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Sample records for gradient recalled echo

  1. Application of velocity imaging and gradient-recalled echo in neuroimaging

    International Nuclear Information System (INIS)

    Boyko, O.B.; Pelc, N.J.; Shimakawa, A.

    1990-01-01

    This paper describes the initial clinical experience with imaging blood flow at 1.5 T by means of a phase-sensitive gradient refocused pulse sequence. A spin-echo flow-encoding technique was modified to a gradient recalled acquisition in a steady state sequence, producing a velocity imaging and gradient recalled echo (VIGRE) sequence (TR = 24 msec, TE = 13 msec, flip angle = 45 degrees, 24-cm field of view, 7 mm contiguous sections). Two views per phase-encoding step are acquired; one using the first-moment flow-compensation gradient waveform and the second having a (selectable) nonzero first moment. A phase subtraction image is obtained where the signal is dependent on the direction and velocity of flow. The sequence was done following routine spin-echo imaging in 35 patients

  2. Comparison of multi-echo and single-echo gradient-recalled echo sequences for SPIO-enhanced Liver MRI at 3 T

    International Nuclear Information System (INIS)

    Choi, J.S.; Kim, M.-J.; Kim, J.H.; Choi, J.-Y.; Chung, Y.E.; Park, M.-S.; Kim, K.W.

    2010-01-01

    Aim: To assess the utility of a T2*-weighted, multi-echo data imaging combination sequenced on superparamagnetic iron oxide (SPIO)-enhanced liver magnetic resonance imaging (MRI) using a 3 T system. Materials and methods: Fifty patients underwent SPIO-enhanced MRI at 3 T using T2*-weighted, single-echo, gradient-recalled echo (GRE) sequences [fast imaging with steady precession; repetition time (TR)/echo time (TE), 126 ms/9 ms; flip angle, 30 o ] and multi-echo GRE (multi-echo data image combination) sequences (TR/TE, 186 ms/9 ms; flip angle, 30 o ). Three radiologists independently reviewed the images in a random order. The sensitivity and accuracy for the detection of focal hepatic lesions (a total of 76 lesions in 33 patients; 48 solid lesions, 28 non-solid lesions) were compared by analysing the area under the receiver operating characteristic curves. Image artefacts (flow artefacts, susceptibility artefacts, dielectric artefacts, and motion artefacts), lesion conspicuity, and overall image quality were evaluated according to a four-point scale: 1, poor; 2, fair; 3, good; 4, excellent. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the lesions were compared. Results: Image artefacts were more frequent with single-echo GRE (p < 0.05). The mean scale of image quality assessment for flow, susceptibility, dielectric, and motion artefacts were 2.76, 3.13, 3.42, and 2.89 with singe-echo, respectively, compared with 3.47, 3.43, 3.47, and 3.39, respectively, with multi-echo GRE. There was no significant difference in lesion conspicuity between single-echo (3.15) and multi-echo (3.30) GRE sequences. The overall image quality was significantly (p < 0.05) better with multi-echo (3.37) than with single-echo GRE (2.89). The mean SNR and CNR of the lesions were significantly (p < 0.05) higher on multi-echo (79 ± 23 and 128 ± 59, respectively) images than on single-echo (38 ± 11 and 102 ± 44, respectively) images. Lesion detection accuracy and

  3. Gradient-recalled echo sequences in direct shoulder MR arthrography for evaluating the labrum

    International Nuclear Information System (INIS)

    Lee, Marc J.; Motamedi, Kambiz; Chow, Kira; Seeger, Leanne L.

    2008-01-01

    The purpose of this study was to determine the utility of fat-suppressed gradient-recalled echo (GRE) compared with conventional spin echo T1-weighted (T1W) sequences in direct shoulder MR arthrography for evaluating labral tears. Three musculoskeletal radiologists retrospectively reviewed MR arthrograms performed over a 12-month period for which surgical correlation was available. Of 180 serial arthrograms, 31 patients had surgery with a mean of 48 days following imaging. Paired coronal oblique and axial T1W or GRE sequences were analyzed by consensus for labral tear (coronal oblique two-dimensional multi-echo data image combination, 2D MEDIC; and axial three-dimensional double-echo steady-state, 3D DESS; Siemens MAGNETOM Sonata 1.5-T MR system). Interpretations were correlated with operative reports. Of 31 shoulders, 25 had labral tears at surgery. The GRE sequences depicted labral tears in 22, while T1W images depicted tears in 16 (sensitivity 88% versus 64%; p 0.7). Specificities were somewhat lower for GRE. Thin section GRE sequences are more sensitive than T1W for the detection of anterior and posterior labral tears. As the specificity of GRE was lower, it should be considered as an adjunctive imaging sequence that may improve depiction of labral tears, particularly smaller tears, in routine MR arthrography protocols. (orig.)

  4. Comparison of gradient-recalled echo and spin-echo echo-planar imaging MR elastography in staging liver fibrosis. A meta-analysis

    International Nuclear Information System (INIS)

    Kim, Yong Seek; Jang, Yu Na; Song, Ji Soo

    2018-01-01

    To compare the diagnostic performance of gradient-recalled echo-based magnetic resonance elastography (GRE-MRE) and spin-echo echo-planar imaging-based MRE (SE-EPI-MRE) in liver fibrosis staging. A systematic literature search was performed to identify studies involving the performance of MRE for the diagnosis of liver fibrosis. Pooled sensitivity, specificity, positive and negative likelihood ratios, the diagnostic odds ratio, and a summary receiver operating characteristic (ROC) curve were estimated by using a bivariate random effects model. Subgroup analyses were performed between different study characteristics. Twenty-six studies with a total of 3,200 patients were included in the meta-analysis. Pooled sensitivity and specificity of GRE-MRE and SE-EPI-MRE did not differ significantly. The area under the summary ROC curve for stage diagnosis of any (F ≥ 1), significant (F ≥ 2), advanced (F ≥ 3), and cirrhosis (F = 4) on GRE-MRE and SE-EPI-MRE were 0.93 versus 0.94, 0.95 versus 0.94, 0.94 versus 0.95, and 0.92 versus 0.93, respectively. Substantial heterogeneity was detected for both sequences. Both GRE and SE-EPI-MRE show high sensitivity and specificity for detection of each stage of liver fibrosis, without significant differences. Magnetic resonance elastography (MRE) may be useful for noninvasive evaluation of liver fibrosis in chronic liver disease. (orig.)

  5. Minimum TE gradient-recalled phosphorus imaging sequence on a whole-body imager

    International Nuclear Information System (INIS)

    Listerud, J.; Lenkinski, R.E.; Axel, L.

    1989-01-01

    To define the lower limits of spatial resolution in gradient-recalled echo phosphorus studies at 1.5 T, the authors have implemented a phosphorus gradient-recalled imaging sequence on the Signa imager. All gradient ramps for the section-selective rephasing lobe, the phase-encoding pulse, and the dephasing pulse of the frequency-encoding gradient are slowed at the maximal rate. Consequently, with a field of view of 24 cm, an in-plane resolution of 3 cm, an echo appropriately offset, an RF bandwidth of 1.2 KHz, and a section thickness of 5 cm, the echo time may be reduced to 1.35 msec. The reconstruction algorithm has been modified to support oversampled data of low spatial resolution appropriate for phosphorus imaging. The sequence will acquire H-1 images and supports the automatic and manual prescan features of the commercial instrument. To facilitate setup in the phosphorus imaging mode the sequence supports the product spectroscopic mode with a DRESS (depth recalled surface coil spectroscopy) sequence and a section profile sequence for appropriate shimming, receiver characteristics, and averaging requirements. The suitability for adaptation of this sequence to three-dimensional chemical shift imaging is discussed

  6. Gradient-recalled echo sequences in direct shoulder MR arthrography for evaluating the labrum

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Marc J.; Motamedi, Kambiz; Chow, Kira; Seeger, Leanne L. [David Geffen School of Medicine at UCLA, Department of Radiology, 200 UCLA Medical Plaza, Suite 165-59, Box 956952, Los Angeles, CA (United States)

    2008-01-15

    The purpose of this study was to determine the utility of fat-suppressed gradient-recalled echo (GRE) compared with conventional spin echo T1-weighted (T1W) sequences in direct shoulder MR arthrography for evaluating labral tears. Three musculoskeletal radiologists retrospectively reviewed MR arthrograms performed over a 12-month period for which surgical correlation was available. Of 180 serial arthrograms, 31 patients had surgery with a mean of 48 days following imaging. Paired coronal oblique and axial T1W or GRE sequences were analyzed by consensus for labral tear (coronal oblique two-dimensional multi-echo data image combination, 2D MEDIC; and axial three-dimensional double-echo steady-state, 3D DESS; Siemens MAGNETOM Sonata 1.5-T MR system). Interpretations were correlated with operative reports. Of 31 shoulders, 25 had labral tears at surgery. The GRE sequences depicted labral tears in 22, while T1W images depicted tears in 16 (sensitivity 88% versus 64%; p < 0.05). Subdividing the labrum, GRE was significantly more sensitive for the posterior labrum (75% versus 25%; p < 0.05) with a trend toward greater sensitivity at the anterior labrum (78% versus 56%; p = 0.157) but not significantly different for the superior labrum (50% versus 57%; p > 0.7). Specificities were somewhat lower for GRE. Thin section GRE sequences are more sensitive than T1W for the detection of anterior and posterior labral tears. As the specificity of GRE was lower, it should be considered as an adjunctive imaging sequence that may improve depiction of labral tears, particularly smaller tears, in routine MR arthrography protocols. (orig.)

  7. Anteroinferior tears of the glenoid labrum: fat-suppressed fast spin-echo T2 versus gradient-recalled echo MR images

    Energy Technology Data Exchange (ETDEWEB)

    Tuite, M J [Department of Radiology, University of Wisconsin Hospital and Clinics, 600 Highland Avenue, Madison, WI 53792 (United States); De Smet, A A [Department of Radiology, University of Wisconsin Hospital and Clinics, 600 Highland Avenue, Madison, WI 53792 (United States); Norris, M A [Department of Radiology, University of Wisconsin Hospital and Clinics, 600 Highland Avenue, Madison, WI 53792 (United States); Orwin, J F [Department of Orthopedic Surgery, University of Wisconsin Hospital and Clinics, 600 Highland Avenue, Madison, WI 53792 (United States)

    1997-05-01

    Objective. To compare fat-suppressed fast spin-echo (FSE) T2-weighted images with gradient-recalled echo (GRE) T2*-weighted images in the evaluation of anteroinferior labral tears. Design. MR images were retrospectively reviewed by two radiologists masked to the history and arthroscopic findings. They separately interpreted the anteroinferior labrum as torn or intact, first on one pulse sequence and then, 4 weeks later, on the other sequence. The MR interpretations were correlated with the arthroscopic findings. Patients. Nine patients with anteroinferior labral tears, and nine similarly-aged patients with normal, labra were studied. Results and conclusions. Observer 1 had a sensitivity of 0.56 on the GRE images and 0.67 on the FSE images (P>0.5), with a specificity of 1.0 for both sequences. Observer 2 had a sensitivity of 0.78 and a specificity of 0.89 for both sequences. In this small study there is no significant difference between GRE and fat-suppressed FSE images in their ability to diagnose anteroinferior labral tears. When evaluating the labrum with conventional MRI, axial fat-suppressed FSE T2-weighted images can be used in place of GRE images without a loss of accuracy. (orig.). With 3 figs., 1 tab.

  8. Rapid Gradient-Echo Imaging

    Science.gov (United States)

    Hargreaves, Brian

    2012-01-01

    Gradient echo sequences are widely used in magnetic resonance imaging (MRI) for numerous applications ranging from angiography to perfusion to functional MRI. Compared with spin-echo techniques, the very short repetition times of gradient-echo methods enable very rapid 2D and 3D imaging, but also lead to complicated “steady states.” Signal and contrast behavior can be described graphically and mathematically, and depends strongly on the type of spoiling: fully balanced (no spoiling), gradient spoiling, or RF-spoiling. These spoiling options trade off between high signal and pure T1 contrast while the flip angle also affects image contrast in all cases, both of which can be demonstrated theoretically and in image examples. As with spin-echo sequences, magnetization preparation can be added to gradient-echo sequences to alter image contrast. Gradient echo sequences are widely used for numerous applications such as 3D perfusion imaging, functional MRI, cardiac imaging and MR angiography. PMID:23097185

  9. Diagnostic accuracy of dual-echo (in- and opposed-phase) T1-weighted gradient recalled echo for detection and grading of hepatic iron using quantitative and visual assessment

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    Schieda, Nicola; Ramanathan, Subramaniyan; Ryan, John; Khanna, Maneesh; Virmani, Vivek; Avruch, Leonard [The University of Ottawa, The Ottawa Hospital, Ottawa, Ontario (Canada)

    2014-07-15

    Detection and quantification of hepatic iron with dual-echo gradient recalled echo (GRE) has been proposed as a rapid alternative to other magnetic resonance imaging (MRI) techniques. Co-existing steatosis and T1 weighting are limitations. This study assesses the accuracy of routine dual-echo GRE. Between 2010 and 2013, 109 consecutive patients underwent multi-echo (ME) MRI and dual-echo GRE for quantification of hepatic iron. Liver iron concentration (LIC) was calculated from ME-MRI. Relative signal intensity (RSI) and fat signal fraction (FSF) were calculated from dual-echo GRE. Four radiologists subjectively evaluated dual-echo GRE (±subtraction). Diagnostic accuracy was compared between techniques and correlated with biopsy using Fisher's exact test, Spearman correlation and regression. The sensitivity of visual detection of iron ranged from 48 to 55 %. Subtraction did not increase sensitivity (p < 0.001). Inter-observer variability was substantial (κ = 0.72). The specificity of visual detection of iron approached 100 % with false-positive diagnoses observed using subtraction. LIC showed a higher correlation with histopathological iron grade (r = 0.94, p < 0.001) compared with RSI (r = 0.65, p = 0.02). Univariate regression showed an association between RSI and LIC (B = 0.98, p < 0.001, CI 0.73-1.23); however, the association was not significant with multi-variate regression including FSF (p = 0.28). Dual-echo GRE has low sensitivity for hepatic iron. Subtraction imaging can result in false-positive diagnoses. (orig.)

  10. Evaluation of short repetition time, partial flip angle, gradient recalled echo pulse sequences in cervical spine imaging

    International Nuclear Information System (INIS)

    Enzmann, D.; Rubin, J.B.

    1987-01-01

    A short repetition time (TR), partial flip angle, gradient recalled echo pulse sequence (GRASS) was prospectively studied to optimize it for the diagnosis of cervical disk and cord disease in 98 patients. Changes in signal-to-noise ratio (SNR) and contrast were measured as the following parameters were varied: flip angle (3 0 to 18 0 ), TR (22-60 msec), and echo time (TE) (12.5-25 msec). Flip angle was the single most important parameter. For disk disease, cerebrospinal fluid (CSF) SNR peaked at an 8 0 flip angle in the axial view but at a 4 0 flip angle in the sagittal view. In the sagittal view, disk-CSF contrast decreased progressively from a flip angle of 3 0 , while in the axial view it peaked at 10 0 . For cord lesions the findings were similar except that lesion-cord contrast could be increased by lengthening both TR and TE. No one combination of parameters proved greatly superior for either disk disease or cord disease. The selection of parameters required balancing of several factors that often had opposing effects

  11. Fat-suppressed three-dimensional fast spoiled gradient-recalled echo imaging: a modified FS 3D SPGR technique for assessment of patellofemoral joint chondromalacia.

    Science.gov (United States)

    Wang, S F; Cheng, H C; Chang, C Y

    1999-01-01

    Fast fat-suppressed (FS) three-dimensional (3D) spoiled gradient-recalled echo (SPGR) imaging of 64 articular cartilage regions in 16 patellofemoral joints was evaluated to assess its feasibility in diagnosing patellofemoral chondromalacia. It demonstrated good correlation with arthroscopic reports and took about half of the examination time that FS 3D SPGR did. This modified, faster technique has the potential to diagnose patellofemoral chondromalacia with shorter examination time than FS 3D SPGR did.

  12. Comparison of spin-echo echoplanar imaging and gradient recalled echo-based MR elastography at 3 Tesla with and without gadoxetic acid administration

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Yong Seek [Chonbuk National University Medical School and Hospital, Department of Radiology, Jeonju, Chonbuk (Korea, Republic of); Song, Ji Soo [Chonbuk National University Medical School and Hospital, Department of Radiology, Jeonju, Chonbuk (Korea, Republic of); Research Institute of Clinical Medicine of Chonbuk National University, Jeonju, Chonbuk (Korea, Republic of); Biomedical Research Institute of Chonbuk National University Hospital, Jeonju, Chonbuk (Korea, Republic of); Kannengiesser, Stephan [Siemens Healthcare, MR Applications Development, Erlangen (Germany); Seo, Seung Young [Research Institute of Clinical Medicine of Chonbuk National University, Jeonju, Chonbuk (Korea, Republic of); Biomedical Research Institute of Chonbuk National University Hospital, Jeonju, Chonbuk (Korea, Republic of); Chonbuk National University Medical School and Hospital, Department of Internal Medicine, Jeonju (Korea, Republic of)

    2017-10-15

    To compare spin-echo echoplanar imaging (SE-EPI) and gradient recalled echo (GRE) MR elastography (MRE) at 3 T with and without gadoxetic acid administration. We included 84 patients who underwent MRE before and after gadoxetic acid administration, each time using SE-EPI and GRE sequences. Diagnostic performance for predicting clinical liver cirrhosis and high-risk oesophageal varices was assessed using the area under the receiver-operating characteristic curve (AUC). The relationships between T2* and success of MRE, and correlations of liver stiffness (LS) values between the two sequences or before and after gadoxetic acid administration, were investigated. SE-EPI-MRE resulted in a significantly lower failure rate than GRE-MRE (1.19% vs. 10.71%, P = 0.018). Increased T2* was related to higher probability of successful LS measurement (odds ratio, 1.426; P = 0.004). The AUC of SE-EPI-MRE was comparable to that of GRE-MRE for the detection of clinical liver cirrhosis (0.938 vs. 0.948, P = 0.235) and high-risk oesophageal varices (0.839 vs. 0.752, P = 0.354). LS values were not significantly different before and after gadoxetic acid administration. SE-EPI-MRE can substitute for GRE-MRE for the detection of clinical liver cirrhosis and high-risk oesophageal varices. SE-EPI-MRE is particularly useful in patients with iron deposition, with lower failure rates than GRE-MRE. (orig.)

  13. Increased flow sensitivity from gradient recalled echoes and short TRs

    International Nuclear Information System (INIS)

    Hearshen, D.O.; Froelich, J.W.; Wehrli, F.W.; Haggar, A.M.; Shimakawa, A.

    1986-01-01

    Time-of-flight effects from flow have been characterized in spin-echo images. ''Paradoxical'' enhancement and flow void are observed. Similar enhancement is seen on GRASS images. With no flow void and gradients existing throughout the volume, spins experiencing radio-frequency pulses will give rise to signals even for fast flow, providing a greater velocity sensitivity. GRASS images were obtained from a volunteer with a blood pressure cuff placed over the right thigh. With the cuff inflated, flow in the popliteal vein results in signal saturation. Increasing TR increases intensity in the popliteal vein relative to other vessels. This suggests a clinical role for the technique in assessment of slow flow

  14. Turbo-Proton Echo Planar Spectroscopic Imaging (t-PEPSI) MR technique in the detection of diffuse axonal damage in brain injury. Comparison with Gradient-Recalled Echo (GRE) sequence.

    Science.gov (United States)

    Giugni, E; Sabatini, U; Hagberg, G E; Formisano, R; Castriota-Scanderbeg, A

    2005-01-01

    Diffuse axonal injury (DAI) is a common type of primary neuronal injury in patients with severe traumatic brain injury, and is frequently accompanied by tissue tear haemorrhage. The T2*-weighted gradient-recalled echo (GRE) sequences are more sensitive than T2-weighted spin-echo images for detection of haemorrhage. This study was undertaken to determine whether turbo-PEPSI, an extremely fast multi-echo-planar-imaging sequence, can be used as an alternative to the GRE sequence for detection of DAI. Nineteen patients (mean age 24,5 year) with severe traumatic brain injury (TBI), occurred at least 3 months earlier, underwent a brain MRI study on a 1.5-Tesla scanner. A qualitative evaluation of the turbo-PEPSI sequences was performed by identifying the optimal echo time and in-plane resolution. The number and size of DAI lesions, as well as the signal intensity contrast ratio (SI CR), were computed for each set of GRE and turbo-PEPSI images, and divided according to their anatomic location into lobar and/or deep brain. There was no significant difference between GRE and turbo-PEPSI sequences in the total number of DAI lesions detected (283 vs 225 lesions, respectively). The GRE sequence identified a greater number of hypointense lesions in the temporal lobe compared to the t-PEPSI sequence (72 vs 35, pPEPSI than for the GRE sequence (pPEPSI sequence can be used as an alternative to the GRE to assess brain DAI in severe TBI patients, especially if uncooperative and medically unstable.

  15. Quantitation of structural distortion with gradient-echo imaging techniques

    International Nuclear Information System (INIS)

    Tien, R.D.; Schwaighofer, B.W.; Hesselink, J.R.; Chu, P.K.

    1990-01-01

    This paper determines the structural distortion and measurement error associated with fast MR imaging of the spinal neural foramina. Dry skeletal specimens and a thin cadaveric sagittal section through the neural foramina were placed in a water bath. MR images were obtained with a 1.5-T unit in different planes and with various pulse sequences. The size and shape of each neural foramen were carefully measured on the images and on the skeletal specimens. Gradient-echo (GRE) techniques (gradient recalled acquisition in a steady state, MPGR, three-dimensional volume acquisition) resulted in structural distortion in up to 10% on the fresh skeleton and 30% of the dry skeleton specimens when a small TE was used (the foramina appear narrower on the images)

  16. Comparison of spin-echo and gradient recalled echo T1 weighted MR images for quantitative voxel-based clinical brain research

    International Nuclear Information System (INIS)

    Barnden, L.R.; Crouch, B.

    2010-01-01

    Full text: New methods to normalise inter-subject global variations in T 1 -weighted MR (T I w) signal levels have permitted their use in voxel based population studies of brain dysfunction. Here we address the question of whether a spin-echo (SE) or a gradient recalled echo (GRE) T I w sequence is better for this purpose. GRE images are commonly referred to as 3D MRL SE has superior signal/noise properties to GRE but is slower to acquire so that typical slice thicknesses are 3-5 mm compared to 1-2 mm for GRE. GRE has better grey/white matter contrast which should permit better spatial normalization. However, unlike SE, GRE is affected by subject-specific magnetic field inhomogeneities that distort the images. We acquired T I brain images for 25 chronic fatigue syndrome (CFS) patients and 25 normal controls (NC) with TRITE/flip-angle of 600 ms/l5 ms/90 deg for SE and 5.76 ms/1.9 ms/9 deg for GRE. For GRE, the magnetic field inhomogeneity related signal level distortions could be corrected, but not the spatial distortions. After spatial normalization we subjected them to voxel-based statistical analysis with adjustment for global signal level using the SPM5 package. Initially, the same spatial normalization deformations were applied to both SE and GRE after coregistering them. Although the SPM regressions of SE and GRE yielded similar spatial distributions of significance, the SE regressions were consistently statistically stronger. For example, in one strong regression, the corrected cluster P value was twenty times stronger (I.Oe-5 versus I.Oe-3). T I w SE have proved better than T I GRE images in quantitative analysis in a clinical research study. (author)

  17. Retrospective comparison of gradient recalled echo R2* and spin-echo R2 magnetic resonance analysis methods for estimating liver iron content in children and adolescents

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    Serai, Suraj D.; Fleck, Robert J. [Cincinnati Children' s Hospital Medical Center, Department of Radiology, MLC 5031, Cincinnati, OH (United States); Quinn, Charles T. [Cincinnati Children' s Hospital Medical Center, Division of Hematology, Cincinnati, OH (United States); Zhang, Bin [Cincinnati Children' s Hospital Medical Center, Division of Biostatistics and Epidemiology, Cincinnati, OH (United States); Podberesky, Daniel J. [Nemours Children' s Health System Nemours Children' s Hospital, Department of Radiology, Orlando, FL (United States)

    2015-10-15

    Serial surveillance of liver iron concentration (LIC) provides guidance for chelation therapy in patients with iron overload. The diagnosis of iron overload traditionally relies on core liver biopsy, which is limited by invasiveness, sampling error, cost and general poor acceptance by pediatric patients and parents. Thus noninvasive diagnostic methods such as MRI are highly attractive for quantification of liver iron concentration. To compare two MRI-based methods for liver iron quantification in children. 64 studies on 48 children and young adults (age range 4-21 years) were examined by gradient recalled echo (GRE) R2* and spin-echo R2 MRI at 1.5T to evaluate liver iron concentration. Scatter plots and Bland-Altman difference plots were generated to display and assess the relationship between the methods. With the protocols used in this investigation, Bland-Altman agreement between the methods is best when LIC is <20 mg/g dry tissue. Scatter plots show that all values with LIC <20 mg/g dry tissue fall within the 95% prediction limits. Liver iron concentration as determined by the R2* and R2 MR methods is statistically comparable, with no statistical difference between these methods for LIC <20 mg/g. (orig.)

  18. Short echo time, fast gradient-echo imaging

    International Nuclear Information System (INIS)

    Haacke, E.M.; Lenz, G.W.

    1987-01-01

    Present fast-gradient-echoes schemes can acquire volume data rapidly and are flexible in T1 or T1/T2 contrast behavior. However, sequences used to date employ echo time (TE) values of about 15 ms +- 5 and, because of in vivo field inhomogeneities (short T2), they suffer badly from signal loss near sinuses and tissue boundaries. The authors implemented sequences with TE = 4-6 ms and found significant improvement in image quality, especially at high fields. Examples with long TEs vs. short TEs are given in the knee, spine, head, and orbits. Further advantages include (1) faster repetition times (15 ms), (2) higher-quality spin-density or T1-weighted images, and (3) reduction of blood motion artifacts

  19. Spontaneous cerebral microbleeds on gradient echo MR imaging in the stroke patients

    International Nuclear Information System (INIS)

    Kwak, Seong Ho; Song, Chang June; Kim, Dae Bong; Jeong, Geum Chae

    2003-01-01

    To investigate the spontaneous cerebral microbleeding occurring at gradient-echo MRI, and its relationship with associated stroke lesions and risk factors. Between September 2001 and December, 2002, 32 patients (21 men and 11 women; mean age 63 years) in whom cerebral microbleeding occurred at gradient-echo MRI were retrospectively investigated. Using a 1.5T MR imager, spin-echo T1-weighted, fast spin-echo T2-weighted, diffusion-weighted, and gradient-echo images were obtained. The number and location of microbleeds seen on gradient echo images, patients data, and associated stroke lesions such as intracerebral hemorrhage and lacunar and territorial infarction were assessed. Among the 32 patients, 563 microbleeds and between 1 and 66 (mean, 17.6) were noted at gradient-echo imaging. Microbleeding occurred in the cortical/subcortical area (n=216), the basal ganglia (n=173), thalamus (n=92), cerebellum (n=41), brainstem (n=36) and corpus callosum (n=1), and in 20 patients was bilateral. Patients had a history of hypertension (n=26), hypertriglycemia (n=12), heart disease (n=4), and diabetes mellitus (n=3). Stroke lesions were seen in 27 patients, intracerebral hemorrhage in ten, lacunar infarction in 24, and territorial infarction in four. The incidence and number of microbleeds was greater in older patients and in those with hypertension, hypertriglycemia, and stroke lesions such as intracerebral hemorrhage or lacunar infarction. The detection of microbleeding at gradient-echo imaging is helpful, since it predicts the possibility of cerebral hemorrhage in these patients

  20. Assessment of diagnosing metastatic bone tumor on T2*-weighted images. Comparison between turbo spin echo (TSE) method and gradient echo (GE) method

    International Nuclear Information System (INIS)

    Hayashi, Takahiko; Sugiyama, Akira; Katayama, Motoyuki

    1996-01-01

    We examined the usefulness of T2 * weighted gradient field echo images for diagnosis for metastatic bone tumors in comparison with T2 weighted turbo spin echo (fast spin echo) images. In T2 * weighted gradient field echo sequence to obtain maximum contrast-to-noise ratio (CNR), we experimentally manipulated flip angle (FA) (5deg-90deg), repetition time (TR) (400, 700 msec), and echo time (TE) (10-50 msec). The best CNR was 16.4 in fast low angle shot (FLASH) (TE: 24 msec, TR: 700 msec, FA: 40deg). Magnetic resonance imaging was carried out in 28 patients with metastatic bone tumors. In addition to conventional T1 weighted spin echo images, T2 weighted turbo spin echo (fast spin echo images) and T2 * weighted gradient field echo images were obtained. T2 * weighted gradient field echo images were superior to T2 weighted turbo spin echo (fast spin echo) images in delineating the tumors, adjacent fat tissues, and bone marrow. (author)

  1. Liver iron content determined by MRI. Spin-echo vs. gradient-echo

    Energy Technology Data Exchange (ETDEWEB)

    Juchems, M.S.; Wunderlich, A.P. [Universitaetskliniken Ulm (Germany). Klinik fuer Diagnostische und Interventionelle Radiologie; Cario, H. [Universitaetskliniken Ulm (Germany). Klinik fuer Kinder- und Jugendmedizin; Schmid, M. [Stadtspital Triemli, Zuerich (Switzerland). Medizinische Onkologie und Haematologie

    2012-05-15

    Purpose: Liver iron content (LIC) measurement plays a central role in the management of patients with transfusional iron overload. Calculating the LIC with data obtained from standardized MRI sequences represents an attractive alternative diagnostic possibility. The purpose of this study was to compare the LIC measurement obtained with gradient-echo (GRE) sequences to the mean liver proton transverse relaxation (R2) acquired with SE sequences. Materials and Methods: 68 patients with iron overload (median age: 24, range: 3 - 88) underwent 1.5 T MRI for liver iron content measurement. All patients received spin-echo (SE) and gradient-echo (GRE) sequences. Results: The two MRI methods revealed different liver iron content results although a significant correlation was found (r = 0.85, p < 0.001). Values evaluated using GRE sequences (median: 260 {mu}mol/g dry weight [d.w.], range: 6 - 732) were generally higher than those obtained by SE examinations (median: 161 {mu}mol /g d.w., range: 5 - 830). Conclusion: In conclusion, our study revealed different results for both MRI measurements, which could lead to different decisions concerning the management of chelation therapy in individual patients. (orig.)

  2. Comparison of fast spin echo, fast multiplanner spoiled gradient recalled and conventional T1 and T2 weighted imaging for experimentally induced hepatic tumors in rats

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    Kim, Myeong Jin; Lee, Jong Tae; Suh, Jin Suk; Choi, Pil Sik; Lee, Yeon Hee; Yoo, Hyung Sik; Kim, Ki Whang [Yonsei University College of Medicine, Seoul (Korea, Republic of)

    1994-10-15

    To compare the ability of tumor detection and the lesion conspicuity between T1- and T2-weighted fast scanning sequence and T1- and T2-weighted conventional spin echo techniques in MR imaging of hepatic tumors. Hepatic tumors were induced on 13 male Sprague-Dawley rats by feeding 3'-methyl-dimethylethyl aminoazobenzene mixed with Miller's III formula for 12 weeks. MR images were obtained with 1.5 T magnet with dual TMJ coil(Sigma, GE Medical systems, Milwaukee, USA). Animals were anesthetized with 150 mg/kg of ketamine hydrochloride. T2 weighted fast spin echo(FSE), conventional spin echo(CSE) T2- and T1WI, fast multiplanner spoiled gradient recalled(FMPSPGR) imaging were obtained. Number of detected tumors and contrast-to-noise ratio of the tumors were compared for each sequence. Overall 110 tumors were developed. 75% of the tumors were detected on FSE. 65% on FMPSPGR, 41% on conventional T2WI, and 41% on T1WI images. For tumors more than 5 mm in diameter, sensitivity was 88% on FMPSPGR, 65% on conventional T2WI, and 81% on T1WI images respectively. CNR of the tumor was 28.94 {+-} 21.6 on FSE, 13.57 {+-} 8.64 on FMPSPGR, 12.62 {+-} 10.65 on CSE T2WI, and 9.47 {+-} 8.05 on CSE T1WI images, which was significantly high on FSE(p<0.05). Fast spin echo T2WI shows highest sensitivity and tumor-to-liver contrast. FMPSPGR imaging is also favorably comparable with conventional T1WI. Therefore, these two pulse sequences can be useful in clinical condition for hepatic MR imaging.

  3. In-phase and out-of-phase gradient-echo imaging in abdominal studies: intra-individual comparison of three different techniques

    Energy Technology Data Exchange (ETDEWEB)

    Ramalho, Miguel; Heredia, Vasco; Campos, Rafael O. P. de; Azevedo, Rafael M.; Semelka, Richard C. (Dept. of Radiology, Univ. of North Carolina at Chapel Hill (United States)); Dale, Brian M. (Siemens Medical Systems, Morrisville (United States)), email: richsem@med.unc.edu

    2012-05-15

    Background: T1-weighted gradient-echo in-phase and out-of-phase imaging is an essential component of comprehensive abdominal MR exams. It is useful for the study of fat-containing lesions and to identify various disease states related to the presence of fat in the liver. Purpose: To compare three T1-weighted in-phase and out-of-phase (IP/OP) gradient-echo imaging sequences in an intra-individual fashion, and to determine whether advantages exist for each of these sequences for various patient types. Material and Methods: One hundred and eighteen consecutive subjects (74 men, 44 women; mean age 53.9 +- 13.8 years) who had MRI examinations containing all three different IP/OP sequences (two-dimensional spoiled gradient-echo [2D-GRE], three-dimensional gradient-echo [3D-GRE], and magnetization-prepared gradient-recall echo [MP-GRE]) were included. Two different reviewers independently and blindly qualitatively evaluated IP/OP sequences to determine image quality, extent of artifacts, lesion detectability and conspicuity, and subjective grading of liver steatosis for the various sequences. Quantitative analysis was also performed. Qualitative and quantitative data were subjected to statistical analysis. Results: Respiratory ghosting, parallel imaging, and truncation artifacts as well as shading and blurring were more pronounced with 3D-GRE IP/OP imaging. Overall image quality was higher with 2D-GRE (P < 0.05). Detectability of low-fluid content lesions was lower with IP/OP MP-GRE sequences. MP-GRE sequences had the lowest SNRs (P < 0.001). Liver-to-spleen and liver-to-lesion CNRs were significantly lower with 3D-GRE and MP-GR, respectively (P < 0.001). Fat liver indexes showed strongly positive correlation between all sequences. Conclusion: Currently, 2D-GRE remains the best approach for clinical IP/OP imaging. The good image quality of MP-GRE sequences acquired in a free-breathing manner should recommend its use in patients unable to suspend breathing

  4. In-phase and out-of-phase gradient-echo imaging in abdominal studies: intra-individual comparison of three different techniques

    International Nuclear Information System (INIS)

    Ramalho, Miguel; Heredia, Vasco; Campos, Rafael O. P. de; Azevedo, Rafael M.; Semelka, Richard C.; Dale, Brian M.

    2012-01-01

    Background: T1-weighted gradient-echo in-phase and out-of-phase imaging is an essential component of comprehensive abdominal MR exams. It is useful for the study of fat-containing lesions and to identify various disease states related to the presence of fat in the liver. Purpose: To compare three T1-weighted in-phase and out-of-phase (IP/OP) gradient-echo imaging sequences in an intra-individual fashion, and to determine whether advantages exist for each of these sequences for various patient types. Material and Methods: One hundred and eighteen consecutive subjects (74 men, 44 women; mean age 53.9 ± 13.8 years) who had MRI examinations containing all three different IP/OP sequences (two-dimensional spoiled gradient-echo [2D-GRE], three-dimensional gradient-echo [3D-GRE], and magnetization-prepared gradient-recall echo [MP-GRE]) were included. Two different reviewers independently and blindly qualitatively evaluated IP/OP sequences to determine image quality, extent of artifacts, lesion detectability and conspicuity, and subjective grading of liver steatosis for the various sequences. Quantitative analysis was also performed. Qualitative and quantitative data were subjected to statistical analysis. Results: Respiratory ghosting, parallel imaging, and truncation artifacts as well as shading and blurring were more pronounced with 3D-GRE IP/OP imaging. Overall image quality was higher with 2D-GRE (P < 0.05). Detectability of low-fluid content lesions was lower with IP/OP MP-GRE sequences. MP-GRE sequences had the lowest SNRs (P < 0.001). Liver-to-spleen and liver-to-lesion CNRs were significantly lower with 3D-GRE and MP-GR, respectively (P < 0.001). Fat liver indexes showed strongly positive correlation between all sequences. Conclusion: Currently, 2D-GRE remains the best approach for clinical IP/OP imaging. The good image quality of MP-GRE sequences acquired in a free-breathing manner should recommend its use in patients unable to suspend breathing

  5. Differentiation between grade 3 and grade 4 articular cartilage defects of the knee: Fat-suppressed proton density-weighted versus fat-suppressed three-dimensional gradient-echo MRI

    Energy Technology Data Exchange (ETDEWEB)

    Lee, So Yeon; Jee, Won-Hee; Kim, Sun Ki (Dept. of Radiology, Seoul St Mary' s Hospital, Catholic Univ. of Korea, Seoul (Korea)), e-mail: whjee@catholic.ac.kr; Koh, In-Jun (Dept. of Joint Reconstruction Center, Seoul National Univ. Bundang Hospital, Seoul (Korea)); Kim, Jung-Man (Dept. of Orthopedic Surgery, Seoul St Mary' s Hospital, Catholic Univ. of Korea, Seoul (Korea))

    2010-05-15

    Background: Fat-suppressed (FS) proton density (PD)-weighted magnetic resonance imaging (MRI) and FS three-dimensional (3D) gradient-echo imaging such as spoiled gradient-recalled (SPGR) sequence have been established as accurate methods for detecting articular cartilage defects. Purpose: To retrospectively compare the diagnostic efficacy between FS PD-weighted and FS 3D gradient-echo MRI for differentiating between grade 3 and grade 4 cartilage defects of the knee with arthroscopy as the standard of reference. Material and Methods: Twenty-one patients who had grade 3 or 4 cartilage defects in medial femoral condyle at arthroscopy and knee MRI were included in this study: grade 3, >50% cartilage defects; grade 4, full thickness cartilage defects exposed to the bone. Sagittal FS PD-weighted MR images and FS 3D gradient-echo images with 1.5 T MR images were independently graded for the cartilage abnormalities of medial femoral condyle by two musculoskeletal radiologists. Statistical analysis was performed by Fisher's exact test. Inter-observer agreement in grading of cartilage was assessed using ? coefficients. Results: Arthroscopy revealed grade 3 defects in 17 patients and grade 4 defects in 4 patients in medial femoral condyles. For FS 3D gradient-echo images grade 3 defects were graded as grade 3 (n=15) and grade 4 (n=2), and all grade 4 defects (n=4) were correctly graded. However, for FS PD-weighted MR images all grade 3 defects were misinterpreted as grade 1 (n=1) and grade 4 (n=16), whereas all grade 4 defects (n=4) were correctly graded. FS 3D gradient-echo MRI could differentiate grade 3 from grade 4 defects (P=0.003), whereas FS PD-weighted imaging could not (P=1.0). Inter-observer agreement was substantial (?=0.70) for grading of cartilage using FS PD-weighted imaging, whereas it was moderate (?=0.46) using FS 3D gradient-echo imaging. Conclusion: FS 3D gradient-echo MRI is more helpful for differentiating between grade 3 and grade 4 cartilage

  6. Clinical characteristics in normal healthy adults with microbleeds on echo-planar gradient-echo T2*-weighted MRI

    International Nuclear Information System (INIS)

    Takahashi, Wakoh; Ide, Michiru; Ohnuki, Tomohide; Takagi, Shigeharu; Shinohara, Yukito

    2004-01-01

    The gradient-echo T 2 * -weighted sequence in magnetic resonance imaging is known to be useful for detecting microbleeds (MBs) in patients with intracranial hemorrhage or lacunar stroke. We investigated the characteristics of apparently healthy adults with MBs but without stroke, employing echo-planar gradient-echo T 2 * -weighted MRI. The subjects were recruited from among 3,537 participants who underwent brain check-ups at the HIMEDIC Imaging Center. Of the 3,537 participants, 3,296 (mean age, 55±11 years) without any history of cerebrovascular disease or apparent focal neurological manifestations were selected for the present study. MBs on echo-planar gradient-echo T 2 * -weighted MRI were observed in 74 (2.2%) of the 3,296 subjects. Of a total of 133 lesions found in these 74 persons, 31 were located in the basal ganglia or cortico-subcortical regions. Thirty were in the deep white matter, 19 in the thalamus, 16 in the cerebellum, and 6 in the brain stem. The subjects with MBs were significantly older than the subjects without MBs, and the mean values for their systolic and diastolic blood pressures were higher than those in the subjects without MBs. Asymptomatic cerebral infarction, periventricular hyperintensity, and deep and subcortical white matter hyperintensity on T 1 - and T 2 -weighted MRI were more frequent in the subjects with MBs, as compared with those without MBs. Asymptomatic cerebral infarction, periventricular hyperintensity, and deep and subcortical white matter hyperintensity on T 1 - and T 2 -weighted MRI were more frequent in the subjects with MBs of the basal ganglia or thalamus than in those with MBs in other regions. MBs on echo-planar gradient-echo T 2 * -weighted MRI were thus relatively rare in apparently healthy adults. However, MBs in the basal ganglia or thalamus are suggested to be closely related to intracerebral microangiopathy. Persons with MBs in such regions should therefore be carefully checked for cerebrovascular risk

  7. Comparison between two.magnetic resonance sequences (spin-echo and gradient-echo) in the analysis of lesions of the knee joint meniscus

    International Nuclear Information System (INIS)

    Marti-Bonati, L.; Casillas, C.

