical artifacts is a relevant part of technological literacy. In this article we draw from the philosophy of technology to develop a conceptualization of technical artifacts that can be used for educational purposes.…

  16. Guided interaction exploration in artifact-centric process models

    NARCIS (Netherlands)

    van Eck, M.L.; Sidorova, N.; van der Aalst, W.M.P.

    2017-01-01

    Artifact-centric process models aim to describe complex processes as a collection of interacting artifacts. Recent development in process mining allow for the discovery of such models. However, the focus is often on the representation of the individual artifacts rather than their interactions. Based

  17. Use of item response curves of the Force and Motion Conceptual Evaluation to compare Japanese and American students' views on force and motion

    Science.gov (United States)

    Ishimoto, Michi; Davenport, Glen; Wittmann, Michael C.

    2017-12-01

    Student views of force and motion reflect the personal experiences and physics education of the student. With a different language, culture, and educational system, we expect that Japanese students' views on force and motion might be different from those of American students. The Force and Motion Conceptual Evaluation (FMCE) is an instrument used to probe student views on force and motion. It was designed using research on American students, and, as such, the items might function differently for Japanese students. Preliminary results from a translated version indicated that Japanese students had similar misconceptions as those of American students. In this study, we used item response curves (IRCs) to make more detailed item-by-item comparisons. IRCs show the functioning of individual items across all levels of performance by plotting the proportion of each response as a function of the total score. Most of the IRCs showed very similar patterns on both correct and incorrect responses; however, a few of the plots indicate differences between the populations. The similar patterns indicate that students tend to interact with FMCE items similarly, despite differences in culture, language, and education. We speculate about the possible causes for the differences in some of the IRCs. This report is intended to show how IRCs can be used as a part of the validation process when making comparisons across languages and nationalities. Differences in IRCs can help to pinpoint artifacts of translation, contextual effects because of differences in culture, and perhaps intrinsic differences in student understanding of Newtonian motion.

  18. Use of item response curves of the Force and Motion Conceptual Evaluation to compare Japanese and American students’ views on force and motion

    Directory of Open Access Journals (Sweden)

    Michi Ishimoto

    2017-11-01

    Full Text Available Student views of force and motion reflect the personal experiences and physics education of the student. With a different language, culture, and educational system, we expect that Japanese students’ views on force and motion might be different from those of American students. The Force and Motion Conceptual Evaluation (FMCE is an instrument used to probe student views on force and motion. It was designed using research on American students, and, as such, the items might function differently for Japanese students. Preliminary results from a translated version indicated that Japanese students had similar misconceptions as those of American students. In this study, we used item response curves (IRCs to make more detailed item-by-item comparisons. IRCs show the functioning of individual items across all levels of performance by plotting the proportion of each response as a function of the total score. Most of the IRCs showed very similar patterns on both correct and incorrect responses; however, a few of the plots indicate differences between the populations. The similar patterns indicate that students tend to interact with FMCE items similarly, despite differences in culture, language, and education. We speculate about the possible causes for the differences in some of the IRCs. This report is intended to show how IRCs can be used as a part of the validation process when making comparisons across languages and nationalities. Differences in IRCs can help to pinpoint artifacts of translation, contextual effects because of differences in culture, and perhaps intrinsic differences in student understanding of Newtonian motion.

  19. Supporting Knowledge Transfer through Decomposable Reasoning Artifacts

    Energy Technology Data Exchange (ETDEWEB)

    Pike, William A.; May, Richard A.; Turner, Alan E.

    2007-01-03

    Technology to support knowledge transfer and cooperative inquiry must offer its users the ability to effectively interpret knowledge structures produced by collaborators. Communicating the reasoning processes that underlie a finding is one method for enhancing interpretation, and can result in more effective evaluation and application of shared knowledge. In knowledge management tools, interpretation is aided by creating knowledge artifacts that can expose their provenance to scrutiny and that can be transformed into diverse representations that suit their consumers’ perspectives and preferences. We outline the information management needs of inquiring communities characterized by hypothesis generation tasks, and propose a model for communication, based in theories of hermeneutics, semiotics, and abduction, in which knowledge structures can be decomposed into the lower-level reasoning artifacts that produced them. We then present a proof-of-concept implementation for an environment to support the capture and communication of analytic products, with emphasis on the domain of intelligence analysis.

  20. A Language of Objects and Artifacts

    DEFF Research Database (Denmark)

    Svabo, Connie

    This is a conceptual inquiry about materiality. It gives an introductory overview to the vocabulary of materiality in a chosen selection of theories. The paper shows a language of artifacts and objects as it is used within practice-based approaches to organizational knowing. The examined...... intellectual traditions are interpretive-cultural approaches; activity theory; and sociology of translation. Similarities and differences are presented in the way these three distinct intellectual traditions conceptualize the array of material objects and artifacts which are central in the tales of practice...... concepts do the theories attempt to grasp tools and design objects – furniture, graphics, flutes-in-making and built space? The paper shows which concepts are used and it demonstrates how the interaction between social and material realities are viewed. Furthermore it highlights some of the ontological...

  1. Panning artifacts in digital pathology images

    Science.gov (United States)

    Avanaki, Ali R. N.; Lanciault, Christian; Espig, Kathryn S.; Xthona, Albert; Kimpe, Tom R. L.

    2017-03-01

    In making a pathologic diagnosis, a pathologist uses cognitive processes: perception, attention, memory, and search (Pena and Andrade-Filho, 2009). Typically, this involves focus while panning from one region of a slide to another, using either a microscope in a traditional workflow or software program and display in a digital pathology workflow (DICOM Standard Committee, 2010). We theorize that during panning operation, the pathologist receives information important to diagnosis efficiency and/or correctness. As compared to an optical microscope, panning in a digital pathology image involves some visual artifacts due to the following: (i) the frame rate is finite; (ii) time varying visual signals are reconstructed using imperfect zero-order hold. Specifically, after pixel's digital drive is changed, it takes time for a pixel to emit the expected amount of light. Previous work suggests that 49% of navigation is conducted in low-power/overview with digital pathology (Molin et al., 2015), but the influence of display factors has not been measured. We conducted a reader study to establish a relationship between display frame rate, panel response time, and threshold panning speed (above which the artifacts become noticeable). Our results suggest visual tasks that involve tissue structure are more impacted by the simulated panning artifacts than those that only involve color (e.g., staining intensity estimation), and that the panning artifacts versus normalized panning speed has a peak behavior which is surprising and may change for a diagnostic task. This is work in progress and our final findings should be considered in designing future digital pathology systems.

  2. An EEG Data Investigation Using Only Artifacts

    Science.gov (United States)

    2017-02-22

    hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and...some conditions, an automation feature was implemented to help the participants find the HVT. When the HVT was within the sensor footprint, a tone...EEG Data Investigation Using Only Artifacts 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 1 Chelsey

  3. Awe and Artifacts: Religious and Scientific Endeavor

    Directory of Open Access Journals (Sweden)

    Ionut Untea

    2017-05-01

    Full Text Available The article takes as its point of departure the reflections of Henry Adams and Jacques Ellul on the possible gradual replacement of objects used in religious worship with objects used in technological worship, and advances the hypothesis that such a substitution is unlikely. Using information from psychology, history of religions, and history of science, the perspective proposed is that of a parallel historical analogous development of both religious and scientific attitudes of awe by the use of artifacts carrying two functions: firstly, to coagulate social participation around questions dealing with humanity’s destiny and interpersonal relationships across communities, and secondly to offer cultural coherence through a communal sense of social stability, comfort, and security. I argue that, though animated by attitudes of awe (“awefull”, both leading scientists and religious founders have encountered the difficulty in representing and introducing this awe to the large public via “awesome” artifacts. The failure to represent coherently the initial awe via artifacts may give rise to “anomalous awefullness”: intolerance, persecutions, global conflicts.

  4. Racial IQ Differences among Transracial Adoptees: Fact or Artifact?

    Directory of Open Access Journals (Sweden)

    Drew Thomas

    2016-12-01

    Full Text Available Some academic publications infer from studies of transracial adoptees’ IQs that East Asian adoptees raised in the West by Whites have higher IQs than Western Whites, and that White adoptees raised by Whites have higher IQs than Black adoptees raised by Whites. Those publications suggest that this is because genetic differences give East Asians a higher mean IQ than Whites, and Whites a higher mean IQ than Blacks. This paper proposes a parsimonious alternative explanation: the apparent IQ advantage of East Asian adoptees is an artifact caused by ignoring the Flynn effect and adoption’s beneficial effect on IQ, and most of the IQ disadvantage of Black adoptees disappears when one allows for attrition in the Minnesota Transracial Adoption Study, and acknowledges the results of other studies. Diagnosing these artifacts suggests a nil hypothesis: East Asian, White, and Black adoptees raised in the same environment would have similar IQs, hinting at a minimal role for genes in racial IQ differences.

  5. Metal artifact reduction in x-ray computed tomography (CT) by constrained optimization

    International Nuclear Information System (INIS)

    Zhang Xiaomeng; Wang Jing; Xing Lei

    2011-01-01

    Purpose: The streak artifacts caused by metal implants have long been recognized as a problem that limits various applications of CT imaging. In this work, the authors propose an iterative metal artifact reduction algorithm based on constrained optimization. Methods: After the shape and location of metal objects in the image domain is determined automatically by the binary metal identification algorithm and the segmentation of ''metal shadows'' in projection domain is done, constrained optimization is used for image reconstruction. It minimizes a predefined function that reflects a priori knowledge of the image, subject to the constraint that the estimated projection data are within a specified tolerance of the available metal-shadow-excluded projection data, with image non-negativity enforced. The minimization problem is solved through the alternation of projection-onto-convex-sets and the steepest gradient descent of the objective function. The constrained optimization algorithm is evaluated with a penalized smoothness objective. Results: The study shows that the proposed method is capable of significantly reducing metal artifacts, suppressing noise, and improving soft-tissue visibility. It outperforms the FBP-type methods and ART and EM methods and yields artifacts-free images. Conclusions: Constrained optimization is an effective way to deal with CT reconstruction with embedded metal objects. Although the method is presented in the context of metal artifacts, it is applicable to general ''missing data'' image reconstruction problems.

  6. Technical Assessment of Artifact Production from Neuro Endovascular Coil At 3 Tesla MRI: An In Vitro Study

    International Nuclear Information System (INIS)

    Kampaengtip, A.; Krisanachinda, A.; Singhara Na Ayudya, S.; Asavaphatiboon, S.

    2012-01-01

    Introduction: Magnetic resonance imaging (MRI) is an essential part of the diagnostic procedures in radiology. MRI 3 Tesla becomes more widespread due to high signal to noise ratio (SNR). The use of the neuro endovascular coil to overcome the neuro aneurysm can introduce the artifact in magnetic resonance imaging. Susceptibility artifacts and geometric distortions caused by magnetic field inhomogeneity- related signal loss is used to refer to an artifact in magnetic resonance images. It consists of a region of signal void with a surrounding area of an increased signal intensity that appears to be considerably larger than the actual size of the device causing the artifact. The objective of the study is to compare the size of the artifact on the MR image to the actual size of endovascular coils using a 3 Tesla magnetic resonance imaging system, in vitro study. Methods: The endovascular coils were made from detachable platinum and aneurysm models were constructed by using silicone tube. MRI 3 Tesla Philips Model Achieva with pulse sequence selections were: spin echo, fast spin echo, inversion recovery, fast gradient echo while additional parameters were echo time and turbo factor. Results: Improved visualization of perianeurysmal soft tissues is best accomplished by spin echo for fast spin echo sequences, even better suited to reduce metal artifact. Furthermore, shorter turbo factor and shorter effective TE in the latter sequences are beneficial for the same reason as sequences having shorter TE. Sequences with a shorter TE are preferred because of less time for dephasing and frequency shifting. Imaging at gradient echo series increases susceptibility artifacts. In this in vitro study, some of the major characteristics related to MRI imaging of coil packs have been defined. Discussion: Pulse sequence spin echo is the best sequence reducing the susceptibility artifact. Reducing the TE is the main factor in improving endovascular coil visualization on MRI images. The

  7. Comparison of cardiac gating and refocusing pulses for correction of cerebrospinal fluid pulsation artifacts in MR images

    International Nuclear Information System (INIS)

    Modic, M.T.; Haacke, E.M.; Lenz, G.W.; Masaryk, T.; Kaufman, B.; Ross, J.S.

    1986-01-01

    This study compared cardiac gating and additional refocusing gradient pulses in combination or alone for correction of cerebrospinal fluid (CSF) pulsation artifacts in both normal volunteers and in patients with suspected spinal pathology. Refocusing pulses or cardiac gating when used alone produced a decrease in ghosting artifacts on sagittal images and reduced the nonuniformity of the CSF signal on axial images. There is improved thin-section T2 imaging of the cord with long TEs and as few as one excitation. The refocusing pulses reduced ghosting artifacts also from respiratory motion and enhanced the CSF signal with shorter TRs leading to increased CSF contrast. When used together, the results were significantly better than either alone. Refocusing schemes can be used with any TR, do not require gating, and are now routinely employed at the authors' institution

  8. Evaluation of two iterative techniques for reducing metal artifacts in computed tomography.

    Science.gov (United States)

    Boas, F Edward; Fleischmann, Dominik

    2011-06-01

    To evaluate two methods for reducing metal artifacts in computed tomography (CT)--the metal deletion technique (MDT) and the selective algebraic reconstruction technique (SART)--and compare these methods with filtered back projection (FBP) and linear interpolation (LI). The institutional review board approved this retrospective HIPAA-compliant study; informed patient consent was waived. Simulated projection data were calculated for a phantom that contained water, soft tissue, bone, and iron. Clinical projection data were obtained retrospectively from 11 consecutively identified CT scans with metal streak artifacts, with a total of 178 sections containing metal. Each scan was reconstructed using FBP, LI, SART, and MDT. The simulated scans were evaluated quantitatively by calculating the average error in Hounsfield units for each pixel compared with the original phantom. Two radiologists who were blinded to the reconstruction algorithms used qualitatively evaluated the clinical scans, ranking the overall severity of artifacts for each algorithm. P values for comparisons of the image quality ranks were calculated from the binomial distribution. The simulations showed that MDT reduces artifacts due to photon starvation, beam hardening, and motion and does not introduce new streaks between metal and bone. MDT had the lowest average error (76% less than FBP, 42% less than LI, 17% less than SART). Blinded comparison of the clinical scans revealed that MDT had the best image quality 100% of the time (95% confidence interval: 72%, 100%). LI had the second best image quality, and SART and FBP had the worst image quality. On images from two CT scans, as compared with images generated by the scanner, MDT revealed information of potential clinical importance. For a wide range of scans, MDT yields reduced metal streak artifacts and better-quality images than does FBP, LI, or SART. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101782/-/DC1. RSNA, 2011

  9. Improving Pulse Rate Measurements during Random Motion Using a Wearable Multichannel Reflectance Photoplethysmograph

    Directory of Open Access Journals (Sweden)

    Kristen M. Warren

    2016-03-01

    Full Text Available Photoplethysmographic (PPG waveforms are used to acquire pulse rate (PR measurements from pulsatile arterial blood volume. PPG waveforms are highly susceptible to motion artifacts (MA, limiting the implementation of PR measurements in mobile physiological monitoring devices. Previous studies have shown that multichannel photoplethysmograms can successfully acquire diverse signal information during simple, repetitive motion, leading to differences in motion tolerance across channels. In this paper, we investigate the performance of a custom-built multichannel forehead-mounted photoplethysmographic sensor under a variety of intense motion artifacts. We introduce an advanced multichannel template-matching algorithm that chooses the channel with the least motion artifact to calculate PR for each time instant. We show that for a wide variety of random motion, channels respond differently to motion artifacts, and the multichannel estimate outperforms single-channel estimates in terms of motion tolerance, signal quality, and PR errors. We have acquired 31 data sets consisting of PPG waveforms corrupted by random motion and show that the accuracy of PR measurements achieved was increased by up to 2.7 bpm when the multichannel-switching algorithm was compared to individual channels. The percentage of PR measurements with error ≤ 5 bpm during motion increased by 18.9% when the multichannel switching algorithm was compared to the mean PR from all channels. Moreover, our algorithm enables automatic selection of the best signal fidelity channel at each time point among the multichannel PPG data.

  10. Motion correction improves image quality of dGEMRIC in finger joints

    International Nuclear Information System (INIS)

    Miese, Falk; Kröpil, Patric; Ostendorf, Benedikt; Scherer, Axel; Buchbender, Christian; Quentin, Michael; Lanzman, Rotem S.; Blondin, Dirk; Schneider, Matthias; Bittersohl, Bernd; Zilkens, Christoph; Jellus, Vladimir; Mamisch, Tallal Ch.; Wittsack, Hans-Jörg

    2011-01-01

    Purpose: To assess motion artifacts in dGEMRIC of finger joints and to evaluate the effectiveness of motion correction. Materials and methods: In 40 subjects (26 patients with finger arthritis and 14 healthy volunteers) dGEMRIC of metacarpophalangeal joint II was performed. Imaging used a dual flip angle approach (TE 3.72 ms, TR 15 ms, flip angles 5° and 26°). Two sets of T1 maps were calculated for dGEMRIC analysis from the imaging data for each subject: one with and one without motion correction. To compare image quality, visual grading analysis and precision of dGEMRIC measurement of both dGEMRIC maps for each case were evaluated. Results: Motion artifacts were present in 82% (33/40) of uncorrected dGEMRIC maps. Motion artifacts were graded as severe or as rendering evaluation impossible in 43% (17/40) of uncorrected dGEMRIC maps. Motion corrected maps showed significantly less motion artifacts (P < 0.001) and were graded as evaluable in 97% (39/40) of cases. Precision was significantly higher in motion corrected images (coefficient of variation (CV = .176 ± .077), compared to uncorrected images (CV .445 ± .347) (P < .001). Motion corrected dGERMIC was different in volunteers and patients (P = .044), whereas uncorrected dGEMRIC was not (P = .234). Conclusion: Motion correction improves image quality, dGEMRIC measurement precision and diagnostic performance in dGEMRIC of finger joints.

  11. Improving consensus structure by eliminating averaging artifacts

    Directory of Open Access Journals (Sweden)

    KC Dukka B

    2009-03-01

    Full Text Available Abstract Background Common structural biology methods (i.e., NMR and molecular dynamics often produce ensembles of molecular structures. Consequently, averaging of 3D coordinates of molecular structures (proteins and RNA is a frequent approach to obtain a consensus structure that is representative of the ensemble. However, when the structures are averaged, artifacts can result in unrealistic local geometries, including unphysical bond lengths and angles. Results Herein, we describe a method to derive representative structures while limiting the number of artifacts. Our approach is based on a Monte Carlo simulation technique that drives a starting structure (an extended or a 'close-by' structure towards the 'averaged structure' using a harmonic pseudo energy function. To assess the performance of the algorithm, we applied our approach to Cα models of 1364 proteins generated by the TASSER structure prediction algorithm. The average RMSD of the refined model from the native structure for the set becomes worse by a mere 0.08 Å compared to the average RMSD of the averaged structures from the native structure (3.28 Å for refined structures and 3.36 A for the averaged structures. However, the percentage of atoms involved in clashes is greatly reduced (from 63% to 1%; in fact, the majority of the refined proteins had zero clashes. Moreover, a small number (38 of refined structures resulted in lower RMSD to the native protein versus the averaged structure. Finally, compared to PULCHRA 1, our approach produces representative structure of similar RMSD quality, but with much fewer clashes. Conclusion The benchmarking results demonstrate that our approach for removing averaging artifacts can be very beneficial for the structural biology community. Furthermore, the same approach can be applied to almost any problem where averaging of 3D coordinates is performed. Namely, structure averaging is also commonly performed in RNA secondary prediction 2, which

  12. Accessing Cultural Artifacts Through Digital Companions

    DEFF Research Database (Denmark)

    Rehm, Matthias; Jensen, Martin Lynge

    2015-01-01

    This paper presents a study that explores how the introduction of a digital companion agent for a museum exploration game changes children’s engagement with the presented artworks. To this end, a mobile application was developed featuring a monster agent that has eaten the artworks, which...... the children had now to find in the museum. Results show that in comparison to the paper-based version of the exploration game, children engaged in more interactions with the actual cultural artifacts and showed a significantly higher retention rate for details of the involved artworks....

  13. A holographic color camera for recording artifacts

    International Nuclear Information System (INIS)

    Jith, Abhay

    2013-01-01

    Advent of 3D televisions has created a new wave of public interest in images with depth. Though these technologies create moving pictures with apparent depth, it lacks the visual appeal and a set of other positive aspects of color holographic images. The above new wave of interest in 3D will definitely help to fuel popularity of holograms. In view of this, a low cost and handy color holography camera is designed for recording color holograms of artifacts. It is believed that such cameras will help to record medium format color holograms outside conventional holography laboratories and to popularize color holography. The paper discusses the design and the results obtained.

  14. Blooming Artifact Reduction in Coronary Artery Calcification by A New De-blooming Algorithm: Initial Study.

    Science.gov (United States)

    Li, Ping; Xu, Lei; Yang, Lin; Wang, Rui; Hsieh, Jiang; Sun, Zhonghua; Fan, Zhanming; Leipsic, Jonathon A

    2018-05-02

    The aim of this study was to investigate the use of de-blooming algorithm in coronary CT angiography (CCTA) for optimal evaluation of calcified plaques. Calcified plaques were simulated on a coronary vessel phantom and a cardiac motion phantom. Two convolution kernels, standard (STND) and high-definition standard (HD STND), were used for imaging reconstruction. A dedicated de-blooming algorithm was used for imaging processing. We found a smaller bias towards measurement of stenosis using the de-blooming algorithm (STND: bias 24.6% vs 15.0%, range 10.2% to 39.0% vs 4.0% to 25.9%; HD STND: bias 17.9% vs 11.0%, range 8.9% to 30.6% vs 0.5% to 21.5%). With use of de-blooming algorithm, specificity for diagnosing significant stenosis increased from 45.8% to 75.0% (STND), from 62.5% to 83.3% (HD STND); while positive predictive value (PPV) increased from 69.8% to 83.3% (STND), from 76.9% to 88.2% (HD STND). In the patient group, reduction in calcification volume was 48.1 ± 10.3%, reduction in coronary diameter stenosis over calcified plaque was 52.4 ± 24.2%. Our results suggest that the novel de-blooming algorithm could effectively decrease the blooming artifacts caused by coronary calcified plaques, and consequently improve diagnostic accuracy of CCTA in assessing coronary stenosis.

  15. Ground motion estimation for the elevated bridges of the Kyushu Shinkansen derailment caused by the foreshock of the 2016 Kumamoto earthquake based on the site-effect substitution method

    Science.gov (United States)

    Hata, Yoshiya; Yabe, Masaaki; Kasai, Akira; Matsuzaki, Hiroshi; Takahashi, Yoshikazu; Akiyama, Mitsuyoshi

    2016-12-01

    An earthquake of JMA magnitude 6.5 (first event) hit Kumamoto Prefecture, Japan, at 21:26 JST, April 14, 2016. Subsequently, an earthquake of JMA magnitude 7.3 (second event) hit Kumamoto and Oita Prefectures at 01:46 JST, April 16, 2016. An out-of-service Kyushu Shinkansen train carrying no passengers traveling on elevated bridges was derailed by the first event. This was the third derailment caused by an earthquake in the history of the Japanese Shinkansen, after one caused by the 2004 Mid-Niigata Prefecture Earthquake and another triggered by the 2011 Tohoku Earthquake. To analyze the mechanism of this third derailment, it is crucial to evaluate the strong ground motion at the derailment site with high accuracy. For this study, temporary earthquake observations were first carried out at a location near the bridge site; these observations were conducted because although the JMA Kumamoto Station site and the derailment site are closely located, the ground response characteristics at these sites differ. Next, empirical site amplification and phase effects were evaluated based on the obtained observation records. Finally, seismic waveforms during the first event at the bridge site of interest were estimated based on the site-effect substitution method. The resulting estimated acceleration and velocity waveforms for the derailment site include much larger amplitudes than the waveforms recorded at the JMA Kumamoto and MLIT Kumamoto station sites. The reliability of these estimates is confirmed by the finding that the same methods reproduce strong ground motions at the MLIT Kumamoto Station site accurately. These estimated ground motions will be useful for reasonable safety assessment of anti-derailment devices on elevated railway bridges.[Figure not available: see fulltext.

  16. Reduction of ring artifacts in CBCT: Detection and correction of pixel gain variations in flat panel detectors

    International Nuclear Information System (INIS)

    Altunbas, Cem; Lai, Chao-Jen; Zhong, Yuncheng; Shaw, Chris C.

    2014-01-01

    Purpose: In using flat panel detectors (FPD) for cone beam computed tomography (CBCT), pixel gain variations may lead to structured nonuniformities in projections and ring artifacts in CBCT images. Such gain variations can be caused by change in detector entrance exposure levels or beam hardening, and they are not accounted by conventional flat field correction methods. In this work, the authors presented a method to identify isolated pixel clusters that exhibit gain variations and proposed a pixel gain correction (PGC) method to suppress both beam hardening and exposure level dependent gain variations. Methods: To modulate both beam spectrum and entrance exposure, flood field FPD projections were acquired using beam filters with varying thicknesses. “Ideal” pixel values were estimated by performing polynomial fits in both raw and flat field corrected projections. Residuals were calculated by taking the difference between measured and ideal pixel values to identify clustered image and FPD artifacts in flat field corrected and raw images, respectively. To correct clustered image artifacts, the ratio of ideal to measured pixel values in filtered images were utilized as pixel-specific gain correction factors, referred as PGC method, and they were tabulated as a function of pixel value in a look-up table. Results: 0.035% of detector pixels lead to clustered image artifacts in flat field corrected projections, where 80% of these pixels were traced back and linked to artifacts in the FPD. The performance of PGC method was tested in variety of imaging conditions and phantoms. The PGC method reduced clustered image artifacts and fixed pattern noise in projections, and ring artifacts in CBCT images. Conclusions: Clustered projection image artifacts that lead to ring artifacts in CBCT can be better identified with our artifact detection approach. When compared to the conventional flat field correction method, the proposed PGC method enables characterization of nonlinear

  17. View-Angle Tilting and Slice-Encoding Metal Artifact Correction for Artifact Reduction in MRI: Experimental Sequence Optimization for Orthopaedic Tumor Endoprostheses and Clinical Application.

    Directory of Open Access Journals (Sweden)

    Pia M Jungmann

    Full Text Available MRI plays a major role in follow-up of patients with malignant bone tumors. However, after limb salvage surgery, orthopaedic tumor endoprostheses might cause significant metal-induced susceptibility artifacts.To evaluate the benefit of view-angle tilting (VAT and slice-encoding metal artifact correction (SEMAC for MRI of large-sized orthopaedic tumor endoprostheses in an experimental model and to demonstrate clinical benefits for assessment of periprosthetic soft tissue abnormalities.In an experimental setting, tumor endoprostheses (n=4 were scanned at 1.5T with three versions of optimized high-bandwidth turbo-spin-echo pulse sequences: (i standard, (ii VAT and (iii combined VAT and SEMAC (VAT&SEMAC. Pulse sequences included coronal short-tau-inversion-recovery (STIR, coronal T1-weighted (w, transverse T1-w and T2-w TSE sequences. For clinical evaluation, VAT&SEMAC was compared to conventional metal artifact-reducing MR sequences (conventional MR in n=25 patients with metal implants and clinical suspicion of tumor recurrence or infection. Diameters of artifacts were measured quantitatively. Qualitative parameters were assessed on a five-point scale (1=best, 5=worst: "image distortion", "artificial signal changes at the edges" and "diagnostic confidence". Imaging findings were correlated with pathology. T-tests and Wilcoxon-signed rank tests were used for statistical analyses.The true size of the prostheses was overestimated on MRI (P<0.05. A significant reduction of artifacts was achieved by VAT (P<0.001 and VAT&SEMAC (P=0.003 compared to the standard group. Quantitative scores improved in the VAT and VAT&SEMAC group (P<0.05. On clinical MR images, artifact diameters were significantly reduced in the VAT&SEMAC-group as compared with the conventional-group (P<0.001. Distortion and artificial signal changes were reduced and diagnostic confidence improved (P<0.05. In two cases, tumor-recurrence, in ten cases infection and in thirteen cases other

  18. GPU-Based Simulation of Ultrasound Imaging Artifacts for Cryosurgery Training

    Science.gov (United States)

    Keelan, Robert; Shimada, Kenji

    2016-01-01

    This study presents an efficient computational technique for the simulation of ultrasound imaging artifacts associated with cryosurgery based on nonlinear ray tracing. This study is part of an ongoing effort to develop computerized training tools for cryosurgery, with prostate cryosurgery as a development model. The capability of performing virtual cryosurgical procedures on a variety of test cases is essential for effective surgical training. Simulated ultrasound imaging artifacts include reverberation and reflection of the cryoprobes in the unfrozen tissue, reflections caused by the freezing front, shadowing caused by the frozen region, and tissue property changes in repeated freeze–thaw cycles procedures. The simulated artifacts appear to preserve the key features observed in a clinical setting. This study displays an example of how training may benefit from toggling between the undisturbed ultrasound image, the simulated temperature field, the simulated imaging artifacts, and an augmented hybrid presentation of the temperature field superimposed on the ultrasound image. The proposed method is demonstrated on a graphic processing unit at 100 frames per second, on a mid-range personal workstation, at two orders of magnitude faster than a typical cryoprocedure. This performance is based on computation with C++ accelerated massive parallelism and its interoperability with the DirectX-rendering application programming interface. PMID:26818026

  19. Motion correction options in PET/MRI.

    Science.gov (United States)

    Catana, Ciprian

    2015-05-01

    Subject motion is unavoidable in clinical and research imaging studies. Breathing is the most important source of motion in whole-body PET and MRI studies, affecting not only thoracic organs but also those in the upper and even lower abdomen. The motion related to the pumping action of the heart is obviously relevant in high-resolution cardiac studies. These two sources of motion are periodic and predictable, at least to a first approximation, which means certain techniques can be used to control the motion (eg, by acquiring the data when the organ of interest is relatively at rest). Additionally, nonperiodic and unpredictable motion can also occur during the scan. One obvious limitation of methods relying on external devices (eg, respiratory bellows or the electrocardiogram signal to monitor the respiratory or cardiac cycle, respectively) to trigger or gate the data acquisition is that the complex motion of internal organs cannot be fully characterized. However, detailed information can be obtained using either the PET or MRI data (or both) allowing the more complete characterization of the motion field so that a motion model can be built. Such a model and the information derived from simple external devices can be used to minimize the effects of motion on the collected data. In the ideal case, all the events recorded during the PET scan would be used to generate a motion-free or corrected PET image. The detailed motion field can be used for this purpose by applying it to the PET data before, during, or after the image reconstruction. Integrating all these methods for motion control, characterization, and correction into a workflow that can be used for routine clinical studies is challenging but could potentially be extremely valuable given the improvement in image quality and reduction of motion-related image artifacts. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. Influence of orthodontic appliance-derived artifacts on 3-T MRI movies.

