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)

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)

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

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

Science.gov (United States)

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.

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

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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.

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

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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.

Reduced aliasing artifacts using shaking projection k-space sampling trajectory

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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.

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

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

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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.

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.

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

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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.

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

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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.

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

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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.

Negligible motion artifacts in scalp electroencephalography (EEG during treadmill walking

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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.

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

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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.

Motion Artifact Quantification and Sensor Fusion for Unobtrusive Health Monitoring.

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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.

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

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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

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

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

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

Motion Artifact Quantification and Sensor Fusion for Unobtrusive Health Monitoring

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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

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.

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.

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.

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

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.

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

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

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.

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

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

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

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.

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

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.

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.

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)

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)

Real-time motion analytics during brain MRI improve data quality and reduce costs.

Science.gov (United States)

Dosenbach, Nico U F; Koller, Jonathan M; Earl, Eric A; Miranda-Dominguez, Oscar; Klein, Rachel L; Van, Andrew N; Snyder, Abraham Z; Nagel, Bonnie J; Nigg, Joel T; Nguyen, Annie L; Wesevich, Victoria; Greene, Deanna J; Fair, Damien A

2017-11-01

Head motion systematically distorts clinical and research MRI data. Motion artifacts have biased findings from many structural and functional brain MRI studies. An effective way to remove motion artifacts is to exclude MRI data frames affected by head motion. However, such post-hoc frame censoring can lead to data loss rates of 50% or more in our pediatric patient cohorts. Hence, many scanner operators collect additional 'buffer data', an expensive practice that, by itself, does not guarantee sufficient high-quality MRI data for a given participant. Therefore, we developed an easy-to-setup, easy-to-use Framewise Integrated Real-time MRI Monitoring (FIRMM) software suite that provides scanner operators with head motion analytics in real-time, allowing them to scan each subject until the desired amount of low-movement data has been collected. Our analyses show that using FIRMM to identify the ideal scan time for each person can reduce total brain MRI scan times and associated costs by 50% or more. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

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

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.

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.

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

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....

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.

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.

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

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.

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.

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....

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

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

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.)

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.

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.

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

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...

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

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.

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

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.

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.

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.

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.

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.

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).

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.

A study on a pedicle-screw-based reduction method for artificially reduced artifacts

Science.gov (United States)

Kim, Hyun-Ju; Lee, Hae-Kag; Cho, Jae-Hwan

2017-09-01

The purpose of this study is a quantitative analysis of the degree of the reduction of the artifacts that are induced by pedicle screws through the application of the recently developed iterative metallic artifact reduction (I MAR) software. Screw-type implants that are composed of 4.5 g/cm3 titanium (Ti) with an approximate average computed tomography (CT) value of 6500 Hounsfield units (HUs) that are used for the treatment of spinal diseases were placed in paraffin, a tissueequivalent material, and then dried. After the insertion, the scanning conditions were fixed as 120 kVp and 250 mA using multidetector computed tomography (MDCT) (Enlarge, Siemens, Germany). The slice thickness and the increment were set at the fields of view (FOVs) of 3 mm and 120 mm, respectively; the pitch is 0.8; the rotation time is 1 s; and the I MAR software was applied to the raw data of the acquired images to compare the CT-value changes of the posterior images. When the I MAR software was applied to animal vertebrae, it was possible to reduce the 65.7% image loss of the black-hole-effect image through the application of the I MAR software. When the I MAR image loss (%) was compared with the white-streak-effect image, the high-intensity image type with the white-streak effect could be reduced by 91.34% through the application of the I MAR software. In conclusion, a metal artifact that is due to a high-density material can be reduced more effectively when the I MAR algorithm is applied compared with that from the application of the conventional MAR algorithm. The I MAR can provide information on the various tissues that form around the artifact and the reduced metal structures, which can be helpful for radiologists and clinicians in their determination of an accurate diagnosis.

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.

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.

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.)

Motion-robust diffusion tensor acquisition at routine 3T magnetic resonance imaging

International Nuclear Information System (INIS)

Yasmin, Hasina; Abe, Osamu; Masutani, Yoshitaka; Hayashi, Naoto; Ohtomo, Kuni; Kabasawa, Hiroyuki; Aoki, Shigeki

2010-01-01

We compared different acquisition and reconstruction methods in phantom and human studies in the clinical setting to validate our hypothesis that optimizing the k-space acquisition and reconstruction method could decrease motion artifacts. Diffusion tensor images of a water phantom were obtained with three table displacement magnitudes: 1 mm, 2 mm, and 3 mm. Images were reconstructed using homodyne and zero-fill reconstruction. Overscanning in 8- and 16-k y lines was tested. We performed visual assessment of the artifacts using reconstructed coronal images and analyzed them with Wilcoxon signed-ranks test both for phantom and human studies. Also, fractional anisotropy (FA) changes between acquisition methods were compared. Artifacts due to smaller displacement (1 and 2 mm) were significantly reduced in 16-k y overscan with zero filling. The Wilcoxon signed-ranks test showed significant differences (P<0.031 for reconstruction methods and P<0.016 for overscanning methods). FA changes were statistically significant (P<0.037; Student's t-test). The Wilcoxon signed-ranks test showed significant reductions (P<0.005) in the human study. Motion-induced artifacts can be reduced by optimizing acquisition and reconstruction methods. The techniques described in this study offer an effective method for robust estimation of diffusion tensor in the presence of motion-related artifactual data points. (author)

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.

Image quality analysis to reduce dental artifacts in head and neck imaging with dual-source computed tomography

Energy Technology Data Exchange (ETDEWEB)

Ketelsen, D.; Werner, M.K.; Thomas, C.; Tsiflikas, I.; Reimann, A.; Claussen, C.D.; Heuschmid, M. [Tuebingen Univ. (Germany). Abt. fuer Diagnostische und Interventionelle Radiologie; Koitschev, A. [Tuebingen Univ. (Germany). Abt. fuer Hals-Nasen-Ohrenheilkunde

2009-01-15

Purpose: Important oropharyngeal structures can be superimposed by metallic artifacts due to dental implants. The aim of this study was to compare the image quality of multiplanar reconstructions and an angulated spiral in dual-source computed tomography (DSCT) of the neck. Materials and Methods: Sixty-two patients were included for neck imaging with DSCT. MPRs from an axial dataset and an additional short spiral parallel to the mouth floor were acquired. Leading anatomical structures were then evaluated with respect to the extent to which they were affected by dental artifacts using a visual scale, ranging from 1 (least artifacts) to 4 (most artifacts). Results: In MPR, 87.1 % of anatomical structures had significant artifacts (3.12 {+-} 0.86), while in angulated slices leading anatomical structures of the oropharynx showed negligible artifacts (1.28 {+-} 0.46). The diagnostic growth due to primarily angulated slices concerning artifact severity was significant (p < 0.01). Conclusion: MPRs are not capable of reducing dental artifacts sufficiently. In patients with dental artifacts overlying the anatomical structures of the oropharynx, an additional short angulated spiral parallel to the floor of the mouth is recommended and should be applied for daily routine. As a result of the static gantry design of DSCT, the use of a flexible head holder is essential. (orig.)

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.

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.

The use of active breathing control (ABC) to reduce margin for breathing motion

International Nuclear Information System (INIS)

Wong, John W.; Sharpe, Michael B.; Jaffray, David A.; Kini, Vijay R.; Robertson, John M.; Stromberg, Jannifer S.; Martinez, Alavro A.

1999-01-01

. The variation of the organ positions and volumes for the different scans were quantified and compared. Results: The ABC procedure was well tolerated in the 12 patients. When ABC was applied near the end of normal expiration, the minimal duration of active breath-hold was 15 s for 1 patient with lung cancer, and 20 s or more for all other patients. The duration was greater than 40 s for 2 patients with Hodgkin's disease when ABC was applied during deep inspiration. Scan artifacts associated with normal breathing motion were not observed in the ABC scans. The analysis of the small set of intrafraction scan data indicated that with ABC, the liver volumes were reproducible at about 1%, and lung volumes to within 6%. The excursions of a 'center of target' parameter for the livers were less than 1 mm at the same respiratory phase, but were larger than 4 mm at the extremes of the breathing cycle. The inter-fraction scan study indicated that daily setup variation contributed to the uncertainty in assessing the reproducibility of organ immobilization with ABC between treatment fractions. Conclusion: The results were encouraging; ABC provides a simple means to minimize breathing motion. When applied for CT scanning and treatment, the ABC procedure requires no more than standard operation of the CT scanner or the medical accelerator. The ABC scans are void of motion artifacts commonly seen on fast spiral CT scans. When acquired at different points in the breathing cycle, these ABC scans show organ motion in three-dimension (3D) that can be used to enhance treatment planning. Reproducibility of organ immobilization with ABC throughout the course of treatment must be quantified before the procedure can be applied to reduce margin for conformal treatment

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

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.

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...

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

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.

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.

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

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.

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.

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

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

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

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.

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

Artifact detection in electrodermal activity using sparse recovery

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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.

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

MRI-Based Nonrigid Motion Correction in Simultaneous PET/MRI

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Chun, Se Young; Reese, Timothy G.; Ouyang, Jinsong; Guerin, Bastien; Catana, Ciprian; Zhu, Xuping; Alpert, Nathaniel M.; El Fakhri, Georges

2014-01-01

Respiratory and cardiac motion is the most serious limitation to whole-body PET, resulting in spatial resolution close to 1 cm. Furthermore, motion-induced inconsistencies in the attenuation measurements often lead to significant artifacts in the reconstructed images. Gating can remove motion artifacts at the cost of increased noise. This paper presents an approach to respiratory motion correction using simultaneous PET/MRI to demonstrate initial results in phantoms, rabbits, and nonhuman primates and discusses the prospects for clinical application. Methods Studies with a deformable phantom, a free-breathing primate, and rabbits implanted with radioactive beads were performed with simultaneous PET/MRI. Motion fields were estimated from concurrently acquired tagged MR images using 2 B-spline nonrigid image registration methods and incorporated into a PET list-mode ordered-subsets expectation maximization algorithm. Using the measured motion fields to transform both the emission data and the attenuation data, we could use all the coincidence data to reconstruct any phase of the respiratory cycle. We compared the resulting SNR and the channelized Hotelling observer (CHO) detection signal-to-noise ratio (SNR) in the motion-corrected reconstruction with the results obtained from standard gating and uncorrected studies. Results Motion correction virtually eliminated motion blur without reducing SNR, yielding images with SNR comparable to those obtained by gating with 5–8 times longer acquisitions in all studies. The CHO study in dynamic phantoms demonstrated a significant improvement (166%–276%) in lesion detection SNR with MRI-based motion correction as compared with gating (P < 0.001). This improvement was 43%–92% for large motion compared with lesion detection without motion correction (P < 0.001). CHO SNR in the rabbit studies confirmed these results. Conclusion Tagged MRI motion correction in simultaneous PET/MRI significantly improves lesion detection

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

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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.

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

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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.

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

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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.

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.

Performances of low-dose dual-energy CT in reducing artifacts from implanted metallic orthopedic devices

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Filograna, Laura [Catholic University of Rome, School of Medicine, University Hospital ' ' A. Gemelli' ' , Department of Radiological Sciences, Institute of Radiology, Rome (Italy); University of Zurich, Department of Forensic Medicine and Imaging, Institute of Forensic Medicine, Zurich (Switzerland); Magarelli, Nicola; Leone, Antonio; Bonomo, Lorenzo [Catholic University of Rome, School of Medicine, University Hospital ' ' A. Gemelli' ' , Department of Radiological Sciences, Institute of Radiology, Rome (Italy); De Waure, Chiara; Calabro, Giovanna Elisa [Catholic University of Rome, School of Medicine, University Hospital ' ' A. Gemelli' ' , Research Centre for Health Technology Assessment, Department of Public Health, Section of Hygiene, Rome (Italy); Finkenstaedt, Tim [University Hospital Zurich, Institute of Diagnostic and Interventional Radiology, Zurich (Switzerland); Thali, Michael John [University of Zurich, Department of Forensic Medicine and Imaging, Institute of Forensic Medicine, Zurich (Switzerland)

2016-07-15

The objective was to evaluate the performances of dose-reduced dual-energy computed tomography (DECT) in decreasing metallic artifacts from orthopedic devices compared with dose-neutral DECT, dose-neutral single-energy computed tomography (SECT), and dose-reduced SECT. Thirty implants in 20 consecutive cadavers underwent both SECT and DECT at three fixed CT dose indexes (CTDI): 20.0, 10.0, and 5.0 mGy. Extrapolated monoenergetic DECT images at 64, 69, 88, 105, 120, and 130 keV, and individually adjusted monoenergy for optimized image quality (OPTkeV) were generated. In each group, the image quality of the seven monoenergetic images and of the SECT image was assessed qualitatively and quantitatively by visually rating and by measuring the maximum streak artifact respectively. The comparison between SECT and OPTkeV evaluated overall within all groups showed a significant difference (p <0.001), with OPTkeV images providing better images. Comparing OPTkeV with the other DECT images, a significant difference was shown (p <0.001), with OPTkeV and 130-keV images providing the qualitatively best results. The OPTkeV images of 5.0-mGy acquisitions provided percentages of images with scores 1 and 2 of 36 % and 30 % respectively, compared with 0 % and 33.3 % of the corresponding SECT images of 10- and 20-mGy acquisitions. Moreover, DECT reconstructions at the OPTkeV of the low-dose group showed higher CT numbers than the SECT images of dose groups 1 and 2. This study demonstrates that low-dose DECT permits a reduction of artifacts due to metallic implants to be obtained in a similar manner to neutral-dose DECT and better than reduced or neutral-dose SECT. (orig.)

Rigid-body motion correction of the liver in image reconstruction for golden-angle stack-of-stars DCE MRI.

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Johansson, Adam; Balter, James; Cao, Yue

2018-03-01

Respiratory motion can affect pharmacokinetic perfusion parameters quantified from liver dynamic contrast-enhanced MRI. Image registration can be used to align dynamic images after reconstruction. However, intra-image motion blur remains after alignment and can alter the shape of contrast-agent uptake curves. We introduce a method to correct for inter- and intra-image motion during image reconstruction. Sixteen liver dynamic contrast-enhanced MRI examinations of nine subjects were performed using a golden-angle stack-of-stars sequence. For each examination, an image time series with high temporal resolution but severe streak artifacts was reconstructed. Images were aligned using region-limited rigid image registration within a region of interest covering the liver. The transformations resulting from alignment were used to correct raw data for motion by modulating and rotating acquired lines in k-space. The corrected data were then reconstructed using view sharing. Portal-venous input functions extracted from motion-corrected images had significantly greater peak signal enhancements (mean increase: 16%, t-test, P <  0.001) than those from images aligned using image registration after reconstruction. In addition, portal-venous perfusion maps estimated from motion-corrected images showed fewer artifacts close to the edge of the liver. Motion-corrected image reconstruction restores uptake curves distorted by motion. Motion correction also reduces motion artifacts in estimated perfusion parameter maps. Magn Reson Med 79:1345-1353, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Motion Detection in Ultrasound Image-Sequences Using Tensor Voting

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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.

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)

Evaluation of tumor localization in respiration motion-corrected cone-beam CT: prospective study in lung.

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Dzyubak, Oleksandr; Kincaid, Russell; Hertanto, Agung; Hu, Yu-Chi; Pham, Hai; Rimner, Andreas; Yorke, Ellen; Zhang, Qinghui; Mageras, Gig S

2014-10-01

Target localization accuracy of cone-beam CT (CBCT) images used in radiation treatment of respiratory disease sites is affected by motion artifacts (blurring and streaking). The authors have previously reported on a method of respiratory motion correction in thoracic CBCT at end expiration (EE). The previous retrospective study was limited to examination of reducing motion artifacts in a small number of patient cases. They report here on a prospective study in a larger group of lung cancer patients to evaluate respiratory motion-corrected (RMC)-CBCT ability to improve lung tumor localization accuracy and reduce motion artifacts in Linac-mounted CBCT images. A second study goal examines whether the motion correction derived from a respiration-correlated CT (RCCT) at simulation yields similar tumor localization accuracy at treatment. In an IRB-approved study, 19 lung cancer patients (22 tumors) received a RCCT at simulation, and on one treatment day received a RCCT, a respiratory-gated CBCT at end expiration, and a 1-min CBCT. A respiration monitor of abdominal displacement was used during all scans. In addition to a CBCT reconstruction without motion correction, the motion correction method was applied to the same 1-min scan. Projection images were sorted into ten bins based on abdominal displacement, and each bin was reconstructed to produce ten intermediate CBCT images. Each intermediate CBCT was deformed to the end expiration state using a motion model derived from RCCT. The deformed intermediate CBCT images were then added to produce a final RMC-CBCT. In order to evaluate the second study goal, the CBCT was corrected in two ways, one using a model derived from the RCCT at simulation [RMC-CBCT(sim)], the other from the RCCT at treatment [RMC-CBCT(tx)]. Image evaluation compared uncorrected CBCT, RMC-CBCT(sim), and RMC-CBCT(tx). The gated CBCT at end expiration served as the criterion standard for comparison. Using automatic rigid image registration, each CBCT was

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.

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

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

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

Removal of eye blink artifacts in wireless EEG sensor networks using reduced-bandwidth canonical correlation analysis.

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Somers, Ben; Bertrand, Alexander

2016-12-01

Chronic, 24/7 EEG monitoring requires the use of highly miniaturized EEG modules, which only measure a few EEG channels over a small area. For improved spatial coverage, a wireless EEG sensor network (WESN) can be deployed, consisting of multiple EEG modules, which interact through short-distance wireless communication. In this paper, we aim to remove eye blink artifacts in each EEG channel of a WESN by optimally exploiting the correlation between EEG signals from different modules, under stringent communication bandwidth constraints. We apply a distributed canonical correlation analysis (CCA-)based algorithm, in which each module only transmits an optimal linear combination of its local EEG channels to the other modules. The method is validated on both synthetic and real EEG data sets, with emulated wireless transmissions. While strongly reducing the amount of data that is shared between nodes, we demonstrate that the algorithm achieves the same eye blink artifact removal performance as the equivalent centralized CCA algorithm, which is at least as good as other state-of-the-art multi-channel algorithms that require a transmission of all channels. Due to their potential for extreme miniaturization, WESNs are viewed as an enabling technology for chronic EEG monitoring. However, multi-channel analysis is hampered in WESNs due to the high energy cost for wireless communication. This paper shows that multi-channel eye blink artifact removal is possible with a significantly reduced wireless communication between EEG modules.

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.)

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.)

Carbon fiber intramedullary nails reduce artifact in postoperative advanced imaging

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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.)

Evaluation of tumor localization in respiration motion-corrected cone-beam CT: Prospective study in lung

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Dzyubak, Oleksandr; Kincaid, Russell; Hertanto, Agung; Hu, Yu-Chi; Pham, Hai; Yorke, Ellen; Zhang, Qinghui; Mageras, Gig S., E-mail: magerasg@mskcc.org [Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, New York 10065 (United States); Rimner, Andreas [Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York 10065 (United States)

2014-10-15

Purpose: Target localization accuracy of cone-beam CT (CBCT) images used in radiation treatment of respiratory disease sites is affected by motion artifacts (blurring and streaking). The authors have previously reported on a method of respiratory motion correction in thoracic CBCT at end expiration (EE). The previous retrospective study was limited to examination of reducing motion artifacts in a small number of patient cases. They report here on a prospective study in a larger group of lung cancer patients to evaluate respiratory motion-corrected (RMC)-CBCT ability to improve lung tumor localization accuracy and reduce motion artifacts in Linac-mounted CBCT images. A second study goal examines whether the motion correction derived from a respiration-correlated CT (RCCT) at simulation yields similar tumor localization accuracy at treatment. Methods: In an IRB-approved study, 19 lung cancer patients (22 tumors) received a RCCT at simulation, and on one treatment day received a RCCT, a respiratory-gated CBCT at end expiration, and a 1-min CBCT. A respiration monitor of abdominal displacement was used during all scans. In addition to a CBCT reconstruction without motion correction, the motion correction method was applied to the same 1-min scan. Projection images were sorted into ten bins based on abdominal displacement, and each bin was reconstructed to produce ten intermediate CBCT images. Each intermediate CBCT was deformed to the end expiration state using a motion model derived from RCCT. The deformed intermediate CBCT images were then added to produce a final RMC-CBCT. In order to evaluate the second study goal, the CBCT was corrected in two ways, one using a model derived from the RCCT at simulation [RMC-CBCT(sim)], the other from the RCCT at treatment [RMC-CBCT(tx)]. Image evaluation compared uncorrected CBCT, RMC-CBCT(sim), and RMC-CBCT(tx). The gated CBCT at end expiration served as the criterion standard for comparison. Using automatic rigid image

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.

A level set method for cupping artifact correction in cone-beam CT

International Nuclear Information System (INIS)

Xie, Shipeng; Li, Haibo; Ge, Qi; Li, Chunming

2015-01-01

Purpose: To reduce cupping artifacts and improve the contrast-to-noise ratio in cone-beam computed tomography (CBCT). Methods: A level set method is proposed to reduce cupping artifacts in the reconstructed image of CBCT. The authors derive a local intensity clustering property of the CBCT image and define a local clustering criterion function of the image intensities in a neighborhood of each point. This criterion function defines an energy in terms of the level set functions, which represent a segmentation result and the cupping artifacts. The cupping artifacts are estimated as a result of minimizing this energy. Results: The cupping artifacts in CBCT are reduced by an average of 90%. The results indicate that the level set-based algorithm is practical and effective for reducing the cupping artifacts and preserving the quality of the reconstructed image. Conclusions: The proposed method focuses on the reconstructed image without requiring any additional physical equipment, is easily implemented, and provides cupping correction through a single-scan acquisition. The experimental results demonstrate that the proposed method successfully reduces the cupping artifacts

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.

Nonlinear Geometric Warping of the Mask Image: A New Method for Reducing Misregistration Artifacts in Digital Subtraction Angiography

International Nuclear Information System (INIS)

Hayashi, Nobushige; Sakai, Toyohiko; Kitagawa, Manabu; Inagaki, Rika; Sadato, Norihiro; Ishii, Yasushi; Nishimoto, Yasuhiro; Tanaka, Masato; Fukushima, Tetsuya; Komuro, Hiroyuki; Ogura, Hisakazu; Kobayashi, Hidenori; Kubota, Toshihiko

1998-01-01

Purpose: Misregistration artifact is the major cause of image degradation in digital subtraction angiography (DSA). The purpose of this study was to evaluate the efficacy of a newly developed nonlinear geometric warping method to reduce misregistration artifact in DSA. Methods: The processing of the images was carried out on a workstation with a fully automatic computerized program. After making differential images with a lapracian filter, 49 regions of interest (ROIs) were set in the image to be processed. Each ROI of the live image scanned the corresponding ROI of the mask image searching for the best position to match itself. Each pixel of the mask image was shifted individually following the data calculated from the shifts of the ROIs. Five radiologists compared the images produced by the conventional parallel shift technique and those processed with this new method in 16 series of cerebral DSA. Results: In 14 of 16 series (88%), more radiologists judged the images processed with the new method to be better in quality. Small arteries near the skull base and veins of low density were clearly visualized in the images processed by the new method. Conclusion: This newly proposed method could be a simple and practical way to automatically reduce misregistration artifacts in DSA

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

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

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.