    1999-01-01

    To compare the diagnostic reliability, the proportion of common diagnoses and the degree of agreement between the results of two magnetic resonance (MR) sequences in the diagnosis of lesions of the meniscus of the knee. One hundred consecutive patients were studied prospectively by MR (1,5 Teslas). All of them underwent T1-weighted spin-echo and T1 and T2-weighted gradient-echo sequences. The final diagnosis was based on the combined results of four imaging sequences. The sensitivity, specificity, positive predictive value (PPV) and negative predictive (NPV) in terms of the final diagnosis were calculated for each meniscus and MR technique. The chi.squared test and kappa test were employed for the statistical analysis. There were discrepancies between the final diagnosis and the spin-echo sequence in 4 cases and between the final diagnosis and the gradient-echo sequences in 5 Both spin-echo and gradient-echo sequences showed the same diagnostic reliabilities: sensitivity of 0.98, specificity of 0.99, PPV of 0.98 and NPV of 0.99. The correlation between the two sequences was highly significant (chi-squared, p < 0.001) with a very high rate of agreement (kappa=0.84). The two sequences can be considered equally reliable in the study of meniscal lesions. (Author) 7 refs

  8. A new technique for MR elastography of the supraspinatus muscle: A gradient-echo type multi-echo sequence.

    Science.gov (United States)

    Ito, Daiki; Numano, Tomokazu; Mizuhara, Kazuyuki; Takamoto, Koichi; Onishi, Takaaki; Nishijo, Hisao

    2016-10-01

    Magnetic resonance elastography (MRE) can measure tissue stiffness quantitatively and noninvasively. Supraspinatus muscle injury is a significant problem among throwing athletes. The purpose of this study was to develop an MRE technique for application to the supraspinatus muscle by using a conventional magnetic resonance imaging (MRI). MRE acquisitions were performed with a gradient-echo type multi-echo MR sequence at 100Hz pneumatic vibration. A custom-designed vibration pad was used as a pneumatic transducer in order to adapt to individual shoulder shapes. In a gradient-echo type multi-echo MR sequence, without motion encoding gradient (MEG) that synchronizes with vibrations, bipolar readout gradient lobes achieved a similar function to MEG (MEG-like effect). In other words, a dedicated MRE sequence (built-in MEG) is not always necessary for MRE. In this study, 7 healthy volunteers underwent MRE. We investigated the effects of direction of the MEG-like effect and selected imaging planes on the patterns of wave propagation (wave image). The results indicated that wave images showed clear wave propagation on a condition that the direction of the MEG-like effect was nearly perpendicular to the long axis of the supraspinatus muscle, and that the imaging plane was superior to the proximal supraspinatus muscle. This limited condition might be ascribed to specific features of fibers in the supraspinatus muscle and wave reflection from the boundaries of the supraspinous fossa. The mean stiffness of the supraspinatus muscle was 10.6±3.17kPa. Our results demonstrated that using MRE, our method can be applied to the supraspinatus muscle by using conventional MRI. Copyright © 2016 Elsevier Inc. All rights reserved.

  9. Diagnosis of partial and complete rotator cuff tears using combined gradient echo and spin echo imaging

    International Nuclear Information System (INIS)

    Tuite, M.J.; Yandow, D.R.; DeSmet, A.A.; Orwin, J.F.; Quintana, F.A.

    1994-01-01

    Most magnetic resonance (MR) studies evaluating the rotator cuff for tears have used T2-weighted imaging in the coronal oblique and sagittal oblique planes. T2 * -weighted gradient echo imaging, however, has advantages over spin echo imaging, including contiguous slices without cross-talk, high contrast around the cuff, and intrinsically shorter imaging times which can be used to increase the number of signals averaged and thus improve the signal-to-noise ratio. We reviewed the shoulder MR scans of 87 consecutive patients who underwent both a MR scan and a shoulder arthroscopy during which the size of tears, if present, was graded. The reviewers were blinded as to the history and arthroscopic results. The MR scans included oblique coronal T2 * -weighted gradient echo and oblique sagittal T2-weighted spin echo images. MR cuff grades were correlated with arthroscopic findings. For complete tears, the sensitivity of MR was 0.91 and the specificity 0.95. For partial tears, the sensitivity was 0.74 and the specificity 0.87. This accuracy is similar to two-plane T2-weighted imaging as previously reported in the literature. There was a statistically significant correlation (p < 0.0005) between the cuff grade as determined by MR and the arthroscopic findings. (orig.)

  10. Diagnosis of partial and complete rotator cuff tears using combined gradient echo and spin echo imaging

    Energy Technology Data Exchange (ETDEWEB)

    Tuite, M J [Dept. of Radiology, Univ. of Wisconsin, Madison, WI (United States); Yandow, D R [Dept. of Radiology, Univ. of Wisconsin, Madison, WI (United States); DeSmet, A A [Dept. of Radiology, Univ. of Wisconsin, Madison, WI (United States); Orwin, J F [Div. of Orthopedic Surgery, Univ. of Wisconsin, Madison, WI (United States); Quintana, F A [Dept. of Biostatistics, Univ. of Wisconsin, Madison, WI (United States)

    1994-10-01

    Most magnetic resonance (MR) studies evaluating the rotator cuff for tears have used T2-weighted imaging in the coronal oblique and sagittal oblique planes. T2{sup *}-weighted gradient echo imaging, however, has advantages over spin echo imaging, including contiguous slices without cross-talk, high contrast around the cuff, and intrinsically shorter imaging times which can be used to increase the number of signals averaged and thus improve the signal-to-noise ratio. We reviewed the shoulder MR scans of 87 consecutive patients who underwent both a MR scan and a shoulder arthroscopy during which the size of tears, if present, was graded. The reviewers were blinded as to the history and arthroscopic results. The MR scans included oblique coronal T2{sup *}-weighted gradient echo and oblique sagittal T2-weighted spin echo images. MR cuff grades were correlated with arthroscopic findings. For complete tears, the sensitivity of MR was 0.91 and the specificity 0.95. For partial tears, the sensitivity was 0.74 and the specificity 0.87. This accuracy is similar to two-plane T2-weighted imaging as previously reported in the literature. There was a statistically significant correlation (p < 0.0005) between the cuff grade as determined by MR and the arthroscopic findings. (orig.)

  11. Gradient-echo imaging of intervertebral disk degeneration and facet joint disease

    International Nuclear Information System (INIS)

    Berns, D.H.; Kormos, D.; Modic, M.T.; Carter, J.; Masaryk, T.J.; Ross, J.S.

    1988-01-01

    The purpose of this study was to evaluate the accuracy of gradient-echo, partial-flip angle images in the evaluation of components of degenerative spine disease. First, cadaveric spines were studied with plain radiographs, high-resolution CT, T1-weighted spin-echo (SE) MR images (repetition time msec/echo time msec=500/17). T2-weighted SE images (2,000/30-90), and fast low-angle shot (FLASH) images (200/10.50 0 ) before and after intradiskal injection of air (0.1-1cc). Second, lumbar spine MR images were retrospectively evaluated to compare gradient-echo and SE sequences. Results indicate that the signal intensity changes of the intervertebral disk related to degeneration were best appreciated on T2-weighted SE studies in both groups. Vacuum phenomenon and calcification were most accurately assessed with FLASH imaging (based on susceptibility changes) and CT images. SE images appeared more sensitive to adjacent marrow change. In the facet joints, CT was more accurate for changes in the subarticular bone, but FLASH images were more sensitive to change in the articular cartilage

  12. MR imaging of articular cartilage : comparison of magnetization transfer contrast and fat-suppression in multiplanar and 3D gradient-echo, spin-echo, turbo spin-echo techniques

    International Nuclear Information System (INIS)

    Lee, Young Joon; Joo, Eun Young; Eun, Choong Ki

    1999-01-01

    The purpose of this study was to evaluate the effects of magnetization transfer contrast(MTC) and fat-suppression(FS) in variable spin-echo and gradient-echo sequences for articular cartilage imaging and to determine the optimal pulse sequences. Using variable 7-pulse sequences, the knees of 15 pigs were imaged Axial images were obtained using proton density and T2-weighted spin-echo (PDWSE and T2WSE), turbo spin-echo (TSE), multiplanar gradient-echo (MPGR), and 3D steady-state gradient-echo (3DGRE) sequences, and the same pulse sequences were then repeated using MTC. Also T1-weighted spin-echo(T1WSE) and 3D spoiled gradient-echo(3DSPGR) images of knees were also acquired, and the procedure was repeated using FS. For each knee, a total of 14 axial images were acquired, and using a 6-band scoring system, the visibility of and the visibilities of the the articular cartilage was analyzed. The visual effect of MTC and FS was scored using a 4-band scale. For each image, the signal intensities of articular cartilage, subchondral bone, muscles, and saline were measured, and signal-to-noise ratios(SNR) and contrast-to-noise ratios(CNR) were also calculated. Visibility of the cartilage was best when 3DSPGR and T1WSE sequences were used. MTC imaging increased the negative contrast between cartilage and saline, but FS imaging provided more positive contrast. CNR between cartilage and saline was highest when using TSE with FS(-351.1±15.3), though CNR between cartilage and bone then fell to -14.7±10.8. In MTC imaging using MPGR showed the greatest increase of negative contrast between cartilage and saline(CNR change=-74.7); the next highest was when 3DGRE was used(CNR change=-34.3). CNR between cartilage and bone was highest with MPGR(161.9±17.7), but with MTC, the greatest CNR decrease(-81.8) was observed. The greatest CNR increase between cartilage and bone was noted in T1WSE with FS. In all scans, FS provided a cartilage-only positive contrast image, though the absolute

  13. A short TE gradient-echo sequence using asymmetric sampling

    International Nuclear Information System (INIS)

    Fujita, Norihiko; Harada, Kohshi; Sakurai, Kosuke; Nakanishi, Katsuyuki; Kim, Shyogen; Kozuka, Takahiro

    1990-01-01

    We have developed a gradient-echo pulse sequence with a short TE less than 4 msec using a data set of asymmetric off-center sampling with a broad bandwidth. The use of such a short TE significantly reduces T 2 * dephasing effect even in a two-dimensional mode, and by collecting an off-center echo, motion-induced phase dispersion is also considerably decreased. High immunity of this sequence to these dephasing effects permits clear visualization of anatomical details near the skull base where large local field inhomogeneities and rapid blood flow such as in the internal carotid artery are present. (author)

  14. Liver Lobe Based Multi-Echo Gradient Recalled Echo T2*-Weighted Imaging in Chronic Hepatitis B-Related Cirrhosis: Association with the Presence and Child-Pugh Class of Cirrhosis.

    Directory of Open Access Journals (Sweden)

    Dan Wang

    Full Text Available To investigate whether liver lobe based T2* values measured on gradient recalled echo T2*-weighted imaging are associated with the presence and Child-Pugh class of hepatitis B-related cirrhosis.Fifty-six patients with hepatitis B-related cirrhosis and 23 healthy control individuals were enrolled in this study and underwent upper abdominal T2*-weighted magnetic resonance imaging. T2* values of the left lateral lobe (LLL, left medial lobe (LML, right lobe (RL and caudate lobe (CL were measured on T2*-weighted imaging. Statistical analyses were performed to determine the association between liver lobe based T2* values and the presence and Child-Pugh class of cirrhosis.The T2* values of the LLL, LML and RL decreased with the progression of cirrhosis from Child-Pugh class A to C (r = -0.231, -0.223, and -0.395, respectively; all P 0.05. To a certain extent, Mann-Whitney U tests with Bonferroni correction for multigroup comparisons showed that the T2* values of the LLL, LML and RL could distinguish cirrhotic liver from healthy liver (all P 0.05. Receiver operating characteristic analysis demonstrated that the T2* value of the RL could best distinguish cirrhosis from healthy liver, with an area under the receiver operating characteristic curve (AUC of 0.713 among T2* values of the liver lobes, and that only the T2* value of the RL could distinguish Child-Pugh class C from A-B, with an AUC of 0.697 (all P < 0.05.The T2* value of the RL can be associated with the presence and Child-Pugh class of hepatitis B-related cirrhosis.

  15. Diuretic-enhanced gadolinium excretory MR urography: comparison of conventional gradient-echo sequences and echo-planar imaging

    Energy Technology Data Exchange (ETDEWEB)

    Nolte-Ernsting, C.C.A.; Tacke, J.; Adam, G.B.; Haage, P.; Guenther, R.W. [Univ. of Technology, Aachen (Germany). Dept. of Diagnostic Radiology; Jung, P.; Jakse, G. [Univ. of Technology, Aachen (Germany). Dept. of Urology

    2001-01-01

    The aim of this study was to investigate the utility of different gadolinium-enhanced T1-weighted gradient-echo techniques in excretory MR urography. In 74 urologic patients, excretory MR urography was performed using various T1-weighted gradient-echo (GRE) sequences after injection of gadolinium-DTPA and low-dose furosemide. The examinations included conventional GRE sequences and echo-planar imaging (GRE EPI), both obtained with 3D data sets and 2D projection images. Breath-hold acquisition was used primarily. In 20 of 74 examinations, we compared breath-hold imaging with respiratory gating. Breath-hold imaging was significantly superior to respiratory gating for the visualization of pelvicaliceal systems, but not for the ureters. Complete MR urograms were obtained within 14-20 s using 3D GRE EPI sequences and in 20-30 s with conventional 3D GRE sequences. Ghost artefacts caused by ureteral peristalsis often occurred with conventional 3D GRE imaging and were almost completely suppressed in EPI sequences (p < 0.0001). Susceptibility effects were more pronounced on GRE EPI MR urograms and calculi measured 0.8-21.7% greater in diameter compared with conventional GRE sequences. Increased spatial resolution degraded the image quality only in GRE-EPI urograms. (orig.)

  16. Spin-echo Echo-planar Imaging MR Elastography versus Gradient-echo MR Elastography for Assessment of Liver Stiffness in Children and Young Adults Suspected of Having Liver Disease.

    Science.gov (United States)

    Serai, Suraj D; Dillman, Jonathan R; Trout, Andrew T

    2017-03-01

    Purpose To compare two-dimensional (2D) gradient-recalled echo (GRE) and 2D spin-echo (SE) echo-planar imaging (EPI) magnetic resonance (MR) elastography for measurement of hepatic stiffness in pediatric and young adult patients suspected of having liver disease. Materials and Methods In this institutional review board-approved, HIPAA-compliant study, 58 patients underwent both 2D GRE and 2D SE-EPI MR elastography at 1.5 T during separate breath holds. Liver stiffness (mean of means; in kilopascals) was measured by five blinded reviewers. Pooled mean liver stiffness and region-of-interest (ROI) size were compared by using paired t tests. Intraclass correlation coefficients (ICCs) were used to assess agreement between techniques. Respiratory motion artifacts were compared across sequences by using the Fisher exact test. Results Mean patient age was 14.7 years ± 5.2 (standard deviation; age range, 0.7-20.5 years), and 55.2% (32 of 58) of patients were male. Mean liver stiffness was 2.92 kPa ± 1.29 measured at GRE MR elastography and 2.76 kPa ± 1.39 at SE-EPI MR elastography (n = 290; P = .15). Mean ROI sizes were 8495 mm 2 ± 4482 for 2D GRE MR elastography and 15 176 mm 2 ± 7609 for 2D SE-EPI MR elastography (n = 290; P range, 0.91-0.95). Moderate or severe breathing artifacts were observed on 27.5% (16 of 58) of 2D GRE images versus 0% 2D SE-EPI images (P < .001). Conclusion There is excellent agreement on measured hepatic stiffness between 2D GRE and 2D SE-EPI MR elastography across multiple reviewers. SE-EPI MR elastography allowed for stiffness measurement across larger areas of the liver and can be performed in a single breath hold. © RSNA, 2016.

  17. Whole brain, high resolution multiband spin-echo EPI fMRI at 7 T: A comparison with gradient-echo EPI using a color-word Stroop task

    NARCIS (Netherlands)

    Boyacioglu, R.; Schulz, J.; Müller, N.C.J.; Koopmans, P.J.; Barth, M.; Norris, David Gordon

    2014-01-01

    A whole brain, multiband spin-echo (SE) echo planar imaging (EPI) sequence employing a high spatial (1.5 mm isotropic) and temporal (TR of 2 s) resolution was implemented at 7 T. Its overall performance (tSNR, sensitivity and CNR) was assessed and compared to a geometrically matched gradient-echo

  18. Myocardial viability: comparison of free-breathing navigator-echo-gated three-dimensional inversion-recovery gradient-echo MR and standard multiple breath-hold two-dimensional inversion-recovery gradient-echo MR

    International Nuclear Information System (INIS)

    Kim, Jin Hee; Seo, Joon Beom; Do, Kyung Hyun; Yang, Dong Hyun; Lee, Soo Hyun; Ko, Sung Min; Heo, Jeong Nam; Lim, Tae Hwan

    2004-01-01

    To compare a free-breathing, navigator-echo-gated, three-dimensional, inversion-recovery, gradient-echo, MR pulse sequence (3D-MRI) with standard, multiple breath-hold, two-dimensional, inversion-recovery, gradient-echo MR (2D-MRI) for the evaluation of delayed hyperenhancement of nonviable myocardium in patients with chronic ischemic heart disease. Ten patients with chronic ischemic heart disease were enrolled in this study. MRI was performed on a 1.5-T system. 3D-MRI was obtained in the short axis plane at 10 minutes after the administration of Gd-DTPA (0.2 mmol/kg, 4 cc/sec). Prospective gating of the acquisition based on the navigator echo was applied. 2D-MRI was performed immediately after finishing 3D-MRI. The area of total and hyperenhanced myocardium measured on both image sets was compared with paired Student t-test and Bland-Altman method. By using a 60-segment model, the transmural extent and segment width of the hyperenhanced area were recorded by 3-scale grading method. The agreement between the two sequences was evaluated with kappa statistics. We also evaluated the agreement of hyperenhancement among the three portions (apical, middle and basal portion) of the left ventricle with kappa statistics. The two sequences showed good agreement for the measured area of total and hyperenhanced myocardium on paired t-test (ρ = 0.11 and ρ = 0.34, respectively). No systematic bias was shown on Bland-Altman analysis. Good agreement was found for the segmental width (Κ = 0.674) and transmural extent (Κ = 0.615) of hyperenhancement on the segmented analysis. However, the agreement of the transmural extent of hyperenhancement in the apical segments was relatively poor compared with that in the middle or basal portions. This study showed good agreement between 3D-MRI and 2D-MRI in evaluation of non-viable myocardium. Therefore, 3D-MRI may be useful in the assessment of myocardial viability in patients with dyspnea and children because it allows free

  19. Fast-gradient-echo variable-flip-angle imaging of the cervical spine

    International Nuclear Information System (INIS)

    Van Dyke, C.W.; Ross, J.S.; Masaryk, T.J.; Tkach, J.; Beale, S.; Hueftle, M.G.; Kaufman, B.; Modic, M.T.

    1987-01-01

    Two hundred consecutive patients were studied with 4-mm sagittal and axial T1-weighted images and gradient echo sequences with 6-msec or 13-msec echo time (TE) and 10 0 or 60 0 flip angles to evaluate cervical extradural disease. Images were independently evaluated for contrast behavior and anatomy, then directly compared for conspicuity of lesions. FLASH sequences produced better conspicuity of disease in half the imaging time. T1-weighted spin-echo (SE) sequences were more sensitive to marrow changes and intradural disease. Shorter TEs produced overall image improvement and reduced susceptibility effects. A fast and sensitive cervical examination combines sagittal T1-weighted SE with sagittal and axial FLASH 10 0 sequences with 6-msec TE

  20. Cardiac T2-mapping using a fast gradient echo spin echo sequence - first in vitro and in vivo experience

    OpenAIRE

    Baessler, Bettina; Schaarschmidt, Frank; Stehning, Christian; Schnackenburg, Bernhard; Maintz, David; Bunck, Alexander C.

    2015-01-01

    Background: The aim of this study was the evaluation of a fast Gradient Spin Echo Technique (GraSE) for cardiac T2-mapping, combining a robust estimation of T2 relaxation times with short acquisition times. The sequence was compared against two previously introduced T2-mapping techniques in a phantom and in vivo. Methods: Phantom experiments were performed at 1.5 T using a commercially available cylindrical gel phantom. Three different T2-mapping techniques were compared: a Multi Echo Spin Ec...

  1. Direct magnetic field estimation based on echo planar raw data.

    Science.gov (United States)

    Testud, Frederik; Splitthoff, Daniel Nicolas; Speck, Oliver; Hennig, Jürgen; Zaitsev, Maxim

    2010-07-01

    Gradient recalled echo echo planar imaging is widely used in functional magnetic resonance imaging. The fast data acquisition is, however, very sensitive to field inhomogeneities which manifest themselves as artifacts in the images. Typically used correction methods have the common deficit that the data for the correction are acquired only once at the beginning of the experiment, assuming the field inhomogeneity distribution B(0) does not change over the course of the experiment. In this paper, methods to extract the magnetic field distribution from the acquired k-space data or from the reconstructed phase image of a gradient echo planar sequence are compared and extended. A common derivation for the presented approaches provides a solid theoretical basis, enables a fair comparison and demonstrates the equivalence of the k-space and the image phase based approaches. The image phase analysis is extended here to calculate the local gradient in the readout direction and improvements are introduced to the echo shift analysis, referred to here as "k-space filtering analysis." The described methods are compared to experimentally acquired B(0) maps in phantoms and in vivo. The k-space filtering analysis presented in this work demonstrated to be the most sensitive method to detect field inhomogeneities.

  2. Spin echoes of nuclear magnetization diffusing in a constant magnetic field gradient and in a restricted geometry

    International Nuclear Information System (INIS)

    Sen, P.N.; Andre, A.; Axelrod, S.

    1999-01-01

    We study the influence of restriction on Carr - Purcell - Meiboom - Gill spin echoes response of magnetization of spins diffusing in a bounded region in the presence of a constant magnetic field gradient. Depending on three main length scales: L S pore size, L G dephasing length and L D diffusion length during half-echo time, three main regimes of decay have been identified: free, localization and motionally averaging regime. In localization regime, the decay exponent depends on a fractional power (2/3) of the gradient, denoting a strong breakdown of the second cumulant or the Gaussian phase approximation (GPA). In the other two regimes, the exponent depends on the gradient squared, and the GPA holds. We find that the transition from the localization to the motionally averaging regime happens when the magnetic field gradients approach special values, corresponding to branch points of the eigenvalues. Transition from one regime to another as a function of echo number for a certain range of parameters is discussed. In this transition region, the signal shows large oscillations with echo number. For large n, asymptotic behavior sets in as a function of n for the decay exponent per echo. This is true for all values of the parameters L S , L G , and L D . copyright 1999 American Institute of Physics

  3. Short echo time proton spectroscopy of the brain in healthy volunteers using an insert gradient head coil

    DEFF Research Database (Denmark)

    Gideon, P; Danielsen, E R; Schneider, M

    1995-01-01

    An insert gradient head coil with built-in X, Y, and Z gradients was used for localized proton spectroscopy in the brain of healthy volunteers, using short echo time stimulated echo acquisition mode (STEAM) sequences. Volume of interest size was 3.4 ml, repetition time was 6.0 s, and echo times...... were 10 and 20 ms, respectively. Good quality proton spectra with practically no eddy current artefacts were acquired allowing observation of strongly coupled compounds, and compounds with short T2 relaxation times. The gradient head coil thus permits further studies of compounds such as glutamine....../glutamate and myo-inositols. These compounds were more prominent within grey matter than within white matter. Rough estimations of metabolite concentrations using water as an internal standard were in good agreement with previous reports....

  4. Importance of T2*-weighted gradient-echo MRI for diagnosis of cortical vein thrombosis

    Energy Technology Data Exchange (ETDEWEB)

    Fellner, Franz A. [Institut fuer Radiologie, Landes-Nervenklinik Wagner Jauregg, Linz (Austria) and Zentrales Radiologie Institut, Allgemeines Krankenhaus der Stadt Linz, Krankenhausstr. 9, 4020 Linz (Austria)]. E-mail: franz.fellner@akh.linz.at; Fellner, Claudia [Institut fuer Radiologie, Landes-Nervenklinik Wagner Jauregg, Linz (Austria); Aichner, Franz T. [Abteilung fuer Neurologie, Landes-Nervenklinik Wagner-Jauregg, Linz (Austria); Moelzer, Guenther [Institut fuer Radiologie, Landes-Nervenklinik Wagner Jauregg, Linz (Austria)

    2005-11-01

    We examined six patients with isolated venous thrombosis (n = 2), or venous thrombosis combined with sinus thrombosis (n = 4) (CVT). The clinical symptoms were non-specific (acute cephalea, paresis, epileptic seizure, progressive speech disorder). All examinations were performed on a 1.5 T system (Magnetom Symphony, Siemens, Erlangen, Germany), maximum gradient field strength 30 mT/m, minimal gradient rise time 450 {mu}s, according to the following protocol: Transverse T2-weighted turbo spin-echo (TSE), fluid attenuated inversion recovery (FLAIR), T1-weighted spin-echo (SE), before and after administration of contrast medium, T2*-weighted conventional gradient-echo (GRE), T2*-weighted spin-echo echo planar imaging (SE EPI), both without and with diffusion weighting as well as two-dimensional (2D) venous time-of-flight (TOF) MRA. The venous thromboses were best detectable in the T2*-weighted conventional GRE sequence in all patients. In two patients, the CVT was discernible only in this sequence. The sinus thrombosis was well discernible only in the T2*-weighted GRE sequence in only one case; in the remaining cases it was detectable only with difficulty. For these cases, other sequences such as SE, diffusion-weighted, or 2D-TOF-MRA sequence were superior. The T2*-weighted conventional GRE sequence was superior to the T2*-weighted SE EPI sequence in all patients. To sum up, it can be concluded, that T2*-weighted conventional GRE sequences are possibly the best method of detection of acute cortical vein thromboses. Therefore, it seems to be of benefit to integrate a T2*-weighted conventional GRE sequence into the MR-protocol for the diagnosis of isolated cortical vein thrombosis.

  5. Importance of T2*-weighted gradient-echo MRI for diagnosis of cortical vein thrombosis

    International Nuclear Information System (INIS)

    Fellner, Franz A.; Fellner, Claudia; Aichner, Franz T.; Moelzer, Guenther

    2005-01-01

    We examined six patients with isolated venous thrombosis (n = 2), or venous thrombosis combined with sinus thrombosis (n = 4) (CVT). The clinical symptoms were non-specific (acute cephalea, paresis, epileptic seizure, progressive speech disorder). All examinations were performed on a 1.5 T system (Magnetom Symphony, Siemens, Erlangen, Germany), maximum gradient field strength 30 mT/m, minimal gradient rise time 450 μs, according to the following protocol: Transverse T2-weighted turbo spin-echo (TSE), fluid attenuated inversion recovery (FLAIR), T1-weighted spin-echo (SE), before and after administration of contrast medium, T2*-weighted conventional gradient-echo (GRE), T2*-weighted spin-echo echo planar imaging (SE EPI), both without and with diffusion weighting as well as two-dimensional (2D) venous time-of-flight (TOF) MRA. The venous thromboses were best detectable in the T2*-weighted conventional GRE sequence in all patients. In two patients, the CVT was discernible only in this sequence. The sinus thrombosis was well discernible only in the T2*-weighted GRE sequence in only one case; in the remaining cases it was detectable only with difficulty. For these cases, other sequences such as SE, diffusion-weighted, or 2D-TOF-MRA sequence were superior. The T2*-weighted conventional GRE sequence was superior to the T2*-weighted SE EPI sequence in all patients. To sum up, it can be concluded, that T2*-weighted conventional GRE sequences are possibly the best method of detection of acute cortical vein thromboses. Therefore, it seems to be of benefit to integrate a T2*-weighted conventional GRE sequence into the MR-protocol for the diagnosis of isolated cortical vein thrombosis

  6. Correction of inhomogeneous RF field using multiple SPGR signals for high-field spin-echo MRI

    International Nuclear Information System (INIS)

    Ishimori, Yoshiyuki; Monma, Masahiko; Yamada, Kazuhiro; Kimura, Hirohiko; Uematsu, Hidemasa; Fujiwara, Yasuhiro; Yamaguchi, Isao

    2007-01-01

    The purpose of this study was to propose a simple and useful method for correcting nonuniformity of high-field (3 Tesla) T 1 -weighted spin-echo (SE) images based on a B1 field map estimated from gradient recalled echo (GRE) signals. The method of this study was to estimate B1 inhomogeneity, spoiled gradient recalled echo (SPGR) images were collected using a fixed repetition time of 70 ms, flip angles of 45 and 90 degrees, and echo times of 4.8 and 10.4 ms. Selection of flip angles was based on the observation that the relative intensity changes in SPGR signals were very similar among different tissues at larger flip angles than the Ernst angle. Accordingly, spatial irregularity that was observed on a signal ratio map of the SPGR images acquired with these 2 flip angles was ascribed to inhomogeneity of the B1 field. Dual echo time was used to eliminate T 2 * effects. The ratio map that was acquired was scaled to provide an intensity correction map for SE images. Both phantom and volunteer studies were performed using a 3T magnetic resonance scanner to validate the method. In the phantom study, the uniformity of the T 1 -weighted SE image improved by 23%. Images of human heads also showed practically sufficient improvement in the image uniformity. The present method improves the image uniformity of high-field T 1 -weighted SE images. (author)

  7. High incidence of microbleeds in hemodialysis patients detected by T2*-weighted gradient-echo magnetic resonance imaging

    International Nuclear Information System (INIS)

    Yokoyama, Shunichi; Uomizu, Kenji; Kajiya, Yoriko; Tajitsu, Kenichiro; Kusumoto, Kazuhiro; Hirano, Hirofumi

    2005-01-01

    The incidence and characteristics of microbleeds in hemodialysis (HD) patients were investigated to elucidate the clinical significance with T 2 * -weighted gradient-echo magnetic resonance (MR) imaging. The 57 patients with chronic renal failure maintained by HD had no previous history of stroke. The control group consisted of 53 patients without previous history of stroke or chronic renal failure. The incidence and the number of microbleeds were assessed in the HD and control groups. The findings of microbleeds with T 2 * -weighted gradient-echo MR imaging were compared with those of T 1 - and T 2 -weighted MR imaging in HD patients. The incidence of microbleeds was significantly greater in the HD patients compared with the control patients. T 2 * -weighted gradient-echo imaging revealed a total of 44 microbleeds in 11 HD patients. T 2 -weighted imaging demonstrated 13 of 44 microbleeds as hyperintensity, whereas T 1 -weighted imaging demonstrated 12 lesions as hypointensity. T 2 - and T 1 -weighted imagings did not demonstrate any findings in 31 and 32 lesions, respectively. T 2 * -weighted gradient-echo MR imaging is effective to detect microbleeds which may be a predictor of intracerebral hemorrhage in HD patients and should be included in the protocol for the study of cerebrovascular disease, because T 2 - and T 1 -weighted MR imaging recognizes microbleeds as lacunar infarction. (author)

  8. Inaudible functional MRI using a truly mute gradient echo sequence

    International Nuclear Information System (INIS)

    Marcar, V.L.; Girard, F.; Rinkel, Y.; Schneider, J.F.; Martin, E.

    2002-01-01

    We performed functional MRI experiments using a mute version of a gradient echo sequence on adult volunteers using either a simple visual stimulus (flicker goggles: 4 subjects) or an auditory stimulus (music: 4 subjects). Because the mute sequence delivers fewer images per unit time than a fast echo planar imaging (EPI) sequence, we explored our data using a parametric ANOVA test and a non-parametric Wilcoxon-Mann-Whitney test in addition to performing a cross-correlation analysis. All three methods were in close agreement regarding the location of the BOLD contrast signal change. We demonstrated that, using appropriate statistical analysis, functional MRI using an MR sequence that is acoustically inaudible to the subject is feasible. Furthermore compared with the ''silent'' event-related procedures involving an EPI protocol, our mGE protocol compares favourably with respect to experiment time and the BOLD signal. (orig.)

  9. Exact algebraization of the signal equation of spoiled gradient echo MRI

    Energy Technology Data Exchange (ETDEWEB)

    Dathe, Henning [Department of Orthodontics, Biomechanics Group, University Medical Centre, Goettingen (Germany); Helms, Gunther, E-mail: ghelms@gwdg.d [MR-Research in Neurology and Psychiatry, University Medical Centre, Goettingen (Germany)

    2010-08-07

    The Ernst equation for Fourier transform nuclear magnetic resonance (MR) describes the spoiled steady-state signal created by periodic partial excitation. In MR imaging (MRI), it is commonly applied to spoiled gradient-echo acquisition in the steady state, created by a small flip angle {alpha} at a repetition time TR much shorter than the longitudinal relaxation time T{sub 1}. We describe two parameter transformations of {alpha} and TR/T{sub 1}, which render the Ernst equation as a low-order rational function. Computer algebra can be readily applied for analytically solving protocol optimization, as shown for the dual flip angle experiment. These transformations are based on the half-angle tangent substitution and its hyperbolic analogue. They are monotonic and approach identity for small {alpha} and small TR/T{sub 1} with a third-order error. Thus, the exact algebraization can be readily applied to fast gradient echo MRI to yield a rational approximation in {alpha} and TR/T{sub 1}. This reveals a fundamental relationship between the square of the flip angle and TR/T{sub 1} which characterizes the Ernst angle, constant degree of T{sub 1}-weighting and the influence of the local radio-frequency field.

  10. Prognostic value of gradient echo T2* sequences for brain MR imaging in preterm infants

    Energy Technology Data Exchange (ETDEWEB)

    Bruine, Francisca T. de; Berg-Huysmans, Annette A. van den; Buchem, Mark A. van; Grond, Jeroen van der [Leiden University Medical Center, Department of Radiology, PO Box 9600, Leiden (Netherlands); Steggerda, Sylke J.; Leijser, Lara M.; Rijken, Monique [Leiden University Medical Center, Department of Pediatrics, subdivision of Neonatology, Leiden (Netherlands); Wezel-Meijler, Gerda van [Leiden University Medical Center, Department of Pediatrics, subdivision of Neonatology, Leiden (Netherlands); Isala Hospital, Department of Neonatology, Zwolle (Netherlands)

    2014-03-15

    Gradient echo T2*-W sequences are more sensitive than T2-W spin-echo sequences for detecting hemorrhages in the brain. The aim of this study is to correlate presence of hemosiderin deposits in the brain of very preterm infants (gestational age <32 weeks) detected by T2*-W gradient echo MRI to white matter injury and neurodevelopmental outcome at 2 years. In 101 preterm infants, presence and location of hemosiderin were assessed on T2*-W gradient echo MRI performed around term-equivalent age (range: 40-60 weeks). White matter injury was defined as the presence of >6 non-hemorrhagic punctate white matter lesions (PWML), cysts and/or ventricular dilatation. Six infants with post-hemorrhagic ventricular dilatation detected by US in the neonatal period were excluded. Infants were seen for follow-up at 2 years. Univariate and regression analysis assessed the relation between presence and location of hemosiderin, white matter injury and neurodevelopmental outcome. In 38/95 (40%) of the infants, hemosiderin was detected. Twenty percent (19/95) of the infants were lost to follow-up. There was a correlation between hemosiderin in the ventricular wall with >6 PWML (P < 0.001) and cysts (P < 0.001) at term-equivalent age, and with a lower psychomotor development index (PDI) (P=0.02) at 2 years. After correcting for known confounders (gestational age, gender, intrauterine growth retardation and white matter injury), the correlation with PDI was no longer significant. The clinical importance of detecting small hemosiderin deposits is limited as there is no independent association with neurodevelopmental outcome. (orig.)

  11. Imaging of the brain using the fast-spin-echo and gradient-spin-echo techniques

    International Nuclear Information System (INIS)

    Umek, W.; Ba-Ssalamah, A.; Prokesch, R.; Mallek, R.; Heimberger, K.; Hittmair, K.

    1998-01-01

    The aim of our study was to compare gradient-spin-echo (GRASE) to fast-spin-echo (FSE) sequences for fast T2-weighted MR imaging of the brain. Thirty-one patients with high-signal-intensity lesions on T2-weighted images were examined on a 1.5-T MR system. The FSE and GRASE sequences with identical sequence parameters were obtained and compared side by side. Image assessment criteria included lesion conspicuity, contrast between different types of normal tissue, and image artifacts. In addition, signal-to-noise, contrast-to-noise, and contrast ratios and were determined. The FSE technique demonstrated more lesions than GRASE and with generally better conspicuity. Smaller lesions in particular were better demonstrated on FSE because of lower image noise and slightly weaker image artifacts. Gray-white differentiation was better on FSE. Ferritin and hemosiderin depositions appeared darker on GRASE, which resulted in better contrast. Fatty tissue was less bright on GRASE. With current standard hardware equipment, the FSE technique seems preferable to GRASE for fast T2-weighted routine MR imaging of the brain. For the assessment of hemosiderin or ferritin depositions, GRASE might be considered. (orig.)

  12. Inaudible functional MRI using a truly mute gradient echo sequence

    Energy Technology Data Exchange (ETDEWEB)

    Marcar, V.L. [University of Zurich, Department of Psychology, Neuropsychology, Treichlerstrasse 10, 8032 Zurich (Switzerland); Girard, F. [GE Medical Systems SA, 283, rue de la Miniere B.P. 34, 78533 Buc Cedex (France); Rinkel, Y.; Schneider, J.F.; Martin, E. [University Children' s Hospital, Neuroradiology and Magnetic Resonance, Department of Diagnostic Imaging, Steinwiesstrasse 75, 8032 Zurich (Switzerland)

    2002-11-01

    We performed functional MRI experiments using a mute version of a gradient echo sequence on adult volunteers using either a simple visual stimulus (flicker goggles: 4 subjects) or an auditory stimulus (music: 4 subjects). Because the mute sequence delivers fewer images per unit time than a fast echo planar imaging (EPI) sequence, we explored our data using a parametric ANOVA test and a non-parametric Wilcoxon-Mann-Whitney test in addition to performing a cross-correlation analysis. All three methods were in close agreement regarding the location of the BOLD contrast signal change. We demonstrated that, using appropriate statistical analysis, functional MRI using an MR sequence that is acoustically inaudible to the subject is feasible. Furthermore compared with the ''silent'' event-related procedures involving an EPI protocol, our mGE protocol compares favourably with respect to experiment time and the BOLD signal. (orig.)

  13. Characterization of anomalous relaxation using the time-fractional Bloch equation and multiple echo T2 *-weighted magnetic resonance imaging at 7 T.

    Science.gov (United States)

    Qin, Shanlin; Liu, Fawang; Turner, Ian W; Yu, Qiang; Yang, Qianqian; Vegh, Viktor

    2017-04-01

    To study the utility of fractional calculus in modeling gradient-recalled echo MRI signal decay in the normal human brain. We solved analytically the extended time-fractional Bloch equations resulting in five model parameters, namely, the amplitude, relaxation rate, order of the time-fractional derivative, frequency shift, and constant offset. Voxel-level temporal fitting of the MRI signal was performed using the classical monoexponential model, a previously developed anomalous relaxation model, and using our extended time-fractional relaxation model. Nine brain regions segmented from multiple echo gradient-recalled echo 7 Tesla MRI data acquired from five participants were then used to investigate the characteristics of the extended time-fractional model parameters. We found that the extended time-fractional model is able to fit the experimental data with smaller mean squared error than the classical monoexponential relaxation model and the anomalous relaxation model, which do not account for frequency shift. We were able to fit multiple echo time MRI data with high accuracy using the developed model. Parameters of the model likely capture information on microstructural and susceptibility-induced changes in the human brain. Magn Reson Med 77:1485-1494, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  14. MRI of the breast with 2D spin-echo and gradient echo sequences in diagnostically difficult cases

    International Nuclear Information System (INIS)

    Allgayer, B.; Lukas, P.; Loos, W.; Kersting-Sommerhoff, B.