    Science.gov (United States)

    Ozawa, Erika; Honda, Ei-Ichi; Parakonthun, Kulthida Nunthayanon; Ohmori, Hiroko; Shimazaki, Kazuo; Kurabayashi, Tohru; Ono, Takashi

    2018-02-19

    Magnetic resonance imaging (MRI) has been used to study configurations of speech organs in the resting state. However, MRI is sensitive to metals, and numerous types of metallic appliances, most of which have a large magnetic susceptibility, are used in orthodontic treatment and may cause severe artifacts on MRI. We have developed techniques for obtaining MRI movies of the oral region, to evaluate articulatory changes, especially movement of the tongue, palate, and teeth, pre- and post-orthodontic/orthognathic treatment. We evaluated the influence of artifacts caused by orthodontic appliances, including fixed retainers, metal brackets, and wires, on measurements in 3-T MRI movies. Sixteen healthy young adults (nine males, seven females; average age, 27 years) with normal occlusion were recruited. Four types of customized maxillary and mandibular plates were prepared by incorporating one of the following into the plate: (a) nothing, (b) a fixed canine-to-canine retainer, (c) metal brackets for the anterior and molar teeth, or (d) clear brackets for the anterior teeth and metal brackets for molars. A 3-T MRI movie, in segmented cine mode, was generated for each plate condition while participants pronounced a vowel-consonant-vowel syllable (/asa/). The size of the artifact due to the metallic brackets was measured. The face size and orthodontically important anatomical structures, such as the velum, the hard palate, and the laryngeal ventricle, were also measured. A large artifact was observed over the entire oral region around orthodontic appliances, altering regional visibility. The velopharyngeal height was measured as significantly longer in the presence of metal brackets. The maximum artifact size due to a metallic bracket was > 8 cm. Our results show that even if it is possible to obtain the measurements of palate length, nasion to sella, and nasion to basion in individuals wearing metal brackets for molars, the measurements might be affected due to the

  1. Evaluation of alignment error due to a speed artifact in stereotactic ultrasound image guidance

    International Nuclear Information System (INIS)

    Salter, Bill J; Wang, Brian; Szegedi, Martin W; Rassiah-Szegedi, Prema; Shrieve, Dennis C; Cheng, Roger; Fuss, Martin

    2008-01-01

    Ultrasound (US) image guidance systems used in radiotherapy are typically calibrated for soft tissue applications, thus introducing errors in depth-from-transducer representation when used in media with a different speed of sound propagation (e.g. fat). This error is commonly referred to as the speed artifact. In this study we utilized a standard US phantom to demonstrate the existence of the speed artifact when using a commercial US image guidance system to image through layers of simulated body fat, and we compared the results with calculated/predicted values. A general purpose US phantom (speed of sound (SOS) = 1540 m s -1 ) was imaged on a multi-slice CT scanner at a 0.625 mm slice thickness and 0.5 mm x 0.5 mm axial pixel size. Target-simulating wires inside the phantom were contoured and later transferred to the US guidance system. Layers of various thickness (1-8 cm) of commercially manufactured fat-simulating material (SOS = 1435 m s -1 ) were placed on top of the phantom to study the depth-related alignment error. In order to demonstrate that the speed artifact is not caused by adding additional layers on top of the phantom, we repeated these measurements in an identical setup using commercially manufactured tissue-simulating material (SOS = 1540 m s -1 ) for the top layers. For the fat-simulating material used in this study, we observed the magnitude of the depth-related alignment errors resulting from the speed artifact to be 0.7 mm cm -1 of fat imaged through. The measured alignment errors caused by the speed artifact agreed with the calculated values within one standard deviation for all of the different thicknesses of fat-simulating material studied here. We demonstrated the depth-related alignment error due to the speed artifact when using US image guidance for radiation treatment alignment and note that the presence of fat causes the target to be aliased to a depth greater than it actually is. For typical US guidance systems in use today, this will

  2. Evaluation of alignment error due to a speed artifact in stereotactic ultrasound image guidance.

    Science.gov (United States)

    Salter, Bill J; Wang, Brian; Szegedi, Martin W; Rassiah-Szegedi, Prema; Shrieve, Dennis C; Cheng, Roger; Fuss, Martin

    2008-12-07

    Ultrasound (US) image guidance systems used in radiotherapy are typically calibrated for soft tissue applications, thus introducing errors in depth-from-transducer representation when used in media with a different speed of sound propagation (e.g. fat). This error is commonly referred to as the speed artifact. In this study we utilized a standard US phantom to demonstrate the existence of the speed artifact when using a commercial US image guidance system to image through layers of simulated body fat, and we compared the results with calculated/predicted values. A general purpose US phantom (speed of sound (SOS) = 1540 m s(-1)) was imaged on a multi-slice CT scanner at a 0.625 mm slice thickness and 0.5 mm x 0.5 mm axial pixel size. Target-simulating wires inside the phantom were contoured and later transferred to the US guidance system. Layers of various thickness (1-8 cm) of commercially manufactured fat-simulating material (SOS = 1435 m s(-1)) were placed on top of the phantom to study the depth-related alignment error. In order to demonstrate that the speed artifact is not caused by adding additional layers on top of the phantom, we repeated these measurements in an identical setup using commercially manufactured tissue-simulating material (SOS = 1540 m s(-1)) for the top layers. For the fat-simulating material used in this study, we observed the magnitude of the depth-related alignment errors resulting from the speed artifact to be 0.7 mm cm(-1) of fat imaged through. The measured alignment errors caused by the speed artifact agreed with the calculated values within one standard deviation for all of the different thicknesses of fat-simulating material studied here. We demonstrated the depth-related alignment error due to the speed artifact when using US image guidance for radiation treatment alignment and note that the presence of fat causes the target to be aliased to a depth greater than it actually is. For typical US guidance systems in use today, this will

  3. Picking Up Artifacts: Storyboarding as a Gateway to Reuse

    Science.gov (United States)

    Wahid, Shahtab; Branham, Stacy M.; Cairco, Lauren; McCrickard, D. Scott; Harrison, Steve

    Storyboarding offers designers the opportunity to illustrate a visual narrative of use. Because designers often refer to past ideas, we argue storyboards can be constructed by reusing shared artifacts. We present a study in which we explore how designers reuse artifacts consisting of images and rationale during storyboard construction. We find images can aid in accessing rationale and that connections among features aid in deciding what to reuse, creating new artifacts, and constructing. Based on requirements derived from our findings, we present a storyboarding tool, PIC-UP, to facilitate artifact sharing and reuse and evaluate its use in an exploratory study. We conclude with remarks on facilitating reuse and future work.

  4. Ultrafast MR imaging with EPI of organs undergoing nonperiodic motion

    International Nuclear Information System (INIS)

    Stehling, M.K.; Ordidge, R.J.; Howseman, A.M.; Coxon, R.; Chapman, B.; Mansfield, P.

    1988-01-01

    Conventional MR imaging employing repetitive data acquisition is susceptible to motion artifacts. Gating overcomes periodic motion effects. Nonperiodic motion, as encountered in the gastronintestinal tract, cardiac arrhythmias, unsedated children, and fetal imaging, thwarts conventional MR imaging. The EPI derivatives BEST and MBEST create a complex 128 x 128-pixel image in 64 msec and 128 msec, respectively, freezing motion almost completely. Sequentially recorded gastrointestinal-tract images allow quantitative evaluation of gastric and gut motility. Cardiac morphology, movement, and blood flow patterns in valvular heart disease have been depicted during atrial fibrillation. Selected clinical results with accompanying technical details illustrate the scope of EPI as a distinctive imaging modality

  5. Initial observations using a novel "cine" magnetic resonance imaging technique to detect changes in abdominal motion caused by encapsulating peritoneal sclerosis.

    Science.gov (United States)

    Wright, Benjamin; Summers, Angela; Fenner, John; Gillott, Richard; Hutchinson, Charles E; Spencer, Paul A; Wilkie, Martin; Hurst, Helen; Herrick, Sarah; Brenchley, Paul; Augustine, Titus; Bardhan, Karna D

    2011-01-01

    Encapsulating peritoneal sclerosis (EPS) is an uncommon complication of peritoneal dialysis (PD), with high mortality and morbidity. The peritoneum thickens, dysfunctions, and forms a cocoon that progressively "strangulates" the small intestine, causing malnutrition, ischemia, and infarction. There is as yet no reliable noninvasive means of diagnosis, but recent developments in image analysis of cine magnetic resonance imaging for the recognition of adhesions offers a way forward. We used this protocol before surgery in 3 patients with suspected EPS. Image analysis revealed patterns of abdominal movement that were markedly different from the patterns in healthy volunteers. The volunteers showed marked movement throughout the abdomen; in contrast, movement in EPS patients was restricted to just below the diaphragm. This clear difference provides early "proof of principle" of the approach that we have developed.

  6. An extension to artifact-free projection overlaps

    International Nuclear Information System (INIS)

    Lin, Jianyu

    2015-01-01

    Purpose: In multipinhole single photon emission computed tomography, the overlapping of projections has been used to increase sensitivity. Avoiding artifacts in the reconstructed image associated with projection overlaps (multiplexing) is a critical issue. In our previous report, two types of artifact-free projection overlaps, i.e., projection overlaps that do not lead to artifacts in the reconstructed image, were formally defined and proved, and were validated via simulations. In this work, a new proposition is introduced to extend the previously defined type-II artifact-free projection overlaps so that a broader range of artifact-free overlaps is accommodated. One practical purpose of the new extension is to design a baffle window multipinhole system with artifact-free projection overlaps. Methods: First, the extended type-II artifact-free overlap was theoretically defined and proved. The new proposition accommodates the situation where the extended type-II artifact-free projection overlaps can be produced with incorrectly reconstructed portions in the reconstructed image. Next, to validate the theory, the extended-type-II artifact-free overlaps were employed in designing the multiplexing multipinhole spiral orbit imaging systems with a baffle window. Numerical validations were performed via simulations, where the corresponding 1-pinhole nonmultiplexing reconstruction results were used as the benchmark for artifact-free reconstructions. The mean square error (MSE) was the metric used for comparisons of noise-free reconstructed images. Noisy reconstructions were also performed as part of the validations. Results: Simulation results show that for noise-free reconstructions, the MSEs of the reconstructed images of the artifact-free multiplexing systems are very similar to those of the corresponding 1-pinhole systems. No artifacts were observed in the reconstructed images. Therefore, the testing results for artifact-free multiplexing systems designed using the

  7. Prior-based artifact correction (PBAC) in computed tomography

    International Nuclear Information System (INIS)

    Heußer, Thorsten; Brehm, Marcus; Ritschl, Ludwig; Sawall, Stefan; Kachelrieß, Marc

    2014-01-01

    Purpose: Image quality in computed tomography (CT) often suffers from artifacts which may reduce the diagnostic value of the image. In many cases, these artifacts result from missing or corrupt regions in the projection data, e.g., in the case of metal, truncation, and limited angle artifacts. The authors propose a generalized correction method for different kinds of artifacts resulting from missing or corrupt data by making use of available prior knowledge to perform data completion. Methods: The proposed prior-based artifact correction (PBAC) method requires prior knowledge in form of a planning CT of the same patient or in form of a CT scan of a different patient showing the same body region. In both cases, the prior image is registered to the patient image using a deformable transformation. The registered prior is forward projected and data completion of the patient projections is performed using smooth sinogram inpainting. The obtained projection data are used to reconstruct the corrected image. Results: The authors investigate metal and truncation artifacts in patient data sets acquired with a clinical CT and limited angle artifacts in an anthropomorphic head phantom data set acquired with a gantry-based flat detector CT device. In all cases, the corrected images obtained by PBAC are nearly artifact-free. Compared to conventional correction methods, PBAC achieves better artifact suppression while preserving the patient-specific anatomy at the same time. Further, the authors show that prominent anatomical details in the prior image seem to have only minor impact on the correction result. Conclusions: The results show that PBAC has the potential to effectively correct for metal, truncation, and limited angle artifacts if adequate prior data are available. Since the proposed method makes use of a generalized algorithm, PBAC may also be applicable to other artifacts resulting from missing or corrupt data

  8. Medical image of the week: polysomnogram artifact

    Directory of Open Access Journals (Sweden)

    Bartell J

    2015-02-01

    Full Text Available A 54 year-old man with a past medical history of attention deficit hyperactivity disorder (ADHD, low back pain, and paroxysmal supraventricular tachycardia presented to the sleep laboratory for evaluation of sleep disordered breathing. Pertinent medications include fluoxetine, ambien, and clonazepam. His Epworth sleepiness score was 18. He had a total sleep time of 12 min. On the night of his sleep study, the patient was restless and repeatedly changed positions in bed. Figures 1 and 2 show the artifact determined to be lead displacement of O1M2 after the patient shifted in bed, inadvertently removing one of his scalp electrodes. The sine waves are 60 Hz in frequency. Once the problem was identified, the lead was quickly replaced to its proper position.

  9. Persuasion through artifacts: Sociological and psychological dimensions

    Directory of Open Access Journals (Sweden)

    Stroe Mihaela

    2015-01-01

    Full Text Available Research suggests that applicants use various impression management tactics during employment interviews to influence interviewers' evaluations of their performance. Yet, little research has examined inteviewers/perceptions of applicant's impression management and their degree of nonverbal influence. This PhD study examines these questions, using both quantitative and qualitative data: Do interviewers accurately perceive applicant's impression management tactics? How are these perceptions integrated into their evaluations of applicant's nonverbal behaviour? Is perception accuracy influenced by artifacts (professional clothing that interviewees wear? It has cross-cultural design, because describes the differences in European Commission interviewers' social perceptions and Romanian human resources managers on one hand, and between social perceptions of European Commission public servants and Romanian employees on the other hand, concerning 12 key concepts: persuasion, first impressions, professional image, credibility, authenticity, competence, self- confidence, self-management, self-presentation, self-promotion, impression management tactics, professional appearance.

  10. Artifact free T2{sup *}-weighted imaging at high spatial resolution using segmented EPI sequences

    Energy Technology Data Exchange (ETDEWEB)

    Heiler, Patrick Michael; Schad, Lothar Rudi [Heidelberg Univ., Mannheim (Germany). Computer Assisted Clinical Medicine; Schmitter, Sebastian [German Cancer Research Center, Heidelberg (Germany). Dept. of Medical Physics in Radiology

    2010-07-01

    The aim of this work was the development of novel measurement techniques that acquire high resolution T2{sup *}-weighted datasets in measurement times as short as possible without suffering from noticeable blurring and ghosting artifacts. Therefore, two new measurement techniques were developed that acquire a smoother k-space than generic multi shot echo planar imaging sequences. One is based on the principle of echo train shifting, the other on the reversed gradient method. Simulations and phantom measurements demonstrate that echo train shifting works properly and reduces artifacts in multi shot echo planar imaging. For maximum SNR-efficiency this technique was further improved by adding a second contrast. Both contrasts can be acquired within a prolongation in measurement time by a factor of 1.5, leading to an SNR increase by approximately {radical}2. Furthermore it is demonstrated that the reversed gradient method remarkably reduces artifacts caused by a discontinuous k-space weighting. Assuming sequence parameters as feasible for fMRI experiments, artifact free T2{sup *}-weighted images with a matrix size of 256 x 256 leading to an in-plane resolution in the submillimeter range can be obtained in about 2 s per slice. (orig.)

  11. Artifact Reduction of Susceptibility-Weighted Imaging Using a Short-Echo Phase Mask

    International Nuclear Information System (INIS)

    Ishimori, Y.; Monma, M.; Kohno, Y.

    2009-01-01

    Background: Susceptibility-weighted imaging (SWI) is utilized in magnetic resonance (MR) venography and other applications, but can include artifacts caused by the phase-masking process. Purpose: To demonstrate risks of filter processes used in making phase masks for SWI, and to propose a simple method for reducing artifacts. Material and Methods: Phase linearity related to echo time (TE) was evaluated for the original phase and high-pass-filtered phase using a CuSO 4 -doped water phantom. Effect of filter size of the Hanning window and background homogeneity were also evaluated in a phantom study. Use of a phase mask generated by data with differing magnitudes of TE was attempted in a human study. Shorter TE was used for making the phase mask, and the number of multiplications was increased. As short and long TEs were necessary simultaneously for phase mask and T2* contrast, a dual-echo technique was used. Results: Linearity of TE and phase value collapsed, and an unexpected negative phase appeared in the high-pass-filtered phase. Using a short-TE phase mask, phase-aliasing artifacts were reduced and visibility of deep veins was equivalent to that under conventional methods with an increased number of multiplications. Conclusion: Use of a short-echo phase mask in SWI is useful for reducing artifacts

  12. Artifact free T2*-weighted imaging at high spatial resolution using segmented EPI sequences

    International Nuclear Information System (INIS)

    Heiler, Patrick Michael; Schad, Lothar Rudi; Schmitter, Sebastian

    2010-01-01

    The aim of this work was the development of novel measurement techniques that acquire high resolution T2 * -weighted datasets in measurement times as short as possible without suffering from noticeable blurring and ghosting artifacts. Therefore, two new measurement techniques were developed that acquire a smoother k-space than generic multi shot echo planar imaging sequences. One is based on the principle of echo train shifting, the other on the reversed gradient method. Simulations and phantom measurements demonstrate that echo train shifting works properly and reduces artifacts in multi shot echo planar imaging. For maximum SNR-efficiency this technique was further improved by adding a second contrast. Both contrasts can be acquired within a prolongation in measurement time by a factor of 1.5, leading to an SNR increase by approximately √2. Furthermore it is demonstrated that the reversed gradient method remarkably reduces artifacts caused by a discontinuous k-space weighting. Assuming sequence parameters as feasible for fMRI experiments, artifact free T2 * -weighted images with a matrix size of 256 x 256 leading to an in-plane resolution in the submillimeter range can be obtained in about 2 s per slice. (orig.)

  13. Artifact Reduction of Susceptibility-Weighted Imaging Using a Short-Echo Phase Mask

    Energy Technology Data Exchange (ETDEWEB)

    Ishimori, Y.; Monma, M. (Dept. of Radiological Sciences, Ibaraki Prefectural Univ. of Health Sciences, Inashiki-gun, Ibaraki (Japan)); Kohno, Y. (Dept. of Neurology, Ibaraki Prefectural Univ. of Health Sciences, Inashiki-gun, Ibaraki (Japan))

    2009-11-15

    Background: Susceptibility-weighted imaging (SWI) is utilized in magnetic resonance (MR) venography and other applications, but can include artifacts caused by the phase-masking process. Purpose: To demonstrate risks of filter processes used in making phase masks for SWI, and to propose a simple method for reducing artifacts. Material and Methods: Phase linearity related to echo time (TE) was evaluated for the original phase and high-pass-filtered phase using a CuSO{sub 4}-doped water phantom. Effect of filter size of the Hanning window and background homogeneity were also evaluated in a phantom study. Use of a phase mask generated by data with differing magnitudes of TE was attempted in a human study. Shorter TE was used for making the phase mask, and the number of multiplications was increased. As short and long TEs were necessary simultaneously for phase mask and T2 contrast, a dual-echo technique was used. Results: Linearity of TE and phase value collapsed, and an unexpected negative phase appeared in the high-pass-filtered phase. Using a short-TE phase mask, phase-aliasing artifacts were reduced and visibility of deep veins was equivalent to that under conventional methods with an increased number of multiplications. Conclusion: Use of a short-echo phase mask in SWI is useful for reducing artifacts

  14. The "Air in the CT X-ray Tube Oil" Artifact-Examples of the Quality Control Images and the Evaluation of Four Potential Clinical Patients' Head Computed Tomography Cases.

    Science.gov (United States)

    Törmänen, Juhani; Rautiainen, Jari; Tahvonen, Pirita; Leinonen, Kimmo; Nieminen, Miika T; Tervonen, Osmo

    We present a newly reposted scanner-based artifact-with 4 potential patients' head computed tomography (CT) cases-the "Air in the CT X-ray Tube Oil" artifact with a 64-slice multidetector CT. This artifact mimics diseases, which cause hypodense findings in CT images. It can be difficult to notice in the clinical patient imaging but can be also very difficult to verify in quality control tests.

  15. On Lifecycle Constraints of Artifact-Centric Workflows

    Science.gov (United States)

    Kucukoguz, Esra; Su, Jianwen

    Data plays a fundamental role in modeling and management of business processes and workflows. Among the recent "data-aware" workflow models, artifact-centric models are particularly interesting. (Business) artifacts are the key data entities that are used in workflows and can reflect both the business logic and the execution states of a running workflow. The notion of artifacts succinctly captures the fluidity aspect of data during workflow executions. However, much of the technical dimension concerning artifacts in workflows is not well understood. In this paper, we study a key concept of an artifact "lifecycle". In particular, we allow declarative specifications/constraints of artifact lifecycle in the spirit of DecSerFlow, and formulate the notion of lifecycle as the set of all possible paths an artifact can navigate through. We investigate two technical problems: (Compliance) does a given workflow (schema) contain only lifecycle allowed by a constraint? And (automated construction) from a given lifecycle specification (constraint), is it possible to construct a "compliant" workflow? The study is based on a new formal variant of artifact-centric workflow model called "ArtiNets" and two classes of lifecycle constraints named "regular" and "counting" constraints. We present a range of technical results concerning compliance and automated construction, including: (1) compliance is decidable when workflow is atomic or constraints are regular, (2) for each constraint, we can always construct a workflow that satisfies the constraint, and (3) sufficient conditions where atomic workflows can be constructed.

  16. Contrast artifacts in tapping tip atomic force microscopy

    DEFF Research Database (Denmark)

    Kyhle, Anders; Sørensen, Alexis Hammer; Zandbergen, Julie Bjerring

    1998-01-01

    When recording images with an atomic force microscope using the resonant vibrating cantilever mode, surprising strange results are often achieved. Typical artifacts are strange contours, unexpected height shifts, and sudden changes of the apparent resolution in the acquired images. Such artifacts...

  17. How Do Artifact Models Help Direct SPI Projects?

    DEFF Research Database (Denmark)

    Kuhrmann, Marco; Richardson, Ita

    2015-01-01

    To overcome shortcomings associated with software process improvement (SPI), we previously recommended that process engineers focus on the artifacts to be developed in SPI projects. These artifacts should define desired outcomes, rather than specific methods. During this prior research, we develo...

  18. Making Digital Artifacts on the Web Verifiable and Reliable

    NARCIS (Netherlands)

    Kuhn, T.; Dumontier, M.

    2015-01-01

    The current Web has no general mechanisms to make digital artifacts - such as datasets, code, texts, and images - verifiable and permanent. For digital artifacts that are supposed to be immutable, there is moreover no commonly accepted method to enforce this immutability. These shortcomings have a

  19. Incidental ferumoxytol artifacts in clinical brain MR imaging

    Energy Technology Data Exchange (ETDEWEB)

    Bowser, Bruce A.; Campeau, Norbert G.; Carr, Carrie M.; Diehn, Felix E.; McDonald, Jennifer S.; Miller, Gary M.; Kaufmann, Timothy J. [Mayo Clinic, Department of Radiology, Rochester, MN (United States)

    2016-11-15

    Ferumoxytol (Feraheme) is a parenteral therapy approved for treatment of iron deficiency anemia. The product insert for ferumoxytol states that it may affect the diagnostic ability of MRI for up to 3 months. However, the expected effects may not be commonly recognized among clinical neuroradiologists. Our purpose is to describe the artifacts we have seen at our institution during routine clinical practice. We reviewed the patients at our institution that had brain MRI performed within 90 days of receiving intravenous ferumoxytol. The imaging was reviewed for specific findings, including diffusion-weighted imaging vascular susceptibility artifact, gradient-echo echo-planar T2*-weighted vascular susceptibility artifact, SWI/SWAN vascular susceptibility artifact, hypointense vascular signal on T2-weighted images, pre-gadolinium contrast vascular enhancement on magnetization-prepared rapid acquisition gradient echo (MPRAGE) imaging, and effects on post-gadolinium contrast T1 imaging. Multiple artifacts were observed in patients having a brain MRI within 3 days of receiving intravenous ferumoxytol. These included susceptibility artifact on DWI, GRE, and SWAN/SWI imaging, pre-gadolinium contrast increased vascular signal on MPRAGE imaging, and decreased expected enhancement on post-gadolinium contrast T1-weighted imaging. Ferumoxytol can create imaging artifacts which complicate clinical interpretation when brain MRI is performed within 3 days of administration. Recognition of the constellation of artifacts produced by ferumoxytol is important in order to obviate additional unnecessary examinations and mitigate errors in interpretation. (orig.)

  20. Quantification of Rain Induced Artifacts on Digital Satellite Television ...

    African Journals Online (AJOL)

    The presence of artifacts on the high definition television (TV) content and the eventual loss of the digital TV signals to rain is still a major concern to satellite operators, digital satellite television (DSTV) and terrestrial television content providers. In this paper, the artifacts present in a typical DSTV signal is examined on a ...

  1. Removing Contamination-Induced Reconstruction Artifacts from Cryo-electron Tomograms

    Science.gov (United States)

    Fernandez, Jose-Jesus; Laugks, Ulrike; Schaffer, Miroslava; Bäuerlein, Felix J.B.; Khoshouei, Maryam; Baumeister, Wolfgang; Lucic, Vladan

    2016-01-01

    Imaging of fully hydrated, vitrified biological samples by electron tomography yields structural information about cellular protein complexes in situ. Here we present a computational procedure that removes artifacts of three-dimensional reconstruction caused by contamination present in samples during imaging by electron microscopy. Applying the procedure to phantom data and electron tomograms of cellular samples significantly improved the resolution and the interpretability of tomograms. Artifacts caused by surface contamination associated with thinning by focused ion beam, as well as those arising from gold fiducial markers and from common, lower contrast contamination, could be removed. Our procedure is widely applicable and is especially suited for applications that strive to reach a higher resolution and involve the use of recently developed, state-of-the-art instrumentation. PMID:26743046

  2. Residual setup errors caused by rotation and non-rigid motion in prone-treated cervical cancer patients after online CBCT image-guidance

    International Nuclear Information System (INIS)

    Ahmad, Rozilawati; Hoogeman, Mischa S.; Quint, Sandra; Mens, Jan Willem; Osorio, Eliana M. Vásquez; Heijmen, Ben J.M.