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

Cardiac motion correction based on partial angle reconstructed images in x-ray CT

International Nuclear Information System (INIS)

Kim, Seungeon; Chang, Yongjin; Ra, Jong Beom

2015-01-01

two conjugate PAR images. To evaluate the proposed algorithm, digital XCAT and physical dynamic cardiac phantom datasets are used. The XCAT phantom datasets were generated with heart rates of 70 and 100 bpm, respectively, by assuming a system rotation time of 300 ms. A physical dynamic cardiac phantom was scanned using a slowly rotating XCT system so that the effective heart rate will be 70 bpm for a system rotation speed of 300 ms. Results: In the XCAT phantom experiment, motion-compensated 3D images obtained from the proposed algorithm show coronary arteries with fewer motion artifacts for all phases. Moreover, object boundaries contaminated by motion are well restored. Even though object positions and boundary shapes are still somewhat different from the ground truth in some cases, the authors see that visibilities of coronary arteries are improved noticeably and motion artifacts are reduced considerably. The physical phantom study also shows that the visual quality of motion-compensated images is greatly improved. Conclusions: The authors propose a novel PAR image-based cardiac motion estimation and compensation algorithm. The algorithm requires an angular scan range of less than 360°. The excellent performance of the proposed algorithm is illustrated by using digital XCAT and physical dynamic cardiac phantom datasets

Cardiac motion correction based on partial angle reconstructed images in x-ray CT

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Kim, Seungeon; Chang, Yongjin; Ra, Jong Beom, E-mail: jbra@kaist.ac.kr [Department of Electrical Engineering, KAIST, Daejeon 305-701 (Korea, Republic of)

2015-05-15

two conjugate PAR images. To evaluate the proposed algorithm, digital XCAT and physical dynamic cardiac phantom datasets are used. The XCAT phantom datasets were generated with heart rates of 70 and 100 bpm, respectively, by assuming a system rotation time of 300 ms. A physical dynamic cardiac phantom was scanned using a slowly rotating XCT system so that the effective heart rate will be 70 bpm for a system rotation speed of 300 ms. Results: In the XCAT phantom experiment, motion-compensated 3D images obtained from the proposed algorithm show coronary arteries with fewer motion artifacts for all phases. Moreover, object boundaries contaminated by motion are well restored. Even though object positions and boundary shapes are still somewhat different from the ground truth in some cases, the authors see that visibilities of coronary arteries are improved noticeably and motion artifacts are reduced considerably. The physical phantom study also shows that the visual quality of motion-compensated images is greatly improved. Conclusions: The authors propose a novel PAR image-based cardiac motion estimation and compensation algorithm. The algorithm requires an angular scan range of less than 360°. The excellent performance of the proposed algorithm is illustrated by using digital XCAT and physical dynamic cardiac phantom datasets.

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.

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)

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

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.

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

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.

Automatic EEG-assisted retrospective motion correction for fMRI (aE-REMCOR).

Science.gov (United States)

Wong, Chung-Ki; Zotev, Vadim; Misaki, Masaya; Phillips, Raquel; Luo, Qingfei; Bodurka, Jerzy

2016-04-01

Head motions during functional magnetic resonance imaging (fMRI) impair fMRI data quality and introduce systematic artifacts that can affect interpretation of fMRI results. Electroencephalography (EEG) recordings performed simultaneously with fMRI provide high-temporal-resolution information about ongoing brain activity as well as head movements. Recently, an EEG-assisted retrospective motion correction (E-REMCOR) method was introduced. E-REMCOR utilizes EEG motion artifacts to correct the effects of head movements in simultaneously acquired fMRI data on a slice-by-slice basis. While E-REMCOR is an efficient motion correction approach, it involves an independent component analysis (ICA) of the EEG data and identification of motion-related ICs. Here we report an automated implementation of E-REMCOR, referred to as aE-REMCOR, which we developed to facilitate the application of E-REMCOR in large-scale EEG-fMRI studies. The aE-REMCOR algorithm, implemented in MATLAB, enables an automated preprocessing of the EEG data, an ICA decomposition, and, importantly, an automatic identification of motion-related ICs. aE-REMCOR has been used to perform retrospective motion correction for 305 fMRI datasets from 16 subjects, who participated in EEG-fMRI experiments conducted on a 3T MRI scanner. Performance of aE-REMCOR has been evaluated based on improvement in temporal signal-to-noise ratio (TSNR) of the fMRI data, as well as correction efficiency defined in terms of spike reduction in fMRI motion parameters. The results show that aE-REMCOR is capable of substantially reducing head motion artifacts in fMRI data. In particular, when there are significant rapid head movements during the scan, a large TSNR improvement and high correction efficiency can be achieved. Depending on a subject's motion, an average TSNR improvement over the brain upon the application of aE-REMCOR can be as high as 27%, with top ten percent of the TSNR improvement values exceeding 55%. The average

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.

Methodological aspects of EEG and Body dynamics measurements during motion.

Directory of Open Access Journals (Sweden)

Pedro eReis

2014-03-01

Full Text Available EEG involves recording, analysis, and interpretation of voltages recorded on the human scalp originating from brain grey matter. EEG is one of the favorite methods to study and understand processes that underlie behavior. This is so, because EEG is relatively cheap, easy to wear, light weight and has high temporal resolution. In terms of behavior, this encompasses actions, such as movements, that are performed in response to the environment. However, there are methodological difficulties when recording EEG during movement such as movement artifacts. Thus, most studies about the human brain have examined activations during static conditions. This article attempts to compile and describe relevant methodological solutions that emerged in order to measure body and brain dynamics during motion. These descriptions cover suggestions of how to avoid and reduce motion artifacts, hardware, software and techniques for synchronously recording EEG, EMG, kinematics, kinetics and eye movements during motion. Additionally, we present various recording systems, EEG electrodes, caps and methods for determination of real/custom electrode positions. In the end we will conclude that it is possible to record and analyze synchronized brain and body dynamics related to movement or exercise tasks.

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.

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)

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

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

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

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...

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.

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)

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.)

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

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....

Apneic oxygenation for elimination of respiratory motion artefact in an intubated patient undergoing helical chest computed tomography angiography.

Directory of Open Access Journals (Sweden)

Ioannis Pneumatikos

2008-10-01

Full Text Available Respiratory motion artifact in intubated and mechanically ventilated patients often reduces the quality of helical computed tomography pulmonary angiography (CTPA. Apneic oxygenation is a well established intra-operative technique that allows adequate oxygenation for short periods (up to 10 min in sedated and paralyzed patients. We describe the use of the apneic oxygenation for elimination of respiratory motion artefact in an intubated patient undergoing helical chest computed tomography angiography.

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.

Improved Image Quality in Head and Neck CT Using a 3D Iterative Approach to Reduce Metal Artifact.

Science.gov (United States)

Wuest, W; May, M S; Brand, M; Bayerl, N; Krauss, A; Uder, M; Lell, M

2015-10-01

Metal artifacts from dental fillings and other devices degrade image quality and may compromise the detection and evaluation of lesions in the oral cavity and oropharynx by CT. The aim of this study was to evaluate the effect of iterative metal artifact reduction on CT of the oral cavity and oropharynx. Data from 50 consecutive patients with metal artifacts from dental hardware were reconstructed with standard filtered back-projection, linear interpolation metal artifact reduction (LIMAR), and iterative metal artifact reduction. The image quality of sections that contained metal was analyzed for the severity of artifacts and diagnostic value. A total of 455 sections (mean ± standard deviation, 9.1 ± 4.1 sections per patient) contained metal and were evaluated with each reconstruction method. Sections without metal were not affected by the algorithms and demonstrated image quality identical to each other. Of these sections, 38% were considered nondiagnostic with filtered back-projection, 31% with LIMAR, and only 7% with iterative metal artifact reduction. Thirty-three percent of the sections had poor image quality with filtered back-projection, 46% with LIMAR, and 10% with iterative metal artifact reduction. Thirteen percent of the sections with filtered back-projection, 17% with LIMAR, and 22% with iterative metal artifact reduction were of moderate image quality, 16% of the sections with filtered back-projection, 5% with LIMAR, and 30% with iterative metal artifact reduction were of good image quality, and 1% of the sections with LIMAR and 31% with iterative metal artifact reduction were of excellent image quality. Iterative metal artifact reduction yields the highest image quality in comparison with filtered back-projection and linear interpolation metal artifact reduction in patients with metal hardware in the head and neck area. © 2015 by American Journal of Neuroradiology.

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...

Patient motion effects on the quantification of regional myocardial blood flow with dynamic PET imaging

Energy Technology Data Exchange (ETDEWEB)

Hunter, Chad R. R. N.; Kemp, Robert A. de, E-mail: RAdeKemp@ottawaheart.ca [Physics Department, Room 3302 Herzberg Laboratories, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada and Cardiac Imaging, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, Ontario K1Y 4W7 (Canada); Klein, Ran [Department of Nuclear Medicine, Ottawa Hospital, Civic Campus, 1053 Carling Avenue, Ottawa, Ontario K1Y 4E9 (Canada); Beanlands, Rob S. [Cardiac Imaging, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, Ontario K1Y 4W7 (Canada)

2016-04-15

also indicated that the magnitude of MBF errors resulting from motion in the superior/inferior and anterior/posterior directions was similar (up to 250%). Body motion effects were more detrimental for higher resolution PET imaging (2 vs 10 mm full-width at half-maximum), and for motion occurring during the mid-to-late time-frames. Motion correction of the reconstructed dynamic image series resulted in significant reduction in MBF errors, but did not account for the residual PET–CTAC misalignment artifacts. MBF bias was reduced further using global partial-volume correction, and using dynamic alignment of the PET projection data to the CT scan for accurate attenuation correction during image reconstruction. Conclusions: Patient body motion can produce MBF estimation errors up to 500%. To reduce these errors, new motion correction algorithms must be effective in identifying motion in the left/right direction, and in the mid-to-late time-frames, since these conditions produce the largest errors in MBF, particularly for high resolution PET imaging. Ideally, motion correction should be done before or during image reconstruction to eliminate PET-CTAC misalignment artifacts.

Patient motion effects on the quantification of regional myocardial blood flow with dynamic PET imaging

International Nuclear Information System (INIS)

Hunter, Chad R. R. N.; Kemp, Robert A. de; Klein, Ran; Beanlands, Rob S.

2016-01-01

also indicated that the magnitude of MBF errors resulting from motion in the superior/inferior and anterior/posterior directions was similar (up to 250%). Body motion effects were more detrimental for higher resolution PET imaging (2 vs 10 mm full-width at half-maximum), and for motion occurring during the mid-to-late time-frames. Motion correction of the reconstructed dynamic image series resulted in significant reduction in MBF errors, but did not account for the residual PET–CTAC misalignment artifacts. MBF bias was reduced further using global partial-volume correction, and using dynamic alignment of the PET projection data to the CT scan for accurate attenuation correction during image reconstruction. Conclusions: Patient body motion can produce MBF estimation errors up to 500%. To reduce these errors, new motion correction algorithms must be effective in identifying motion in the left/right direction, and in the mid-to-late time-frames, since these conditions produce the largest errors in MBF, particularly for high resolution PET imaging. Ideally, motion correction should be done before or during image reconstruction to eliminate PET-CTAC misalignment artifacts.

Patient motion effects on the quantification of regional myocardial blood flow with dynamic PET imaging.

Science.gov (United States)

Hunter, Chad R R N; Klein, Ran; Beanlands, Rob S; deKemp, Robert A

2016-04-01

magnitude of MBF errors resulting from motion in the superior/inferior and anterior/posterior directions was similar (up to 250%). Body motion effects were more detrimental for higher resolution PET imaging (2 vs 10 mm full-width at half-maximum), and for motion occurring during the mid-to-late time-frames. Motion correction of the reconstructed dynamic image series resulted in significant reduction in MBF errors, but did not account for the residual PET-CTAC misalignment artifacts. MBF bias was reduced further using global partial-volume correction, and using dynamic alignment of the PET projection data to the CT scan for accurate attenuation correction during image reconstruction. Patient body motion can produce MBF estimation errors up to 500%. To reduce these errors, new motion correction algorithms must be effective in identifying motion in the left/right direction, and in the mid-to-late time-frames, since these conditions produce the largest errors in MBF, particularly for high resolution PET imaging. Ideally, motion correction should be done before or during image reconstruction to eliminate PET-CTAC misalignment artifacts.

Simultaneous motion estimation and image reconstruction (SMEIR) for 4D cone-beam CT

International Nuclear Information System (INIS)

Wang, Jing; Gu, Xuejun

2013-01-01

-blurring artifacts are present, leading to a 24.4% relative reconstruction error in the NACT phantom. View aliasing artifacts are present in 4D-CBCT reconstructed by FDK from 20 projections, with a relative error of 32.1%. When total variation minimization is used to reconstruct 4D-CBCT, the relative error is 18.9%. Image quality of 4D-CBCT is substantially improved by using the SMEIR algorithm and relative error is reduced to 7.6%. The maximum error (MaxE) of tumor motion determined from the DVF obtained by demons registration on a FDK-reconstructed 4D-CBCT is 3.0, 2.3, and 7.1 mm along left–right (L-R), anterior–posterior (A-P), and superior–inferior (S-I) directions, respectively. From the DVF obtained by demons registration on 4D-CBCT reconstructed by total variation minimization, the MaxE of tumor motion is reduced to 1.5, 0.5, and 5.5 mm along L-R, A-P, and S-I directions. From the DVF estimated by SMEIR algorithm, the MaxE of tumor motion is further reduced to 0.8, 0.4, and 1.5 mm along L-R, A-P, and S-I directions, respectively.Conclusions: The proposed SMEIR algorithm is able to estimate a motion model and reconstruct motion-compensated 4D-CBCT. The SMEIR algorithm improves image reconstruction accuracy of 4D-CBCT and tumor motion trajectory estimation accuracy as compared to conventional sequential 4D-CBCT reconstruction and motion estimation

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.

PET Motion Compensation for Radiation Therapy Using a CT-Based Mid-Position Motion Model: Methodology and Clinical Evaluation

International Nuclear Information System (INIS)

Kruis, Matthijs F.; Kamer, Jeroen B. van de; Houweling, Antonetta C.; Sonke, Jan-Jakob; Belderbos, José S.A.; Herk, Marcel van

2013-01-01

Purpose: Four-dimensional positron emission tomography (4D PET) imaging of the thorax produces sharper images with reduced motion artifacts. Current radiation therapy planning systems, however, do not facilitate 4D plan optimization. When images are acquired in a 2-minute time slot, the signal-to-noise ratio of each 4D frame is low, compromising image quality. The purpose of this study was to implement and evaluate the construction of mid-position 3D PET scans, with motion compensated using a 4D computed tomography (CT)-derived motion model. Methods and Materials: All voxels of 4D PET were registered to the time-averaged position by using a motion model derived from the 4D CT frames. After the registration the scans were summed, resulting in a motion-compensated 3D mid-position PET scan. The method was tested with a phantom dataset as well as data from 27 lung cancer patients. Results: PET motion compensation using a CT-based motion model improved image quality of both phantoms and patients in terms of increased maximum SUV (SUV max ) values and decreased apparent volumes. In homogenous phantom data, a strong relationship was found between the amplitude-to-diameter ratio and the effects of the method. In heterogeneous patient data, the effect correlated better with the motion amplitude. In case of large amplitudes, motion compensation may increase SUV max up to 25% and reduce the diameter of the 50% SUV max volume by 10%. Conclusions: 4D CT-based motion-compensated mid-position PET scans provide improved quantitative data in terms of uptake values and volumes at the time-averaged position, thereby facilitating more accurate radiation therapy treatment planning of pulmonary lesions

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.

Motion compensation in extremity cone-beam CT using a penalized image sharpness criterion

Science.gov (United States)

Sisniega, A.; Stayman, J. W.; Yorkston, J.; Siewerdsen, J. H.; Zbijewski, W.

2017-05-01

Cone-beam CT (CBCT) for musculoskeletal imaging would benefit from a method to reduce the effects of involuntary patient motion. In particular, the continuing improvement in spatial resolution of CBCT may enable tasks such as quantitative assessment of bone microarchitecture (0.1 mm-0.2 mm detail size), where even subtle, sub-mm motion blur might be detrimental. We propose a purely image based motion compensation method that requires no fiducials, tracking hardware or prior images. A statistical optimization algorithm (CMA-ES) is used to estimate a motion trajectory that optimizes an objective function consisting of an image sharpness criterion augmented by a regularization term that encourages smooth motion trajectories. The objective function is evaluated using a volume of interest (VOI, e.g. a single bone and surrounding area) where the motion can be assumed to be rigid. More complex motions can be addressed by using multiple VOIs. Gradient variance was found to be a suitable sharpness metric for this application. The performance of the compensation algorithm was evaluated in simulated and experimental CBCT data, and in a clinical dataset. Motion-induced artifacts and blurring were significantly reduced across a broad range of motion amplitudes, from 0.5 mm to 10 mm. Structure similarity index (SSIM) against a static volume was used in the simulation studies to quantify the performance of the motion compensation. In studies with translational motion, the SSIM improved from 0.86 before compensation to 0.97 after compensation for 0.5 mm motion, from 0.8 to 0.94 for 2 mm motion and from 0.52 to 0.87 for 10 mm motion (~70% increase). Similar reduction of artifacts was observed in a benchtop experiment with controlled translational motion of an anthropomorphic hand phantom, where SSIM (against a reconstruction of a static phantom) improved from 0.3 to 0.8 for 10 mm motion. Application to a clinical dataset of a lower extremity showed dramatic reduction

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

SU-F-J-74: High Z Geometric Integrity and Beam Hardening Artifact Assessment Using a Retrospective Metal Artifact Reduction (MAR) Reconstruction Algorithm

Energy Technology Data Exchange (ETDEWEB)

Woods, K; DiCostanzo, D; Gupta, N [Ohio State University Columbus, OH (United States)

2016-06-15

Purpose: To test the efficacy of a retrospective metal artifact reduction (MAR) reconstruction algorithm for a commercial computed tomography (CT) scanner for radiation therapy purposes. Methods: High Z geometric integrity and artifact reduction analysis was performed with three phantoms using General Electric’s (GE) Discovery CT. The three phantoms included: a Computerized Imaging Reference Systems (CIRS) electron density phantom (Model 062) with a 6.5 mm diameter titanium rod insert, a custom spine phantom using Synthes Spine hardware submerged in water, and a dental phantom with various high Z fillings submerged in water. Each phantom was reconstructed using MAR and compared against the original scan. Furthermore, each scenario was tested using standard and extended Hounsfield Unit (HU) ranges. High Z geometric integrity was performed using the CIRS phantom, while the artifact reduction was performed using all three phantoms. Results: Geometric integrity of the 6.5 mm diameter rod was slightly overestimated for non-MAR scans for both standard and extended HU. With MAR reconstruction, the rod was underestimated for both standard and extended HU. For artifact reduction, the mean and standard deviation was compared in a volume of interest (VOI) in the surrounding material (water and water equivalent material, ∼0HU). Overall, the mean value of the VOI was closer to 0 HU for the MAR reconstruction compared to the non-MAR scan for most phantoms. Additionally, the standard deviations for all phantoms were greatly reduced using MAR reconstruction. Conclusion: GE’s MAR reconstruction algorithm improves image quality with the presence of high Z material with minimal degradation of its geometric integrity. High Z delineation can be carried out with proper contouring techniques. The effects of beam hardening artifacts are greatly reduced with MAR reconstruction. Tissue corrections due to these artifacts can be eliminated for simple high Z geometries and greatly

SU-F-J-74: High Z Geometric Integrity and Beam Hardening Artifact Assessment Using a Retrospective Metal Artifact Reduction (MAR) Reconstruction Algorithm

International Nuclear Information System (INIS)

Woods, K; DiCostanzo, D; Gupta, N

2016-01-01

Purpose: To test the efficacy of a retrospective metal artifact reduction (MAR) reconstruction algorithm for a commercial computed tomography (CT) scanner for radiation therapy purposes. Methods: High Z geometric integrity and artifact reduction analysis was performed with three phantoms using General Electric’s (GE) Discovery CT. The three phantoms included: a Computerized Imaging Reference Systems (CIRS) electron density phantom (Model 062) with a 6.5 mm diameter titanium rod insert, a custom spine phantom using Synthes Spine hardware submerged in water, and a dental phantom with various high Z fillings submerged in water. Each phantom was reconstructed using MAR and compared against the original scan. Furthermore, each scenario was tested using standard and extended Hounsfield Unit (HU) ranges. High Z geometric integrity was performed using the CIRS phantom, while the artifact reduction was performed using all three phantoms. Results: Geometric integrity of the 6.5 mm diameter rod was slightly overestimated for non-MAR scans for both standard and extended HU. With MAR reconstruction, the rod was underestimated for both standard and extended HU. For artifact reduction, the mean and standard deviation was compared in a volume of interest (VOI) in the surrounding material (water and water equivalent material, ∼0HU). Overall, the mean value of the VOI was closer to 0 HU for the MAR reconstruction compared to the non-MAR scan for most phantoms. Additionally, the standard deviations for all phantoms were greatly reduced using MAR reconstruction. Conclusion: GE’s MAR reconstruction algorithm improves image quality with the presence of high Z material with minimal degradation of its geometric integrity. High Z delineation can be carried out with proper contouring techniques. The effects of beam hardening artifacts are greatly reduced with MAR reconstruction. Tissue corrections due to these artifacts can be eliminated for simple high Z geometries and greatly

Usefulness of IDEAL T2-weighted FSE and SPGR imaging in reducing metallic artifacts in the postoperative ankles with metallic hardware

International Nuclear Information System (INIS)

Lee, Jung Bin; Cha, Jang Gyu; Lee, Min Hee; Lee, Eun Hye; Lee, Young Koo; Jeon, Chan Hong

2013-01-01

The aim of this work is to prospectively compare the effectiveness of iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL), T2-weighted fast spin-echo (FSE), and spoiled gradient-echo (SPGR) MR imaging to frequency selective fat suppression (FSFS) protocols for minimizing metallic artifacts in postoperative ankles with metallic hardware. The T2-weighted and SPGR imaging with IDEAL and FSFS were performed on 21 ankles of 21 patients with metallic hardware. Two musculoskeletal radiologists independently analyzed techniques for visualization of ankle ligaments and articular cartilage, uniformity of fat saturation, and relative size of the metallic artifacts. A paired t test was used for statistical comparisons of MR images between IDEAL and FSFS groups. IDEAL T2-weighted FSE and SPGR images enabled significantly improved visualization of articular cartilage (p < 0.05), the size of metallic artifact (p < 0.05), and the uniformity of fat saturation (p < 0.05). However, no significant improvement was found in the visibility of ligaments. IDEAL T2-weighted FSE and SPGR imaging effectively reduces the degree of tissue-obscuring artifacts produced by fixation hardware in ankle joints and improves image quality compared to FSFS T2-weighted FSE and SPGR imaging. However, visibility of ligaments was not improved using IDEAL imaging. (orig.)

TH-CD-206-12: Image-Based Motion Estimation for Plaque Visualization in Coronary Computed Tomography Angiography

Energy Technology Data Exchange (ETDEWEB)

Zhang, X; Sisniega, A; Zbijewski, W; Stayman, J [Johns Hopkins University, Balitmore, MD (United States); Contijoch, F; McVeigh, E [University of California, San Diego, San Diego, CA (United States)

2016-06-15

Purpose: Visualization and quantification of coronary artery calcification and atherosclerotic plaque benefits from coronary artery motion (CAM) artifact elimination. This work applies a rigid linear motion model to a Volume of Interest (VoI) for estimating motion estimation and compensation of image degradation in Coronary Computed Tomography Angiography (CCTA). Methods: In both simulation and testbench experiments, translational CAM was generated by displacement of the imaging object (i.e. simulated coronary artery and explanted human heart) by ∼8 mm, approximating the motion of a main coronary branch. Rotation was assumed to be negligible. A motion degraded region containing a calcification was selected as the VoI. Local residual motion was assumed to be rigid and linear over the acquisition window, simulating motion observed during diastasis. The (negative) magnitude of the image gradient of the reconstructed VoI was chosen as the motion estimation objective and was minimized with Covariance Matrix Adaptation Evolution Strategy (CMAES). Results: Reconstruction incorporated the estimated CAM yielded signification recovery of fine calcification structures as well as reduced motion artifacts within the selected local region. The compensated reconstruction was further evaluated using two image similarity metrics, the structural similarity index (SSIM) and Root Mean Square Error (RMSE). At the calcification site, the compensated data achieved a 3% increase in SSIM and a 91.2% decrease in RMSE in comparison with the uncompensated reconstruction. Conclusion: Results demonstrate the feasibility of our image-based motion estimation method exploiting a local rigid linear model for CAM compensation. The method shows promising preliminary results for the application of such estimation in CCTA. Further work will involve motion estimation of complex motion corrupted patient data acquired from clinical CT scanner.

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.

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

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

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

Metal Artifact Suppression in Dental Cone Beam Computed Tomography Images Using Image Processing Techniques.

Science.gov (United States)

Johari, Masoumeh; Abdollahzadeh, Milad; Esmaeili, Farzad; Sakhamanesh, Vahideh

2018-01-01

Dental cone beam computed tomography (CBCT) images suffer from severe metal artifacts. These artifacts degrade the quality of acquired image and in some cases make it unsuitable to use. Streaking artifacts and cavities around teeth are the main reason of degradation. In this article, we have proposed a new artifact reduction algorithm which has three parallel components. The first component extracts teeth based on the modeling of image histogram with a Gaussian mixture model. Striking artifact reduction component reduces artifacts using converting image into the polar domain and applying morphological filtering. The third component fills cavities through a simple but effective morphological filtering operation. Finally, results of these three components are combined into a fusion step to create a visually good image which is more compatible to human visual system. Results show that the proposed algorithm reduces artifacts of dental CBCT images and produces clean images.