    1993-01-01

    One or both breasts of 296 patients with equivocal clinical or mammographical findings were examined with MRI. T 1 weighted spinecho (SE) and gradient echo (FFE) sequences were acquired before and after i.v. application of Gadolinium DTPA. 50 lesions with enhancement after Gd-DTPA were biopsied -26 carcinomas, 17 proliferating mastopathic tissues, 5 fibroadenomas and 1 abscess were found. Contrast enhanced MRI with 2D-SE and FFE sequences is an effective technqiue for evaluating suspicious breast lesions with high diagnostic acurracy. (orig.) [de

  15. Self-calibrated multiple-echo acquisition with radial trajectories using the conjugate gradient method (SMART-CG).

    Science.gov (United States)

    Jung, Youngkyoo; Samsonov, Alexey A; Bydder, Mark; Block, Walter F

    2011-04-01

    To remove phase inconsistencies between multiple echoes, an algorithm using a radial acquisition to provide inherent phase and magnitude information for self correction was developed. The information also allows simultaneous support for parallel imaging for multiple coil acquisitions. Without a separate field map acquisition, a phase estimate from each echo in multiple echo train was generated. When using a multiple channel coil, magnitude and phase estimates from each echo provide in vivo coil sensitivities. An algorithm based on the conjugate gradient method uses these estimates to simultaneously remove phase inconsistencies between echoes, and in the case of multiple coil acquisition, simultaneously provides parallel imaging benefits. The algorithm is demonstrated on single channel, multiple channel, and undersampled data. Substantial image quality improvements were demonstrated. Signal dropouts were completely removed and undersampling artifacts were well suppressed. The suggested algorithm is able to remove phase cancellation and undersampling artifacts simultaneously and to improve image quality of multiecho radial imaging, the important technique for fast three-dimensional MRI data acquisition. Copyright © 2011 Wiley-Liss, Inc.

  16. In vivo quantitative NMR imaging of fruit tissues during growth using Spoiled Gradient Echo sequence

    DEFF Research Database (Denmark)

    Kenouche, S.; Perrier, M.; Bertin, N.

    2014-01-01

    of this study was to design a robust and accurate quantitative measurement method based on NMR imaging combined with contrast agent (CA) for mapping and quantifying water transport in growing cherry tomato fruits. A multiple flip-angle Spoiled Gradient Echo (SGE) imaging sequence was used to evaluate...

  17. Usefulness of enhanced breathhold 3D spoiled gradient-echo MRA for intrathoracic mass

    International Nuclear Information System (INIS)

    Kobayashi, Takeshi; Kadoya, Masumi; Kamimura, Ryoichi; Takashima, Tsutomu

    1999-01-01

    Enhanced Breathhold 3D Spoiled Gradient-echo MRA was very attractive method for not only evaluating relationship between intrathoracic mass and intrathoracic vessels, but also visualizing small pulmonary vessels that could not be detected conventional MRA methods. Moreover, this methods could be applied for evaluating vascularity of the lesions. This method will be accepted as routine pulse sequence for evaluating intrathoracic mass especially malignant tumors. (author)

  18. MR contrast of ferritin and hemosiderin in the brain: comparison among gradient-echo, conventional spin-echo and fast spin-echo sequences

    Energy Technology Data Exchange (ETDEWEB)

    Haque, Tabassum Laz; Miki, Yukio; Kanagaki, Mitsunori; Takahashi, Takahiro; Yamamoto, Akira; Konishi, Junya; Nozaki, Kazuhiko; Hashimoto, Nobuo; Konishi, Junji

    2003-12-01

    Objective: To compare the magnetic resonance image contrasts due to ferritin and hemosiderin in the brain tissue among different pulse sequences. Materials and methods: Fourteen patients with cavernous hemangioma in the brain prospectively underwent MR imaging with T2*-weighted gradient-echo (GRE), T2-weighted conventional spin-echo (SE) and fast spin-echo (FSE) sequences. The relative contrast ratios (CRs) of the hypointense part of cavernous hemangioma, globus pallidus and putamen to the deep frontal white matter were measured on each pulse sequence and statistically analyzed using analysis of variance followed by paired t-test. Results: In the hypointense part of cavernous hemangioma, relative CRs were significantly lower on T2*-weighted GRE than on T2-weighted SE images (P=0.0001), and on T2-weighted SE than on T2-weighted FSE images (P=0.0001). In the globus pallidus, relative CRs were significantly lower on T2-weighted SE than on T2*-weighted GRE images (P=0.002), and on T2*-weighted GRE than on T2-weighted FSE images (P=0.0002). In the putamen, relative CRs were significantly lower on T2-weighted SE than on T2*-weighted GRE images (P=0.001), and there was no significant difference between CRs on T2-weighted FSE and T2*-weighted GRE images (P=0.90). Conclusion: Hemosiderin showed best image contrast on T2*-weighted GRE images but ferritin showed more prominent image contrast on T2-weighted SE than on T2*-weighted GRE images, which may help to determine an appropriate pulse sequence in neurological diseases associated with excessive ferritin accumulation.

  19. MR contrast of ferritin and hemosiderin in the brain: comparison among gradient-echo, conventional spin-echo and fast spin-echo sequences

    International Nuclear Information System (INIS)

    Haque, Tabassum Laz; Miki, Yukio; Kanagaki, Mitsunori; Takahashi, Takahiro; Yamamoto, Akira; Konishi, Junya; Nozaki, Kazuhiko; Hashimoto, Nobuo; Konishi, Junji

    2003-01-01

    Objective: To compare the magnetic resonance image contrasts due to ferritin and hemosiderin in the brain tissue among different pulse sequences. Materials and methods: Fourteen patients with cavernous hemangioma in the brain prospectively underwent MR imaging with T2*-weighted gradient-echo (GRE), T2-weighted conventional spin-echo (SE) and fast spin-echo (FSE) sequences. The relative contrast ratios (CRs) of the hypointense part of cavernous hemangioma, globus pallidus and putamen to the deep frontal white matter were measured on each pulse sequence and statistically analyzed using analysis of variance followed by paired t-test. Results: In the hypointense part of cavernous hemangioma, relative CRs were significantly lower on T2*-weighted GRE than on T2-weighted SE images (P=0.0001), and on T2-weighted SE than on T2-weighted FSE images (P=0.0001). In the globus pallidus, relative CRs were significantly lower on T2-weighted SE than on T2*-weighted GRE images (P=0.002), and on T2*-weighted GRE than on T2-weighted FSE images (P=0.0002). In the putamen, relative CRs were significantly lower on T2-weighted SE than on T2*-weighted GRE images (P=0.001), and there was no significant difference between CRs on T2-weighted FSE and T2*-weighted GRE images (P=0.90). Conclusion: Hemosiderin showed best image contrast on T2*-weighted GRE images but ferritin showed more prominent image contrast on T2-weighted SE than on T2*-weighted GRE images, which may help to determine an appropriate pulse sequence in neurological diseases associated with excessive ferritin accumulation

  20. Mixed model phase evolution for correction of magnetic field inhomogeneity effects in 3D quantitative gradient echo-based MRI

    DEFF Research Database (Denmark)

    Fatnassi, Chemseddine; Boucenna, Rachid; Zaidi, Habib

    2017-01-01

    PURPOSE: In 3D gradient echo magnetic resonance imaging (MRI), strong field gradients B0macro are visually observed at air/tissue interfaces. At low spatial resolution in particular, the respective field gradients lead to an apparent increase in intravoxel dephasing, and subsequently, to signal...... loss or inaccurate R2* estimates. If the strong field gradients are measured, their influence can be removed by postprocessing. METHODS: Conventional corrections usually assume a linear phase evolution with time. For high macroscopic gradient inhomogeneities near the edge of the brain...

  1. Magnetic resonance imaging of lumbar spine. Comparison of multiple spin echo and low flip angle gradient echo imaging

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, Takamichi; Fujita, Norihiko; Harada, Koushi; Kozuka, Takahiro (Osaka Univ. (Japan). Faculty of Medicine)

    1989-07-01

    Sixteen patients including 13 cases with disk herniation and 3 cases with spondylosis of lumbar spine were examined on a resistive MRI system operating at 0.1 T. All lesions were studied with both multiple spin echo (MSE) and low flip angle gradient echo (LF) techniques to evaluate which technique is more effective in detecting the disk degeneration and the indentation on subarachnoid space. MSE images were obtained with repetition time (TR) of 1100-1500 ms or cardiac gating, an echo time (TE) of 30, 60, 90, 120, 150, and 180 ms symmetrical 6 echoes, and total acquisition time of more than 281 sec. LF images were obtained with TR of 500, 250, and 100 ms, TE of 18 ms, a flip angle of 30 degree, and total acquisition time of 128 sec. Eleven lesions of spinal disk degeneration and 12 of indentation on subarachnoid space were detected with LF. On the other hand, 26 lesions of spinal disk degeneration and 38 of indentation on subarachnoid space were detected with MSE. Although the parameters of LF employed in this study were relatively effective to emphasize T2{sup *}-based contrast, the ability of LF in detection of spinal disk degeneration and indentation on subarachnoid space is less than that of MSE. Signal contrast to noise ratios for normal disk and degenerative disk, epidural-fat and disk herniated material, CSF and disk herniated material, and epidural-fat and CSF were less than 4 with LF, but more than 4 with MSE. This difference of contrast to noise ratio between MSE and LF was one of the main causes of the difference of the detection rate of spinal disk degeneration and indentation on subarachnoid space. (author).

  2. Quantification of liver iron concentration with magnetic resonance imaging by combining T1-, T2-weighted spin echo sequences and a gradient echo sequence

    NARCIS (Netherlands)

    Kreeftenberg, HG; Mooyaart, EL; Sluiter, WJ; Kreeftenberg, HG; Huizenga, Reint

    Background: The aim of the study was to quantify hepatic iron by MRI for practical use. Methods: In twenty-three patients with various degrees of iron overload, measurements were carried out with a 1.5 Tesla MR unit. A combination of pulse sequences (T1, T2 and gradient echo) enabled us to quantify

  3. Inner ear malformations in patients with sensorineural heating loss: detection with gradient-echo (3DFT-CISS) MRI

    Energy Technology Data Exchange (ETDEWEB)

    Casselman, J.W. [Dept. of Radiology, A.Z. St.-Jan Brugge, Bruges (Belgium); Kuhweide, R. [Dept. of Otorhinolaryngology, A.Z. St.-Jan Brugge, Bruges (Belgium); Ampe, W. [Dept. of Otorhinolaryngology, A.Z. St.-Jan Brugge, Bruges (Belgium); D`Hont, G.D. [Dept. of Otorhinolaryngology, A.Z. St.-Jan Brugge, Bruges (Belgium); Offeciers, E.F. [ENT Dept., Sint-Augustinus Medical Inst., Univ. of Antwerp (Belgium); Faes, W.K. [Dept. of Radiology, A.Z. St.-Jan Brugge, Bruges (Belgium); Pattyn, G. [Dept. of Radiology, A.Z. St.-Jan Brugge, Bruges (Belgium)

    1996-04-01

    The sensitivity of different MRI sequences in the detection of inner ear malformations in patients presenting with sensorineural hearing loss (SNHL) and/or vertigo was evaluated. We studied 650 patients presenting with SNHL and/or vertigo, clinically not suspected of having inner ear malformations. The sensitivity of T1-weigted, Gd-enhanced T1-weighted and (when available) T2-weighted spin-echo images, and three-dimensional Fourier transformation-constructive interference in steady state (3DFT-CISS) gradient-echo images, to unexpected malformations was assessed. Inner ear malformations were found in 15 (2.3%) of these patients. Enlargement of the endolymphatic duct and sac was the most frequent malformation, found in 11 patients. The 3DFT-CISS images showed all lesions; the other sequences were less sensitive and the pathology was missed, partially or only retrospectively seen in 11 of the 15 patients. Therefore, in addition to the routine unenhanced and Gd-enhanced T1-weighted and T2-weighted images, thin gradient-echo (3DFT-CISS) images are necessary to detect all clinically unexpected inner ear malformations in patients presenting with vertigo and/or SNHL. (orig.)

  4. Inner ear malformations in patients with sensorineural heating loss: detection with gradient-echo (3DFT-CISS) MRI

    International Nuclear Information System (INIS)

    Casselman, J.W.; Kuhweide, R.; Ampe, W.; D'Hont, G.D.; Offeciers, E.F.; Faes, W.K.; Pattyn, G.

    1996-01-01

    The sensitivity of different MRI sequences in the detection of inner ear malformations in patients presenting with sensorineural hearing loss (SNHL) and/or vertigo was evaluated. We studied 650 patients presenting with SNHL and/or vertigo, clinically not suspected of having inner ear malformations. The sensitivity of T1-weigted, Gd-enhanced T1-weighted and (when available) T2-weighted spin-echo images, and three-dimensional Fourier transformation-constructive interference in steady state (3DFT-CISS) gradient-echo images, to unexpected malformations was assessed. Inner ear malformations were found in 15 (2.3%) of these patients. Enlargement of the endolymphatic duct and sac was the most frequent malformation, found in 11 patients. The 3DFT-CISS images showed all lesions; the other sequences were less sensitive and the pathology was missed, partially or only retrospectively seen in 11 of the 15 patients. Therefore, in addition to the routine unenhanced and Gd-enhanced T1-weighted and T2-weighted images, thin gradient-echo (3DFT-CISS) images are necessary to detect all clinically unexpected inner ear malformations in patients presenting with vertigo and/or SNHL. (orig.)

  5. Evaluation of cardiac function using multi-shot echo planar imaging

    Energy Technology Data Exchange (ETDEWEB)

    Nakanishi, Tadashi; Tanitame, Nobuko; Hata, Ryoichiro; Hirai, Nobuhiko; Ikeda, Midori; Ono, Chiaki; Fukuoka, Haruhito; Ito, Katsuhide [Hiroshima Univ. (Japan). School of Medicine

    1998-01-01

    In this study, we performed multi-shot echo planar imaging (8 shot, TR/TE/FL=55 ms/18 ms/60 degrees) and k-space segmented fast gradient echo sequence (8 views per segment, TR/TE/FL=9.9 ms/1.8 ms/30 degrees) to assess cardiac function in healthy volunteers. Transaxial sections of the entire heart were obtained with both sequences in ECG triggered, breath hold, and with a 256 x 128 matrix. Resulting temporal resolution was 55 ms for echo planar imaging, and 71 ms for k-space segmented fast gradient echo sequence, respectively. Ventricular volume and ejection fraction of both ventricles and left ventricular mass obtained with multi-shot echo planar imaging were assessed in comparison with k-space segmented fast gradient echo sequence. Measurements of left ventricular volume, ejection fraction and mass obtained with multi-shot echo planar imaging demonstrated close correlation with those obtained with k-space segmented fast gradient echo sequence. Right ventricular volumes obtained with echo planar imaging were significantly higher than those obtained with k-space segmented fast gradient echo sequence. This tendency is considered to be due to differing contrast between right ventricular myocardium and fat tissue observed with echo planar imaging relative to that observed with fast gradient echo sequence, because fat suppression is always performed in echo planar images. Multi-shot echo planar imaging can be a reliable tool for measurement of cardiac functional parameters, although wall motion analysis of the left ventricle requires higher temporal resolution and a short axial section. (K.H.)

  6. A fast random walk algorithm for computing the pulsed-gradient spin-echo signal in multiscale porous media.

    Science.gov (United States)

    Grebenkov, Denis S

    2011-02-01

    A new method for computing the signal attenuation due to restricted diffusion in a linear magnetic field gradient is proposed. A fast random walk (FRW) algorithm for simulating random trajectories of diffusing spin-bearing particles is combined with gradient encoding. As random moves of a FRW are continuously adapted to local geometrical length scales, the method is efficient for simulating pulsed-gradient spin-echo experiments in hierarchical or multiscale porous media such as concrete, sandstones, sedimentary rocks and, potentially, brain or lungs. Copyright © 2010 Elsevier Inc. All rights reserved.

  7. An analysis of the uncertainty and bias in DCE-MRI measurements using the spoiled gradient-recalled echo pulse sequence

    International Nuclear Information System (INIS)

    Subashi, Ergys; Choudhury, Kingshuk R.; Johnson, G. Allan

    2014-01-01

    Purpose: The pharmacokinetic parameters derived from dynamic contrast-enhanced (DCE) MRI have been used in more than 100 phase I trials and investigator led studies. A comparison of the absolute values of these quantities requires an estimation of their respective probability distribution function (PDF). The statistical variation of the DCE-MRI measurement is analyzed by considering the fundamental sources of error in the MR signal intensity acquired with the spoiled gradient-echo (SPGR) pulse sequence. Methods: The variance in the SPGR signal intensity arises from quadrature detection and excitation flip angle inconsistency. The noise power was measured in 11 phantoms of contrast agent concentration in the range [0–1] mM (in steps of 0.1 mM) and in onein vivo acquisition of a tumor-bearing mouse. The distribution of the flip angle was determined in a uniform 10 mM CuSO 4 phantom using the spin echo double angle method. The PDF of a wide range of T1 values measured with the varying flip angle (VFA) technique was estimated through numerical simulations of the SPGR equation. The resultant uncertainty in contrast agent concentration was incorporated in the most common model of tracer exchange kinetics and the PDF of the derived pharmacokinetic parameters was studied numerically. Results: The VFA method is an unbiased technique for measuringT1 only in the absence of bias in excitation flip angle. The time-dependent concentration of the contrast agent measured in vivo is within the theoretically predicted uncertainty. The uncertainty in measuring K trans with SPGR pulse sequences is of the same order, but always higher than, the uncertainty in measuring the pre-injection longitudinal relaxation time (T1 0 ). The lowest achievable bias/uncertainty in estimating this parameter is approximately 20%–70% higher than the bias/uncertainty in the measurement of the pre-injection T1 map. The fractional volume parameters derived from the extended Tofts model were found to be

  8. Simultaneous pH-sensitive and oxygen-sensitive MRI of human gliomas at 3 T using multi-echo amine proton chemical exchange saturation transfer spin-and-gradient echo echo-planar imaging (CEST-SAGE-EPI).

    Science.gov (United States)

    Harris, Robert J; Yao, Jingwen; Chakhoyan, Ararat; Raymond, Catalina; Leu, Kevin; Liau, Linda M; Nghiemphu, Phioanh L; Lai, Albert; Salamon, Noriko; Pope, Whitney B; Cloughesy, Timothy F; Ellingson, Benjamin M

    2018-04-06

    To introduce a new pH-sensitive and oxygen-sensitive MRI technique using amine proton CEST echo spin-and-gradient echo (SAGE) EPI (CEST-SAGE-EPI). pH-weighting was obtained using CEST estimations of magnetization transfer ratio asymmetry (MTR asym ) at 3 ppm, and oxygen-weighting was obtained using R2' measurements. Glutamine concentration, pH, and relaxation rates were varied in phantoms to validate simulations and estimate relaxation rates. The values of MTR asym and R2' in normal-appearing white matter, T 2 hyperintensity, contrast enhancement, and macroscopic necrosis were measured in 47 gliomas. Simulation and phantom results confirmed an increase in MTR asym with decreasing pH. The CEST-SAGE-EPI estimates of R 2 , R2*, and R2' varied linearly with gadolinium diethylenetriamine penta-acetic acid concentration (R 2  = 6.2 mM -1 ·sec -1 and R2* = 6.9 mM -1 ·sec -1 ). The CEST-SAGE-EPI and Carr-Purcell-Meiboom-Gill estimates of R 2 (R 2  = 0.9943) and multi-echo gradient-echo estimates of R2* (R 2  = 0.9727) were highly correlated. T 2 lesions had lower R2' and higher MTR asym compared with normal-appearing white matter, suggesting lower hypoxia and high acidity, whereas contrast-enhancement tumor regions had elevated R2' and MTR asym , indicating high hypoxia and acidity. The CEST-SAGE-EPI technique provides simultaneous pH-sensitive and oxygen-sensitive image contrasts for evaluation of the brain tumor microenvironment. Advantages include fast whole-brain acquisition, in-line B 0 correction, and simultaneous estimation of CEST effects, R 2 , R2*, and R2' at 3 T. © 2018 International Society for Magnetic Resonance in Medicine.

  9. Analysis of artefacts and detail resolution of lung MRI with breath-hold T1-weighted gradient-echo and T2-weighted fast spin-echo sequences with respiratory triggering

    International Nuclear Information System (INIS)

    Biederer, J.; Reuter, M.; Both, M.; Grimm, J.; Heller, M.; Muhle, C.; Graessner, J.

    2002-01-01

    The aim of this study was to evaluate feasibility and limitations of two MR sequences for imaging of the lung using a semi-quantitative rating scale. Ten healthy volunteers were assessed with a breath-hold T1-weighted gradient-recalled-echo (TR/TE=129/2.2 ms, matrix 173 x 256) and a T2-weighted turbo spin-echo (TSE) sequence with respiratory triggering (TR/TE=3000-5000/120 ms, matrix 270 x 512) in axial 6-mm slices. The T1-weighted GRE protocol included a pre-saturation pulse over the mediastinal structures. Artefacts and resolution of vessel/airway structures in each lung segment were evaluated by two observers (10 volunteers, 180 segments). Cardiac and vessel pulsation artefacts predominated on T1-weighted GRE, respiration artefacts on T2-weighted TSE (lingula and middle lobe). Pre-saturation of the mediastinum reduced pulsation artefacts on T1-weighted GRE. T1-weighted GRE images were improved by bright flow signal of vessels, whereas image quality of T2-weighted TSE was reduced by black-blood effects in central parts of the lung. Delineation of lung periphery and the mediastinum was superior with T2-weighted TSE. Segmental/sub-segmental vessels (up to fourth/fifth order) and bronchi (up to third order) were identified. All 180 lung segments were imaged in diagnostic quality with at least one of the two sequences (T1-weighted GRE not diagnostic in 9 of 180, T2-weighted TSE in 4 of 180). Both sequences were found to be complementary: superior identification of gross lung anatomy with T1-weighted GRE and higher detail resolution in the periphery and the mediastinum with T2-weighted TSE. (orig.)

  10. Contrast-enhanced MR imaging of metastatic brain tumor at 3 Tesla. Utility of T1-weighted SPACE compared with 2D spin echo and 3D gradient echo sequence

    International Nuclear Information System (INIS)

    Komada, Tomohiro; Naganawa, Shinji; Ogawa, Hiroshi

    2008-01-01

    We evaluated the newly developed whole-brain, isotropic, 3-dimensional turbo spin-echo imaging with variable flip angle echo train (SPACE) for contrast-enhanced T 1 -weighted imaging in detecting brain metastases at 3 tesla (T). Twenty-two patients with suspected brain metastases underwent postcontrast study with SPACE, magnetization-prepared rapid gradient-echo (MP-RAGE), and 2-dimensional T 1 -weighted spin echo (2D-SE) imaging at 3 T. We quantitatively compared SPACE, MP-RAGE, and 2D-SE images by using signal-to-noise ratios (SNRs) for gray matter (GM) and white matter (WM) and contrast-to-noise ratios (CNRs) for GM-to-WM, lesion-to-GM, and lesion-to-WM. Two blinded radiologists evaluated the detection of brain metastases by segment-by-segment analysis and continuously-distributed test. The CNR between GM and WM was significantly higher on MP-RAGE images than on SPACE images (P 1 -weighted imaging. (author)

  11. Cerebral hemodynamic changes measured by gradient-echo or spin-echo bolus tracking and its correlation to changes in ICA blood flow measured by phase-mapping MRI

    DEFF Research Database (Denmark)

    Marstrand, J.R.; Rostrup, Egill; Garde, Ellen

    2001-01-01

    Changes in cerebral blood flow (CBF) induced by Acetazolamide (ACZ) were measured using dynamic susceptibility contrast MRI (DSC-MRI) with both spin echo (SE) EPI and gradient echo (GE) EPI, and related to changes in internal carotid artery (ICA) flow measured by phase-mapping. Also examined...... increase in CBF and CBV in response to ACZ, while SE-EPI measured a significant increase in CBV and MTT. CBV and MTT change measured by SE-EPI was sensitive to previous bolus injections. There was a significant linear relation between change in CBF measured by GE-EPI and change in ICA flow. In conclusion......, GE-EPI under the present condition was superior to SE-EPI in monitoring cerebral vascular changes...

  12. MR imaging characteristics of intracranial hemorrhage using gradient-echo signal acquisition at 1.5 T: Comparison with spin-echo imaging and clinical applications

    International Nuclear Information System (INIS)

    Atlas, S.W.; Grossman, R.I.; Gomori, J.M.; Hackney, D.B.; Goldberg, H.I.; Bilaniuk, L.T.; Zimmerman, R.A.

    1987-01-01

    Evolving paramagnetic blood-breakdown products create static local magnetic susceptibility gradients, which induce rapid phase dispersion on the basis of T2/sup */ shortening. The authors evaluated 30 patients with 50 separate hemorrhagic intracranial lesions with both spin-echo (SE) and gradient echo signal acquisition (GESA) MR imaging at 1.5 T. GESA sequences used repetition time (TR) of 200-750 msec, echo time (TE) of 50-80 msec, and flip angles of 10 0 to 15 0 to emphasize T2/sup */-based contributions to contrast. SE sequences in all cases utilized both short and long TR (600 and 2,500-3,000 msec), with TE of 20-120 msec. Advantages of GESA imaging with Long TE and short flip angles in the evaluation of intracranial hemorrhage include (1) increased sensitivity to susceptibility-induced phase loss from T2/sup */ shortening, resulting in detection of hemorrhagic lesions not seen on conventional long TR/long TE SE images, and (2) very rapid acquisition of images with T2/sup */-based contrast. Limitations of this sequence include (1) severe diamagnetic susceptibility-induced artifacts, especially near air-brain interfaces, which often obscure large portions of the brain and occasionally simulate serious pathology, (2) characteristic internal signal intensity patterns demonstrated by SE imaging, such as in evolving hematomas, occult vascular malformations, and hemorrhagic malignancies, are often obscured by marked hypointensity on GESA images, and (3) reduced signal-noise ratio. The authors conclude that, although images with marked sensitivity to T2/sup */ effects can be rapidly generated by GESA, there is only a limited role for this sequence when evaluating intracranial hemorrhage at 1.5 T, and, in fact, significant information is lost when compared to SE images

  13. Cartilage destruction in small joints by rheumatoid arthritis: assessment of fat-suppressed three-dimensional gradient-echo MR pulse sequences in vitro

    International Nuclear Information System (INIS)

    Uhl, M.; Allmann, K.H.; Hauer, M.P.; Langer, M.; Ihling, C.; Conca, W.

    1998-01-01

    Purpose. To assess the accuracy of different MR sequences for the detection of articular cartilage abnormalities in rheumatoid arthritis. Design and patients. Ten metacarpophalangeal joints and 10 metatarsophalangeal joints (specimens from arthritis patients undergoing ablative joint surgery) were examined with a fat-suppressed (FS) 3D FLASH, a FS 3D FISP, a FS 2D fast spin-echo T2-weighted, and a 2D FS spin-echo T1-weighted sequence. Each cartilage lesion and each cortical lesion was graded from 0 to 4 (modified Outerbridge staging system). Subsequently, the results of each sequence were compared with the macroscopic findings and statistically tested against each other. Results. The study shows that 3D gradient-echo sequences with fat suppression were best for imaging and grading of cartilage lesions in arthritis of the small joints of the hands and feet. Using 3D techniques, all grade 2, grade 3, and grade 4 lesions of cartilage or cortical bone were detected. Conclusion. FS 3D gradient-echo techniques were best for the detection and grading of hyaline cartilage and subchondral bone lesions in rheumatoid arthritis. MRI has a great potential as an objective method of evaluating cartilage damage and bone erosions in rheumatoid arthritis. (orig.)

  14. Cartilage destruction in small joints by rheumatoid arthritis: assessment of fat-suppressed three-dimensional gradient-echo MR pulse sequences in vitro

    Energy Technology Data Exchange (ETDEWEB)

    Uhl, M.; Allmann, K.H.; Hauer, M.P.; Langer, M. [Department of Diagnostic Radiology, University Hospital Freiburg (Germany); Ihling, C. [Department of Pathology, University Hospital Freiburg, Freiburg (Germany); Conca, W. [Department of Rheumatology, University Hospital Freiburg (Germany)

    1998-12-01

    Purpose. To assess the accuracy of different MR sequences for the detection of articular cartilage abnormalities in rheumatoid arthritis. Design and patients. Ten metacarpophalangeal joints and 10 metatarsophalangeal joints (specimens from arthritis patients undergoing ablative joint surgery) were examined with a fat-suppressed (FS) 3D FLASH, a FS 3D FISP, a FS 2D fast spin-echo T2-weighted, and a 2D FS spin-echo T1-weighted sequence. Each cartilage lesion and each cortical lesion was graded from 0 to 4 (modified Outerbridge staging system). Subsequently, the results of each sequence were compared with the macroscopic findings and statistically tested against each other. Results. The study shows that 3D gradient-echo sequences with fat suppression were best for imaging and grading of cartilage lesions in arthritis of the small joints of the hands and feet. Using 3D techniques, all grade 2, grade 3, and grade 4 lesions of cartilage or cortical bone were detected. Conclusion. FS 3D gradient-echo techniques were best for the detection and grading of hyaline cartilage and subchondral bone lesions in rheumatoid arthritis. MRI has a great potential as an objective method of evaluating cartilage damage and bone erosions in rheumatoid arthritis. (orig.) With 5 figs., 19 refs.

  15. Three-dimensional gradient echo versus spin echo sequence in contrast-enhanced imaging of the pituitary gland at 3 T

    Energy Technology Data Exchange (ETDEWEB)

    Kakite, Suguru, E-mail: sugkaki@med.tottori-u.ac.jp [Division of Radiology, Department of Pathophysiological and Therapeutic Science, Faculty of Medicine, Tottori University, 36-1, Nishicho, Yonago 683-8503 (Japan); Fujii, Shinya [Division of Radiology, Department of Pathophysiological and Therapeutic Science, Faculty of Medicine, Tottori University, 36-1, Nishicho, Yonago 683-8503 (Japan); Kurosaki, Masamichi [Department of Neurosurgery, Faculty of Medicine, Tottori University, 36-1, Nishicho, Yonago 683-8503 (Japan); Kanasaki, Yoshiko; Matsusue, Eiji; Kaminou, Toshio; Ogawa, Toshihide [Division of Radiology, Department of Pathophysiological and Therapeutic Science, Faculty of Medicine, Tottori University, 36-1, Nishicho, Yonago 683-8503 (Japan)

    2011-07-15

    Introduction: To clarify whether a three-dimensional-gradient echo (3D-GRE) or spin echo (SE) sequence is more useful for evaluating sellar lesions on contrast-enhanced T1-weighted MR imaging at 3.0 Tesla (T). Methods: We retrospectively assessed contrast-enhanced T1-weighted images using 3D-GRE and SE sequences at 3.0 T obtained from 33 consecutive patients with clinically suspected sellar lesions. Two experienced neuroradiologists evaluated the images qualitatively in terms of the following criteria: boundary edge of the cavernous sinus and pituitary gland, border of sellar lesions, delineation of the optic nerve and cranial nerves within the cavernous sinus, susceptibility and flow artifacts, and overall image quality. Results: At 3.0 T, 3D-GRE provided significantly better images than the SE sequence in terms of the border of sellar lesions, delineation of cranial nerves, and overall image quality; there was no significant difference regarding the boundary edge of the cavernous sinus and pituitary gland. In addition, the 3D-GRE sequence showed fewer pulsation artifacts but more susceptibility artifacts. Conclusion: Our results indicate that 3D-GRE is the more suitable sequence for evaluating sellar lesions on contrast-enhanced T1-weighted imaging at 3.0 T.

  16. Echo-Planar Imaging for a 9.4 Tesla Vertical-Bore Superconducting Magnet Using an Unshielded Gradient Coil.

    Science.gov (United States)

    Kodama, Nao; Kose, Katsumi

    2016-10-11

    Echo-planar imaging (EPI) sequences were developed for a 9.4 Tesla vertical standard bore (~54 mm) superconducting magnet using an unshielded gradient coil optimized for live mice imaging and a data correction technique with reference scans. Because EPI requires fast switching of intense magnetic field gradients, eddy currents were induced in the surrounding metallic materials, e.g., the room temperature bore, and this produced serious artifacts on the EPI images. We solved the problem using an unshielded gradient coil set of proper size (outer diameter = 39 mm, inner diameter = 32 mm) with time control of the current rise and reference scans. The obtained EPI images of a phantom and a plant sample were almost artifact-free and demonstrated the promise of our approach.

  17. Echo-Planar Imaging for a 9.4 Tesla Vertical-Bore Superconducting Magnet Using an Unshielded Gradient Coil

    Science.gov (United States)

    KODAMA, Nao; KOSE, Katsumi

    2016-01-01

    Echo-planar imaging (EPI) sequences were developed for a 9.4 Tesla vertical standard bore (∼54 mm) superconducting magnet using an unshielded gradient coil optimized for live mice imaging and a data correction technique with reference scans. Because EPI requires fast switching of intense magnetic field gradients, eddy currents were induced in the surrounding metallic materials, e.g., the room temperature bore, and this produced serious artifacts on the EPI images. We solved the problem using an unshielded gradient coil set of proper size (outer diameter = 39 mm, inner diameter = 32 mm) with time control of the current rise and reference scans. The obtained EPI images of a phantom and a plant sample were almost artifact-free and demonstrated the promise of our approach. PMID:27001398

  18. Storage and manipulation of light using a Raman gradient-echo process

    International Nuclear Information System (INIS)

    Hosseini, M; Sparkes, B M; Campbell, G T; Lam, P K; Buchler, B C

    2012-01-01

    The gradient-echo memory (GEM) scheme has potential to be a suitable protocol for storage and retrieval of optical quantum information. In this paper, we review the properties of the Λ-GEM method that stores information in the ground states of three-level atomic ensembles via Raman coupling. The scheme is versatile in that it can store and re-sequence multiple pulses of light. To date, this scheme has been implemented using warm rubidium gas cells. There are different phenomena that can influence the performance of these atomic systems. We investigate the impact of atomic motion and four-wave mixing and present experiments that show how parasitic four-wave mixing can be mitigated. We also use the memory to demonstrate preservation of pulse shape and the backward retrieval of pulses. (paper)

  19. Signal changes in gradient echo images of human brain induced by hypo- and hyperoxia

    DEFF Research Database (Denmark)

    Rostrup, Egill; Larsson, H B; Toft, P B

    1995-01-01

    The effect of hypoxia (inspired oxygen fraction, FiO2 of 10% and 16%) and hyperoxia (FiO2) of 100%) on gradient echo images of the brain using long echo times was investigated in six healthy volunteers (age 24-28 years). Different flip angles were used with an FiO2 of 10% to assess the importance...... of saturation effects. The total cerebral blood flow was measured by a phase mapping technique during normoxia as well as hypoxia (FiO2 of 10% and 16%) and hyperoxia (FiO2 of 50% and 100%). High relative signal changes were found, independently of the flip angle, with FiO2 of 10%. With a flip angle of 40...... degrees the values of delta R2* for cortical grey matter, central grey matter, white matter and the sagittal sinus were 0.79, 0.41, 0.26 and 3.00/s; with a flip angle of 10 degrees the corresponding values were 0.70, 0.37, 0.24 and 3.15/s. The total cerebral blood flow increased by 41% during inhalation...

  20. Analysis of Partial Volume Effects on Arterial Input Functions Using Gradient Echo: A Simulation Study

    DEFF Research Database (Denmark)

    Kjølby, Birgitte Fuglsang; Mikkelsen, Irene Klærke; Pedersen, Michael

    2009-01-01

    of an AIF voxel including the relaxation properties of blood and tissue. Artery orientations parallel and perpendicular to the main magnetic field were investigated and AIF voxels were modeled to either include or be situated close to a large artery. The impact of partial volume effects on quantitative...... perfusion metrics was investigated for the gradient echo pulse sequence at 1.5 T and 3.0 T. It is shown that the tissue contribution broadens and introduces fluctuations in the AIF. Furthermore, partial volume effects bias perfusion metrics in a nonlinear fashion, compromising quantitative perfusion...

  1. Cerebral hemodynamic changes measured by gradient-echo or spin-echo bolus tracking and its correlation to changes in ICA blood flow measured by phase-mapping MRI

    DEFF Research Database (Denmark)

    Marstrand, J.R.; Rostrup, Egill; Garde, Ellen

    2001-01-01

    Changes in cerebral blood flow (CBF) induced by Acetazolamide (ACZ) were measured using dynamic susceptibility contrast MRI (DSC-MRI) with both spin echo (SE) EPI and gradient echo (GE) EPI, and related to changes in internal carotid artery (ICA) flow measured by phase-mapping. Also examined...... was the effect of repeated bolus injections. CBF, cerebral blood volume (CBV), and mean transit time (MTT) were calculated by singular value decomposition (SVD) and by deconvolution using an exponential function as kernel. The results showed no dependency on calculation method. GE-EPI measured a significant...... increase in CBF and CBV in response to ACZ, while SE-EPI measured a significant increase in CBV and MTT. CBV and MTT change measured by SE-EPI was sensitive to previous bolus injections. There was a significant linear relation between change in CBF measured by GE-EPI and change in ICA flow. In conclusion...

  2. Dual-echo, chemical shift gradient-echo magnetic resonance imaging to quantify hepatic steatosis: Implications for living liver donation.

    Science.gov (United States)

    Rinella, Mary E; McCarthy, Richard; Thakrar, Kiran; Finn, John Paul; Rao, Sambasiva M; Koffron, Alan J; Abecassis, Michael; Blei, Andres T

    2003-08-01

    In living liver donation, a fatty liver poses risks for both recipient and donor. Currently, liver biopsy is the standard for assessing the presence and extent of steatosis. The goals of this study were to correlate a steatosis index derived from magnetic resonance imaging (MRI) to the histologic grade on biopsy as well as to determine the topographic distribution of steatosis within the liver. We examined the ability of dual-echo, chemical shift gradient-echo MRI to predict the degree of steatosis on liver biopsy. A total of 22 subjects received both a liver biopsy and detailed MRI evaluation. These individuals included 15 potential living donors and 7 patients with nonalcoholic fatty liver disease. MRI steatosis index was then compared with histologic grade on liver biopsy. The topographic distribution of hepatic steatosis was determined from those subjects in whom MRI detected hepatic steatosis. The steatosis index had a positive correlation with grade of steatosis on liver biopsy (correlation coefficient, 0.84). There was no significant variation in the degree of steatosis among segments. A steatosis index of >0.2 had good positive and negative predictive value for the presence of significant steatosis (>15%) on biopsy. Our quantitative MRI protocol can predict the degree of hepatic steatosis when it is minimal to moderate, and may obviate the need for liver biopsy for the purpose of quantification of steatosis in living donors. Fat saturation added to the MRI protocol may further improve diagnostic accuracy. This technique may be applicable to the larger population with hepatic steatosis.

  3. Normal range of hepatic fat fraction on dual- and triple-echo fat quantification MR in children.

    Science.gov (United States)

    Shin, Hyun Joo; Kim, Hyun Gi; Kim, Myung-Joon; Koh, Hong; Kim, Ha Yan; Roh, Yun Ho; Lee, Mi-Jung

    2015-01-01

    To evaluate hepatic fat fraction on dual- and triple-echo gradient-recalled echo MRI sequences in healthy children. We retrospectively reviewed the records of children in a medical check-up clinic from May 2012 to November 2013. We excluded children with abnormal laboratory findings or those who were overweight. Hepatic fat fraction was measured on dual- and triple-echo sequences using 3T MRI. We compared fat fractions using the Wilcoxon signed rank test and the Bland-Altman 95% limits of agreement. The correlation between fat fractions and clinical and laboratory findings was evaluated using Spearman's correlation test, and the cut-off values of fat fractions for diagnosing fatty liver were obtained from reference intervals. In 54 children (M:F = 26:28; 5-15 years; mean 9 years), the dual fat fraction (0.1-8.0%; median 1.6%) was not different from the triple fat fraction (0.4-6.5%; median 2.7%) (p = 0.010). The dual- and triple-echo fat fractions showed good agreement using a Bland-Altman plot (-0.6 ± 2.8%). Eight children (14.8%) on dual-echo sequences and six (11.1%) on triple-echo sequences had greater than 5% fat fraction. From these children, six out of eight children on dual-echo sequences and four out of six children on triple-echo sequences had a 5-6% hepatic fat fraction. When using a cut-off value of a 6% fat fraction derived from a reference interval, only 3.7% of children were diagnosed with fatty liver. There was no significant correlation between clinical and laboratory findings with dual and triple-echo fat fractions. Dual fat fraction was not different from triple fat fraction. We suggest a cut-off value of a 6% fat fraction is more appropriate for diagnosing fatty liver on both dual- and triple-echo sequences in children.