    2012-01-01

    Purpose: To quantify the impact of uncorrected or partially corrected pelvis rotation and spine bending on region-specific residual setup errors in prone-treated cervical cancer patients. Methods and materials: Fifteen patients received an in-room CBCT scan twice a week. CBCT scans were registered to the planning CT-scan using a pelvic clip box and considering both translations and rotations. For daily correction of the detected translational pelvis setup errors by couch shifts, residual setup errors were determined for L5, L4 and seven other points of interest (POIs). The same was done for a procedure with translational corrections and limited rotational correction (±3°) by a 6D positioning device. Results: With translational correction only, residual setup errors were large especially for L5/L4 in AP direction (Σ = 5.1/5.5 mm). For the 7 POIs the residual setup errors ranged from 1.8 to 5.6 mm (AP). Using the 6D positioning device, the errors were substantially smaller (for L5/L4 in AP direction Σ = 2.7/2.2 mm). Using this device, the percentage of fractions with a residual AP displacement for L4 > 5 mm reduced from 47% to 9%. Conclusions: Setup variations caused by pelvis rotations are large and cannot be ignored in prone treatment of cervical cancer patients. Corrections with a 6D positioning device may considerably reduce resulting setup errors, but the residual setup errors should still be accounted for by appropriate CTV-to-PTV margins.

  3. Investigation of the saturation pulse artifact in non-enhanced MR angiography of the lower extremity arteries at 7 Tesla.

    Directory of Open Access Journals (Sweden)

    Sören Johst

    Full Text Available When performing non-enhanced time-of-flight MR angiography of the lower extremity arteries at 7 T with cardiac triggering, the acquisition time is a crucial consideration. Therefore, in previous studies, saturation RF pulses were applied only every second TR. In the axial source images a slight artifact with an appearance similar to aliasing could be observed. The purpose of this study was to investigate the origin of this artifact. The reason for the artifact is supposed to be related to the two effective TRs during acquisition caused by the sparsely applied saturation RF pulse. Several sequence variants were simulated and implemented within the sequence source code to examine this hypothesis. An adaptation of the excitation flip angles for each TR as well as a correction factor for the k-space data was calculated. Additionally, a different ordering of the k-space data during acquisition was implemented as well as the combination of the latter with the k-space correction factor. The observations from the simulations were verified using both a static and a flow phantom and, finally, in a healthy volunteer using the same measurement setup as in previous volunteer and patient studies. Of all implemented techniques, only the reordering of the k-space was capable of suppressing the artifact almost completely at the cost of creating a ringing artifact. The phantom measurements showed the same results as the simulations and could thus confirm the hypothesis regarding the origin of the artifact. This was additionally verified in the healthy volunteer. The origin of the artifact could be confirmed to be the periodic signal variation caused by two effective TRs during acquisition.

  4. Investigation of the saturation pulse artifact in non-enhanced MR angiography of the lower extremity arteries at 7 Tesla.

    Science.gov (United States)

    Johst, Sören; Maderwald, Stefan; Fischer, Anja; Quick, Harald H; Ladd, Mark E; Orzada, Stephan

    2015-01-01

    When performing non-enhanced time-of-flight MR angiography of the lower extremity arteries at 7 T with cardiac triggering, the acquisition time is a crucial consideration. Therefore, in previous studies, saturation RF pulses were applied only every second TR. In the axial source images a slight artifact with an appearance similar to aliasing could be observed. The purpose of this study was to investigate the origin of this artifact. The reason for the artifact is supposed to be related to the two effective TRs during acquisition caused by the sparsely applied saturation RF pulse. Several sequence variants were simulated and implemented within the sequence source code to examine this hypothesis. An adaptation of the excitation flip angles for each TR as well as a correction factor for the k-space data was calculated. Additionally, a different ordering of the k-space data during acquisition was implemented as well as the combination of the latter with the k-space correction factor. The observations from the simulations were verified using both a static and a flow phantom and, finally, in a healthy volunteer using the same measurement setup as in previous volunteer and patient studies. Of all implemented techniques, only the reordering of the k-space was capable of suppressing the artifact almost completely at the cost of creating a ringing artifact. The phantom measurements showed the same results as the simulations and could thus confirm the hypothesis regarding the origin of the artifact. This was additionally verified in the healthy volunteer. The origin of the artifact could be confirmed to be the periodic signal variation caused by two effective TRs during acquisition.

  5. A Single Image Deblurring Algorithm for Nonuniform Motion Blur Using Uniform Defocus Map Estimation

    Directory of Open Access Journals (Sweden)

    Chia-Feng Chang

    2017-01-01

    Full Text Available One of the most common artifacts in digital photography is motion blur. When capturing an image under dim light by using a handheld camera, the tendency of the photographer’s hand to shake causes the image to blur. In response to this problem, image deblurring has become an active topic in computational photography and image processing in recent years. From the view of signal processing, image deblurring can be reduced to a deconvolution problem if the kernel function of the motion blur is assumed to be shift invariant. However, the kernel function is not always shift invariant in real cases; for example, in-plane rotation of a camera or a moving object can blur different parts of an image according to different kernel functions. An image that is degraded by multiple blur kernels is called a nonuniform blur image. In this paper, we propose a novel single image deblurring algorithm for nonuniform motion blur images that is blurred by moving object. First, a proposed uniform defocus map method is presented for measurement of the amounts and directions of motion blur. These blurred regions are then used to estimate point spread functions simultaneously. Finally, a fast deconvolution algorithm is used to restore the nonuniform blur image. We expect that the proposed method can achieve satisfactory deblurring of a single nonuniform blur image.

  6. Distributed Cognition and Distributed Morality: Agency, Artifacts and Systems.

    Science.gov (United States)

    Heersmink, Richard

    2017-04-01

    There are various philosophical approaches and theories describing the intimate relation people have to artifacts. In this paper, I explore the relation between two such theories, namely distributed cognition and distributed morality theory. I point out a number of similarities and differences in these views regarding the ontological status they attribute to artifacts and the larger systems they are part of. Having evaluated and compared these views, I continue by focussing on the way cognitive artifacts are used in moral practice. I specifically conceptualise how such artifacts (a) scaffold and extend moral reasoning and decision-making processes, (b) have a certain moral status which is contingent on their cognitive status, and (c) whether responsibility can be attributed to distributed systems. This paper is primarily written for those interested in the intersection of cognitive and moral theory as it relates to artifacts, but also for those independently interested in philosophical debates in extended and distributed cognition and ethics of (cognitive) technology.

  7. Inter-slice motion correction using spatiotemporal interpolation for functional magnetic resonance imaging of the moving fetus

    OpenAIRE

    Limperopoulos, Catherine; You, Wonsang

    2017-01-01

    Fetal motion continues to be one of the major artifacts in in-utero functional MRI; interestingly few methods have been developed to address fetal motion correction. In this study, we propose a robust method for motion correction in fetal fMRI by which both inter-slice and inter-volume motion artifacts are jointly corrected. To accomplish this, an original volume is temporally split into odd and even slices, and then voxel intensities are spatially and temporally interpolated in the process o...

  8. Reduction of metal artifact in three-dimensional computed tomography (3D CT) with dental impression materials.

    Science.gov (United States)

    Park, W S; Kim, K D; Shin, H K; Lee, S H

    2007-01-01

    Metal Artifact still remains one of the main drawbacks in craniofacial Three-Dimensional Computed Tomography (3D CT). In this study, we tried to test the efficacy of additional silicone dental impression materials as a "tooth shield" for the reduction of metal artifact caused by metal restorations and orthodontic appliances. 6 phantoms with 4 teeth were prepared for this in vitro study. Orthodontic bracket, bands and amalgam restorations were placed in each tooth to reproduce various intraoral conditions. Standardized silicone shields were fabricated and placed around the teeth. CT image acquisition was performed with and without silicone shields. Maximum value, mean, and standard deviation of Hounsfield Units (HU) were compared with the presence of silicone shields. In every situation, metal artifacts were reduced in quality and quantity when silicone shields are used. Amalgam restoration made most serious metal artifact. Silicone shields made by dental impression material might be effective way to reduce the metal artifact caused by dental restoration and orthodontic appliances. This will help more excellent 3D image from 3D CT in craniofacial area.

  9. Potential hazards and artifacts of ferromagnetic and nonferromagnetic surgical and dental materials and devices in nuclear magnetic resonance imaging

    International Nuclear Information System (INIS)

    New, P.F.J.; Rosen, B.R.; Brady, T.J.

    1983-01-01

    The risks to patients with metal surgical implants who are undergoing nuclear magnetic resonance (NMR) imaging and the artifacts caused by such implants were studied. Twenty-one aneurysm and other hemostatic clips and a variety of other materials (e.g., dental amalgam, 14 karat gold) were used. Longitudinal forces and torques were found to be exerted upon 16 of the 21 clips. With five aneurysm clips, forces and torques sufficient to produce risk of hemorrhage from dislocation of the clip from the vessel or aneurysm, or cerebral injury by clip displacement without dislodgement were identified. The induced ferromagnetism was shown to be related to the composition of the alloys from which the clips were manufactured. Clips with 10-14% nickel are evidently without sufficient induced ferromagnetism to cause hazard. The extent of NMR imaging artifacts was greater for materials with measurable ferromagnetic properties, but metals without measurable ferromagnetism in our tests also resulted in significant artifacts. Dental amalgam and 14 karat gold produced no imaging artifacts, but stainless steels in dentures and orthodontic braces produced extensive artifacts in the facial region

  10. Development of a unique phantom to assess dose error of metal artifact in head and neck cancer

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Min Young; Kang, Sang Won; Suh, Tae Suk [Dept. of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul (Korea, Republic of); Lee, Jeong Woo [Dept. of Radiation Oncology, Konkuk University Medical Center, Seoul (Korea, Republic of); Park, Ji Yeon [Dept. of Pediatrics and Molecular Imaging Program at Stanford, Stanford University, Stanford (United States)

    2016-04-15

    The artifacts not only blur the CT images and lead to inaccuracies in diagnosis, but also make the delineation of anatomical structures intractable, which is important in image-guided intervention procedures. These artifacts obscure the underlying anatomy, leading to uncertainty in the delineation of the target volumes and compromising the integrity of the density representation that is crucial for accurate dose calculation. Because head and neck cancer patients tend to be over the age of 50 years, they constitute a group likely to have dental prostheses. This kind of side effects considerably disturbs the therapeutic procedure. Radiation scatter from high atomic number (Z) materials is established to cause both soft tissue and bony complications in the oral cavity, making scattered radiation an important factor in head and neck region radiotherapy planning. In this study, we carried out theoretical analysis of the metal artifact, that is, streak artifact and dark artifact, and also critical analysis of dosimetric effect which cause by dental implants in CT images of head and neck cancer patients with the genuine teeth and implants inserted humanoid phantom. The phantom provides a unique and useful tool in head and neck dosimetry research. It can be used in the development of new imaging instrumentation, image acquisition strategies, and image processing and reconstruction methods.

  11. Iterative metal artifact reduction for x-ray computed tomography using unmatched projector/backprojector pairs

    International Nuclear Information System (INIS)

    Zhang, Hanming; Wang, Linyuan; Li, Lei; Cai, Ailong; Hu, Guoen; Yan, Bin

    2016-01-01

    inspecting regions of interest and by comparing the root-mean-square errors, normalized mean absolute distance, and universal quality index metrics of the images. Both iFBP-TV and TV-FADM methods outperform other counterparts in all cases. Unlike the conventional iterative methods, the proposed strategy utilizing unmatched projector/backprojector pairs shows excellent performance in detail preservation and prevention of the introduction of new artifacts. Conclusions: Qualitative and quantitative evaluations of experimental results indicate that the developed method outperforms classical MAR algorithms in suppressing streak artifacts and preserving the edge structural information of the object. In particular, structures lying close to metals can be gradually recovered because of the reduction of artifacts caused by inconsistency effects.

  12. Artificial neural network for suppression of banding artifacts in balanced steady-state free precession MRI.

    Science.gov (United States)

    Kim, Ki Hwan; Park, Sung-Hong

    2017-04-01

    The balanced steady-state free precession (bSSFP) MR sequence is frequently used in clinics, but is sensitive to off-resonance effects, which can cause banding artifacts. Often multiple bSSFP datasets are acquired at different phase cycling (PC) angles and then combined in a special way for banding artifact suppression. Many strategies of combining the datasets have been suggested for banding artifact suppression, but there are still limitations in their performance, especially when the number of phase-cycled bSSFP datasets is small. The purpose of this study is to develop a learning-based model to combine the multiple phase-cycled bSSFP datasets for better banding artifact suppression. Multilayer perceptron (MLP) is a feedforward artificial neural network consisting of three layers of input, hidden, and output layers. MLP models were trained by input bSSFP datasets acquired from human brain and knee at 3T, which were separately performed for two and four PC angles. Banding-free bSSFP images were generated by maximum-intensity projection (MIP) of 8 or 12 phase-cycled datasets and were used as targets for training the output layer. The trained MLP models were applied to another brain and knee datasets acquired with different scan parameters and also to multiple phase-cycled bSSFP functional MRI datasets acquired on rat brain at 9.4T, in comparison with the conventional MIP method. Simulations were also performed to validate the MLP approach. Both the simulations and human experiments demonstrated that MLP suppressed banding artifacts significantly, superior to MIP in both banding artifact suppression and SNR efficiency. MLP demonstrated superior performance over MIP for the 9.4T fMRI data as well, which was not used for training the models, while visually preserving the fMRI maps very well. Artificial neural network is a promising technique for combining multiple phase-cycled bSSFP datasets for banding artifact suppression. Copyright © 2016 Elsevier Inc. All

  13. Adiabatic Low-Pass J Filters for Artifact Suppression in Heteronuclear NMR

    DEFF Research Database (Denmark)

    Meier, Sebastian; Benie, Andrew J; Duus, Jens Øllgaard

    2009-01-01

    NMR artifact purging: Modern NMR experiments depend on efficient coherence transfer pathways for their sensitivity and on suppression of undesired pathways leading to artifacts for their spectral clarity. A novel robust adiabatic element suppresses hard-to-get-at artifacts....

  14. Searching for alien artifacts on the moon

    Science.gov (United States)

    Davies, P. C. W.; Wagner, R. V.

    2013-08-01

    The Search for Extraterrestrial Intelligence (SETI) has a low probability of success, but it would have a high impact if successful. Therefore it makes sense to widen the search as much as possible within the confines of the modest budget and limited resources currently available. To date, SETI has been dominated by the paradigm of seeking deliberately beamed radio messages. However, indirect evidence for extraterrestrial intelligence could come from any incontrovertible signatures of non-human technology. Existing searchable databases from astronomy, biology, earth and planetary sciences all offer low-cost opportunities to seek a footprint of extraterrestrial technology. In this paper we take as a case study one particular new and rapidly-expanding database: the photographic mapping of the Moon's surface by the Lunar Reconnaissance Orbiter (LRO) to 0.5 m resolution. Although there is only a tiny probability that alien technology would have left traces on the moon in the form of an artifact or surface modification of lunar features, this location has the virtue of being close, and of preserving traces for an immense duration. Systematic scrutiny of the LRO photographic images is being routinely conducted anyway for planetary science purposes, and this program could readily be expanded and outsourced at little extra cost to accommodate SETI goals, after the fashion of the SETI@home and Galaxy Zoo projects.

  15. Ground motion predictions

    Energy Technology Data Exchange (ETDEWEB)

    Loux, P C [Environmental Research Corporation, Alexandria, VA (United States)

    1969-07-01

    Nuclear generated ground motion is defined and then related to the physical parameters that cause it. Techniques employed for prediction of ground motion peak amplitude, frequency spectra and response spectra are explored, with initial emphasis on the analysis of data collected at the Nevada Test Site (NTS). NTS postshot measurements are compared with pre-shot predictions. Applicability of these techniques to new areas, for example, Plowshare sites, must be questioned. Fortunately, the Atomic Energy Commission is sponsoring complementary studies to improve prediction capabilities primarily in new locations outside the NTS region. Some of these are discussed in the light of anomalous seismic behavior, and comparisons are given showing theoretical versus experimental results. In conclusion, current ground motion prediction techniques are applied to events off the NTS. Predictions are compared with measurements for the event Faultless and for the Plowshare events, Gasbuggy, Cabriolet, and Buggy I. (author)

  16. Ground motion predictions

    International Nuclear Information System (INIS)

    Loux, P.C.

    1969-01-01

    Nuclear generated ground motion is defined and then related to the physical parameters that cause it. Techniques employed for prediction of ground motion peak amplitude, frequency spectra and response spectra are explored, with initial emphasis on the analysis of data collected at the Nevada Test Site (NTS). NTS postshot measurements are compared with pre-shot predictions. Applicability of these techniques to new areas, for example, Plowshare sites, must be questioned. Fortunately, the Atomic Energy Commission is sponsoring complementary studies to improve prediction capabilities primarily in new locations outside the NTS region. Some of these are discussed in the light of anomalous seismic behavior, and comparisons are given showing theoretical versus experimental results. In conclusion, current ground motion prediction techniques are applied to events off the NTS. Predictions are compared with measurements for the event Faultless and for the Plowshare events, Gasbuggy, Cabriolet, and Buggy I. (author)

  17. A Combined Methodology to Eliminate Artifacts in Multichannel Electrogastrogram Based on Independent Component Analysis and Ensemble Empirical Mode Decomposition.

    Science.gov (United States)

    Sengottuvel, S; Khan, Pathan Fayaz; Mariyappa, N; Patel, Rajesh; Saipriya, S; Gireesan, K

    2018-06-01

    Cutaneous measurements of electrogastrogram (EGG) signals are heavily contaminated by artifacts due to cardiac activity, breathing, motion artifacts, and electrode drifts whose effective elimination remains an open problem. A common methodology is proposed by combining independent component analysis (ICA) and ensemble empirical mode decomposition (EEMD) to denoise gastric slow-wave signals in multichannel EGG data. Sixteen electrodes are fixed over the upper abdomen to measure the EGG signals under three gastric conditions, namely, preprandial, postprandial immediately, and postprandial 2 h after food for three healthy subjects and a subject with a gastric disorder. Instantaneous frequencies of intrinsic mode functions that are obtained by applying the EEMD technique are analyzed to individually identify and remove each of the artifacts. A critical investigation on the proposed ICA-EEMD method reveals its ability to provide a higher attenuation of artifacts and lower distortion than those obtained by the ICA-EMD method and conventional techniques, like bandpass and adaptive filtering. Characteristic changes in the slow-wave frequencies across the three gastric conditions could be determined from the denoised signals for all the cases. The results therefore encourage the use of the EEMD-based technique for denoising gastric signals to be used in clinical practice.

  18. Physiological artifacts in scalp EEG and ear-EEG.

    Science.gov (United States)

    Kappel, Simon L; Looney, David; Mandic, Danilo P; Kidmose, Preben

    2017-08-11

    A problem inherent to recording EEG is the interference arising from noise and artifacts. While in a laboratory environment, artifacts and interference can, to a large extent, be avoided or controlled, in real-life scenarios this is a challenge. Ear-EEG is a concept where EEG is acquired from electrodes in the ear. We present a characterization of physiological artifacts generated in a controlled environment for nine subjects. The influence of the artifacts was quantified in terms of the signal-to-noise ratio (SNR) deterioration of the auditory steady-state response. Alpha band modulation was also studied in an open/closed eyes paradigm. Artifacts related to jaw muscle contractions were present all over the scalp and in the ear, with the highest SNR deteriorations in the gamma band. The SNR deterioration for jaw artifacts were in general higher in the ear compared to the scalp. Whereas eye-blinking did not influence the SNR in the ear, it was significant for all groups of scalps electrodes in the delta and theta bands. Eye movements resulted in statistical significant SNR deterioration in both frontal, temporal and ear electrodes. Recordings of alpha band modulation showed increased power and coherence of the EEG for ear and scalp electrodes in the closed-eyes periods. Ear-EEG is a method developed for unobtrusive and discreet recording over long periods of time and in real-life environments. This study investigated the influence of the most important types of physiological artifacts, and demonstrated that spontaneous activity, in terms of alpha band oscillations, could be recorded from the ear-EEG platform. In its present form ear-EEG was more prone to jaw related artifacts and less prone to eye-blinking artifacts compared to state-of-the-art scalp based systems.

  19. Towards a concept of community artifact ecology in HCI?

    DEFF Research Database (Denmark)

    Saad-Sulonen, Joanna; Korsgaard, Henrik

    or workplaces do. This has implications on understanding how to research and design HCI for communities but also on refining the ecological perspective in HCI. We look in particular at examples from preliminary research on a local self-organised urban community and discuss what existing concepts in the ecology......In this paper we introduce the concept of community artifact ecology. We argue that taking a community perspective on the concept of artifact ecologies is relevant in HCI because communities are also dealing with multitudes of artifacts, in ways di↵erent that individuals, organizations...

  20. Thermoluminescent determination of prehistoric heat treatment of chert artifacts

    International Nuclear Information System (INIS)

    Melcher, C.L.; Zimmerman, D.W.

    1977-01-01

    In recent years archeologists have become interested in the extent to which prehistoric peoples heat-treated chert prior to shaping it into tools. Thermoluminescent determination of the radiation dose accumulated by an artifact since it was formed or last heated provides a simple, reliable test for such heat treatment. This test can be applied to single artifacts without the need for raw source material for comparison. Results on 25 artifacts from four sites indicate that, for many chert sources, color and luster are not useful indicators of heat treatment by prehistoric peoples

  1. Artifacts Affecting Musculoskeletal Magnetic Resonance Imaging: Their Origins and Solutions.

    Science.gov (United States)

    Roth, Eira; Hoff, Michael; Richardson, Michael L; Ha, Alice S; Porrino, Jack

    2016-01-01

    Among articles within the radiology literature, few present the manifestations of magnetic resonance imaging artifacts in a clinically oriented manner. Recognizing such artifacts is imperative given the increasing clinical use of magnetic resonance imaging and the emphasis by the American Board of Radiology on practical physics applications. The purpose of this article is to present magnetic resonance physics principles visually and conceptually in the context of common musculoskeletal radiology artifacts and their solutions, described using nonmathematical explanations. Copyright © 2016 Elsevier Inc. All rights reserved.

  2. Artifact in Pediatric Oculomotor Findings during Videonystagmography: A Retrospective Analysis.

    Science.gov (United States)

    Doettl, Steven M; Plyler, Patrick N; McCaslin, Devin L

    2017-04-01

    Accurate measurement of oculomotor function using videonystagmography (VNG) is imperative for diagnosis and management of patients with reported dizziness. The oculomotor evaluation during VNG utilizes video-oculography providing valuable information regarding the central structures and pathways that control eye movements. Artifact may have an effect on the overall validity and reliability of VNG oculomotor tracings and can result from patient and/or recording errors. It is postulated that artifact could occur more frequently in the pediatric population due to both patient and equipment factors. The purpose of this study was to systematically evaluate the occurrence and impact of artifact on saccades, smooth pursuit, and optokinetic (OPK) testing in normal pediatric and adult subjects using commercially available clinical VNG equipment and standard clinical protocols for oculomotor testing. The present study utilized a retrospective analysis of a repeated measures design. Oculomotor results from a total of 62 participants were analyzed. Portions of these data have been presented in a previous research study. Group 1 consisted of twenty-nine 4- to 6-yr-olds with an average age of 4.86 (SD = 0.88) yr. Group 2 consisted of thirty-three 22- to 44-yr-olds with an average age of 25.2 (SD = 5.34) yr. Raw oculomotor recordings were analyzed "offline" by a single masked, trained investigator. Each tracing was evaluated for instances of artifact including eye blinks, eye closure, eyes moving in opposite direction of the target, eye tracking software problems, and overall poor morphology. The number of instances of artifact were noted and recorded for each participant in both groups. Individual eye movements not affected by artifact were included for final analysis. Artifact rejection techniques were also compared. The results indicated increased artifact for the pediatric group for saccade and smooth pursuit testing. Additionally, a significant decrease in instances of

  3. Applications of Phase-Based Motion Processing

    Science.gov (United States)

    Branch, Nicholas A.; Stewart, Eric C.

    2018-01-01

    Image pyramids provide useful information in determining structural response at low cost using commercially available cameras. The current effort applies previous work on the complex steerable pyramid to analyze and identify imperceptible linear motions in video. Instead of implicitly computing motion spectra through phase analysis of the complex steerable pyramid and magnifying the associated motions, instead present a visual technique and the necessary software to display the phase changes of high frequency signals within video. The present technique quickly identifies regions of largest motion within a video with a single phase visualization and without the artifacts of motion magnification, but requires use of the computationally intensive Fourier transform. While Riesz pyramids present an alternative to the computationally intensive complex steerable pyramid for motion magnification, the Riesz formulation contains significant noise, and motion magnification still presents large amounts of data that cannot be quickly assessed by the human eye. Thus, user-friendly software is presented for quickly identifying structural response through optical flow and phase visualization in both Python and MATLAB.

  4. Implications of CT noise and artifacts for quantitative 99mTc SPECT/CT imaging

    International Nuclear Information System (INIS)

    Hulme, K. W.; Kappadath, S. C.

    2014-01-01

    Purpose: This paper evaluates the effects of computed tomography (CT) image noise and artifacts on quantitative single-photon emission computed-tomography (SPECT) imaging, with the aim of establishing an appropriate range of CT acquisition parameters for low-dose protocols with respect to accurate SPECT attenuation correction (AC). Methods: SPECT images of two geometric and one anthropomorphic phantom were reconstructed iteratively using CT scans acquired at a range of dose levels (CTDI vol = 0.4 to 46 mGy). Resultant SPECT image quality was evaluated by comparing mean signal, background noise, and artifacts to SPECT images reconstructed using the highest dose CT for AC. Noise injection was performed on linear-attenuation (μ) maps to determine the CT noise threshold for accurate AC. Results: High levels of CT noise (σ ∼ 200–400 HU) resulted in low μ-maps noise (σ ∼ 1%–3%). Noise levels greater than ∼10% in 140 keV μ-maps were required to produce visibly perceptible increases of ∼15% in 99m Tc SPECT images. These noise levels would be achieved at low CT dose levels (CTDI vol = 4 μGy) that are over 2 orders of magnitude lower than the minimum dose for diagnostic CT scanners. CT noise could also lower (bias) the expected μ values. The relative error in reconstructed SPECT signal trended linearly with the relative shift in μ. SPECT signal was, on average, underestimated in regions corresponding with beam-hardening artifacts in CT images. Any process that has the potential to change the CT number of a region by ∼100 HU (e.g., misregistration between CT images and SPECT images due to motion, the presence of contrast in CT images) could introduce errors in μ 140 keV on the order of 10%, that in turn, could introduce errors on the order of ∼10% into the reconstructed 99m Tc SPECT image. Conclusions: The impact of CT noise on SPECT noise was demonstrated to be negligible for clinically achievable CT parameters. Because CT dose levels that affect

  5. Accelerated acquisition of tagged MRI for cardiac motion correction in simultaneous PET-MR: Phantom and patient studies

    International Nuclear Information System (INIS)

    Huang, Chuan; Petibon, Yoann; Ouyang, Jinsong; El Fakhri, Georges; Reese, Timothy G.; Ahlman, Mark A.; Bluemke, David A.