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.

Integrated SSFP for functional brain mapping at 7 T with reduced susceptibility artifact

Science.gov (United States)

Sun, Kaibao; Xue, Rong; Zhang, Peng; Zuo, Zhentao; Chen, Zhongwei; Wang, Bo; Martin, Thomas; Wang, Yi; Chen, Lin; He, Sheng; Wang, Danny J. J.

2017-03-01

Balanced steady-state free precession (bSSFP) offers an alternative and potentially important tool to the standard gradient-echo echo-planar imaging (GE-EPI) for functional MRI (fMRI). Both passband and transition band based bSSFP have been proposed for fMRI. The applications of these methods, however, are limited by banding artifacts due to the sensitivity of bSSFP signal to off-resonance effects. In this article, a unique case of the SSFP-FID sequence, termed integrated-SSFP or iSSFP, was proposed to overcome the obstacle by compressing the SSFP profile into the width of a single voxel. The magnitude of the iSSFP signal was kept constant irrespective of frequency shift. Visual stimulation studies were performed to demonstrate the feasibility of fMRI using iSSFP at 7 T with flip angles of 4° and 25°, compared to standard bSSFP and gradient echo (GRE) imaging. The signal changes for the complex iSSFP signal in activated voxels were 2.48 ± 0.53 (%) and 2.96 ± 0.87 (%) for flip angles (FA) of 4° and 25° respectively at the TR of 9.88 ms. Simultaneous multi-slice acquisition (SMS) with the CAIPIRIHNA technique was carried out with iSSFP scanning to detect the anterior temporal lobe activation using a semantic processing task fMRI, compared with standard 2D GE-EPI. This study demonstrates the feasibility of iSSFP for fMRI with reduced susceptibility artifacts, while maintaining robust functional contrast at 7 T.

Metal artifact reduction in CT using tissue-class modeling and adaptive prefiltering

International Nuclear Information System (INIS)

Bal, Matthieu; Spies, Lothar

2006-01-01

High-density objects such as metal prostheses, surgical clips, or dental fillings generate streak-like artifacts in computed tomography images. We present a novel method for metal artifact reduction by in-painting missing information into the corrupted sinogram. The information is provided by a tissue-class model extracted from the distorted image. To this end the image is first adaptively filtered to reduce the noise content and to smooth out streak artifacts. Consecutively, the image is segmented into different material classes using a clustering algorithm. The corrupted and missing information in the original sinogram is completed using the forward projected information from the tissue-class model. The performance of the correction method is assessed on phantom images. Clinical images featuring a broad spectrum of metal artifacts are studied. Phantom and clinical studies show that metal artifacts, such as streaks, are significantly reduced and shadows in the image are eliminated. Furthermore, the novel approach improves detectability of organ contours. This can be of great relevance, for instance, in radiation therapy planning, where images affected by metal artifacts may lead to suboptimal treatment plans

Evaluation of the reconstruction of image acquired from CT simulator to reduce metal artifact

International Nuclear Information System (INIS)

Choi, Ji Hun; Park, Jin Hong; Choi, Byung Don; Won, Hui Su; Chang, Nam Jun; Goo, Jang Hyun; Hong, Joo Wan

2014-01-01

This study presents the usefulness assessment of metal artifact reduction for orthopedic implants(O-MAR) to decrease metal artifacts from materials with high density when acquired CT images. By CT simulator, original CT images were acquired from Gammex and Rando phantom and those phantoms inserted with high density materials were scanned for other CT images with metal artifacts and then O-MAR was applied to those images, respectively. To evaluate CT images using Gammex phantom, 5 regions of interest(ROIs) were placed at 5 organs and 3 ROIs were set up at points affected by artifacts. The averages of standard deviation(SD) and CT numbers were compared with a plan using original image. For assessment of variations in dose of tissue around materials with high density, the volume of a cylindrical shape was designed at 3 places in images acquired from Rando phantom by Eclipse. With 6 MV, 7-fields, 15x15cm 2 and 100 cGy per fraction, treatment planning was created and the mean dose were compared with a plan using original image. In the test with the Gammex phantom, CT numbers had a few difference at established points and especially 3 points affected by artifacts had most of the same figures. In the case of O-MAR image, the more reduction in SD appeared at all of 8 points than non O-MAR image. In the test using the Rando Phantom, the variations in dose of tissue around high density materials had a few difference between original CT image and CT image with O-MAR. The CT images using O-MAR were acquired clearly at the boundary of tissue around high density materials and applying O-MAR was useful for correcting CT numbers

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...

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.

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...

Motion estimation by data assimilation in reduced dynamic models

International Nuclear Information System (INIS)

Drifi, Karim

2013-01-01

Motion estimation is a major challenge in the field of image sequence analysis. This thesis is a study of the dynamics of geophysical flows visualized by satellite imagery. Satellite image sequences are currently underused for the task of motion estimation. A good understanding of geophysical flows allows a better analysis and forecast of phenomena in domains such as oceanography and meteorology. Data assimilation provides an excellent framework for achieving a compromise between heterogeneous data, especially numerical models and observations. Hence, in this thesis we set out to apply variational data assimilation methods to estimate motion on image sequences. As one of the major drawbacks of applying these assimilation techniques is the considerable computation time and memory required, we therefore define and use a model reduction method in order to significantly decrease the necessary computation time and the memory. We then explore the possibilities that reduced models provide for motion estimation, particularly the possibility of strictly imposing some known constraints on the computed solutions. In particular, we show how to estimate a divergence free motion with boundary conditions on a complex spatial domain [fr

Evaluation of the effects of an arm artifact reduction filter in computed tomography

International Nuclear Information System (INIS)

Nozaki, Fumie; Ohno, Hajime; Hirako, Tetsuya

2002-01-01

While performing CT during arterial portography (CTAP) or CT arteriography (CTA), we have instructed patients to in order to reduce streak artifacts. However the repetitive raising and lowering their arms has made it difficult to keep a clean zone and as well as to maintain the position of a target organ. An arm artifact reduction (AAR) filter developed by GE Yokokawa Medical System has been reported to be useful for reducing streak artifacts in CTAP and CTA. The purpose of this study was to estimate the effectiveness of the AAR filter in terms of artifact reduction ratio, CT value, standard deviation and spatial resolution. The use of an AAR filter reduced streak artifacts on images by 15-22% compared with those on images obtained by without the use of the filter and limited deterioration of spatial resolution to within 1%. Moreover, CT value in examination using AAR filter showed no significant change compared with that in non-filter's examination. It is concluded that the use of an AAR filter reduces the burden for the patient and increase the accuracy and flexibility of CT examination while minimizing the reduction in the image quality in CTAP and CTA. (author)

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

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.

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

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.

Dual-energy CT and ceramic or titanium prostheses material reduce CT artifacts and provide superior image quality of total knee arthroplasty.

Science.gov (United States)

Kasparek, Maximilian F; Töpker, Michael; Lazar, Mathias; Weber, Michael; Kasparek, Michael; Mang, Thomas; Apfaltrer, Paul; Kubista, Bernd; Windhager, Reinhard; Ringl, Helmut

2018-06-07

To evaluate the influence of different scan parameters for single-energy CT and dual-energy CT, as well as the impact of different material used in a TKA prosthesis on image quality and the extent of metal artifacts. Eight pairs of TKA prostheses from different vendors were examined in a phantom set-up. Each pair consisted of a conventional CoCr prosthesis and the corresponding anti-allergic prosthesis (full titanium, ceramic, or ceramic-coated) from the same vendor. Nine different (seven dual-energy CT and two single-energy CT) scan protocols with different characteristics were used to determine the most suitable CT protocol for TKA imaging. Quantitative image analysis included assessment of blooming artifacts (metal implants appear thicker on CT than they are, given as virtual growth in mm in this paper) and streak artifacts (thick dark lines around metal). Qualitative image analysis was used to investigate the bone-prosthesis interface. The full titanium prosthesis and full ceramic knee showed significantly fewer blooming artifacts compared to the standard CoCr prosthesis (mean virtual growth 0.6-2.2 mm compared to 2.9-4.6 mm, p energy CT protocols showed less blooming (range 3.3-3.8 mm) compared to single-energy protocols (4.6-5.5 mm). The full titanium and full ceramic prostheses showed significantly fewer streak artifacts (mean standard deviation 77-86 Hounsfield unit (HU)) compared to the standard CoCr prosthesis (277-334 HU, p energy CT protocols had fewer metal streak artifacts (215-296 HU compared to single-energy CT protocols (392-497 HU)). Full titanium and ceramic prostheses were ranked superior with regard to the image quality at the bone/prosthesis interface compared to a standard CoCr prosthesis, and all dual-energy CT protocols were ranked better than single-energy protocols. Dual-energy CT and ceramic or titanium prostheses reduce CT artifacts and provide superior image quality of total knee arthroplasty at the bone/prosthesis interface

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

The effects of tumor motion on planning and delivery of respiratory-gated IMRT

International Nuclear Information System (INIS)

Hugo, Geoffrey D.; Agazaryan, Nzhde; Solberg, Timothy D.

2003-01-01

The purpose of this study is to investigate the effects of object motion on the planning and delivery of IMRT. Two phantoms containing objects were imaged using CT under a variety of motion conditions. The effects of object motion on axial CT acquisition with and without gating were assessed qualitatively and quantitatively. Measurements of effective slice width and position for the CT scans were made. Mutual information image fusion was adapted for use as a quantitative measure of object deformation in CT images. IMRT plans were generated on the CT scans of the moving and gated object images. These plans were delivered with motion, with and without gating, and the delivery error between the moving deliveries and a nonmoving delivery was assessed using a scalable vector-based index. Motion during CT acquisition produces motion artifact, object deformation, and object mispositioning, which can be substantially reduced with gating. Objects that vary in cross section in the direction of motion exhibit the most deformation in CT images. Mutual information provides a useful quantitative estimate of object deformation. The delivery of IMRT in the presence of target motion significantly alters the delivered dose distribution in relation to the planned distribution. The utilization of gating for IMRT treatment, including imaging, planning, and delivery, significantly reduces the errors introduced by object motion

An efficient motion-resistant method for wearable pulse oximeter.

Science.gov (United States)

Yan, Yong-Sheng; Zhang, Yuan-Ting

2008-05-01

Reduction of motion artifact and power saving are crucial in designing a wearable pulse oximeter for long-term telemedicine application. In this paper, a novel algorithm, minimum correlation discrete saturation transform (MCDST) has been developed for the estimation of arterial oxygen saturation (SaO2), based on an optical model derived from photon diffusion analysis. The simulation shows that the new algorithm MCDST is more robust under low SNRs than the clinically verified motion-resistant algorithm discrete saturation transform (DST). Further, the experiment with different severity of motions demonstrates that MCDST has a slightly better performance than DST algorithm. Moreover, MCDST is more computationally efficient than DST because the former uses linear algebra instead of the time-consuming adaptive filter used by latter, which indicates that MCDST can reduce the required power consumption and circuit complexity of the implementation. This is vital for wearable devices, where the physical size and long battery life are crucial.

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.

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.)

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.)

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

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

Designing a compact MRI motion phantom

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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.

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.

Effective motion design applied to energy-efficient handling processes

Energy Technology Data Exchange (ETDEWEB)

Brett, Tobias

2013-10-01

Industrial robots are available in a large variety of mechanical alternatives regarding size, motor power, link length ratio or payload. The four major types of serial kinematics dominating the market are complemented by various parallel kinematics for special purpose. In contrast, few other path planning alternatives are applied in industrial robotics which are based on similar analytic solution principles. The objective of this thesis is to develop a systematic design method for artifacts in motion, to integrate motion design and mechanical design to enable new processes for production. For each design, a theoretical benchmark is developed, which cannot be attained by conventional robots in principle. A key performance indicator enables to measure the degree of goal achievement towards the benchmark during all design phases. Motion behaviors are identified on a local level by dynamic systems modeling and are integrated into new global behavior featuring a new quality, suitable for exceeding the design benchmark in industrial processes. Two exemplary handling robot designs are presented. The first concept enables motion behavior to consume less electrical power than kinetic energy transferred to and from its payload during motion. The second concept enables motion with four degrees of freedom by single motor stimulation, reducing idle power consumption on factor 4 towards conventional robots.

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.

An embedded optical tracking system for motion-corrected magnetic resonance imaging at 7T.

Science.gov (United States)

Schulz, Jessica; Siegert, Thomas; Reimer, Enrico; Labadie, Christian; Maclaren, Julian; Herbst, Michael; Zaitsev, Maxim; Turner, Robert

2012-12-01

Prospective motion correction using data from optical tracking systems has been previously shown to reduce motion artifacts in MR imaging of the head. We evaluate a novel optical embedded tracking system. The home-built optical embedded tracking system performs image processing within a 7 T scanner bore, enabling high speed tracking. Corrected and uncorrected in vivo MR volumes are acquired interleaved using a modified 3D FLASH sequence, and their image quality is assessed and compared. The latency between motion and correction of the slice position was measured to be (19 ± 5) ms, and the tracking noise has a standard deviation no greater than 10 μm/0.005° during conventional MR scanning. Prospective motion correction improved the edge strength by 16 % on average, even though the volunteers were asked to remain motionless during the acquisitions. Using a novel method for validating the effectiveness of in vivo prospective motion correction, we have demonstrated that prospective motion correction using motion data from the embedded tracking system considerably improved image quality.

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

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.

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....

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

An illustrative review to understand and manage metal-induced artifacts in musculoskeletal MRI: a primer and updates

Energy Technology Data Exchange (ETDEWEB)

Dillenseger, J.P.; Choquet, P.; Goetz, C.; Bierry, G. [University Hospital of Strasbourg, Medical Imaging Department, Strasbourg (France); Icube, CNRS, University of Strasbourg, Strasbourg (France); University of Strasbourg, Translational Medicine Research Federation, Strasbourg Medical School, Strasbourg (France); Moliere, S. [University Hospital of Strasbourg, Medical Imaging Department, Strasbourg (France); Ehlinger, M. [Icube, CNRS, University of Strasbourg, Strasbourg (France); University of Strasbourg, Translational Medicine Research Federation, Strasbourg Medical School, Strasbourg (France); University Hospital of Strasbourg, Department of Orthopedic Surgery, Strasbourg (France)

2016-05-15

This article reviews and explains the basic physical principles of metal-induced MRI artifacts, describes simple ways to reduce them, and presents specific reduction solutions. Artifacts include signal loss, pile-up artifacts, geometric distortion, and failure of fat suppression. Their nature and origins are reviewed and explained though schematic representations that ease the understanding. Then, optimization of simple acquisition parameters is detailed. Lastly, dedicated sequences and options specifically developed to reduce metal artifacts (VAT, SEMAC, and MAVRIC) are explained. (orig.)

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.

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.

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.

Artifact reduction of different metallic implants in flat detector C-arm CT.

Science.gov (United States)

Hung, S-C; Wu, C-C; Lin, C-J; Guo, W-Y; Luo, C-B; Chang, F-C; Chang, C-Y

2014-07-01

Flat detector CT has been increasingly used as a follow-up examination after endovascular intervention. Metal artifact reduction has been successfully demonstrated in coil mass cases, but only in a small series. We attempted to objectively and subjectively evaluate the feasibility of metal artifact reduction with various metallic objects and coil lengths. We retrospectively reprocessed the flat detector CT data of 28 patients (15 men, 13 women; mean age, 55.6 years) after they underwent endovascular treatment (20 coiling ± stent placement, 6 liquid embolizers) or shunt drainage (n = 2) between January 2009 and November 2011 by using a metal artifact reduction correction algorithm. We measured CT value ranges and noise by using region-of-interest methods, and 2 experienced neuroradiologists rated the degrees of improved imaging quality and artifact reduction by comparing uncorrected and corrected images. After we applied the metal artifact reduction algorithm, the CT value ranges and the noise were substantially reduced (1815.3 ± 793.7 versus 231.7 ± 95.9 and 319.9 ± 136.6 versus 45.9 ± 14.0; both P metallic objects and various sizes of coil masses. The rater study achieved an overall improvement of imaging quality and artifact reduction (85.7% and 78.6% of cases by 2 raters, respectively), with the greatest improvement in the coiling group, moderate improvement in the liquid embolizers, and the smallest improvement in ventricular shunting (overall agreement, 0.857). The metal artifact reduction algorithm substantially reduced artifacts and improved the objective image quality in every studied case. It also allowed improved diagnostic confidence in most cases. © 2014 by American Journal of Neuroradiology.

Respiratory-Gated Positron Emission Tomography and Breath-Hold Computed Tomography Coupling to Reduce the Influence of Respiratory Motion: Methodology and Feasibility

International Nuclear Information System (INIS)

Daouk, J.; Fin, L.; Bailly, P.; Meyer, M.E.

2009-01-01

Background: Respiratory motion causes uptake in positron emission tomography (PET) images of chest and abdominal structures to be blurred and reduced in intensity. Purpose: To compare two respiratory-gated PET binning methods (based on frequency and amplitude analyses of the respiratory signal) and to propose a 'BH-based' method based on an additional breath-hold computed tomography (CT) acquisition. Material and Methods: Respiratory-gated PET consists in list-mode (LM) acquisition with simultaneous respiratory signal recording. A phantom study featured rectilinear movement of a 0.5-ml sphere filled with 18 F-fluorodeoxyglucose ( 18 F-FDG) solution, placed in a radioactive background (sphere-to-background contrast 6:1). Two patients were also examined. Three figures of merit were calculated: the target-to-background ratio profile (TBRP) in the axial direction through the uptake (i.e., the sphere or lesion), full-width-at-half-maximum (FWHM) values, and maximized standard uptake values (SUVmax). Results: In the phantom study, the peak TBRP was 0.9 for non-gated volume, 1.83 for BH-based volume, and varied between 1.13 and 1.73 for Freq-based volumes and between 1.34 and 1.66 for Amp-based volumes. A reference volume (REF-static) was also acquired for the phantom (in a static, 'expiratory' state), with a peak TBRP at 1.88. TBRPs were computed for patient data, with higher peak values for all gated volumes than for non-gated volumes. Conclusion: Respiratory-gated PET acquisition reduces the blurring effect and increases image contrast. However, Freq-based and Amp-based volumes are still influenced by inappropriate attenuation correction and misregistration of mobile lesions on CT images. The proposed BH-based method both reduces motion artifacts and improves PET-CT registration

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.

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.

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.

TH-EF-BRA-03: Assessment of Data-Driven Respiratory Motion-Compensation Methods for 4D-CBCT Image Registration and Reconstruction Using Clinical Datasets

Energy Technology Data Exchange (ETDEWEB)

Riblett, MJ; Weiss, E; Hugo, GD [Virginia Commonwealth University, Richmond, VA (United States); Christensen, GE [University of Iowa, Iowa City, IA (United States)

2016-06-15

Purpose: To evaluate the performance of a 4D-CBCT registration and reconstruction method that corrects for respiratory motion and enhances image quality under clinically relevant conditions. Methods: Building on previous work, which tested feasibility of a motion-compensation workflow using image datasets superior to clinical acquisitions, this study assesses workflow performance under clinical conditions in terms of image quality improvement. Evaluated workflows utilized a combination of groupwise deformable image registration (DIR) and image reconstruction. Four-dimensional cone beam CT (4D-CBCT) FDK reconstructions were registered to either mean or respiratory phase reference frame images to model respiratory motion. The resulting 4D transformation was used to deform projection data during the FDK backprojection operation to create a motion-compensated reconstruction. To simulate clinically realistic conditions, superior quality projection datasets were sampled using a phase-binned striding method. Tissue interface sharpness (TIS) was defined as the slope of a sigmoid curve fit to the lung-diaphragm boundary or to the carina tissue-airway boundary when no diaphragm was discernable. Image quality improvement was assessed in 19 clinical cases by evaluating mitigation of view-aliasing artifacts, tissue interface sharpness recovery, and noise reduction. Results: For clinical datasets, evaluated average TIS recovery relative to base 4D-CBCT reconstructions was observed to be 87% using fixed-frame registration alone; 87% using fixed-frame with motion-compensated reconstruction; 92% using mean-frame registration alone; and 90% using mean-frame with motion-compensated reconstruction. Soft tissue noise was reduced on average by 43% and 44% for the fixed-frame registration and registration with motion-compensation methods, respectively, and by 40% and 42% for the corresponding mean-frame methods. Considerable reductions in view aliasing artifacts were observed for each

TH-EF-BRA-03: Assessment of Data-Driven Respiratory Motion-Compensation Methods for 4D-CBCT Image Registration and Reconstruction Using Clinical Datasets

International Nuclear Information System (INIS)

Riblett, MJ; Weiss, E; Hugo, GD; Christensen, GE

2016-01-01

Purpose: To evaluate the performance of a 4D-CBCT registration and reconstruction method that corrects for respiratory motion and enhances image quality under clinically relevant conditions. Methods: Building on previous work, which tested feasibility of a motion-compensation workflow using image datasets superior to clinical acquisitions, this study assesses workflow performance under clinical conditions in terms of image quality improvement. Evaluated workflows utilized a combination of groupwise deformable image registration (DIR) and image reconstruction. Four-dimensional cone beam CT (4D-CBCT) FDK reconstructions were registered to either mean or respiratory phase reference frame images to model respiratory motion. The resulting 4D transformation was used to deform projection data during the FDK backprojection operation to create a motion-compensated reconstruction. To simulate clinically realistic conditions, superior quality projection datasets were sampled using a phase-binned striding method. Tissue interface sharpness (TIS) was defined as the slope of a sigmoid curve fit to the lung-diaphragm boundary or to the carina tissue-airway boundary when no diaphragm was discernable. Image quality improvement was assessed in 19 clinical cases by evaluating mitigation of view-aliasing artifacts, tissue interface sharpness recovery, and noise reduction. Results: For clinical datasets, evaluated average TIS recovery relative to base 4D-CBCT reconstructions was observed to be 87% using fixed-frame registration alone; 87% using fixed-frame with motion-compensated reconstruction; 92% using mean-frame registration alone; and 90% using mean-frame with motion-compensated reconstruction. Soft tissue noise was reduced on average by 43% and 44% for the fixed-frame registration and registration with motion-compensation methods, respectively, and by 40% and 42% for the corresponding mean-frame methods. Considerable reductions in view aliasing artifacts were observed for each

Spectral CT with monochromatic imaging and metal artifacts reduction software for artifacts reduction of ¹²⁵I radioactive seeds in liver brachytherapy.

Science.gov (United States)

Yang, Qiuxia; Peng, Sheng; Wu, Jing; Ban, Xiaohua; He, Mingyan; Xie, Chuanmiao; Zhang, Rong

2015-11-01

To investigate the optimal monochromatic energy for artifacts reduction from (125)I seeds as well as image improvement in the vicinity of seeds on monochromatic images with and without metal artifacts reduction software (MARS) and to compare this with traditional 120-kVp images, so as to evaluate the application value of gemstone spectral imaging for reducing artifacts from (125)I seeds in liver brachytherapy. A total of 45 tumors from 25 patients treated with (125)I seed brachytherapy in the liver were enrolled in this study. Multiphasic spectral computed tomography (CT) scanning was performed for each patient. After a delay time of 15 s of portal vein phase, a traditional 120-kVp scan was performed, focusing on several planes of (125)I seeds only. The artifact index (AI) in the vicinity of seeds and the standard deviation (SD) of the CT density of region of interest in the outside liver parenchyma were calculated. Artifact appearance was evaluated and classified on reconstructed monochromatic S and 120-kVp images. Image quality in the vicinity of seeds of three data sets were evaluated using a 1-5 scale scoring method. The Friedman rank-sum test was used to estimate the scoring results of image quality. The greatest noise in monochromatic images was found at 40 keV (SD = 27.38, AI = 206.40). The optimal monochromatic energy was found at 75 keV, which provided almost the least image noise (SD = 10.01) and good performance in artifact reduction (AI = 102.73). Image noise and AI reduction at 75 keV was decreased by 63.44 and 50.23%, compared with at 40 keV. Near-field thick artifacts were obvious in all 45 lesions, in 120-kVp images, and 75-keV images, but basically reduced in 75 keV MARS images and artifacts completely invisible in 7 lesions. The number of diagnosable images (score ≥3) was significantly more in the 75-keV MARS group (28/45), and the 75-keV group (22/45) than in the 120-kVp group (11/45) (p improve image quality, even to a state of being

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

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 reduce the quality of the images. Although pharmacologic suppression of motion is effective, no study has being conducted to analyze the influence of drug motion suppression on fast breath-hold 1.5-T examinations of the upper abdomen. A prospective, randomized, double-blind trial was conducted in 50 patients. Patients were randomly distributed into two groups: The control group received only an oral solution, whereas the other group received the oral solution plus a subcutaneous injection of 20 mg of butylscopolamine 10 min before the MR examination. Breath-hold T1-weighted gradient-recalled-echo (GRE) MR images were obtained in a 1.5-T superconductive unit. Quantitative image analysis was performed with region-of-interest (ROI) measurements of the signal intensity of the liver and in background air anterior and lateral to the patient. A qualitative analysis of the subjective quality of the T1-weighted images was also done, and the adverse reactions were registered. The groups were homogeneous regarding age, gender, and weight distribution. No significant differences in the signal intensity of the liver and in the incoherent noise measurements were found between the two groups. Gastrointestinal noise showed significant differences between groups, with lower values for the butylscopolamine group compared with the control group. There was also a statistically significant difference in the image quality between groups, and optimal studies were only found in the butylscopolamine group, where most patients had a good-quality evaluation. Regarding adverse events, there were non-significant differences between groups. In conclusion, administration of an antiperistaltic agent to reduce the movements of the gastrointestinal tract diminishes the motion artifacts generated on MR imaging of the abdomen, even at high field strength and with fast imaging sequences. Images of the upper abdomen obtained

Evaluation of artifact-corrected electroencephalographic (EEG) training: a pilot study.