  4. Magnetization transfer contrast on gradient echo MR imaging of the temporomandibular joint

    International Nuclear Information System (INIS)

    Niitsu, M.; Hirohata, H.; Yoshioka, H.; Anno, I.; Campeau, N.G.; Itai, Y.

    1995-01-01

    Thirty-nine temporomandibular joints (TMJ) from 20 patients with suspected internal derangements were imaged by a 1.5 T MR imager. The on-resonance binomial magnetization transfer contrast (MTC) pulse was applied to gradient echo images with a dual receiver coil (9 s/section). With the use of an opening device, a series of sequential images were obtained at increments of mouth opening and closing. The tissue signal intensities with (Ms) and without (Mo) MTC were measured and subjective image analysis was performed. Compared with the standard images, MTC technique provided selective signal suppression of disks. The average of Ms/Mo ratio of the disks (0.56) was lower than that of the retrodiskal pad (0.79) and of the effusion (0.89). With MTC technique, fluid conspicuity was superior to standard image. However, no significant superiority was found in disk definition subjectively. (orig.)

  5. Hippocampal Microbleed on a Post-Mortem T2*-Weighted Gradient-Echo 7.0-Tesla Magnetic Resonance Imaging

    Directory of Open Access Journals (Sweden)

    J. De Reuck

    2011-09-01

    Full Text Available The present post-mortem study of a brain from an Alzheimer patient showed on a T2*-weighted gradient-echo 7.0-T MRI of a coronal brain section a hyposignal in the hippocampus, suggesting a microbleed. On the corresponding histological examination, only iron deposits around the granular cellular layer and in blood vessel walls of the hippocampus were observed without evidence of a bleeding. This case report illustrates that the detection of microbleeds on MRI has to be interpreted with caution.

  6. Magnetic resonance in cartilaginous lesions of the knee joint with three-dimensional gradient-echo imaging

    International Nuclear Information System (INIS)

    Reiser, M.F.; Bongartz, G.; Erlemann, R.; Gaebert, K.; Stoeber, U.; Peters, P.E.; Strobel, M.; Pauly, T.

    1988-01-01

    Diagnosis of chondromalacia of the patellofemoral joint using three-dimensional gradient-echo sequences was investigated in 41 patients, with arthroscopic verification in 25 patients. In vitro examinations in human caderveric patellae were performed in order to determine optimal imaging parameters. FLASH (T R =40 ms, T E =10 ms, flip angle=30 0 ) and FISP (T R =40 ms, T E =10 ms, flip angle=40 0 ) were used in clinical studies. The therapeutically relevant differentiation of major and minor degrees of chondromalacia seems to be possible. 30 0 FLASH-images in the axial plane proved to be the most efficacious technique for the diagnosis of chondromalacia. (orig./GDG)

  7. Self-normalizing multiple-echo technique for measuring the in vivo apparent diffusion coefficient

    International Nuclear Information System (INIS)

    Perman, W.H.; Gado, M.; Sandstrom, J.C.

    1989-01-01

    This paper presents work to develop a new technique for quantitating the in vivo apparent diffusion/perfusion coefficient (ADC) by obtaining multiple data points from only two images with the capability to normalize the data from consecutive images, thus minimizing the effect of interimage variation. Two multiple-echo (six-to eight-echo) cardiac-gated images are obtained, one without and one with additional diffusion/perfusion encoding gradients placed about the 180 RF pulses of all but the first echo. Since the first echoes of both images have identical pulse sequence parameters, variations in signal intensity-between the first echoes represent image-to-image variation. The signal intensities of the subsequent echoes with additional diffusion/perfusion encoding gradients are then normalized by using the ratio of the first-echo signal intensities

  8. Utility of two types of MR cisternography for patency evaluation of aqueduct and third ventriculostomy site: Three dimentsional sagittal fast spin echo sequence and steady-state coherent fast gradient echo sequence

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jung Hyun; Kim, Eun Hee; Park, Jong Bin; Kim, Jae Hyoung; Choi, Byung Se; Jung, Cheol Kyu; Bae, Yun Jung; Lee, Kyung Mi [Dept. of Radiology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam (Korea, Republic of)

    2015-07-15

    We aimed to evaluate the utility of two types of MR cisternography [fast spin echo sequence and steady-state coherent gradient echo (GRE) sequence] in addition to phase contrast-cine imaging (PC-cine), for assessing patency at the aqueduct and third ventriculostomy site. 43 patients (35 patients with suspected aqueductal stenosis and 8 patients with third ventriculostomy) were retrospectively analyzed. PC-cine, 3 dimensional sagittal fast spin echo sequence [driven-equilibrium imaging (DRIVE) or volumetric isotrophic T2-weighted acquisition (T2 VISTA)] and steady-state coherent fast GRE sequence (balanced turbo field echo; bTFE) imaging were performed in all patients. The patency of the aqueduct or third ventriculostomy site was scored. Some pitfalls of each sequence were also analyzed in individual cases. 93% of all cases showed consistent scores in PC-cine, DRIVE/T2 VISTA, and bTFE imaging. DRIVE/T2 VISTA imaging provided functional information of cerebrospinal fluid flow with flow-related artifacts, while bTFE imaging allowed direct visualization of the aqueduct or ventriculostomy site. However, evaluation of anatomical structures was difficult in three cases with strong flow-related artifacts on DRIVE/T2 VISTA and in 2 cases with susceptibility artifacts on bTFE. Both DRIVE/T2 VISTA and bTFE imaging have complementary roles in evaluating the patency of the aqueduct and 3rd ventriculostomy site.

  9. Utility of two types of MR cisternography for patency evaluation of aqueduct and third ventriculostomy site: Three dimentsional sagittal fast spin echo sequence and steady-state coherent fast gradient echo sequence

    International Nuclear Information System (INIS)

    Park, Jung Hyun; Kim, Eun Hee; Park, Jong Bin; Kim, Jae Hyoung; Choi, Byung Se; Jung, Cheol Kyu; Bae, Yun Jung; Lee, Kyung Mi

    2015-01-01

    We aimed to evaluate the utility of two types of MR cisternography [fast spin echo sequence and steady-state coherent gradient echo (GRE) sequence] in addition to phase contrast-cine imaging (PC-cine), for assessing patency at the aqueduct and third ventriculostomy site. 43 patients (35 patients with suspected aqueductal stenosis and 8 patients with third ventriculostomy) were retrospectively analyzed. PC-cine, 3 dimensional sagittal fast spin echo sequence [driven-equilibrium imaging (DRIVE) or volumetric isotrophic T2-weighted acquisition (T2 VISTA)] and steady-state coherent fast GRE sequence (balanced turbo field echo; bTFE) imaging were performed in all patients. The patency of the aqueduct or third ventriculostomy site was scored. Some pitfalls of each sequence were also analyzed in individual cases. 93% of all cases showed consistent scores in PC-cine, DRIVE/T2 VISTA, and bTFE imaging. DRIVE/T2 VISTA imaging provided functional information of cerebrospinal fluid flow with flow-related artifacts, while bTFE imaging allowed direct visualization of the aqueduct or ventriculostomy site. However, evaluation of anatomical structures was difficult in three cases with strong flow-related artifacts on DRIVE/T2 VISTA and in 2 cases with susceptibility artifacts on bTFE. Both DRIVE/T2 VISTA and bTFE imaging have complementary roles in evaluating the patency of the aqueduct and 3rd ventriculostomy site

  10. A 3D T1-weighted gradient-echo sequence for routine use in 3D radiosurgical treatment planning of brain metastases: first clinical results

    International Nuclear Information System (INIS)

    Hawighorst, H.; Schad, L.R.; Gademann, G.; Knopp, M.V.; Wenz, F.; Kaick, G. van

    1995-01-01

    The authors report on a 3D sequence for MRI of the brain and its application in radiosurgical treatment planning of 35 brain metastases. The measuring sequence, called magnetization - prepared rapid gradient echo (MPRAGE), was compared with 2D T1-weighted spin-echo (SE) sequences following intravenous contrast-medium application in 19 patients with brain metastases. The average diameter of all lesions was similar in both sequences, with 16.8 and 17.0 mm for SE and MPRAGE, respectively. Target point definition was equal in 29 metastases, and in 6 cases superior on MPRAGE, due to better gray-white matter contrast and increased contrast enhancement. In cases of bleeding metastases there was improved depiction of internal structures in 3D MRI. Postprocessing of 3D MPRAGE data created multiplanar reconstruction along any chosen plane with isotropic spatial resolution, which helped to improve radiosurgical isodose distribution in 4 cases when compared to 2D SE. However, sensitivity of 3D MPRAGE to detect small lesions (< 3 mm) was decreased in one patient with more than 50 metastases. We conclude that 3D gradient-echo (GE) imaging might be of great value for radiosurgical treatment planning, but does not replace 2D SE with its current parameters. (orig.)

  11. Magnetic resonance in cartilaginous lesions of the knee joint with three-dimensional gradient-echo imaging

    Energy Technology Data Exchange (ETDEWEB)

    Reiser, M.F.; Bongartz, G.; Erlemann, R.; Gaebert, K.; Stoeber, U.; Peters, P.E.; Strobel, M.; Pauly, T.

    1988-10-01

    Diagnosis of chondromalacia of the patellofemoral joint using three-dimensional gradient-echo sequences was investigated in 41 patients, with arthroscopic verification in 25 patients. In vitro examinations in human caderveric patellae were performed in order to determine optimal imaging parameters. FLASH (T/sub R/=40 ms, T/sub E/=10 ms, flip angle=30/sup 0/) and FISP (T/sub R/=40 ms, T/sub E/=10 ms, flip angle=40/sup 0/) were used in clinical studies. The therapeutically relevant differentiation of major and minor degrees of chondromalacia seems to be possible. 30/sup 0/ FLASH-images in the axial plane proved to be the most efficacious technique for the diagnosis of chondromalacia. (orig./GDG).

  12. Prognostic value of gradient echo T2* sequences for brain MR imaging in preterm infants

    International Nuclear Information System (INIS)

    Bruine, Francisca T. de; Berg-Huysmans, Annette A. van den; Buchem, Mark A. van; Grond, Jeroen van der; Steggerda, Sylke J.; Leijser, Lara M.; Rijken, Monique; Wezel-Meijler, Gerda van

    2014-01-01

    Gradient echo T2*-W sequences are more sensitive than T2-W spin-echo sequences for detecting hemorrhages in the brain. The aim of this study is to correlate presence of hemosiderin deposits in the brain of very preterm infants (gestational age 6 non-hemorrhagic punctate white matter lesions (PWML), cysts and/or ventricular dilatation. Six infants with post-hemorrhagic ventricular dilatation detected by US in the neonatal period were excluded. Infants were seen for follow-up at 2 years. Univariate and regression analysis assessed the relation between presence and location of hemosiderin, white matter injury and neurodevelopmental outcome. In 38/95 (40%) of the infants, hemosiderin was detected. Twenty percent (19/95) of the infants were lost to follow-up. There was a correlation between hemosiderin in the ventricular wall with >6 PWML (P < 0.001) and cysts (P < 0.001) at term-equivalent age, and with a lower psychomotor development index (PDI) (P=0.02) at 2 years. After correcting for known confounders (gestational age, gender, intrauterine growth retardation and white matter injury), the correlation with PDI was no longer significant. The clinical importance of detecting small hemosiderin deposits is limited as there is no independent association with neurodevelopmental outcome. (orig.)

  13. Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE MRI.

    Directory of Open Access Journals (Sweden)

    Noam Shemesh

    Full Text Available Objects making up complex porous systems in Nature usually span a range of sizes. These size distributions play fundamental roles in defining the physicochemical, biophysical and physiological properties of a wide variety of systems - ranging from advanced catalytic materials to Central Nervous System diseases. Accurate and noninvasive measurements of size distributions in opaque, three-dimensional objects, have thus remained long-standing and important challenges. Herein we describe how a recently introduced diffusion-based magnetic resonance methodology, Non-Uniform-Oscillating-Gradient-Spin-Echo (NOGSE, can determine such distributions noninvasively. The method relies on its ability to probe confining lengths with a (length6 parametric sensitivity, in a constant-time, constant-number-of-gradients fashion; combined, these attributes provide sufficient sensitivity for characterizing the underlying distributions in μm-scaled cellular systems. Theoretical derivations and simulations are presented to verify NOGSE's ability to faithfully reconstruct size distributions through suitable modeling of their distribution parameters. Experiments in yeast cell suspensions - where the ground truth can be determined from ancillary microscopy - corroborate these trends experimentally. Finally, by appending to the NOGSE protocol an imaging acquisition, novel MRI maps of cellular size distributions were collected from a mouse brain. The ensuing micro-architectural contrasts successfully delineated distinctive hallmark anatomical sub-structures, in both white matter and gray matter tissues, in a non-invasive manner. Such findings highlight NOGSE's potential for characterizing aberrations in cellular size distributions upon disease, or during normal processes such as development.

  14. Optimizing the magnetization-prepared rapid gradient-echo (MP-RAGE sequence.

    Directory of Open Access Journals (Sweden)

    Jinghua Wang

    Full Text Available The three-dimension (3D magnetization-prepared rapid gradient-echo (MP-RAGE sequence is one of the most popular sequences for structural brain imaging in clinical and research settings. The sequence captures high tissue contrast and provides high spatial resolution with whole brain coverage in a short scan time. In this paper, we first computed the optimal k-space sampling by optimizing the contrast of simulated images acquired with the MP-RAGE sequence at 3.0 Tesla using computer simulations. Because the software of our scanner has only limited settings for k-space sampling, we then determined the optimal k-space sampling for settings that can be realized on our scanner. Subsequently we optimized several major imaging parameters to maximize normal brain tissue contrasts under the optimal k-space sampling. The optimal parameters are flip angle of 12°, effective inversion time within 900 to 1100 ms, and delay time of 0 ms. In vivo experiments showed that the quality of images acquired with our optimal protocol was significantly higher than that of images obtained using recommended protocols in prior publications. The optimization of k-spacing sampling and imaging parameters significantly improved the quality and detection sensitivity of brain images acquired with MP-RAGE.

  15. Free-breathing contrast-enhanced T1-weighted gradient-echo imaging with radial k-space sampling for paediatric abdominopelvic MRI

    Energy Technology Data Exchange (ETDEWEB)

    Chandarana, Hersh; Block, Kai T.; Winfeld, Matthew J.; Lala, Shailee V.; Mazori, Daniel; Giuffrida, Emalyn; Babb, James S.; Milla, Sarah S. [New York University Langone Medical Center, Department of Radiology, New York, NY (United States)

    2014-02-15

    To compare the image quality of contrast-enhanced abdominopelvic 3D fat-suppressed T1-weighted gradient-echo imaging with radial and conventional Cartesian k-space acquisition schemes in paediatric patients. Seventy-three consecutive paediatric patients were imaged at 1.5 T with sequential contrast-enhanced T1-weighted Cartesian (VIBE) and radial gradient echo (GRE) acquisition schemes with matching parameters when possible. Cartesian VIBE was acquired as a breath-hold or as free breathing in patients who could not suspend respiration, followed by free-breathing radial GRE in all patients. Two paediatric radiologists blinded to the acquisition schemes evaluated multiple parameters of image quality on a five-point scale, with higher score indicating a more optimal examination. Lesion presence or absence, conspicuity and edge sharpness were also evaluated. Mixed-model analysis of variance was performed to compare radial GRE and Cartesian VIBE. Radial GRE had significantly (all P < 0.001) higher scores for overall image quality, hepatic edge sharpness, hepatic vessel clarity and respiratory motion robustness than Cartesian VIBE. More lesions were detected on radial GRE by both readers than on Cartesian VIBE, with significantly higher scores for lesion conspicuity and edge sharpness (all P < 0.001). Radial GRE has better image quality and lesion conspicuity than conventional Cartesian VIBE in paediatric patients undergoing contrast-enhanced abdominopelvic MRI. (orig.)

  16. Characteristics of magnetic resonance imaging with partial flip angle and gradient field echo

    International Nuclear Information System (INIS)

    Hamada, Tatsumi; Uto, Tatsurou; Okafuji, Tatsumasa; Ookusa, Akihiko; Oonishi, Takuya; Mabuchi, Nobuhisa; Fujii, Kouichi; Yoshioka, Hiroyasu; Ishida, Osamu

    1988-01-01

    Characteristics of a magnetic resonance (MR) imaging pulse sequence with short repetition time (Tr), short echo time (Te), partial flip angle and gradient field echo, at 0.5 T, were studied. A series of sagittal images of the cerebrospinal region was obtained with varied Tr, Te and flip angle, signal intensities were measured by means of a region of interest (ROI) function, and optimal parameters to achieve maximum tissue contrast were found. Of the parameters flip angle had the greatest effect on tissue contrast. Flip angles less than 20 or more than 60 degrees were necessary to discriminate between spinal cord and cerebrospinal fluid. So called MR myelography was obtained with the flip angle of 15 degrees. Opposed and inphase images were obtained at the Te levels of 21 and 28 ms, respectively. Likewise, a series of transverse images of the abdomen with short Tr, short Te and varied flip angles was obtained in a breath-holding interval, and signal intensities of ROIs were measured. Maximum intensities of the liver, the spleen and perirenal fat were obtained at the flip angles of 40, 30 and 60 degrees, respectively. Although maximum intensity was found at the flip angle of 30 degrees for both of the renal cortex and medulla, the maximum contrast between the two tissues was obtained at the flip angles of 50-60 degrees. The image contrast obtained by these pulse sequences was also theoretically predictable, and so it is thought possible that flip angle, Tr and Te are manipulated to yield a desired contrast. (author)

  17. Radar observations of density gradients, electric fields, and plasma irregularities near polar cap patches in the context of the gradient-drift instability

    Science.gov (United States)

    Lamarche, Leslie J.; Makarevich, Roman A.

    2017-03-01

    We present observations of plasma density gradients, electric fields, and small-scale plasma irregularities near a polar cap patch made by the Super Dual Auroral Radar Network radar at Rankin Inlet (RKN) and the northern face of Resolute Bay Incoherent Scatter Radar (RISR-N). RKN echo power and occurrence are analyzed in the context of gradient-drift instability (GDI) theory, with a particular focus on the previously uninvestigated 2-D dependencies on wave propagation, electric field, and gradient vectors, with the latter two quantities evaluated directly from RISR-N measurements. It is shown that higher gradient and electric field components along the wave vector generally lead to the higher observed echo occurrence, which is consistent with the expected higher GDI growth rate, but the relationship with echo power is far less straightforward. The RKN echo power increases monotonically as the predicted linear growth rate approaches zero from negative values but does not continue this trend into positive growth rate values, in contrast with GDI predictions. The observed greater consistency of echo occurrence with GDI predictions suggests that GDI operating in the linear regime can control basic plasma structuring, but measured echo strength may be affected by other processes and factors, such as multistep or nonlinear processes or a shear-driven instability.

  18. MRI of the breast with 2D spin-echo and gradient echo sequences in diagnostically difficult cases. MRT der Mamma mit 2D-Spinecho- und Gradientenecho-Sequenzen in diagnostischen Problemfaellen

    Energy Technology Data Exchange (ETDEWEB)

    Allgayer, B. (Technische Univ. Muenchen (Germany). Inst. fuer Roentgendiagnostik); Lukas, P. (Technische Univ. Muenchen (Germany). Inst. und Poliklinik fuer Strahlentherapie und Radiologische Onkologie); Loos, W. (Technische Univ. Muenchen (Germany). Frauenklinik und Poliklinik); Kersting-Sommerhoff, B. (Technische Univ. Muenchen (Germany). Inst. fuer Roentgendiagnostik)

    1993-05-01

    One or both breasts of 296 patients with equivocal clinical or mammographical findings were examined with MRI. T[sub 1] weighted spinecho (SE) and gradient echo (FFE) sequences were acquired before and after i.v. application of Gadolinium DTPA. 50 lesions with enhancement after Gd-DTPA were biopsied - 26 carcinomas, 17 proliferating mastopathic tissues, 5 fibroadenomas and 1 abscess were found. Contrast enhanced MRI with 2D-SE and FFE sequences is an effective technqiue for evaluating suspicious breast lesions with high diagnostic acurracy. (orig.)

  19. Validity of gradient-echo three-dimensional delayed gadolinium-enhanced magnetic resonance imaging of hip joint cartilage: A histologically controlled study

    Energy Technology Data Exchange (ETDEWEB)

    Zilkens, Christoph, E-mail: christoph.zilkens@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany); Miese, Falk, E-mail: falk.miese@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Moorenstraße 5, D-40225 Dusseldorf (Germany); Herten, Monika, E-mail: Moherten@web.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany); Kurzidem, Sabine, E-mail: sabine.kurzidem@uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany); Jäger, Marcus [Univ Essen, Medical Faculty, Department of Orthopaedic Surgery, D-45147 Essen (Germany); König, Dietmar, E-mail: Dietmarpierre.koenig@lvr.de [LVR Clinic for Orthopedic Surgery, D-41749 Viersen (Germany); Antoch, Gerald, E-mail: antoch@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Moorenstraße 5, D-40225 Dusseldorf (Germany); Krauspe, Rüdiger, E-mail: krauspe@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany); Bittersohl, Bernd, E-mail: bernd.bittersohl@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany)

    2013-02-15

    Objective: To validate gradient-echo three-dimensional (3D) delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) by means of histological analyses in the assessment of hip joint cartilage. Materials and methods: Twenty-one femoral head specimens collected from 21 patients (7 males, 14 females, mean age: 60.9 ± 9.6 years; range: 37.6–77.3 years), who underwent total hip replacement for symptomatic hip joint osteoarthritis, underwent MRI and histological assessment. A region of 2 cm{sup 2} at the weight-bearing area was marked with four pins to enable multi-planar MRI reformatting to be matched with histological sections. MRI was performed at 3 T with a 3D double-echo steady-state (DESS) sequence for morphological cartilage assessment and 3D Volumetric Interpolated Breathhold Examination (VIBE) for T1{sub Gd} mapping. Histological sections were evaluated according to the Mankin score system. Total Mankin score, grade of toluidine staining (sensitive for glycosaminoglycan content) and a modified Mankin score classification system with four sub-groups of cartilage damage were correlated with MRI data. Results: Spearman's rho correlation analyses revealed a statistically significant correlation between T1{sub Gd} mapping and histological analyses in all categories including total Mankin score (r = −0.658, p-value ≤ 0.001), toluidine staining (r = −0.802, p-value < 0.001) and modified Mankin score (r = −0.716, p-value < 0.001). The correlation between morphological MRI and histological cartilage assessment was statistically significant but inferior to the biochemical cartilage MRI (r-values ranging from −0.411 to 0.525, p-values < 0.001). Conclusions: Gradient-echo dGEMRIC is reliable while offering the unique features of high image resolution and 3D biochemically sensitive MRI for the assessment of early cartilage degeneration.

  20. Detection and quantification of regional cortical gray matter damage in multiple sclerosis utilizing gradient echo MRI

    Directory of Open Access Journals (Sweden)

    Jie Wen

    2015-01-01

    Full Text Available Cortical gray matter (GM damage is now widely recognized in multiple sclerosis (MS. The standard MRI does not reliably detect cortical GM lesions, although cortical volume loss can be measured. In this study, we demonstrate that the gradient echo MRI can reliably and quantitatively assess cortical GM damage in MS patients using standard clinical scanners. High resolution multi-gradient echo MRI was used for regional mapping of tissue-specific MRI signal transverse relaxation rate values (R2* in 10 each relapsing–remitting, primary-progressive and secondary-progressive MS subjects. A voxel spread function method was used to correct artifacts induced by background field gradients. R2* values from healthy controls (HCs of varying ages were obtained to establish baseline data and calculate ΔR2* values – age-adjusted differences between MS patients and HC. Thickness of cortical regions was also measured in all subjects. In cortical regions, ΔR2* values of MS patients were also adjusted for changes in cortical thickness. Symbol digit modalities (SDMT and paced auditory serial addition (PASAT neurocognitive tests, as well as Expanded Disability Status Score, 25-foot timed walk and nine-hole peg test results were also obtained on all MS subjects. We found that ΔR2* values were lower in multiple cortical GM and normal appearing white matter (NAWM regions in MS compared with HC. ΔR2* values of global cortical GM and several specific cortical regions showed significant (p < 0.05 correlations with SDMT and PASAT scores, and showed better correlations than volumetric measures of the same regions. Neurological tests not focused on cognition (Expanded Disability Status Score, 25-foot timed walk and nine-hole peg tests showed no correlation with cortical GM ΔR2* values. The technique presented here is robust and reproducible. It requires less than 10 min and can be implemented on any MRI scanner. Our results show that quantitative tissue-specific R2

  1. Parameter Optimization for Quantitative Signal-Concentration Mapping Using Spoiled Gradient Echo MRI

    Directory of Open Access Journals (Sweden)

    Gasser Hathout

    2012-01-01

    Full Text Available Rationale and Objectives. Accurate signal to tracer concentration maps are critical to quantitative MRI. The purpose of this study was to evaluate and optimize spoiled gradient echo (SPGR MR sequences for the use of gadolinium (Gd-DTPA as a kinetic tracer. Methods. Water-gadolinium phantoms were constructed for a physiologic range of gadolinium concentrations. Observed and calculated SPGR signal to concentration curves were generated. Using a percentage error determination, optimal pulse parameters for signal to concentration mapping were obtained. Results. The accuracy of the SPGR equation is a function of the chosen MR pulse parameters, particularly the time to repetition (TR and the flip angle (FA. At all experimental values of TR, increasing FA decreases the ratio between observed and calculated signals. Conversely, for a constant FA, increasing TR increases this ratio. Using optimized pulse parameter sets, it is possible to achieve excellent accuracy (approximately 5% over a physiologic range of concentration tracer concentrations. Conclusion. Optimal pulse parameter sets exist and their use is essential for deriving accurate signal to concentration curves in quantitative MRI.

  2. Evaluation of grades 3 and 4 chondromalacia of the knee using T2*-weighted 3D gradient-echo articular cartilage imaging.

    Science.gov (United States)

    Murphy, B J

    2001-06-01

    To determine the accuracy of T2*-weighted three-dimensional (3D) gradient-echo articular cartilage imaging in the identification of grades 3 and 4 chondromalacia of the knee. A retrospective evaluation of 80 patients who underwent both arthroscopic and MRI evaluation was performed. The 3D images were interpreted by one observer without knowledge of the surgical results. The medial and lateral femoral condyles, the medial and lateral tibial plateau, the patellar cartilage and trochlear groove were evaluated. MR cartilage images were considered positive if focal reduction of cartilage thickness was present (grade 3 chondromalacia) or if complete loss of cartilage was present (grade 4 chondromalacia). Comparison of the 3D MR results with the arthroscopic findings was performed. Eighty patients were included in the study group. A total of 480 articular cartilage sites were evaluated with MRI and arthroscopy. Results of MR identification of grades 3 and 4 chondromalacia, all sites combined, were: sensitivity 83%, specificity 97%, false negative rate 17%, false positive rate 3%, positive predictive value 87%, negative predictive value 95%, overall accuracy 93%. The results demonstrate that T2*-weighted 3D gradient-echo articular cartilage imaging can identify grades 3 and 4 chondromalacia of the knee.

  3. Evaluation of grades 3 and 4 chondromalacia of the knee using T2*-weighted 3D gradient-echo articular cartilage imaging

    International Nuclear Information System (INIS)

    Murphy, B.J.

    2001-01-01

    Objective. To determine the accuracy of T2*-weighted three-dimensional (3D) gradient-echo articular cartilage imaging in the identification of grades 3 and 4 chondromalacia of the knee.Design and patients. A retrospective evaluation of 80 patients who underwent both arthroscopic and MRI evaluation was performed. The 3D images were interpreted by one observer without knowledge of the surgical results. The medial and lateral femoral condyles, the medial and lateral tibial plateau, the patellar cartilage and trochlear groove were evaluated. MR cartilage images were considered positive if focal reduction of cartilage thickness was present (grade 3 chondromalacia) or if complete loss of cartilage was present (grade 4 chondromalacia). Comparison of the 3D MR results with the arthroscopic findings was performed.Results. Eighty patients were included in the study group. A total of 480 articular cartilage sites were evaluated with MRI and arthroscopy. Results of MR identification of grades 3 and 4 chondromalacia, all sites combined, were: sensitivity 83%, specificity 97%, false negative rate 17%, false positive rate 3%, positive predictive value 87%, negative predictive value 95%, overall accuracy 93%.Conclusion. The results demonstrate that T2*-weighted 3D gradient-echo articular cartilage imaging can identify grades 3 and 4 chondromalacia of the knee. (orig.)

  4. Evaluation of grades 3 and 4 chondromalacia of the knee using T2*-weighted 3D gradient-echo articular cartilage imaging

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, B.J. [Dept. of Radiology, Univ. of Miami School of Medicine, FL (United States)

    2001-06-01

    Objective. To determine the accuracy of T2*-weighted three-dimensional (3D) gradient-echo articular cartilage imaging in the identification of grades 3 and 4 chondromalacia of the knee.Design and patients. A retrospective evaluation of 80 patients who underwent both arthroscopic and MRI evaluation was performed. The 3D images were interpreted by one observer without knowledge of the surgical results. The medial and lateral femoral condyles, the medial and lateral tibial plateau, the patellar cartilage and trochlear groove were evaluated. MR cartilage images were considered positive if focal reduction of cartilage thickness was present (grade 3 chondromalacia) or if complete loss of cartilage was present (grade 4 chondromalacia). Comparison of the 3D MR results with the arthroscopic findings was performed.Results. Eighty patients were included in the study group. A total of 480 articular cartilage sites were evaluated with MRI and arthroscopy. Results of MR identification of grades 3 and 4 chondromalacia, all sites combined, were: sensitivity 83%, specificity 97%, false negative rate 17%, false positive rate 3%, positive predictive value 87%, negative predictive value 95%, overall accuracy 93%.Conclusion. The results demonstrate that T2*-weighted 3D gradient-echo articular cartilage imaging can identify grades 3 and 4 chondromalacia of the knee. (orig.)

  5. The role of T2*-weighted gradient echo in the diagnosis of tumefactive intrahepatic extramedullary hematopoiesis in myelodysplastic syndrome and diffuse hepatic iron overload: a case report and review of the literature.

    Science.gov (United States)

    Belay, Abel A; Bellizzi, Andrew M; Stolpen, Alan H

    2018-01-15

    Extramedullary hematopoiesis is the proliferation of hematopoietic cells outside bone marrow secondary to marrow hematopoiesis failure. Extramedullary hematopoiesis rarely presents as a mass-forming hepatic lesion; in this case, imaging-based differentiation from primary and metastatic hepatic neoplasms is difficult, often leading to biopsy for definitive diagnosis. We report a case of tumefactive hepatic extramedullary hematopoiesis in the setting of myelodysplastic syndrome with concurrent hepatic iron overload, and the role of T2*-weighted gradient-echo magnetic resonance imaging in differentiating extramedullary hematopoiesis from primary and metastatic hepatic lesions. To the best of our knowledge, T2*-weighted gradient-echo evaluation of extramedullary hematopoiesis in the setting of diffuse hepatic hemochromatosis has not been previously described. A 52-year-old white man with myelodysplastic syndrome and marrow fibrosis was found to have a 4 cm hepatic lesion on ultrasound during workup for bone marrow transplantation. Magnetic resonance imaging revealed diffuse hepatic iron overload and non-visualization of the lesion on T2* gradient-echo sequence suggesting the presence of iron deposition within the lesion similar to that in background hepatic parenchyma. Subsequent ultrasound-guided biopsy of the lesion revealed extramedullary hematopoiesis. Six months later, while still being evaluated for bone marrow transplant, our patient was found to have poor pulmonary function tests. Follow-up computed tomography angiogram showed a mass within his right main pulmonary artery. Bronchoscopic biopsy of this mass once again revealed extramedullary hematopoiesis. He received radiation therapy to his chest. However, 2 weeks later, he developed mediastinal hematoma and died shortly afterward, secondary to respiratory arrest. Mass-forming extramedullary hematopoiesis is rare; however, our report emphasizes that it needs to be considered in the initial differential

  6. Utility of echo-planar gradient-echo T2*-weighted MR images in patients with primary intracerebral hemorrhage

    International Nuclear Information System (INIS)

    Yokoe, Toshio; Yoshida, Tazuka; Kobayashi, Nozomu; Nakamura, Yukihiro; Kubota, Kazuyuki

    2005-01-01

    Magnetic resonance imaging (MRI) has the potential to reveal residues of intracerabral hemorrhage (ICH) throughout life because of the high sensitivity for iron-containing compounds. Gradient-echo T2 * -weighted MR imaging (T2 * MRI) requiring short times for complete acquisition is known to detect small areas of signal loss without surrounding edema representing microbleeds (MBs). MBs in the basal ganglia including the thalami are suggested to be closely related to intracerebral atherosclerotic microangiopathy. We looked for more than 3 MBs in basal ganglia or thalamus of patients with and without episodes of previous ICH. Twelve patients with previous hemorrhagic stroke and 82 without were studied. Multiple MBs in those regions were significantly more frequent in patients with recurrent ICH. In addition, a 76-year-old woman with a history of hypertension was transferred to our hospital for treatment of head injury. She had multiple incidental old basal ganglionic and thalamic MBs. The patient had an asymptomatic primary ICH on computed tomography (CT) 3 months later. In conclusion, MR evidence of multiple MBs in the basal ganglia and thalamus might identify patients at a risk for new and recurrent ICH. Therefore, patients with multiple MBs in those regions should be treated for cerebrovascular risk factors, especially hypertension. Our results appear to confirm the utility of T2 * MRI in hemorrhagic stroke. (author)

  7. Numerical calculation of spin echo amplitude in pulsed NMR: effects of quadrupole interaction

    International Nuclear Information System (INIS)

    Sobral, R.R.

    1986-01-01

    The spin echo obtained by nuclear magnetic resonance, in systems which atomic nuclei interact with magnetic fields and electric field gradients, present oscillations in function of the time interval between two excitations pulses. Using the density matrix formalism, the amplitudes of these echo is calculated, analytically. In this work, echo amplitudes obtained under different excitation conditions for nuclei of different nuclear spin values are calculated. The numerical results are compared with disposable analytical solutions. Applications of this method to the case of electric field gradient without axial symmetry were studied. Within the used approximation limits, an expression for attnuation of oscillatory behaviour of echo amplitude in function of the time interval between experimentally observed pulses was obtained. (M.C.K.) [pt

  8. Mapping axonal density and average diameter using non-monotonic time-dependent gradient-echo MRI

    DEFF Research Database (Denmark)

    Nunes, Daniel; Cruz, Tomás L; Jespersen, Sune N

    2017-01-01

    available in the clinic, or extremely long acquisition schemes to extract information from parameter-intensive models. In this study, we suggest that simple and time-efficient multi-gradient-echo (MGE) MRI can be used to extract the axon density from susceptibility-driven non-monotonic decay in the time...... the quantitative results are compared against ground-truth histology, they seem to reflect the axonal fraction (though with a bias, as evident from Bland-Altman analysis). As well, the extra-axonal fraction can be estimated. The results suggest that our model is oversimplified, yet at the same time evidencing......-dependent signal. We show, both theoretically and with simulations, that a non-monotonic signal decay will occur for multi-compartmental microstructures – such as axons and extra-axonal spaces, which we here used in a simple model for the microstructure – and that, for axons parallel to the main magnetic field...

  9. Fast susceptibility-weighted imaging with three-dimensional short-axis propeller (SAP)-echo-planar imaging.

    Science.gov (United States)

    Holdsworth, Samantha J; Yeom, Kristen W; Moseley, Michael E; Skare, S

    2015-05-01

    Susceptibility-weighted imaging (SWI) in neuroimaging can be challenging due to long scan times of three-dimensional (3D) gradient recalled echo (GRE), while faster techniques such as 3D interleaved echo-planar imaging (iEPI) are prone to motion artifacts. Here we outline and implement a 3D short-axis propeller echo-planar imaging (SAP-EPI) trajectory as a faster, motion-correctable approach for SWI. Experiments were conducted on a 3T MRI system. The 3D SAP-EPI, 3D iEPI, and 3D GRE SWI scans were acquired on two volunteers. Controlled motion experiments were conducted to test the motion-correction capability of 3D SAP-EPI. The 3D SAP-EPI SWI data were acquired on two pediatric patients as a potential alternative to 2D GRE used clinically. The 3D GRE images had a better target resolution (0.47 × 0.94 × 2 mm, scan time = 5 min), iEPI and SAP-EPI images (resolution = 0.94 × 0.94 × 2 mm) were acquired in a faster scan time (1:52 min) with twice the brain coverage. SAP-EPI showed motion-correction capability and some immunity to undersampling from rejected data. While 3D SAP-EPI suffers from some geometric distortion, its short scan time and motion-correction capability suggest that SAP-EPI may be a useful alternative to GRE and iEPI for use in SWI, particularly in uncooperative patients. © 2014 Wiley Periodicals, Inc.

  10. A rapid and robust gradient measurement technique using dynamic single-point imaging.

    Science.gov (United States)

    Jang, Hyungseok; McMillan, Alan B

    2017-09-01

    We propose a new gradient measurement technique based on dynamic single-point imaging (SPI), which allows simple, rapid, and robust measurement of k-space trajectory. To enable gradient measurement, we utilize the variable field-of-view (FOV) property of dynamic SPI, which is dependent on gradient shape. First, one-dimensional (1D) dynamic SPI data are acquired from a targeted gradient axis, and then relative FOV scaling factors between 1D images or k-spaces at varying encoding times are found. These relative scaling factors are the relative k-space position that can be used for image reconstruction. The gradient measurement technique also can be used to estimate the gradient impulse response function for reproducible gradient estimation as a linear time invariant system. The proposed measurement technique was used to improve reconstructed image quality in 3D ultrashort echo, 2D spiral, and multi-echo bipolar gradient-echo imaging. In multi-echo bipolar gradient-echo imaging, measurement of the k-space trajectory allowed the use of a ramp-sampled trajectory for improved acquisition speed (approximately 30%) and more accurate quantitative fat and water separation in a phantom. The proposed dynamic SPI-based method allows fast k-space trajectory measurement with a simple implementation and no additional hardware for improved image quality. Magn Reson Med 78:950-962, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  11. Magnetic resonance, especially spin echo, in spinor Bose-Einstein condensates

    International Nuclear Information System (INIS)

    Yasunaga, Masashi; Tsubota, Makoto

    2009-01-01

    Magnetic resonance, especially NMR and ESR, has been studied in magnetic materials for a long time, having been used in various fields. Spin echo is typical phenomenon in magnetic resonance. The magnetic resonance should be applied to spinor Bose-Einstein condensates (BECs). We numerically study spin echo of a spinor BEC in a gradient magnetic field by calculating the spin-1 two-dimensional Gross-Pitaevskii equations, obtaining the recovery of the signal of the spins, which is called spin echo. We will discuss the relation between the spin echo and the Stern-Gelrach separation in the system.

  12. Gradient field echo imaging and Gd-DTPA for the assessment of renal function in humans

    International Nuclear Information System (INIS)

    Von Schulthess, G.K.; Kikinis, R.; Durr, R.; Bino, M.; Jager, P.; Kubler, O.