    2015-01-01

    Purpose: Degradation of image quality caused by cardiac and respiratory motions hampers the diagnostic quality of cardiac PET. It has been shown that improved diagnostic accuracy of myocardial defect can be achieved by tagged MR (tMR) based PET motion correction using simultaneous PET-MR. However, one major hurdle for the adoption of tMR-based PET motion correction in the PET-MR routine is the long acquisition time needed for the collection of fully sampled tMR data. In this work, the authors propose an accelerated tMR acquisition strategy using parallel imaging and/or compressed sensing and assess the impact on the tMR-based motion corrected PET using phantom and patient data. Methods: Fully sampled tMR data were acquired simultaneously with PET list-mode data on two simultaneous PET-MR scanners for a cardiac phantom and a patient. Parallel imaging and compressed sensing were retrospectively performed by GRAPPA and kt-FOCUSS algorithms with various acceleration factors. Motion fields were estimated using nonrigid B-spline image registration from both the accelerated and fully sampled tMR images. The motion fields were incorporated into a motion corrected ordered subset expectation maximization reconstruction algorithm with motion-dependent attenuation correction. Results: Although tMR acceleration introduced image artifacts into the tMR images for both phantom and patient data, motion corrected PET images yielded similar image quality as those obtained using the fully sampled tMR images for low to moderate acceleration factors (<4). Quantitative analysis of myocardial defect contrast over ten independent noise realizations showed similar results. It was further observed that although the image quality of the motion corrected PET images deteriorates for high acceleration factors, the images were still superior to the images reconstructed without motion correction. Conclusions: Accelerated tMR images obtained with more than 4 times acceleration can still provide

  6. Accelerated acquisition of tagged MRI for cardiac motion correction in simultaneous PET-MR: Phantom and patient studies

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Chuan, E-mail: chuan.huang@stonybrookmedicine.edu [Center for Advanced Medical Imaging Sciences, Division of Nuclear Medicine and Molecular Imaging, Department of Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114 (United States); Department of Radiology, Harvard Medical School, Boston, Massachusetts 02115 (United States); Departments of Radiology, Psychiatry, Stony Brook Medicine, Stony Brook, New York 11794 (United States); Petibon, Yoann [Center for Advanced Medical Imaging Sciences, Division of Nuclear Medicine and Molecular Imaging, Department of Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114 (United States); Ouyang, Jinsong; El Fakhri, Georges [Center for Advanced Medical Imaging Sciences, Division of Nuclear Medicine and Molecular Imaging, Department of Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114 and Department of Radiology, Harvard Medical School, Boston, Massachusetts 02115 (United States); Reese, Timothy G. [Department of Radiology, Harvard Medical School, Boston, Massachusetts 02115 and Martinos Center for Biomedical Imaging, Charlestown, Massachusetts 02129 (United States); Ahlman, Mark A.; Bluemke, David A. [Radiology and Imaging Sciences, National Institutes of Health Clinical Center, Bethesda, Maryland 20892 (United States)

    2015-02-15

    Purpose: Degradation of image quality caused by cardiac and respiratory motions hampers the diagnostic quality of cardiac PET. It has been shown that improved diagnostic accuracy of myocardial defect can be achieved by tagged MR (tMR) based PET motion correction using simultaneous PET-MR. However, one major hurdle for the adoption of tMR-based PET motion correction in the PET-MR routine is the long acquisition time needed for the collection of fully sampled tMR data. In this work, the authors propose an accelerated tMR acquisition strategy using parallel imaging and/or compressed sensing and assess the impact on the tMR-based motion corrected PET using phantom and patient data. Methods: Fully sampled tMR data were acquired simultaneously with PET list-mode data on two simultaneous PET-MR scanners for a cardiac phantom and a patient. Parallel imaging and compressed sensing were retrospectively performed by GRAPPA and kt-FOCUSS algorithms with various acceleration factors. Motion fields were estimated using nonrigid B-spline image registration from both the accelerated and fully sampled tMR images. The motion fields were incorporated into a motion corrected ordered subset expectation maximization reconstruction algorithm with motion-dependent attenuation correction. Results: Although tMR acceleration introduced image artifacts into the tMR images for both phantom and patient data, motion corrected PET images yielded similar image quality as those obtained using the fully sampled tMR images for low to moderate acceleration factors (<4). Quantitative analysis of myocardial defect contrast over ten independent noise realizations showed similar results. It was further observed that although the image quality of the motion corrected PET images deteriorates for high acceleration factors, the images were still superior to the images reconstructed without motion correction. Conclusions: Accelerated tMR images obtained with more than 4 times acceleration can still provide

  7. Timing and related artifacts in multidimensional NMR

    International Nuclear Information System (INIS)

    Marion, Dominique

    2012-01-01

    The information content of multidimensional NMR spectra is limited by the presence of several kinds of artifacts that originate from incorrect timing of evolution periods. The objective of this review is to provide tools for successful implementation of published pulse sequences, in which timing and pulse compensations are often implicit. We will analyze the constraints set by the use of Fourier transformation, the spin precession during rectangular or shaped pulses, the Bloch-Siegert effects due to pulse on other spins and the delay introduced by the filters for the acquisition dimension. A frequency dependent phase correction or an incorrect scaling of the first data point leads to baseline offsets or curvature due to the properties of the Fourier transform. Because any r.f. pulse has a finite length, chemical shift is always active during excitation, flip-back, inversion, and refocusing pulses. Rectangular or selective shaped pulses can be split into three periods: an ideal rotation surrounded by two chemical shift evolution periods, which should be subtracted from the adjacent delays to avoid linear phase correction. Bloch-Siegert effects originate from irradiation at frequencies near those observed in the spectrum and can lead to phase or frequency shifts. They can be minimized by simultaneous irradiation on both sides of the observed spins. In terms of timing, the very end of the pulse sequence the acquisition behaves differently since the data are filtered by either analog or digital means. This additional delay is filter and spectrometer specific and should be tuned to minimize the required phase correction. Combined together, all these adjustments lead to perfectly phased spectra with flat baseline and no peak shifts or distortion. (author)

  8. Cultural Artifact Detection in Long Wave Infrared Imagery.

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, Dylan Zachary [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Craven, Julia M. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Ramon, Eric [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2017-01-01

    Detection of cultural artifacts from airborne remotely sensed data is an important task in the context of on-site inspections. Airborne artifact detection can reduce the size of the search area the ground based inspection team must visit, thereby improving the efficiency of the inspection process. This report details two algorithms for detection of cultural artifacts in aerial long wave infrared imagery. The first algorithm creates an explicit model for cultural artifacts, and finds data that fits the model. The second algorithm creates a model of the background and finds data that does not fit the model. Both algorithms are applied to orthomosaic imagery generated as part of the MSFE13 data collection campaign under the spectral technology evaluation project.

  9. Adaptive noise canceling of electrocardiogram artifacts in single channel electroencephalogram.

    Science.gov (United States)

    Cho, Sung Pil; Song, Mi Hye; Park, Young Cheol; Choi, Ho Seon; Lee, Kyoung Joung

    2007-01-01

    A new method for estimating and eliminating electrocardiogram (ECG) artifacts from single channel scalp electroencephalogram (EEG) is proposed. The proposed method consists of emphasis of QRS complex from EEG using least squares acceleration (LSA) filter, generation of synchronized pulse with R-peak and ECG artifacts estimation and elimination using adaptive filter. The performance of the proposed method was evaluated using simulated and real EEG recordings, we found that the ECG artifacts were successfully estimated and eliminated in comparison with the conventional multi-channel techniques, which are independent component analysis (ICA) and ensemble average (EA) method. From this we can conclude that the proposed method is useful for the detecting and eliminating the ECG artifacts from single channel EEG and simple to use for ambulatory/portable EEG monitoring system.

  10. quantification of rain quantification of rain induced artifacts on digital

    African Journals Online (AJOL)

    eobe

    DSTV) ... satellite television, rain attenuation, digital artifacts, pixelation, rainfall rate. 1. ... screen and blocking are commonly observed in .... The precipitation data was collected using a self- ..... Networks: Comparison at Equatorial and Subtropical.

  11. Visibility and artifacts of gold fiducial markers used for image guided radiation therapy of pancreatic cancer on MRI

    International Nuclear Information System (INIS)

    Gurney-Champion, Oliver J.; Lens, Eelco; Horst, Astrid van der; Houweling, Antonetta C.; Tienhoven, Geertjan van; Bel, Arjan; Klaassen, Remy; Hooft, Jeanin E. van; Stoker, Jaap; Nederveen, Aart J.

    2015-01-01

    Purpose: In radiation therapy of pancreatic cancer, tumor alignment prior to each treatment fraction is improved when intratumoral gold fiducial markers (from here onwards: markers), which are visible on computed tomography (CT) and cone beam CT, are used. Visibility of these markers on magnetic resonance imaging (MRI) might improve image registration between CT and magnetic resonance (MR) images for tumor delineation purposes. However, concomitant image artifacts induced by markers are undesirable. The extent of visibility and artifact size depend on MRI-sequence parameters. The authors’ goal was to determine for various markers their potential to be visible and to generate artifacts, using measures that are independent of the MRI-sequence parameters. Methods: The authors selected ten different markers suitable for endoscopic placement in the pancreas and placed them into a phantom. The markers varied in diameter (0.28–0.6 mm), shape, and iron content (0%–0.5%). For each marker, the authors calculated T 2 ∗ -maps and ΔB 0 -maps using MRI measurements. A decrease in relaxation time T 2 ∗ can cause signal voids, associated with visibility, while a change in the magnetic field B 0 can cause signal shifts, which are associated with artifacts. These shifts inhibit accurate tumor delineation. As a measure for potential visibility, the authors used the volume of low T 2 ∗ , i.e., the volume for which T 2 ∗ differed from the background by >15 ms. As a measure for potential artifacts, the authors used the volume for which |ΔB 0 | > 9.4 × 10 −8 T (4 Hz). To test whether there is a correlation between visibility and artifact size, the authors calculated the Spearman’s correlation coefficient (R s ) between the volume of low T 2 ∗ and the volume of high |ΔB 0 |. The authors compared the maps with images obtained using a clinical MR-sequence. Finally, for the best visible marker as well as the marker that showed the smallest artifact, the authors

  12. Ground motion effects

    Energy Technology Data Exchange (ETDEWEB)

    Blume, J A [John A. Blume and Associates, San Francisco, CA (United States)

    1969-07-01

    Ground motion caused by natural earthquakes or by nuclear explosion causes buildings and other structures to respond in such manner as possibly to have high unit stresses and to be subject to damage or-in some cases-collapse. Even minor damage may constitute a hazard to persons within or adjacent to buildings. The risk of damage may well be the governing restraint on the uses of nuclear energy for peaceful purposes. Theory is advanced regarding structural-dynamic response but real buildings and structures are complex, highly variable, and often difficult to model realistically. This paper discusses the state of knowledge, the art of damage prediction and safety precautions, and shows ground motion effects from explosions of underground nuclear devices in the continental United States including events Salmon, Gasbuggy, Boxcar, Faultless and Benham. (author)

  13. Ground motion effects

    International Nuclear Information System (INIS)

    Blume, J.A.

    1969-01-01

    Ground motion caused by natural earthquakes or by nuclear explosion causes buildings and other structures to respond in such manner as possibly to have high unit stresses and to be subject to damage or-in some cases-collapse. Even minor damage may constitute a hazard to persons within or adjacent to buildings. The risk of damage may well be the governing restraint on the uses of nuclear energy for peaceful purposes. Theory is advanced regarding structural-dynamic response but real buildings and structures are complex, highly variable, and often difficult to model realistically. This paper discusses the state of knowledge, the art of damage prediction and safety precautions, and shows ground motion effects from explosions of underground nuclear devices in the continental United States including events Salmon, Gasbuggy, Boxcar, Faultless and Benham. (author)

  14. Mitigation of artifacts in rtm with migration kernel decomposition

    KAUST Repository

    Zhan, Ge

    2012-01-01

    The migration kernel for reverse-time migration (RTM) can be decomposed into four component kernels using Born scattering and migration theory. Each component kernel has a unique physical interpretation and can be interpreted differently. In this paper, we present a generalized diffraction-stack migration approach for reducing RTM artifacts via decomposition of migration kernel. The decomposition leads to an improved understanding of migration artifacts and, therefore, presents us with opportunities for improving the quality of RTM images.

  15. Preliminary experimental insights into differential heat impact among lithic artifacts

    OpenAIRE

    Guillermo Bustos-Pérez; Javier Baena Preysler

    2016-01-01

    The presence of thermally altered and broken flint artifacts is common at archaeological sites. Most studies focus their attention on the effects of heat treatment on flint to improve knapping qualities, disregarding the effects of fire over flint under uncontrolled conditions. This paper aims to show how under uncontrolled heating processes flint artifacts develop different heat alterations (such as levels of breakage, presence of scales, etc.) as a result of vertical distribution, volume or...

  16. Cyber Event Artifact Investigation Training in a Virtual Environment

    Science.gov (United States)

    2017-12-01

    information was desired in the logs as well as best practices provided by Microsoft: 1. Every Success or Failure for: Account Logon Events, Account ...use this artifact in conjunction with information discovered through investigation of other artifacts, such as logs and accounts . For instance, the...when coupled with logs, accounts , and process data, this information may provide enough evidence for transition into the reporting and Preliminary

  17. Evaluation of motion and its effect on brain magnetic resonance image quality in children

    Energy Technology Data Exchange (ETDEWEB)

    Afacan, Onur; Erem, Burak; Roby, Diona P.; Prabhu, Sanjay P.; Warfield, Simon K. [Boston Children' s Hospital and Harvard Medical School, Department of Radiology, Boston, MA (United States); Roth, Noam; Roth, Amir [Robin Medical Inc., Baltimore, MD (United States)

    2016-11-15

    Motion artifacts pose significant problems for the acquisition of MR images in pediatric populations. To evaluate temporal motion metrics in MRI scanners and their effect on image quality in pediatric populations in neuroimaging studies. We report results from a large pediatric brain imaging study that shows the effect of motion on MRI quality. We measured motion metrics in 82 pediatric patients, mean age 13.4 years, in a T1-weighted brain MRI scan. As a result of technical difficulties, 5 scans were not included in the subsequent analyses. A radiologist graded the images using a 4-point scale ranging from clinically non-diagnostic because of motion artifacts to no motion artifacts. We used these grades to correlate motion parameters such as maximum motion, mean displacement from a reference point, and motion-free time with image quality. Our results show that both motion-free time (as a ratio of total scan time) and average displacement from a position at a fixed time (when the center of k-space was acquired) were highly correlated with image quality, whereas maximum displacement was not as good a predictor. Among the 77 patients whose motion was measured successfully, 17 had average displacements of greater than 0.5 mm, and 11 of those (14.3%) resulted in non-diagnostic images. Similarly, 14 patients (18.2%) had less than 90% motion-free time, which also resulted in non-diagnostic images. We report results from a large pediatric study to show how children and young adults move in the MRI scanner and the effect that this motion has on image quality. The results will help the motion-correction community in better understanding motion patterns in pediatric populations and how these patterns affect MR image quality. (orig.)

  18. Evaluation of motion and its effect on brain magnetic resonance image quality in children

    International Nuclear Information System (INIS)

    Afacan, Onur; Erem, Burak; Roby, Diona P.; Prabhu, Sanjay P.; Warfield, Simon K.; Roth, Noam; Roth, Amir

    2016-01-01

    Motion artifacts pose significant problems for the acquisition of MR images in pediatric populations. To evaluate temporal motion metrics in MRI scanners and their effect on image quality in pediatric populations in neuroimaging studies. We report results from a large pediatric brain imaging study that shows the effect of motion on MRI quality. We measured motion metrics in 82 pediatric patients, mean age 13.4 years, in a T1-weighted brain MRI scan. As a result of technical difficulties, 5 scans were not included in the subsequent analyses. A radiologist graded the images using a 4-point scale ranging from clinically non-diagnostic because of motion artifacts to no motion artifacts. We used these grades to correlate motion parameters such as maximum motion, mean displacement from a reference point, and motion-free time with image quality. Our results show that both motion-free time (as a ratio of total scan time) and average displacement from a position at a fixed time (when the center of k-space was acquired) were highly correlated with image quality, whereas maximum displacement was not as good a predictor. Among the 77 patients whose motion was measured successfully, 17 had average displacements of greater than 0.5 mm, and 11 of those (14.3%) resulted in non-diagnostic images. Similarly, 14 patients (18.2%) had less than 90% motion-free time, which also resulted in non-diagnostic images. We report results from a large pediatric study to show how children and young adults move in the MRI scanner and the effect that this motion has on image quality. The results will help the motion-correction community in better understanding motion patterns in pediatric populations and how these patterns affect MR image quality. (orig.)

  19. Metal Artifacts Reduction of Pedicle Screws on Spine Computed Tomography Images Using Variable Thresholding Technique

    International Nuclear Information System (INIS)

    Kaewlek, T.; Koolpiruck, D.; Thongvigitmanee, S.; Mongkolsuk, M.; Chiewvit, P.; Thammakittiphan, S.

    2012-01-01

    Metal artifacts are one of significant problems in computed tomography (CT). The streak lines and air gaps arise from metal implants of orthopedic patients, such as prosthesis, dental bucket, and pedicle screws that cause incorrect diagnosis and local treatment planning. A common technique to suppressed artifacts is by adjusting windows, but those artifacts still remain on the images. To improve the detail of spine CT images, the variable thresholding technique is proposed in this paper. Three medical cases of spine CT images categorized by the severity of artifacts (screws head, one full screw, and two full screws) were investigated. Metal regions were segmented by k-mean clustering, then transformed into a sinogram domain. The metal sinogram was identified by the variable thresholding method, and then replaced the new estimated values by linear interpolation. The modified sinogram was reconstructed by the filtered back- projection algorithm, and added the metal region back to the modified reconstructed image in order to reproduce the final image. The image quality of the proposed technique, the automatic thresholding (Kalender) technique, and window adjustment technique was compared in term of noise and signal to noise ratio (SNR). The propose method can reduce metal artifacts between pedicle screws. After processing by our proposed technique, noise in the modified images is reduced (screws head 121.15 to73.83, one full screw 160.88 to 94.04, and two full screws 199.73 to 110.05 from the initial image) and SNR is increased (screws head 0.87 to 1.88, one full screw 1.54 to 2.82, and two full screws 0.32 to 0.41 from the initial image). The variable thresholding technique can identify the suitable boundary for restoring the missing data. The efficiency of the metal artifacts reduction is indicated on the case of partial and full pedicle screws. Our technique can improve the detail of spine CT images better than automatic thresholding (Kalender) technique, and

  20. Universal artifacts affect the branching of phylogenetic trees, not universal scaling laws.

    Science.gov (United States)

    Altaba, Cristian R

    2009-01-01

    The superficial resemblance of phylogenetic trees to other branching structures allows searching for macroevolutionary patterns. However, such trees are just statistical inferences of particular historical events. Recent meta-analyses report finding regularities in the branching pattern of phylogenetic trees. But is this supported by evidence, or are such regularities just methodological artifacts? If so, is there any signal in a phylogeny? In order to evaluate the impact of polytomies and imbalance on tree shape, the distribution of all binary and polytomic trees of up to 7 taxa was assessed in tree-shape space. The relationship between the proportion of outgroups and the amount of imbalance introduced with them was assessed applying four different tree-building methods to 100 combinations from a set of 10 ingroup and 9 outgroup species, and performing covariance analyses. The relevance of this analysis was explored taking 61 published phylogenies, based on nucleic acid sequences and involving various taxa, taxonomic levels, and tree-building methods. All methods of phylogenetic inference are quite sensitive to the artifacts introduced by outgroups. However, published phylogenies appear to be subject to a rather effective, albeit rather intuitive control against such artifacts. The data and methods used to build phylogenetic trees are varied, so any meta-analysis is subject to pitfalls due to their uneven intrinsic merits, which translate into artifacts in tree shape. The binary branching pattern is an imposition of methods, and seldom reflects true relationships in intraspecific analyses, yielding artifactual polytomies in short trees. Above the species level, the departure of real trees from simplistic random models is caused at least by two natural factors--uneven speciation and extinction rates; and artifacts such as choice of taxa included in the analysis, and imbalance introduced by outgroups and basal paraphyletic taxa. This artifactual imbalance accounts

  1. SU-F-J-115: Target Volume and Artifact Evaluation of a New Device-Less 4D CT Algorithm

    Energy Technology Data Exchange (ETDEWEB)

    Martin, R; Pan, T [UT MD Anderson Cancer Center, Houston, TX (United States)

    2016-06-15

    Purpose: 4DCT is often used in radiation therapy treatment planning to define the extent of motion of the visible tumor (IGTV). Recent available software allows 4DCT images to be created without the use of an external motion surrogate. This study aims to compare this device-less algorithm to a standard device-driven technique (RPM) in regards to artifacts and the creation of treatment volumes. Methods: 34 lung cancer patients who had previously received a cine 4DCT scan on a GE scanner with an RPM determined respiratory signal were selected. Cine images were sorted into 10 phases based on both the RPM signal and the device-less algorithm. Contours were created on standard and device-less maximum intensity projection (MIP) images using a region growing algorithm and manual adjustment to remove other structures. Variations in measurements due to intra-observer differences in contouring were assessed by repeating a subset of 6 patients 2 additional times. Artifacts in each phase image were assessed using normalized cross correlation at each bed position transition. A score between +1 (artifacts “better” in all phases for device-less) and −1 (RPM similarly better) was assigned for each patient based on these results. Results: Device-less IGTV contours were 2.1 ± 1.0% smaller than standard IGTV contours (not significant, p = 0.15). The Dice similarity coefficient (DSC) was 0.950 ± 0.006 indicating good similarity between the contours. Intra-observer variation resulted in standard deviations of 1.2 percentage points in percent volume difference and 0.005 in DSC measurements. Only two patients had improved artifacts with RPM, and the average artifact score (0.40) was significantly greater than zero. Conclusion: Device-less 4DCT can be used in place of the standard method for target definition due to no observed difference between standard and device-less IGTVs. Phase image artifacts were significantly reduced with the device-less method.

  2. Historical Artifact Collection at the East Tennessee Technology Park

    International Nuclear Information System (INIS)

    Goodpasture, S.T.; Wood, S.K.

    2009-01-01

    The East Tennessee Technology Park (ETTP) was originally built during World War II as part of the Manhattan Project. Known as the K-25 Site, its primary mission was to enrich uranium for use in atomic weapons. During the Cold War, the site's mission was changed to include the enrichment of uranium for nuclear reactor fuel elements and to recycle spent fuel. In the 1980's, a reduction in the demand for nuclear fuel resulted in the shutdown of the enrichment process and production ceased. The emphasis of the mission for the ETTP was then changed to environmental management and restoration operation. Beginning in the 1990's, re-industrialization (conversion of under-utilized government facilities for use by the private sector) became a major mission at the ETTP. These activities involve cleaning and demolishing facilities. Decommission and demolition (D and D) of facilities at the ETTP or Manhattan Project K-25 Gaseous Diffusion Plant on the U.S. Department of Energy's (DOE) Oak Ridge Reservation (ORR) presented significant challenges complying with the requirements of the National Historic Preservation Act (NHPA) Memorandum of Agreement (MOA) that was negotiated with the stakeholders. Development of a process to identify, record and preserve the artifacts and the cooperation of several agencies and contractors were critical to completing the collection of the artifacts without impacting the D and D project schedule. Additional challenges included contaminated and classified artifacts, entry to facilities with hazardous conditions, schedule pressures and funding for collection and permanent storage. A process was developed to achieve compliance with the requirements of the NHPA. The NHPA requirements and implementing instruments at the ETTP as well as the process developed to preserve significant Manhattan Project era artifacts at the ETTP will be discussed. Implementation of the artifact collection process is also summarized. The challenge of complying with the

  3. Respiratory guiding system for respiratory motion management in respiratory gated radiotherapy

    International Nuclear Information System (INIS)

    Kang, Seong Hee; Kim, Dong Su; Kim, Tae Ho; Suh, Tae Suk

    2013-01-01

    Respiratory guiding systems have been shown to improve the respiratory regularity. This, in turn, improves the efficiency of synchronized moving aperture radiation therapy, and it reduces the artifacts caused by irregular breathing in imaging techniques such as four-dimensional computed tomography (4D CT), which is used for treatment planning in RGRT. We have previously developed a respiratory guiding system that incorporates an individual-specific guiding waveform, which is easy to follow for each volunteer, to improve the respiratory regularity. The present study evaluates the application of this system to improve the respiratory regularity for respiratory-gated radiation therapy (RGRT). In this study, we evaluated the effectiveness of an in-house-developed respiratory guiding system incorporating an individual specific guiding waveform to improve the respiratory regularity for RGRT. Most volunteers showed significantly less residual motion at each phase during guided breathing owing to the improvement in respiratory regularity. Therefore, the respiratory guiding system can clearly reduce the residual, or respiratory, motion in each phase. From the result, the CTV and the PTV margins during RGRT can be reduced by using the respiratory guiding system, which reduces the residual motions, thus improving the accuracy of RGRT

  4. Characterization of ultrasound elevation beamwidth artifacts for prostate brachytherapy needle insertion

    International Nuclear Information System (INIS)

    Peikari, Mohammad; Chen, Thomas Kuriran; Lasso, Anras; Heffter, Tamas; Fichtinger, Gabor; Burdette, Everette C.

    2012-01-01

    Purpose: Ultrasound elevation beamwidth leads to image artifacts and uncertainties in localizing objects (such as a surgical needle) in ultrasound images. The authors examined the clinical significance of errors caused by elevation beamwidth artifacts and imaging parameters in needle insertion procedures. Methods: Beveled prostate brachytherapy needles were inserted through all holes of a grid template under real-time transrectal ultrasound (TRUS) guidance. The needle tip position as indicated by the TRUS image was compared to their observed physical location. A new device was developed to measure the ultrasound elevation beamwidth. Results: Imaging parameters of the TRUS scanner have direct impact on the localization error ranging from 0.5 up to 4 mm. The smallest localization error was observed laterally close to the center of the grid template and axially within the beam's focal zone. Largest localization error occurs laterally around both sides of the grid template and axially within the beam's far field. The authors also found that the localization errors vary with both lateral and elevation offsets. Conclusions: The authors found properly adjusting the TRUS imaging settings to lower the ultrasound gain and power effectively minimized the appearance of elevation beamwidth artifacts and in turn reduced the localization errors of the needle tip.

  5. Management of respiratory motion in radiation oncology

    International Nuclear Information System (INIS)

    Vedam, Subrahmanya Sastry

    2003-01-01

    images obtained during simulation by reducing the motion artifacts typically seen during CT imaging. An analysis of several patient breathing patterns with (audio instructions and visual feedback) and without training, indicated that breathing training improved the reproducibility of amplitude and/or frequency of patient breathing cycles. A phantom based study by superposition of sinusoidal motion of a 'simulated' tumor onto the initial beam aperture as formed by the multileaf collimator revealed that target dose measurements obtained with such a motion synchronized setup were equivalent to those delivered to a static target by a static beam. An attempt to acquire respiration synchronized (4D) CT images of a motion phantom and a patient also yielded a 4D CT data set with reduced motion artifacts. Respiratory gated and respiration synchronized radiotherapy are both viable approaches to account for respiratory motion during radiotherapy. While respiratory gated radiotherapy has been successfully implemented in some centers, several technical advances are required for clinical implementation of respiration synchronized radiotherapy. Future applicability of either of the above approaches as routine treatment procedures will be determined by their potential clinical gains over currently available methods

  6. List mode reconstructions for PET with motion compensation: A simulation study

    International Nuclear Information System (INIS)

    Qi, Jinyi; Huesman, Ronald H.

    2002-01-01

    Motion artifacts can be a significant factor that limits the image quality in high-resolution PET. Surveillance systems have been developed to track the movements of the subject during a scan. Development of reconstruction algorithms that are able to compensate for the subject motion will increase the potential of PET. In this paper we present a list mode likelihood reconstruction algorithm with the ability of motion compensation. The subject motion is explicitly modeled in the likelihood function. The detections of each detector pair are modeled as a Poisson process with time-varying rate function. The proposed method has several advantages over the existing methods. It uses all detected events and does not introduce any interpolation error. Computer simulations show that the proposed method can compensate simulated subject movements and that the reconstructed images have no visible motion artifacts

  7. A novel forward projection-based metal artifact reduction method for flat-detector computed tomography

    Energy Technology Data Exchange (ETDEWEB)

    Prell, Daniel; Kyriakou, Yiannis; Beister, Marcel; Kalender, Willi A [Institute of Medical Physics, University of Erlangen-Nuernberg, Henkestrasse 91, 91052 Erlangen (Germany)], E-mail: daniel.prell@imp.uni-erlangen.de

    2009-11-07

    Metallic implants generate streak-like artifacts in flat-detector computed tomography (FD-CT) reconstructed volumetric images. This study presents a novel method for reducing these disturbing artifacts by inserting discarded information into the original rawdata using a three-step correction procedure and working directly with each detector element. Computation times are minimized by completely implementing the correction process on graphics processing units (GPUs). First, the original volume is corrected using a three-dimensional interpolation scheme in the rawdata domain, followed by a second reconstruction. This metal artifact-reduced volume is then segmented into three materials, i.e. air, soft-tissue and bone, using a threshold-based algorithm. Subsequently, a forward projection of the obtained tissue-class model substitutes the missing or corrupted attenuation values directly for each flat detector element that contains attenuation values corresponding to metal parts, followed by a final reconstruction. Experiments using tissue-equivalent phantoms showed a significant reduction of metal artifacts (deviations of CT values after correction compared to measurements without metallic inserts reduced typically to below 20 HU, differences in image noise to below 5 HU) caused by the implants and no significant resolution losses even in areas close to the inserts. To cover a variety of different cases, cadaver measurements and clinical images in the knee, head and spine region were used to investigate the effectiveness and applicability of our method. A comparison to a three-dimensional interpolation correction showed that the new approach outperformed interpolation schemes. Correction times are minimized, and initial and corrected images are made available at almost the same time (12.7 s for the initial reconstruction, 46.2 s for the final corrected image compared to 114.1 s and 355.1 s on central processing units (CPUs))

  8. Direct investigation of (sub-) surface preparation artifacts in GaAs based materials by FIB sectioning

    Energy Technology Data Exchange (ETDEWEB)

    Belz, Jürgen; Beyer, Andreas; Torunski, Torsten; Stolz, Wolfgang; Volz, Kerstin

    2016-04-15

    The introduction of preparation artifacts is almost inevitable when producing samples for (scanning) transmission electron microscopy ((S)TEM). These artifacts can be divided in extrinsic artifacts like damage processes and intrinsic artifacts caused by the deviations from the volume strain state in thin elastically strained material systems. The reduction and estimation of those effects is of great importance for the quantitative analysis of (S)TEM images. Thus, optimized ion beam preparation conditions are investigated for high quality samples. Therefore, the surface topology is investigated directly with atomic force microscopy (AFM) on the actual TEM samples. Additionally, the sectioning of those samples by a focused ion beam (FIB) is used to investigate the damage depth profile directly in the TEM. The AFM measurements show good quantitative agreement of sample height modulation due to strain relaxation to finite elements simulations. Strong indications of (sub-) surface damage by ion beams are observed. Their influence on high angle annular dark field (HAADF) imaging is estimated with focus on thickness determination by absolute intensity methods. Data consolidation of AFM and TEM measurements reveals a 3.5 nm surface amorphization, negligible surface roughness on the scale of angstroms and a sub-surface damage profile in the range of up to 8.0 nm in crystalline gallium arsenide (GaAs) and GaAs-based ternary alloys. A correction scheme for thickness evaluation of absolute HAADF intensities is proposed and applied for GaAs based materials. - Highlights: • The damage by Ar-ion milling during TEM sample preparation is investigated directly. • After FIB sectioning damage and deep disorder of c-GaAs is seen in cross-section. • The influence of such disorder on conventional ADF measurements is estimated. • A correction for HAADF measurements is proposed with focus on thickness estimations.