Science.gov (United States)

La Marca, Jeffry P; Cruz, Daniel; Fandino, Jennifer; Cacciaguerra, Fabiana R; Fresco, Joseph J; Guerra, Austin T

2018-07-01

This double-blind study examined the effect of electromyographical (EMG) artifacts, which contaminate electroencephalographical (EEG) signals, by comparing artifact-corrected (AC) and non-artifact-corrected (NAC) neurofeedback (NF) training procedures. 14 unmedicated college students were randomly assigned to two groups: AC (n = 7) or NAC (n = 7). Both groups received 12 sessions of NF and were trained using identical NF treatment protocols to reduce their theta/beta power ratios (TBPR). Outcomes on a continuous performance test revealed that the AC group had statistically significant increases across measures of auditory and visual attention. The NAC group showed smaller gains that only reached statistical significance on measures of visual attention. Only the AC group reduced their TBPR, the NAC group did not. AC NF appears to play an important role during training that leads to improvements in both auditory and visual attention. Additional research is required to confirm the results of this study.

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.

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

RubiShort: Reducing scan time in 82Rb heart scans to minimize movements artifacts

DEFF Research Database (Denmark)

Madsen, Jeppe; Vraa, Kaspar J.; Harms, Hans

.013x, R2=0.98; %Reversible: y=1.008x, R2=0.95; TPD: y=1.000x, R2=0.99). Conclusion:, Scan time of myocardial perfusion scans using 82Rb can be reduced from 7 min. to 5 min. without loss of quantitative accuracy. Since patient motion is frequent in the last minutes of the scans, scan time reduction...

Complementary contrast media for metal artifact reduction in dual-energy computed tomography.

Science.gov (United States)

Lambert, Jack W; Edic, Peter M; FitzGerald, Paul F; Torres, Andrew S; Yeh, Benjamin M

2015-07-01

Metal artifacts have been a problem associated with computed tomography (CT) since its introduction. Recent techniques to mitigate this problem have included utilization of high-energy (keV) virtual monochromatic spectral (VMS) images, produced via dual-energy CT (DECT). A problem with these high-keV images is that contrast enhancement provided by all commercially available contrast media is severely reduced. Contrast agents based on higher atomic number elements can maintain contrast at the higher energy levels where artifacts are reduced. This study evaluated three such candidate elements: bismuth, tantalum, and tungsten, as well as two conventional contrast elements: iodine and barium. A water-based phantom with vials containing these five elements in solution, as well as different artifact-producing metal structures, was scanned with a DECT scanner capable of rapid operating voltage switching. In the VMS datasets, substantial reductions in the contrast were observed for iodine and barium, which suffered from contrast reductions of 97% and 91%, respectively, at 140 versus 40 keV. In comparison under the same conditions, the candidate agents demonstrated contrast enhancement reductions of only 20%, 29%, and 32% for tungsten, tantalum, and bismuth, respectively. At 140 versus 40 keV, metal artifact severity was reduced by 57% to 85% depending on the phantom configuration.

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

Metal artifact reduction algorithm based on model images and spatial information

Energy Technology Data Exchange (ETDEWEB)

Wu, Jay [Institute of Radiological Science, Central Taiwan University of Science and Technology, Taichung, Taiwan (China); Shih, Cheng-Ting [Department of Biomedical Engineering and Environmental Sciences, National Tsing-Hua University, Hsinchu, Taiwan (China); Chang, Shu-Jun [Health Physics Division, Institute of Nuclear Energy Research, Taoyuan, Taiwan (China); Huang, Tzung-Chi [Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung, Taiwan (China); Sun, Jing-Yi [Institute of Radiological Science, Central Taiwan University of Science and Technology, Taichung, Taiwan (China); Wu, Tung-Hsin, E-mail: tung@ym.edu.tw [Department of Biomedical Imaging and Radiological Sciences, National Yang-Ming University, No.155, Sec. 2, Linong Street, Taipei 112, Taiwan (China)

2011-10-01

Computed tomography (CT) has become one of the most favorable choices for diagnosis of trauma. However, high-density metal implants can induce metal artifacts in CT images, compromising image quality. In this study, we proposed a model-based metal artifact reduction (MAR) algorithm. First, we built a model image using the k-means clustering technique with spatial information and calculated the difference between the original image and the model image. Then, the projection data of these two images were combined using an exponential weighting function. At last, the corrected image was reconstructed using the filter back-projection algorithm. Two metal-artifact contaminated images were studied. For the cylindrical water phantom image, the metal artifact was effectively removed. The mean CT number of water was improved from -28.95{+-}97.97 to -4.76{+-}4.28. For the clinical pelvic CT image, the dark band and the metal line were removed, and the continuity and uniformity of the soft tissue were recovered as well. These results indicate that the proposed MAR algorithm is useful for reducing metal artifact and could improve the diagnostic value of metal-artifact contaminated CT images.

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.

Bias field inconsistency correction of motion-scattered multislice MRI for improved 3D image reconstruction.

Science.gov (United States)

Kim, Kio; Habas, Piotr A; Rajagopalan, Vidya; Scott, Julia A; Corbett-Detig, James M; Rousseau, Francois; Barkovich, A James; Glenn, Orit A; Studholme, Colin

2011-09-01

A common solution to clinical MR imaging in the presence of large anatomical motion is to use fast multislice 2D studies to reduce slice acquisition time and provide clinically usable slice data. Recently, techniques have been developed which retrospectively correct large scale 3D motion between individual slices allowing the formation of a geometrically correct 3D volume from the multiple slice stacks. One challenge, however, in the final reconstruction process is the possibility of varying intensity bias in the slice data, typically due to the motion of the anatomy relative to imaging coils. As a result, slices which cover the same region of anatomy at different times may exhibit different sensitivity. This bias field inconsistency can induce artifacts in the final 3D reconstruction that can impact both clinical interpretation of key tissue boundaries and the automated analysis of the data. Here we describe a framework to estimate and correct the bias field inconsistency in each slice collectively across all motion corrupted image slices. Experiments using synthetic and clinical data show that the proposed method reduces intensity variability in tissues and improves the distinction between key tissue types.

PET motion correction in context of integrated PET/MR: Current techniques, limitations, and future projections.

Science.gov (United States)

Gillman, Ashley; Smith, Jye; Thomas, Paul; Rose, Stephen; Dowson, Nicholas

2017-12-01

Patient motion is an important consideration in modern PET image reconstruction. Advances in PET technology mean motion has an increasingly important influence on resulting image quality. Motion-induced artifacts can have adverse effects on clinical outcomes, including missed diagnoses and oversized radiotherapy treatment volumes. This review aims to summarize the wide variety of motion correction techniques available in PET and combined PET/CT and PET/MR, with a focus on the latter. A general framework for the motion correction of PET images is presented, consisting of acquisition, modeling, and correction stages. Methods for measuring, modeling, and correcting motion and associated artifacts, both in literature and commercially available, are presented, and their relative merits are contrasted. Identified limitations of current methods include modeling of aperiodic and/or unpredictable motion, attaining adequate temporal resolution for motion correction in dynamic kinetic modeling acquisitions, and maintaining availability of the MR in PET/MR scans for diagnostic acquisitions. Finally, avenues for future investigation are discussed, with a focus on improvements that could improve PET image quality, and that are practical in the clinical environment. © 2017 American Association of Physicists in Medicine.

Spatial presaturation: Method for suppressing flow artifacts and improving depiction of vascular anatomy in clinical MR imaging

International Nuclear Information System (INIS)

Felmlee, J.P.; Ehman, R.; Julsrud, P.; Gray, J.

1987-01-01

MR images are often degraded by flow artifacts that obscure anatomic details and reduce contrast. Vascular structures are frequently depicted poorly because flow voids are obliterated by spurious intraluminal signals. This exhibit presents an analysis of the physical mechanisms of flow artifact formation and describes a presaturation technique for suppressing such artifacts. The technique incorporates additional spectrally shaped radio frequency pulses into standard imaging sequences. It has proved effective for reducing flow artifacts in experimental and clinical imaging studies. The technique is particularly helpful for high-resolution surface coil examinations of the neck, mediastinal imaging, and gated cardiac imaging, and for detecting thrombus and other intravastcular pathology

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.

Deep learning methods for CT image-domain metal artifact reduction

Science.gov (United States)

Gjesteby, Lars; Yang, Qingsong; Xi, Yan; Shan, Hongming; Claus, Bernhard; Jin, Yannan; De Man, Bruno; Wang, Ge

2017-09-01

Artifacts resulting from metal objects have been a persistent problem in CT images over the last four decades. A common approach to overcome their effects is to replace corrupt projection data with values synthesized from an interpolation scheme or by reprojection of a prior image. State-of-the-art correction methods, such as the interpolation- and normalization-based algorithm NMAR, often do not produce clinically satisfactory results. Residual image artifacts remain in challenging cases and even new artifacts can be introduced by the interpolation scheme. Metal artifacts continue to be a major impediment, particularly in radiation and proton therapy planning as well as orthopedic imaging. A new solution to the long-standing metal artifact reduction (MAR) problem is deep learning, which has been successfully applied to medical image processing and analysis tasks. In this study, we combine a convolutional neural network (CNN) with the state-of-the-art NMAR algorithm to reduce metal streaks in critical image regions. Training data was synthesized from CT simulation scans of a phantom derived from real patient images. The CNN is able to map metal-corrupted images to artifact-free monoenergetic images to achieve additional correction on top of NMAR for improved image quality. Our results indicate that deep learning is a novel tool to address CT reconstruction challenges, and may enable more accurate tumor volume estimation for radiation therapy planning.

Effective noise-suppressed and artifact-reduced reconstruction of SPECT data using a preconditioned alternating projection algorithm

Energy Technology Data Exchange (ETDEWEB)

Li, Si; Xu, Yuesheng, E-mail: yxu06@syr.edu [Guangdong Provincial Key Laboratory of Computational Science, School of Mathematics and Computational Sciences, Sun Yat-sen University, Guangzhou 510275 (China); Zhang, Jiahan; Lipson, Edward [Department of Physics, Syracuse University, Syracuse, New York 13244 (United States); Krol, Andrzej; Feiglin, David [Department of Radiology, SUNY Upstate Medical University, Syracuse, New York 13210 (United States); Schmidtlein, C. Ross [Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, New York 10065 (United States); Vogelsang, Levon [Carestream Health, Rochester, New York 14608 (United States); Shen, Lixin [Guangdong Provincial Key Laboratory of Computational Science, School of Mathematics and Computational Sciences, Sun Yat-sen University, Guangzhou 510275, China and Department of Mathematics, Syracuse University, Syracuse, New York 13244 (United States)

2015-08-15

square errors (MSEs), and report the convergence speed and computation time. Results: HOTV-PAPA yields the best signal-to-noise ratio, followed by TV-PAPA and TV-OSL/GPF-EM. The local spatial resolution of HOTV-PAPA is somewhat worse than that of TV-PAPA and TV-OSL. Images reconstructed using HOTV-PAPA have the lowest local noise power spectrum (LNPS) amplitudes, followed by TV-PAPA, TV-OSL, and GPF-EM. The LNPS peak of GPF-EM is shifted toward higher spatial frequencies than those for the three other methods. The PAPA-type methods exhibit much lower ensemble noise, ensemble voxel variance, and image roughness. HOTV-PAPA performs best in these categories. Whereas images reconstructed using both TV-PAPA and TV-OSL are degraded by severe staircase artifacts; HOTV-PAPA substantially reduces such artifacts. It also converges faster than the other three methods and exhibits the lowest overall reconstruction error level, as measured by MSE. Conclusions: For high-noise simulated SPECT data, HOTV-PAPA outperforms TV-PAPA, GPF-EM, and TV-OSL in terms of hot lesion detectability, noise suppression, MSE, and computational efficiency. Unlike TV-PAPA and TV-OSL, HOTV-PAPA does not create sizable staircase artifacts. Moreover, HOTV-PAPA effectively suppresses noise, with only limited loss of local spatial resolution. Of the four methods, HOTV-PAPA shows the best lesion detectability, thanks to its superior noise suppression. HOTV-PAPA shows promise for clinically useful reconstructions of low-dose SPECT data.

Effective noise-suppressed and artifact-reduced reconstruction of SPECT data using a preconditioned alternating projection algorithm

International Nuclear Information System (INIS)

Li, Si; Xu, Yuesheng; Zhang, Jiahan; Lipson, Edward; Krol, Andrzej; Feiglin, David; Schmidtlein, C. Ross; Vogelsang, Levon; Shen, Lixin

2015-01-01

square errors (MSEs), and report the convergence speed and computation time. Results: HOTV-PAPA yields the best signal-to-noise ratio, followed by TV-PAPA and TV-OSL/GPF-EM. The local spatial resolution of HOTV-PAPA is somewhat worse than that of TV-PAPA and TV-OSL. Images reconstructed using HOTV-PAPA have the lowest local noise power spectrum (LNPS) amplitudes, followed by TV-PAPA, TV-OSL, and GPF-EM. The LNPS peak of GPF-EM is shifted toward higher spatial frequencies than those for the three other methods. The PAPA-type methods exhibit much lower ensemble noise, ensemble voxel variance, and image roughness. HOTV-PAPA performs best in these categories. Whereas images reconstructed using both TV-PAPA and TV-OSL are degraded by severe staircase artifacts; HOTV-PAPA substantially reduces such artifacts. It also converges faster than the other three methods and exhibits the lowest overall reconstruction error level, as measured by MSE. Conclusions: For high-noise simulated SPECT data, HOTV-PAPA outperforms TV-PAPA, GPF-EM, and TV-OSL in terms of hot lesion detectability, noise suppression, MSE, and computational efficiency. Unlike TV-PAPA and TV-OSL, HOTV-PAPA does not create sizable staircase artifacts. Moreover, HOTV-PAPA effectively suppresses noise, with only limited loss of local spatial resolution. Of the four methods, HOTV-PAPA shows the best lesion detectability, thanks to its superior noise suppression. HOTV-PAPA shows promise for clinically useful reconstructions of low-dose SPECT data

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.

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

MRI-Based Computed Tomography Metal Artifact Correction Method for Improving Proton Range Calculation Accuracy

International Nuclear Information System (INIS)

Park, Peter C.; Schreibmann, Eduard; Roper, Justin; Elder, Eric; Crocker, Ian; Fox, Tim; Zhu, X. Ronald; Dong, Lei; Dhabaan, Anees

2015-01-01

Purpose: Computed tomography (CT) artifacts can severely degrade dose calculation accuracy in proton therapy. Prompted by the recently increased popularity of magnetic resonance imaging (MRI) in the radiation therapy clinic, we developed an MRI-based CT artifact correction method for improving the accuracy of proton range calculations. Methods and Materials: The proposed method replaces corrupted CT data by mapping CT Hounsfield units (HU number) from a nearby artifact-free slice, using a coregistered MRI. MRI and CT volumetric images were registered with use of 3-dimensional (3D) deformable image registration (DIR). The registration was fine-tuned on a slice-by-slice basis by using 2D DIR. Based on the intensity of paired MRI pixel values and HU from an artifact-free slice, we performed a comprehensive analysis to predict the correct HU for the corrupted region. For a proof-of-concept validation, metal artifacts were simulated on a reference data set. Proton range was calculated using reference, artifactual, and corrected images to quantify the reduction in proton range error. The correction method was applied to 4 unique clinical cases. Results: The correction method resulted in substantial artifact reduction, both quantitatively and qualitatively. On respective simulated brain and head and neck CT images, the mean error was reduced from 495 and 370 HU to 108 and 92 HU after correction. Correspondingly, the absolute mean proton range errors of 2.4 cm and 1.7 cm were reduced to less than 2 mm in both cases. Conclusions: Our MRI-based CT artifact correction method can improve CT image quality and proton range calculation accuracy for patients with severe CT artifacts

WE-D-18C-01: Art of Imaging: Diagnostic Ultrasound Image Artifacts

Energy Technology Data Exchange (ETDEWEB)

Zagzebski, J [University of Wisconsin, Madison, WI (United States); Lu, Z [University of Chicago, Chicago, IL (United States)

2014-06-15

Assumptions followed during construction of B-mode and color flow images are that the pulse-echo transit time can be converted to reflector depth through uniform tissue models, echoes originate only from locations along the transmit-receive axes of pulse propagation, and first order correction schemes adequately account for acoustic wave attenuation and absorption. The latter allows the display brightness to encode tissue echogenicity. This course will challenge participants to identify imaging artifacts whose origins stem from the more complex and realistic propagating and scattering conditions common in clinical ultrasound. Speckle, a very common artifact but a clinically employed feature, originates from simultaneous echoes from diffuse scatterers and is a result of coherent detection of signals. One of the most bothersome artifacts are those due to reverberations especially that originating from superficial tissue interfaces. Methods to overcome these will be discussed. This presentation also will describe and illustrate speed of sound, refraction, enhancement, shadowing, mirroring, beam width, beam-forming, and slice thickness artifacts. All are useful examples of limitations introduced by acoustic waves propagating through complex tissue paths. New formats for physician board certification exams are demanding the inclusion of image-based examples of ultrasound physics. Instructors' knowledge of, and access to examples of ultrasound artifacts are important in this effort. The presentation will incorporate an audience response system to challenge participants in correct identification of some of these artifacts. Learning Objectives: Review basic mechanisms for producing ultrasound images. Identify the etiology of speckle, reverberation noise, beam width and slice thickness artifacts, and artifacts associated with pulse propagation. Discuss methods that reduce the impact of artifacts OR employ artifacts effectively to facilitate clinical diagnosis.

Artifact reduction of compressed images and video combining adaptive fuzzy filtering and directional anisotropic diffusion

DEFF Research Database (Denmark)

Nadernejad, Ehsan; Forchhammer, Søren; Korhonen, Jari

2011-01-01

and ringing artifacts, we have applied directional anisotropic diffusion. Besides that, the selection of the adaptive threshold parameter for the diffusion coefficient has also improved the performance of the algorithm. Experimental results on JPEG compressed images as well as MJPEG and H.264 compressed......Fuzzy filtering is one of the recently developed methods for reducing distortion in compressed images and video. In this paper, we combine the powerful anisotropic diffusion equations with fuzzy filtering in order to reduce the impact of artifacts. Based on the directional nature of the blocking...... videos show improvement in artifact reduction of the proposed algorithm over other directional and spatial fuzzy filters....

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.

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...

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

Hybrid PET/MR imaging: an algorithm to reduce metal artifacts from dental implants in Dixon-based attenuation map generation using a multiacquisition variable-resonance image combination sequence.

Science.gov (United States)

Burger, Irene A; Wurnig, Moritz C; Becker, Anton S; Kenkel, David; Delso, Gaspar; Veit-Haibach, Patrick; Boss, Andreas

2015-01-01

It was the aim of this study to implement an algorithm modifying Dixon-based MR imaging datasets for attenuation correction in hybrid PET/MR imaging with a multiacquisition variable resonance image combination (MAVRIC) sequence to reduce metal artifacts. After ethics approval, in 8 oncologic patients with dental implants data were acquired in a trimodality setup with PET/CT and MR imaging. The protocol included a whole-body 3-dimensional dual gradient-echo sequence (Dixon) used for MR imaging-based PET attenuation correction and a high-resolution MAVRIC sequence, applied in the oral area compromised by dental implants. An algorithm was implemented correcting the Dixon-based μ maps using the MAVRIC in areas of Dixon signal voids. The artifact size of the corrected μ maps was compared with the uncorrected MR imaging μ maps. The algorithm was robust in all patients. There was a significant reduction in mean artifact size of 70.5% between uncorrected and corrected μ maps from 697 ± 589 mm(2) to 202 ± 119 mm(2) (P = 0.016). The proposed algorithm could improve MR imaging-based attenuation correction in critical areas, when standard attenuation correction is hampered by metal artifacts, using a MAVRIC. © 2015 by the Society of Nuclear Medicine and Molecular Imaging, Inc.

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

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...

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.

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

Optimization-based reconstruction for reduction of CBCT artifact in IGRT

Science.gov (United States)

Xia, Dan; Zhang, Zheng; Paysan, Pascal; Seghers, Dieter; Brehm, Marcus; Munro, Peter; Sidky, Emil Y.; Pelizzari, Charles; Pan, Xiaochuan

2016-04-01

Kilo-voltage cone-beam computed tomography (CBCT) plays an important role in image guided radiation therapy (IGRT) by providing 3D spatial information of tumor potentially useful for optimizing treatment planning. In current IGRT CBCT system, reconstructed images obtained with analytic algorithms, such as FDK algorithm and its variants, may contain artifacts. In an attempt to compensate for the artifacts, we investigate optimization-based reconstruction algorithms such as the ASD-POCS algorithm for potentially reducing arti- facts in IGRT CBCT images. In this study, using data acquired with a physical phantom and a patient subject, we demonstrate that the ASD-POCS reconstruction can significantly reduce artifacts observed in clinical re- constructions. Moreover, patient images reconstructed by use of the ASD-POCS algorithm indicate a contrast level of soft-tissue improved over that of the clinical reconstruction. We have also performed reconstructions from sparse-view data, and observe that, for current clinical imaging conditions, ASD-POCS reconstructions from data collected at one half of the current clinical projection views appear to show image quality, in terms of spatial and soft-tissue-contrast resolution, higher than that of the corresponding clinical reconstructions.

XD-GRASP: Golden-angle radial MRI with reconstruction of extra motion-state dimensions using compressed sensing.

Science.gov (United States)

Feng, Li; Axel, Leon; Chandarana, Hersh; Block, Kai Tobias; Sodickson, Daniel K; Otazo, Ricardo

2016-02-01

To develop a novel framework for free-breathing MRI called XD-GRASP, which sorts dynamic data into extra motion-state dimensions using the self-navigation properties of radial imaging and reconstructs the multidimensional dataset using compressed sensing. Radial k-space data are continuously acquired using the golden-angle sampling scheme and sorted into multiple motion-states based on respiratory and/or cardiac motion signals derived directly from the data. The resulting undersampled multidimensional dataset is reconstructed using a compressed sensing approach that exploits sparsity along the new dynamic dimensions. The performance of XD-GRASP is demonstrated for free-breathing three-dimensional (3D) abdominal imaging, two-dimensional (2D) cardiac cine imaging and 3D dynamic contrast-enhanced (DCE) MRI of the liver, comparing against reconstructions without motion sorting in both healthy volunteers and patients. XD-GRASP separates respiratory motion from cardiac motion in cardiac imaging, and respiratory motion from contrast enhancement in liver DCE-MRI, which improves image quality and reduces motion-blurring artifacts. XD-GRASP represents a new use of sparsity for motion compensation and a novel way to handle motions in the context of a continuous acquisition paradigm. Instead of removing or correcting motion, extra motion-state dimensions are reconstructed, which improves image quality and also offers new physiological information of potential clinical value. © 2015 Wiley Periodicals, Inc.