    1986-01-01

    To evaluate renal parenchymal function, 1.5 T gradient field echo imaging using a sequence of repetitive 10-second scans was performed in apneic patients after injection of Gd-DTPA (0.1 mmol/kg body weight). During the 10-second pauses the patients were allowed to breathe. Angled coronal images (TR=40 msec, TE =20 msec, flip angle = 40 0 ) were obtained in four volunteers and four patients with hydronephrosis. Image quality was excellent, suggesting unprecedented spatial resolution for renal function studies. Initially, cortical perfusion was observed. Then the papilae became isointense; after 70 seconds they became hypointense; and finally the renal pelvic signal dropped. No papillary signal drop was seen in hydronephrosis, as confirmed by region-of-interest analysis. These results strongly suggest that in MR renal ''function'' studies with Gd-DTPA, T1 and T2 paramagnetic effects are operative

  13. Gradient waveform pre-emphasis based on the gradient system transfer function.

    Science.gov (United States)

    Stich, Manuel; Wech, Tobias; Slawig, Anne; Ringler, Ralf; Dewdney, Andrew; Greiser, Andreas; Ruyters, Gudrun; Bley, Thorsten A; Köstler, Herbert

    2018-02-25

    The gradient system transfer function (GSTF) has been used to describe the distorted k-space trajectory for image reconstruction. The purpose of this work was to use the GSTF to determine the pre-emphasis for an undistorted gradient output and intended k-space trajectory. The GSTF of the MR system was determined using only standard MR hardware without special equipment such as field probes or a field camera. The GSTF was used for trajectory prediction in image reconstruction and for a gradient waveform pre-emphasis. As test sequences, a gradient-echo sequence with phase-encoding gradient modulation and a gradient-echo sequence with a spiral read-out trajectory were implemented and subsequently applied on a structural phantom and in vivo head measurements. Image artifacts were successfully suppressed by applying the GSTF-based pre-emphasis. Equivalent results are achieved with images acquired using GSTF-based post-correction of the trajectory as a part of image reconstruction. In contrast, the pre-emphasis approach allows reconstruction using the initially intended trajectory. The artifact suppression shown for two sequences demonstrates that the GSTF can serve for a novel pre-emphasis. A pre-emphasis based on the GSTF information can be applied to any arbitrary sequence type. © 2018 International Society for Magnetic Resonance in Medicine.

  14. Evaluation of renal function with dynamic MRI-T2-weighted gradient echo technique

    International Nuclear Information System (INIS)

    Kato, Katsuya

    1995-01-01

    To evaluate the usefulness of dynamic MRI of kidneys in healthy volunteers and patients with different 24-hour creatinine clearance (Ccr) levels, a dynamic study that employed the T2 weighted gradient echo technique (FLASH: TR/TE=34/25 msec, flip angle= 20 degrees) with single images during breathhold was performed on 10 healthy volunteers and 35 patients, all examined for the Ccr and suspected of having renal parenchymal disease after a phantom study. T1-weighted and dynamic MR imagings were obtained with a 1.5T imager. I analyzed the time-intensity curve of renal cortex and medulla, and defined a cortex decreased ratio (CDR) and medulla decreased ratio (MDR) in comparison with the Ccr. The cortico-medullary difference ratio (CMDR) of T1WI was also compared with the Ccr. The parameters of the T2 dynamic MRI study (CDR, MDR) better correlated with the Ccr than CMDR. Renal function can be quantitatively evaluated with the T2 dynamic MRI and there is a possibility that we can qualitatively evaluate the renal dysfunction and estimate its cause. (author)

  15. Comparison of dynamic dual spin-echo and fast-gradient-echo techniques in the evaluation of cardiac diseases

    International Nuclear Information System (INIS)

    Pettigrew, R.I.; Eisner, R.L.; Groen, J.P.; Baron, M.G.

    1987-01-01

    To determine the relative roles of a dynamic spin-echo method and a fast acquisition with multiphase excitations (FAME) technique, ten patients with myocardial infarction (MI), five with myocardial masses, and five healthy patients were studied with both methods. The dynamic dual-spin-echo (DSE) technique allows acquisition of each of seven sections at 14 cardiac phases in 20 minutes. Wall motion abnormalities were seen equally well with both techniques, but FAME usually required a shorter study time (10 minutes). DSE, however, was superior for evaluating cardiac masses and provided superior wall blood contrast. Thus, these techniques are complementary, and both are now a routine part of the authors' study of cardiac patients

  16. First results in rapid MR imaging of focal liver and spleen lesions using field echos and small angle excitation (gradient echo sequences)

    International Nuclear Information System (INIS)

    Griebel, J.; Hess, C.F.; Kurtz, B.; Klose, U.; Kueper, K.

    1987-01-01

    15 healthy subjects and 39 patients with focal liver and spleen lesions were examined via MR tomography at 1.5 tesla. Gradient field echos at small angle excitation ( 0 ) were employed. The imaging time per layer was 10 seconds so that rapid imaging could be carried out at respiratory standstill. This enabled visualisation of liver and spleen without interference by breathing artifacts and with accurate localisation. Focal lesions can be imaged best at low flip-angle pulses (liver) or low to medium-angle pulses (spleen). The primary liver cell carcinoma is visualised as an inhomogeneous structure with similar signal intensity as the surrounding tissue. All other examined liver lesions (metastases, haemangiomas, lymphatic infiltrates, echinococcus cysts, FNH, gummae) showed greater signal intensity than the remaining organ at small angle excitation. Furthermore, contrast reversals were seen at medium-angle pulses. Contrariwise, with the exception of the light-coloured spleen infarcts, spleen lesions (lymphatic infiltrate, Boeck's disease or sarcoidosis) appeared darker at all excitation angles than the surrounding tissue. (orig.) [de

  17. First results in rapid MR imaging of focal liver and spleen lesions using field echos and small angle excitation (gradient echo sequences)

    Energy Technology Data Exchange (ETDEWEB)

    Griebel, J.; Hess, C.F.; Kurtz, B.; Klose, U.; Kueper, K.

    1987-01-01

    15 healthy subjects and 39 patients with focal liver and spleen lesions were examined via MR tomography at 1.5 tesla. Gradient field echos at small angle excitation (< 90/sup 0/) were employed. The imaging time per layer was 10 seconds so that rapid imaging could be carried out at respiratory standstill. This enabled visualisation of liver and spleen without interference by breathing artifacts and with accurate localisation. Focal lesions can be imaged best at low flip-angle pulses (liver) or low to medium-angle pulses (spleen). The primary liver cell carcinoma is visualised as an inhomogeneous structure with similar signal intensity as the surrounding tissue. All other examined liver lesions (metastases, haemangiomas, lymphatic infiltrates, echinococcus cysts, FNH, gummae) showed greater signal intensity than the remaining organ at small angle excitation. Furthermore, contrast reversals were seen at medium-angle pulses. Contrariwise, with the exception of the light-coloured spleen infarcts, spleen lesions (lymphatic infiltrate, Boeck's disease or sarcoidosis) appeared darker at all excitation angles than the surrounding tissue.

  18. Magnetic resonance imaging of the sacroiliac joints in patients with suspected spondyloarthritis. Comparison of turbo spin-echo and gradient-echo sequences for the detection of structural alterations

    International Nuclear Information System (INIS)

    Dornia, C.; Hoffstetter, P.; Asklepios Klinikum, Bad Abbach; Fleck, M.; Asklepios Klinikum, Bad Abbach; Hartung, W.; Niessen, C.; Stroszczynski, C.

    2015-01-01

    Magnetic resonance imaging (MRI) is the method of choice for the evaluation of spondyloarthritis (SpA). According to the guidelines of the Assessment of Spondyloarthritis International Society (ASAS) and Outcome Measures in Rheumatology (OMERACT), MRI findings in SpA of the spine and the sacroiliac joints (SIJ) are classified as inflammatory and structural alterations. Modern gradient-echo sequences (GRE) are recommended for optimized detection of structural alterations of the SIJ. We assess the benefit of GRE in the detection of structural alterations of the SIJ in comparison to conventional turbo spin-echo sequences (TSE). Retrospective study of 114 patients who received MRI of the SIJ for the evaluation of SpA. Structural alterations of the SIJ were assessed by two blinded readers separately for T1 TSE and T2 * GRE. The findings were classified according to a previously published chronicity score separately for both sides and sequences. Interobserver reliability was calculated with Cohen's Kappa, and the significance of findings was assessed with the Wilcoxon test. P-values * GRE showed a high interobserver reliability in the detection of structural alterations in patients with SpA. However, T2 * GRE detected significantly more structural alterations than T1 TSE and should be an integral part of a modern MRI protocol for the diagnostic workup of patients with suspected SpA.

  19. MRI detection of hypointense brain lesions in patients with multiple sclerosis: T1 spin-echo vs. gradient-echo

    Energy Technology Data Exchange (ETDEWEB)

    Dupuy, Sheena L.; Tauhid, Shahamat; Kim, Gloria; Chu, Renxin; Tummala, Subhash [Departments of Neurology, Brigham and Women' s Hospital, Laboratory for Neuroimaging Research, Partners MS Center, Harvard Medical School, Boston, MA (United States); Hurwitz, Shelley [Departments of Medicine, Brigham and Women' s Hospital, Harvard Medical School, Boston, MA (United States); Bakshi, Rohit, E-mail: rbakshi@bwh.harvard.edu [Departments of Neurology, Brigham and Women' s Hospital, Laboratory for Neuroimaging Research, Partners MS Center, Harvard Medical School, Boston, MA (United States); Departments of Radiology, Brigham and Women' s Hospital, Harvard Medical School, Boston, MA (United States)

    2015-08-15

    Highlights: • Compared T1SE and T1GE in detecting hypointense brain lesions in MS patients. • T1GE detected a higher cerebral lesion volume and number than T1SE. • T1SE correlated significantly with disability, while T1GE did not. • Hypointense lesions on T1SE and T1GE are not interchangeable in patients with MS. - Abstract: Objective: Compare T1 spin-echo (T1SE) and T1 gradient-echo (T1GE) sequences in detecting hypointense brain lesions in multiple sclerosis (MS). Background: Chronic hypointense lesions on T1SE MRI scans are a surrogate of severe demyelination and axonal loss in MS. The role of T1GE images in the detection of such lesions has not been clarified. Design/methods: In 45 patients with MS [Expanded Disability Status Scale (EDSS) score (mean ± SD) 3.5 ± 2.0; 37 relapsing-remitting (RR); 8 secondary progressive (SP)], cerebral T1SE, T1GE, and T2-weighted fluid-attenuated inversion-recovery (FLAIR) images were acquired on a 1.5 T MRI scanner. Images were re-sampled to axial 5 mm slices before directly comparing lesion detectability using Jim (v.7, Xinapse Systems). Statistical methods included Wilcoxon signed rank tests to compare sequences and Spearman correlations to test associations. Results: Considering the entire cohort, T1GE detected a higher lesion volume (5.90 ± 6.21 vs. 4.17 ± 4.84 ml, p < 0.0001) and higher lesion number (27.82 ± 20.66 vs. 25.20 ± 20.43, p < 0.05) than T1SE. Lesion volume differences persisted when considering RR and SP patients separately (both p < 0.01). A higher lesion number by T1GE was seen only in the RR group (p < 0.05). When comparing correlations between lesion volume and overall neurologic disability (EDSS score), T1SE correlated with EDSS (Spearman r = 0.29, p < 0.05) while T1GE (r = 0.23, p = 0.13) and FLAIR (r = 0.24, p = 0.12) did not. Conclusion: Our data suggest that hypointense lesions on T1SE and T1GE are not interchangeable in patients with MS. Based on these results, we hypothesize that T1GE

  20. MRI detection of hypointense brain lesions in patients with multiple sclerosis: T1 spin-echo vs. gradient-echo

    International Nuclear Information System (INIS)

    Dupuy, Sheena L.; Tauhid, Shahamat; Kim, Gloria; Chu, Renxin; Tummala, Subhash; Hurwitz, Shelley; Bakshi, Rohit

    2015-01-01

    Highlights: • Compared T1SE and T1GE in detecting hypointense brain lesions in MS patients. • T1GE detected a higher cerebral lesion volume and number than T1SE. • T1SE correlated significantly with disability, while T1GE did not. • Hypointense lesions on T1SE and T1GE are not interchangeable in patients with MS. - Abstract: Objective: Compare T1 spin-echo (T1SE) and T1 gradient-echo (T1GE) sequences in detecting hypointense brain lesions in multiple sclerosis (MS). Background: Chronic hypointense lesions on T1SE MRI scans are a surrogate of severe demyelination and axonal loss in MS. The role of T1GE images in the detection of such lesions has not been clarified. Design/methods: In 45 patients with MS [Expanded Disability Status Scale (EDSS) score (mean ± SD) 3.5 ± 2.0; 37 relapsing-remitting (RR); 8 secondary progressive (SP)], cerebral T1SE, T1GE, and T2-weighted fluid-attenuated inversion-recovery (FLAIR) images were acquired on a 1.5 T MRI scanner. Images were re-sampled to axial 5 mm slices before directly comparing lesion detectability using Jim (v.7, Xinapse Systems). Statistical methods included Wilcoxon signed rank tests to compare sequences and Spearman correlations to test associations. Results: Considering the entire cohort, T1GE detected a higher lesion volume (5.90 ± 6.21 vs. 4.17 ± 4.84 ml, p < 0.0001) and higher lesion number (27.82 ± 20.66 vs. 25.20 ± 20.43, p < 0.05) than T1SE. Lesion volume differences persisted when considering RR and SP patients separately (both p < 0.01). A higher lesion number by T1GE was seen only in the RR group (p < 0.05). When comparing correlations between lesion volume and overall neurologic disability (EDSS score), T1SE correlated with EDSS (Spearman r = 0.29, p < 0.05) while T1GE (r = 0.23, p = 0.13) and FLAIR (r = 0.24, p = 0.12) did not. Conclusion: Our data suggest that hypointense lesions on T1SE and T1GE are not interchangeable in patients with MS. Based on these results, we hypothesize that T1GE

  1. Diagnositc value of 3D-gradient echo dynamic contrast enhanced MRI in breast cancer

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ik; Chung, Soo Young; Park, Hai Jung; Lee, Yul; Chung, Bong Wha; Shim, Jeong Won [Hallym Univ. College of Medicine, Seoul (Korea, Republic of)

    1997-10-01

    To assess the usefulness of 3D-gradient echo dynamic contrast enhanced MRI (3D-DMRI) in the diagnosis of breast cancer and to determine the most useful parameter for this diagnosis. Using a 1.0T MR unit, (Magnetom, Siemens, Erlaugen, Germany), 3D-DMRI (TR/TE=3D30/12) with Gd-DTPA was performed in 38 cases of breast cancer, 22 of fibroadenoma, and in three normal volunteers. We retrospectively evaluated the findings according to the speed on dynamic study and maximal amount of contrast enhancement during the delayed phase;we calculated the contrast index and morphology of the cancers and compared diagnostic accuracy among these three diagnostic parameters. On conventional spin-echo T1-and T2-weighted images, there was no significant difference of signal intensity between benign fibroadenoma and breast carcinoma. Rapid contrast enhancement (within one minute) was noted in 35 breast cancer lesions (92.1%), but relatively low and slow contrast enhancement (after five minutes) was noted in three such lesions (7.9%). Gradual contrast enhancement was noted in 21 lesions of fibroadenoma(95.5%), but a moderate degree of rapid contrast enhancement (from three to five minutes) was noted in the other case (7.9%). of On the delayed enhanced phase of 3D-DMRI, the maximal amount of contrast enhancement showed no significant difference between fibroadenoma and cancer. On 3D-DMRI, an irregular, spiculated border, with high contrast enhancement was noted in all cases of breast cancer, in particular, irregular thick peripheral contrast enhancement with central necrosis was noted 11cases(28.9%). For the diagnosis of breast cancer, 3D-DMRI is a useful technique. Among the diagnostic criteria of speed, maximal amount of contrast enhancement and morphology, morphologic change after contrast enhancement study was the most useful diagnostic parameter.=20.

  2. Diagnositc value of 3D-gradient echo dynamic contrast enhanced MRI in breast cancer

    International Nuclear Information System (INIS)

    Yang, Ik; Chung, Soo Young; Park, Hai Jung; Lee, Yul; Chung, Bong Wha; Shim, Jeong Won

    1997-01-01

    To assess the usefulness of 3D-gradient echo dynamic contrast enhanced MRI (3D-DMRI) in the diagnosis of breast cancer and to determine the most useful parameter for this diagnosis. Using a 1.0T MR unit, (Magnetom, Siemens, Erlaugen, Germany), 3D-DMRI (TR/TE=3D30/12) with Gd-DTPA was performed in 38 cases of breast cancer, 22 of fibroadenoma, and in three normal volunteers. We retrospectively evaluated the findings according to the speed on dynamic study and maximal amount of contrast enhancement during the delayed phase;we calculated the contrast index and morphology of the cancers and compared diagnostic accuracy among these three diagnostic parameters. On conventional spin-echo T1-and T2-weighted images, there was no significant difference of signal intensity between benign fibroadenoma and breast carcinoma. Rapid contrast enhancement (within one minute) was noted in 35 breast cancer lesions (92.1%), but relatively low and slow contrast enhancement (after five minutes) was noted in three such lesions (7.9%). Gradual contrast enhancement was noted in 21 lesions of fibroadenoma(95.5%), but a moderate degree of rapid contrast enhancement (from three to five minutes) was noted in the other case (7.9%). of On the delayed enhanced phase of 3D-DMRI, the maximal amount of contrast enhancement showed no significant difference between fibroadenoma and cancer. On 3D-DMRI, an irregular, spiculated border, with high contrast enhancement was noted in all cases of breast cancer, in particular, irregular thick peripheral contrast enhancement with central necrosis was noted 11cases(28.9%). For the diagnosis of breast cancer, 3D-DMRI is a useful technique. Among the diagnostic criteria of speed, maximal amount of contrast enhancement and morphology, morphologic change after contrast enhancement study was the most useful diagnostic parameter.=20

  3. 31P NMR imaging of solid bone with solid echoes combined with refocused gradients

    International Nuclear Information System (INIS)

    Li, L.; Utah Univ., Salt Lake City, UT; Kruger, R.A.

    1990-01-01

    This note on 31 p NMR imaging presents some observations of the solid echoes acquired from solid bone and how the proposed solid echo imaging method can be employed to obtain the 31 images of solid bone. (UK)

  4. Gadolinium-Enhanced Three-Dimensional Magnetization - Prepared Rapid Gradient-Echo (3D MP-RAGE) Imaging is Superior to Spin-Echo Imaging in Delineating Brain Metastases

    International Nuclear Information System (INIS)

    Takeda, T.; Takeda, A.; Nagaoka, T.; Kunieda, E.; Takemasa, K.; Watanabe, M.; Hatou, T.; Oguro, S.; Katayama, M.

    2008-01-01

    Background: Precisely defining the number and location of brain metastases is very important for establishing a treatment strategy for malignancies. Although magnetic resonance imaging (MRI) is now considered the best modality, various improvements in sequences are still being made. Purpose: To prospectively compare the diagnostic ability of three-dimensional, magnetization-prepared rapid gradient-echo (3D MP-RAGE) imaging in detecting metastatic brain tumors, with that of two-dimensional spin-echo (2D SE) T1-weighted imaging. Material and Methods: A total of 123 examinations were included in this study, and 119 examinations from 88 patients with known malignancies were analyzed. All patients underwent T1- and T2-weighted 2D SE transverse imaging, followed by gadolinium-enhanced T1-weighted transverse and coronal 2D SE imaging and 3D MP-RAGE transverse imaging. Four radiologists interpreted the images to compare the accuracy and the time required for interpretation for each imaging. Results: 3D MP-RAGE imaging was significantly better than 2D SE imaging for detecting metastatic brain lesions, regardless of the readers' experience. The sensitivities of the 3D MP-RAGE and 2D SE imaging for all observers were 0.81 vs. 0.80 (P>0.05), specificities were 0.93 vs. 0.87 (P 0.05), and accuracies were 0.84 vs. 0.78 (P<0.05), respectively. There was no significant difference in the time required for image interpretation between the two modalities (15.6±4.0 vs. 15.4±4.1 min). Conclusion: 3D MP-RAGE imaging proved superior to 2D SE imaging in the detection of brain metastases

  5. Comparison between gadolinium-enhanced 2D T1-weighted gradient-echo and spin-echo sequences in the detection of active multiple sclerosis lesions on 3.0T MRI

    Energy Technology Data Exchange (ETDEWEB)

    Aymerich, F.X. [Hospital Universitari Vall d' Hebron, Universitat Autonoma de Barcelona, MR Unit. Department of Radiology (IDI), Barcelona (Spain); Universitat Politecnica de Catalunya - Barcelona Tech (UPC), Department of Automatic Control (ESAII), Barcelona (Spain); Auger, C.; Alcaide-Leon, P.; Pareto, D.; Huerga, E.; Corral, J.F.; Mitjana, R.; Rovira, A. [Hospital Universitari Vall d' Hebron, Universitat Autonoma de Barcelona, MR Unit. Department of Radiology (IDI), Barcelona (Spain); Sastre-Garriga, J.; Montalban, X. [Hospital Universitari Vall d' Hebron, Universitat Autonoma de Barcelona, Centre d' Esclerosi Multiple de Catalunya (Cemcat), Department of Neurology/Neuroimmunology, Barcelona (Spain)

    2017-04-15

    To compare the sensitivity of enhancing multiple sclerosis (MS) lesions in gadolinium-enhanced 2D T1-weighted gradient-echo (GRE) and spin-echo (SE) sequences, and to assess the influence of visual conspicuity and laterality on detection of these lesions. One hundred MS patients underwent 3.0T brain MRI including gadolinium-enhanced 2D T1-weighted GRE and SE sequences. The two sets of contrast-enhanced scans were evaluated in random fashion by three experienced readers. Lesion conspicuity was assessed by the image contrast ratio (CR) and contrast-to-noise ratio (CNR). The intracranial region was divided into four quadrants and the impact of lesion location on detection was assessed in each slice. Six hundred and seven gadolinium-enhancing MS lesions were identified. GRE images were more sensitive for lesion detection (0.828) than SE images (0.767). Lesions showed a higher CR in SE than in GRE images, whereas the CNR was higher in GRE than SE. Most misclassifications occurred in the right posterior quadrant. The gadolinium-enhanced 2D T1-weighted GRE sequence at 3.0T MRI enables detection of enhancing MS lesions with higher sensitivity and better lesion conspicuity than 2D T1-weighted SE. Hence, we propose the use of gadolinium-enhanced GRE sequences rather than SE sequences for routine scanning of MS patients at 3.0T. (orig.)

  6. Echo III: The study of electric and magnetic fields with conjugate echoes from artificial electron beams injected into the auroral zone ionosphere

    International Nuclear Information System (INIS)

    Hendrickson, R.A.; Winckler, J.R.; Arnoldy, R.L.

    1976-01-01

    The third in a series of rocket flights carrying large electron guns for electron beam-plasma analysis and magnetosphere probing has been carried out from the Poker Flat rocket range near Fairbanks, Alaska at L=6. Echoes from the injected electrons mirroring at the southern hemisphere conjugate point were observed on the rocket by particle detectors and in the nearby ionosphere by photometers on board the rocket. The bounce time and drift velocities of the echoes were measured using the known trajectory and aspect of the rocket. Ionospheric electric fields near the rocket were inferred from drift motion of the ambient ion population measured by two techniques, electrostatic analyzers on board the rocket and incoherent backscatter radar from the ground. Using model magnetic fields, gradient and curvature drift and bound times have been computed under the conditions appropriate for this experiment. Assuming that field lines are equipotentials, the addition of the observed ionospheric electric field drift to the model-independent gradient and curvature drifts predicts a net echo drift velocity that is in agreement with the observations, provided the Mead-Fairfield 1972--73 model is used. The observed bounce time constitutes an independent model check and is in better agreement with the Olson-Pfitzer model. Echo spatial and temporal fluctuations reflected the turbulence associated with the diffuse aurora into which the rocket was launched

  7. MUSIC. a fast T2* - sensitive MRI technique with enhanced volume coverage

    International Nuclear Information System (INIS)

    Loenneker, Thomas; Hennig, Juergen

    1994-01-01

    A fast imaging method based on gradient-recalled echoes and echo time inter-leaved multi-slice excitation is presented. This method maintains the sensitivity of T 2 * by using a long echo time of at least 35 milliseconds. Bipolar gradients are used to shift the gradient echoes in order to ensure constant TE for each slab and prevent ghost-artefacts within the images caused by spin- or stimulated echoes. This method enhances the total imaging time of a conventional multi-slice gradient echo technique, while maintaining the high volume coverage. Thus, stimulated human cortical activation maps can be detected on standard clinical MR instruments at several planes within measuring times of a few seconds. The efficiency of the technique is demonstrated in the detection of temporary changes in T 2 * in functional MRI experiments of the human visual cortex at a magnetic field strength of 2 tesla. (author). 18 refs., 6 figs

  8. T2{sup *} mapping from multi-echo dixon sequence on gadoxetic acid-enhanced magnetic resonance imaging for the hepatic fat quantification: Can it be used for hepatic function assessment?

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Hyun Suk; Lee, Jeong Min; Yoon, Jeong Hee; Kang, Hyo Jin; Lee, Sang Min; Yang, Hyun Kyung; Han, Joon Koo [Dept. of Radiology, Seoul National University Hospital, Seoul (Korea, Republic of)

    2017-08-01

    To evaluate the diagnostic value of T2{sup *} mapping using 3D multi-echo Dixon gradient echo acquisition on gadoxetic acid-enhanced liver magnetic resonance imaging (MRI) as a tool to evaluate hepatic function. This retrospective study was approved by the IRB and the requirement of informed consent was waived. 242 patients who underwent liver MRIs, including 3D multi-echo Dixon fast gradient-recalled echo (GRE) sequence at 3T, before and after administration of gadoxetic acid, were included. Based on clinico-laboratory manifestation, the patients were classified as having normal liver function (NLF, n = 50), mild liver damage (MLD, n = 143), or severe liver damage (SLD, n = 30). The 3D multi-echo Dixon GRE sequence was obtained before, and 10 minutes after, gadoxetic acid administration. Pre- and post-contrast T2{sup *} values, as well as T2{sup *} reduction rates, were measured from T2{sup *} maps, and compared among the three groups. There was a significant difference in T2{sup *} reduction rates between the NLF and SLD groups (−0.2 ± 4.9% vs. 5.0 ± 6.9%, p = 0.002), and between the MLD and SLD groups (3.2 ± 6.0% vs. 5.0 ± 6.9%, p = 0.003). However, there was no significant difference in both the pre- and post-contrast T2{sup *} values among different liver function groups (p = 0.735 and 0.131, respectively). A receiver operating characteristic (ROC) curve analysis showed that the area under the ROC curve for using T2{sup *} reduction rates to differentiate the SLD group from the NLF group was 0.74 (95% confidence interval: 0.63–0.83). Incorporation of T2{sup *} mapping using 3D multi-echo Dixon GRE sequence in gadoxetic acid-enhanced liver MRI protocol may provide supplemental information for liver function deterioration in patients with SLD.

  9. New spoiled spin-echo technique for three-dimensional MR imaging

    International Nuclear Information System (INIS)

    Darrasse, L.; Mao, L.; Saint-Jalmes, H.

    1989-01-01

    For 3D MR imaging within a convenient scanning time, the authors propose an improved spin-echo technique that permits the use of TRs shorter than 100 msec. They use a two-pulse RF sequence (α-π echo). The echo is read with conventional 3DFT encoding. To avoid steady-state signal refocusing before either α or (imperfect) π pulses, we apply randomized gradient spoilers both before each α pulse and on each side of the π pulse. So the sequence works like standard spin- echo sequences, with the z-magnetization recovery being adjusted by means of α rather than TR. The authors have investigated the method on a new 0.1-T Magnetom system dedicated for 3D MR imaging

  10. NMR multiple-echo phase-contrast blood flow imaging

    International Nuclear Information System (INIS)

    O'Donnell, M.

    1986-01-01

    A method is described for magnetic resonance imaging of fluid flow in a sample, comprising the steps of: (a) immersing the sample in a static magnetic field disposed in a first direction; (b) applying a first sequence of magnetic field gradients and radio-frequency signals to the sample to both define a slab, of the sample to be imaged, in a plane substantially orthogonal to a selected direction for which flow velocity is to be measured, and to obtain a plurality N of spin-echo response signals form that slab; (c) processing the plurality of first sequence spin-echo signals to obtain a complex value A/sub 1/(X,Y,Z) relating both the spin density rho'(X,Y,Z),... and the phase rotation phi(X,Y,Z), induced by the first sequence, for each of a selected number of sequential locations (X,Y,Z) in the sample slab; (d) applying a second sequence of magnetic field gradient and radio-frequency signals to both define the same sample slab as in step (b) and to obtain another plurality N of spin-echo response signals from that slab; (e) including a waveform in at least one of the magnetic field gradient and radio-frequency signals applied in step (d) for imparting to each of the spin-echo signal components from each slab location having a flowing material therein a phase rotation dependent upon the magnitude of the flow velocity therein in the selected direction; (f) processing the plurality of second sequence spin-echo signals to obtain a complex value A/sub 2/(X,Y,Z) relating the spin density rho'(X,Y,Z) and the imparted phase rotation of the sample material along the selected flow measurement direction for each of the sequential locations (X,Y,Z) in the sample slab; and (g) processing the complex values A/sub 1/(X,Y,Z) and A/sub 2/(X,Y,Z) for each sample location to obtain a differential phase-contrast value related to the velocity of the flowing material therein in the selected measurement direction

  11. Imaging of the Achilles tendon in spondyloarthritis: a comparison of ultrasound and conventional, short and ultrashort echo time MRI with and without intravenous contrast

    International Nuclear Information System (INIS)

    Hodgson, R.J.; Emery, P.; Grainger, A.J.; O'Connor, P.J.; Evans, R.; Coates, L.; Marzo-Ortega, H.; Helliwell, P.; McGonagle, D.; Robson, M.D.

    2011-01-01

    To compare conventional MRI, ultrashort echo time MRI and ultrasound for assessing the extent of tendon abnormalities in spondyloarthritis. 25 patients with spondyloarthritis and Achilles symptoms were studied with MRI and ultrasound. MR images of the Achilles tendon were acquired using T1-weighted spin echo, gradient echo and ultrashort echo time (UTE) sequences with echo times (TE) between 0.07 and 16 ms, before and after intravenous contrast medium. Greyscale and power Doppler ultrasound were also performed. The craniocaudal extent of imaging abnormalities measured by a consultant musculoskeletal radiologist was compared between the different techniques. Abnormalities were most extensive on spoiled gradient echo images with TE=2 ms. Contrast enhancement after intravenous gadolinium was greatest on the UTE images (TE=0.07 ms). Fewer abnormalities were demonstrated using unenhanced UTE. Abnormalities were more extensive on MRI than ultrasound. Contrast enhancement was more extensive than power Doppler signal. 3D spoiled gradient echo images with an echo time of 2 ms demonstrate more extensive tendon abnormalities than the other techniques in spondyloarthritis. Abnormalities of vascularity are best demonstrated on enhanced ultrashort echo time images. (orig.)

  12. Correction of echo shift in reconstruction processing for ultra-short TE pulse sequence

    International Nuclear Information System (INIS)

    Takizawa, Masahiro; Ootsuka, Takehiro; Abe, Takayuki; Takahashi, Tetsuhiko

    2010-01-01

    An ultra-short echo time (TE) pulse sequence is composed of a radial sampling that acquires echo signals radially in the K-space and a half-echo acquisition that acquires only half of the echo signal. The shift in the position of the echo signal (echo shift) caused by the timing errors in the gradient magnetic field pulses affects the image quality in the radial sampling with the half-echo acquisition. To improve image quality, we have developed a signal correction algorithm that detects and eliminates this echo shift during reconstruction by performing a pre-scan within 10 seconds. The results showed that image quality is improved under oblique and/or off-centering conditions that frequently cause image distortion due to hardware error. In conclusion, we have developed a robust ultra-short TE pulse sequence that allows wide latitude in the scan parameters, including oblique and off-centering conditions. (author)

  13. A paradoxical signal intensity increase in fatty livers using opposed-phase gradient echo imaging with fat-suppression pulses

    International Nuclear Information System (INIS)

    Mulkern, Robert V.; Voss, Stephan; Loeb Salsberg, Sandra; Krauel, Marta Ramon; Ludwig, David S.

    2008-01-01

    With the increase in obese and overweight children, nonalcoholic fatty liver disease has become more prevalent in the pediatric population. Appreciating subtleties of magnetic resonance (MR) signal intensity behavior from fatty livers under different imaging conditions thus becomes important to pediatric radiologists. We report an initially confusing signal behavior - increased signal from fatty livers when fat-suppression pulses are applied in an opposed-phase gradient echo imaging sequence - and seek to explain the physical mechanisms for this paradoxical signal intensity behavior. Abdominal MR imaging at 3 T with a 3-D volumetric interpolated breath-hold (VIBE) sequence in the opposed-phase condition (TR/TE 3.3/1.3 ms) was performed in five obese boys (14±2 years of age, body mass index >95th percentile for age and sex) with spectroscopically confirmed fatty livers. Two VIBE acquisitions were performed, one with and one without the use of chemical shift selective (CHESS) pulse fat suppression. The ratios of fat-suppressed over non-fat-suppressed signal intensities were assessed in regions-of-interest (ROIs) in five tissues: subcutaneous fat, liver, vertebral marrow, muscle and spleen. The boys had spectroscopically estimated hepatic fat levels between 17% and 48%. CHESS pulse fat suppression decreased subcutaneous fat signals dramatically, by more than 85% within regions of optimal fat suppression. Fatty liver signals, in contrast, were elevated by an average of 87% with CHESS pulse fat suppression. Vertebral marrow signal was also significantly elevated with CHESS pulse fat suppression, while spleen and muscle signals demonstrated only small signal increases on the order of 10%. We demonstrated that CHESS pulse fat suppression actually increases the signal intensity from fatty livers in opposed-phase gradient echo imaging conditions. The increase can be attributed to suppression of one partner of the opposed-phase pair that normally contributes to the

  14. A paradoxical signal intensity increase in fatty livers using opposed-phase gradient echo imaging with fat-suppression pulses

    Energy Technology Data Exchange (ETDEWEB)

    Mulkern, Robert V.; Voss, Stephan [Harvard Medical School, Department of Radiology, Children' s Hospital Boston, Boston, MA (United States); Loeb Salsberg, Sandra; Krauel, Marta Ramon; Ludwig, David S. [Harvard Medical School, Department of Medicine, Children' s Hospital Boston, Boston, MA (United States)

    2008-10-15

    With the increase in obese and overweight children, nonalcoholic fatty liver disease has become more prevalent in the pediatric population. Appreciating subtleties of magnetic resonance (MR) signal intensity behavior from fatty livers under different imaging conditions thus becomes important to pediatric radiologists. We report an initially confusing signal behavior - increased signal from fatty livers when fat-suppression pulses are applied in an opposed-phase gradient echo imaging sequence - and seek to explain the physical mechanisms for this paradoxical signal intensity behavior. Abdominal MR imaging at 3 T with a 3-D volumetric interpolated breath-hold (VIBE) sequence in the opposed-phase condition (TR/TE 3.3/1.3 ms) was performed in five obese boys (14{+-}2 years of age, body mass index >95th percentile for age and sex) with spectroscopically confirmed fatty livers. Two VIBE acquisitions were performed, one with and one without the use of chemical shift selective (CHESS) pulse fat suppression. The ratios of fat-suppressed over non-fat-suppressed signal intensities were assessed in regions-of-interest (ROIs) in five tissues: subcutaneous fat, liver, vertebral marrow, muscle and spleen. The boys had spectroscopically estimated hepatic fat levels between 17% and 48%. CHESS pulse fat suppression decreased subcutaneous fat signals dramatically, by more than 85% within regions of optimal fat suppression. Fatty liver signals, in contrast, were elevated by an average of 87% with CHESS pulse fat suppression. Vertebral marrow signal was also significantly elevated with CHESS pulse fat suppression, while spleen and muscle signals demonstrated only small signal increases on the order of 10%. We demonstrated that CHESS pulse fat suppression actually increases the signal intensity from fatty livers in opposed-phase gradient echo imaging conditions. The increase can be attributed to suppression of one partner of the opposed-phase pair that normally contributes to the

  15. Magnetic resonance cisternography using the fast spin echo method for the evaluation of vestibular schwannoma

    Energy Technology Data Exchange (ETDEWEB)

    Nishizawa, Shigeru; Yokoyama, Tetsuo; Uemura, Kenichi [Hamamatsu Univ. School of Medicine, Shizuoka (Japan)

    1999-04-01

    Neuroimaging of vestibular schwannoma was performed with the fat-suppression spoiled gradient recalled acquisition in the steady state (SPGR) method and magnetic resonance (MR) cisternography, which is a fast spin echo method using a long echo train length, for the preoperative evaluation of the lateral extension of the tumor in the internal auditory canal, and the anatomical identification of the posterior semicircular canal and the nerves in the canal distal to the tumor. The SPGR method overestimated the lateral extension in eight cases, probably because of enhancement of the nerves adjacent to the tumor in the canal. The posterior semicircular canal could not be clearly identified, and the cranial nerves in the canal were shown only as a nerve bundle. In contrast, MR cisternography showed clear images of the lateral extension of the tumor and the facial and cochlear nerves adjacent to the tumor in the internal auditory canal. The anatomical location of the posterior semicircular canal was also clearly shown. These preoperative findings are very useful to plan the extent to which the internal auditory canal can be opened, and for intraoperative identification of the nerves in the canal. MR cisternography is less invasive since no contrast material or radiation is required, as with thin-slice high-resolution computed tomography (CT). MR cisternography should replace high-resolution CT for the preoperative neuroradiological evaluation of vestibular schwannoma. (author)

  16. Differentiation between focal malignant marrow-replacing lesions and benign red marrow deposition of the spine with T2*-corrected fat-signal fraction map using a three -echo volume interpolated breath-hold gradient echo dixon sequence

    International Nuclear Information System (INIS)

    Kim, Yong Pyo; Kim, Sung Jun; Chung, Tae Sub; Yoo, Yeon Hwa; Yoon, Choon Sik; Kanneengiesser, Stephan; Paek, Moon Young; Song, Ho Taek; Lee, Young Han; Suh, Jin Suck

    2014-01-01

    To assess the feasibility of T2 * -corrected fat-signal fraction (FF) map by using the three-echo volume interpolated breath-hold gradient echo (VIBE) Dixon sequence to differentiate between malignant marrow-replacing lesions and benign red marrow deposition of vertebrae. We assessed 32 lesions from 32 patients who underwent magnetic resonance imaging after being referred for assessment of a known or possible vertebral marrow abnormality. The lesions were divided into 21 malignant marrow-replacing lesions and 11 benign red marrow depositions. Three sequences for the parameter measurements were obtained by using a 1.5-T MR imaging scanner as follows: three-echo VIBE Dixon sequence for FF; conventional T1-weighted imaging for the lesion-disc ratio (LDR); pre- and post-gadolinium enhanced fat-suppressed T1-weighted images for the contrast-enhancement ratio (CER). A region of interest was drawn for each lesion for parameter measurements. The areas under the curve (AUC) of the parameters and their sensitivities and specificities at the most ideal cutoff values from receiver operating characteristic curve analysis were obtained. AUC, sensitivity, and specificity were respectively compared between FF and CER. The AUCs of FF, LDR, and CER were 0.96, 0.80, and 0.72, respectively. In the comparison of diagnostic performance between the FF and CER, the FF showed a significantly larger AUC as compared to the CER (p = 0.030), although the difference of sensitivity (p = 0.157) and specificity (p = 0.157) were not significant. Fat-signal fraction measurement using T2 * -corrected three-echo VIBE Dixon sequence is feasible and has a more accurate diagnostic performance, than the CER, in distinguishing benign red marrow deposition from malignant bone marrow-replacing lesions.

  17. Patterns of premature physeal arrest: MR imaging of 111 children.

    Science.gov (United States)

    Ecklund, Kirsten; Jaramillo, Diego

    2002-04-01

    The purpose of this study was to use MR imaging, especially fat-suppressed three-dimensional (3D) spoiled gradient-recalled echo sequences, to identify patterns of growth arrest after physeal insult in children. We evaluated 111 children with physeal bone bridges (median age, 11.4 years) using MR imaging to analyze bridge size, location in physis, signal intensity, growth recovery lines, avascular necrosis, and metaphyseal cartilage tongues. Fifty-eight patients underwent fat-suppressed 3D spoiled gradient-recalled echo imaging with physeal mapping. The cause, bone involved, radiographic appearance, and surgical interventions (60/111) were also correlated. Data were analyzed with the two-tailed Fisher's exact test. Posttraumatic bridges, accounting for 70% (78/111) of patients, were most often distal, especially of the tibia (n = 43) and femur (n = 14), whereas those due to the other miscellaneous causes were more frequently proximal (p children is most often posttraumatic and disproportionately involves the distal tibia and femur where bridges tend to develop at the sites of earliest physiologic closure, namely anteromedially and centrally, respectively. MR imaging, especially with the use of fat-suppressed 3D spoiled gradient-recalled echo imaging, exquisitely shows the growth disturbance and associated abnormalities that may follow physeal injury and guides surgical management.