  9. Constraining earthquake source inversions with GPS data: 1. Resolution-based removal of artifacts

    Science.gov (United States)

    Page, M.T.; Custodio, S.; Archuleta, R.J.; Carlson, J.M.

    2009-01-01

    We present a resolution analysis of an inversion of GPS data from the 2004 Mw 6.0 Parkfield earthquake. This earthquake was recorded at thirteen 1-Hz GPS receivers, which provides for a truly coseismic data set that can be used to infer the static slip field. We find that the resolution of our inverted slip model is poor at depth and near the edges of the modeled fault plane that are far from GPS receivers. The spatial heterogeneity of the model resolution in the static field inversion leads to artifacts in poorly resolved areas of the fault plane. These artifacts look qualitatively similar to asperities commonly seen in the final slip models of earthquake source inversions, but in this inversion they are caused by a surplus of free parameters. The location of the artifacts depends on the station geometry and the assumed velocity structure. We demonstrate that a nonuniform gridding of model parameters on the fault can remove these artifacts from the inversion. We generate a nonuniform grid with a grid spacing that matches the local resolution length on the fault and show that it outperforms uniform grids, which either generate spurious structure in poorly resolved regions or lose recoverable information in well-resolved areas of the fault. In a synthetic test, the nonuniform grid correctly averages slip in poorly resolved areas of the fault while recovering small-scale structure near the surface. Finally, we present an inversion of the Parkfield GPS data set on the nonuniform grid and analyze the errors in the final model. Copyright 2009 by the American Geophysical Union.

  10. A novel forward projection-based metal artifact reduction method for flat-detector computed tomography

    International Nuclear Information System (INIS)

    Prell, Daniel; Kyriakou, Yiannis; Beister, Marcel; Kalender, Willi A

    2009-01-01

    Metallic implants generate streak-like artifacts in flat-detector computed tomography (FD-CT) reconstructed volumetric images. This study presents a novel method for reducing these disturbing artifacts by inserting discarded information into the original rawdata using a three-step correction procedure and working directly with each detector element. Computation times are minimized by completely implementing the correction process on graphics processing units (GPUs). First, the original volume is corrected using a three-dimensional interpolation scheme in the rawdata domain, followed by a second reconstruction. This metal artifact-reduced volume is then segmented into three materials, i.e. air, soft-tissue and bone, using a threshold-based algorithm. Subsequently, a forward projection of the obtained tissue-class model substitutes the missing or corrupted attenuation values directly for each flat detector element that contains attenuation values corresponding to metal parts, followed by a final reconstruction. Experiments using tissue-equivalent phantoms showed a significant reduction of metal artifacts (deviations of CT values after correction compared to measurements without metallic inserts reduced typically to below 20 HU, differences in image noise to below 5 HU) caused by the implants and no significant resolution losses even in areas close to the inserts. To cover a variety of different cases, cadaver measurements and clinical images in the knee, head and spine region were used to investigate the effectiveness and applicability of our method. A comparison to a three-dimensional interpolation correction showed that the new approach outperformed interpolation schemes. Correction times are minimized, and initial and corrected images are made available at almost the same time (12.7 s for the initial reconstruction, 46.2 s for the final corrected image compared to 114.1 s and 355.1 s on central processing units (CPUs)).

  11. Combined electrocardiography- and respiratory-triggered CT of the lung to reduce respiratory misregistration artifacts between imagining slabs in free-breathing children: Initial experience

    Energy Technology Data Exchange (ETDEWEB)

    Goo, Hyun Woo [Dept. of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul (Korea, Republic of); Allmendinger, Thomas [Siemens Healthcare, GmbH, Computed Tomography Division, Forchheim (Germany)

    2017-09-15

    Cardiac and respiratory motion artifacts degrade the image quality of lung CT in free-breathing children. The aim of this study was to evaluate the effect of combined electrocardiography (ECG) and respiratory triggering on respiratory misregistration artifacts on lung CT in free-breathing children. In total, 15 children (median age 19 months, range 6 months–8 years; 7 boys), who underwent free-breathing ECG-triggered lung CT with and without respiratory-triggering were included. A pressure-sensing belt of a respiratory gating system was used to obtain the respiratory signal. The degree of respiratory misregistration artifacts between imaging slabs was graded on a 4-point scale (1, excellent image quality) on coronal and sagittal images and compared between ECG-triggered lung CT studies with and without respiratory triggering. A p value < 0.05 was considered significant. Lung CT with combined ECG and respiratory triggering showed significantly less respiratory misregistration artifacts than lung CT with ECG triggering only (1.1 ± 0.4 vs. 2.2 ± 1.0, p = 0.003). Additional respiratory-triggering reduces respiratory misregistration artifacts on ECG-triggered lung CT in free-breathing children.

  12. Combined electrocardiography- and respiratory-triggered CT of the lung to reduce respiratory misregistration artifacts between imagining slabs in free-breathing children: Initial experience

    International Nuclear Information System (INIS)

    Goo, Hyun Woo; Allmendinger, Thomas

    2017-01-01

    Cardiac and respiratory motion artifacts degrade the image quality of lung CT in free-breathing children. The aim of this study was to evaluate the effect of combined electrocardiography (ECG) and respiratory triggering on respiratory misregistration artifacts on lung CT in free-breathing children. In total, 15 children (median age 19 months, range 6 months–8 years; 7 boys), who underwent free-breathing ECG-triggered lung CT with and without respiratory-triggering were included. A pressure-sensing belt of a respiratory gating system was used to obtain the respiratory signal. The degree of respiratory misregistration artifacts between imaging slabs was graded on a 4-point scale (1, excellent image quality) on coronal and sagittal images and compared between ECG-triggered lung CT studies with and without respiratory triggering. A p value < 0.05 was considered significant. Lung CT with combined ECG and respiratory triggering showed significantly less respiratory misregistration artifacts than lung CT with ECG triggering only (1.1 ± 0.4 vs. 2.2 ± 1.0, p = 0.003). Additional respiratory-triggering reduces respiratory misregistration artifacts on ECG-triggered lung CT in free-breathing children

  13. Preliminary study on helical CT algorithms for patient motion estimation and compensation

    International Nuclear Information System (INIS)

    Wang, G.; Vannier, M.W.

    1995-01-01

    Helical computed tomography (helical/spiral CT) has replaced conventional CT in many clinical applications. In current helical CT, a patient is assumed to be rigid and motionless during scanning and planar projection sets are produced from raw data via longitudinal interpolation. However, rigid patient motion is a problem in some cases (such as in the skull base and temporal bone imaging). Motion artifacts thus generated in reconstructed images can prevent accurate diagnosis. Modeling a uniform translational movement, the authors address how patient motion is ascertained and how it may be compensated. First, mismatch between adjacent fan-beam projections of the same orientation is determined via classical correlation, which is approximately proportional to the patient displacement projected onto an axis orthogonal to the central ray of the involved fan-beam. Then, the patient motion vector (the patient displacement per gantry rotation) is estimated from its projections using a least-square-root method. To suppress motion artifacts, adaptive interpolation algorithms are developed that synthesize full-scan and half-scan planar projection data sets, respectively. In the adaptive scheme, the interpolation is performed along inclined paths dependent upon the patient motion vector. The simulation results show that the patient motion vector can be accurately and reliably estimated using their correlation and least-square-root algorithm, patient motion artifacts can be effectively suppressed via adaptive interpolation, and adaptive half-scan interpolation is advantageous compared with its full-scale counterpart in terms of high contrast image resolution

  14. Magnetic resonance imaging of metal artifact reduction sequences in the assessment of metal-on-metal hip prostheses

    Directory of Open Access Journals (Sweden)

    Aboelmagd SM

    2014-05-01

    Full Text Available Sharief M Aboelmagd, Paul N Malcolm, Andoni P Toms Department of Radiology, Norfolk and Norwich University Hospital National Health Service Trust, Norwich, UK Abstract: Recent developments in metal artifact reduction techniques in magnetic resonance (MR have, in large part, been stimulated by the advent of soft tissue complications associated with modern metal-on-metal total hip replacements. Metallic orthopedic implants can result in severe degradation of MR images because ferromagnetic susceptibility causes signal loss, signal pile-up, geometric distortion, and failure of fat suppression. There are several approaches to controlling these susceptibility artifacts. Standard fast spin echo sequences can be adapted by modifying echo times, matrix, receiver bandwidth, slice thickness, and echo trains to minimize frequency encoding misregistration. Short tau inversion recovery and 2-point Dixon techniques are both more resistant to susceptibility artifacts than spectral fat suppression. A number of dedicated metal artifact reduction sequences are now available commercially. The common approach of these multispectral techniques is to generate three dimensional datasets from which the final images are reconstructed. Frequency encoding misregistration is controlled using a variety of techniques, including specific resonant frequency acquisition, view-angle tilting, and phase encoding. Metal artifact reduction MR imaging has been the key to understanding the prevalence, severity, and prognosis of adverse reactions to metal debris in metal-on-metal hip replacements. Conventional radiographs are typically normal or demonstrate minimal change and are unable to demonstrate the often extensive soft tissue abnormalities, which include necrosis, soft tissue masses and fluid collections, myositis, muscle atrophy, tendon avulsions, and osteonecrosis. These MR findings correlate poorly with clinical and serological measures of disease, and therefore MR imaging is

  15. Mitigation of near-band balanced steady-state free precession through-plane flow artifacts using partial dephasing.

    Science.gov (United States)

    Datta, Anjali; Cheng, Joseph Y; Hargreaves, Brian A; Baron, Corey A; Nishimura, Dwight G

    2018-06-01

    To mitigate artifacts from through-plane flow at the locations of steady-state stopbands in balanced steady-state free precession (SSFP) using partial dephasing. A 60° range in the phase accrual during a TR was created over the voxel by slightly unbalancing the slice-select dephaser. The spectral profiles of SSFP with partial dephasing for various constant flow rates and during pulsatile flow were simulated to determine if partial dephasing decreases through-plane flow artifacts originating near SSFP dark bands while maintaining on-resonant signal. Simulations were then validated in a flow phantom. Lastly, phase-cycled SSFP cardiac cine images were acquired with and without partial dephasing in six subjects. Partial dephasing decreased the strength and non-linearity of the dependence of the signal at the stopbands on the through-plane flow rate. It thus mitigated hyper-enhancement from out-of-slice signal contributions and transient-related artifacts caused by variable flow both in the phantom and in vivo. In six volunteers, partial dephasing noticeably decreased artifacts in all of the phase-cycled cardiac cine datasets. Partial dephasing can mitigate the flow artifacts seen at the stopbands in balanced SSFP while maintaining the sequence's desired signal. By mitigating hyper-enhancement and transient-related artifacts originating from the stopbands, partial dephasing facilitates robust multiple-acquisition phase-cycled SSFP in the heart. Magn Reson Med 79:2944-2953, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  16. A real-time artifact reduction algorithm based on precise threshold during short-separation optical probe insertion in neurosurgery

    Directory of Open Access Journals (Sweden)

    Weitao Li

    2017-01-01

    Full Text Available During neurosurgery, an optical probe has been used to guide the micro-electrode, which is punctured into the globus pallidus (GP to create a lesion that can relieve the cardinal symptoms. Accurate target localization is the key factor to affect the treatment. However, considering the scattering nature of the tissue, the “look ahead distance (LAD” of optical probe makes the boundary between the different tissues blurred and difficult to be distinguished, which is defined as artifact. Thus, it is highly desirable to reduce the artifact caused by LAD. In this paper, a real-time algorithm based on precise threshold was proposed to eliminate the artifact. The value of the threshold was determined by the maximum error of the measurement system during the calibration procession automatically. Then, the measured data was processed sequentially only based on the threshold and the former data. Moreover, 100μm double-fiber probe and two-layer and multi-layer phantom models were utilized to validate the precision of the algorithm. The error of the algorithm is one puncture step, which was proved in the theory and experiment. It was concluded that the present method could reduce the artifact caused by LAD and make the real boundary sharper and less blurred in real-time. It might be potentially used for the neurosurgery navigation.

  17. Motion-map constrained image reconstruction (MCIR): Application to four-dimensional cone-beam computed tomography

    International Nuclear Information System (INIS)

    Park, Justin C.; Kim, Jin Sung; Park, Sung Ho; Liu, Zhaowei; Song, Bongyong; Song, William Y.

    2013-01-01

    Purpose: Utilization of respiratory correlated four-dimensional cone-beam computed tomography (4DCBCT) has enabled verification of internal target motion and volume immediately prior to treatment. However, with current standard CBCT scan, 4DCBCT poses challenge for reconstruction due to the fact that multiple phase binning leads to insufficient number of projection data to reconstruct and thus cause streaking artifacts. The purpose of this study is to develop a novel 4DCBCT reconstruction algorithm framework called motion-map constrained image reconstruction (MCIR), that allows reconstruction of high quality and high phase resolution 4DCBCT images with no more than the imaging dose as well as projections used in a standard free breathing 3DCBCT (FB-3DCBCT) scan.Methods: The unknown 4DCBCT volume at each phase was mathematically modeled as a combination of FB-3DCBCT and phase-specific update vector which has an associated motion-map matrix. The motion-map matrix, which is the key innovation of the MCIR algorithm, was defined as the matrix that distinguishes voxels that are moving from stationary ones. This 4DCBCT model was then reconstructed with compressed sensing (CS) reconstruction framework such that the voxels with high motion would be aggressively updated by the phase-wise sorted projections and the voxels with less motion would be minimally updated to preserve the FB-3DCBCT. To evaluate the performance of our proposed MCIR algorithm, we evaluated both numerical phantoms and a lung cancer patient. The results were then compared with the (1) clinical FB-3DCBCT reconstructed using the FDK, (2) 4DCBCT reconstructed using the FDK, and (3) 4DCBCT reconstructed using the well-known prior image constrained compressed sensing (PICCS).Results: Examination of the MCIR algorithm showed that high phase-resolved 4DCBCT with sets of up to 20 phases using a typical FB-3DCBCT scan could be reconstructed without compromising the image quality. Moreover, in comparison with

  18. Motion-map constrained image reconstruction (MCIR): Application to four-dimensional cone-beam computed tomography

    Energy Technology Data Exchange (ETDEWEB)

    Park, Justin C. [Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California 92093 and Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, California 92093 (United States); Kim, Jin Sung [Department of Radiation Oncology, Samsung Medical Center, Seoul 135-710 (Korea, Republic of); Park, Sung Ho [Department of Medical Physics, Asan Medical Center, College of Medicine, University of Ulsan, Seoul 138-736 (Korea, Republic of); Liu, Zhaowei [Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, California 92093 (United States); Song, Bongyong; Song, William Y. [Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California 92093 (United States)

    2013-12-15

    Purpose: Utilization of respiratory correlated four-dimensional cone-beam computed tomography (4DCBCT) has enabled verification of internal target motion and volume immediately prior to treatment. However, with current standard CBCT scan, 4DCBCT poses challenge for reconstruction due to the fact that multiple phase binning leads to insufficient number of projection data to reconstruct and thus cause streaking artifacts. The purpose of this study is to develop a novel 4DCBCT reconstruction algorithm framework called motion-map constrained image reconstruction (MCIR), that allows reconstruction of high quality and high phase resolution 4DCBCT images with no more than the imaging dose as well as projections used in a standard free breathing 3DCBCT (FB-3DCBCT) scan.Methods: The unknown 4DCBCT volume at each phase was mathematically modeled as a combination of FB-3DCBCT and phase-specific update vector which has an associated motion-map matrix. The motion-map matrix, which is the key innovation of the MCIR algorithm, was defined as the matrix that distinguishes voxels that are moving from stationary ones. This 4DCBCT model was then reconstructed with compressed sensing (CS) reconstruction framework such that the voxels with high motion would be aggressively updated by the phase-wise sorted projections and the voxels with less motion would be minimally updated to preserve the FB-3DCBCT. To evaluate the performance of our proposed MCIR algorithm, we evaluated both numerical phantoms and a lung cancer patient. The results were then compared with the (1) clinical FB-3DCBCT reconstructed using the FDK, (2) 4DCBCT reconstructed using the FDK, and (3) 4DCBCT reconstructed using the well-known prior image constrained compressed sensing (PICCS).Results: Examination of the MCIR algorithm showed that high phase-resolved 4DCBCT with sets of up to 20 phases using a typical FB-3DCBCT scan could be reconstructed without compromising the image quality. Moreover, in comparison with

  19. Ensemble Artifact Design For Context Sensitive Decision Support

    Directory of Open Access Journals (Sweden)

    Shah J Miah

    2014-06-01

    Full Text Available Although an improvement of design knowledge is an essential goal of design research, current design research predominantly focuses on knowledge concerning the IT artifact (tool design process, rather than a more holistic understanding encompassing the dynamic usage contexts of a technological artifact. Conceptualising a design in context as an “ensemble artifact” (Sein et al., 2011 provides the basis for a more rigorous treatment. This paper describes an IS artifact design framework that has been generated from the development of several practitioner-oriented decision support systems (DSS in which contextual aspects relevant to practitioners’ decision making are considered as integral design themes. We describe five key dimensions of an ensemble artifact design and show their value in designing practitioner-oriented DSS. The features are user centredness, knowledge sharing, situation-specific customisation, reduced model orientation, and practice based secondary design abilities. It is argued that this understanding can contribute to design research knowledge more effectively both to develop dynamic DSS, and by its extensibility to other artifact designs.

  20. Preliminary experimental insights into differential heat impact among lithic artifacts

    Directory of Open Access Journals (Sweden)

    Guillermo Bustos-Pérez

    2016-09-01

    Full Text Available The presence of thermally altered and broken flint artifacts is common at archaeological sites. Most studies focus their attention on the effects of heat treatment on flint to improve knapping qualities, disregarding the effects of fire over flint under uncontrolled conditions. This paper aims to show how under uncontrolled heating processes flint artifacts develop different heat alterations (such as levels of breakage, presence of scales, etc. as a result of vertical distribution, volume or raw material and to establish a gradient of rock changes and behavior. Artifacts where macroscopically analyzed and a series of uncontrolled heating experiments through the distribution of flint blanks under two hearths were carried out, allowing a comparison of the before and after of the blanks. Preliminary results show how levels of breakage, surface alteration or development of heat alteration features can be differentiated according to artifact volume, vertical distribution and level of surface alteration. Results also show how two different raw materials react differently to similar thermal impact, and how surface alteration reacts at different rhythm in the case of recycled artifacts. We conclude that levels of thermal alteration can be differentiated through macroscopic analysis of flint surface.

  1. Motion correction in thoracic positron emission tomography

    CERN Document Server

    Gigengack, Fabian; Dawood, Mohammad; Schäfers, Klaus P

    2015-01-01

    Respiratory and cardiac motion leads to image degradation in Positron Emission Tomography (PET), which impairs quantification. In this book, the authors present approaches to motion estimation and motion correction in thoracic PET. The approaches for motion estimation are based on dual gating and mass-preserving image registration (VAMPIRE) and mass-preserving optical flow (MPOF). With mass-preservation, image intensity modulations caused by highly non-rigid cardiac motion are accounted for. Within the image registration framework different data terms, different variants of regularization and parametric and non-parametric motion models are examined. Within the optical flow framework, different data terms and further non-quadratic penalization are also discussed. The approaches for motion correction particularly focus on pipelines in dual gated PET. A quantitative evaluation of the proposed approaches is performed on software phantom data with accompanied ground-truth motion information. Further, clinical appl...

  2. Structuring Design and Evaluation of an Interactive Installation Through Swarms of Light Rays with Human-Artifact Model

    DEFF Research Database (Denmark)

    Erkut, Cumhur; Fehr, Jonas

    2016-01-01

    We present the design and evaluation of an interactive installation to be explored by movement and sound under Human-Activity Model. In the installation, movement qualities that are extracted from the motion tracking data excite a dynamical system (a synthetic flock of agents), which responds...... out a questionnaire afterwards. In this paper, we report our preliminary work on the analysis of the tensions of interaction with the installation under the Human-Artifact Model. Our results indicate exploration and discovery as the main motives of the interaction. This is different than utilitarian...

  3. Distinction of Fly Artifacts from Human Blood using Immunodetection.

    Science.gov (United States)

    Rivers, David B; Acca, Gillian; Fink, Marc; Brogan, Rebecca; Chen, Dorothy; Schoeffield, Andrew

    2018-02-21

    Insect stains produced by necrophagous flies are indistinguishable morphologically from human bloodstains. At present, no diagnostic tests exist to overcome this deficiency. As the first step toward developing a chemical test to recognize fly artifacts, polyclonal antisera were generated in rats against three distinct antigenic sequences of fly cathepsin D-like proteinase, an enzyme that is structurally distinct in cyclorrhaphous Diptera from other animals. The resulting rat antisera bound to artifacts produced by Protophormia terraenovae and synthetic peptides used to generate the polyclonal antisera, but not with any type of mammalian blood tested in immunoassays. Among the three antisera, anti-md3 serum displayed the highest reactivity for fly stains, demonstrated cross-reactivity for all synthetic peptides representing antigenic sequences of the mature fly enzyme, and bound artifacts originating from the fly digestive tract. Further work is needed to determine whether the antisera are suitable for non-laboratory conditions. © 2018 American Academy of Forensic Sciences.

  4. Correction of ring artifacts in X-ray tomographic images

    DEFF Research Database (Denmark)

    Lyckegaard, Allan; Johnson, G.; Tafforeau, P.

    2011-01-01

    Ring artifacts are systematic intensity distortions located on concentric circles in reconstructed tomographic X-ray images. When using X-ray tomography to study for instance low-contrast grain boundaries in metals it is crucial to correct for the ring artifacts in the images as they may have...... the same intensity level as the grain boundaries and thus make it impossible to perform grain segmentation. This paper describes an implementation of a method for correcting the ring artifacts in tomographic X-ray images of simple objects such as metal samples where the object and the background...... are separable. The method is implemented in Matlab, it works with very little user interaction and may run in parallel on a cluster if applied to a whole stack of images. The strength and robustness of the method implemented will be demonstrated on three tomographic X-ray data sets: a mono-phase β...

  5. Medical image of the week: DBS polysomnogram artifact

    Directory of Open Access Journals (Sweden)

    Shetty S,

    2015-10-01

    Full Text Available A 79-year-old man with known Parkinson’s disease and status post deep brain stimulator (DBS implantation underwent an overnight polysomnogram for clinical suspicion of obstructive sleep apnea. Artifact was seen on the polysomnogram recording (Figures 1 & 2. Patient-related electrical artifacts may be seen from devices such as pacemakers, deep brain stimulators and vagal nerve simulators. Abrupt discontinuation of DBS is associated with a high likelihood of worsening of symptoms in patients with Parkinson’s disease (1. Patients with DBS are most commonly programmed in monopolar mode. Bipolar configuration, forms a short electrical dipole that affects a relatively smaller volume of tissue and generates far less artifact, suggesting that this may be an effective option in a Parkinsonian patient with indications for polysomnography (2.

  6. Motion Detection in Ultrasound Image-Sequences Using Tensor Voting

    Science.gov (United States)

    Inba, Masafumi; Yanagida, Hirotaka; Tamura, Yasutaka

    2008-05-01

    Motion detection in ultrasound image sequences using tensor voting is described. We have been developing an ultrasound imaging system adopting a combination of coded excitation and synthetic aperture focusing techniques. In our method, frame rate of the system at distance of 150 mm reaches 5000 frame/s. Sparse array and short duration coded ultrasound signals are used for high-speed data acquisition. However, many artifacts appear in the reconstructed image sequences because of the incompleteness of the transmitted code. To reduce the artifacts, we have examined the application of tensor voting to the imaging method which adopts both coded excitation and synthetic aperture techniques. In this study, the basis of applying tensor voting and the motion detection method to ultrasound images is derived. It was confirmed that velocity detection and feature enhancement are possible using tensor voting in the time and space of simulated ultrasound three-dimensional image sequences.

  7. Ring artifacts removal from synchrotron CT image slices

    International Nuclear Information System (INIS)

    Wei Zhouping; Chapman, Dean; Wiebe, Sheldon

    2013-01-01

    Ring artifacts can occur in reconstructed images from x-ray Computerized Tomography (CT) as full or partial concentric rings superimposed on the scanned structures. Due to the data corruption by those ring artifacts in CT images, qualitative and quantitative analysis of these images are compromised. In this paper, we propose to correct the ring artifacts on the reconstructed synchrotron radiation (SR) CT image slices. The proposed correction procedure includes the following steps: (1). transform the reconstructed CT images into polar coordinates; (2) apply discrete two-dimensional (2D) wavelet transform to the polar image to decompose it into four image components: low pass band image component, as well as the components from horizontal, vertical and diagonal details bands; (3). apply 2D Fourier transform to the vertical details band image component only, since the ring artifacts become vertical lines in the polar coordinates; (4). apply Gaussian filtering in Fourier domain along the abscissa direction to suppress the vertical lines, since the information of the vertical lines in Fourier domain is completely condensed to that direction; (5). perform inverse Fourier transform to get the corrected vertical details band image component; (6). perform inverse wavelet transform to get the corrected polar image; (7). transform the corrected polar image back to Cartesian coordinates to get the CT image slice with reduced ring artifacts. This approach has been successfully used on CT data acquired from the Biomedical Imaging and Therapy (BMIT) beamline in Canadian Light Source (CLS), and the results show that the ring artifacts in original SR CT images have been effectively suppressed with all the structure information in the image preserved.

  8. Three-dimensional digital tomosynthesis iterative reconstruction, artifact reduction and alternative acquisition geometry

    CERN Document Server

    Levakhina, Yulia

    2014-01-01

    Yulia Levakhina gives an introduction to the major challenges of image reconstruction in Digital Tomosynthesis (DT), particularly to the connection of the reconstruction problem with the incompleteness of the DT dataset. The author discusses the factors which cause the formation of limited angle artifacts and proposes how to account for them in order to improve image quality and axial resolution of modern DT. The addressed methods include a weighted non-linear back projection scheme for algebraic reconstruction and?novel dual-axis acquisition geometry. All discussed algorithms and methods are supplemented by detailed illustrations, hints for practical implementation, pseudo-code, simulation results and real patient case examples.

  9. Auditory Motion Elicits a Visual Motion Aftereffect

    Directory of Open Access Journals (Sweden)

    Christopher C. Berger

    2016-12-01

    Full Text Available The visual motion aftereffect is a visual illusion in which exposure to continuous motion in one direction leads to a subsequent illusion of visual motion in the opposite direction. Previous findings have been mixed with regard to whether this visual illusion can be induced cross-modally by auditory stimuli. Based on research on multisensory perception demonstrating the profound influence auditory perception can have on the interpretation and perceived motion of visual stimuli, we hypothesized that exposure to auditory stimuli with strong directional motion cues should induce a visual motion aftereffect. Here, we demonstrate that horizontally moving auditory stimuli induced a significant visual motion aftereffect—an effect that was driven primarily by a change in visual motion perception following exposure to leftward moving auditory stimuli. This finding is consistent with the notion that visual and auditory motion perception rely on at least partially overlapping neural substrates.

  10. Auditory Motion Elicits a Visual Motion Aftereffect.

    Science.gov (United States)

    Berger, Christopher C; Ehrsson, H Henrik

    2016-01-01

    The visual motion aftereffect is a visual illusion in which exposure to continuous motion in one direction leads to a subsequent illusion of visual motion in the opposite direction. Previous findings have been mixed with regard to whether this visual illusion can be induced cross-modally by auditory stimuli. Based on research on multisensory perception demonstrating the profound influence auditory perception can have on the interpretation and perceived motion of visual stimuli, we hypothesized that exposure to auditory stimuli with strong directional motion cues should induce a visual motion aftereffect. Here, we demonstrate that horizontally moving auditory stimuli induced a significant visual motion aftereffect-an effect that was driven primarily by a change in visual motion perception following exposure to leftward moving auditory stimuli. This finding is consistent with the notion that visual and auditory motion perception rely on at least partially overlapping neural substrates.