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.

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...

Analysis of metal artifact reduction tools for dental hardware in CT scans of the oral cavity: kVp, iterative reconstruction, dual-energy CT, metal artifact reduction software: does it make a difference?

Energy Technology Data Exchange (ETDEWEB)

Crop, An de; Hoof, Tom van; Herde, Katharina d' ; Thierens, Hubert; Bacher, Klaus [Ghent University, Department of Basic Medical Sciences, Gent (Belgium); Casselman, Jan; Vereecke, Elke; Bossu, Nicolas [AZ Sint Jan Bruges Ostend AV, Department of Radiology, Bruges (Belgium); Dierens, Melissa [Ghent University, Dental School, Unit for Oral and Maxillofacial Imaging, Ghent (Belgium); Pamplona, Jaime [Hospital Lisboa Central, Department of Neuroradiology, Lisbon (Portugal)

2015-08-15

Metal artifacts may negatively affect radiologic assessment in the oral cavity. The aim of this study was to evaluate different metal artifact reduction techniques for metal artifacts induced by dental hardware in CT scans of the oral cavity. Clinical image quality was assessed using a Thiel-embalmed cadaver. A Catphan phantom and a polymethylmethacrylate (PMMA) phantom were used to evaluate physical-technical image quality parameters such as artifact area, artifact index (AI), and contrast detail (IQF{sub inv}). Metal cylinders were inserted in each phantom to create metal artifacts. CT images of both phantoms and the Thiel-embalmed cadaver were acquired on a multislice CT scanner using 80, 100, 120, and 140 kVp; model-based iterative reconstruction (Veo); and synthesized monochromatic keV images with and without metal artifact reduction software (MARs). Four radiologists assessed the clinical image quality, using an image criteria score (ICS). Significant influence of increasing kVp and the use of Veo was found on clinical image quality (p = 0.007 and p = 0.014, respectively). Application of MARs resulted in a smaller artifact area (p < 0.05). However, MARs reconstructed images resulted in lower ICS. Of all investigated techniques, Veo shows to be most promising, with a significant improvement of both the clinical and physical-technical image quality without adversely affecting contrast detail. MARs reconstruction in CT images of the oral cavity to reduce dental hardware metallic artifacts is not sufficient and may even adversely influence the image quality. (orig.)

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.)

SU-E-J-115: Correlation of Displacement Vector Fields Calculated by Deformable Image Registration Algorithms with Motion Parameters of CT Images with Well-Defined Targets and Controlled-Motion

Energy Technology Data Exchange (ETDEWEB)

Jaskowiak, J; Ahmad, S; Ali, I [University of Oklahoma Health Sciences Center, Oklahoma City, OK (United States); Alsbou, N [Ohio Northern University, Ada, OH (United States)

2015-06-15

Purpose: To investigate correlation of displacement vector fields (DVF) calculated by deformable image registration algorithms with motion parameters in helical axial and cone-beam CT images with motion artifacts. Methods: A mobile thorax phantom with well-known targets with different sizes that were made from water-equivalent material and inserted in foam to simulate lung lesions. The thorax phantom was imaged with helical, axial and cone-beam CT. The phantom was moved with a cyclic motion with different motion amplitudes and frequencies along the superior-inferior direction. Different deformable image registration algorithms including demons, fast demons, Horn-Shunck and iterative-optical-flow from the DIRART software were used to deform CT images for the phantom with different motion patterns. The CT images of the mobile phantom were deformed to CT images of the stationary phantom. Results: The values of displacement vectors calculated by deformable image registration algorithm correlated strongly with motion amplitude where large displacement vectors were calculated for CT images with large motion amplitudes. For example, the maximal displacement vectors were nearly equal to the motion amplitudes (5mm, 10mm or 20mm) at interfaces between the mobile targets lung tissue, while the minimal displacement vectors were nearly equal to negative the motion amplitudes. The maximal and minimal displacement vectors matched with edges of the blurred targets along the Z-axis (motion-direction), while DVF’s were small in the other directions. This indicates that the blurred edges by phantom motion were shifted largely to match with the actual target edge. These shifts were nearly equal to the motion amplitude. Conclusions: The DVF from deformable-image registration algorithms correlated well with motion amplitude of well-defined mobile targets. This can be used to extract motion parameters such as amplitude. However, as motion amplitudes increased, image artifacts increased

Metallic artifact mitigation and organ-constrained tissue assignment for Monte Carlo calculations of permanent implant lung brachytherapy

Energy Technology Data Exchange (ETDEWEB)

Sutherland, J. G. H.; Miksys, N.; Thomson, R. M., E-mail: rthomson@physics.carleton.ca [Carleton Laboratory for Radiotherapy Physics, Department of Physics, Carleton University, Ottawa, Ontario K1S 5B6 (Canada); Furutani, K. M. [Department of Radiation Oncology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905 (United States)

2014-01-15

Purpose: To investigate methods of generating accurate patient-specific computational phantoms for the Monte Carlo calculation of lung brachytherapy patient dose distributions. Methods: Four metallic artifact mitigation methods are applied to six lung brachytherapy patient computed tomography (CT) images: simple threshold replacement (STR) identifies high CT values in the vicinity of the seeds and replaces them with estimated true values; fan beam virtual sinogram replaces artifact-affected values in a virtual sinogram and performs a filtered back-projection to generate a corrected image; 3D median filter replaces voxel values that differ from the median value in a region of interest surrounding the voxel and then applies a second filter to reduce noise; and a combination of fan beam virtual sinogram and STR. Computational phantoms are generated from artifact-corrected and uncorrected images using several tissue assignment schemes: both lung-contour constrained and unconstrained global schemes are considered. Voxel mass densities are assigned based on voxel CT number or using the nominal tissue mass densities. Dose distributions are calculated using the EGSnrc user-code BrachyDose for{sup 125}I, {sup 103}Pd, and {sup 131}Cs seeds and are compared directly as well as through dose volume histograms and dose metrics for target volumes surrounding surgical sutures. Results: Metallic artifact mitigation techniques vary in ability to reduce artifacts while preserving tissue detail. Notably, images corrected with the fan beam virtual sinogram have reduced artifacts but residual artifacts near sources remain requiring additional use of STR; the 3D median filter removes artifacts but simultaneously removes detail in lung and bone. Doses vary considerably between computational phantoms with the largest differences arising from artifact-affected voxels assigned to bone in the vicinity of the seeds. Consequently, when metallic artifact reduction and constrained tissue

Audiovisual biofeedback improves image quality and reduces scan time for respiratory-gated 3D MRI

Science.gov (United States)

Lee, D.; Greer, P. B.; Arm, J.; Keall, P.; Kim, T.

2014-03-01

The purpose of this study was to test the hypothesis that audiovisual (AV) biofeedback can improve image quality and reduce scan time for respiratory-gated 3D thoracic MRI. For five healthy human subjects respiratory motion guidance in MR scans was provided using an AV biofeedback system, utilizing real-time respiratory motion signals. To investigate the improvement of respiratory-gated 3D MR images between free breathing (FB) and AV biofeedback (AV), each subject underwent two imaging sessions. Respiratory-related motion artifacts and imaging time were qualitatively evaluated in addition to the reproducibility of external (abdominal) motion. In the results, 3D MR images in AV biofeedback showed more anatomic information such as a clear distinction of diaphragm, lung lobes and sharper organ boundaries. The scan time was reduced from 401±215 s in FB to 334±94 s in AV (p-value 0.36). The root mean square variation of the displacement and period of the abdominal motion was reduced from 0.4±0.22 cm and 2.8±2.5 s in FB to 0.1±0.15 cm and 0.9±1.3 s in AV (p-value of displacement audiovisual biofeedback improves image quality and reduces scan time for respiratory-gated 3D MRI. These results suggest that AV biofeedback has the potential to be a useful motion management tool in medical imaging and radiation therapy procedures.

Clinical evaluation of TOF versus non-TOF on PET artifacts in simultaneous PET/MR: a dual centre experience

Energy Technology Data Exchange (ETDEWEB)

Voert, Edwin E.G.W. ter [University Hospital Zurich, Department of Nuclear Medicine, Zurich (Switzerland); University of Zurich, Zurich (Switzerland); Veit-Haibach, Patrick [University Hospital Zurich, Department of Nuclear Medicine, Zurich (Switzerland); University of Zurich, Zurich (Switzerland); University Hospital Zurich, Department of Diagnostic and Interventional Radiology, Zurich (Switzerland); Ahn, Sangtae [GE Global Research, Niskayuna, NY (United States); Wiesinger, Florian [GE Global Research, Muenchen (Germany); Khalighi, M.M.; Delso, Gaspar [GE Healthcare, Waukesha, WI (United States); Levin, Craig S. [Stanford University, Department of Radiology, Molecular Imaging Program at Stanford, Stanford, CA (United States); Iagaru, Andrei H. [Stanford University, Department of Radiology, Division of Nuclear Medicine and Molecular Imaging, Stanford, CA (United States); Zaharchuk, Greg [Stanford University, Department of Radiology, Neuroradiology, Stanford, CA (United States); Huellner, Martin [University Hospital Zurich, Department of Nuclear Medicine, Zurich (Switzerland); University of Zurich, Zurich (Switzerland); University Hospital Zurich, Department of Neuroradiology, Zurich (Switzerland)

2017-07-15

Our objective was to determine clinically the value of time-of-flight (TOF) information in reducing PET artifacts and improving PET image quality and accuracy in simultaneous TOF PET/MR scanning. A total 65 patients who underwent a comparative scan in a simultaneous TOF PET/MR scanner were included. TOF and non-TOF PET images were reconstructed, clinically examined, compared and scored. PET imaging artifacts were categorized as large or small implant-related artifacts, as dental implant-related artifacts, and as implant-unrelated artifacts. Differences in image quality, especially those related to (implant) artifacts, were assessed using a scale ranging from 0 (no artifact) to 4 (severe artifact). A total of 87 image artifacts were found and evaluated. Four patients had large and eight patients small implant-related artifacts, 27 patients had dental implants/fillings, and 48 patients had implant-unrelated artifacts. The average score was 1.14 ± 0.82 for non-TOF PET images and 0.53 ± 0.66 for TOF images (p < 0.01) indicating that artifacts were less noticeable when TOF information was included. Our study indicates that PET image artifacts are significantly mitigated with integration of TOF information in simultaneous PET/MR. The impact is predominantly seen in patients with significant artifacts due to metal implants. (orig.)

Combining monoenergetic extrapolations from dual-energy CT with iterative reconstructions. Reduction of coil and clip artifacts from intracranial aneurysm therapy

Energy Technology Data Exchange (ETDEWEB)

Winklhofer, Sebastian; Baltsavias, Gerasimos; Michels, Lars; Valavanis, Antonios [University of Zurich, Department of Neuroradiology, University Hospital Zurich, Zurich (Switzerland); Hinzpeter, Ricarda; Stocker, Daniel; Alkadhi, Hatem [University of Zurich, Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich (Switzerland); Burkhardt, Jan-Karl; Regli, Luca [University of Zurich, Department of Neurosurgery, University Hospital Zurich, Zurich (Switzerland)

2018-03-15

To compare and to combine iterative metal artifact reduction (MAR) and virtual monoenergetic extrapolations (VMEs) from dual-energy computed tomography (DECT) for reducing metal artifacts from intracranial clips and coils. Fourteen clips and six coils were scanned in a phantom model with DECT at 100 and 150SnkVp. Four datasets were reconstructed: non-corrected images (filtered-back projection), iterative MAR, VME from DECT at 120 keV, and combined iterative MAR + VME images. Artifact severity scores and visibility of simulated, contrast-filled, adjacent vessels were assessed qualitatively and quantitatively by two independent, blinded readers. Iterative MAR, VME, and combined iterative MAR + VME resulted in a significant reduction of qualitative (p < 0.001) and quantitative clip artifacts (p < 0.005) and improved the visibility of adjacent vessels (p < 0.05) compared to non-corrected images, with lowest artifact scores found in combined iterative MAR + VME images. Titanium clips demonstrated less artifacts than Phynox clips (p < 0.05), and artifact scores increased with clip size. Coil artifacts increased with coil size but were reducible when applying iterative MAR + VME compared to non-corrected images. However, no technique improved the severe artifacts from large, densely packed coils. Combining iterative MAR with VME allows for an improved metal artifact reduction from clips and smaller, loosely packed coils. Limited value was found for large and densely packed coils. (orig.)

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.

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....

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.

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.

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.

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.

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.

Improving best-phase image quality in cardiac CT by motion correction with MAM optimization

Energy Technology Data Exchange (ETDEWEB)

Rohkohl, Christopher; Bruder, Herbert; Stierstorfer, Karl [Siemens AG, Healthcare Sector, Siemensstrasse 1, 91301 Forchheim (Germany); Flohr, Thomas [Siemens AG, Healthcare Sector, Siemensstrasse 1, 91301 Forchheim (Germany); Institute of Diagnostic Radiology, Eberhard Karls University, Hoppe-Seyler-Str. 3, 72076 Tuebingen (Germany)

2013-03-15

Purpose: Research in image reconstruction for cardiac CT aims at using motion correction algorithms to improve the image quality of the coronary arteries. The key to those algorithms is motion estimation, which is currently based on 3-D/3-D registration to align the structures of interest in images acquired in multiple heart phases. The need for an extended scan data range covering several heart phases is critical in terms of radiation dose to the patient and limits the clinical potential of the method. Furthermore, literature reports only slight quality improvements of the motion corrected images when compared to the most quiet phase (best-phase) that was actually used for motion estimation. In this paper a motion estimation algorithm is proposed which does not require an extended scan range but works with a short scan data interval, and which markedly improves the best-phase image quality. Methods: Motion estimation is based on the definition of motion artifact metrics (MAM) to quantify motion artifacts in a 3-D reconstructed image volume. The authors use two different MAMs, entropy, and positivity. By adjusting the motion field parameters, the MAM of the resulting motion-compensated reconstruction is optimized using a gradient descent procedure. In this way motion artifacts are minimized. For a fast and practical implementation, only analytical methods are used for motion estimation and compensation. Both the MAM-optimization and a 3-D/3-D registration-based motion estimation algorithm were investigated by means of a computer-simulated vessel with a cardiac motion profile. Image quality was evaluated using normalized cross-correlation (NCC) with the ground truth template and root-mean-square deviation (RMSD). Four coronary CT angiography patient cases were reconstructed to evaluate the clinical performance of the proposed method. Results: For the MAM-approach, the best-phase image quality could be improved for all investigated heart phases, with a maximum

Improving best-phase image quality in cardiac CT by motion correction with MAM optimization

International Nuclear Information System (INIS)

Rohkohl, Christopher; Bruder, Herbert; Stierstorfer, Karl; Flohr, Thomas

2013-01-01

Purpose: Research in image reconstruction for cardiac CT aims at using motion correction algorithms to improve the image quality of the coronary arteries. The key to those algorithms is motion estimation, which is currently based on 3-D/3-D registration to align the structures of interest in images acquired in multiple heart phases. The need for an extended scan data range covering several heart phases is critical in terms of radiation dose to the patient and limits the clinical potential of the method. Furthermore, literature reports only slight quality improvements of the motion corrected images when compared to the most quiet phase (best-phase) that was actually used for motion estimation. In this paper a motion estimation algorithm is proposed which does not require an extended scan range but works with a short scan data interval, and which markedly improves the best-phase image quality. Methods: Motion estimation is based on the definition of motion artifact metrics (MAM) to quantify motion artifacts in a 3-D reconstructed image volume. The authors use two different MAMs, entropy, and positivity. By adjusting the motion field parameters, the MAM of the resulting motion-compensated reconstruction is optimized using a gradient descent procedure. In this way motion artifacts are minimized. For a fast and practical implementation, only analytical methods are used for motion estimation and compensation. Both the MAM-optimization and a 3-D/3-D registration-based motion estimation algorithm were investigated by means of a computer-simulated vessel with a cardiac motion profile. Image quality was evaluated using normalized cross-correlation (NCC) with the ground truth template and root-mean-square deviation (RMSD). Four coronary CT angiography patient cases were reconstructed to evaluate the clinical performance of the proposed method. Results: For the MAM-approach, the best-phase image quality could be improved for all investigated heart phases, with a maximum

Audiovisual biofeedback improves diaphragm motion reproducibility in MRI

Science.gov (United States)

Kim, Taeho; Pollock, Sean; Lee, Danny; O’Brien, Ricky; Keall, Paul

2012-01-01

Purpose: In lung radiotherapy, variations in cycle-to-cycle breathing results in four-dimensional computed tomography imaging artifacts, leading to inaccurate beam coverage and tumor targeting. In previous studies, the effect of audiovisual (AV) biofeedback on the external respiratory signal reproducibility has been investigated but the internal anatomy motion has not been fully studied. The aim of this study is to test the hypothesis that AV biofeedback improves diaphragm motion reproducibility of internal anatomy using magnetic resonance imaging (MRI). Methods: To test the hypothesis 15 healthy human subjects were enrolled in an ethics-approved AV biofeedback study consisting of two imaging sessions spaced ∼1 week apart. Within each session MR images were acquired under free breathing and AV biofeedback conditions. The respiratory signal to the AV biofeedback system utilized optical monitoring of an external marker placed on the abdomen. Synchronously, serial thoracic 2D MR images were obtained to measure the diaphragm motion using a fast gradient-recalled-echo MR pulse sequence in both coronal and sagittal planes. The improvement in the diaphragm motion reproducibility using the AV biofeedback system was quantified by comparing cycle-to-cycle variability in displacement, respiratory period, and baseline drift. Additionally, the variation in improvement between the two sessions was also quantified. Results: The average root mean square error (RMSE) of diaphragm cycle-to-cycle displacement was reduced from 2.6 mm with free breathing to 1.6 mm (38% reduction) with the implementation of AV biofeedback (p-value biofeedback (p-value biofeedback (p-value = 0.012). The diaphragm motion reproducibility improvements with AV biofeedback were consistent with the abdominal motion reproducibility that was observed from the external marker motion variation. Conclusions: This study was the first to investigate the potential of AV biofeedback to improve the motion

Iterative Metallic Artifact Reduction for In-Plane Gonadal Shielding During Computed Tomographic Venography of Young Males.

Science.gov (United States)

Choi, Jin Woo; Lee, Sang Yub; Kim, Jong Hyo; Jin, Hyeongmin; Lee, Jaewon; Choi, Young Hun; Lee, Hyeon-Kyeong; Park, Jae Hyung

The purpose of this study was to evaluate a gonadal shield (GS) and iterative metallic artifact reduction (IMAR) during computed tomography scans, regarding the image quality and radiation dose. A phantom was imaged with and without a GS. Prospectively enrolled, young male patients underwent lower extremity computed tomography venography (precontrast imaging without the GS and postcontrast imaging with the GS). Radiation dose was measured each time, and the GS-applied images were reconstructed by weighted filtered back projection and IMAR. In the phantom study, image artifacts were significantly reduced by using IMAR (P = 0.031), whereas the GS reduced the radiation dose by 61.3%. In the clinical study (n = 29), IMAR mitigated artifacts from the GS, thus 96.6% of the IMAR image sets were clinically usable. Gonadal shielding reduced the radiation dose to the testes by 69.0%. The GS in conjunction with IMAR significantly reduced the radiation dose to the testes while maintaining the image quality.

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

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.

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.

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.)

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…

SU-F-I-08: CT Image Ring Artifact Reduction Based On Prior Image

Energy Technology Data Exchange (ETDEWEB)

Yuan, C; Qi, H; Chen, Z; Wu, S; Xu, Y; Zhou, L [Southern Medical University, Guangzhou, Guangdong (China)

2016-06-15

Purpose: In computed tomography (CT) system, CT images with ring artifacts will be reconstructed when some adjacent bins of detector don’t work. The ring artifacts severely degrade CT image quality. We present a useful CT ring artifacts reduction based on projection data correction, aiming at estimating the missing data of projection data accurately, thus removing the ring artifacts of CT images. Methods: The method consists of ten steps: 1) Identification of abnormal pixel line in projection sinogram; 2) Linear interpolation within the pixel line of projection sinogram; 3) FBP reconstruction using interpolated projection data; 4) Filtering FBP image using mean filter; 5) Forwarding projection of filtered FBP image; 6) Subtraction forwarded projection from original projection; 7) Linear interpolation of abnormal pixel line area in the subtraction projection; 8) Adding the interpolated subtraction projection on the forwarded projection; 9) FBP reconstruction using corrected projection data; 10) Return to step 4 until the pre-set iteration number is reached. The method is validated on simulated and real data to restore missing projection data and reconstruct ring artifact-free CT images. Results: We have studied impact of amount of dead bins of CT detector on the accuracy of missing data estimation in projection sinogram. For the simulated case with a resolution of 256 by 256 Shepp-Logan phantom, three iterations are sufficient to restore projection data and reconstruct ring artifact-free images when the dead bins rating is under 30%. The dead-bin-induced artifacts are substantially reduced. More iteration number is needed to reconstruct satisfactory images while the rating of dead bins increases. Similar results were found for a real head phantom case. Conclusion: A practical CT image ring artifact correction scheme based on projection data is developed. This method can produce ring artifact-free CT images feasibly and effectively.

SU-F-I-08: CT Image Ring Artifact Reduction Based On Prior Image

International Nuclear Information System (INIS)

Yuan, C; Qi, H; Chen, Z; Wu, S; Xu, Y; Zhou, L

2016-01-01

Purpose: In computed tomography (CT) system, CT images with ring artifacts will be reconstructed when some adjacent bins of detector don’t work. The ring artifacts severely degrade CT image quality. We present a useful CT ring artifacts reduction based on projection data correction, aiming at estimating the missing data of projection data accurately, thus removing the ring artifacts of CT images. Methods: The method consists of ten steps: 1) Identification of abnormal pixel line in projection sinogram; 2) Linear interpolation within the pixel line of projection sinogram; 3) FBP reconstruction using interpolated projection data; 4) Filtering FBP image using mean filter; 5) Forwarding projection of filtered FBP image; 6) Subtraction forwarded projection from original projection; 7) Linear interpolation of abnormal pixel line area in the subtraction projection; 8) Adding the interpolated subtraction projection on the forwarded projection; 9) FBP reconstruction using corrected projection data; 10) Return to step 4 until the pre-set iteration number is reached. The method is validated on simulated and real data to restore missing projection data and reconstruct ring artifact-free CT images. Results: We have studied impact of amount of dead bins of CT detector on the accuracy of missing data estimation in projection sinogram. For the simulated case with a resolution of 256 by 256 Shepp-Logan phantom, three iterations are sufficient to restore projection data and reconstruct ring artifact-free images when the dead bins rating is under 30%. The dead-bin-induced artifacts are substantially reduced. More iteration number is needed to reconstruct satisfactory images while the rating of dead bins increases. Similar results were found for a real head phantom case. Conclusion: A practical CT image ring artifact correction scheme based on projection data is developed. This method can produce ring artifact-free CT images feasibly and effectively.

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.

Audiovisual biofeedback improves image quality and reduces scan time for respiratory-gated 3D MRI

International Nuclear Information System (INIS)

Lee, D; Keall, P; Kim, T; Greer, P B; Arm, J

2014-01-01

The purpose of this study was to test the hypothesis that audiovisual (AV) biofeedback can improve image quality and reduce scan time for respiratory-gated 3D thoracic MRI. For five healthy human subjects respiratory motion guidance in MR scans was provided using an AV biofeedback system, utilizing real-time respiratory motion signals. To investigate the improvement of respiratory-gated 3D MR images between free breathing (FB) and AV biofeedback (AV), each subject underwent two imaging sessions. Respiratory-related motion artifacts and imaging time were qualitatively evaluated in addition to the reproducibility of external (abdominal) motion. In the results, 3D MR images in AV biofeedback showed more anatomic information such as a clear distinction of diaphragm, lung lobes and sharper organ boundaries. The scan time was reduced from 401±215 s in FB to 334±94 s in AV (p-value 0.36). The root mean square variation of the displacement and period of the abdominal motion was reduced from 0.4±0.22 cm and 2.8±2.5 s in FB to 0.1±0.15 cm and 0.9±1.3 s in AV (p-value of displacement <0.01 and p-value of period 0.12). This study demonstrated that audiovisual biofeedback improves image quality and reduces scan time for respiratory-gated 3D MRI. These results suggest that AV biofeedback has the potential to be a useful motion management tool in medical imaging and radiation therapy procedures.