  18. Evaluation of a multiple spin- and gradient-echo (SAGE) EPI acquisition with SENSE acceleration: applications for perfusion imaging in and outside the brain.

    Science.gov (United States)

    Skinner, Jack T; Robison, Ryan K; Elder, Christopher P; Newton, Allen T; Damon, Bruce M; Quarles, C Chad

    2014-12-01

    Perfusion-based changes in MR signal intensity can occur in response to the introduction of exogenous contrast agents and endogenous tissue properties (e.g. blood oxygenation). MR measurements aimed at capturing these changes often implement single-shot echo planar imaging (ssEPI). In recent years ssEPI readouts have been combined with parallel imaging (PI) to allow fast dynamic multi-slice imaging as well as the incorporation of multiple echoes. A multiple spin- and gradient-echo (SAGE) EPI acquisition has recently been developed to allow measurement of transverse relaxation rate (R2 and R2(*)) changes in dynamic susceptibility contrast (DSC)-MRI experiments in the brain. With SAGE EPI, the use of PI can influence image quality, temporal resolution, and achievable echo times. The effect of PI on dynamic SAGE measurements, however, has not been evaluated. In this work, a SAGE EPI acquisition utilizing SENSE PI and partial Fourier (PF) acceleration was developed and evaluated. Voxel-wise measures of R2 and R2(*) in healthy brain were compared using SAGE EPI and conventional non-EPI multiple echo acquisitions with varying SENSE and PF acceleration. A conservative SENSE factor of 2 with PF factor of 0.73 was found to provide accurate measures of R2 and R2(*) in white (WM) (rR2=[0.55-0.79], rR2*=[0.47-0.71]) and gray (GM) matter (rR2=[0.26-0.59], rR2*=[0.39-0.74]) across subjects. The combined use of SENSE and PF allowed the first dynamic SAGE EPI measurements in muscle, with a SENSE factor of 3 and PF factor of 0.6 providing reliable relaxation rate estimates when compared to multi-echo methods. Application of the optimized SAGE protocol in DSC-MRI of high-grade glioma patients provided T1 leakage-corrected estimates of CBV and CBF as well as mean vessel diameter (mVD) and simultaneous measures of DCE-MRI parameters K(trans) and ve. Likewise, application of SAGE in a muscle reperfusion model allowed dynamic measures of R2', a parameter that has been shown to correlate

  19. Comparison of a T1-weighted inversion-recovery-, gradient-echo- and spin-echo sequence for imaging of the brain at 3.0 Tesla

    International Nuclear Information System (INIS)

    Stehling, C.; Niederstadt, T.; Kraemer, S.; Kugel, H.; Schwindt, W.; Heindel, W.; Bachmann, R.

    2005-01-01

    Purpose: The increased T1 relaxation times at 3.0 Tesla lead to a reduced T1 contrast, requiring adaptation of imaging protocols for high magnetic fields. This prospective study assesses the performance of three techniques for T1-weighted imaging (T1w) at 3.0 T with regard to gray-white differentiation and contrast-to-noise-ratio (CNR). Materials and Methods: Thirty-one patients were examined at a 3.0 T system with axial T1 w inversion recovery (IR), spin-echo (SE) and gradient echo (GE) sequences and after contrast enhancement (CE) with CE-SE and CE-GE sequences. For qualitative analysis, the images were ranked with regard to artifacts, gray-white differentiation, image noise and overall diagnostic quality. For quantitative analysis, the CNR was calculated, and cortex and basal ganglia were compared with the white matter. Results: In the qualitative analysis, IR was judged superior to SE and GE for gray-white differentiation, image noise and overall diagnostic quality, but inferior to the GE sequence with regard to artifacts. CE-GE proved superior to CE-SE in all categories. In the quantitative analysis, CNR of the based ganglia was highest for IR, followed by GE and SE. For the CNR of the cortex, no significant difference was found between IR (16.9) and GE (15.4) but both were superior to the SE (9.4). The CNR of the cortex was significantly higher for CE-GE compared to CE-SE (12.7 vs. 7.6, p<0.001), but the CNR of the basal ganglia was not significantly different. Conclusion: For unenhanced T1w imaging at 3.0 T, the IR technique is, despite increased artifacts, the method of choice due to its superior gray-white differentiation and best overall image quality. For CE-studies, GE sequences are recommended. For cerebral imaging, SE sequences give unsatisfactory results at 3.0 T. (orig.)

  20. MRI of bone marrow: opposed-phase gradient-echo sequences with long repetition time

    International Nuclear Information System (INIS)

    Seiderer, M.; Staebler, A.; Wagner, H.

    1999-01-01

    Signal intensity for opposed-phase gradient-echo (GE) sequences of tissues composed of fat- and water-equivalent cells such as red bone marrow is extremely sensitive to variation of the ratio of both cell populations (fat-to-water ratio Q F/W ). Because most bone marrow pathology results in variation of Q F/W , GE sequences are characterized by high-contrast imaging of pathology. The aim of this study was to evaluate the influence of TR, TE, FA, Q F/W and histology on signal intensity. Signal intensity of opposed-phase GE sequences as a function of TR, TE, FA, and Q F/W was measured for a fat-water phantom and cadaver specimens of normal bone marrow (red and yellow) and pathological bone marrow (tumors). All specimens were correlated to histology. Opposed-phase GE imaging of red bone marrow pathology results in low-signal-intensity imaging of intact red bone marrow and high-signal-intensity positive contrast imaging of pathology associated with a change in Q F/W . In first-order approximation the signal intensity of pathology is linearly correlated to the change in Q F/W . Opposed-phase GE imaging is a sensitive imaging technique for red bone marrow pathology. Relative contrast of red bone marrow pathology is similar to fat-suppressed imaging techniques. Acquisition time is identical to T1-weighted SE sequences. (orig.)

  1. E-region echo characteristics governed by auroral arc electrodynamics

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    2003-07-01

    Full Text Available Observations of a pair of auroral arc features by two imagers, one ground- and one space-based, allows the associated field-aligned current (FAC and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularity-generating mechanisms. This is especially interesting for the E-region echoes observed, which form the focus of our analysis, and from which several conclusions can be drawn, summarized as follows. Latitudinal variations in echo characteristics are governed by the FAC and electric field background. Particularly sharp boundaries are found at the edges of auroral arcs. Within regions of auroral luminosity, echoes have Doppler shifts below the ion-acoustic speed and are proportional to the electric field, suggesting scatter from gradient drift waves. Regions of downward FAC are associated with mixed high and low Doppler shift echoes. The high Doppler shift component is greatly in excess of the ion-acoustic speed, but seems to be commensurate with the driving electric field. The low Doppler shift component appears to be much depressed below expectations.Key words. Ionosphere (ionospheric irregularities; electric fields and currents

  2. E-region echo characteristics governed by auroral arc electrodynamics

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    Full Text Available Observations of a pair of auroral arc features by two imagers, one ground- and one space-based, allows the associated field-aligned current (FAC and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularity-generating mechanisms. This is especially interesting for the E-region echoes observed, which form the focus of our analysis, and from which several conclusions can be drawn, summarized as follows. Latitudinal variations in echo characteristics are governed by the FAC and electric field background. Particularly sharp boundaries are found at the edges of auroral arcs. Within regions of auroral luminosity, echoes have Doppler shifts below the ion-acoustic speed and are proportional to the electric field, suggesting scatter from gradient drift waves. Regions of downward FAC are associated with mixed high and low Doppler shift echoes. The high Doppler shift component is greatly in excess of the ion-acoustic speed, but seems to be commensurate with the driving electric field. The low Doppler shift component appears to be much depressed below expectations.

    Key words. Ionosphere (ionospheric irregularities; electric fields and currents

  3. Clinical utility of partial flip angle T2-weighted spin-echo imaging of the brain

    International Nuclear Information System (INIS)

    Chang, K.H.; Yi, J.G.; Han, M.H.; Han, M.C.; Kim, C.W.; Cho, M.H.; Cho, Z.H.

    1990-01-01

    To assess the clinical usefulness of partial flip angle (PFA) spin-echo (SE) brain imaging, a total of eighty patients were examined with both conventional double echo T2-weighted SE (2500/30, 80/90deg/one excitation) and PFA double echo SE (1200/30, 70/45deg/two excitations) on 2.0T system. Two comparative studies were performed: (1) In 65 patients PFA SE technique was compared with conventional SE without flow compensating gradients, and (2) in 15 patients the former was compared with the latter with flow compensating gradients. Imaging time was nearly identical in each sequence. In both studies we found that PFA T2-weighted SE images were almost identical to those obtained with the conventional SE technique in the contrast characteristics and the detection rate of the abnormalities (100%, 85/85 lesions), and more importantly, PFA SE revealed few flow artifacts in the brain stem, temporal lobes and basal ganglia which were frequently seen on conventional SE without flow compensating gradients. Additionally, PFA SE images demonstrated no suppression of CSF flow void in the aqueduct which was commonly seen on conventional SE with flow compensating gradients. In overall image quality, the PFA SE images, particularly the second echo images, were almost comparable with those of conventional SE with flow compensating gradients. A flip angle of 45deg seems to be close to Ernst angle, the angle at which maximum signal occurs, for a given TR of 1200 msec for CSF and most of the abnormalities containing higher water content. In conclusion, PFA SE sequence (i.e. 1200/30, 70/45deg/2) appears to be useful as a primary or an adjunctive technique in certain clinical circumstances, particularly in imaging of hydrocephalic patients for assessing aqueductal patency. (orig.)

  4. Modified echo peak correction for radial acquisition regime (RADAR).

    Science.gov (United States)

    Takizawa, Masahiro; Ito, Taeko; Itagaki, Hiroyuki; Takahashi, Tetsuhiko; Shimizu, Kanichirou; Harada, Junta

    2009-01-01

    Because radial sampling imposes many limitations on magnetic resonance (MR) imaging hardware, such as on the accuracy of the gradient magnetic field or the homogeneity of B(0), some correction of the echo signal is usually needed before image reconstruction. In our previous study, we developed an echo-peak-shift correction (EPSC) algorithm not easily affected by hardware performance. However, some artifacts remained in lung imaging, where tissue is almost absent, or in cardiac imaging, which is affected by blood flow. In this study, we modified the EPSC algorithm to improve the image quality of the radial aquisition regime (RADAR) and expand its application sequences. We assumed the artifacts were mainly caused by errors in the phase map for EPSC and used a phantom on a 1.5-tesla (T) MR scanner to investigate whether to modify the EPSC algorithm. To evaluate the effectiveness of EPSC, we compared results from T(1)- and T(2)-weighted images of a volunteer's lung region using the current and modified EPSC. We then applied the modified EPSC to RADAR spin echo (SE) and RADAR balanced steady-state acquisition with rewound gradient echo (BASG) sequence. The modified EPSC reduced phase discontinuity in the reference data used for EPSC and improved visualization of blood vessels in the lungs. Motion and blood flow caused no visible artifacts in the resulting images in either RADAR SE or RADAR BASG sequence. Use of the modified EPSC eliminated artifacts caused by signal loss in the reference data for EPSC. In addition, the modified EPSC was applied to RADAR SE and RADAR BASG sequences.

  5. Modified echo peak correction for radial acquisition regime (RADAR)

    International Nuclear Information System (INIS)

    Takizawa, Masahiro; Ito, Taeko; Itagaki, Hiroyuki; Takahashi, Tetsuhiko; Shimizu, Kanichirou; Harada, Junta

    2009-01-01

    Because radial sampling imposes many limitations on magnetic resonance (MR) imaging hardware, such as on the accuracy of the gradient magnetic field or the homogeneity of B 0 , some correction of the echo signal is usually needed before image reconstruction. In our previous study, we developed an echo-peak-shift correction (EPSC) algorithm not easily affected by hardware performance. However, some artifacts remained in lung imaging, where tissue is almost absent, or in cardiac imaging, which is affected by blood flow. In this study, we modified the EPSC algorithm to improve the image quality of the radial acquisition regime (RADAR) and expand its application sequences. We assumed the artifacts were mainly caused by errors in the phase map for EPSC and used a phantom on a 1.5-tesla (T) MR scanner to investigate whether to modify the EPSC algorithm. To evaluate the effectiveness of EPSC, we compared results from T 1 -and T 2 -weighted images of a volunteer's lung region using the current and modified EPSC. We then applied the modified EPSC to RADAR spin echo (SE) and RADAR balanced steady-state acquisition with rewound gradient echo (BASG) sequence. The modified EPSC reduced phase discontinuity in the reference data used for EPSC and improved visualization of blood vessels in the lungs. Motion and blood flow caused no visible artifacts in the resulting images in either RADAR SE or RADAR BASG sequence. Use of the modified EPSC eliminated artifacts caused by signal loss in the reference data for EPSC. In addition, the modified EPSC was applied to RADAR SE and RADAR BASG sequences. (author)

  6. Contrast-enhanced dynamic MR imaging of parasellar tumor using fast spin-echo sequence

    International Nuclear Information System (INIS)

    Kusunoki, Katsusuke; Ohue, Shiro; Ichikawa, Haruhisa; Saito, Masahiro; Sadamoto, Kazuhiko; Sakaki, Saburo; Miki, Hitoshi.

    1995-01-01

    We have applied a new dynamic MRI technique that uses a fast spin-echo sequence to parasellar tumors. This sequence has less susceptible effect and better spatial resolution than a gradient echo sequence, providing faster images than a short spin-echo sequence does. Image was obtained in the coronal or sagittal plane using a 1.5T clinical MRI system, and then, dynamic MR images were acquired every 10 to 20 sec after administration of Gd-DTPA (0.1 mmol/kg). The subjects were 12 patients (5 microadenomas, 5 macroadenomas and 2 Rathke's cleft cysts) and 5 normal volunteers. As for volunteers, the cavernous sinus, pituitary stalk and posterior pituitary gland were contrasted on the first image, followed by visualization of the proximal portion adjacent to the junction of the infundibulum and the anterior pituitary gland, and finally by contrasting the distal portion of the anterior pituitary gland. There was a difference with respect to tumor contrast between microadenomas and macroadenomas. In the case of the macroadenomas, the tumor was contrasted at the same time as, or faster than the anterior pituitary gland, while with the microadenomas the tumor was enhanced later than the anterior pituitary gland. No enhancement with contrast medium was seen in Rathke's cleft cysts. In addition, it was possible to differentiate a recurrent tumor from a piece of muscle placed at surgery since the images obtained by the fast spin-echo sequence were clearer than those obtained by gradient echo sequence. (author)

  7. Screening for skeletal metastases of the spine and pelvis: gradient echo opposed-phase MRI compared with bone scintigraphy

    International Nuclear Information System (INIS)

    Neumann, K.; Hosten, N.; Venz, S.

    1995-01-01

    Opposed-phase gradient echo (GRE) MRI at 0.5 T was compared with T1-weighted GRE MRI and bone scintigraphy regarding the detection of malignant bone marrow infiltrates of the spine and pelvis. Seventeen control patients and 41 patients with suspected skeletal metastases were studied with plain and gadolinium-enhanced MRI. In the control group only a vertebral haemangioma showed contrast enhancement, while all metastases (confirmed histologically or by follow-up) were enhancing. Opposed-phase surface coil MRI showed a significantly higher contrast-to-noise ratio of 56 metastases than T1-weighted images. In 28 patients body coil opposed-phase MRI detected more metastatic foci of the spine and pelvis than did bone scintigraphy (84 vs 56). No scintigraphically visualised lesion was missed by MRI. In conclusion, body coil gadolinium-enhanced opposed-phase GRE MRI may be applied as a screening method for skeletal metastases of the spine and pelvis at intermediate field strengths. (orig.)

  8. Screening for skeletal metastases of the spine and pelvis: gradient echo opposed-phase MRI compared with bone scintigraphy

    Energy Technology Data Exchange (ETDEWEB)

    Neumann, K. [Zentralinstitut fuer Roentgendiagnostik, Universitaetsklinikum Essen, Gesamthochschule Essen (Germany); Hosten, N. [Strahlenklinik und Poliklinik, Universitaetsklinikum Rudolf Virchow, Freie Univ. Berlin (Germany); Venz, S. [Strahlenklinik und Poliklinik, Universitaetsklinikum Rudolf Virchow, Freie Univ. Berlin (Germany)

    1995-11-01

    Opposed-phase gradient echo (GRE) MRI at 0.5 T was compared with T1-weighted GRE MRI and bone scintigraphy regarding the detection of malignant bone marrow infiltrates of the spine and pelvis. Seventeen control patients and 41 patients with suspected skeletal metastases were studied with plain and gadolinium-enhanced MRI. In the control group only a vertebral haemangioma showed contrast enhancement, while all metastases (confirmed histologically or by follow-up) were enhancing. Opposed-phase surface coil MRI showed a significantly higher contrast-to-noise ratio of 56 metastases than T1-weighted images. In 28 patients body coil opposed-phase MRI detected more metastatic foci of the spine and pelvis than did bone scintigraphy (84 vs 56). No scintigraphically visualised lesion was missed by MRI. In conclusion, body coil gadolinium-enhanced opposed-phase GRE MRI may be applied as a screening method for skeletal metastases of the spine and pelvis at intermediate field strengths. (orig.)

  9. Reduction of vascular artifact on T1-weighted images of the brain by using three-dimensional double IR fast spoiled gradient echo recalled acquisition in the steady state (FSPGR) at 3.0 Tesla

    International Nuclear Information System (INIS)

    Fujiwara, Yasuhiro; Yamaguchi, Isao; Ookoshi, Yusuke; Ootani, Yuriko; Matsuda, Tsuyoshi; Ishimori, Yoshiyuki; Hayashi, Hiroyuki; Miyati, Tosiaki; Kimura, Hirohiko

    2007-01-01

    The purpose of this study was to decrease vascular artifacts caused by the in-flow effect in three-dimensional inversion recovery prepared fast spoiled gradient recalled acquisition in the steady state (3D IR FSPGR) at 3.0 Tesla. We developed 3D double IR FSPGR and investigated the signal characteristics of the new sequence. The 3D double IR FSPGR sequence uses two inversion pulses, the first for obtaining tissue contrast and the second for nulling vascular signal, which is applied at the time of the first IR period at the neck region. We have optimized scan parameters based on both phantom and in-vivo study. As a result, optimized parameters (1st TI=700 ms, 2nd TI=400 ms) successfully have produced much less vessel signal at reduction than conventional 3D IR FSPGR over a wide imaging range, while preserving the signal-to-noise ratio (SNR) and gray/white matter contrast. Moreover, the decreased artifact was also confirmed by visual inspection of the images obtained in vivo using those parameters. Thus, 3D double IR FSPGR was a useful sequence for the acquisition of T1-weighted images at 3.0 Tesla. (author)

  10. MRI of the cervical spine with 3D gradient echo sequence at 3 T: initial experience

    International Nuclear Information System (INIS)

    Xiao, L.; Siu, C.W.J.; Yeung, K.; Leung, A.; Yuen, M.K.; Wong, Y.C.

    2015-01-01

    Aim: The aim of this study was to compare three-dimensional (3D) high resolution T2*-weighted gradient echo (3D FFE) magnetic resonance (MR) sequence with conventional 2D T2-weighted turbo spin echo (TSE) MR sequence for imaging of the cervical spine, especially to assess the detectability of the internal anatomy of the cervical spinal cord, i.e. to distinguish the grey and white matter. Methods: Fifteen volunteers were examined at 3.0T MR unit. Signal-to-noise (SNR), contrast-to-noise (CNR) and image homogeneity were evaluated. In the visual analysis, the visibility of anatomical structures of the cervical spine and artifacts were assessed. The nonparametric method of paired sample t-test was adopted to evaluate the differences between the sequences. Results: The 3D FFE sequence provided better results for CNR, cerebrospinal fluid (CSF) versus white matter, grey matter, disk and bone. Moreover, it yielded good results for the CNR grey matter versus white matter. The butterfly-shaped “H” is clearly displayed in the 3D FFE sequence. The statistical analysis revealed the statistically significant difference between the 2D TSE and 3D FFE sequences for the contrast of CSF versus spinal cord (both grey matter and white matter). Conclusion: The 3D FFE sequence in MR imaging of the cervical spinal cord is superior in delineation of spinal cord anatomical structures compared to 2D TSE sequence. -- Highlights: •We investigate the potential of 3D FFE sequence to distinguish the grey-white of the cervical spinal cord at 3T MRI system. •We optimized The 3D FFE sequence was optimized to increase the grey-white contrast. •Utilizing medium TE for T2W and the shortest TR for reduction of susceptibility related artifacts and motion artefacts. •This technique may increase the confidence in the diagnosis of disease with the improved delineation of cord anatomy

  11. Mapping brain activity in gradient-echo functional MRI using principal component analysis

    Science.gov (United States)

    Khosla, Deepak; Singh, Manbir; Don, Manuel

    1997-05-01

    The detection of sites of brain activation in functional MRI has been a topic of immense research interest and many technique shave been proposed to this end. Recently, principal component analysis (PCA) has been applied to extract the activated regions and their time course of activation. This method is based on the assumption that the activation is orthogonal to other signal variations such as brain motion, physiological oscillations and other uncorrelated noises. A distinct advantage of this method is that it does not require any knowledge of the time course of the true stimulus paradigm. This technique is well suited to EPI image sequences where the sampling rate is high enough to capture the effects of physiological oscillations. In this work, we propose and apply tow methods that are based on PCA to conventional gradient-echo images and investigate their usefulness as tools to extract reliable information on brain activation. The first method is a conventional technique where a single image sequence with alternating on and off stages is subject to a principal component analysis. The second method is a PCA-based approach called the common spatial factor analysis technique (CSF). As the name suggests, this method relies on common spatial factors between the above fMRI image sequence and a background fMRI. We have applied these methods to identify active brain ares during visual stimulation and motor tasks. The results from these methods are compared to those obtained by using the standard cross-correlation technique. We found good agreement in the areas identified as active across all three techniques. The results suggest that PCA and CSF methods have good potential in detecting the true stimulus correlated changes in the presence of other interfering signals.

  12. ADAPTIVE ANT COLONY OPTIMIZATION BASED GRADIENT FOR EDGE DETECTION

    Directory of Open Access Journals (Sweden)

    Febri Liantoni

    2014-08-01

    Full Text Available Ant Colony Optimization (ACO is a nature-inspired optimization algorithm which is motivated by ants foraging behavior. Due to its favorable advantages, ACO has been widely used to solve several NP-hard problems, including edge detection. Since ACO initially distributes ants at random, it may cause imbalance ant distribution which later affects path discovery process. In this paper an adaptive ACO is proposed to optimize edge detection by adaptively distributing ant according to gradient analysis. Ants are adaptively distributed according to gradient ratio of each image regions. Region which has bigger gradient ratio, will have bigger number of ant distribution. Experiments are conducted using images from various datasets. Precision and recall are used to quantitatively evaluate performance of the proposed algorithm. Precision and recall of adaptive ACO reaches 76.98 % and 96.8 %. Whereas highest precision and recall for standard ACO are 69.74 % and 74.85 %. Experimental results show that the adaptive ACO outperforms standard ACO which randomly distributes ants.

  13. [3D FSPGR (fast spoiled gradient echo) magnetic resonance imaging in the diagnosis of focal cortical dysplasia in children].

    Science.gov (United States)

    Alikhanov, A A; Sinitsyn, V E; Perepelova, E M; Mukhin, K Iu; Demushkina, A A; Omarova, M O; Piliia, S V

    2001-01-01

    Small dysplastic lesions of the cerebral cortex are often missed by conventional MRI methods. The identification of subtle structural abnormalities by traditional multiplanar rectilinear slices is often limited by the complex convolutional pattern of the brain. We used a method of FSPGR (fast spoiled gradient-echo) of three-dimensional MRI data that improves the anatomical display of the sulcal structure of the hemispheric convexities. It also reduces the asymmetric sampling of gray-white matter that may lead to false-positive results. We present 5 from 12 patients with dysplastic cortical lesions in whom conventional two-dimensional and three-dimensional MRI with multiplanar reformatting was initially considered normal. Subsequent studies using 3D FSPGR identified various types of focal cortical dysplasia in all. These results indicate that an increase in the detection of subtle focal dysplastic lesions may be accomplished when one improves the anatomical display of the brain sulcal structure by performing 3D FSPGR.

  14. Can a single-shot black-blood T2-weighted spin-echo echo-planar imaging sequence with sensitivity encoding replace the respiratory-triggered turbo spin-echo sequence for the liver? An optimization and feasibility study.

    Science.gov (United States)

    Hussain, Shahid M; De Becker, Jan; Hop, Wim C J; Dwarkasing, Soendersing; Wielopolski, Piotr A

    2005-03-01

    To optimize and assess the feasibility of a single-shot black-blood T2-weighted spin-echo echo-planar imaging (SSBB-EPI) sequence for MRI of the liver using sensitivity encoding (SENSE), and compare the results with those obtained with a T2-weighted turbo spin-echo (TSE) sequence. Six volunteers and 16 patients were scanned at 1.5T (Philips Intera). In the volunteer study, we optimized the SSBB-EPI sequence by interactively changing the parameters (i.e., the resolution, echo time (TE), diffusion weighting with low b-values, and polarity of the phase-encoding gradient) with regard to distortion, suppression of the blood signal, and sensitivity to motion. The influence of each change was assessed. The optimized SSBB-EPI sequence was applied in patients (N = 16). A number of items, including the overall image quality (on a scale of 1-5), were used for graded evaluation. In addition, the signal-to-noise ratio (SNR) of the liver was calculated. Statistical analysis was carried out with the use of Wilcoxon's signed rank test for comparison of the SSBB-EPI and TSE sequences, with P = 0.05 considered the limit for significance. The SSBB-EPI sequence was improved by the following steps: 1) less frequency points than phase-encoding steps, 2) a b-factor of 20, and 3) a reversed polarity of the phase-encoding gradient. In patients, the mean overall image quality score for the optimized SSBB-EPI (3.5 (range: 1-4)) and TSE (3.6 (range: 3-4)), and the SNR of the liver on SSBB-EPI (mean +/- SD = 7.6 +/- 4.0) and TSE (8.9 +/- 4.6) were not significantly different (P > .05). Optimized SSBB-EPI with SENSE proved to be feasible in patients, and the overall image quality and SNR of the liver were comparable to those achieved with the standard respiratory-triggered T2-weighted TSE sequence. (c) 2005 Wiley-Liss, Inc.

  15. MR imaging studies of multiple myeloma in the vertebral column

    International Nuclear Information System (INIS)

    Albert, S.; Leeds, N.E.

    1990-01-01

    This paper studies the sensitivity and characteristics of MR imaging in the diagnosis of myeloma in the vertebral column. The cervical, thoracic, and lumbar spines of 12 patients with known multiple myeloma were imaged with small flip angle, fast gradient-echo, proton-density (FPD) as well as spin-echo T1-weighted, T2-weighted, and intermediate (SE 2,000/20-30) imaging. The FPD images were acquired with pulse sequence gradient recalled acquisition in a steady state at a magnetic field strength of 1.5T with use of a license-plate and a circular surface coil

  16. On the factors controlling occurrence of F-region coherent echoes

    Directory of Open Access Journals (Sweden)

    D. W. Danskin

    2002-09-01

    Full Text Available Several factors are known to control the HF echo occurrence rate, including electron density distribution in the ionosphere (affecting the propagation path of the radar wave, D-region radio wave absorption, and ionospheric irregularity intensity. In this study, we consider 4 days of CUTLASS Finland radar observations over an area where the EISCAT incoherent scatter radar has continuously monitored ionospheric parameters. We illustrate that for the event under consideration, the D-region absorption was not the major factor affecting the echo appearance. We show that the electron density distribution and the radar frequency selection were much more significant factors. The electron density magnitude affects the echo occurrence in two different ways. For small F-region densities, a minimum value of 1 × 1011 m-3 is required to have sufficient radio wave refraction so that the orthogonality (with the magnetic field lines condition is met. For too large densities, radio wave strong "over-refraction" leads to the ionospheric echo disappearance. We estimate that the over-refraction is important for densities greater than 4 × 1011 m-3. We also investigated the backscatter power and the electric field magnitude relationship and found no obvious relationship contrary to the expectation that the gradient-drift plasma instability would lead to stronger irregularity intensity/echo power for larger electric fields.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; auroral ionosphere

  17. Independence of echo-threshold and echo-delay in the barn owl.

    Directory of Open Access Journals (Sweden)

    Brian S Nelson

    Full Text Available Despite their prevalence in nature, echoes are not perceived as events separate from the sounds arriving directly from an active source, until the echo's delay is long. We measured the head-saccades of barn owls and the responses of neurons in their auditory space-maps while presenting a long duration noise-burst and a simulated echo. Under this paradigm, there were two possible stimulus segments that could potentially signal the location of the echo. One was at the onset of the echo; the other, after the offset of the direct (leading sound, when only the echo was present. By lengthening the echo's duration, independently of its delay, spikes and saccades were evoked by the source of the echo even at delays that normally evoked saccades to only the direct source. An echo's location thus appears to be signaled by the neural response evoked after the offset of the direct sound.

  18. Agreement between manual relaxometry and semi-automated scanner-based multi-echo Dixon technique for measuring liver T2* in a pediatric and young adult population

    International Nuclear Information System (INIS)

    Serai, Suraj D.; Trout, Andrew T.; Dillman, Jonathan R.; Smith, Ethan A.

    2018-01-01

    Commercially available 3D multi-echo Dixon (mDixon) sequences provide parametric maps of liver T2*, obviating manual curve fitting that is often required with conventional gradient recalled echo (GRE)-based multi-echo relaxometry, potentially simplifying clinical work flow. The purpose of our study was to compare T2* values generated by a 3D mDixon sequence to values generated by GRE-based T2* relaxometry with manual curve fitting in a pediatric and young adult population. We reviewed clinical MRI exams performed at 1.5T for liver iron content estimation between February 2015 and June 2016 that included both mDixon and multi-echo GRE pulse sequences. We obtained mean T2* measurements based on each sequence by drawing regions of interest on each of four axial slices through the mid-liver. We compared mDixon-based and GRE-based T2* measurements using paired t-tests and assessed agreement using single-measure intra-class correlation coefficients and Bland-Altman difference plots. One hundred nine patients met inclusion criteria (site 1=82; site 2=27). Mean age was 12.4±5.8 years, and 42 subjects (39%) were female. There was no statistically significant difference in mean T2* values for the two sequences (pooled means: 11.7±11.0 [GRE] vs. 11.7±10.9 ms [mDixon]; P=0.93). There was excellent absolute agreement between sequences (intraclass correlation coefficient [ICC]=0.98 for patients at both sites, confidence interval [CI]: 0.97-0.98 with mean bias of 0.0 ms [-4.2 ms to +4.2 ms]). 3D mDixon is accurate for measuring liver T2* and can likely replace 2D GRE-based relaxometry. (orig.)

  19. Agreement between manual relaxometry and semi-automated scanner-based multi-echo Dixon technique for measuring liver T2* in a pediatric and young adult population

    Energy Technology Data Exchange (ETDEWEB)

    Serai, Suraj D.; Trout, Andrew T.; Dillman, Jonathan R. [Cincinnati Children' s Hospital Medical Center, Department of Radiology, MLC 5031, Cincinnati, OH (United States); Smith, Ethan A. [Cincinnati Children' s Hospital Medical Center, Department of Radiology, MLC 5031, Cincinnati, OH (United States); University of Michigan Health System, Section of Pediatric Radiology, C.S. Mott Children' s Hospital, Department of Radiology, Ann Arbor, MI (United States)

    2018-01-15

    Commercially available 3D multi-echo Dixon (mDixon) sequences provide parametric maps of liver T2*, obviating manual curve fitting that is often required with conventional gradient recalled echo (GRE)-based multi-echo relaxometry, potentially simplifying clinical work flow. The purpose of our study was to compare T2* values generated by a 3D mDixon sequence to values generated by GRE-based T2* relaxometry with manual curve fitting in a pediatric and young adult population. We reviewed clinical MRI exams performed at 1.5T for liver iron content estimation between February 2015 and June 2016 that included both mDixon and multi-echo GRE pulse sequences. We obtained mean T2* measurements based on each sequence by drawing regions of interest on each of four axial slices through the mid-liver. We compared mDixon-based and GRE-based T2* measurements using paired t-tests and assessed agreement using single-measure intra-class correlation coefficients and Bland-Altman difference plots. One hundred nine patients met inclusion criteria (site 1=82; site 2=27). Mean age was 12.4±5.8 years, and 42 subjects (39%) were female. There was no statistically significant difference in mean T2* values for the two sequences (pooled means: 11.7±11.0 [GRE] vs. 11.7±10.9 ms [mDixon]; P=0.93). There was excellent absolute agreement between sequences (intraclass correlation coefficient [ICC]=0.98 for patients at both sites, confidence interval [CI]: 0.97-0.98 with mean bias of 0.0 ms [-4.2 ms to +4.2 ms]). 3D mDixon is accurate for measuring liver T2* and can likely replace 2D GRE-based relaxometry. (orig.)

  20. Contrast-enhanced MR venography of the head using magnetization prepared rapid gradient echo imaging. Comparison between head and body radiofrequency transmitter coil systems

    International Nuclear Information System (INIS)

    Matsunobu, Satosi; Amanuma, Makoto; Tsukuda, Shunji

    2004-01-01

    The purpose of this study was to evaluate the image quality and vascular selectivity of MR venography of the head using an magnetization prepared rapid gradient echo (MP-RAGE) technique when obtained with a body radiofrequency transmitter coil system. A total of 24 patients were imaged with a head or body radiofrequency (RF) transmission system. Subtraction MR angiography (MRA) was processed with 0.1 mmol Gd-DTPA administration, and signal-to-noise ratios of the vascular system were measured. Venous demonstration and selectivity were also assessed. MP-RAGE MR venography with a body transmission system showed almost the same signal intensity for the venous and arterial systems, resulting in nonspecific vascular demonstration, while the head transmission system showed semi-selective venograms owing to inflow-induced high signal on precontrast images. However, MRA with a body transmission system provided a 1.5- to 2.5-fold higher signal-to-noise ratios based on higher gradient performance and excellent demonstration of the head veins, especially those below the skull base. Although selective venography was difficult, MRA with a body transmission coil provided excellent vascular images of the brain. (author)

  1. Echo

    Energy Technology Data Exchange (ETDEWEB)

    Harvey, Dustin Yewell [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-01-25

    This document is a white paper marketing proposal for Echo™ is a data analysis platform designed for efficient, robust, and scalable creation and execution of complex workflows. Echo’s analysis management system refers to the ability to track, understand, and reproduce workflows used for arriving at results and decisions. Echo improves on traditional scripted data analysis in MATLAB, Python, R, and other languages to allow analysts to make better use of their time. Additionally, the Echo platform provides a powerful data management and curation solution allowing analysts to quickly find, access, and consume datasets. After two years of development and a first release in early 2016, Echo is now available for use with many data types in a wide range of application domains. Echo provides tools that allow users to focus on data analysis and decisions with confidence that results are reported accurately.

  2. The reliability of magnetic resonance imaging in traumatic brain injury lesion detection

    NARCIS (Netherlands)

    Geurts, B.H.J.; Andriessen, T.M.J.C.; Goraj, B.M.; Vos, P.E.

    2012-01-01

    Objective: This study compares inter-rater-reliability, lesion detection and clinical relevance of T2-weighted imaging (T2WI), Fluid Attenuated Inversion Recovery (FLAIR), T2*-gradient recalled echo (T2*-GRE) and Susceptibility Weighted Imaging (SWI) in Traumatic Brain Injury (TBI). Methods: Three

  3. Differentiation of diffuse liver disease with computer-aided tissue echo quantification

    International Nuclear Information System (INIS)

    Cha, Joo Hee; Choi, Byung Ihm; Yun, Eun Joo; Ko, Young Hwan; Song, Chi Sung; Kim, Seung Hyup; Han, Joon Koo; Kim, Tae Kyoung; Lee, Dong Hyuk; Kim, Jong Hyo

    1999-01-01

    The purpose of this study was to evaluate the efficacy of computer-aided tissue echo quantification technique in the differentiation of diffuse liver diseases. Sixty-five patients with chronic liver disease including chronic hepatitis in 21 patients, fatty liver in 11, and liver cirrhosis in 33, and 55 normal volunteers were included in this study. The sonographic images by the Sono-PACS(MARO, Seoul) was recalled and the analysis was done for the hepatic parenchymal coarseness by the program using Visual C++. Difference histogram variation (DHV), edge density (ED) and intertia of concurrence matrix (ICM) were used as the coarseness index. These three indexes were statistically significant (p<0.05) in the differentiation of these four groups. The accuracy of the differentiation between any two of four groups was 83.0%. The accuracy of the differentiation of these four groups was 70.8% at the same time. The computer-aided tissue echo quantification technique is a complementary study for the differentiation of diffuse liver disease.

  4. Relationship between the trochlear groove angle and patellar cartilage morphology defined by 3D spoiled gradient-echo imaging

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Yuko; Tokuda, Osamu; Matsunaga, Naofumi [Yamaguchi University Graduate School of Medicine, Department of Radiology, Yamaguchi (Japan); Fukuda, Kouji [Shunan Memorial Hospital, Division of Radiological Technology, Yamaguchi (Japan); Shiraishi, Gen; Motomura, Tetsuhisa [Shunan Memorial Hospital, Department of Orthopedics Surgery, Yamaguchi (Japan); Kimura, Motoichi [Customer Application Gr., GE Healthcare MR Sales and Marketing Department, Osaka (Japan)

    2012-05-15

    To examine whether the femoral trochlear groove angle (TGA) is a determinant of the patellar cartilage volume and patellar cartilage damage. Patellar cartilage was evaluated by MR imaging in 66 patients (22 males and 44 females) with knee pain. Fat-suppressed 3D spoiled gradient-echo images were used to calculate the cartilage volume and to grade the cartilage damage. The proximal and distal TGAs were measured from axial PD-weighted FSE MR images with fat suppression. For every increase in the TGA at the distal femur, the patellar cartilage volume was significantly increased by 6.07 x 10{sup -3} cm{sup 3} (95% CI: 1.27 x 10{sup -3}, 10.9 x 10{sup -3}) after adjustment for age, gender, and patellar bone volume (P < 0.05). The MR grade of medial patellar cartilage damage progressed as the distal TGA became narrower, although there was no significant correlation between the distal TGA and the MR grading of patellar cartilage damage. A more flattened distal TGA was associated with increased patellar cartilage volume. However, there was no association between TGA and patellar cartilage defects. (orig.)

  5. Initial study of stability and repeatability of measuring R2' and oxygen extraction fraction values in the healthy brain with gradient-echo sampling of spin-echo sequence

    International Nuclear Information System (INIS)

    Hui Lihong; Zhang Xiaodong; He Chao; Xie Sheng; Xiao Jiangxi; Zhang jue; Wang Xiaoying; Jiang Xuexiang

    2010-01-01

    Objective: To evaluate the stability and repeatability of gradient-echo sampling of spin- echo (GESSE) sequence in measuring the R 2 ' value in volunteers, by comparison with traditional GRE sequence (T 2 * ]nap and T 2 map). Methods: Eight normal healthy volunteers were enrolled in this study and written informed consents were obtained from all subjects. MR scanning including sequences of GESSE, T 2 map and T 2 * map were performed in these subjects at resting status. The same protocol was repeated one day later. Raw data from GESSE sequence were transferred to PC to conduct postprocessing with the software built in house. R 2 ' map and OEF map were got consequently. To obtain quantitative R 2 ' and OEF values in the brain parenchyma, six ROIs were equally placed in the anterior, middle and posterior part of bilateral hemispheres. Both mean and standard deviation of R 2 ' and OEF were recorded. All images from T 2 * map and T 2 map were transferred to the Workstation for postprocessing. The ROIs were put at the same areas as those for GESSE sequence. R 2 ' is defined as R 2 ' = R 2 * - R 2 , R 2 * = 1/T 2 * . The R 2 ' value of GESSE sequence were compared with that of GRE sequence. Results: The mean R 2 ' values of GESSE at the first and second scan and those of the GRE were (4.21±0.92), (4.45±0.94) Hz and (7.37±1.47), (6.42±2.33) Hz respectively. The mean OEF values of GESSE at the first and second scan is 0.327±0.036 and 0.336± 0.035 respectively. The R 2 ' value and OEF value obtained from GESSE were not significantly different between the first and second scan (t=-0.83, -1.48, P>0.05). The R 2 ' value of first GRE imaging had significantly statistical difference from that of second GRE imaging (t=1.80, P 2 ' value of GESSE sequence was less than that of GRE sequence, and there was significantly statistical difference between them (t=1.71, P<0.05). Conclusion: The GESSE sequence has good stability and repeatability with promising clinical practicability

  6. Low-field MR imaging of the spine. A comparative study of a traditional and a new, completely balanced gradient-echo sequence

    International Nuclear Information System (INIS)

    Drejer, J.; Thomsen, H.S.; Tanttu, J.