  11. Auditory motion capturing ambiguous visual motion

    Directory of Open Access Journals (Sweden)

    Arjen eAlink

    2012-01-01

    Full Text Available In this study, it is demonstrated that moving sounds have an effect on the direction in which one sees visual stimuli move. During the main experiment sounds were presented consecutively at four speaker locations inducing left- or rightwards auditory apparent motion. On the path of auditory apparent motion, visual apparent motion stimuli were presented with a high degree of directional ambiguity. The main outcome of this experiment is that our participants perceived visual apparent motion stimuli that were ambiguous (equally likely to be perceived as moving left- or rightwards more often as moving in the same direction than in the opposite direction of auditory apparent motion. During the control experiment we replicated this finding and found no effect of sound motion direction on eye movements. This indicates that auditory motion can capture our visual motion percept when visual motion direction is insufficiently determinate without affecting eye movements.

  12. Dosimetric impact of image artifact from a wide-bore CT scanner in radiotherapy treatment planning

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Vincent; Podgorsak, Matthew B.; Tran, Tuan-Anh; Malhotra, Harish K.; Wang, Iris Z. [Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263 (United States); Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263 and Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York 14214 (United States); Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263 (United States); Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, New York 14263 and Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York 14214 (United States)

    2011-07-15

    average CT number changes of up to -49 HU. Wider distribution (i.e., standard deviation) of the HU values was seen when the phantom was placed at more than 2.8 cm beyond the 50 cm sFOV. Anthropomorphic phantom studies with several standard beam configurations show that body contour distortion causes tumor dose calculation reduction of 3.0 and 1.9% for 6 and 23 MV x-rays, respectively, when not accounting for tissue heterogeneities during dose computation. When heterogeneity correction is used in planning, the competing effects of the body contour distortion and the CT number distortion cause a smaller error in tumor dose calculation. Less than 0.9% error in calculated dose was observed in volumetric modulated arc therapy (VMAT) treatment plans. Conclusions: The image artifacts from eFOV reconstruction alter the CT numbers and body contours of the imaged objects, which has the potential to produce inaccuracies in dose calculations during radiotherapy treatment planning. The radiation therapy team should be aware of these image artifacts and their effects on target dose calculations during CT simulation as well as treatment planning.

  13. Inter-deriving Semantic Artifacts for Object-Oriented Programming

    DEFF Research Database (Denmark)

    Danvy, Olivier; Johannsen, Jacob

    2008-01-01

    We present a new abstract machine for Abadi and Cardelli's untyped calculus of objects. What is special about this semantic artifact (i.e., man-made construct) is that is mechanically corresponds to both the reduction semantics (i.e., small-step operational semantics) and the natural semantics (i...... actual substitutions, we then represent object methods as closures and in the same inter-derivational spirit, we present three new semantic artifacts: a reduction semantics for a version of Abadi and Cardelli's untyped calculus of objects with explicit substitutions, an environment-based abstract machine...

  14. EEG Artifact Removal Using a Wavelet Neural Network

    Science.gov (United States)

    Nguyen, Hoang-Anh T.; Musson, John; Li, Jiang; McKenzie, Frederick; Zhang, Guangfan; Xu, Roger; Richey, Carl; Schnell, Tom

    2011-01-01

    !n this paper we developed a wavelet neural network. (WNN) algorithm for Electroencephalogram (EEG) artifact removal without electrooculographic (EOG) recordings. The algorithm combines the universal approximation characteristics of neural network and the time/frequency property of wavelet. We. compared the WNN algorithm with .the ICA technique ,and a wavelet thresholding method, which was realized by using the Stein's unbiased risk estimate (SURE) with an adaptive gradient-based optimal threshold. Experimental results on a driving test data set show that WNN can remove EEG artifacts effectively without diminishing useful EEG information even for very noisy data.

  15. ["Long-branch Attraction" artifact in phylogenetic reconstruction].

    Science.gov (United States)

    Li, Yi-Wei; Yu, Li; Zhang, Ya-Ping

    2007-06-01

    Phylogenetic reconstruction among various organisms not only helps understand their evolutionary history but also reveal several fundamental evolutionary questions. Understanding of the evolutionary relationships among organisms establishes the foundation for the investigations of other biological disciplines. However, almost all the widely used phylogenetic methods have limitations which fail to eliminate systematic errors effectively, preventing the reconstruction of true organismal relationships. "Long-branch Attraction" (LBA) artifact is one of the most disturbing factors in phylogenetic reconstruction. In this review, the conception and analytic method as well as the avoidance strategy of LBA were summarized. In addition, several typical examples were provided. The approach to avoid and resolve LBA artifact has been discussed.

  16. Analysis of main artifacts in scanning probe microscopy (1)

    International Nuclear Information System (INIS)

    Alekperov, S.D.; Alekperov, S.D.

    2012-01-01

    The analysis of experiment carrying methodology in the scanning probe microscopy (SPM) region is carried out, the main parameters influencing on image quality are revealed. In order to reveal the artifact reason the main components of SPM signal which are divided on 5 groups : the useful signal; noises connected with external influences and temperature drift; distortions connected with piezoceramics and piezo-scanner non-ideality; probe geometry influence; apparatus noises are considered. The main methods of removal and minimization of the given artifacts are considered. The second and third groups of main components of SPM signal are considered in the articles first part

  17. "Diabetes and literacy: negotiating control through artifacts of medicalization".

    Science.gov (United States)

    Martins, David S

    2009-06-01

    My experience with the California Department of Motor Vehicles offers a case to explore how bureaucratic institutions monitor, classify, and control individuals. By examining artifacts created for and used by the DMV through the lens of literacy studies, I discuss the variety of rhetorical strategies used in each document and the effects and implications of those strategies, for example on subjectivity or identity, and move beyond the language of the artifacts themselves to attend to how they are invested with power in the management and control of populations.

  18. Depolarization artifacts in dual rotating-compensator Mueller matrix ellipsometry

    International Nuclear Information System (INIS)

    Li, Weiqi; Zhang, Chuanwei; Jiang, Hao; Chen, Xiuguo; Liu, Shiyuan

    2016-01-01

    Noticeable depolarization effects are observed in the measurement of the air using an in-house developed dual rotating-compensator Mueller matrix ellipsometer. We demonstrate that these depolarization effects are essentially artifacts and mainly induced when the compensator with wavelength-dependent optical properties is integrated with the finite bandwidth detector. We define a general formula to represent the actual Mueller matrix of the compensator by taking into account the depolarization artifacts. After incorporating this formula into the system model, a correction method is further proposed, and consequently, improved accuracy can be achieved in the Mueller matrix measurement. (paper)

  19. Motion correction in neurological fan beam SPECT using motion tracking and fully 3D reconstruction

    International Nuclear Information System (INIS)

    Fulton, R.R.; Hutton, B.; Eberl, S.; Meikle, S.; Braun, M.; Westmead Hospital, Westmead, NSW; University of Technology, Sydney, NSW

    1998-01-01

    Full text: We have previously proposed the use of fully three-dimensional (3D) reconstruction and continuous monitoring of head position to correct for motion artifacts in neurological SPECT and PET. Knowledge of the motion during acquisition provided by a head tracking system can be used to reposition the projection data in space in such a way as to negate motion effects during reconstruction. The reconstruction algorithm must deal with variations in the projection geometry resulting from differences in the timing and nature of motion between patients. Rotational movements about any axis other than the camera's axis of rotation give rise to projection geometries which necessitate the use of a fully 3D reconstruction algorithm. Our previous work with computer simulations assuming parallel hole collimation demonstrated the feasibility of correcting for motion. We have now refined our iterative 3D reconstruction algorithm to support fan beam data and attenuation correction, and developed a practical head tracking system for use on a Trionix Triad SPECT system. The correction technique has been tested in fan beam SPECT studies of the 3D Hoffman brain phantom. Arbitrary movements were applied to the phantom during acquisition and recorded by the head tracker which monitored the position and orientation of the phantom throughout the study. 3D reconstruction was then performed using the motion data provided by the tracker. The accuracy of correction was assessed by comparing the corrected images with a motion free study acquired immediately beforehand, visually and by calculating mean squared error (MSE). Motion correction reduced distortion perceptibly and, depending on the motions applied, improved MSE by up to an order of magnitude. 3D reconstruction of the 128x128x128 data set took 20 minutes on a SUN Ultra 1 workstation. The results of these phantom experiments suggest that the technique can effectively compensate for head motion under clinical SPECT imaging

  20. What motion is: William Neile and the laws of motion.

    Science.gov (United States)

    Kemeny, Max

    2017-07-01

    In 1668-1669 William Neile and John Wallis engaged in a protracted correspondence regarding the nature of motion. Neile was unhappy with the laws of motion that had been established by the Royal Society in three papers published in 1668, deeming them not explanations of motion at all, but mere descriptions. Neile insisted that science could not be informative without a discussion of causes, meaning that Wallis's purely kinematic account of collision could not be complete. Wallis, however, did not consider Neile's objections to his work to be serious. Rather than engage in a discussion of the proper place of natural philosophy in science, Wallis decided to show how Neile's preferred treatment of motion lead to absurd conclusions. This dispute is offered as a case study of dispute resolution within the early Royal Society.

  1. Inter-plane artifact suppression in tomosynthesis using 3D CT image data

    Directory of Open Access Journals (Sweden)

    Kim Jae G

    2011-12-01

    Full Text Available Abstract Background Despite its superb lateral resolution, flat-panel-detector (FPD based tomosynthesis suffers from low contrast and inter-plane artifacts caused by incomplete cancellation of the projection components stemming from outside the focal plane. The incomplete cancellation of the projection components, mostly due to the limited scan angle in the conventional tomosynthesis scan geometry, often makes the image contrast too low to differentiate the malignant tissues from the background tissues with confidence. Methods In this paper, we propose a new method to suppress the inter-plane artifacts in FPD-based tomosynthesis. If 3D whole volume CT images are available before the tomosynthesis scan, the CT image data can be incorporated into the tomosynthesis image reconstruction to suppress the inter-plane artifacts, hence, improving the image contrast. In the proposed technique, the projection components stemming from outside the region-of-interest (ROI are subtracted from the measured tomosynthesis projection data to suppress the inter-plane artifacts. The projection components stemming from outside the ROI are calculated from the 3D whole volume CT images which usually have lower lateral resolution than the tomosynthesis images. The tomosynthesis images are reconstructed from the subtracted projection data which account for the x-ray attenuation through the ROI. After verifying the proposed method by simulation, we have performed both CT scan and tomosynthesis scan on a phantom and a sacrificed rat using a FPD-based micro-CT. Results We have measured contrast-to-noise ratio (CNR from the tomosynthesis images which is an indicator of the residual inter-plane artifacts on the focal-plane image. In both cases of the simulation and experimental imaging studies of the contrast evaluating phantom, CNRs have been significantly improved by the proposed method. In the rat imaging also, we have observed better visual contrast from the tomosynthesis

  2. Inter-plane artifact suppression in tomosynthesis using 3D CT image data

    Science.gov (United States)

    2011-01-01

    Background Despite its superb lateral resolution, flat-panel-detector (FPD) based tomosynthesis suffers from low contrast and inter-plane artifacts caused by incomplete cancellation of the projection components stemming from outside the focal plane. The incomplete cancellation of the projection components, mostly due to the limited scan angle in the conventional tomosynthesis scan geometry, often makes the image contrast too low to differentiate the malignant tissues from the background tissues with confidence. Methods In this paper, we propose a new method to suppress the inter-plane artifacts in FPD-based tomosynthesis. If 3D whole volume CT images are available before the tomosynthesis scan, the CT image data can be incorporated into the tomosynthesis image reconstruction to suppress the inter-plane artifacts, hence, improving the image contrast. In the proposed technique, the projection components stemming from outside the region-of-interest (ROI) are subtracted from the measured tomosynthesis projection data to suppress the inter-plane artifacts. The projection components stemming from outside the ROI are calculated from the 3D whole volume CT images which usually have lower lateral resolution than the tomosynthesis images. The tomosynthesis images are reconstructed from the subtracted projection data which account for the x-ray attenuation through the ROI. After verifying the proposed method by simulation, we have performed both CT scan and tomosynthesis scan on a phantom and a sacrificed rat using a FPD-based micro-CT. Results We have measured contrast-to-noise ratio (CNR) from the tomosynthesis images which is an indicator of the residual inter-plane artifacts on the focal-plane image. In both cases of the simulation and experimental imaging studies of the contrast evaluating phantom, CNRs have been significantly improved by the proposed method. In the rat imaging also, we have observed better visual contrast from the tomosynthesis images reconstructed by

  3. Degradation of glass artifacts: application of modern surface analytical techniques.

    Science.gov (United States)

    Melcher, Michael; Wiesinger, Rita; Schreiner, Manfred

    2010-06-15

    A detailed understanding of the stability of glasses toward liquid or atmospheric attack is of considerable importance for preserving numerous objects of our cultural heritage. Glasses produced in the ancient periods (Egyptian, Greek, or Roman glasses), as well as modern glass, can be classified as soda-lime-silica glasses. In contrast, potash was used as a flux in medieval Northern Europe for the production of window panes for churches and cathedrals. The particular chemical composition of these potash-lime-silica glasses (low in silica and rich in alkali and alkaline earth components), in combination with increased levels of acidifying gases (such as SO(2), CO(2), NO(x), or O(3)) and airborne particulate matter in today's urban or industrial atmospheres, has resulted in severe degradation of important cultural relics, particularly over the last century. Rapid developments in the fields of microelectronics and computer sciences, however, have contributed to the development of a variety of nondestructive, surface analytical techniques for the scientific investigation and material characterization of these unique and valuable objects. These methods include scanning electron microscopy in combination with energy- or wavelength-dispersive spectrometry (SEM/EDX or SEM/WDX), secondary ion mass spectrometry (SIMS), and atomic force microscopy (AFM). In this Account, we address glass analysis and weathering mechanisms, exploring the possibilities (and limitations) of modern analytical techniques. Corrosion by liquid substances is well investigated in the glass literature. In a tremendous number of case studies, the basic reaction between aqueous solutions and the glass surfaces was identified as an ion-exchange reaction between hydrogen-bearing species of the attacking liquid and the alkali and alkaline earth ions in the glass, causing a depletion of the latter in the outermost surface layers. Although mechanistic analogies to liquid corrosion are obvious, atmospheric

  4. Influence of geometric and material properties on artifacts generated by interventional MRI devices: Relevance to PRF-shift thermometry

    Energy Technology Data Exchange (ETDEWEB)

    Tatebe, Ken, E-mail: Ken.Tatebe@gmail.com [Department of Radiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (United States); Ramsay, Elizabeth; Kazem, Mohammad; Peikari, Hamed [Physical Sciences, Sunnybrook Research Institute, 2075 Bayview Avenue, Toronto, Ontario M4N3M5 (Canada); Mougenot, Charles [Philips Healthcare, 281 Hillmount Road, Markham, Ontario L6C 2S3 (Canada); Bronskill, Michael [Physical Sciences, Sunnybrook Research Institute, 2075 Bayview Avenue, Toronto, Ontario M4N3M5, Canada and Department of Medical Biophysics, University of Toronto, 610 University Avenue, Toronto, Ontario M5G2M9 (Canada); Chopra, Rajiv [Department of Radiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (United States); Advanced Imaging Research Center, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390 (United States); Physical Sciences, Sunnybrook Research Institute, 2075 Bayview Avenue, Toronto, Ontario M4N3M5 (Canada); Department of Medical Biophysics, University of Toronto, 610 University Avenue, Toronto, Ontario M5G2M9 (Canada)

    2016-01-15

    Purpose: Magnetic resonance imaging (MRI) is capable of providing valuable real-time feedback during medical procedures, partly due to the excellent soft-tissue contrast available. Several technical hurdles still exist to seamless integration of medical devices with MRI due to incompatibility of most conventional devices with this imaging modality. In this study, the effect of local perturbations in the magnetic field caused by the magnetization of medical devices was examined using finite element analysis modeling. As an example, the influence of the geometric and material characteristics of a transurethral high-intensity ultrasound applicator on temperature measurements using proton resonance frequency (PRF)-shift thermometry was investigated. Methods: The effect of local perturbations in the magnetic field, caused by the magnetization of medical device components, was examined using finite element analysis modeling. The thermometry artifact generated by a transurethral ultrasound applicator was simulated, and these results were validated against analytic models and scans of an applicator in a phantom. Several parameters were then varied to identify which most strongly impacted the level of simulated thermometry artifact, which varies as the applicator moves over the course of an ablative high-intensity ultrasound treatment. Results: Key design parameters identified as having a strong influence on the magnitude of thermometry artifact included the susceptibility of materials and their volume. The location of components was also important, particularly when positioned to maximize symmetry of the device. Finally, the location of component edges and the inclination of the device relative to the magnetic field were also found to be important factors. Conclusions: Previous design strategies to minimize thermometry artifact were validated, and novel design strategies were identified that substantially reduce PRF-shift thermometry artifacts for a variety of device

  5. Influence of geometric and material properties on artifacts generated by interventional MRI devices: Relevance to PRF-shift thermometry

    International Nuclear Information System (INIS)

    Tatebe, Ken; Ramsay, Elizabeth; Kazem, Mohammad; Peikari, Hamed; Mougenot, Charles; Bronskill, Michael; Chopra, Rajiv

    2016-01-01

    Purpose: Magnetic resonance imaging (MRI) is capable of providing valuable real-time feedback during medical procedures, partly due to the excellent soft-tissue contrast available. Several technical hurdles still exist to seamless integration of medical devices with MRI due to incompatibility of most conventional devices with this imaging modality. In this study, the effect of local perturbations in the magnetic field caused by the magnetization of medical devices was examined using finite element analysis modeling. As an example, the influence of the geometric and material characteristics of a transurethral high-intensity ultrasound applicator on temperature measurements using proton resonance frequency (PRF)-shift thermometry was investigated. Methods: The effect of local perturbations in the magnetic field, caused by the magnetization of medical device components, was examined using finite element analysis modeling. The thermometry artifact generated by a transurethral ultrasound applicator was simulated, and these results were validated against analytic models and scans of an applicator in a phantom. Several parameters were then varied to identify which most strongly impacted the level of simulated thermometry artifact, which varies as the applicator moves over the course of an ablative high-intensity ultrasound treatment. Results: Key design parameters identified as having a strong influence on the magnitude of thermometry artifact included the susceptibility of materials and their volume. The location of components was also important, particularly when positioned to maximize symmetry of the device. Finally, the location of component edges and the inclination of the device relative to the magnetic field were also found to be important factors. Conclusions: Previous design strategies to minimize thermometry artifact were validated, and novel design strategies were identified that substantially reduce PRF-shift thermometry artifacts for a variety of device

  6. Robust motion correction and outlier rejection of in vivo functional MR images of the fetal brain and placenta during maternal hyperoxia

    OpenAIRE

    You, Wonsang; Serag, Ahmed; Evangelou, Iordanis E.; Andescavage, Nickie; Limperopoulos, Catherine

    2017-01-01

    Subject motion is a major challenge in functional magnetic resonance imaging studies (fMRI) of the fetal brain and placenta during maternal hyperoxia. We propose a motion correction and volume outlier rejection method for the correction of severe motion artifacts in both fetal brain and placenta. The method is optimized to the experimental design by processing different phases of acquisition separately. It also automatically excludes high-motion volumes and all the missing data are regressed ...

  7. Robust motion correction and outlier rejection of in vivo functional MR images of the fetal brain and placenta during maternal hyperoxia

    OpenAIRE

    You, Wonsang; Serag, Ahmed; Evangelou, Iordanis E.; Andescavage, Nickie; Limperopoulos, Catherine

    2015-01-01

    Subject motion is a major challenge in functional magnetic resonance imaging studies (fMRI) of the fetal brain and placenta during maternal hyperoxia. We propose a motion correction and volume outlier rejection method for the correction of severe motion artifacts in both fetal brain and placenta. The method is optimized to the experimental design by processing different phases of acquisition separately. It also automatically excludes high-motion volumes and all the missing data are regressed ...

  8. Radiation-induced refraction artifacts in the optical CT readout of polymer gel dosimeters

    International Nuclear Information System (INIS)

    Campbell, Warren G.; Jirasek, Andrew; Wells, Derek M.

    2014-01-01

    Purpose: The objective of this work is to demonstrate imaging artifacts that can occur during the optical computed tomography (CT) scanning of polymer gel dosimeters due to radiation-induced refractive index (RI) changes in polyacrylamide gels. Methods: A 1 L cylindrical polyacrylamide gel dosimeter was irradiated with 3 × 3 cm 2 square beams of 6 MV photons. A prototype fan-beam optical CT scanner was used to image the dosimeter. Investigative optical CT scans were performed to examine two types of rayline bending: (i) bending within the plane of the fan-beam and (ii) bending out the plane of the fan-beam. To address structured errors, an iterative Savitzky–Golay (ISG) filtering routine was designed to filter 2D projections in sinogram space. For comparison, 2D projections were alternatively filtered using an adaptive-mean (AM) filter. Results: In-plane rayline bending was most notably observed in optical CT projections where rays of the fan-beam confronted a sustained dose gradient that was perpendicular to their trajectory but within the fan-beam plane. These errors caused distinct streaking artifacts in image reconstructions due to the refraction of higher intensity rays toward more opaque regions of the dosimeter. Out-of-plane rayline bending was observed in slices of the dosimeter that featured dose gradients perpendicular to the plane of the fan-beam. These errors caused widespread, severe overestimations of dose in image reconstructions due to the higher-than-actual opacity that is perceived by the scanner when light is bent off of the detector array. The ISG filtering routine outperformed AM filtering for both in-plane and out-of-plane rayline errors caused by radiation-induced RI changes. For in-plane rayline errors, streaks in an irradiated region (>7 Gy) were as high as 49% for unfiltered data, 14% for AM, and 6% for ISG. For out-of-plane rayline errors, overestimations of dose in a low-dose region (∼50 cGy) were as high as 13 Gy for unfiltered

  9. Cervical spine motion: radiographic study

    International Nuclear Information System (INIS)

    Morgan, J.P.; Miyabayashi, T.; Choy, S.

    1986-01-01

    Knowledge of the acceptable range of motion of the cervical spine of the dog is used in the radiographic diagnosis of both developmental and degenerative diseases. A series of radiographs of mature Beagle dogs was used to identify motion within sagittal and transverse planes. Positioning of the dog's head and neck was standardized, using a restraining board, and mimicked those thought to be of value in diagnostic radiology. The range of motion was greatest between C2 and C5. Reports of severe disk degeneration in the cervical spine of the Beagle describe the most severely involved disks to be C4 through C7. Thus, a high range of motion between vertebral segments does not seem to be the cause for the severe degenerative disk disease. Dorsoventral slippage between vertebral segments was seen, but was not accurately measured. Wedging of disks was clearly identified. At the atlantoaxio-occipital region, there was a high degree of motion within the sagittal plane at the atlantoaxial and atlanto-occipital joints; the measurement can be a guideline in the radiographic diagnosis of instability due to developmental anomalies in this region. Lateral motion within the transverse plane was detected at the 2 joints; however, motion was minimal, and the measurements seemed to be less accurate because of rotation of the cervical spine. Height of the vertebral canal was consistently noted to be greater at the caudal orifice, giving some warning to the possibility of overdiagnosis in suspected instances of cervical spondylopathy

  10. Motion control report

    CERN Document Server

    2013-01-01

    Please note this is a short discount publication. In today's manufacturing environment, Motion Control plays a major role in virtually every project.The Motion Control Report provides a comprehensive overview of the technology of Motion Control:* Design Considerations* Technologies* Methods to Control Motion* Examples of Motion Control in Systems* A Detailed Vendors List

  11. Motion-compensating gradients in the study of multiple sclerosis

    International Nuclear Information System (INIS)

    Runge, V.M.; Wood, M.L.; Kaufman, D.L.

    1987-01-01

    A low bandwidth motion compensating technique (no. 1) was compared with a conventional spin-echo technique (no. 2) in 20 patients with multiple sclerosis using a 1.0-T MR imaging system. In technique 1, refocusing gradients were employed to compensate for motion of constant velocity along the frequency-encoding direction. The sampling time was also increased to provide a greater S/N. Use of technique 1 was resulted in detection of 42% +- 23% more lesions (n = 8). The contrast-to-noise ratio for gray versus white matter improved by 87% +- 54% and that for lesion versus white matter by 66% +- 22%. The S/N for white matter improved by 56% +- 25%. An increase in chemical shift artifact was noted but not felt to be detrimental to lesion visualization. In the majority of cases, normal brain stem structures were more distinctly visualized. In two cases, pontine lesions were more clearly demarcated due to reduced pulsation artifacts. The combined use of refocusing gradients and low bandwidth techniques provides reduction of motion artifacts (from CSF and vessel pulsation) and improved S/N, leading to improved lesion detection

  12. Using an eye tracker for accurate eye movement artifact correction

    NARCIS (Netherlands)

    Kierkels, J.J.M.; Riani, J.; Bergmans, J.W.M.; Boxtel, van G.J.M.

    2007-01-01

    We present a new method to correct eye movement artifacts in electroencephalogram (EEG) data. By using an eye tracker, whose data cannot be corrupted by any electrophysiological signals, an accurate method for correction is developed. The eye-tracker data is used in a Kalman filter to estimate which

  13. Soft tissue artifact in canine kinematic gait analysis

    NARCIS (Netherlands)

    Schwencke, M.; Smolders, L.A.; Bergknut, N.; Gustas, P.; Meij, B.P.; Hazewinkel, H.A.W.

    2012-01-01

    Vet Surg. 2012 Oct;41(7):829-37. doi: 10.1111/j.1532-950X.2012.01021.x. Soft tissue artifact in canine kinematic gait analysis. Schwencke M, Smolders LA, Bergknut N, Gustås P, Meij BP, Hazewinkel HA. Source Department of Clinical Sciences of Companion Animals,, Faculty of Veterinary Medicine,

  14. Interacting with piles of artifacts on digital tables

    NARCIS (Netherlands)

    Aliakseyeu, D.; Lucero Vera, A.A.; Subramanian, S.

    2007-01-01

    Designers and architects regularly use piles to organise visual artifacts. Recent efforts have now made it possible for users to create piles in digital systems as well. However, there is still little understanding of how users shouldinteract with digital piles. In this paper we investigate this

  15. Interacting with piles of artifacts on digital tables

    NARCIS (Netherlands)

    Aliakseyeu, D.; Subramanian, S.; Lucero Vera, A.A.; Gutwin, C.

    2006-01-01

    Designers and architects regularly use piles to organize visual artifacts. Recent efforts have now made it possible for users to create piles in digital systems as well. However, there is still little understanding of how users should interact with digital piles. In this paper we investigate this

  16. Image correction for computed tomography to remove crosstalk artifacts

    International Nuclear Information System (INIS)

    King, K.F.

    1990-01-01

    A correction method and apparatus for Computed Tomography (CT) which removes ring and streak artifacts from images by correcting for data contamination by crosstalk errors comprises subtracting from the output S o of a detector, a crosstalk factor derived from outputs of adjacent detectors. The crosstalk factors are obtained by scanning an off-centre phantom. (author)

  17. Automatic correction of dental artifacts in PET/MRI

    DEFF Research Database (Denmark)

    Ladefoged, Claes N.; Andersen, Flemming L.; Keller, Sune

    2015-01-01

    A challenge when using current magnetic resonance (MR)-based attenuation correction in positron emission tomography/MR imaging (PET/MRI) is that the MRIs can have a signal void around the dental fillings that is segmented as artificial air-regions in the attenuation map. For artifacts connected...

  18. Controlling simulations of human-artifact interaction with scenario bundles

    NARCIS (Netherlands)

    Van der Vegte, W.F.; Rusák, Z.

    2008-01-01

    We introduce a methodology for modeling and simulating fully virtual human-artifact systems, aiming to resolve two issues in virtual prototyping: (i) integration of distinct modeling and simulation approaches, and (ii) extending the deployability of simulations towards conceptual design. We are

  19. Artifacts as Stories: Understanding Families, Digital Literacies, and Storied Lives

    Science.gov (United States)

    Lewis Ellison, Tisha

    2016-01-01

    This column focuses on the interactions during family and group conversation circles that not only helped participants talk about personal, emotional, and social issues in their digital stories but also helped them make sense of artifacts and the meanings that stories carry in shared spaces and practices. This work adds to the bourgeoning…

  20. Coevolution of variability models and related software artifacts

    DEFF Research Database (Denmark)

    Passos, Leonardo; Teixeira, Leopoldo; Dinztner, Nicolas

    2015-01-01

    models coevolve with other artifact types, we study a large and complex real-world variant-rich software system: the Linux kernel. Specifically, we extract variability-coevolution patterns capturing changes in the variability model of the Linux kernel with subsequent changes in Makefiles and C source...