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.

Refinement of motion correction strategies for lower-cost CT for under-resourced regions of the world

Science.gov (United States)

Wells, Jered R.; Segars, W. Paul; Kigongo, Christopher J. N.; Dobbins, James T., III

2011-03-01

This paper describes a recently developed post-acquisition motion correction strategy for application to lower-cost computed tomography (LCCT) for under-resourced regions of the world. Increased awareness regarding global health and its challenges has encouraged the development of more affordable healthcare options for underserved people worldwide. In regions such as sub-Saharan Africa, intermediate level medical facilities may serve millions with inadequate or antiquated equipment due to financial limitations. In response, the authors have proposed a LCCT design which utilizes a standard chest x-ray examination room with a digital flat panel detector (FPD). The patient rotates on a motorized stage between the fixed cone-beam source and FPD, and images are reconstructed using a Feldkamp algorithm for cone-beam scanning. One of the most important proofs-of-concept in determining the feasibility of this system is the successful correction of undesirable motion. A 3D motion correction algorithm was developed in order to correct for potential patient motion, stage instabilities and detector misalignments which can all lead to motion artifacts in reconstructed images. Motion will be monitored by the radiographic position of fiducial markers to correct for rigid body motion in three dimensions. Based on simulation studies, projection images corrupted by motion were re-registered with average errors of 0.080 mm, 0.32 mm and 0.050 mm in the horizontal, vertical and depth dimensions, respectively. The overall absence of motion artifacts in motion-corrected reconstructions indicates that reasonable amounts of motion may be corrected using this novel technique without significant loss of image quality.

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

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)

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

Comparing the Performance of Popular MEG/EEG Artifact Correction Methods in an Evoked-Response Study

DEFF Research Database (Denmark)

Haumann, Niels Trusbak; Parkkonen, Lauri; Kliuchko, Marina

2016-01-01

We here compared results achieved by applying popular methods for reducing artifacts in magnetoencephalography (MEG) and electroencephalography (EEG) recordings of the auditory evoked Mismatch Negativity (MMN) responses in healthy adult subjects. We compared the Signal Space Separation (SSS......) and temporal SSS (tSSS) methods for reducing noise from external and nearby sources. Our results showed that tSSS reduces the interference level more reliably than plain SSS, particularly for MEG gradiometers, also for healthy subjects not wearing strongly interfering magnetic material. Therefore, tSSS...... is recommended over SSS. Furthermore, we found that better artifact correction is achieved by applying Independent Component Analysis (ICA) in comparison to Signal Space Projection (SSP). Although SSP reduces the baseline noise level more than ICA, SSP also significantly reduces the signal—slightly more than...

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.)

Comparison of the shock artifacts induced by tripolar and bipolar electrical stimulation techniques.

Science.gov (United States)

Wee, A S; Jiles, K; Brennan, R

2001-01-01

Tripolar and bipolar electrical stimulation procedures were performed on the upper limbs of eight subjects. The mid-forearm was stimulated electrically (tripolar or bipolar) by surface electrodes, and the induced stimulus shock artifacts were recorded simultaneously from the wrist and elbow. During tripolar stimulation, two types of stimulating configurations were utilized: with the center electrode designated as the cathode and the two outermost electrodes connected to a common anode, and vice versa. During bipolar stimulation, the center electrode served as one pole of the stimulator, and one of the two outermost electrodes of the tripolar stimulator was disconnected. The stimulus intensity was kept constant in all stimulating procedures. Artifacts were reduced significantly during tripolar compared to bipolar stimulation, if the outermost electrodes of the tripolar stimulator (which were facing the recording electrodes) were also oriented toward the recording sites during bipolar stimulation and had the same stimulus polarity. Artifacts were slightly reduced in amplitude from tripolar stimulation, if the center electrode were oriented toward the recording sites during bipolar stimulation and had the same stimulus polarity as previously used during tripolar stimulation.

Respiratory gated lung CT using 320-row area detector CT

International Nuclear Information System (INIS)

Sakamoto, Ryo; Noma, Satoshi; Higashino, Takanori

2010-01-01

Three hundred and twenty-row Area Detector CT (ADCT) has made it possible to scan whole lung field with prospective respiratory gated wide volume scan. We evaluated whether the respiratory gated wide volume scan enables to reduce motion induced artifacts in the lung area. Helical scan and respiratory gated wide volume scan were performed in 5 patients and 10 healthy volunteers under spontaneous breathing. Significant reduction of motion artifact and superior image quality were obtained in respiratory gated scan in comparison with helical scan. Respiratory gated wide volume scan is an unique method using ADCT, and is able to reduce motion artifacts in lung CT scans of patients unable to suspend respiration in clinical scenes. (author)

A biomechanical modeling-guided simultaneous motion estimation and image reconstruction technique (SMEIR-Bio) for 4D-CBCT reconstruction

Science.gov (United States)

Huang, Xiaokun; Zhang, You; Wang, Jing

2018-02-01

Reconstructing four-dimensional cone-beam computed tomography (4D-CBCT) images directly from respiratory phase-sorted traditional 3D-CBCT projections can capture target motion trajectory, reduce motion artifacts, and reduce imaging dose and time. However, the limited numbers of projections in each phase after phase-sorting decreases CBCT image quality under traditional reconstruction techniques. To address this problem, we developed a simultaneous motion estimation and image reconstruction (SMEIR) algorithm, an iterative method that can reconstruct higher quality 4D-CBCT images from limited projections using an inter-phase intensity-driven motion model. However, the accuracy of the intensity-driven motion model is limited in regions with fine details whose quality is degraded due to insufficient projection number, which consequently degrades the reconstructed image quality in corresponding regions. In this study, we developed a new 4D-CBCT reconstruction algorithm by introducing biomechanical modeling into SMEIR (SMEIR-Bio) to boost the accuracy of the motion model in regions with small fine structures. The biomechanical modeling uses tetrahedral meshes to model organs of interest and solves internal organ motion using tissue elasticity parameters and mesh boundary conditions. This physics-driven approach enhances the accuracy of solved motion in the organ’s fine structures regions. This study used 11 lung patient cases to evaluate the performance of SMEIR-Bio, making both qualitative and quantitative comparisons between SMEIR-Bio, SMEIR, and the algebraic reconstruction technique with total variation regularization (ART-TV). The reconstruction results suggest that SMEIR-Bio improves the motion model’s accuracy in regions containing small fine details, which consequently enhances the accuracy and quality of the reconstructed 4D-CBCT images.

Evaluation and reduction of magnetic resonance imaging artifacts induced by distinct plates for osseous fixation: an in vitro study @ 3T.

Science.gov (United States)

Rendenbach, Carsten; Schoellchen, Maximilian; Bueschel, Julie; Gauer, Tobias; Sedlacik, Jan; Kutzner, Daniel; Vallittu, Pekka K; Heiland, Max; Smeets, Ralf; Fiehler, Jens; Siemonsen, Susanne

2018-05-02

To analyze Magnetic Resonance Imaging (MRI) artifact induced at 3 Tesla by bioresorbable, titanium and glass fiber reinforced composite (GFRC) plates for osseous reconstruction. Fixation plates including bioresorbable polymers (Inion CPS, Inion Oy, Tampere, Finland; Rapidsorb, DePuy Synthes, Umkirch, Germany; Resorb X, Gebrueder KLS Martin GmbH, Tuttlingen, Germany), Glass fiber reinforced composite (Skulle Implants Oy, Turku, Finland) and titanium plates of varying thickness and design (DePuy Synthes, Umkirch, Germany) were embedded in agarose gel and a 3T MRI was performed using a standard protocol for head and neck imaging including T1w and T2w sequences. Additionally, different artifact reducing sequence techniques (slice encoding for metal artifact reduction (SEMAC) & ultrashort echotime (UTE)) were used and their impact on the extent of artifacts evaluated for each material. All titanium plates induced significantly more artefacts than resorbable plates in T1w and T2w sequences. Glass fiber-reinforced composites induced the least artefacts in both sequences. The total extent of artefacts increased with plate thickness and height. Plate thickness had no influence on the percentage of overestimation in all three dimensions. Titanium induced artefacts were significantly reduced by both artifact reducing sequence techniques. Polylactide, glass fiber-reinforced composite and magnesium plates produce less susceptibility artefacts in MRI compared to titanium, while the dimensions of titanium plates directly influence artifact extension. SEMAC and UTE significantly reduce metal artefacts at the expense of image resolution.

Synchronized multiartifact reduction with tomographic reconstruction (SMART-RECON): A statistical model based iterative image reconstruction method to eliminate limited-view artifacts and to mitigate the temporal-average artifacts in time-resolved CT.

Science.gov (United States)

Chen, Guang-Hong; Li, Yinsheng

2015-08-01

In x-ray computed tomography (CT), a violation of the Tuy data sufficiency condition leads to limited-view artifacts. In some applications, it is desirable to use data corresponding to a narrow temporal window to reconstruct images with reduced temporal-average artifacts. However, the need to reduce temporal-average artifacts in practice may result in a violation of the Tuy condition and thus undesirable limited-view artifacts. In this paper, the authors present a new iterative reconstruction method, synchronized multiartifact reduction with tomographic reconstruction (SMART-RECON), to eliminate limited-view artifacts using data acquired within an ultranarrow temporal window that severely violates the Tuy condition. In time-resolved contrast enhanced CT acquisitions, image contrast dynamically changes during data acquisition. Each image reconstructed from data acquired in a given temporal window represents one time frame and can be denoted as an image vector. Conventionally, each individual time frame is reconstructed independently. In this paper, all image frames are grouped into a spatial-temporal image matrix and are reconstructed together. Rather than the spatial and/or temporal smoothing regularizers commonly used in iterative image reconstruction, the nuclear norm of the spatial-temporal image matrix is used in SMART-RECON to regularize the reconstruction of all image time frames. This regularizer exploits the low-dimensional structure of the spatial-temporal image matrix to mitigate limited-view artifacts when an ultranarrow temporal window is desired in some applications to reduce temporal-average artifacts. Both numerical simulations in two dimensional image slices with known ground truth and in vivo human subject data acquired in a contrast enhanced cone beam CT exam have been used to validate the proposed SMART-RECON algorithm and to demonstrate the initial performance of the algorithm. Reconstruction errors and temporal fidelity of the reconstructed

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

Motion-insensitive carotid intraplaque hemorrhage imaging using 3D inversion recovery preparation stack of stars (IR-prep SOS) technique.

Science.gov (United States)

Kim, Seong-Eun; Roberts, John A; Eisenmenger, Laura B; Aldred, Booth W; Jamil, Osama; Bolster, Bradley D; Bi, Xiaoming; Parker, Dennis L; Treiman, Gerald S; McNally, J Scott

2017-02-01

Carotid artery imaging is important in the clinical management of patients at risk for stroke. Carotid intraplaque hemorrhage (IPH) presents an important diagnostic challenge. 3D magnetization prepared rapid acquisition gradient echo (MPRAGE) has been shown to accurately image carotid IPH; however, this sequence can be limited due to motion- and flow-related artifact. The purpose of this work was to develop and evaluate an improved 3D carotid MPRAGE sequence for IPH detection. We hypothesized that a radial-based k-space trajectory sequence such as "Stack of Stars" (SOS) incorporated with inversion recovery preparation would offer reduced motion sensitivity and more robust flow suppression by oversampling of central k-space. A total of 31 patients with carotid disease (62 carotid arteries) were imaged at 3T magnetic resonance imaging (MRI) with 3D IR-prep Cartesian and SOS sequences. Image quality was determined between SOS and Cartesian MPRAGE in 62 carotid arteries using t-tests and multivariable linear regression. Kappa analysis was used to determine interrater reliability. In all, 25 among 62 carotid plaques had carotid IPH by consensus from the reviewers on SOS compared to 24 on Cartesian sequence. Image quality was significantly higher with SOS compared to Cartesian (mean 3.74 vs. 3.11, P SOS acquisition yielded sharper image features with less motion (19.4% vs. 45.2%, P SOS (kappa = 0.89), higher than that of Cartesian (kappa = 0.84). By minimizing flow and motion artifacts and retaining high interrater reliability, the SOS MPRAGE has important advantages over Cartesian MPRAGE in carotid IPH detection. 1 J. Magn. Reson. Imaging 2017;45:410-417. © 2016 International Society for Magnetic Resonance in Medicine.

Metal-induced streak artifact reduction using iterative reconstruction algorithms in x-ray computed tomography image of the dentoalveolar region.

Science.gov (United States)

Dong, Jian; Hayakawa, Yoshihiko; Kannenberg, Sven; Kober, Cornelia

2013-02-01

The objective of this study was to reduce metal-induced streak artifact on oral and maxillofacial x-ray computed tomography (CT) images by developing the fast statistical image reconstruction system using iterative reconstruction algorithms. Adjacent CT images often depict similar anatomical structures in thin slices. So, first, images were reconstructed using the same projection data of an artifact-free image. Second, images were processed by the successive iterative restoration method where projection data were generated from reconstructed image in sequence. Besides the maximum likelihood-expectation maximization algorithm, the ordered subset-expectation maximization algorithm (OS-EM) was examined. Also, small region of interest (ROI) setting and reverse processing were applied for improving performance. Both algorithms reduced artifacts instead of slightly decreasing gray levels. The OS-EM and small ROI reduced the processing duration without apparent detriments. Sequential and reverse processing did not show apparent effects. Two alternatives in iterative reconstruction methods were effective for artifact reduction. The OS-EM algorithm and small ROI setting improved the performance. Copyright © 2012 Elsevier Inc. All rights reserved.

WE-AB-BRA-08: Correction of Patient Motion in C-Arm Cone-Beam CT Using 3D-2D Registration

International Nuclear Information System (INIS)

Ouadah, S; Jacobson, M; Stayman, JW; Siewerdsen, JH; Ehtiati, T

2016-01-01

Purpose: Intraoperative C-arm cone-beam CT (CBCT) is subject to artifacts arising from patient motion during the fairly long (∼5–20 s) scan times. We present a fiducial free method to mitigate motion artifacts using 3D-2D image registration that simultaneously corrects residual errors in geometric calibration. Methods: A 3D-2D registration process was used to register each projection to DRRs computed from the 3D image by maximizing gradient orientation (GO) using the CMA-ES optimizer. The resulting rigid 6 DOF transforms were applied to the system projection matrices, and a 3D image was reconstructed via model-based image reconstruction (MBIR, which accommodates the resulting noncircular orbit). Experiments were conducted using a Zeego robotic C-arm (20 s, 200°, 496 projections) to image a head phantom undergoing various types of motion: 1) 5° lateral motion; 2) 15° lateral motion; and 3) 5° lateral motion with 10 mm periodic inferior-superior motion. Images were reconstructed using a penalized likelihood (PL) objective function, and structural similarity (SSIM) was measured for axial slices of the reconstructed images. A motion-free image was acquired using the same protocol for comparison. Results: There was significant improvement (p 0.99, indicating near identity to the motion-free reference. The point spread function (PSF) measured from a wire in the phantom was restored to that of the reference in each case. Conclusion: The 3D-2D registration method provides a robust framework for mitigation of motion artifacts and is expected to hold for applications in the head, pelvis, and extremities with reasonably constrained operative setup. Further improvement can be achieved by incorporating multiple rigid components and non-rigid deformation within the framework. The method is highly parallelizable and could in principle be run with every acquisition. Research supported by National Institutes of Health Grant No. R01-EB-017226 and academic

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.

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...

Investigation of the density wave oscillation in ocean motions with reduced order models

International Nuclear Information System (INIS)

Yan, B.H.; Li, R.

2018-01-01

Highlights: •The parameter about the degree of instability is defined. •The results are in satisfactory agreement with experimental results. •The effect of ocean motions on DWO is analyzed quantitatively. •The results are of good universality and generality. -- Abstract: The two phase flow instability is an important phenomenon in nuclear power and thermal systems. In the research and design of small modular reactor, the effect of ocean motions on the two phase flow instability should be evaluated. In this work, the density wave oscillation in a uniformly heated channel in ocean motions is investigated with reduced order model by transforming the partial differential equations to ordinary differential equations. This kind of frequency domain method is complementary to the time domain analysis with system codes, not as alternatives. The parameter about the degree of instability is defined for the quantitative analysis of two phase flow instability. The results are in satisfactory agreement with experimental results. The effect of ocean motions on density wave oscillation in a uniformly heated channel is analyzed quantitatively. The parametric study is also carried out.

Demand artifact: objectively detecting biased participants in advertising research.

Science.gov (United States)

Miller, Felicia; Schertzer, Susan

2014-12-01

Detecting and reducing the effect of biased participants continues to be an important task for researchers. However, the lack of objective measures to assess demand artifact has made it difficult to effectively address this issue. This paper reports two experiments that apply a theory-based post-experimental inquiry that can systematically identify biased participants in consumer research. The results demonstrate how easily and effectively researchers can incorporate this tool into experimental studies of all types and reduce the likelihood of systematic error.

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.

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.

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

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.

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...

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.

The efficacy of airflow and seat vibration on reducing visually induced motion sickness

NARCIS (Netherlands)

D’Amour, Sarah; Bos, Jelte E.; Keshavarz, Behrang

2017-01-01

Visually induced motion sickness (VIMS) is a well-known sensation in virtual environments and simulators, typically characterized by a variety of symptoms such as pallor, sweating, dizziness, fatigue, and/or nausea. Numerous methods to reduce VIMS have been previously introduced; however, a reliable

Independent component analysis for cochlear implant artifacts attenuation from electrically evoked auditory steady-state response measurements

Science.gov (United States)

Deprez, Hanne; Gransier, Robin; Hofmann, Michael; van Wieringen, Astrid; Wouters, Jan; Moonen, Marc

2018-02-01

Objective. Electrically evoked auditory steady-state responses (EASSRs) are potentially useful for objective cochlear implant (CI) fitting and follow-up of the auditory maturation in infants and children with a CI. EASSRs are recorded in the electro-encephalogram (EEG) in response to electrical stimulation with continuous pulse trains, and are distorted by significant CI artifacts related to this electrical stimulation. The aim of this study is to evaluate a CI artifacts attenuation method based on independent component analysis (ICA) for three EASSR datasets. Approach. ICA has often been used to remove CI artifacts from the EEG to record transient auditory responses, such as cortical evoked auditory potentials. Independent components (ICs) corresponding to CI artifacts are then often manually identified. In this study, an ICA based CI artifacts attenuation method was developed and evaluated for EASSR measurements with varying CI artifacts and EASSR characteristics. Artifactual ICs were automatically identified based on their spectrum. Main results. For 40 Hz amplitude modulation (AM) stimulation at comfort level, in high SNR recordings, ICA succeeded in removing CI artifacts from all recording channels, without distorting the EASSR. For lower SNR recordings, with 40 Hz AM stimulation at lower levels, or 90 Hz AM stimulation, ICA either distorted the EASSR or could not remove all CI artifacts in most subjects, except for two of the seven subjects tested with low level 40 Hz AM stimulation. Noise levels were reduced after ICA was applied, and up to 29 ICs were rejected, suggesting poor ICA separation quality. Significance. We hypothesize that ICA is capable of separating CI artifacts and EASSR in case the contralateral hemisphere is EASSR dominated. For small EASSRs or large CI artifact amplitudes, ICA separation quality is insufficient to ensure complete CI artifacts attenuation without EASSR distortion.

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.

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.

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.

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)

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 ...

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 ...

Incidental ferumoxytol artifacts in clinical brain MR imaging

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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.)

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.…

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.

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.

Comparison of visual biofeedback system with a guiding waveform and abdomen-chest motion self-control system for respiratory motion management

International Nuclear Information System (INIS)

Nakajima, Yujiro; Kadoya, Noriyuki; Kanai, Takayuki; Ito, Kengo; Sato, Kiyokazu; Dobashi, Suguru; Yamamoto, Takaya; Ishikawa, Yojiro; Matsushita, Haruo; Takeda, Ken; Jingu, Keiichi

2016-01-01

Irregular breathing can influence the outcome of 4D computed tomography imaging and cause artifacts. Visual biofeedback systems associated with a patient-specific guiding waveform are known to reduce respiratory irregularities. In Japan, abdomen and chest motion self-control devices (Abches) (representing simpler visual coaching techniques without a guiding waveform) are used instead; however, no studies have compared these two systems to date. Here, we evaluate the effectiveness of respiratory coaching in reducing respiratory irregularities by comparing two respiratory management systems. We collected data from 11 healthy volunteers. Bar and wave models were used as visual biofeedback systems. Abches consisted of a respiratory indicator indicating the end of each expiration and inspiration motion. Respiratory variations were quantified as root mean squared error (RMSE) of displacement and period of breathing cycles. All coaching techniques improved respiratory variation, compared with free-breathing. Displacement RMSEs were 1.43 ± 0.84, 1.22 ± 1.13, 1.21 ± 0.86 and 0.98 ± 0.47 mm for free-breathing, Abches, bar model and wave model, respectively. Period RMSEs were 0.48 ± 0.42, 0.33 ± 0.31, 0.23 ± 0.18 and 0.17 ± 0.05 s for free-breathing, Abches, bar model and wave model, respectively. The average reduction in displacement and period RMSE compared with the wave model were 27% and 47%, respectively. For variation in both displacement and period, wave model was superior to the other techniques. Our results showed that visual biofeedback combined with a wave model could potentially provide clinical benefits in respiratory management, although all techniques were able to reduce respiratory irregularities

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.

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

Contrast-enhanced Spectral Mammography: Modality-Specific Artifacts and Other Factors Which May Interfere with Image Quality.

Science.gov (United States)

Bhimani, Chandni; Li, Luna; Liao, Lydia; Roth, Robyn G; Tinney, Elizabeth; Germaine, Pauline

2017-01-01

Contrast-enhanced spectral mammography (CESM) uses full field digital mammography with the added benefit of intravenous contrast administration to significantly reduce false-positive and false-negative results and improve specificity while maintaining high sensitivity. For CESM to fulfill its purpose, one should be aware of possible artifacts and other factors which may interfere with image quality, and attention should be taken to minimize these factors. This pictorial demonstration will depict types of artifacts detected and other factors that interfere with image acquisition in our practice since CESM implementation. Many of the artifacts and other factors we have encountered while using CESM have simple solutions to resolve them. The illustrated artifacts and other factors interfering with image quality will serve as a useful reference to anyone using CESM. Copyright © 2017 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.

The efficacy of airflow and seat vibration on reducing visually induced motion sickness.

Science.gov (United States)

D'Amour, Sarah; Bos, Jelte E; Keshavarz, Behrang

2017-09-01

Visually induced motion sickness (VIMS) is a well-known sensation in virtual environments and simulators, typically characterized by a variety of symptoms such as pallor, sweating, dizziness, fatigue, and/or nausea. Numerous methods to reduce VIMS have been previously introduced; however, a reliable countermeasure is still missing. In the present study, the effect of airflow and seat vibration to alleviate VIMS was investigated. Eighty-two participants were randomly assigned to one of four groups (airflow, vibration, combined airflow and vibration, and control) and then exposed to a 15 min long video of a bicycle ride shot from first-person view. VIMS was measured using the Fast Motion Sickness Scale (FMS) and the Simulator Sickness Questionnaire (SSQ). Results showed that the exposure of airflow significantly reduced VIMS, whereas the presence of seat vibration, in contrast, did not have an impact on VIMS. Additionally, we found that females reported higher FMS scores than males, however, this sex difference was not found in the SSQ scores. Our findings demonstrate that airflow can be an effective and easy-to-apply technique to reduce VIMS in virtual environments and simulators, while vibration applied to the seat is not a successful method.