    1995-01-01

    49 patients underwent 53 examinations with both a traditional T1-weighted gradient-echo (PS) sequence and a new completely balanced steady-state 3-D (CBASS3D) sequence; 20 examinations included the cervical spine, 8 the thoracic spine and 25 the lumbar spine. All 106 examinations were reviewed twice regarding visibility of selected structures in the spinal region and diagnostic usefulness. The CBASS3D sequence delineated the medulla, nerve roots, CSF, the intervertebral discs and the posterior longitudinal ligament significantly better than the PS sequence. Disc hernia was also better visualised (p<0.01). There were significantly more artefacts on images obtained with the CBASS3D sequence, but they were usually outside the region of interest and occurred less frequently over time due to increased experience of the staff. Both reviewers found the diagnostic usefulness of CBASS3D to be superior compared to that of PS and excellent for diagnostic purposes. (orig./MG)

  7. Low-field MR imaging of the spine. A comparative study of a traditional and a new, completely balanced gradient-echo sequence

    Energy Technology Data Exchange (ETDEWEB)

    Drejer, J. [Dept. of Diagnostic Radiology, Herlev Hospital, Univ. Copenhagen (Denmark); Thomsen, H.S. [Dept. of Diagnostic Radiology, Herlev Hospital, Univ. Copenhagen (Denmark); Tanttu, J. [Picker Nordstar, Helsinki (Finland)

    1995-09-01

    49 patients underwent 53 examinations with both a traditional T1-weighted gradient-echo (PS) sequence and a new completely balanced steady-state 3-D (CBASS3D) sequence; 20 examinations included the cervical spine, 8 the thoracic spine and 25 the lumbar spine. All 106 examinations were reviewed twice regarding visibility of selected structures in the spinal region and diagnostic usefulness. The CBASS3D sequence delineated the medulla, nerve roots, CSF, the intervertebral discs and the posterior longitudinal ligament significantly better than the PS sequence. Disc hernia was also better visualised (p<0.01). There were significantly more artefacts on images obtained with the CBASS3D sequence, but they were usually outside the region of interest and occurred less frequently over time due to increased experience of the staff. Both reviewers found the diagnostic usefulness of CBASS3D to be superior compared to that of PS and excellent for diagnostic purposes. (orig./MG).

  8. K-space trajectory mapping and its application for ultrashort Echo time imaging

    Czech Academy of Sciences Publication Activity Database

    Latta, P.; Starčuk jr., Zenon; Gruwel, M. L. H.; Weber, M.H.; Tomanek, B.

    2017-01-01

    Roč. 36, February (2017), s. 68-76 ISSN 0730-725X R&D Projects: GA ČR(CZ) GA15-12607S Institutional support: RVO:68081731 Keywords : gradient imperfections * K-space deviation * trajectrory estaimation * ultrashort echo time Subject RIV: FS - Medical Facilities ; Equipment OBOR OECD: Medical engineering Impact factor: 2.225, year: 2016

  9. Myocardial first pass perfusion imaging with gadobutrol: impact of parallel imaging algorithms on image quality and signal behavior.

    Science.gov (United States)

    Theisen, Daniel; Wintersperger, Bernd J; Huber, Armin; Dietrich, Olaf; Reiser, Maximilian F; Schönberg, Stefan O

    2007-07-01

    To implement parallel imaging algorithms in fast gradient recalled echo sequences for myocardial perfusion imaging and evaluate image quality, signal-to-noise ratio (SNR), contrast-enhancement ratio (CER), and semiquantitative perfusion parameters. In 20 volunteers, myocardial perfusion imaging with gadobutrol was performed at rest using an accelerated TurboFLASH sequence (TR 2.3 milliseconds, TE 0.93 milliseconds, flip angle [FA] 15 degrees) with GRAPPA, R=2. A nonaccelerated TurboFLASH sequence with similar scan parameters served as standard of reference. Artifacts were assessed qualitatively. SNR, CER, and CNR were calculated and semiquantitative perfusion parameters were determined from fitted SI-time curves. Phantom measurements yielded significant higher SNR for nonaccelerated images (Pimages (Pimages for artifacts by 2 board-certified radiologists yielded a significant reduction in dark rim artifacts with GRAPPA, R=2 (P<0.001). The application of GRAPPA with an acceleration factor of R=2 leads to a significant reduction of dark rim artifacts in fast gradient recalled echo sequences.

  10. Ultimate gradient in solid-state accelerators

    International Nuclear Information System (INIS)

    Whittum, D.H.

    1998-08-01

    The authors recall the motivation for research in high-gradient acceleration and the problems posed by a compact collider. They summarize the phenomena known to appear in operation of a solid-state structure with large fields, and research relevant to the question of the ultimate gradient. They take note of new concepts, and examine one in detail, a miniature particle accelerator based on an active millimeter-wave circuit and parallel particle beams

  11. ECHO Gov Login | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  12. Comparison of third-order plasma wave echoes with ballistic second-order plasma wave echoes

    International Nuclear Information System (INIS)

    Leppert, H.D.; Schuelter, H.; Wiesemann, K.

    1982-01-01

    The apparent dispersion of third-order plasma wave echoes observed in a high frequency plasma is compared with that of simultaneously observed ballistic second-order echoes. Amplitude and wavelength of third-order echoes are found to be always smaller than those of second-order echoes, however, the dispersion curves of both types of echoes are very similar. These observations are in qualitative agreement with calculations of special ballistic third-order echoes. The ballistic nature of the observed third-order echoes may, therefore, be concluded from these measurements. (author)

  13. Gradient pre-emphasis to counteract first-order concomitant fields on asymmetric MRI gradient systems.

    Science.gov (United States)

    Tao, Shengzhen; Weavers, Paul T; Trzasko, Joshua D; Shu, Yunhong; Huston, John; Lee, Seung-Kyun; Frigo, Louis M; Bernstein, Matt A

    2017-06-01

    To develop a gradient pre-emphasis scheme that prospectively counteracts the effects of the first-order concomitant fields for any arbitrary gradient waveform played on asymmetric gradient systems, and to demonstrate the effectiveness of this approach using a real-time implementation on a compact gradient system. After reviewing the first-order concomitant fields that are present on asymmetric gradients, we developed a generalized gradient pre-emphasis model assuming arbitrary gradient waveforms to counteract their effects. A numerically straightforward, easily implemented approximate solution to this pre-emphasis problem was derived that was compatible with the current hardware infrastructure of conventional MRI scanners for eddy current compensation. The proposed method was implemented on the gradient driver subsystem, and its real-time use was tested using a series of phantom and in vivo data acquired from two-dimensional Cartesian phase-difference, echo-planar imaging, and spiral acquisitions. The phantom and in vivo results demonstrated that unless accounted for, first-order concomitant fields introduce considerable phase estimation error into the measured data and result in images with spatially dependent blurring/distortion. The resulting artifacts were effectively prevented using the proposed gradient pre-emphasis. We have developed an efficient and effective gradient pre-emphasis framework to counteract the effects of first-order concomitant fields of asymmetric gradient systems. Magn Reson Med 77:2250-2262, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  14. Efficacy of T2*-Weighted Gradient-Echo MRI in Early Diagnosis of Cerebral Venous Thrombosis with Unilateral Thalamic Lesion

    Directory of Open Access Journals (Sweden)

    Shingo Mitaki

    2013-01-01

    Full Text Available Cerebral venous thrombosis (CVT is an uncommon cause of stroke with diverse etiologies and varied clinical presentations. Because of variability in clinical presentation and neuroimaging, CVT remains a diagnostic challenge. Recently, some studies have highlighted the value of T2*-weighted gradient-echo MRI (T2*WI in the diagnosis of CVT. We report the case of a 79-year-old woman with CVT due to a hypercoagulable state associated with cancer. On the initial T2-weighted image (T2WI, there was a diffuse high-intensity lesion in the right thalamus, extending into the posterior limb of the internal capsule and midbrain. T2*WI showed diminished signal and enlargement of the right basilar vein and the vein of Galen. Even though there is a wide range of differential diagnoses in unilateral thalamic lesions, and a single thalamus lesion is a rare entity of CVT, based on T2*WI findings we could make an early diagnosis and perform treatment. Our case report suggests that T2*WI could detect thrombosed veins and be a useful method of early diagnosis in CVT.

  15. Application of diffusion-weighted echo planar imaging for diagnosis of small acute and subacute brain ischemic lesions

    International Nuclear Information System (INIS)

    Enomoto, Kyoko; Watanabe, Tsuneya; Amanuma, Makoto; Heshiki, Atsuko

    1997-01-01

    The aim of this study was to determine the utility of diffusion-weighted echo planar imaging (DW-EPI) for detecting acute and subacute brain ischemic foci less than 2 cm in size. Thirty patients underwent DW-EPI on a 1.5 T super-conducting unit using a SE-EPI sequence with an arbitrary pair of Stejskal-Tanner gradients applied along the imaging axes. DW-EPI demonstrated all the mast recent ischemic lesions as areas of decreased diffusion, providing greater conspicuity and larger size than conventional spin-echo imaging. DW-EPI is a promising method to detect within a subsecond early ischemia and reversible ischemic changes that are not demonstrate on routine spin-echo images. (author)

  16. Slow flow and mural thrombus in aortic diseases: Spin-echo MR findings and their differentiation

    International Nuclear Information System (INIS)

    Chung, Jin Wook; Park, Jae Hyung; Han, Man Chung

    1993-01-01

    In order to evaluate the ability of spin-echo MR imaging to differentiate slow flow from mural thrombus in aortic diseases, we reviewed the spin-echo MR images of 13 patients with intraaortic thrombus documented by CT (N=11) or aortography (N=2). Six patients had aortic aneurysms and seven had aortic dissections. Intraaortic mural thrombi were accompanied by flow-related intraluminal signal of various pattern and extents in all 13 patients. On 10 gated MR studies, slow flow regions showed ever-echo rephasing phenomenon (N=8), interslice variation of signal intensities of the intraluminal signal (N=7) and flow-related ghost artifact (N=2). However, these MR flow phenomena were obscured on two of three non-gated studies. Seven of 13 intraaortic thrombi remained hyperintense on T2-weighted second-echo images. In these circumstance, a hypointense boundary layer between slow flow and mural thrombus, which was caused by either ' boundary layer dephasing phenomenon' of slow flow or 'paramagnetic T2 shortening' of fresh clot at the edge of mural thrombus, was very useful in discriminating the area of slow flow from that of mural thrombus. Proper interpretation of spin-echo MR images may obviate the need for phase display imaging or gradient-echo imaging in differentiating slow flow and mural thrombus

  17. ECHO virus

    Science.gov (United States)

    ... page: //medlineplus.gov/ency/article/001340.htm ECHO virus To use the sharing features on this page, please enable JavaScript. Enteric cytopathic human orphan (ECHO) viruses are a group of viruses that can lead ...

  18. Fast spin-echo imaging

    International Nuclear Information System (INIS)

    Mackey, K.; Zoarski, G.; Bentson, J.R.; Lufkin, R.B.; Melki, P.; Jolesz, F.

    1991-01-01

    This paper reports on a partial radio-frequency (RF) echo-planar pulse sequence called contiguous slice fast spin echo (CSFSE) which is undergoing clinical trials for spine MR imaging. In this variation of rapid acquisition relaxation enhanced (RARE) spin-echo imaging, rapid 180 degrees RF pulse generated refocused echoes, producing T2-weighted images in about one-third the time of conventional double-echo technique. Forty patients with suspected pathology of the spine were imaged with conventional double-echo and closely matched CSFSE techniques on a GE Signa 1.5-T Advantage system. Cases were reviewed by two board-certified neuroradiologists. In all cases the CSFSE images were of equal or superior quality compared with those obtained with the conventional double-echo technique. Pathologic processes that were imaged consisted of inflammatory, neoplastic, posttraumatic, and degenerative conditions

  19. Diffusional behavior of n-paraffins with various chain lengths in urea adduct channels by pulsed field-gradient spin-echo NMR spectroscopy

    International Nuclear Information System (INIS)

    Kim, Sunmi; Kuroki, Shigeki; Ando, Isao

    2006-01-01

    The diffusion coefficients (D) of n-paraffin molecules (n-C n H 2n+2 ) with various chain-lengths (n = 8, 12, 21, 26, 28 and 32) in the long channels of a deuterated urea-d 4 adduct have been measured at 25 deg. C by means of pulsed field-gradient spin-echo 1 H NMR method. The aim is to clarify diffusional behavior of the n-paraffin molecules in the urea adduct channels. From the experimental results, it is found that n-paraffin molecules are diffusing in the long channels and have two kinds of diffusion components, namely a fast (D ∼ 10 -10 m 2 /s) and a slow diffusion component (D ∼ 10 -11 m 2 /s). The diffusing-time (Δ) dependence of the diffusion coefficients of the n-paraffins shows some likely evidence of restricted diffusion since the n-paraffin molecules are confined in the urea channel. The diffusion coefficients (D) decrease as the carbon number increases from 8 to 28, and very slowly decreases as the carbon number increases from 28 to 32

  20. Measurement of gradient magnetic field temporal characteristics

    International Nuclear Information System (INIS)

    Bartusek, K.; Jflek, B.

    1994-01-01

    We describe a technique of measuring the time dependence and field distortions of magnetic fields due to eddy currents (EC) produced by time-dependent magnetic field gradients. The EC measuring technique makes use of a large volume sample and selective RF excitation pulses and free induction decay (FID) (or a spin or gradient echo) to measure the out-of-phase component of the FID, which is proportional to γδB, i.e. the amount the signal is off resonance. The measuring technique is sensitive, easy to implement and interpret, and used for determining pre-emphasis compensation parameters

  1. Grating stimulated echo

    International Nuclear Information System (INIS)

    Dubetsky, B.; Berman, P.R.; Sleator, T.

    1992-01-01

    A theory of a grating simulated echo (GTE) is developed. The GSE involves the sequential excitation of atoms by two counterpropagating traveling waves, a standing wave, and a third traveling wave. It is shown that the echo signal is very sensitive to small changes in atomic velocity, much more sensitive than the normal stimulated echo. Use of the GSE as a collisional probe or accelerometer is discussed

  2. Larmor labeling by time-gradient magnetic fields

    International Nuclear Information System (INIS)

    Ioffe, Alexander; Bodnarchuk, Victor; Bussmann, Klaus; Mueller, Robert

    2007-01-01

    The Larmor labeling of neutrons, due to the Larmor precession of neutron spin in a magnetic field, opens the unique possibility for the development of neutron spin-echo (NSE) based on neutron scattering techniques, featuring an extremely high energy (momentum) resolution. Here, we present the experimental proof of a new method of the Larmor labeling using time-gradient magnetic fields

  3. B1 gradient coherence selection using a tapered stripline.

    Science.gov (United States)

    van Meerten, S G J; Tijssen, K C H; van Bentum, P J M; Kentgens, A P M

    2018-01-01

    Pulsed-field gradients are common in modern liquid state NMR pulse sequences. They are often used instead of phase cycles for the selection of coherence pathways, thereby decreasing the time required for the NMR experiment. Soft off-resonance pulses with a B 1 gradient result in a spatial encoding similar to that created by pulsed-field (B 0 ) gradients. In this manuscript we show that pulse sequences with pulsed-field gradients can easily be converted to one which uses off-resonance B 1 field gradient (OFFBEAT) pulses. The advantage of B 1 gradient pulses for coherence selection is that the chemical shift evolution during the pulses is (partially) suppressed. Therefore no refocusing echos are required to correct for evolution during the gradient pulses. A tapered stripline is shown to be a convenient tool for creating a well-defined gradient in the B 1 field strength. B 1 gradient coherence selection using a tapered stripline is a simple and cheap alternative to B 0 pulsed-field gradients. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

  4. MR-Imaging optimisation of the articular hip cartilage by using a T{sub 1}-weighted 3-dimensional gradient-echo sequence and the application of a hip joint traction; Magnetresonanztomographische Optimierung der Hueftknorpeldarstellung durch die Wahl einer T{sub 1}-Volumen-Gradienten-Echo-Sequenz und die Anwendung einer Hueftgelenkstraktion

    Energy Technology Data Exchange (ETDEWEB)

    Rosenberg, R. [Heidelberg Univ. (Germany). Orthopaedische Klinik und Poliklinik; Bernd, L. [Heidelberg Univ. (Germany). Orthopaedische Klinik und Poliklinik; Wrazidlo, W. [ATOS-Praxisklinik, Heidelberg (Germany). Radiologische Gemeinschaftspraxis Drs. Lederer, Schneider und Wrazidlo; Lederer, W. [ATOS-Praxisklinik, Heidelberg (Germany). Radiologische Gemeinschaftspraxis Drs. Lederer, Schneider und Wrazidlo; Schneider, S. [ATOS-Praxisklinik, Heidelberg (Germany). Radiologische Gemeinschaftspraxis Drs. Lederer, Schneider und Wrazidlo

    1995-10-01

    Images of three animal cadaver hips, 8 dissected patient femoral heads and 18 hip joints of human corpses, all either with arthrosis stage I-III or artificial cartilage defects, were compared with their corresponding anatomic sections. Additional histomorphologic examinations of the arthrotic cartilages were conducted, and MR-Imaging of 20 healthy and 21 arthrotic patient hips was performed using a specific traction method. Using a T{sub 1}-weighted 3-dimensional gradient-echo sequence and a traction of the hip joint, it was possible due to the low-signal imaging of the joint space to separate in vivo the high-signal femoral head cartilage from the high-signal acetabular cartilage. In horizontal position of the phase-encoding parameter, minimisation of the chemical-shift artifact, mainly in the ventro-lateral areas, was accomplished. MRI measurements of the articular cartilage widths showed significant correlations (p < 0.001) with the corresponding anatomic sections. At the same time the T{sub 1} 3-dimensional gradient-echo sequence of the lateral femoral head with r = 0.94 showed the lowest deviations of the measurements. It was possible with MR-Imaging to distinguish four cartilage qualities. (orig./MG) [Deutsch] Im experimentellen Teil der Studie wurden den MRT-Bildern von drei Kadavertierhueften, 8 resezierten Patientenhueftkoepfen und 18 Leichenhueftgelenken, an denen entweder artifizielle Knorpeldefekte gesetzt wurden oder die ein Koxarthrose-Stadium I-III aufwiesen, die korrespondierenden makroskopischen Kryomikrotomschnitte zugeordnet. Bei den Koxarthrosen erfolgten zusaetzliche histomorphologische Knorpeluntersuchungen. Im klinischen Teil der Studie wurden 20 gesunde und 21 arthrotische Probandenhueftgelenke mit einem speziellen Traktionsverfahren untersucht. Unter Anwendung einer T{sub 1}-Volumen-Gradienten-Echo-Sequenz und einer Traktion am zu untersuchenden Hueftgelenk konnte in vivo durch die signalarme Darstellung des Gelenkspaltes der

  5. Technical Failure of MR Elastography Examinations of the Liver: Experience from a Large Single-Center Study.

    Science.gov (United States)

    Wagner, Mathilde; Corcuera-Solano, Idoia; Lo, Grace; Esses, Steven; Liao, Joseph; Besa, Cecilia; Chen, Nelson; Abraham, Ginu; Fung, Maggie; Babb, James S; Ehman, Richard L; Taouli, Bachir

    2017-08-01

    Purpose To assess the determinants of technical failure of magnetic resonance (MR) elastography of the liver in a large single-center study. Materials and Methods This retrospective study was approved by the institutional review board. Seven hundred eighty-one MR elastography examinations performed in 691 consecutive patients (mean age, 58 years; male patients, 434 [62.8%]) in a single center between June 2013 and August 2014 were retrospectively evaluated. MR elastography was performed at 3.0 T (n = 443) or 1.5 T (n = 338) by using a gradient-recalled-echo pulse sequence. MR elastography and anatomic image analysis were performed by two observers. Additional observers measured liver T2* and fat fraction. Technical failure was defined as no pixel value with a confidence index higher than 95% and/or no apparent shear waves imaged. Logistic regression analysis was performed to assess potential predictive factors of technical failure of MR elastography. Results The technical failure rate of MR elastography at 1.5 T was 3.5% (12 of 338), while it was higher, 15.3% (68 of 443), at 3.0 T. On the basis of univariate analysis, body mass index, liver iron deposition, massive ascites, use of 3.0 T, presence of cirrhosis, and alcoholic liver disease were all significantly associated with failure of MR elastography (P analysis, only body mass index, liver iron deposition, massive ascites, and use of 3.0 T were significantly associated with failure of MR elastography (P technical failure rate of MR elastography with a gradient-recalled-echo pulse sequence was low at 1.5 T but substantially higher at 3.0 T. Massive ascites, iron deposition, and high body mass index were additional independent factors associated with failure of MR elastography of the liver with a two-dimensional gradient-recalled-echo pulse sequence. © RSNA, 2017.

  6. Three-dimensional cine MRI in free-breathing infants and children with congenital heart disease

    Energy Technology Data Exchange (ETDEWEB)

    Seeger, Achim; Fenchel, Michael C.; Kramer, Ulrich; Bretschneider, Christiane; Doering, Joerg; Claussen, Claus D.; Miller, Stephan [University of Tuebingen (Germany). Department of Diagnostic and Interventional Radiology; Greil, Gerald F. [St. Thomas Hospital, Division of Imaging Sciences, King' s College London (United Kingdom); Martirosian, Petros [University of Tuebingen, Section of Experimental Radiology, Tuebingen (Germany); Sieverding, Ludger [University of Tuebingen, Department of Pediatric Cardiology, Tuebingen (Germany)

    2009-12-15

    Patients with congenital heart disease frequently have complex cardiac and vascular malformations requiring detailed non-invasive diagnostic evaluation including functional parameters. To evaluate the morphological and functional information provided by a novel 3-D cine steady-state free-precession (SSFP) sequence. Twenty consecutive children (mean age 2.2 years, nine boys) were examined using a 1.5-T MR system including 2-D cine gradient-recalled-echo sequences, static 3-D SSFP and 3-D cine SSFP sequences. Measurement of ventricular structures and volumes showed close agreement between the 3-D cine SSFP sequence and the 2-D cine gradient-recalled-echo and static 3-D SSFP sequences (left ventricular volumes mean difference 1.0-1.9 ml and 8.8-11.4%, respectively; right ventricular volumes 1.7-2.1 ml and 9.9-16.9%, respectively). No systematic bias was observed. 3-D cine MRI provides anatomic as well as functional information with sufficient spatial and temporal resolution in free-breathing infants with congenital heart disease. (orig.)

  7. Three-dimensional cine MRI in free-breathing infants and children with congenital heart disease

    International Nuclear Information System (INIS)

    Seeger, Achim; Fenchel, Michael C.; Kramer, Ulrich; Bretschneider, Christiane; Doering, Joerg; Claussen, Claus D.; Miller, Stephan; Martirosian, Petros; Sieverding, Ludger

    2009-01-01

    Patients with congenital heart disease frequently have complex cardiac and vascular malformations requiring detailed non-invasive diagnostic evaluation including functional parameters. To evaluate the morphological and functional information provided by a novel 3-D cine steady-state free-precession (SSFP) sequence. Twenty consecutive children (mean age 2.2 years, nine boys) were examined using a 1.5-T MR system including 2-D cine gradient-recalled-echo sequences, static 3-D SSFP and 3-D cine SSFP sequences. Measurement of ventricular structures and volumes showed close agreement between the 3-D cine SSFP sequence and the 2-D cine gradient-recalled-echo and static 3-D SSFP sequences (left ventricular volumes mean difference 1.0-1.9 ml and 8.8-11.4%, respectively; right ventricular volumes 1.7-2.1 ml and 9.9-16.9%, respectively). No systematic bias was observed. 3-D cine MRI provides anatomic as well as functional information with sufficient spatial and temporal resolution in free-breathing infants with congenital heart disease. (orig.)

  8. A Magnetic Resonance Measurement Technique for Rapidly Switched Gradient Magnetic Fields in a Magnetic Resonance Tomograph

    Directory of Open Access Journals (Sweden)

    K. Bartušek

    2003-01-01

    Full Text Available This paper describes a method for measuring of the gradient magnetic field in Nuclear Magnetic Resonance (NMR tomography, which is one of the modern medical diagnostic methods. A very important prerequisite for high quality imaging is a gradient magnetic field in the instrument with exactly defined properties. Nuclear magnetic resonance enables us to measure the pulse gradient magnetic field characteristics with high accuracy. These interesting precise methods were designed, realised, and tested at the Institute of Scientific Instruments (ISI of the Academy of Sciences of the Czech Republic. The first of them was the Instantaneous Frequency (IF method, which was developed into the Instantaneous Frequency of Spin Echo (IFSE and the Instantaneous Frequency of Spin Echo Series (IFSES methods. The above named methods are described in this paper and their a comparison is also presented.

  9. ECHO-UseFY17.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  10. Help Content for ECHO Reports | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  11. Temporomandibular joint motion

    International Nuclear Information System (INIS)

    Maeda, M.; Kawamura, Y.; Matsuda, T.; Itou, S.; Odori, T.; Ishii, Y.; Torizuka, K.

    1990-01-01

    This paper evaluates MR imaging with the therapeutic effect after splint therapy in internal derangement of the temporomandibular joint (TMJ). Fifteen patients (19 TMJs) with internal derangement of the TMJ and five normal volunteers (10 TMJs) were examined with sagittal T1-weighted spin-echo and gradient recalled acquisition in a steady state (GRASS) MR imaging. MR studies of the patients undergoing splint therapy were performed with an without splints. Pseudodynamic images of TMJ motion provide information that was not available from spin-echo T1-weighted images

  12. Rapid line scan MR angiography

    International Nuclear Information System (INIS)

    Frahm, J.; Merboldt, K.D.; Hanicke, W.; Bruhn, H.

    1987-01-01

    Direct MR angiography may be performed using line scan imaging techniques combined with presaturation of stationary spins. Thus, a single line scan echo yields a projection of vessels due to the signal from reflowing unsaturated spins. Reconstruction of an angiographic image is performed line by line at slightly incremented positions. In particular, line scan angiography is direct and fast without a sensitivity to artifacts even for high flow rates. Image resolution and field of view may be chosen without restrictions, and zoom images using enhanced gradients may be recorded without aliasing artifacts. The method is robust with respect to eddy currents and pulsatile flow. Line scan MR angiograms of phantoms, animals, and human volunteers have been recorded using 90 0 radio frequency pulses and gradient-recalled echoes

  13. SU-D-207A-04: Use of Gradient Echo Plural Contrast Imaging (GEPCI) in MR-Guided Radiation Therapy: A Feasibility Study Targeting Brain Treatment

    International Nuclear Information System (INIS)

    Cai, B; Rao, Y; Tsien, C; Huang, J; Green, O; Mutic, S; Gach, H; Wen, J; Yablonskiy, D

    2016-01-01

    Purpose: To implement the Gradient Echo Plural Contrast Imaging(GEPCI) technique in MRI-simulation for radiation therapy and assess the feasibility of using GEPCI images with advanced inhomogeneity correction in MRI-guided radiotherapy for brain treatment. Methods: An optimized multigradient-echo GRE sequence (TR=50ms;TE1=4ms;delta-TE=4ms;flip angle=300,11 Echoes) was developed to generate both structural (T1w and T2*w) and functional MRIs (field and susceptibility maps) from a single acquisition. One healthy subject (Subject1) and one post-surgical brain cancer patient (Subject2) were scanned on a Philips Ingenia 1.5T MRI used for radiation therapy simulation. Another healthy subject (Subject3) was scanned on a 0.35T MRI-guided radiotherapy (MR-IGRT) system (ViewRay). A voxel spread function (VSF) was used to correct the B0 inhomogeneities caused by surgical cavities and edema for Subject2. GEPCI images and standard radiotherapy planning MRIs for this patient were compared focusing the delineation of radiotherapy target region. Results: GEPCI brain images were successfully derived from all three subjects with scan times of <7 minutes. The images derived for Subjects1&2 demonstrated that GEPCI can be applied and combined into radiotherapy MRI simulation. Despite low field, T1-weighted and R2* images were successfully reconstructed for Subject3 and were satisfactory for contour and target delineation. The R2* distribution of grey matter (center=12,FWHM=4.5) and white matter (center=14.6, FWHM=2) demonstrated the feasibility for tissue segmentation and quantification. The voxel spread function(VSF) corrected surgical site related inhomogeneities for Subject2. R2* and quantitative susceptibility map(QSM) images for Subject2 can be used to quantitatively assess the brain structure response to radiation over the treatment course. Conclusion: We implemented the GEPCI technique in MRI-simulation and in MR-IGRT system for radiation therapy. The images demonstrated that it

  14. MR diagnosis of temporomandibular arthrosis

    Energy Technology Data Exchange (ETDEWEB)

    Suenaga, Shigeaki [Kagoshima Univ. (Japan). Faculty of Dentistry

    1996-09-01

    This review described lesions of articular disk and its surrounding tissues revealed by MR examination in temporomandibular arthrosis, and problems and limits of the examination. Apparatus and imaging methods: Spin echo method was generally used and gradient echo method was alternatively used. Author`s apparatus was 1.5 tesla Signa, Advantage type, equipped with surface coil for temporomandibular joint. Imaging conditions were T1-weighted spin echo method, T2-weighted fast spin echo method, spoiled GRASS (gradient recalled acquisition in the steady state) method and GRASS method. MR findings of articular disk: MR images of normal and abnormal temporomandibular joint were presented together with computed radiographic findings. The role of dynamic imaging was described for evaluation and analysis of the joint functioning. MR findings of surrounding tissues of the disk: Dynamic MRI of the tissues was found useful to see whether the cause of pain was present inside or outside of the articular capsule. Joint effusion could not be fully imaged in T2-weighted conditions. (K.H.)

  15. MR diagnosis of temporomandibular arthrosis

    International Nuclear Information System (INIS)

    Suenaga, Shigeaki

    1996-01-01

    This review described lesions of articular disk and its surrounding tissues revealed by MR examination in temporomandibular arthrosis, and problems and limits of the examination. Apparatus and imaging methods: Spin echo method was generally used and gradient echo method was alternatively used. Author's apparatus was 1.5 tesla Signa, Advantage type, equipped with surface coil for temporomandibular joint. Imaging conditions were T1-weighted spin echo method, T2-weighted fast spin echo method, spoiled GRASS (gradient recalled acquisition in the steady state) method and GRASS method. MR findings of articular disk: MR images of normal and abnormal temporomandibular joint were presented together with computed radiographic findings. The role of dynamic imaging was described for evaluation and analysis of the joint functioning. MR findings of surrounding tissues of the disk: Dynamic MRI of the tissues was found useful to see whether the cause of pain was present inside or outside of the articular capsule. Joint effusion could not be fully imaged in T2-weighted conditions. (K.H.)

  16. Rotary spin echoes

    Energy Technology Data Exchange (ETDEWEB)

    Solomon, I. [Commissariat a l' energie atomique et aux energies alternatives - CEA, Centre d' Etudes Nucleaires de Saclay, BP2, Gif-sur-Yvette (France)

    1959-07-01

    Torrey has observed the free precession of nuclear spins around an r-f field H{sub 1}, fixed in a frame rotating at the Larmor frequency ω{sub 0} = γH{sub 0} around a large d-c magnetic field H{sub 0}. He showed that for an H{sub 1}, much larger than inhomogeneity of H{sub 0}, the latter has a negligible effect on the decay of the spin magnetization which is mainly due to the inhomogeneity of H{sub 1}. We report here on a method of overcoming the inhomogeneity of H{sub 1}, by production of echoes in the rotating frame ('rotary echoes'). These echoes are obtained by a 180 deg. phase shift at t = τ on the r-f field so that H{sub 1}, is suddenly reversed, producing a re-focussing of the magnetization vectors at the time t = 2 τ. The rotary echoes so obtained are very similar to the usual spin-echoes with, however some specific features that make them particularly suitable for the measurement of long relaxation times. Reprint of a paper published in Physical Review Letters, vol. 2, no. 7, Apr 1959, p. 301-302.

  17. Rotary spin echoes

    International Nuclear Information System (INIS)

    Solomon, I.

    1959-01-01

    Torrey has observed the free precession of nuclear spins around an r-f field H 1 , fixed in a frame rotating at the Larmor frequency ω 0 = γH 0 around a large d-c magnetic field H 0 . He showed that for an H 1 , much larger than inhomogeneity of H 0 , the latter has a negligible effect on the decay of the spin magnetization which is mainly due to the inhomogeneity of H 1 . We report here on a method of overcoming the inhomogeneity of H 1 , by production of echoes in the rotating frame ('rotary echoes'). These echoes are obtained by a 180 deg. phase shift at t = τ on the r-f field so that H 1 , is suddenly reversed, producing a re-focussing of the magnetization vectors at the time t = 2 τ. The rotary echoes so obtained are very similar to the usual spin-echoes with, however some specific features that make them particularly suitable for the measurement of long relaxation times. Reprint of a paper published in Physical Review Letters, vol. 2, no. 7, Apr 1959, p. 301-302

  18. Multi-gradient echo MR thermometry for monitoring of the near-field area during MR-guided high intensity focused ultrasound heating.

    Science.gov (United States)

    Lam, Mie K; de Greef, Martijn; Bouwman, Job G; Moonen, Chrit T W; Viergever, Max A; Bartels, Lambertus W

    2015-10-07

    The multi-gradient echo MR thermometry (MGE MRT) method is proposed to use at the interface of the muscle and fat layers found in the abdominal wall, to monitor MR-HIFU heating. As MGE MRT uses fat as a reference, it is field-drift corrected. Relative temperature maps were reconstructed by subtracting absolute temperature maps. Because the absolute temperature maps are reconstructed of individual scans, MGE MRT provides the flexibility of interleaved mapping of temperature changes between two arbitrary time points. The method's performance was assessed in an ex vivo water bath experiment. An ex vivo HIFU experiment was performed to show the method's ability to monitor heating of consecutive HIFU sonications and to estimate cooling time constants, in the presence of field drift. The interleaved use between scans of a clinical protocol was demonstrated in vivo in a patient during a clinical uterine fibroid treatment. The relative temperature measurements were accurate (mean absolute error 0.3 °C) and provided excellent visualization of the heating of consecutive HIFU sonications. Maps were reconstructed of estimated cooling time constants and mean ROI values could be well explained by the applied heating pattern. Heating upon HIFU sonication and subsequent cooling could be observed in the in vivo demonstration.

  19. How can dolphins recognize fish according to their echoes? A statistical analysis of fish echoes.

    Directory of Open Access Journals (Sweden)

    Yossi Yovel

    Full Text Available Echo-based object classification is a fundamental task of animals that use a biosonar system. Dolphins and porpoises should be able to rely on echoes to discriminate a predator from a prey or to select a desired prey from an undesired object. Many studies have shown that dolphins and porpoises can discriminate between objects according to their echoes. All of these studies however, used unnatural objects that can be easily characterized in human terminologies (e.g., metallic spheres, disks, cylinders. In this work, we collected real fish echoes from many angles of acquisition using a sonar system that mimics the emission properties of dolphins and porpoises. We then tested two alternative statistical approaches in classifying these echoes. Our results suggest that fish species can be classified according to echoes returning from porpoise- and dolphin-like signals. These results suggest how dolphins and porpoises can classify fish based on their echoes and provide some insight as to which features might enable the classification.

  20. Radar cross sections for mesospheric echoes at Jicamarca

    Directory of Open Access Journals (Sweden)

    G. A. Lehmacher

    2009-07-01

    Full Text Available Radar cross sections (RCS of mesospheric layers at 50 MHz observed at Jicamarca, Peru, range from 10−18 to 10−16 m−1, three orders of magnitudes smaller than cross sections reported for polar mesospheric winter echoes during solar proton events and six orders of magnitude smaller than polar mesospheric summer echoes. Large RCS are found in thick layers around 70 km that also show wide radar spectra, which is interpreted as turbulent broadening. For typical atmospheric and ionospheric conditions, volume scattering RCS for stationary, homogeneous, isotropic turbulence at 3 m are also in the range 10−18 to 10−16 m−1, in reasonable agreement with measurements. Moreover, theory predicts maximum cross sections around 70 km, also in agreement with observations. Theoretical values are still a matter of order-of-magnitude estimation, since the Bragg scale of 3 m is near or inside the viscous subrange, where the form of the turbulence spectrum is not well known. In addition, steep electron density gradients can increase cross-sections significantly. For thin layers with large RCS and narrow spectra, isotropic turbulence theory fails and scattering or reflection from anisotropic irregularities may gain relevance.

  1. STrategically Acquired Gradient Echo (STAGE) imaging, part I: Creating enhanced T1 contrast and standardized susceptibility weighted imaging and quantitative susceptibility mapping.

    Science.gov (United States)

    Chen, Yongsheng; Liu, Saifeng; Wang, Yu; Kang, Yan; Haacke, E Mark

    2018-02-01

    To provide whole brain grey matter (GM) to white matter (WM) contrast enhanced T1W (T1WE) images, multi-echo quantitative susceptibility mapping (QSM), proton density (PD) weighted images, T1 maps, PD maps, susceptibility weighted imaging (SWI), and R2* maps with minimal misregistration in scanning times creating enhanced GM/WM contrast (the T1WE). The proposed T1WE image was created from a combination of the proton density weighted (6°, PDW) and T1W (24°) images and corrected for RF transmit field variations. Prior to the QSM calculation, a multi-echo phase unwrapping strategy was implemented using the unwrapped short echo to unwrap the longer echo to speed up computation. R2* maps were used to mask deep grey matter and veins during the iterative QSM calculation. A weighted-average sum of susceptibility maps was generated to increase the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR). The proposed T1WE image has a significantly improved CNR both for WM to deep GM and WM to cortical GM compared to the acquired T1W image (the first echo of 24° scan) and the T1MPRAGE image. The weighted-average susceptibility maps have 80±26%, 55±22%, 108±33% SNR increases across the ten subjects compared to the single echo result of 17.5ms for the putamen, caudate nucleus, and globus pallidus, respectively. STAGE imaging offers the potential to create a standardized brain imaging protocol providing four pieces of quantitative tissue property information and multiple types of qualitative information in just 5min. Published by Elsevier Inc.

  2. Wind yield forecast with Echo State Networks; Windertragsprognose mit Echo State Networks

    Energy Technology Data Exchange (ETDEWEB)

    Kobialka, Hans-Ulrich [Fraunhofer IAIS, Sankt Augustin (Germany)

    2012-07-01

    Statistical methods are able to create models of complex system dynamics which are difficult to capture analytically. This paper describes a wind energy prediction system based on a machine learning method, called Echo State Networks. Echo State Networks enable the training of large recurrent neural networks which are able to model and predict highly non-linear system dynamics. This paper gives a short description of Echo State Networks and the realization of the wind energy prediction system. (orig.)

  3. Quantification of early fatty infiltration of the rotator cuff muscles: comparison of multi-echo Dixon with single-voxel MR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Agten, Christoph A.; Rosskopf, Andrea B.; Pfirrmann, Christian W.A. [Balgrist University Hospital, Radiology, Zurich (Switzerland); University of Zurich, Faculty of Medicine, Zurich (Switzerland); Gerber, Christian [Balgrist University Hospital, Orthopaedic Surgery, Zurich (Switzerland); University of Zurich, Faculty of Medicine, Zurich (Switzerland)

    2016-10-15

    To evaluate quantification of early fatty infiltration in supraspinatus muscles with magnetic resonance (MR) imaging using a T2*-corrected multi-echo 3D-gradient-echo Dixon-based sequence (multi-echo Dixon) and compare it to proton-MR-spectroscopy. Sixty subjects (mean age 46 years, 41 men) with good supraspinatus muscle quality on 1.5 T MR imaging were included. Fat percentage (FP) in the supraspinatus muscle was quantified using a multi-echo Dixon compared to single-voxel MR spectroscopy as reference standard. In 18 subjects the multi-echo Dixon was repeated to assess test-retest reliability. Measurements based on multi-echo Dixon were performed by two independent readers by placing regions-of-interest (ROIs) in the supraspinatus muscle corresponding to the MR-spectroscopy voxel. Intraclass and concordance correlation coefficients (ICC/CCC) were used for statistical analysis. Test-retest reliability was substantial for reader 1 (ICC = 0.757) and almost perfect for reader 2 (ICC = 0.873). Inter-reader reliability for multi-echo Dixon was almost perfect (ICC = 0.893, P <.0005). Mean FP in all 60 subjects with multi-echo Dixon was 3.5 ± 1.6 for reader 1, 3.7 ± 1.8 for reader 2, and 2.8 ± 1.4 with MR spectroscopy. Correlation between multi-echo Dixon and MR spectroscopy was moderate (CCC = 0.641). The multi-echo Dixon sequence is a reliable method and comparable to MR-spectroscopy for quantification of low levels of fatty infiltration in the supraspinatus muscle. (orig.)