  1. 77 FR 40914 - Arts and Artifacts Indemnity Panel Advisory Committee

    Science.gov (United States)

    2012-07-11

    ... NATIONAL FOUNDATION ON THE ARTS AND THE HUMANITIES Arts and Artifacts Indemnity Panel Advisory Committee AGENCY: Federal Council on the Arts and the Humanities, National Endowment for the Humanities, National Foundation on the Arts and the Humanities. ACTION: Notice of meeting. SUMMARY: Pursuant to section...

  2. 77 FR 64146 - Arts and Artifacts Indemnity Panel Advisory Committee

    Science.gov (United States)

    2012-10-18

    ... NATIONAL FOUNDATION ON THE ARTS AND THE HUMANITIES Arts and Artifacts Indemnity Panel Advisory Committee AGENCY: Federal Council on the Arts and the Humanities, National Endowment for the Humanities... U.S.C. App.), notice is hereby given that the Federal Council on the Arts and the Humanities will...

  3. 78 FR 4878 - Arts and Artifacts Indemnity Panel Advisory Committee

    Science.gov (United States)

    2013-01-23

    ... NATIONAL FOUNDATION ON THE ARTS AND THE HUMANITIES Arts and Artifacts Indemnity Panel Advisory Committee AGENCY: Federal Council on the Arts and the Humanities; National Endowment for the Humanities... U.S.C. App.), notice is hereby given that the Federal Council on the Arts and the Humanities will...

  4. Artifact suppression and analysis of brain activities with electroencephalography signals.

    Science.gov (United States)

    Rashed-Al-Mahfuz, Md; Islam, Md Rabiul; Hirose, Keikichi; Molla, Md Khademul Islam

    2013-06-05

    Brain-computer interface is a communication system that connects the brain with computer (or other devices) but is not dependent on the normal output of the brain (i.e., peripheral nerve and muscle). Electro-oculogram is a dominant artifact which has a significant negative influence on further analysis of real electroencephalography data. This paper presented a data adaptive technique for artifact suppression and brain wave extraction from electroencephalography signals to detect regional brain activities. Empirical mode decomposition based adaptive thresholding approach was employed here to suppress the electro-oculogram artifact. Fractional Gaussian noise was used to determine the threshold level derived from the analysis data without any training. The purified electroencephalography signal was composed of the brain waves also called rhythmic components which represent the brain activities. The rhythmic components were extracted from each electroencephalography channel using adaptive wiener filter with the original scale. The regional brain activities were mapped on the basis of the spatial distribution of rhythmic components, and the results showed that different regions of the brain are activated in response to different stimuli. This research analyzed the activities of a single rhythmic component, alpha with respect to different motor imaginations. The experimental results showed that the proposed method is very efficient in artifact suppression and identifying individual motor imagery based on the activities of alpha component.

  5. From Artifacts to Archives: Digging into a Community's Past.

    Science.gov (United States)

    Morgan, Judy

    1991-01-01

    Presents a two-month historical research project for use in a sixth grade social studies class. Includes student use of artifacts, photographs, news clippings, maps, and oral histories obtained by interviews. Suggests that children compile a chronological history of their community to analyze, organize, and record what they have learned. (DK)

  6. List mode reconstruction for PET with motion compensation: A simulation study

    International Nuclear Information System (INIS)

    Qi, Jinyi; Huesman, Ronald H.

    2002-01-01

    Motion artifacts can be a significant factor that limits the image quality in high-resolution PET. Surveillance systems have been developed to track the movements of the subject during a scan. Development of reconstruction algorithms that are able to compensate for the subject motion will increase the potential of PET. In this paper we present a list mode likelihood reconstruction algorithm with the ability of motion compensation. The subject moti is explicitly modeled in the likelihood function. The detections of each detector pair are modeled as a Poisson process with time vary ingrate function. The proposed method has several advantages over the existing methods. It uses all detected events and does not introduce any interpolation error. Computer simulations show that the proposed method can compensate simulated subject movements and that the reconstructed images have no visible motion artifacts

  7. Assessment of metal artifact reduction methods in pelvic CT

    Energy Technology Data Exchange (ETDEWEB)

    Abdoli, Mehrsima [Department of Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, Amsterdam 1066 CX (Netherlands); Mehranian, Abolfazl [Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, Geneva CH-1211 (Switzerland); Ailianou, Angeliki; Becker, Minerva [Division of Radiology, Geneva University Hospital, Geneva CH-1211 (Switzerland); Zaidi, Habib, E-mail: habib.zaidi@hcuge.ch [Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, Geneva CH-1211 (Switzerland); Geneva Neuroscience Center, Geneva University, Geneva CH-1205 (Switzerland); Department of Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, University of Groningen, Hanzeplein 1, Groningen 9700 RB (Netherlands)

    2016-04-15

    Purpose: Metal artifact reduction (MAR) produces images with improved quality potentially leading to confident and reliable clinical diagnosis and therapy planning. In this work, the authors evaluate the performance of five MAR techniques for the assessment of computed tomography images of patients with hip prostheses. Methods: Five MAR algorithms were evaluated using simulation and clinical studies. The algorithms included one-dimensional linear interpolation (LI) of the corrupted projection bins in the sinogram, two-dimensional interpolation (2D), a normalized metal artifact reduction (NMAR) technique, a metal deletion technique, and a maximum a posteriori completion (MAPC) approach. The algorithms were applied to ten simulated datasets as well as 30 clinical studies of patients with metallic hip implants. Qualitative evaluations were performed by two blinded experienced radiologists who ranked overall artifact severity and pelvic organ recognition for each algorithm by assigning scores from zero to five (zero indicating totally obscured organs with no structures identifiable and five indicating recognition with high confidence). Results: Simulation studies revealed that 2D, NMAR, and MAPC techniques performed almost equally well in all regions. LI falls behind the other approaches in terms of reducing dark streaking artifacts as well as preserving unaffected regions (p < 0.05). Visual assessment of clinical datasets revealed the superiority of NMAR and MAPC in the evaluated pelvic organs and in terms of overall image quality. Conclusions: Overall, all methods, except LI, performed equally well in artifact-free regions. Considering both clinical and simulation studies, 2D, NMAR, and MAPC seem to outperform the other techniques.

  8. A study of metal artifacts on MR imaging. Evaluation of scanning parameters

    International Nuclear Information System (INIS)

    Yamashiro, Mitsuaki

    1999-01-01

    The purpose of this study was to evaluate scanning parameters on MR imaging for reducing metal artifacts using phantom study. Metal artifacts on sagittal images, perpendicular to static magnetic direction showed round shape in the relationship between shape of metal artifacts on MR images and scanning direction. Metal artifacts on both axial and coronal images, parallel to static magnetic direction showed oval shape in the direction of X-axis. In spin echo sequences, the largest dimension of metal artifacts was coronal image, followed by axial image and then sagittal image. In gradient echo sequences, the largest dimension of metal artifacts was axial image, followed by coronal image and then sagittal image. The best scanning plane for reducing metal artifacts was perpendicular to static magnetic direction. In scanning sequences, the largest dimensions of metal artifacts were gradient echo sequences, followed by T2-weighted spin echo sequence and then proton density-weighted and T1-weighted spin echo sequences. Large flip angle increased much metal artifacts on both axial and coronal images in gradient echo sequences. Small flip angle was useful for reducing metal artifacts on both axial and coronal images. The influence of flip angle on metal artifacts in sagittal images perpendicular static magnetic direction was less than for images in coronal and axial planes on gradient echo sequences. These results suggested that a study of metal artifacts on MR imaging about evaluation of scanning parameters was useful to reduce metal artifacts on MR images. (K.H.)

  9. Correction of patient motion in cone-beam CT using 3D-2D registration

    Science.gov (United States)

    Ouadah, S.; Jacobson, M.; Stayman, J. W.; Ehtiati, T.; Weiss, C.; Siewerdsen, J. H.

    2017-12-01

    Cone-beam CT (CBCT) is increasingly common in guidance of interventional procedures, but can be subject to artifacts arising from patient motion during fairly long (~5-60 s) scan times. We present a fiducial-free method to mitigate motion artifacts using 3D-2D image registration that simultaneously corrects residual errors in the intrinsic and extrinsic parameters of geometric calibration. The 3D-2D registration process registers each projection to a prior 3D image by maximizing gradient orientation using the covariance matrix adaptation-evolution strategy optimizer. The resulting rigid transforms are applied to the system projection matrices, and a 3D image is reconstructed via model-based iterative reconstruction. Phantom experiments were conducted using a Zeego robotic C-arm to image a head phantom undergoing 5-15 cm translations and 5-15° rotations. To further test the algorithm, clinical images were acquired with a CBCT head scanner in which long scan times were susceptible to significant patient motion. CBCT images were reconstructed using a penalized likelihood objective function. For phantom studies the structural similarity (SSIM) between motion-free and motion-corrected images was  >0.995, with significant improvement (p  values of uncorrected images. Additionally, motion-corrected images exhibited a point-spread function with full-width at half maximum comparable to that of the motion-free reference image. Qualitative comparison of the motion-corrupted and motion-corrected clinical images demonstrated a significant improvement in image quality after motion correction. This indicates that the 3D-2D registration method could provide a useful approach to motion artifact correction under assumptions of local rigidity, as in the head, pelvis, and extremities. The method is highly parallelizable, and the automatic correction of residual geometric calibration errors provides added benefit that could be valuable in routine use.

  10. The role of trapped bubbles in kidney stone detection with the color Doppler ultrasound twinkling artifact

    Science.gov (United States)

    Simon, Julianna C.; Sapozhnikov, Oleg A.; Kreider, Wayne; Breshock, Michael; Williams, James C., Jr.; Bailey, Michael R.

    2018-01-01

    The color Doppler ultrasound twinkling artifact, which highlights kidney stones with rapidly changing color, has the potential to improve stone detection; however, its inconsistent appearance has limited its clinical utility. Recently, it was proposed stable crevice bubbles on the kidney stone surface cause twinkling; however, the hypothesis is not fully accepted because the bubbles have not been directly observed. In this paper, the micron or submicron-sized bubbles predicted by the crevice bubble hypothesis are enlarged in kidney stones of five primary compositions by exposure to acoustic rarefaction pulses or hypobaric static pressures in order to simultaneously capture their appearance by high-speed photography and ultrasound imaging. On filming stones that twinkle, consecutive rarefaction pulses from a lithotripter caused some bubbles to reproducibly grow from specific locations on the stone surface, suggesting the presence of pre-existing crevice bubbles. Hyperbaric and hypobaric static pressures were found to modify the twinkling artifact; however, the simple expectation that hyperbaric exposures reduce and hypobaric pressures increase twinkling by shrinking and enlarging bubbles, respectively, largely held for rough-surfaced stones but was inadequate for smoother stones. Twinkling was found to increase or decrease in response to elevated static pressure on smooth stones, perhaps because of the compression of internal voids. These results support the crevice bubble hypothesis of twinkling and suggest the kidney stone crevices that give rise to the twinkling phenomenon may be internal as well as external.

  11. The role of trapped bubbles in kidney stone detection with the color Doppler ultrasound twinkling artifact.

    Science.gov (United States)

    Simon, Julianna C; Sapozhnikov, Oleg A; Kreider, Wayne; Breshock, Michael; Williams, James C; Bailey, Michael R

    2018-01-09

    The color Doppler ultrasound twinkling artifact, which highlights kidney stones with rapidly changing color, has the potential to improve stone detection; however, its inconsistent appearance has limited its clinical utility. Recently, it was proposed stable crevice bubbles on the kidney stone surface cause twinkling; however, the hypothesis is not fully accepted because the bubbles have not been directly observed. In this paper, the micron or submicron-sized bubbles predicted by the crevice bubble hypothesis are enlarged in kidney stones of five primary compositions by exposure to acoustic rarefaction pulses or hypobaric static pressures in order to simultaneously capture their appearance by high-speed photography and ultrasound imaging. On filming stones that twinkle, consecutive rarefaction pulses from a lithotripter caused some bubbles to reproducibly grow from specific locations on the stone surface, suggesting the presence of pre-existing crevice bubbles. Hyperbaric and hypobaric static pressures were found to modify the twinkling artifact; however, the simple expectation that hyperbaric exposures reduce and hypobaric pressures increase twinkling by shrinking and enlarging bubbles, respectively, largely held for rough-surfaced stones but was inadequate for smoother stones. Twinkling was found to increase or decrease in response to elevated static pressure on smooth stones, perhaps because of the compression of internal voids. These results support the crevice bubble hypothesis of twinkling and suggest the kidney stone crevices that give rise to the twinkling phenomenon may be internal as well as external.

  12. Total Variation-Based Reduction of Streak Artifacts, Ring Artifacts and Noise in 3D Reconstruction from Optical Projection Tomography

    Czech Academy of Sciences Publication Activity Database

    Michálek, Jan

    2015-01-01

    Roč. 21, č. 6 (2015), s. 1602-1615 ISSN 1431-9276 R&D Projects: GA MŠk(CZ) LH13028; GA ČR(CZ) GA13-12412S Institutional support: RVO:67985823 Keywords : optical projection tomography * microscopy * artifacts * total variation * data mismatch Subject RIV: EA - Cell Biology Impact factor: 1.730, year: 2015

  13. Practical aspects of data-driven motion correction approach for brain SPECT

    International Nuclear Information System (INIS)

    Kyme, A.Z.; Hutton, B.F.; Hatton, R.L.; Skerrett, D.; Barnden, L.

    2002-01-01

    Full text: Patient motion can cause image artifacts in SPECT despite restraining measures. Data-driven detection and correction of motion can be achieved by comparison of acquired data with the forward-projections. By optimising the orientation of a partial reconstruction, parameters can be obtained for each misaligned projection and applied to update this volume using a 3D reconstruction algorithm. Phantom validation was performed to explore practical aspects of this approach. Noisy projection datasets simulating a patient undergoing at least one fully 3D movement during acquisition were compiled from various projections of the digital Hoffman brain phantom. Motion correction was then applied to the reconstructed studies. Correction success was assessed visually and quantitatively. Resilience with respect to subset order and missing data in the reconstruction and updating stages, detector geometry considerations, and the need for implementing an iterated correction were assessed in the process. Effective correction of the corrupted studies was achieved. Visually, artifactual regions in the reconstructed slices were suppressed and/or removed. Typically the ratio of mean square difference between the corrected and reference studies compared to that between the corrupted and reference studies was > 2. Although components of the motions are missed using a single-head implementation, improvement was still evident in the correction. The need for multiple iterations in the approach was small due to the bulk of misalignment errors being corrected in the first pass. Dispersion of subsets for reconstructing and updating the partial reconstruction appears to give optimal correction. Further validation is underway using triple-head physical phantom data. Copyright (2002) The Australian and New Zealand Society of Nuclear Medicine Inc

  14. Metal artifact reduction image reconstruction algorithm for CT of implanted metal orthopedic devices: a work in progress

    International Nuclear Information System (INIS)

    Liu, Patrick T.; Pavlicek, William P.; Peter, Mary B.; Roberts, Catherine C.; Paden, Robert G.; Spangehl, Mark J.

    2009-01-01

    Despite recent advances in CT technology, metal orthopedic implants continue to cause significant artifacts on many CT exams, often obscuring diagnostic information. We performed this prospective study to evaluate the effectiveness of an experimental metal artifact reduction (MAR) image reconstruction program for CT. We examined image quality on CT exams performed in patients with hip arthroplasties as well as other types of implanted metal orthopedic devices. The exam raw data were reconstructed using two different methods, the standard filtered backprojection (FBP) program and the MAR program. Images were evaluated for quality of the metal-cement-bone interfaces, trabeculae ≤1 cm from the metal, trabeculae 5 cm apart from the metal, streak artifact, and overall soft tissue detail. The Wilcoxon Rank Sum test was used to compare the image scores from the large and small prostheses. Interobserver agreement was calculated. When all patients were grouped together, the MAR images showed mild to moderate improvement over the FBP images. However, when the cases were divided by implant size, the MAR images consistently received higher image quality scores than the FBP images for large metal implants (total hip prostheses). For small metal implants (screws, plates, staples), conversely, the MAR images received lower image quality scores than the FBP images due to blurring artifact. The difference of image scores for the large and small implants was significant (p=0.002). Interobserver agreement was found to be high for all measures of image quality (k>0.9). The experimental MAR reconstruction algorithm significantly improved CT image quality for patients with large metal implants. However, the MAR algorithm introduced blurring artifact that reduced image quality with small metal implants. (orig.)

  15. Improving image quality for digital breast tomosynthesis: an automated detection and diffusion-based method for metal artifact reduction

    Science.gov (United States)

    Lu, Yao; Chan, Heang-Ping; Wei, Jun; Hadjiiski, Lubomir M.; Samala, Ravi K.

    2017-10-01

    In digital breast tomosynthesis (DBT), the high-attenuation metallic clips marking a previous biopsy site in the breast cause errors in the estimation of attenuation along the ray paths intersecting the markers during reconstruction, which result in interplane and inplane artifacts obscuring the visibility of subtle lesions. We proposed a new metal artifact reduction (MAR) method to improve image quality. Our method uses automatic detection and segmentation to generate a marker location map for each projection (PV). A voting technique based on the geometric correlation among different PVs is designed to reduce false positives (FPs) and to label the pixels on the PVs and the voxels in the imaged volume that represent the location and shape of the markers. An iterative diffusion method replaces the labeled pixels on the PVs with estimated tissue intensity from the neighboring regions while preserving the original pixel values in the neighboring regions. The inpainted PVs are then used for DBT reconstruction. The markers are repainted on the reconstructed DBT slices for radiologists’ information. The MAR method is independent of reconstruction techniques or acquisition geometry. For the training set, the method achieved 100% success rate with one FP in 19 views. For the test set, the success rate by view was 97.2% for core biopsy microclips and 66.7% for clusters of large post-lumpectomy markers with a total of 10 FPs in 58 views. All FPs were large dense benign calcifications that also generated artifacts if they were not corrected by MAR. For the views with successful detection, the metal artifacts were reduced to a level that was not visually apparent in the reconstructed slices. The visibility of breast lesions obscured by the reconstruction artifacts from the metallic markers was restored.

  16. The effects of breathing motion on DCE-MRI images: Phantom studies simulating respiratory motion to compare CAIPARINHA-VIBE, radial VIBE, and conventional VIBE

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Chang Kyung; Seo, Nieun; Kim, Bohyun; Huh, Jimi; Kim, Jeong Kon; Lee, Seung Soo; KIm, Kyung Won [Dept. of Radiology, and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul (Korea, Republic of); Kim, In Seong [Siemens Healthcare Korea, Seoul (Korea, Republic of); Nickel, Dominik [MR Application Predevelopment, Siemens Healthcare, Erlangen (Germany)

    2017-04-15

    To compare the breathing effects on dynamic contrast-enhanced (DCE)-MRI between controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA)-volumetric interpolated breath-hold examination (VIBE), radial VIBE with k-space-weighted image contrast view-sharing (radial-VIBE), and conventional VIBE (c-VIBE) sequences using a dedicated phantom experiment. We developed a moving platform to simulate breathing motion. We conducted dynamic scanning on a 3T machine (MAGNETOM Skyra, Siemens Healthcare) using CAIPIRINHA-VIBE, radial-VIBE, and c-VIBE for six minutes per sequence. We acquired MRI images of the phantom in both static and moving modes, and we also obtained motion-corrected images for the motion mode. We compared the signal stability and signal-to-noise ratio (SNR) of each sequence according to motion state and used the coefficients of variation (CoV) to determine the degree of signal stability. With motion, CAIPIRINHA-VIBE showed the best image quality, and the motion correction aligned the images very well. The CoV (%) of CAIPIRINHA-VIBE in the moving mode (18.65) decreased significantly after the motion correction (2.56) (p < 0.001). In contrast, c-VIBE showed severe breathing motion artifacts that did not improve after motion correction. For radial-VIBE, the position of the phantom in the images did not change during motion, but streak artifacts significantly degraded image quality, also after motion correction. In addition, SNR increased in both CAIPIRINHA-VIBE (from 3.37 to 9.41, p < 0.001) and radial-VIBE (from 4.3 to 4.96, p < 0.001) after motion correction. CAIPIRINHA-VIBE performed best for free-breathing DCE-MRI after motion correction, with excellent image quality.

  17. Measuring Motion-Induced B0-Fluctuations in the Brain Using Field Probes

    DEFF Research Database (Denmark)

    Andersen, Mads; Hanson, Lars G.; Madsen, Kristoffer Hougaard

    2016-01-01

    Purpose: Fluctuations of the background magnetic field (B0) due to body and breathing motion can lead to significant artifacts in brain imaging at ultrahigh field. Corrections based on real-time sensing using external field probes show great potential. This study evaluates different aspects of fi...

  18. Separating complex compound patient motion tracking data using independent component analysis

    Science.gov (United States)

    Lindsay, C.; Johnson, K.; King, M. A.

    2014-03-01

    In SPECT imaging, motion from respiration and body motion can reduce image quality by introducing motion-related artifacts. A minimally-invasive way to track patient motion is to attach external markers to the patient's body and record their location throughout the imaging study. If a patient exhibits multiple movements simultaneously, such as respiration and body-movement, each marker location data will contain a mixture of these motions. Decomposing this complex compound motion into separate simplified motions can have the benefit of applying a more robust motion correction to the specific type of motion. Most motion tracking and correction techniques target a single type of motion and either ignore compound motion or treat it as noise. Few methods account for compound motion exist, but they fail to disambiguate super-position in the compound motion (i.e. inspiration in addition to body movement in the positive anterior/posterior direction). We propose a new method for decomposing the complex compound patient motion using an unsupervised learning technique called Independent Component Analysis (ICA). Our method can automatically detect and separate different motions while preserving nuanced features of the motion without the drawbacks of previous methods. Our main contributions are the development of a method for addressing multiple compound motions, the novel use of ICA in detecting and separating mixed independent motions, and generating motion transform with 12 DOFs to account for twisting and shearing. We show that our method works with clinical datasets and can be employed to improve motion correction in single photon emission computed tomography (SPECT) images.

  19. Anharmonicity in nuclear wobbling motion

    International Nuclear Information System (INIS)

    Oi, M.

    2007-01-01

    An unexpected strong anharmonicity was observed in the wobbling spectrum in 163 Lu. In an attempt to understand what causes the deviation from the original wobbling model by Bohr and Mottelson, an analysis is presented using several different approaches, such as exact diagonalization, a semiclassical model to deal with anharmonic wobbling motion, and a microscopic method based on the self-consistent cranking calculation

  20. General rigid motion correction for computed tomography imaging based on locally linear embedding

    Science.gov (United States)

    Chen, Mianyi; He, Peng; Feng, Peng; Liu, Baodong; Yang, Qingsong; Wei, Biao; Wang, Ge

    2018-02-01

    The patient motion can damage the quality of computed tomography images, which are typically acquired in cone-beam geometry. The rigid patient motion is characterized by six geometric parameters and are more challenging to correct than in fan-beam geometry. We extend our previous rigid patient motion correction method based on the principle of locally linear embedding (LLE) from fan-beam to cone-beam geometry and accelerate the computational procedure with the graphics processing unit (GPU)-based all scale tomographic reconstruction Antwerp toolbox. The major merit of our method is that we need neither fiducial markers nor motion-tracking devices. The numerical and experimental studies show that the LLE-based patient motion correction is capable of calibrating the six parameters of the patient motion simultaneously, reducing patient motion artifacts significantly.

  1. Unidirectional Motion of Vehicle on Sinusoidal Path

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 17; Issue 4. Unidirectional Motion of Vehicle on Sinusoidal Path: Can it Cause Illusory Forward and Backward Motion? Anuj Bhatnagar. Classroom Volume 17 Issue 4 April 2012 pp 387-392 ...

  2. 14 CFR 406.141 - Motions.

    Science.gov (United States)

    2010-01-01

    ... cause shown, a party must file any prehearing motion with the Federal Docket Management System and serve... for more definite statement. A respondent may file a motion requesting a more definite statement of... pleading and must submit the details that the party believes would make the allegation or response definite...

  3. Motion compensation for MRI-guided radiotherapy

    NARCIS (Netherlands)

    Glitzner, M.

    2017-01-01

    Radiotherapy aims to deliver a lethal radiation dose to cancer cells immersed in the body using a high energetic photon beam. Due to physiologic motion of the human anatomy (e.g. caused by filling of internal organs or breathing), the target volume is under permanent motion during irradiation,

  4. A generic EEG artifact removal algorithm based on the multi-channel Wiener filter

    Science.gov (United States)

    Somers, Ben; Francart, Tom; Bertrand, Alexander

    2018-06-01

    Objective. The electroencephalogram (EEG) is an essential neuro-monitoring tool for both clinical and research purposes, but is susceptible to a wide variety of undesired artifacts. Removal of these artifacts is often done using blind source separation techniques, relying on a purely data-driven transformation, which may sometimes fail to sufficiently isolate artifacts in only one or a few components. Furthermore, some algorithms perform well for specific artifacts, but not for others. In this paper, we aim to develop a generic EEG artifact removal algorithm, which allows the user to annotate a few artifact segments in the EEG recordings to inform the algorithm. Approach. We propose an algorithm based on the multi-channel Wiener filter (MWF), in which the artifact covariance matrix is replaced by a low-rank approximation based on the generalized eigenvalue decomposition. The algorithm is validated using both hybrid and real EEG data, and is compared to other algorithms frequently used for artifact removal. Main results. The MWF-based algorithm successfully removes a wide variety of artifacts with better performance than current state-of-the-art methods. Significance. Current EEG artifact removal techniques often have limited applicability due to their specificity to one kind of artifact, their complexity, or simply because they are too ‘blind’. This paper demonstrates a fast, robust and generic algorithm for removal of EEG artifacts of various types, i.e. those that were annotated as unwanted by the user.

  5. A dialectical take on artifact ecologies and the physical - digital divide

    DEFF Research Database (Denmark)

    Bødker, Susanne; Klokmose, Clemens Nylandsted

    In this position paper, we will present and discuss our understanding of artifact ecologies as we have developed it, rooted in activity theoretical HCI and dialectical thinking . Our basis is in the Human-Artifact Model, as well as well as cases where we have worked with artifact ecologies...

  6. Prospective motion correction with volumetric navigators (vNavs) reduces the bias and variance in brain morphometry induced by subject motion.

    Science.gov (United States)

    Tisdall, M Dylan; Reuter, Martin; Qureshi, Abid; Buckner, Randy L; Fischl, Bruce; van der Kouwe, André J W

    2016-02-15

    Recent work has demonstrated that subject motion produces systematic biases in the metrics computed by widely used morphometry software packages, even when the motion is too small to produce noticeable image artifacts. In the common situation where the control population exhibits different behaviors in the scanner when compared to the experimental population, these systematic measurement biases may produce significant confounds for between-group analyses, leading to erroneous conclusions about group differences. While previous work has shown that prospective motion correction can improve perceived image quality, here we demonstrate that, in healthy subjects performing a variety of directed motions, the use of the volumetric navigator (vNav) prospective motion correction system significantly reduces the motion-induced bias and variance in morphometry. Copyright © 2015 Elsevier Inc. All rights reserved.