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

WE-AB-BRA-08: Correction of Patient Motion in C-Arm Cone-Beam CT Using 3D-2D Registration

Energy Technology Data Exchange (ETDEWEB)

Ouadah, S; Jacobson, M; Stayman, JW; Siewerdsen, JH [Johns Hopkins University, Baltimore, MD (United States); Ehtiati, T [Siemens Medical Solutions USA, Inc., Hoffman Estates, IL (United States)

2016-06-15

Purpose: Intraoperative C-arm cone-beam CT (CBCT) is subject to artifacts arising from patient motion during the fairly long (∼5–20 s) scan times. We present a fiducial free method to mitigate motion artifacts using 3D-2D image registration that simultaneously corrects residual errors in geometric calibration. Methods: A 3D-2D registration process was used to register each projection to DRRs computed from the 3D image by maximizing gradient orientation (GO) using the CMA-ES optimizer. The resulting rigid 6 DOF transforms were applied to the system projection matrices, and a 3D image was reconstructed via model-based image reconstruction (MBIR, which accommodates the resulting noncircular orbit). Experiments were conducted using a Zeego robotic C-arm (20 s, 200°, 496 projections) to image a head phantom undergoing various types of motion: 1) 5° lateral motion; 2) 15° lateral motion; and 3) 5° lateral motion with 10 mm periodic inferior-superior motion. Images were reconstructed using a penalized likelihood (PL) objective function, and structural similarity (SSIM) was measured for axial slices of the reconstructed images. A motion-free image was acquired using the same protocol for comparison. Results: There was significant improvement (p < 0.001) in the SSIM of the motion-corrected (MC) images compared to uncorrected images. The SSIM in MC-PL images was >0.99, indicating near identity to the motion-free reference. The point spread function (PSF) measured from a wire in the phantom was restored to that of the reference in each case. Conclusion: The 3D-2D registration method provides a robust framework for mitigation of motion artifacts and is expected to hold for applications in the head, pelvis, and extremities with reasonably constrained operative setup. Further improvement can be achieved by incorporating multiple rigid components and non-rigid deformation within the framework. The method is highly parallelizable and could in principle be run with every

A Randomized Controlled Trial of Lorazepam to Reduce Liver Motion in Patients Receiving Upper Abdominal Radiation Therapy

Energy Technology Data Exchange (ETDEWEB)

Tsang, Derek S.; Voncken, Francine E.M.; Tse, Regina V. [Princess Margaret Cancer Centre, University Health Network, Department of Radiation Oncology, University of Toronto, Toronto (Canada); Sykes, Jenna [Department of Biostatistics, Princess Margaret Cancer Centre, University Health Network, Toronto (Canada); Wong, Rebecca K.S.; Dinniwell, Rob E.; Kim, John; Ringash, Jolie; Brierley, James D.; Cummings, Bernard J.; Brade, Anthony [Princess Margaret Cancer Centre, University Health Network, Department of Radiation Oncology, University of Toronto, Toronto (Canada); Dawson, Laura A., E-mail: laura.dawson@rmp.uhn.on.ca [Princess Margaret Cancer Centre, University Health Network, Department of Radiation Oncology, University of Toronto, Toronto (Canada)

2013-12-01

Purpose: Reduction of respiratory motion is desirable to reduce the volume of normal tissues irradiated, to improve concordance of planned and delivered doses, and to improve image guided radiation therapy (IGRT). We hypothesized that pretreatment lorazepam would lead to a measurable reduction of liver motion. Methods and Materials: Thirty-three patients receiving upper abdominal IGRT were recruited to a double-blinded randomized controlled crossover trial. Patients were randomized to 1 of 2 study arms: arm 1 received lorazepam 2 mg by mouth on day 1, followed by placebo 4 to 8 days later; arm 2 received placebo on day 1, followed by lorazepam 4 to 8 days later. After tablet ingestion and daily radiation therapy, amplitude of liver motion was measured on both study days. The primary outcomes were reduction in craniocaudal (CC) liver motion using 4-dimensional kV cone beam computed tomography (CBCT) and the proportion of patients with liver motion ≤5 mm. Secondary endpoints included motion measured with cine magnetic resonance imaging and kV fluoroscopy. Results: Mean relative and absolute reduction in CC amplitude with lorazepam was 21% and 2.5 mm respectively (95% confidence interval [CI] 1.1-3.9, P=.001), as assessed with CBCT. Reduction in CC amplitude to ≤5 mm residual liver motion was seen in 13% (95% CI 1%-25%) of patients receiving lorazepam (vs 10% receiving placebo, P=NS); 65% (95% CI 48%-81%) had reduction in residual CC liver motion to ≤10 mm (vs 52% with placebo, P=NS). Patients with large respiratory movement and patients who took lorazepam ≥60 minutes before imaging had greater reductions in liver CC motion. Mean reductions in liver CC amplitude on magnetic resonance imaging and fluoroscopy were nonsignificant. Conclusions: Lorazepam reduces liver motion in the CC direction; however, average magnitude of reduction is small, and most patients have residual motion >5 mm.

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

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.)

Clinical experience of titanium cerebral aneurysm clips. Evaluation of artifact of CT and MRI

International Nuclear Information System (INIS)

Ninomiya, Takashi; Kato, Yoko; Sano, Hirotoshi

1996-01-01

The titanium aneurysm clips manufactured by AESCULAP Company are expected to be useful, not only for clinical applications, but also for reducing artifacts in post-operative CT and MRI. We carried out an investigation of the behavior of the new Yasargil titanium clips in a 1.5T MR imager. The new titanium clips showed considerably smaller clip-induced MR and CT artifacts than phynox and elgiloy clips. No movement of the titanium clips was seen by introducing them to the MR imager. Subsequent to these experimental studies, we applied titanium clips to 25 cerebral aneurysms. Post-operative CT, especially helical scanning CT and MR showed minimal artifacts, leading to the conclusion that the titanium clips are better than the other types of clips for the evaluation of post-operative neuroradiological images. (author)

Impact of subject head motion on quantitative brain 15O PET and its correction by image-based registration algorithm

International Nuclear Information System (INIS)

Matsubara, Keisuke; Ibaraki, Masanobu; Nakamura, Kazuhiro; Yamaguchi, Hiroshi; Umetsu, Atsushi; Kinoshita, Fumiko; Kinoshita, Toshibumi

2013-01-01

Subject head motion during sequential 15 O positron emission tomography (PET) scans can result in artifacts in cerebral blood flow (CBF) and oxygen metabolism maps. However, to our knowledge, there are no systematic studies examining this issue. Herein, we investigated the effect of head motion on quantification of CBF and oxygen metabolism, and proposed an image-based motion correction method dedicated to 15 O PET study, correcting for transmission-emission mismatch and inter-scan mismatch of emission scans. We analyzed 15 O PET data for patients with major arterial steno-occlusive disease (n=130) to determine the occurrence frequency of head motion during 15 O PET examination. Image-based motion correction without and with realignment between transmission and emission scans, termed simple and 2-step method, respectively, was applied to the cases that showed severe inter-scan motion. Severe inter-scan motion (>3 mm translation or >5deg rotation) was observed in 27 of 520 adjacent scan pairs (5.2%). In these cases, unrealistic values of oxygen extraction fraction (OEF) or cerebrovascular reactivity (CVR) were observed without motion correction. Motion correction eliminated these artifacts. The volume-of-interest (VOI) analysis demonstrated that the motion correction changed the OEF on the middle cerebral artery territory by 17.3% at maximum. The inter-scan motion also affected cerebral blood volume (CBV), cerebral metabolism rate of oxygen (CMRO 2 ) and CBF, which were improved by the motion correction. A difference of VOI values between the simple and 2-step method was also observed. These data suggest that image-based motion correction is useful for accurate measurement of CBF and oxygen metabolism by 15 O PET. (author)

Cervix Motion in 50 Cervical Cancer Patients Assessed by Daily Cone Beam Computed Tomographic Imaging of a New Type of Marker

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Langerak, Thomas, E-mail: t.langerak@erasmusmc.nl; Mens, Jan Willem; Quint, Sandra; Bondar, Luiza; Heijkoop, Sabrina; Heijmen, Ben; Hoogeman, Mischa

2015-11-01

Purpose: To evaluate a new type of marker and a new method of marker implantation and to assess interfraction cervix motion for a large population of patients with locally advanced cervical cancer by daily cone beam computed tomographic (CBCT) imaging. Methods and Materials: We investigated the position of markers in 50 patients treated in prone position during at least 23 fractions. To reduce streaking artifacts in the planning CT scan, a new type of polymeric marker was used and compared with conventional gold markers. In addition, a new method of implantation was used in an attempt to reduce marker loss. In each fraction, a CT scan was acquired before dose delivery and aligned to the bony anatomy of the planning CT scan, simulating the clinical setup protocol. First, sufficient visibility of the markers was verified. Then, systematic and random displacement of the marker centroids was recorded and analyzed in 3 directions with regard to the planning CT and the first CBCT (to evaluate the presence of a vaginal catheter in the planning CT). Streaking artifacts were quantified with the standard deviation of the mean squared intensity difference in a radius around the marker. Results: Marker loss was minimal during treatment: in only 3 of the 50 patients 1 marker was lost. Streaking artifacts for the new markers were reduced compared with conventional gold markers. For the planning CT, M/Σ/σ were 0.4/3.4/2.2 mm, 1.0/5.5/4.5 mm, and −3.9/5.1/3.6 mm for the left-right, anterior-posterior, and cranial-caudal directions, respectively. With regard to the first CBCT scan, M/Σ/σ were 0.8/2.8/2.1, 0.6/4.4/4.4, and −1.3/4.5/3.6 mm. Conclusions: A new type of marker and implantation method was shown to have significantly reduced marker loss and streaking artifacts compared with gold fiducial markers. The recorded marker displacement confirms results reported in the existing literature but for a larger dataset.

Utility of Electrocardiography (ECG)-Gated Computed Tomography (CT) for Preoperative Evaluations of Thymic Epithelial Tumors.

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Ozawa, Yoshiyuki; Hara, Masaki; Nakagawa, Motoo; Shibamoto, Yuta

2016-01-01

Preoperative evaluation of invasion to the adjacent organs is important for the thymic epithelial tumors on CT. The purpose of our study was to evaluate the utility of electrocardiography (ECG)-gated CT for assessing thymic epithelial tumors with regard to the motion artifacts produced and the preoperative diagnostic accuracy of the technique. Forty thymic epithelial tumors (36 thymomas and 4 thymic carcinomas) were examined with ECG-gated contrast-enhanced CT using a dual source scanner. The scan delay after the contrast media injection was 30 s for the non-ECG-gated CT and 100 s for the ECG-gated CT. Two radiologists blindly evaluated both the non-ECG-gated and ECG-gated CT images for motion artifacts and determined whether the tumors had invaded adjacent structures (mediastinal fat, superior vena cava, brachiocephalic veins, aorta, pulmonary artery, pericardium, or lungs) on each image. Motion artifacts were evaluated using a 3-grade scale. Surgical and pathological findings were used as a reference standard for tumor invasion. Motion artifacts were significantly reduced for all structures by ECG gating ( p =0.0089 for the lungs and p ECG-gated CT and ECG-gated CT demonstrated 79% and 95% accuracy, respectively, during assessments of pericardial invasion ( p =0.03). ECG-gated CT reduced the severity of motion artifacts and might be useful for preoperative assessment whether thymic epithelial tumors have invaded adjacent structures.

A dual-Kinect approach to determine torso surface motion for respiratory motion correction in PET

International Nuclear Information System (INIS)

Heß, Mirco; Büther, Florian; Dawood, Mohammad; Schäfers, Klaus P.; Gigengack, Fabian

2015-01-01

Purpose: Respiratory gating is commonly used to reduce blurring effects and attenuation correction artifacts in positron emission tomography (PET). Established clinically available methods that employ body-attached hardware for acquiring respiration signals rely on the assumption that external surface motion and internal organ motion are well correlated. In this paper, the authors present a markerless method comprising two Microsoft Kinects for determining the motion on the whole torso surface and aim to demonstrate its validity and usefulness—including the potential to study the external/internal correlation and to provide useful information for more advanced correction approaches. Methods: The data of two Kinects are used to calculate 3D representations of a patient’s torso surface with high spatial coverage. Motion signals can be obtained for any position by tracking the mean distance to a virtual camera with a view perpendicular to the surrounding surface. The authors have conducted validation experiments including volunteers and a moving high-precision platform to verify the method’s suitability for providing meaningful data. In addition, the authors employed it during clinical 18 F-FDG-PET scans and exemplarily analyzed the acquired data of ten cancer patients. External signals of abdominal and thoracic regions as well as data-driven signals were used for gating and compared with respect to detected displacement of present lesions. Additionally, the authors quantified signal similarities and time shifts by analyzing cross-correlation sequences. Results: The authors’ results suggest a Kinect depth resolution of approximately 1 mm at 75 cm distance. Accordingly, valid signals could be obtained for surface movements with small amplitudes in the range of only few millimeters. In this small sample of ten patients, the abdominal signals were better suited for gating the PET data than the thoracic signals and the correlation of data-driven signals was found

A dual-Kinect approach to determine torso surface motion for respiratory motion correction in PET

Energy Technology Data Exchange (ETDEWEB)

Heß, Mirco, E-mail: mirco.hess@uni-muenster.de; Büther, Florian; Dawood, Mohammad; Schäfers, Klaus P. [European Institute for Molecular Imaging, University of Münster, Münster 48149 (Germany); Gigengack, Fabian [European Institute for Molecular Imaging, University of Münster, Münster 48149, Germany and Department of Mathematics and Computer Science, University of Münster, Münster 48149 (Germany)

2015-05-15

Purpose: Respiratory gating is commonly used to reduce blurring effects and attenuation correction artifacts in positron emission tomography (PET). Established clinically available methods that employ body-attached hardware for acquiring respiration signals rely on the assumption that external surface motion and internal organ motion are well correlated. In this paper, the authors present a markerless method comprising two Microsoft Kinects for determining the motion on the whole torso surface and aim to demonstrate its validity and usefulness—including the potential to study the external/internal correlation and to provide useful information for more advanced correction approaches. Methods: The data of two Kinects are used to calculate 3D representations of a patient’s torso surface with high spatial coverage. Motion signals can be obtained for any position by tracking the mean distance to a virtual camera with a view perpendicular to the surrounding surface. The authors have conducted validation experiments including volunteers and a moving high-precision platform to verify the method’s suitability for providing meaningful data. In addition, the authors employed it during clinical {sup 18}F-FDG-PET scans and exemplarily analyzed the acquired data of ten cancer patients. External signals of abdominal and thoracic regions as well as data-driven signals were used for gating and compared with respect to detected displacement of present lesions. Additionally, the authors quantified signal similarities and time shifts by analyzing cross-correlation sequences. Results: The authors’ results suggest a Kinect depth resolution of approximately 1 mm at 75 cm distance. Accordingly, valid signals could be obtained for surface movements with small amplitudes in the range of only few millimeters. In this small sample of ten patients, the abdominal signals were better suited for gating the PET data than the thoracic signals and the correlation of data-driven signals was

Detection of artifacts from high energy bursts in neonatal EEG.

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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

PVR: Patch-to-Volume Reconstruction for Large Area Motion Correction of Fetal MRI.

Science.gov (United States)

Alansary, Amir; Rajchl, Martin; McDonagh, Steven G; Murgasova, Maria; Damodaram, Mellisa; Lloyd, David F A; Davidson, Alice; Rutherford, Mary; Hajnal, Joseph V; Rueckert, Daniel; Kainz, Bernhard

2017-10-01

In this paper, we present a novel method for the correction of motion artifacts that are present in fetal magnetic resonance imaging (MRI) scans of the whole uterus. Contrary to current slice-to-volume registration (SVR) methods, requiring an inflexible anatomical enclosure of a single investigated organ, the proposed patch-to-volume reconstruction (PVR) approach is able to reconstruct a large field of view of non-rigidly deforming structures. It relaxes rigid motion assumptions by introducing a specific amount of redundant information that is exploited with parallelized patchwise optimization, super-resolution, and automatic outlier rejection. We further describe and provide an efficient parallel implementation of PVR allowing its execution within reasonable time on commercially available graphics processing units, enabling its use in the clinical practice. We evaluate PVR's computational overhead compared with standard methods and observe improved reconstruction accuracy in the presence of affine motion artifacts compared with conventional SVR in synthetic experiments. Furthermore, we have evaluated our method qualitatively and quantitatively on real fetal MRI data subject to maternal breathing and sudden fetal movements. We evaluate peak-signal-to-noise ratio, structural similarity index, and cross correlation with respect to the originally acquired data and provide a method for visual inspection of reconstruction uncertainty. We further evaluate the distance error for selected anatomical landmarks in the fetal head, as well as calculating the mean and maximum displacements resulting from automatic non-rigid registration to a motion-free ground truth image. These experiments demonstrate a successful application of PVR motion compensation to the whole fetal body, uterus, and placenta.

Characterizing the reduction of stimulation artifact noise in a tripolar nerve cuff electrode by application of a conductive shield layer.

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Sabetian, Parisa; Sadeghlo, Bita; Zhang, Chengran Harvey; Yoo, Paul B

2017-02-01

Tripolar nerve cuff electrodes have been widely used for measuring peripheral nerve activity. However, despite the high signal-to-noise ratio levels that can be achieved with this recording configuration, the clinical use of cuff electrodes in closed-loop controlled neuroprostheses remains limited. This is largely attributed to artifact noise signals that contaminate the recorded neural activity. In this study, we investigated the use of a conductive shield layer (CSL) as a means of reducing the artifact noise recorded by nerve cuff electrodes. Using both computational simulations and in vivo experiments, we found that the CSL can result in up to an 85% decrease in the recorded artifact signal. Both the electrical conductivity and the surface area of the CSL were identified as important design criteria. Although this study shows that the CSL can significantly reduce artifact noise in tripolar nerve cuff electrodes, long-term implant studies are needed to validate our findings. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

Tactile motion adaptation reduces perceived speed but shows no evidence of direction sensitivity.

Directory of Open Access Journals (Sweden)

Sarah McIntyre

Full Text Available INTRODUCTION: While the directionality of tactile motion processing has been studied extensively, tactile speed processing and its relationship to direction is little-researched and poorly understood. We investigated this relationship in humans using the 'tactile speed aftereffect' (tSAE, in which the speed of motion appears slower following prolonged exposure to a moving surface. METHOD: We used psychophysical methods to test whether the tSAE is direction sensitive. After adapting to a ridged moving surface with one hand, participants compared the speed of test stimuli on the adapted and unadapted hands. We varied the direction of the adapting stimulus relative to the test stimulus. RESULTS: Perceived speed of the surface moving at 81 mms(-1 was reduced by about 30% regardless of the direction of the adapting stimulus (when adapted in the same direction, Mean reduction = 23 mms(-1, SD = 11; with opposite direction, Mean reduction = 26 mms(-1, SD = 9. In addition to a large reduction in perceived speed due to adaptation, we also report that this effect is not direction sensitive. CONCLUSIONS: Tactile motion is susceptible to speed adaptation. This result complements previous reports of reliable direction aftereffects when using a dynamic test stimulus as together they describe how perception of a moving stimulus in touch depends on the immediate history of stimulation. Given that the tSAE is not direction sensitive, we argue that peripheral adaptation does not explain it, because primary afferents are direction sensitive with friction-creating stimuli like ours (thus motion in their preferred direction should result in greater adaptation, and if perceived speed were critically dependent on these afferents' response intensity, the tSAE should be direction sensitive. The adaptation that reduces perceived speed therefore seems to be of central origin.

Electronic noise in CT detectors: Impact on image noise and artifacts.

Science.gov (United States)

Duan, Xinhui; Wang, Jia; Leng, Shuai; Schmidt, Bernhard; Allmendinger, Thomas; Grant, Katharine; Flohr, Thomas; McCollough, Cynthia H

2013-10-01

The objective of our study was to evaluate in phantoms the differences in CT image noise and artifact level between two types of commercial CT detectors: one with distributed electronics (conventional) and one with integrated electronics intended to decrease system electronic noise. Cylindric water phantoms of 20, 30, and 40 cm in diameter were scanned using two CT scanners, one equipped with integrated detector electronics and one with distributed detector electronics. All other scanning parameters were identical. Scans were acquired at four tube potentials and 10 tube currents. Semianthropomorphic phantoms were scanned to mimic the shoulder and abdominal regions. Images of two patients were also selected to show the clinical values of the integrated detector. Reduction of image noise with the integrated detector depended on phantom size, tube potential, and tube current. Scans that had low detected signal had the greatest reductions in noise, up to 40% for a 30-cm phantom scanned using 80 kV. This noise reduction translated into up to 50% in dose reduction to achieve equivalent image noise. Streak artifacts through regions of high attenuation were reduced by up to 45% on scans obtained using the integrated detector. Patient images also showed superior image quality for the integrated detector. For the same applied radiation level, the use of integrated electronics in a CT detector showed a substantially reduced level of electronic noise, resulting in reductions in image noise and artifacts, compared with detectors having distributed electronics.

SU-E-I-63: Quantitative Evaluation of the Effects of Orthopedic Metal Artifact Reduction (OMAR) Software On CT Images for Radiotherapy Simulation

Energy Technology Data Exchange (ETDEWEB)

Jani, S [Sharp Memorial Hospital, San Diego, CA (United States)

2014-06-01

Purpose: CT simulation for patients with metal implants can often be challenging due to artifacts that obscure tumor/target delineation and normal organ definition. Our objective was to evaluate the effectiveness of Orthopedic Metal Artifact Reduction (OMAR), a commercially available software, in reducing metal-induced artifacts and its effect on computed dose during treatment planning. Methods: CT images of water surrounding metallic cylindrical rods made of aluminum, copper and iron were studied in terms of Hounsfield Units (HU) spread. Metal-induced artifacts were characterized in terms of HU/Volume Histogram (HVH) using the Pinnacle treatment planning system. Effects of OMAR on enhancing our ability to delineate organs on CT and subsequent dose computation were examined in nine (9) patients with hip implants and two (2) patients with breast tissue expanders. Results: Our study characterized water at 1000 HU with a standard deviation (SD) of about 20 HU. The HVHs allowed us to evaluate how the presence of metal changed the HU spread. For example, introducing a 2.54 cm diameter copper rod in water increased the SD in HU of the surrounding water from 20 to 209, representing an increase in artifacts. Subsequent use of OMAR brought the SD down to 78. Aluminum produced least artifacts whereas Iron showed largest amount of artifacts. In general, an increase in kVp and mA during CT scanning showed better effectiveness of OMAR in reducing artifacts. Our dose analysis showed that some isodose contours shifted by several mm with OMAR but infrequently and were nonsignificant in planning process. Computed volumes of various dose levels showed <2% change. Conclusions: In our experience, OMAR software greatly reduced the metal-induced CT artifacts for the majority of patients with implants, thereby improving our ability to delineate tumor and surrounding organs. OMAR had a clinically negligible effect on computed dose within tissues. Partially funded by unrestricted

Improved abdominal MRI in non-breath-holding children using a radial k-space sampling technique

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Lee, Jong Hyuk; Choi, Young Hun; Cheon, Jung Eun; Lee, So Mi; Cho, Hyun Hae; Kim, Woo Sun; Kim, In One [Seoul National University Children' s Hospital, Department of Radiology, Seoul (Korea, Republic of); Shin, Su Mi [SMG-SNU Boramae Medical Center, Department of Radiology, Seoul (Korea, Republic of)

2015-06-15

Radial k-space sampling techniques have been shown to reduce motion artifacts in adult abdominal MRI. To compare a T2-weighted radial k-space sampling MRI pulse sequence (BLADE) with standard respiratory-triggered T2-weighted turbo spin echo (TSE) in pediatric abdominal imaging. Axial BLADE and respiratory-triggered turbo spin echo sequences were performed without fat suppression in 32 abdominal MR examinations in children. We retrospectively assessed overall image quality, the presence of respiratory, peristaltic and radial artifact, and lesion conspicuity. We evaluated signal uniformity of each sequence. BLADE showed improved overall image quality (3.35 ± 0.85 vs. 2.59 ± 0.59, P < 0.001), reduced respiratory motion artifact (0.51 ± 0.56 vs. 1.89 ± 0.68, P < 0.001), and improved lesion conspicuity (3.54 ± 0.88 vs. 2.92 ± 0.77, P = 0.006) compared to respiratory triggering turbo spin-echo (TSE) sequences. The bowel motion artifact scores were similar for both sequences (1.65 ± 0.77 vs. 1.79 ± 0.74, P = 0.691). BLADE introduced a radial artifact that was not observed on the respiratory triggering-TSE images (1.10 ± 0.85 vs. 0, P < 0.001). BLADE was associated with diminished signal variation compared with respiratory triggering-TSE in the liver, spleen and air (P < 0.001). The radial k-space sampling technique improved the quality and reduced respiratory motion artifacts in young children compared with conventional respiratory-triggered turbo spin-echo sequences. (orig.)

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

Respiratory Motion Correction for Compressively Sampled Free Breathing Cardiac MRI Using Smooth l1-Norm Approximation

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Muhammad Bilal

2018-01-01

Full Text Available Transformed domain sparsity of Magnetic Resonance Imaging (MRI has recently been used to reduce the acquisition time in conjunction with compressed sensing (CS theory. Respiratory motion during MR scan results in strong blurring and ghosting artifacts in recovered MR images. To improve the quality of the recovered images, motion needs to be estimated and corrected. In this article, a two-step approach is proposed for the recovery of cardiac MR images in the presence of free breathing motion. In the first step, compressively sampled MR images are recovered by solving an optimization problem using gradient descent algorithm. The L1-norm based regularizer, used in optimization problem, is approximated by a hyperbolic tangent function. In the second step, a block matching algorithm, known as Adaptive Rood Pattern Search (ARPS, is exploited to estimate and correct respiratory motion among the recovered images. The framework is tested for free breathing simulated and in vivo 2D cardiac cine MRI data. Simulation results show improved structural similarity index (SSIM, peak signal-to-noise ratio (PSNR, and mean square error (MSE with different acceleration factors for the proposed method. Experimental results also provide a comparison between k-t FOCUSS with MEMC and the proposed method.

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))

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)).

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

Methodology for stereoscopic motion-picture quality assessment

Science.gov (United States)

Voronov, Alexander; Vatolin, Dmitriy; Sumin, Denis; Napadovsky, Vyacheslav; Borisov, Alexey

2013-03-01

Creating and processing stereoscopic video imposes additional quality requirements related to view synchronization. In this work we propose a set of algorithms for detecting typical stereoscopic-video problems, which appear owing to imprecise setup of capture equipment or incorrect postprocessing. We developed a methodology for analyzing the quality of S3D motion pictures and for revealing their most problematic scenes. We then processed 10 modern stereo films, including Avatar, Resident Evil: Afterlife and Hugo, and analyzed changes in S3D-film quality over the years. This work presents real examples of common artifacts (color and sharpness mismatch, vertical disparity and excessive horizontal disparity) in the motion pictures we processed, as well as possible solutions for each problem. Our results enable improved quality assessment during the filming and postproduction stages.

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.

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

Symmetry breaking in fluid dynamics: Lie group reducible motions for real fluids

International Nuclear Information System (INIS)

Holm, D.D.

1976-07-01

The physics of fluids is based on certain kinematical invariance principles, which refer to coordinate systems, dimensions, and Galilean reference frames. Other, thermodynamic, symmetry principles are introduced by the material description. In the present work, the interplay between these two kinds of invariance principles is used to solve for classes of one-dimensional non-steady isentropic motions of a fluid whose equation of state is of Mie-Gruneisen type. Also, the change in profile and attenuation of weak shock waves in a dissipative medium is studied at the level of Burgers' approximation from the viewpoint of its underlying symmetry structure. The mathematical method of approach is based on the theory of infinitesimal Lie groups. Fluid motions are characterized according to inequivalent subgroups of the full invariance group of the flow description and exact group reducible solutions are presented

Symmetry breaking in fluid dynamics: Lie group reducible motions for real fluids

Energy Technology Data Exchange (ETDEWEB)

Holm, D.D.

1976-07-01

The physics of fluids is based on certain kinematical invariance principles, which refer to coordinate systems, dimensions, and Galilean reference frames. Other, thermodynamic, symmetry principles are introduced by the material description. In the present work, the interplay between these two kinds of invariance principles is used to solve for classes of one-dimensional non-steady isentropic motions of a fluid whose equation of state is of Mie-Gruneisen type. Also, the change in profile and attenuation of weak shock waves in a dissipative medium is studied at the level of Burgers' approximation from the viewpoint of its underlying symmetry structure. The mathematical method of approach is based on the theory of infinitesimal Lie groups. Fluid motions are characterized according to inequivalent subgroups of the full invariance group of the flow description and exact group reducible solutions are presented.

Dynamic re-weighted total variation technique and statistic Iterative reconstruction method for x-ray CT metal artifact reduction

Science.gov (United States)

Peng, Chengtao; Qiu, Bensheng; Zhang, Cheng; Ma, Changyu; Yuan, Gang; Li, Ming

2017-07-01

Over the years, the X-ray computed tomography (CT) has been successfully used in clinical diagnosis. However, when the body of the patient to be examined contains metal objects, the image reconstructed would be polluted by severe metal artifacts, which affect the doctor's diagnosis of disease. In this work, we proposed a dynamic re-weighted total variation (DRWTV) technique combined with the statistic iterative reconstruction (SIR) method to reduce the artifacts. The DRWTV method is based on the total variation (TV) and re-weighted total variation (RWTV) techniques, but it provides a sparser representation than TV and protects the tissue details better than RWTV. Besides, the DRWTV can suppress the artifacts and noise, and the SIR convergence speed is also accelerated. The performance of the algorithm is tested on both simulated phantom dataset and clinical dataset, which are the teeth phantom with two metal implants and the skull with three metal implants, respectively. The proposed algorithm (SIR-DRWTV) is compared with two traditional iterative algorithms, which are SIR and SIR constrained by RWTV regulation (SIR-RWTV). The results show that the proposed algorithm has the best performance in reducing metal artifacts and protecting tissue details.

Artifact in Pediatric Oculomotor Findings during Videonystagmography: A Retrospective Analysis.

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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

Robust and Accurate Anomaly Detection in ECG Artifacts Using Time Series Motif Discovery

Science.gov (United States)

Sivaraks, Haemwaan

2015-01-01

Electrocardiogram (ECG) anomaly detection is an important technique for detecting dissimilar heartbeats which helps identify abnormal ECGs before the diagnosis process. Currently available ECG anomaly detection methods, ranging from academic research to commercial ECG machines, still suffer from a high false alarm rate because these methods are not able to differentiate ECG artifacts from real ECG signal, especially, in ECG artifacts that are similar to ECG signals in terms of shape and/or frequency. The problem leads to high vigilance for physicians and misinterpretation risk for nonspecialists. Therefore, this work proposes a novel anomaly detection technique that is highly robust and accurate in the presence of ECG artifacts which can effectively reduce the false alarm rate. Expert knowledge from cardiologists and motif discovery technique is utilized in our design. In addition, every step of the algorithm conforms to the interpretation of cardiologists. Our method can be utilized to both single-lead ECGs and multilead ECGs. Our experiment results on real ECG datasets are interpreted and evaluated by cardiologists. Our proposed algorithm can mostly achieve 100% of accuracy on detection (AoD), sensitivity, specificity, and positive predictive value with 0% false alarm rate. The results demonstrate that our proposed method is highly accurate and robust to artifacts, compared with competitive anomaly detection methods. PMID:25688284

Automatic removal of eye-movement and blink artifacts from EEG signals.

Science.gov (United States)

Gao, Jun Feng; Yang, Yong; Lin, Pan; Wang, Pei; Zheng, Chong Xun

2010-03-01

Frequent occurrence of electrooculography (EOG) artifacts leads to serious problems in interpreting and analyzing the electroencephalogram (EEG). In this paper, a robust method is presented to automatically eliminate eye-movement and eye-blink artifacts from EEG signals. Independent Component Analysis (ICA) is used to decompose EEG signals into independent components. Moreover, the features of topographies and power spectral densities of those components are extracted to identify eye-movement artifact components, and a support vector machine (SVM) classifier is adopted because it has higher performance than several other classifiers. The classification results show that feature-extraction methods are unsuitable for identifying eye-blink artifact components, and then a novel peak detection algorithm of independent component (PDAIC) is proposed to identify eye-blink artifact components. Finally, the artifact removal method proposed here is evaluated by the comparisons of EEG data before and after artifact removal. The results indicate that the method proposed could remove EOG artifacts effectively from EEG signals with little distortion of the underlying brain signals.

Correction of Non-Linear Propagation Artifact in Contrast-Enhanced Ultrasound Imaging of Carotid Arteries: Methods and in Vitro Evaluation.

Science.gov (United States)

Yildiz, Yesna O; Eckersley, Robert J; Senior, Roxy; Lim, Adrian K P; Cosgrove, David; Tang, Meng-Xing

2015-07-01

Non-linear propagation of ultrasound creates artifacts in contrast-enhanced ultrasound images that significantly affect both qualitative and quantitative assessments of tissue perfusion. This article describes the development and evaluation of a new algorithm to correct for this artifact. The correction is a post-processing method that estimates and removes non-linear artifact in the contrast-specific image using the simultaneously acquired B-mode image data. The method is evaluated on carotid artery flow phantoms with large and small vessels containing microbubbles of various concentrations at different acoustic pressures. The algorithm significantly reduces non-linear artifacts while maintaining the contrast signal from bubbles to increase the contrast-to-tissue ratio by up to 11 dB. Contrast signal from a small vessel 600 μm in diameter buried in tissue artifacts before correction was recovered after the correction. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

High-fidelity artifact correction for cone-beam CT imaging of the brain

Science.gov (United States)

Sisniega, A.; Zbijewski, W.; Xu, J.; Dang, H.; Stayman, J. W.; Yorkston, J.; Aygun, N.; Koliatsos, V.; Siewerdsen, J. H.

2015-02-01

CT is the frontline imaging modality for diagnosis of acute traumatic brain injury (TBI), involving the detection of fresh blood in the brain (contrast of 30-50 HU, detail size down to 1 mm) in a non-contrast-enhanced exam. A dedicated point-of-care imaging system based on cone-beam CT (CBCT) could benefit early detection of TBI and improve direction to appropriate therapy. However, flat-panel detector (FPD) CBCT is challenged by artifacts that degrade contrast resolution and limit application in soft-tissue imaging. We present and evaluate a fairly comprehensive framework for artifact correction to enable soft-tissue brain imaging with FPD CBCT. The framework includes a fast Monte Carlo (MC)-based scatter estimation method complemented by corrections for detector lag, veiling glare, and beam hardening. The fast MC scatter estimation combines GPU acceleration, variance reduction, and simulation with a low number of photon histories and reduced number of projection angles (sparse MC) augmented by kernel de-noising to yield a runtime of ~4 min per scan. Scatter correction is combined with two-pass beam hardening correction. Detector lag correction is based on temporal deconvolution of the measured lag response function. The effects of detector veiling glare are reduced by deconvolution of the glare response function representing the long range tails of the detector point-spread function. The performance of the correction framework is quantified in experiments using a realistic head phantom on a testbench for FPD CBCT. Uncorrected reconstructions were non-diagnostic for soft-tissue imaging tasks in the brain. After processing with the artifact correction framework, image uniformity was substantially improved, and artifacts were reduced to a level that enabled visualization of ~3 mm simulated bleeds throughout the brain. Non-uniformity (cupping) was reduced by a factor of 5, and contrast of simulated bleeds was improved from ~7 to 49.7 HU, in good agreement

The HURRA filter: An easy method to eliminate collimator artifacts in high-energy gamma camera images.

Science.gov (United States)

Perez-Garcia, H; Barquero, R

The correct determination and delineation of tumor/organ size is crucial in 2-D imaging in 131 I therapy. These images are usually obtained using a system composed of a Gamma camera and high-energy collimator, although the system can produce artifacts in the image. This article analyses these artifacts and describes a correction filter that can eliminate those collimator artifacts. Using free software, ImageJ, a central profile in the image is obtained and analyzed. Two components can be seen in the fluctuation of the profile: one associated with the stochastic nature of the radiation, plus electronic noise and the other periodically across the position in space due to the collimator. These frequencies are analytically obtained and compared with the frequencies in the Fourier transform of the profile. A specially developed filter removes the artifacts in the 2D Fourier transform of the DICOM image. This filter is tested using a 15-cm-diameter Petri dish with 131 I radioactive water (big object size) image, a 131 I clinical pill (small object size) image, and an image of the remainder of the lesion of two patients treated with 3.7GBq (100mCi), and 4.44GBq (120mCi) of 131 I, respectively, after thyroidectomy. The artifact is due to the hexagonal periodic structure of the collimator. The use of the filter on large-sized images reduces the fluctuation by 5.8-3.5%. In small-sized images, the FWHM can be determined in the filtered image, while this is impossible in the unfiltered image. The definition of tumor boundary and the visualization of the activity distribution inside patient lesions improve drastically when the filter is applied to the corresponding images obtained with HE gamma camera. The HURRA filter removes the artifact of high-energy collimator artifacts in planar images obtained with a Gamma camera without reducing the image resolution. It can be applied in any study of patient quantification because the number of counts remains invariant. The filter makes

MSVAT-SPACE-STIR and SEMAC-STIR for Reduction of Metallic Artifacts in 3T Head and Neck MRI.

Science.gov (United States)

Hilgenfeld, T; Prager, M; Schwindling, F S; Nittka, M; Rammelsberg, P; Bendszus, M; Heiland, S; Juerchott, A

2018-05-24

The incidence of metallic dental restorations and implants is increasing, and head and neck MR imaging is becoming challenging regarding artifacts. Our aim was to evaluate whether multiple-slab acquisition with view angle tilting gradient based on a sampling perfection with application-optimized contrasts by using different flip angle evolution (MSVAT-SPACE)-STIR and slice-encoding for metal artifact correction (SEMAC)-STIR are beneficial regarding artifact suppression compared with the SPACE-STIR and TSE-STIR in vitro and in vivo. At 3T, 3D artifacts of 2 dental implants, supporting different single crowns, were evaluated. Image quality was evaluated quantitatively (normalized signal-to-noise ratio) and qualitatively (2 reads by 2 blinded radiologists). Feasibility was tested in vivo in 5 volunteers and 5 patients, respectively. Maximum achievable resolution and the normalized signal-to-noise ratio of MSVAT-SPACE-STIR were higher compared with SEMAC-STIR. Performance in terms of artifact correction was dependent on the material composition. For highly paramagnetic materials, SEMAC-STIR was superior to MSVAT-SPACE-STIR (27.8% smaller artifact volume) and TSE-STIR (93.2% less slice distortion). However, MSVAT-SPACE-STIR reduced the artifact size compared with SPACE-STIR by 71.5%. For low-paramagnetic materials, MSVAT-SPACE-STIR performed as well as SEMAC-STIR. Furthermore, MSVAT-SPACE-STIR decreased artifact volume by 69.5% compared with SPACE-STIR. The image quality of all sequences did not differ systematically. In vivo results were comparable with in vitro results. Regarding susceptibility artifacts and acquisition time, MSVAT-SPACE-STIR might be advantageous over SPACE-STIR for high-resolution and isotropic head and neck imaging. Only for materials with high-susceptibility differences to soft tissue, the use of SEMAC-STIR might be beneficial. Within limited acquisition times, SEMAC-STIR cannot exploit its full advantage over TSE-STIR regarding artifact

Evaluation of a direct motion estimation/correction method in respiratory-gated PET/MRI with motion-adjusted attenuation.

Science.gov (United States)

Bousse, Alexandre; Manber, Richard; Holman, Beverley F; Atkinson, David; Arridge, Simon; Ourselin, Sébastien; Hutton, Brian F; Thielemans, Kris

2017-06-01

Respiratory motion compensation in PET/CT and PET/MRI is essential as motion is a source of image degradation (motion blur, attenuation artifacts). In previous work, we developed a direct method for joint image reconstruction/motion estimation (JRM) for attenuation-corrected (AC) respiratory-gated PET, which uses a single attenuation-map (μ-map). This approach was successfully implemented for respiratory-gated PET/CT, but since it relied on an accurate μ-map for motion estimation, the question of its applicability in PET/MRI is open. The purpose of this work is to investigate the feasibility of JRM in PET/MRI and to assess the robustness of the motion estimation when a degraded μ-map is used. We performed a series of JRM reconstructions from simulated PET data using a range of simulated Dixon MRI sequence derived μ-maps with wrong attenuation values in the lungs, from -100% (no attenuation) to +100% (double attenuation), as well as truncated arms. We compared the estimated motions with the one obtained from JRM in ideal conditions (no noise, true μ-map as an input). We also applied JRM on 4 patient datasets of the chest, 3 of them containing hot lesions. Patient list-mode data were gated using a principal component analysis method. We compared SUV max values of the JRM reconstructed activity images and non motion-corrected images. We also assessed the estimated motion fields by comparing the deformed JRM-reconstructed activity with individually non-AC reconstructed gates. Experiments on simulated data showed that JRM-motion estimation is robust to μ-map degradation in the sense that it produces motion fields similar to the ones obtained when using the true μ-map, regardless of the attenuation errors in the lungs (PET/MRI clinical datasets. It provides a potential alternative to existing methods where the motion fields are pre-estimated from separate MRI measurements. © 2017 University College London (UCL). Medical Physics published by Wiley Periodicals, Inc

New technologies to reduce pediatric radiation doses

International Nuclear Information System (INIS)

Bernhardt, Philipp; Lendl, Markus; Deinzer, Frank

2006-01-01

X-ray dose reduction in pediatrics is particularly important because babies and children are very sensitive to radiation exposure. We present new developments to further decrease pediatric patient dose. With the help of an advanced exposure control, a constant image quality can be maintained for all patient sizes, leading to dose savings for babies and children of up to 30%. Because objects of interest are quite small and the speed of motion is high in pediatric patients, short pulse widths down to 4 ms are important to reduce motion blurring artifacts. Further, a new noise-reduction algorithm is presented that detects and processes signal and noise in different frequency bands, generating smooth images without contrast loss. Finally, we introduce a super-resolution technique: two or more medical images, which are shifted against each other in a subpixel region, are combined to resolve structures smaller than the size of a single pixel. Advanced exposure control, short exposure times, noise reduction and super-resolution provide improved image quality, which can also be invested to save radiation exposure. All in all, the tools presented here offer a large potential to minimize the deterministic and stochastic risks of radiation exposure. (orig.)

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.

Exploration of Methodological and Participant-Related Influences on the Number of Artifacts in ERP Data

Directory of Open Access Journals (Sweden)

Stephanie M. Shields

2017-11-01

Full Text Available Event-related potential (ERP data has low signal-to-noise ratio, requiring the conduction of a large number of trials in order to collect sufficient amounts of data for subsequent analysis. Therefore, it would be highly beneficial if researchers could minimize the number of artifacts that occur in the data, minimizing the number of discarded trials and the total number of trials needed. This study thus examined connections between the number of trials that have to be eliminated due to artifacts and a set of methodological variables, physical considerations, and individual differences. In half of the electroencephalography (EEG data collection blocks, naïve undergraduate participants were asked not to blink for the duration of the block (approximately 2.5 minutes, but in the other half, the stimulus set included blinking cues to give participants a chance to blink during blocks. The number of artifacts did not differ based on whether participants were cued to blink during blocks nor which type of block participants experienced first. However, the first block had significantly more artifacts than other blocks, and the third block had significantly fewer. Participants who had previously known one or both investigators had significantly fewer artifacts in their data than participants who had not, but no significant relationship was found between the number of artifacts and any other individual difference or physical consideration examined. These results imply that researchers could preemptively reduce the number of artifacts in their EEG data by including practice blocks and recruiting friends or acquaintances for studies if possible. Based on subjective, unsolicited participant feedback, the authors also recommend having blink cues in data collection blocks in order to make the task more comfortable for participants. Future studies with similar aims could use different equipment setups, e.g. electrode caps, and experimental manipulation of

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...

Practical implementation of spectral-intensity dispersion-canceled optical coherence tomography with artifact suppression

Science.gov (United States)

Shirai, Tomohiro; Friberg, Ari T.

2018-04-01

Dispersion-canceled optical coherence tomography (OCT) based on spectral intensity interferometry was devised as a classical counterpart of quantum OCT to enhance the basic performance of conventional OCT. In this paper, we demonstrate experimentally that an alternative method of realizing this kind of OCT by means of two optical fiber couplers and a single spectrometer is a more practical and reliable option than the existing methods proposed previously. Furthermore, we develop a recipe for reducing multiple artifacts simultaneously on the basis of simple averaging and verify experimentally that it works successfully in the sense that all the artifacts are mitigated effectively and only the true signals carrying structural information about the sample survive.

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...

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...

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.

Automatic detection and classification of artifacts in single-channel EEG

DEFF Research Database (Denmark)

Olund, Thomas; Duun-Henriksen, Jonas; Kjaer, Troels W.

2014-01-01

Ambulatory EEG monitoring can provide medical doctors important diagnostic information, without hospitalizing the patient. These recordings are however more exposed to noise and artifacts compared to clinically recorded EEG. An automatic artifact detection and classification algorithm for single......-channel EEG is proposed to help identifying these artifacts. Features are extracted from the EEG signal and wavelet subbands. Subsequently a selection algorithm is applied in order to identify the best discriminating features. A non-linear support vector machine is used to discriminate among different...... artifact classes using the selected features. Single-channel (Fp1-F7) EEG recordings are obtained from experiments with 12 healthy subjects performing artifact inducing movements. The dataset was used to construct and validate the model. Both subject-specific and generic implementation, are investigated...

SU-F-J-158: Respiratory Motion Resolved, Self-Gated 4D-MRI Using Rotating Cartesian K-Space Sampling

Energy Technology Data Exchange (ETDEWEB)

Han, F; Zhou, Z; Yang, Y; Sheng, K; Hu, P [UCLA School of Medicine, Los Angeles, CA (United States)

2016-06-15

Purpose: Dynamic MRI has been used to quantify respiratory motion of abdominal organs in radiation treatment planning. Many existing 4D-MRI methods based on 2D acquisitions suffer from limited slice resolution and additional stitching artifacts when evaluated in 3D{sup 1}. To address these issues, we developed a 4D-MRI (3D dynamic) technique with true 3D k-space encoding and respiratory motion self-gating. Methods: The 3D k-space was acquired using a Rotating Cartesian K-space (ROCK) pattern, where the Cartesian grid was reordered in a quasi-spiral fashion with each spiral arm rotated using golden angle{sup 2}. Each quasi-spiral arm started with the k-space center-line, which were used as self-gating{sup 3} signal for respiratory motion estimation. The acquired k-space data was then binned into 8 respiratory phases and the golden angle ensures a near-uniform k-space sampling in each phase. Finally, dynamic 3D images were reconstructed using the ESPIRiT technique{sup 4}. 4D-MRI was performed on 6 healthy volunteers, using the following parameters (bSSFP, Fat-Sat, TE/TR=2ms/4ms, matrix size=500×350×120, resolution=1×1×1.2mm, TA=5min, 8 respiratory phases). Supplemental 2D real-time images were acquired in 9 different planes. Dynamic locations of the diaphragm dome and left kidney were measured from both 4D and 2D images. The same protocol was also performed on a MRI-compatible motion phantom where the motion was programmed with different amplitude (10–30mm) and frequency (3–10/min). Results: High resolution 4D-MRI were obtained successfully in 5 minutes. Quantitative motion measurements from 4D-MRI agree with the ones from 2D CINE (<5% error). The 4D images are free of the stitching artifacts and their near-isotropic resolution facilitates 3D visualization and segmentation of abdominal organs such as the liver, kidney and pancreas. Conclusion: Our preliminary studies demonstrated a novel ROCK 4D-MRI technique with true 3D k-space encoding and respiratory

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.

Reduced mandibular range of motion in Duchenne Muscular Dystrophy: predictive factors.

Science.gov (United States)

van Bruggen, H W; Van Den Engel-Hoek, L; Steenks, M H; Bronkhorst, E M; Creugers, N H J; de Groot, I J M; Kalaykova, S I

2015-06-01

Patients with Duchenne muscular dystrophy (DMD) experience negative effects upon feeding and oral health. We aimed to determine whether the mandibular range of motion in DMD is impaired and to explore predictive factors for the active maximum mouth opening (aMMO). 23 patients with DMD (mean age 16.7 ± 7.7 years) and 23 controls were assessed using a questionnaire about mandibular function and impairments. All participants underwent a clinical examination of the masticatory system, including measurement of mandibular range of motion and variables related to mandibular movements. In all patients, quantitative ultrasound of the digastric muscle and the geniohyoid muscle and the motor function measure (MFM) scale were performed. The patients were divided into early and late ambulatory stage (AS), early non-ambulatory stage (ENAS) and late non-ambulatory stage (LNAS). All mandibular movements were reduced in the patient group (P < 0.001) compared to the controls. Reduction in the aMMO (<40 mm) was found in 26% of the total patient group. LNAS patients had significantly smaller mandibular movements compared to AS and ENAS (P < 0.05). Multiple linear regression analysis for aMMO revealed a positive correlation with the body height and disease progression, with MFM total score as the strongest independent risk factor (R(2) = 0.71). Mandibular movements in DMD are significantly reduced and become more hampered with loss of motor function, including the sitting position, arm function, and neck and head control. We suggest that measurement of the aMMO becomes a part of routine care of patients with DMD. © 2015 John Wiley & Sons Ltd.