  7. The application of metal artifact reduction (MAR) in CT scans for radiation oncology by monoenergetic extrapolation with a DECT scanner

    Energy Technology Data Exchange (ETDEWEB)

    Schwahofer, Andrea [German Cancer Research Center, Heidelberg (Germany). Dept. of Medical Physics in Radiation Oncology; Clinical Center Vivantes, Neukoelln (Germany). Dept. of Radiotherapy and Oncology; Baer, Esther [German Cancer Research Center, Heidelberg (Germany). Dept. of Medical Physics in Radiation Oncology; Kuchenbecker, Stefan; Kachelriess, Marc [German Cancer Research Center, Heidelberg (Germany). Dept. of Medical Physics in Radiology; Grossmann, J. Guenter [German Cancer Research Center, Heidelberg (Germany). Dept. of Medical Physics in Radiation Oncology; Ortenau Klinikum Offenburg-Gengenbach (Germany). Dept. of Radiooncology; Sterzing, Florian [Heidelberg Univ. (Germany). Dept. of Radiation Oncology; German Cancer Research Center, Heidelberg (Germany). Dept. of Radiotherapy

    2015-07-01

    Metal artifacts in computed tomography CT images are one of the main problems in radiation oncology as they introduce uncertainties to target and organ at risk delineation as well as dose calculation. This study is devoted to metal artifact reduction (MAR) based on the monoenergetic extrapolation of a dual energy CT (DECT) dataset. In a phantom study the CT artifacts caused by metals with different densities: aluminum (ρ{sub Al} = 2.7 g/cm{sup 3}), titanium (ρ{sub Ti} = 4.5 g/cm{sup 3}), steel (ρ{sub steel} = 7.9 g/cm{sup 3}) and tungsten (ρ{sub W} = 19.3 g/cm{sup 3}) have been investigated. Data were collected using a clinical dual source dual energy CT (DECT) scanner (Siemens Sector Healthcare, Forchheim, Germany) with tube voltages of 100 kV and 140 kV (Sn). For each tube voltage the data set in a given volume was reconstructed. Based on these two data sets a voxel by voxel linear combination was performed to obtain the monoenergetic data sets. The results were evaluated regarding the optical properties of the images as well as the CT values (HU) and the dosimetric consequences in computed treatment plans. A data set without metal substitute served as the reference. Also, a head and neck patient with dental fillings (amalgam ρ = 10 g/cm{sup 3}) was scanned with a single energy CT (SECT) protocol and a DECT protocol. The monoenergetic extrapolation was performed as described above and evaluated in the same way. Visual assessment of all data shows minor reductions of artifacts in the images with aluminum and titanium at a monoenergy of 105 keV. As expected, the higher the densities the more distinctive are the artifacts. For metals with higher densities such as steel or tungsten, no artifact reduction has been achieved. Likewise in the CT values, no improvement by use of the monoenergetic extrapolation can be detected. The dose was evaluated at a point 7 cm behind the isocenter of a static field. Small improvements (around 1%) can be seen with 105 ke

  8. The application of metal artifact reduction (MAR) in CT scans for radiation oncology by monoenergetic extrapolation with a DECT scanner

    International Nuclear Information System (INIS)

    Schwahofer, Andrea; Clinical Center Vivantes, Neukoelln; Baer, Esther; Kuchenbecker, Stefan; Kachelriess, Marc; Grossmann, J. Guenter; Ortenau Klinikum Offenburg-Gengenbach; Sterzing, Florian; German Cancer Research Center, Heidelberg

    2015-01-01

    Metal artifacts in computed tomography CT images are one of the main problems in radiation oncology as they introduce uncertainties to target and organ at risk delineation as well as dose calculation. This study is devoted to metal artifact reduction (MAR) based on the monoenergetic extrapolation of a dual energy CT (DECT) dataset. In a phantom study the CT artifacts caused by metals with different densities: aluminum (ρ Al = 2.7 g/cm 3 ), titanium (ρ Ti = 4.5 g/cm 3 ), steel (ρ steel = 7.9 g/cm 3 ) and tungsten (ρ W = 19.3 g/cm 3 ) have been investigated. Data were collected using a clinical dual source dual energy CT (DECT) scanner (Siemens Sector Healthcare, Forchheim, Germany) with tube voltages of 100 kV and 140 kV (Sn). For each tube voltage the data set in a given volume was reconstructed. Based on these two data sets a voxel by voxel linear combination was performed to obtain the monoenergetic data sets. The results were evaluated regarding the optical properties of the images as well as the CT values (HU) and the dosimetric consequences in computed treatment plans. A data set without metal substitute served as the reference. Also, a head and neck patient with dental fillings (amalgam ρ = 10 g/cm 3 ) was scanned with a single energy CT (SECT) protocol and a DECT protocol. The monoenergetic extrapolation was performed as described above and evaluated in the same way. Visual assessment of all data shows minor reductions of artifacts in the images with aluminum and titanium at a monoenergy of 105 keV. As expected, the higher the densities the more distinctive are the artifacts. For metals with higher densities such as steel or tungsten, no artifact reduction has been achieved. Likewise in the CT values, no improvement by use of the monoenergetic extrapolation can be detected. The dose was evaluated at a point 7 cm behind the isocenter of a static field. Small improvements (around 1%) can be seen with 105 keV. However, the dose uncertainty remains of the

  9. Effects of arm truncation on the appearance of the halo artifact in {sup 68}Ga-PSMA-11 (HBED-CC) PET/MRI

    Energy Technology Data Exchange (ETDEWEB)

    Afshar-Oromieh, Ali; Haberkorn, Uwe [Heidelberg University Hospital, Department of Nuclear Medicine, Heidelberg (Germany); German Cancer Research Center, Clinical Cooperation Unit Nuclear Medicine, Heidelberg (Germany); Wolf, Maya; Gnirs, Regula; Schlemmer, Heinz-Peter; Freitag, Martin T. [German Cancer Research Center, Department of Radiology, Heidelberg (Germany); Kachelriess, Marc [German Cancer Research Center, Department of Medical Physics in Radiology, Heidelberg (Germany); Kopka, Klaus [German Cancer Research Center, Division of Radiopharmaceutical Chemistry, Heidelberg (Germany)

    2017-09-15

    PSMA ligand imaging with hybrid PET/MRI scanners could be an integral part of the clinical routine in the future. However, the first study about this novel method revealed a severe photopenic artifact (''halo artifact'') around the urinary bladder causing significantly reduced tumor visibility. The aim of this evaluation was to analyze the role of arm truncation on the appearance of the halo artifact in {sup 68}Ga-PSMA-11 PET/MRI hypothesizing that this influences the appearance. Twenty-seven consecutive patients were subjected to {sup 68}Ga-PSMA-11 PET/CT (1 h p.i.) followed by PET/MRI (3 h p.i.). PET/MRI was first started with scans of the abdomen to pelvis with arms positioned up above the head. Immediately thereafter, additional scans from the pelvis to abdomen were conducted with arms positioned down beside the trunk. All investigations were first analyzed separately and then compared with respect to tumor detection and tumor uptake (SUV) as well as the presence and intensity of the halo artifact. The Wilcoxon signed rank test was used to determine statistical differences including Bonferroni correction. The halo was significantly reduced if the arms were elevated. Lesions inside the halo artifact (n = 16) demonstrated significantly increased SUVmean (p = 0.0007) and SUVmax (p = 0.0024) with arms positioned up. The halo appearance and intensity was not dependent on the total activity and activity concentration of the urinary bladder. Positioning the arms down was shown to be significantly associated with the appearance of the halo artifact in PET/MRI. Positioning the arms up above the head can significantly reduce the halo artifact, thereby detecting more tumor lesions. (orig.)

  10. Simulation of spatiotemporal CT data sets using a 4D MRI-based lung motion model.

    Science.gov (United States)

    Marx, Mirko; Ehrhardt, Jan; Werner, René; Schlemmer, Heinz-Peter; Handels, Heinz

    2014-05-01

    Four-dimensional CT imaging is widely used to account for motion-related effects during radiotherapy planning of lung cancer patients. However, 4D CT often contains motion artifacts, cannot be used to measure motion variability, and leads to higher dose exposure. In this article, we propose using 4D MRI to acquire motion information for the radiotherapy planning process. From the 4D MRI images, we derive a time-continuous model of the average patient-specific respiratory motion, which is then applied to simulate 4D CT data based on a static 3D CT. The idea of the motion model is to represent the average lung motion over a respiratory cycle by cyclic B-spline curves. The model generation consists of motion field estimation in the 4D MRI data by nonlinear registration, assigning respiratory phases to the motion fields, and applying a B-spline approximation on a voxel-by-voxel basis to describe the average voxel motion over a breathing cycle. To simulate a patient-specific 4D CT based on a static CT of the patient, a multi-modal registration strategy is introduced to transfer the motion model from MRI to the static CT coordinates. Differences between model-based estimated and measured motion vectors are on average 1.39 mm for amplitude-based binning of the 4D MRI data of three patients. In addition, the MRI-to-CT registration strategy is shown to be suitable for the model transformation. The application of our 4D MRI-based motion model for simulating 4D CT images provides advantages over standard 4D CT (less motion artifacts, radiation-free). This makes it interesting for radiotherapy planning.

  11. MRI Artifacts of a Metallic Stent Derived From a Human Aorta Specimen

    International Nuclear Information System (INIS)

    Soto, M. E.; Flores, P.; Marrufo, O.; Hidalgo, S. S.; Rodriguez, A. O.

    2010-01-01

    Magnetic resonance imaging has proved to be a useful technique to get images of the whole body. However, the presence of ferromagnetic material can cause susceptibility artifacts, which result from microscopic gradients that occur near the boundaries between areas displaying different magnetic susceptibility. These gradients cause dephasing of spins and frequency shifts in the surrounding tissues. Intravoxel dephasing and spatial mis-registration can degrade image quality. An aorta with a metallic stent was preserved in formaldehyde at 10% inside acrylic cylinders and used to obtain MR images. We tested pulsed spin echo and gradient echo sequences to improve image quality. All experiments were performed on a 7T/21 cm Varian system (Varian, Inc, Palo Alto, CA) equipped with Direct Drive technology and a 16-rung birdcage coil transceiver. The presence of metallic stents produces a lack of signal that might give falsely reassuring appearances within the vessel lumen.

  12. TH-C-BRD-06: A Novel MRI Based CT Artifact Correction Method for Improving Proton Range Calculation in the Presence of Severe CT Artifacts

    International Nuclear Information System (INIS)

    Park, P; Schreibmann, E; Fox, T; Roper, J; Elder, E; Tejani, M; Crocker, I; Curran, W; Dhabaan, A

    2014-01-01

    Purpose: Severe CT artifacts can impair our ability to accurately calculate proton range thereby resulting in a clinically unacceptable treatment plan. In this work, we investigated a novel CT artifact correction method based on a coregistered MRI and investigated its ability to estimate CT HU and proton range in the presence of severe CT artifacts. Methods: The proposed method corrects corrupted CT data using a coregistered MRI to guide the mapping of CT values from a nearby artifact-free region. First patient MRI and CT images were registered using 3D deformable image registration software based on B-spline and mutual information. The CT slice with severe artifacts was selected as well as a nearby slice free of artifacts (e.g. 1cm away from the artifact). The two sets of paired MRI and CT images at different slice locations were further registered by applying 2D deformable image registration. Based on the artifact free paired MRI and CT images, a comprehensive geospatial analysis was performed to predict the correct CT HU of the CT image with severe artifact. For a proof of concept, a known artifact was introduced that changed the ground truth CT HU value up to 30% and up to 5cm error in proton range. The ability of the proposed method to recover the ground truth was quantified using a selected head and neck case. Results: A significant improvement in image quality was observed visually. Our proof of concept study showed that 90% of area that had 30% errors in CT HU was corrected to 3% of its ground truth value. Furthermore, the maximum proton range error up to 5cm was reduced to 4mm error. Conclusion: MRI based CT artifact correction method can improve CT image quality and proton range calculation for patients with severe CT artifacts

  13. Coulomb artifacts and bottomonium hyperfine splitting in lattice NRQCD

    Energy Technology Data Exchange (ETDEWEB)

    Liu, T. [Department of Physics, University of Alberta,11455 Saskatchewan Drive, Edmonton, Alberta T6G 2J1 (Canada); Penin, A.A. [Department of Physics, University of Alberta,11455 Saskatchewan Drive, Edmonton, Alberta T6G 2J1 (Canada); Institut für Theoretische Teilchenphysik, Karlsruhe Institute of Technology,Wolfgang-Gaede-Strasse 1, 76128 Karlsruhe (Germany); Rayyan, A. [Department of Physics, University of Alberta,11455 Saskatchewan Drive, Edmonton, Alberta T6G 2J1 (Canada)

    2017-02-16

    We study the role of the lattice artifacts associated with the Coulomb binding effects in the analysis of the heavy quarkonium within lattice NRQCD. We find that a “naïve” perturbative matching generates spurious linear Coulomb artifacts, which result in a large systematic error in the lattice predictions for the heavy quarkonium spectrum. This effect is responsible, in particular, for the discrepancy between the recent determinations of the bottomonium hyperfine splitting in the radiatively improved lattice NRQCD (DOI: 10.1103/PhysRevD.92.054502; Arxiv:1309.5797). We show that the correct matching procedure which provides full control over discretization errors is based on the asymptotic expansion of the lattice theory about the continuum limit, which gives M{sub Υ(1S)}−M{sub η{sub b(1S)}}=52.9±5.5 MeV (DOI: 10.1103/PhysRevD.92.054502).

  14. Santeria and Palo Mayombe: skulls, mercury, and artifacts.

    Science.gov (United States)

    Gill, James R; Rainwater, Christopher W; Adams, Bradley J

    2009-11-01

    Santeria and Palo Mayombe are syncretic religions created in the New World based upon African religious beliefs combined with Christianity. The main worship of Palo Mayombe involves religious receptacles that may contain earth, sticks, varied artifacts, and animal and human remains. Due to the use of human and nonhuman remains, discovery of these items often leads to involvement by the police due to a concern of homicide. We review in detail the medical examiner records of two of these ritualistic cases including the autopsy, anthropology, police, and investigators' reports. For the human remains, careful consideration of the context in which the remains were recovered, their state of preservation, and the associated artifacts (e.g., beads and mercury) are important in determining the appropriate level of forensic significance. Anthropological examination with particular attention to taphonomic characteristics also may help determine the origin and forensic significance.

  15. Inter-deriving Semantic Artifacts for Object-Oriented Programming

    DEFF Research Database (Denmark)

    Danvy, Olivier; Johannsen, Jacob

    2008-01-01

    .e., big-step operational semantics) specified in Abadi and Cardelli's monograph. This abstract machine therefore embodies the soundness of Abadi and Cardelli's reduction semantics and natural semantics relative to each other. To move closer to actual implementations, which use environments rather than......We present a new abstract machine for Abadi and Cardelli's untyped calculus of objects. What is special about this semantic artifact (i.e., man-made construct) is that is mechanically corresponds to both the reduction semantics (i.e., small-step operational semantics) and the natural semantics (i...... actual substitutions, we then represent object methods as closures and in the same inter-derivational spirit, we present three new semantic artifacts: a reduction semantics for a version of Abadi and Cardelli's untyped calculus of objects with explicit substitutions, an environment-based abstract machine...

  16. Interpolation strategies for reducing IFOV artifacts in microgrid polarimeter imagery.

    Science.gov (United States)

    Ratliff, Bradley M; LaCasse, Charles F; Tyo, J Scott

    2009-05-25

    Microgrid polarimeters are composed of an array of micro-polarizing elements overlaid upon an FPA sensor. In the past decade systems have been designed and built in all regions of the optical spectrum. These systems have rugged, compact designs and the ability to obtain a complete set of polarimetric measurements during a single image capture. However, these systems acquire the polarization measurements through spatial modulation and each measurement has a varying instantaneous field-of-view (IFOV). When these measurements are combined to estimate the polarization images, strong edge artifacts are present that severely degrade the estimated polarization imagery. These artifacts can be reduced when interpolation strategies are first applied to the intensity data prior to Stokes vector estimation. Here we formally study IFOV error and the performance of several bilinear interpolation strategies used for reducing it.

  17. Essential Layers, Artifacts, and Dependencies of Enterprise Architecture

    OpenAIRE

    Winter, Robert; Fischer, Ronny

    2007-01-01

    After a period where implementation speed was more important than integration, consistency and reduction of complexity, architectural considerations have become a key issue of information management in recent years again. Enterprise architecture is widely accepted as an essential mechanism for ensuring agility and consistency, compliance and efficiency. Although standards like TOGAF and FEAF have developed, however, there is no common agreement on which architecture layers, which artifact typ...

  18. An Improved Method to Watermark Images Sensitive to Blocking Artifacts

    OpenAIRE

    Afzel Noore

    2007-01-01

    A new digital watermarking technique for images that are sensitive to blocking artifacts is presented. Experimental results show that the proposed MDCT based approach produces highly imperceptible watermarked images and is robust to attacks such as compression, noise, filtering and geometric transformations. The proposed MDCT watermarking technique is applied to fingerprints for ensuring security. The face image and demographic text data of an individual are used as multi...

  19. Carbon fiber intramedullary nails reduce artifact in postoperative advanced imaging

    International Nuclear Information System (INIS)

    Zimel, Melissa N.; Hwang, Sinchun; Riedel, Elyn R.; Healey, John H.

    2015-01-01

    This study assessed whether radiolucent carbon fiber reinforced-polyetheretherketone (CFR-PEEK) intramedullary nails decreased hardware artifact on magnetic resonance imaging (MRI) and computed tomography (CT) in vitro and in an oncologic patient population. In vitro and clinical evaluations were done. A qualitative assessment of metal artifact was performed using CFR-PEEK and titanium nail MRI phantoms. Eight patients with a femoral or tibial prophylactic CFR-PEEK nail were retrospectively identified. All patients had postoperative surveillance imaging by MRI, CT, and were followed for a median 20 months (range, 12-28 months). CFR-PEEK images were compared to images from a comparative group of patients with titanium femoral intramedullary nails who had a postoperative MRI or CT. A musculoskeletal-trained radiologist graded visualization of the cortex, corticomedullary junction, and bone-muscle interface, on T1-weighted (T1W), STIR, and contrast-enhanced T1-weighted fat-saturated (T1W FS) sequences of both groups with a five-point scale, performing independent reviews 4 months apart. Statistical analysis used the Wilcoxon rank-sum test and a weighted kappa. Substantially less MRI signal loss occurred in the CFR-PEEK phantom than in the titanium phantom simulation, particularly as the angle increased with respect to direction of the static magnetic field. CFR-PEEK nails had less MRI artifact than titanium nails on scored T1W, STIR, and contrast-enhanced T1W FS MRI sequences (p ≤ 0.03). The mean weighted kappa was 0.64, showing excellent intraobserver reliability between readings. CFR-PEEK intramedullary nail fixation is a superior alternative to minimize implant artifact on MRI or CT imaging for patients requiring long bone fixation. (orig.)

  20. Carbon fiber intramedullary nails reduce artifact in postoperative advanced imaging

    Energy Technology Data Exchange (ETDEWEB)

    Zimel, Melissa N. [Memorial Sloan Kettering Cancer Center, Orthopaedic Surgery Service, Department of Surgery, New York, NY (United States); Hwang, Sinchun [Memorial Sloan Kettering Cancer Center, Department of Radiology, New York, NY (United States); Riedel, Elyn R. [Memorial Sloan Kettering Cancer Center, Department of Epidemiology and Biostatistics, New York, NY (United States); Healey, John H. [Memorial Sloan Kettering Cancer Center, Orthopaedic Surgery Service, Department of Surgery, New York, NY (United States); Weill Medical College of Cornell University, Department of Orthopaedic Surgery, New York, NY (United States)

    2015-09-15

    This study assessed whether radiolucent carbon fiber reinforced-polyetheretherketone (CFR-PEEK) intramedullary nails decreased hardware artifact on magnetic resonance imaging (MRI) and computed tomography (CT) in vitro and in an oncologic patient population. In vitro and clinical evaluations were done. A qualitative assessment of metal artifact was performed using CFR-PEEK and titanium nail MRI phantoms. Eight patients with a femoral or tibial prophylactic CFR-PEEK nail were retrospectively identified. All patients had postoperative surveillance imaging by MRI, CT, and were followed for a median 20 months (range, 12-28 months). CFR-PEEK images were compared to images from a comparative group of patients with titanium femoral intramedullary nails who had a postoperative MRI or CT. A musculoskeletal-trained radiologist graded visualization of the cortex, corticomedullary junction, and bone-muscle interface, on T1-weighted (T1W), STIR, and contrast-enhanced T1-weighted fat-saturated (T1W FS) sequences of both groups with a five-point scale, performing independent reviews 4 months apart. Statistical analysis used the Wilcoxon rank-sum test and a weighted kappa. Substantially less MRI signal loss occurred in the CFR-PEEK phantom than in the titanium phantom simulation, particularly as the angle increased with respect to direction of the static magnetic field. CFR-PEEK nails had less MRI artifact than titanium nails on scored T1W, STIR, and contrast-enhanced T1W FS MRI sequences (p ≤ 0.03). The mean weighted kappa was 0.64, showing excellent intraobserver reliability between readings. CFR-PEEK intramedullary nail fixation is a superior alternative to minimize implant artifact on MRI or CT imaging for patients requiring long bone fixation. (orig.)

  1. Iterative metal artifact reduction improves dose calculation accuracy. Phantom study with dental implants

    Energy Technology Data Exchange (ETDEWEB)

    Maerz, Manuel; Mittermair, Pia; Koelbl, Oliver; Dobler, Barbara [Regensburg University Medical Center, Department of Radiotherapy, Regensburg (Germany); Krauss, Andreas [Siemens Healthcare GmbH, Forchheim (Germany)

    2016-06-15

    Metallic dental implants cause severe streaking artifacts in computed tomography (CT) data, which affect the accuracy of dose calculations in radiation therapy. The aim of this study was to investigate the benefit of the metal artifact reduction algorithm iterative metal artifact reduction (iMAR) in terms of correct representation of Hounsfield units (HU) and dose calculation accuracy. Heterogeneous phantoms consisting of different types of tissue equivalent material surrounding metallic dental implants were designed. Artifact-containing CT data of the phantoms were corrected using iMAR. Corrected and uncorrected CT data were compared to synthetic CT data to evaluate accuracy of HU reproduction. Intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were calculated in Oncentra v4.3 on corrected and uncorrected CT data and compared to Gafchromic trademark EBT3 films to assess accuracy of dose calculation. The use of iMAR increased the accuracy of HU reproduction. The average deviation of HU decreased from 1006 HU to 408 HU in areas including metal and from 283 HU to 33 HU in tissue areas excluding metal. Dose calculation accuracy could be significantly improved for all phantoms and plans: The mean passing rate for gamma evaluation with 3 % dose tolerance and 3 mm distance to agreement increased from 90.6 % to 96.2 % if artifacts were corrected by iMAR. The application of iMAR allows metal artifacts to be removed to a great extent which leads to a significant increase in dose calculation accuracy. (orig.) [German] Metallische Implantate verursachen streifenfoermige Artefakte in CT-Bildern, welche die Dosisberechnung beeinflussen. In dieser Studie soll der Nutzen des iterativen Metall-Artefakt-Reduktions-Algorithmus iMAR hinsichtlich der Wiedergabetreue von Hounsfield-Werten (HU) und der Genauigkeit von Dosisberechnungen untersucht werden. Es wurden heterogene Phantome aus verschiedenen Arten gewebeaequivalenten Materials mit

  2. Reducing Interpolation Artifacts for Mutual Information Based Image Registration

    Science.gov (United States)

    Soleimani, H.; Khosravifard, M.A.

    2011-01-01

    Medical image registration methods which use mutual information as similarity measure have been improved in recent decades. Mutual Information is a basic concept of Information theory which indicates the dependency of two random variables (or two images). In order to evaluate the mutual information of two images their joint probability distribution is required. Several interpolation methods, such as Partial Volume (PV) and bilinear, are used to estimate joint probability distribution. Both of these two methods yield some artifacts on mutual information function. Partial Volume-Hanning window (PVH) and Generalized Partial Volume (GPV) methods are introduced to remove such artifacts. In this paper we show that the acceptable performance of these methods is not due to their kernel function. It's because of the number of pixels which incorporate in interpolation. Since using more pixels requires more complex and time consuming interpolation process, we propose a new interpolation method which uses only four pixels (the same as PV and bilinear interpolations) and removes most of the artifacts. Experimental results of the registration of Computed Tomography (CT) images show superiority of the proposed scheme. PMID:22606673

  3. Trails of meaning construction: Symbolic artifacts engage the social brain.

    Science.gov (United States)

    Tylén, Kristian; Philipsen, Johanne Stege; Roepstorff, Andreas; Fusaroli, Riccardo

    2016-07-01

    Symbolic artifacts present a challenge to theories of neurocognitive processing due to their hybrid nature: they are at the same time physical objects and vehicles of intangible social meanings. While their physical properties can be read of their perceptual appearance, the meaning of symbolic artifacts depends on the perceiver's interpretative attitude and embeddedness in cultural practices. In this study, participants built models of LEGO bricks to illustrate their understanding of abstract concepts. They were then scanned with fMRI while presented to photographs of their own and others' models. When participants attended to the meaning of the models in contrast to their bare physical properties, we observed activations in mPFC and TPJ, areas often associated with social cognition, and IFG, possibly related to semantics. When contrasting own and others' models, we also found activations in precuneus, an area associated with autobiographical memory and agency, while looking at one's own collective models yielded interaction effects in rostral ACC, right IFG and left Insula. Interestingly, variability in the insula was predicted by individual differences in participants' feeling of relatedness to their fellow group members during LEGO construction activity. Our findings support a view of symbolic artifacts as neuro-cognitive trails of human social interactions. Copyright © 2016 Elsevier Inc. All rights reserved.

  4. Motion Transplantation Techniques: A Survey

    NARCIS (Netherlands)

    van Basten, Ben; Egges, Arjan

    2012-01-01

    During the past decade, researchers have developed several techniques for transplanting motions. These techniques transplant a partial auxiliary motion, possibly defined for a small set of degrees of freedom, on a base motion. Motion transplantation improves motion databases' expressiveness and

  5. Numerical artifacts in the Generalized Porous Medium Equation: Why harmonic averaging itself is not to blame

    Science.gov (United States)

    Maddix, Danielle C.; Sampaio, Luiz; Gerritsen, Margot

    2018-05-01

    The degenerate parabolic Generalized Porous Medium Equation (GPME) poses numerical challenges due to self-sharpening and its sharp corner solutions. For these problems, we show results for two subclasses of the GPME with differentiable k (p) with respect to p, namely the Porous Medium Equation (PME) and the superslow diffusion equation. Spurious temporal oscillations, and nonphysical locking and lagging have been reported in the literature. These issues have been attributed to harmonic averaging of the coefficient k (p) for small p, and arithmetic averaging has been suggested as an alternative. We show that harmonic averaging is not solely responsible and that an improved discretization can mitigate these issues. Here, we investigate the causes of these numerical artifacts using modified equation analysis. The modified equation framework can be used for any type of discretization. We show results for the second order finite volume method. The observed problems with harmonic averaging can be traced to two leading error terms in its modified equation. This is also illustrated numerically through a Modified Harmonic Method (MHM) that can locally modify the critical terms to remove the aforementioned numerical artifacts.

  6. Artifact reduction method in ultrasound-guided diffuse optical tomography using exogenous contrast agents

    Science.gov (United States)

    Ardeshirpour, Yasaman; Biswal, Nrusingh; Aguirre, Andres; Zhu, Quing

    2011-04-01

    In diffuse optical tomography (DOT), a typical perturbation approach requires two sets of measurements obtained at the lesion breast (lesion or target site) and a contra-lateral location of the normal breast (reference site) for image reconstruction. For patients who have a small amount of breast tissue, the chest-wall underneath the breast tissue at both sites affects the imaging results. In this group of patients, the perturbation, which is the difference between measurements obtained at the lesion and reference sites, may include the information of background mismatch which can generate artifacts or affect the reconstructed quantitative absorption coefficient of the lesion. Also, for patients who have a single breast due to prior surgery, the contra-lateral reference is not available. To improve the DOT performance or overcome its limitation, we introduced a new method based on an exogenous contrast agent and demonstrate its performance using animal models. Co-registered ultrasound was used to guide the lesion localization. The results have shown that artifacts caused by background mismatch can be reduced significantly by using this new method.

  7. Correction of Bowtie-Filter Normalization and Crescent Artifacts for a Clinical CBCT System.

    Science.gov (United States)

    Zhang, Hong; Kong, Vic; Huang, Ke; Jin, Jian-Yue

    2017-02-01

    To present our experiences in understanding and minimizing bowtie-filter crescent artifacts and bowtie-filter normalization artifacts in a clinical cone beam computed tomography system. Bowtie-filter position and profile variations during gantry rotation were studied. Two previously proposed strategies (A and B) were applied to the clinical cone beam computed tomography system to correct bowtie-filter crescent artifacts. Physical calibration and analytical approaches were used to minimize the norm phantom misalignment and to correct for bowtie-filter normalization artifacts. A combined procedure to reduce bowtie-filter crescent artifacts and bowtie-filter normalization artifacts was proposed and tested on a norm phantom, CatPhan, and a patient and evaluated using standard deviation of Hounsfield unit along a sampling line. The bowtie-filter exhibited not only a translational shift but also an amplitude variation in its projection profile during gantry rotation. Strategy B was better than strategy A slightly in minimizing bowtie-filter crescent artifacts, possibly because it corrected the amplitude variation, suggesting that the amplitude variation plays a role in bowtie-filter crescent artifacts. The physical calibration largely reduced the misalignment-induced bowtie-filter normalization artifacts, and the analytical approach further reduced bowtie-filter normalization artifacts. The combined procedure minimized both bowtie-filter crescent artifacts and bowtie-filter normalization artifacts, with Hounsfield unit standard deviation being 63.2, 45.0, 35.0, and 18.8 Hounsfield unit for the best correction approaches of none, bowtie-filter crescent artifacts, bowtie-filter normalization artifacts, and bowtie-filter normalization artifacts + bowtie-filter crescent artifacts, respectively. The combined procedure also demonstrated reduction of bowtie-filter crescent artifacts and bowtie-filter normalization artifacts in a CatPhan and a patient. We have developed a step

  8. Effect of subcutaneous butylscopolamine administration in the reduction of peristaltic artifacts in 1.5-T MR fast abdominal examinations

    International Nuclear Information System (INIS)

    Dosda, Rosa; Marti-Bonmati, Luis; Molla, Enrique; Arana, Estanislao; Ronchera-Oms, Crisanto L.

    2003-01-01

    In abdominal MR imaging, ghost artifacts from noncyclic bowel movements can redu