  4. Happy birthday Echo!

    CERN Document Server

    Staff Association

    2010-01-01

    You are reading the number hundred and one (no. 101) edition of our bulletin Echo. Just over four years ago, on 27th March 2006, the first untitled edition was published (Fig. 1 on the left). The title Echo appeared on the second edition on 10th April 2006 (Fig. 1 in the centre). Today (see Fig. 1 on the right), the layout is slightly different, but the structure of each edition has remained more or less the same: an editorial informing you of the important issues, followed by articles on club life, cultural activities (exhibitions and conferences), information from GAC-EPA, and special offers for our members.     Fig. 1 : Nos. 1, 2 and 100 of our twice-monthly publication Echo Echo was created in March 2006 when, much to our regret, CERN official communication and that of your representatives were separated. November 2009 saw a return to normal practice, and since then the CERN st...

  5. Measurement of short transverse relaxation times by pseudo-echo nutation experiments

    Science.gov (United States)

    Ferrari, Maude; Moyne, Christian; Canet, Daniel

    2018-07-01

    Very short NMR transverse relaxation times may be difficult to measure by conventional methods. Nutation experiments constitute an alternative approach. Nutation is, in the rotating frame, the equivalent of precession in the laboratory frame. It consists in monitoring the rotation of magnetization around the radio-frequency (rf) field when on-resonance conditions are fulfilled. Depending on the amplitude of the rf field, nutation may be sensitive to the two relaxation rates R1 and R2. A full theoretical development has been worked out for demonstrating how these two relaxation rates could be deduced from a simple nutation experiment, noticing however that inhomogeneity of the rf field may lead to erroneous results. This has led us to devise new experiments which are the equivalent of echo techniques in the rotating frame (pseudo spin-echo nutation experiment and pseudo gradient-echo experiment). Full equations of motion have been derived. Although complicated, they indicate that the sum of the two relaxation rates can be obtained very accurately and not altered by rf field inhomogeneity. This implies however an appropriate data processing accounting for the oscillations which are superposed to the echo decays and, anyway, theoretically predicted. A series of experiments has been carried out for different values of the rf field amplitude on samples of water doped with a paramagnetic compound at different concentrations. Pragmatically, as R1 can be easily measured by conventional methods, its value is entered in the data processing algorithm which then returns exclusively the value of the transverse relaxation time. Very consistent results are obtained that way.

  6. A comparison of multi-echo spin-echo and triple-echo steady-state T2 mapping for in vivo evaluation of articular cartilage

    International Nuclear Information System (INIS)

    Juras, Vladimir; Szomolanyi, Pavol; Bohndorf, Klaus; Kronnerwetter, Claudia; Hager, Benedikt; Zbyn, Stefan; Heule, Rahel; Bieri, Oliver; Trattnig, Siegfried

    2016-01-01

    To assess the clinical relevance of T 2 relaxation times, measured by 3D triple-echo steady-state (3D-TESS), in knee articular cartilage compared to conventional multi-echo spin-echo T 2 -mapping. Thirteen volunteers and ten patients with focal cartilage lesions were included in this prospective study. All subjects underwent 3-Tesla MRI consisting of a multi-echo multi-slice spin-echo sequence (CPMG) as a reference method for T 2 mapping, and 3D TESS with the same geometry settings, but variable acquisition times: standard (TESSs 4:35min) and quick (TESSq 2:05min). T 2 values were compared in six different regions in the femoral and tibial cartilage using a Wilcoxon signed ranks test and the Pearson correlation coefficient (r). The local ethics committee approved this study, and all participants gave written informed consent. The mean quantitative T 2 values measured by CPMG (mean: 46±9ms) in volunteers were significantly higher compared to those measured with TESS (mean: 31±5ms) in all regions. Both methods performed similarly in patients, but CPMG provided a slightly higher difference between lesions and native cartilage (CPMG: 90ms→61ms [31%],p=0.0125;TESS 32ms→24ms [24%],p=0.0839). 3D-TESS provides results similar to those of a conventional multi-echo spin-echo sequence with many benefits, such as shortening of total acquisition time and insensitivity to B 1 and B 0 changes. (orig.)

  7. The primacy model: a new model of immediate serial recall.

    Science.gov (United States)

    Page, M P; Norris, D

    1998-10-01

    A new model of immediate serial recall is presented: the primacy model. The primacy model stores order information by means of the assumption that the strength of activation of successive list items decreases across list position to form a primacy gradient. Ordered recall is supported by a repeated cycle of operations involving a noisy choice of the most active item followed by suppression of the chosen item. Word-length and list-length effects are attributed to a decay process that occurs both during input, when effective rehearsal is prevented, and during output. The phonological similarity effect is attributed to a second stage of processing at which phonological confusions occur. The primacy model produces accurate simulations of the effects of word length, list length, and phonological similarity.

  8. A comparison of multi-echo spin-echo and triple-echo steady-state T2 mapping for in vivo evaluation of articular cartilage

    Energy Technology Data Exchange (ETDEWEB)

    Juras, Vladimir; Szomolanyi, Pavol [Medical University of Vienna, High Field MR Centre, Department of Biomedical Imaging and Image-Guided Therapy, Vienna (Austria); Institute of Measurement Science, Department of Imaging Methods, Bratislava (Slovakia); Bohndorf, Klaus; Kronnerwetter, Claudia; Hager, Benedikt; Zbyn, Stefan [Medical University of Vienna, High Field MR Centre, Department of Biomedical Imaging and Image-Guided Therapy, Vienna (Austria); Heule, Rahel; Bieri, Oliver [University of Basel Hospital, Division of Radiological Physics, Department of Radiology, Basel (Switzerland); Trattnig, Siegfried [Medical University of Vienna, High Field MR Centre, Department of Biomedical Imaging and Image-Guided Therapy, Vienna (Austria); Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna (Austria); Ludwig Boltzmann Institute for Experimental and Clinical Traumatology, Austrian Cluster for Tissue Regeneration, Vienna (Austria)

    2016-06-15

    To assess the clinical relevance of T{sub 2} relaxation times, measured by 3D triple-echo steady-state (3D-TESS), in knee articular cartilage compared to conventional multi-echo spin-echo T{sub 2}-mapping. Thirteen volunteers and ten patients with focal cartilage lesions were included in this prospective study. All subjects underwent 3-Tesla MRI consisting of a multi-echo multi-slice spin-echo sequence (CPMG) as a reference method for T{sub 2} mapping, and 3D TESS with the same geometry settings, but variable acquisition times: standard (TESSs 4:35min) and quick (TESSq 2:05min). T{sub 2} values were compared in six different regions in the femoral and tibial cartilage using a Wilcoxon signed ranks test and the Pearson correlation coefficient (r). The local ethics committee approved this study, and all participants gave written informed consent. The mean quantitative T{sub 2} values measured by CPMG (mean: 46±9ms) in volunteers were significantly higher compared to those measured with TESS (mean: 31±5ms) in all regions. Both methods performed similarly in patients, but CPMG provided a slightly higher difference between lesions and native cartilage (CPMG: 90ms→61ms [31%],p=0.0125;TESS 32ms→24ms [24%],p=0.0839). 3D-TESS provides results similar to those of a conventional multi-echo spin-echo sequence with many benefits, such as shortening of total acquisition time and insensitivity to B{sub 1} and B{sub 0} changes. (orig.)

  9. Adaptive Memory: Animacy Enhances Free Recall but Impairs Cued Recall

    Science.gov (United States)

    Popp, Earl Y.; Serra, Michael J.

    2016-01-01

    Recent research suggests that human memory systems evolved to remember animate things better than inanimate things. In the present experiments, we examined whether these effects occur for both free recall and cued recall. In Experiment 1, we directly compared the effect of animacy on free recall and cued recall. Participants studied lists of…

  10. Ultrasonic particle image velocimetry for improved flow gradient imaging: algorithms, methodology and validation

    International Nuclear Information System (INIS)

    Niu Lili; Qian Ming; Yu Wentao; Jin Qiaofeng; Ling Tao; Zheng Hairong; Wan Kun; Gao Shen

    2010-01-01

    This paper presents a new algorithm for ultrasonic particle image velocimetry (Echo PIV) for improving the flow velocity measurement accuracy and efficiency in regions with high velocity gradients. The conventional Echo PIV algorithm has been modified by incorporating a multiple iterative algorithm, sub-pixel method, filter and interpolation method, and spurious vector elimination algorithm. The new algorithms' performance is assessed by analyzing simulated images with known displacements, and ultrasonic B-mode images of in vitro laminar pipe flow, rotational flow and in vivo rat carotid arterial flow. Results of the simulated images show that the new algorithm produces much smaller bias from the known displacements. For laminar flow, the new algorithm results in 1.1% deviation from the analytically derived value, and 8.8% for the conventional algorithm. The vector quality evaluation for the rotational flow imaging shows that the new algorithm produces better velocity vectors. For in vivo rat carotid arterial flow imaging, the results from the new algorithm deviate 6.6% from the Doppler-measured peak velocities averagely compared to 15% of that from the conventional algorithm. The new Echo PIV algorithm is able to effectively improve the measurement accuracy in imaging flow fields with high velocity gradients.

  11. Spin echo SPI methods for quantitative analysis of fluids in porous media.

    Science.gov (United States)

    Li, Linqing; Han, Hui; Balcom, Bruce J

    2009-06-01

    Fluid density imaging is highly desirable in a wide variety of porous media measurements. The SPRITE class of MRI methods has proven to be robust and general in their ability to generate density images in porous media, however the short encoding times required, with correspondingly high magnetic field gradient strengths and filter widths, and low flip angle RF pulses, yield sub-optimal S/N images, especially at low static field strength. This paper explores two implementations of pure phase encode spin echo 1D imaging, with application to a proposed new petroleum reservoir core analysis measurement. In the first implementation of the pulse sequence, we modify the spin echo single point imaging (SE-SPI) technique to acquire the k-space origin data point, with a near zero evolution time, from the free induction decay (FID) following a 90 degrees excitation pulse. Subsequent k-space data points are acquired by separately phase encoding individual echoes in a multi-echo acquisition. T(2) attenuation of the echo train yields an image convolution which causes blurring. The T(2) blur effect is moderate for porous media with T(2) lifetime distributions longer than 5 ms. As a robust, high S/N, and fast 1D imaging method, this method will be highly complementary to SPRITE techniques for the quantitative analysis of fluid content in porous media. In the second implementation of the SE-SPI pulse sequence, modification of the basic measurement permits fast determination of spatially resolved T(2) distributions in porous media through separately phase encoding each echo in a multi-echo CPMG pulse train. An individual T(2) weighted image may be acquired from each echo. The echo time (TE) of each T(2) weighted image may be reduced to 500 micros or less. These profiles can be fit to extract a T(2) distribution from each pixel employing a variety of standard inverse Laplace transform methods. Fluid content 1D images are produced as an essential by product of determining the

  12. Failure to recall.

    Science.gov (United States)

    Laming, Donald

    2009-01-01

    Mathematical analysis shows that if the pattern of rehearsal in free-recall experiments (of necessity, the pattern observed when participants rehearse aloud) be continued without any further interruption by stimuli (as happens during recall), it terminates with the retrieval of the same 1 word over and over again. Such a terminal state is commonly reached before some of the words in the list have been retrieved even once; those words are not recalled. The 1 minute frequently allowed for recall in free-recall experiments is ample time for retrieval to seize up in this way. The author proposes a model that represents the essential features of the pattern of rehearsal; validates that model by reference to the overt rehearsal data from B. B. Murdock, Jr., and J. Metcalfe (1978) and the recall data from B. B. Murdock, Jr., and R. Okada (1970); demonstrates the long-term properties of continued sequences of retrievals and, also, a fundamental relation linking recall to the total time of presentation; and, finally, compares failure to recall in free-recall experiments with forgetting in general.

  13. Classification of radar echoes using fractal geometry

    International Nuclear Information System (INIS)

    Azzaz, Nafissa; Haddad, Boualem

    2017-01-01

    Highlights: • Implementation of two concepts of fractal geometry to classify two types of meteorological radar echoes. • A new approach, called a multi-scale fractal dimension is used for classification between fixed echoes and rain echoes. • An Automatic identification system of meteorological radar echoes was proposed using fractal geometry. - Abstract: This paper deals with the discrimination between the precipitation echoes and the ground echoes in meteorological radar images using fractal geometry. This study aims to improve the measurement of precipitations by weather radars. For this, we considered three radar sites: Bordeaux (France), Dakar (Senegal) and Me lbourne (USA). We showed that the fractal dimension based on contourlet and the fractal lacunarity are pertinent to discriminate between ground and precipitation echoes. We also demonstrated that the ground echoes have a multifractal structure but the precipitations are more homogeneous than ground echoes whatever the prevailing climate. Thereby, we developed an automatic classification system of radar using a graphic interface. This interface, based on the fractal geometry makes possible the identification of radar echoes type in real time. This system can be inserted in weather radar for the improvement of precipitation estimations.

  14. WE-DE-206-04: MRI Pulse Sequences - Spin Echo, Gradient Echo, EPI, Non-Cartesia

    Energy Technology Data Exchange (ETDEWEB)

    Pooley, R. [Mayo Clinic (United States)

    2016-06-15

    Magnetic resonance imaging (MRI) has become an essential part of clinical imaging due to its ability to render high soft tissue contrast. Instead of ionizing radiation, MRI use strong magnetic field, radio frequency waves and field gradients to create diagnostic useful images. It can be used to image the anatomy and also functional and physiological activities within the human body. Knowledge of the basic physical principles underlying MRI acquisition is vitally important to successful image production and proper image interpretation. This lecture will give an overview of the spin physics, imaging principle of MRI, the hardware of the MRI scanner, and various pulse sequences and their applications. It aims to provide a conceptual foundation to understand the image formation process of a clinical MRI scanner. Learning Objectives: Understand the origin of the MR signal and contrast from the spin physics level. Understand the main hardware components of a MRI scanner and their purposes Understand steps for MR image formation including spatial encoding and image reconstruction Understand the main kinds of MR pulse sequences and their characteristics.

  15. A comparison of multi-echo spin-echo and triple-echo steady-state T2 mapping for in vivo evaluation of articular cartilage.

    Science.gov (United States)

    Juras, Vladimir; Bohndorf, Klaus; Heule, Rahel; Kronnerwetter, Claudia; Szomolanyi, Pavol; Hager, Benedikt; Bieri, Oliver; Zbyn, Stefan; Trattnig, Siegfried

    2016-06-01

    To assess the clinical relevance of T2 relaxation times, measured by 3D triple-echo steady-state (3D-TESS), in knee articular cartilage compared to conventional multi-echo spin-echo T2-mapping. Thirteen volunteers and ten patients with focal cartilage lesions were included in this prospective study. All subjects underwent 3-Tesla MRI consisting of a multi-echo multi-slice spin-echo sequence (CPMG) as a reference method for T2 mapping, and 3D TESS with the same geometry settings, but variable acquisition times: standard (TESSs 4:35min) and quick (TESSq 2:05min). T2 values were compared in six different regions in the femoral and tibial cartilage using a Wilcoxon signed ranks test and the Pearson correlation coefficient (r). The local ethics committee approved this study, and all participants gave written informed consent. The mean quantitative T2 values measured by CPMG (mean: 46±9ms) in volunteers were significantly higher compared to those measured with TESS (mean: 31±5ms) in all regions. Both methods performed similarly in patients, but CPMG provided a slightly higher difference between lesions and native cartilage (CPMG: 90ms→61ms [31%],p=0.0125;TESS 32ms→24ms [24%],p=0.0839). 3D-TESS provides results similar to those of a conventional multi-echo spin-echo sequence with many benefits, such as shortening of total acquisition time and insensitivity to B1 and B0 changes. • 3D-TESS T 2 mapping provides clinically comparable results to CPMG in shorter scan-time. • Clinical and investigational studies may benefit from high temporal resolution of 3D-TESS. • 3D-TESS T 2 values are able to differentiate between healthy and damaged cartilage.

  16. Lithium ion diffusion measurements on a garnet-type solid conductor Li6.6La3Zr1.6Ta0.4O12 by using a pulsed-gradient spin-echo NMR method.

    Science.gov (United States)

    Hayamizu, Kikuko; Matsuda, Yasuaki; Matsui, Masaki; Imanishi, Nobuyuki

    2015-09-01

    The garnet-type solid conductor Li7-xLa3Zr2-xTaxO12 is known to have high ionic conductivity. We synthesized a series of compositions of this conductor and found that cubic Li6.6La3Zr1.6Ta0.4O12 (LLZO-Ta) has a high ionic conductivity of 3.7×10(-4)Scm(-1) at room temperature. The (7)Li NMR spectrum of LLZO-Ta was composed of narrow and broad components, and the linewidth of the narrow component varied from 0.69kHz (300K) to 0.32kHz (400K). We carried out lithium ion diffusion measurements using pulsed-field spin-echo (PGSE) NMR spectroscopy and found that echo signals were observed at T≥313K with reasonable sensitivity. The lithium diffusion behavior was measured by varying the observation time and pulsed-field gradient (PFG) strength between 313 and 384K. We found that lithium diffusion depended significantly on the observation time and strength of the PFG, which is quite different from lithium ion diffusion in liquids. It was shown that lithium ion migration in the solid conductor was distributed widely in both time and space. Copyright © 2015 Elsevier Inc. All rights reserved.

  17. Longitudinal collective echoes in coasting particle beams

    Directory of Open Access Journals (Sweden)

    Ahmed Al-Khateeb

    2003-01-01

    Full Text Available Longitudinal ballistic and collective beam echoes with diffusion effects are investigated theoretically. In the presence of the space-charge impedance, the collective echo amplitude is obtained as a closed form expression. In contrast to the ballistic case, the collective echo amplitude consists of one maximum at time t_{echo}. The echo amplitude grows up and damps down with a rate proportional to the Landau damping rate of space-charge waves. The effect of weak diffusion is found to modify the ballistic and the collective echo amplitudes in the same manner. This effect of diffusion was confirmed using a “noiseless,” grid-based simulation code. As a first application the amount of numerical diffusion in our simulation code was determined using the echo effect.

  18. Is the relationship between pattern recall and decision-making influenced by anticipatory recall?

    Science.gov (United States)

    Gorman, Adam D; Abernethy, Bruce; Farrow, Damian

    2013-01-01

    The present study compared traditional measures of pattern recall to measures of anticipatory recall and decision-making to examine the underlying mechanisms of expert pattern perception and to address methodological limitations in previous studies where anticipatory recall has generally been overlooked. Recall performance in expert and novice basketball players was measured by examining the spatial error in recalling player positions both for a target image (traditional recall) and at 40-ms increments following the target image (anticipatory recall). Decision-making performance was measured by comparing the participant's response to those identified by a panel of expert coaches. Anticipatory recall was observed in the recall task and was significantly more pronounced for the experts, suggesting that traditional methods of spatial recall analysis may not have provided a completely accurate determination of the full magnitude of the experts' superiority. Accounting for anticipatory recall also increased the relative contribution of recall skill to decision-making accuracy although the gains in explained variance were modest and of debatable functional significance.

  19. Self-diffusion imaging by spin echo in Earth's magnetic field.

    Science.gov (United States)

    Mohoric, A; Stepisnik, J; Kos, M; Planinsi

    1999-01-01

    The NMR of the Earth's magnetic field is used for diffusion-weighted imaging of phantoms. Due to a weak Larmor field, care needs to be taken regarding the use of the usual high field assumption in calculating the effect of the applied inhomogeneous magnetic field. The usual definition of the magnetic field gradient must be replaced by a generalized formula valid when the strength of a nonuniform magnetic field and a Larmor field are comparable (J. Stepisnik, Z. Phys. Chem. 190, 51-62 (1995)). It turns out that the expression for spin echo attenuation is identical to the well-known Torrey formula only when the applied nonuniform field has a proper symmetry. This kind of problem may occur in a strong Larmor field as well as when the slow diffusion rate of particles needs an extremely strong gradient to be applied. The measurements of the geomagnetic field NMR demonstrate the usefulness of the method for diffusion and flow-weighted imaging. Copyright 1999 Academic Press.

  20. The effects of recall-concurrent visual-motor distraction on picture and word recall.

    Science.gov (United States)

    Warren, M W

    1977-05-01

    The dual-coding model (Paivio, 1971, 1975) predicts a larger imaginal component in the recall of pictures relative to words and a larger imaginal component in the recall of concrete words relative to abstract words. These predictions were tested by examining the effect of a recall-concurrent imagery-suppression task (pursuit-rotor tracking) on the recall of pictures vs picture labels and on the recall of concrete words vs abstract words. The results showed that recall-concurrent pursuit-rotor tracking interfered with picture recall, but not word recall (Experiments 1 and 2); however, there was no evidence of an effect of recall-concurrent tracking on the recall of concrete words (Experiment 3). The results suggested a revision of the dual-coding model.

  1. The thermal and dynamical state of the atmosphere during polar mesosphere winter echoes

    Directory of Open Access Journals (Sweden)

    F.-J. Lübken

    2006-01-01

    Full Text Available In January 2005, a total of 18 rockets were launched from the Andøya Rocket Range in Northern Norway (69° N into strong VHF radar echoes called 'Polar Mesosphere Winter Echoes' (PMWE. The echoes were observed in the lower and middle mesosphere during large solar proton fluxes. In general, PMWE occur much more seldom compared to their summer counterparts PMSE (typical occurrence rates at 69° N are 1–3% vs. 80%, respectively. Our in-situ measurements by falling sphere, chaff, and instrumented payloads provide detailed information about the thermal and dynamical state of the atmosphere and therefore allow an unprecedented study of the background atmosphere during PMWE. There are a number of independent observations indicating that neutral air turbulence has caused PMWE. Ion density fluctuations show a turbulence spectrum within PMWE and no fluctuations outside. Temperature lapse rates close to the adiabatic gradient are observed in the vicinity of PMWE indicating persistent turbulent mixing. The spectral broadening of radar echoes is consistent with turbulent velocity fluctuations. Turbulence also explains the mean occurrence height of PMWE (~68–75 km: viscosity increases rapidly with altitude and destroys any small scale fluctuations in the upper mesosphere, whereas electron densities are usually too low in the lower mesosphere to cause significant backscatter. The seasonal variation of echoes in the lower mesosphere is in agreement with a turbulence climatology derived from earlier sounding rocket flights. We have performed model calculations to study the radar backscatter from plasma fluctuations caused by neutral air turbulence. We find that volume reflectivities observed during PMWE are in quantitative agreement with theory. Apart from turbulence the most crucial requirement for PMWE is a sufficiently large number of electrons, for example produced by solar proton events. We have studied the sensitivity of the radar echo strength on

  2. Multishot echo-planar MREIT for fast imaging of conductivity, current density, and electric field distributions.

    Science.gov (United States)

    Chauhan, Munish; Vidya Shankar, Rohini; Ashok Kumar, Neeta; Kodibagkar, Vikram D; Sadleir, Rosalind

    2018-01-01

    Magnetic resonance electrical impedance tomography (MREIT) sequences typically use conventional spin or gradient echo-based acquisition methods for reconstruction of conductivity and current density maps. Use of MREIT in functional and electroporation studies requires higher temporal resolution and faster sequences. Here, single and multishot echo planar imaging (EPI) based MREIT sequences were evaluated to see whether high-quality MREIT phase data could be obtained for rapid reconstruction of current density, conductivity, and electric fields. A gel phantom with an insulating inclusion was used as a test object. Ghost artifact, geometric distortion, and MREIT correction algorithms were applied to the data. The EPI-MREIT-derived phase-projected current density and conductivity images were compared with simulations and spin-echo images as a function of EPI shot number. Good agreement among measures in simulated, spin echo, and EPI data was achieved. Current density errors were stable and below 9% as the shot number decreased from 64 to 2, but increased for single-shot images. Conductivity reconstruction relative contrast ratios were stable as the shot number decreased. The derived electric fields also agreed with the simulated data. The EPI methods can be combined successfully with MREIT reconstruction algorithms to achieve fast imaging of current density, conductivity, and electric field. Magn Reson Med 79:71-82, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  3. Optimization of three-dimensional triple IR fast spoiled gradient recalled acquisition in the steady state (FSPGR) to decrease vascular artifact at 3.0 Tesla

    International Nuclear Information System (INIS)

    Fujiwara, Yasuhiro; Fukuya, Yuko; Yamaguchi, Isao; Matsuda, Tsuyoshi; Ishimori, Yoshiyuki; Yamada, Kazuhiro; Kimura, Hirohiko; Miyati, Tosiaki

    2006-01-01

    The purpose of this study was to decrease vascular artifacts caused by the in-flow effect in three-dimensional inversion recovery prepared fast spoiled gradient recalled acquisition in the steady state (3D IR FSPGR) at 3.0 Tesla. We developed 3D triple IR (3IR) FSPGR and examined the signal characteristics of the new sequence. We have optimized scan parameters based on simulation, phantom, and in-vivo studies. As a result, optimized parameters (1st TI=600 ms, 3rd TI=500 ms) successfully have produced the vessel signal at more than 40% reduction, while gray-white matter contrast was preserved. Moreover, the reduced artifact was also confirmed by visual inspection of the in-vivo images for which this condition was used. Thus, 3D 3IR FSPGR was a useful sequence for the acquisition of T1-weighted images at 3.0 Tesla. (author)

  4. Cognitive factors affecting free recall, cued recall, and recognition tasks in Alzheimer's disease.

    Science.gov (United States)

    Yamagishi, Takashi; Sato, Takuya; Sato, Atsushi; Imamura, Toru

    2012-01-01

    Our aim was to identify cognitive factors affecting free recall, cued recall, and recognition tasks in patients with Alzheimer's disease (AD). We recruited 349 consecutive AD patients who attended a memory clinic. Each patient was assessed using the Alzheimer's Disease Assessment Scale (ADAS) and the extended 3-word recall test. In this task, each patient was asked to freely recall 3 previously presented words. If patients could not recall 1 or more of the target words, the examiner cued their recall by providing the category of the target word and then provided a forced-choice recognition of the target word with 2 distracters. The patients were divided into groups according to the results of the free recall, cued recall, and recognition tasks. Multivariate logistic regression analysis for repeated measures was carried out to evaluate the net effects of cognitive factors on the free recall, cued recall, and recognition tasks after controlling for the effects of age and recent memory deficit. Performance on the ADAS Orientation task was found to be related to performance on the free and cued recall tasks, performance on the ADAS Following Commands task was found to be related to performance on the cued recall task, and performance on the ADAS Ideational Praxis task was found to be related to performance on the free recall, cued recall, and recognition tasks. The extended 3-word recall test reflects deficits in a wider range of memory and other cognitive processes, including memory retention after interference, divided attention, and executive functions, compared with word-list recall tasks. The characteristics of the extended 3-word recall test may be advantageous for evaluating patients' memory impairments in daily living.

  5. Common Modality Effects in Immediate Free Recall and Immediate Serial Recall

    Science.gov (United States)

    Grenfell-Essam, Rachel; Ward, Geoff; Tan, Lydia

    2017-01-01

    In 2 experiments, participants were presented with lists of between 2 and 12 words for either immediate free recall (IFR) or immediate serial recall (ISR). Auditory recall advantages at the end of the list (modality effects) and visual recall advantages early in the list (inverse modality effects) were observed in both tasks and the extent and…

  6. Theory of single-photon echo (SP-echo) and the possibility of its experimental study in the gamma-region

    International Nuclear Information System (INIS)

    Moiseev, S.A.

    1997-01-01

    The single-photon echo (SP-echo) effect is predicted to appear in the case of three-level medium excitation by means of a single photon propagating to the medium along two optical paths with a mutual time delay surpassing the temporal duration of the photon wave packet. The quantum electrodynamical theory describing this interaction is presented and the S-matrix of the field is shown for infinite time (t=∞). Using the S-matrix approach, physical properties of the scattering field are studied. Hence, it is shown that the field has an echo signal at the ω 32 0 carrier frequency. It has been shown that the echo signal exists only in the field amplitude while being absent in its intensity behaviour. Thus, SP-echo is an interference effect and is not influenced by the energy irradiation. The problems of SP-echo detection in the gamma-region (where special generation difficulties appear) are discussed. The influence of the additional detection of theω 21 0 frequency field on the echo signal has been shown. A special case is the EPR-paradox which can appear within the echo phenomenon

  7. Theory of single-photon echo (SP-echo) and the possibility of its experimental study in the gamma-region

    Energy Technology Data Exchange (ETDEWEB)

    Moiseev, S.A

    1997-05-15

    The single-photon echo (SP-echo) effect is predicted to appear in the case of three-level medium excitation by means of a single photon propagating to the medium along two optical paths with a mutual time delay surpassing the temporal duration of the photon wave packet. The quantum electrodynamical theory describing this interaction is presented and the S-matrix of the field is shown for infinite time (t={infinity}). Using the S-matrix approach, physical properties of the scattering field are studied. Hence, it is shown that the field has an echo signal at the {omega}{sub 32}{sup 0} carrier frequency. It has been shown that the echo signal exists only in the field amplitude while being absent in its intensity behaviour. Thus, SP-echo is an interference effect and is not influenced by the energy irradiation. The problems of SP-echo detection in the gamma-region (where special generation difficulties appear) are discussed. The influence of the additional detection of the{omega}{sub 21}{sup 0} frequency field on the echo signal has been shown. A special case is the EPR-paradox which can appear within the echo phenomenon.

  8. A radar-echo model for Mars

    International Nuclear Information System (INIS)

    Thompson, T.W.; Moore, H.J.

    1990-01-01

    Researchers developed a radar-echo model for Mars based on 12.6 cm continuous wave radio transmissions backscattered from the planet. The model broadly matches the variations in depolarized and polarized total radar cross sections with longitude observed by Goldstone in 1986 along 7 degrees S. and yields echo spectra that are generally similiar to the observed spectra. Radar map units in the model include an extensive cratered uplands unit with weak depolarized echo cross sections, average thermal inertias, moderate normal refelectivities, and moderate rms slopes; the volcanic units of Tharsis, Elysium, and Amazonis regions with strong depolarized echo cross sections, low thermal inertia, low normal reflectivities, and large rms slopes; and the northern planes units with moderate to strong depolarized echo cross sections, moderate to very high thermal inertias, moderate to large normal reflectivities, and moderate rms slopes. The relevance of the model to the interpretation of radar echoes from Mars is discussed

  9. The acoustics of the echo cornet

    Science.gov (United States)

    Pyle, Robert W., Jr.; Klaus, Sabine K.

    2002-11-01

    The echo cornet was an instrument produced by a number of makers in several countries from about the middle of the nineteenth to the early twentieth centuries. It consists of an ordinary three-valve cornet to which a fourth valve has been added, downstream of the three normal valves. The extra valve diverts the airstream from the normal bell to an ''echo'' bell that gives a muted tone quality. Although the air column through the echo bell is typically 15 cm longer than the path through the normal bell, there is no appreciable change of playing pitch when the echo bell is in use. Acoustic input impedance and impulse response measurements and consideration of the standing-wave pattern within the echo bell show how this can be so. Acoustically, the echo bell is more closely related to hand-stopping on the French horn than to the mutes commonly used on the trumpet and cornet.

  10. Study of optimal flip angle for inversion-recovery gradient echo method in delayed contrast-enhanced cardiac magnetic resonance imaging

    International Nuclear Information System (INIS)

    Ogawa, Masashi; Matsumura, Yoshio; Tsuchihashi, Toshio

    2013-01-01

    Delayed contrast-enhanced cardiac magnetic resonance imaging (MRI) is a valuable tool for detecting myocardial infarction and assessing myocardial viability. The standard viability MRI technique is the inversion-recovery gradient echo (IR-GRE) method. Several previous studies have demonstrated that this imaging technique provides superior image quality at high magnetic field strengths, e.g., 3.0 T. However, there are numerous possible flip angles. We investigated the optimal flip angle of IR-GRE in delayed contrast-enhanced cardiac MRI. Phantoms were made that modeled infarcted myocardium and normal myocardium after administration of contrast agent. To determine optimal flip angle, we compared the contrast-to-noise ratio (CNR) among these phantoms and evaluated the degree of artifacts induced by increased flip angle. The flip angle that showed the highest CNR for 2D IR-GRE and 3D IR-GRE was 30deg/15deg at 1.5 T and 25deg/15deg at 3.0 T. The flip angle that showed the highest CNR was independent of R-R interval. Streak artifacts induced by increased flip angle tended to occur more readily at 3.0 T than 1.5 T. The optimal flip angle for 2D IR-GRE and 3D IR-GRE at 1.5 T was 30deg and 15deg, respectively. At 3.0 T, taking into account the results for both CNR and streak artifacts, we concluded the optimal flip angle of 2D IR-GRE to be 15-20deg. (author)

  11. Examining the relationship between free recall and immediate serial recall: the serial nature of recall and the effect of test expectancy.

    Science.gov (United States)

    Bhatarah, Parveen; Ward, Geoff; Tan, Lydia

    2008-01-01

    In two experiments, we examined the relationship between free recall and immediate serial recall (ISR), using a within-subjects (Experiment 1) and a between-subjects (Experiment 2) design. In both experiments, participants read aloud lists of eight words and were precued or postcued to respond using free recall or ISR. The serial position curves were U-shaped for free recall and showed extended primacy effects with little or no recency for ISR, and there was little or no difference between recall for the precued and the postcued conditions. Critically, analyses of the output order showed that although the participants started their recall from different list positions in the two tasks, the degree to which subsequent recall was serial in a forward order was strikingly similar. We argue that recalling in a serial forward order is a general characteristic of memory and that performance on ISR and free recall is underpinned by common memory mechanisms.

  12. Temporal compression of quantum-information-carrying photons using a photon-echo quantum memory approach

    International Nuclear Information System (INIS)

    Moiseev, S. A.; Tittel, W.

    2010-01-01

    We study quantum compression and decompression of light pulses that carry quantum information using a photon-echo quantum memory technique with controllable inhomogeneous broadening of an isolated atomic absorption line. We investigate media with differently broadened absorption profiles, transverse and longitudinal, finding that the recall efficiency can be as large as unity and that the quantum information encoded into the photonic qubits can remain unperturbed. Our results provide insight into reversible light-atom interaction and are interesting in view of future quantum communication networks, where pulse compression and decompression may play an important role in increasing the qubit rate or in mapping quantum information from photonic carriers with large optical bandwidth into atomic memories with smaller bandwidth.

  13. Physiological noise in murine solid tumours using T2*-weighted gradient-echo imaging: a marker of tumour acute hypoxia?

    International Nuclear Information System (INIS)

    Baudelet, Christine; Ansiaux, Reginald; Jordan, Benedicte F; Havaux, Xavier; Macq, Benoit; Gallez, Bernard

    2004-01-01

    T2*-weighted gradient-echo magnetic resonance imaging (T2*-weighted GRE MRI) was used to investigate spontaneous fluctuations in tumour vasculature non-invasively. FSa fibrosarcomas, implanted intramuscularly (i.m.) in the legs of mice, were imaged at 4.7 T, over a 30 min or 1 h sampling period. On a voxel-by-voxel basis, time courses of signal intensity were analysed using a power spectrum density (PSD) analysis to isolate voxels for which signal changes did not originate from Gaussian white noise or linear drift. Under baseline conditions, the tumours exhibited spontaneous signal fluctuations showing spatial and temporal heterogeneity over the tumour. Statistically significant fluctuations occurred at frequencies ranging from 1 cycle/3 min to 1 cycle/h. The fluctuations were independent of the scanner instabilities. Two categories of signal fluctuations were reported: (i) true fluctuations (TFV), i.e., sequential signal increase and decrease, and (ii) profound drop in signal intensity with no apparent signal recovery (SDV). No temporal correlation between tumour and contralateral muscle fluctuations was observed. Furthermore, treatments aimed at decreasing perfusion-limited hypoxia, such as carbogen combined with nicotinamide and flunarizine, decreased the incidence of tumour T2*-weighted GRE fluctuations. We also tracked dynamic changes in T2* using multiple GRE imaging. Fluctuations of T2* were observed; however, fluctuation maps using PSD analysis could not be generated reliably. An echo-time dependency of the signal fluctuations was observed, which is typical to physiological noise. Finally, at the end of T2*-weighted GRE MRI acquisition, a dynamic contrast-enhanced MRI was performed to characterize the microenvironment in which tumour signal fluctuations occurred in terms of vessel functionality, vascularity and microvascular permeability. Our data showed that TFV were predominantly located in regions with functional vessels, whereas SDV occurred in regions

  14. A high-performance gradient insert for rapid and short-T2 imaging at full duty cycle.

    Science.gov (United States)

    Weiger, Markus; Overweg, Johan; Rösler, Manuela Barbara; Froidevaux, Romain; Hennel, Franciszek; Wilm, Bertram Jakob; Penn, Alexander; Sturzenegger, Urs; Schuth, Wout; Mathlener, Menno; Borgo, Martino; Börnert, Peter; Leussler, Christoph; Luechinger, Roger; Dietrich, Benjamin Emanuel; Reber, Jonas; Brunner, David Otto; Schmid, Thomas; Vionnet, Laetitia; Pruessmann, Klaas P

    2018-06-01

    The goal of this study was to devise a gradient system for MRI in humans that reconciles cutting-edge gradient strength with rapid switching and brings up the duty cycle to 100% at full continuous amplitude. Aiming to advance neuroimaging and short-T 2 techniques, the hardware design focused on the head and the extremities as target anatomies. A boundary element method with minimization of power dissipation and stored magnetic energy was used to design anatomy-targeted gradient coils with maximally relaxed geometry constraints. The design relies on hollow conductors for high-performance cooling and split coils to enable dual-mode gradient amplifier operation. With this approach, strength and slew rate specifications of either 100 mT/m with 1200 mT/m/ms or 200 mT/m with 600 mT/m/ms were reached at 100% duty cycle, assuming a standard gradient amplifier and cooling unit. After manufacturing, the specified values for maximum gradient strength, maximum switching rate, and field geometry were verified experimentally. In temperature measurements, maximum local values of 63°C were observed, confirming that the device can be operated continuously at full amplitude. Testing for peripheral nerve stimulation showed nearly unrestricted applicability in humans at full gradient performance. In measurements of acoustic noise, a maximum average sound pressure level of 132 dB(A) was determined. In vivo capability was demonstrated by head and knee imaging. Full gradient performance was employed with echo planar and zero echo time readouts. Combining extreme gradient strength and switching speed without duty cycle limitations, the described system offers unprecedented options for rapid and short-T 2 imaging. Magn Reson Med 79:3256-3266, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  15. A multi-slice gradient sequence for contrast enhanced MR diagnosis of intracranial tumours

    International Nuclear Information System (INIS)

    Schoerner, W.; Sander, B.; Kornmesser, W.; Laniado, M.; Nakamura, T.; Felix, R.

    1988-01-01

    A multi-slice gradient echo sequence (FLASH) was compared with a conventional spin-echo (SE) technique with regard to its value for contrast enhanced MR diagnosis. In 28 patients with cerebral tumours, SE images (SE 400/30; four images/3.4 minutes) and FLASH images (FLASH 315/14; 15 images/1.4 minutes) were obtained before and after gadolinium DTPA. After gadolinium-DTPA results were comparable for both techniques with respect to contrast enhancement, tumor contrast and delineation. Because of the higher efficiency of the FLASH 315/14 technique, this sequence is the method of choice for contrast enhanced cerebral MR imaging. (orig.) [de

  16. Suppressing magnetization exchange effects in stimulated-echo diffusion experiments.

    Science.gov (United States)

    Pagès, Guilhem; Dvinskikh, Sergey V; Furó, István

    2013-09-01

    Exchange of nuclear magnetization between spin pools, either by chemical exchange or by cross-relaxation or both, has a significant influence on the signal attenuation in stimulated-echo-type pulsed field gradient experiments. Hence, in such cases the obtained molecular self-diffusion coefficients can carry a large systematic error. We propose a modified stimulated echo pulse sequence that contains T2-filters during the z-magnetization store period. We demonstrate, using a common theoretical description for chemical exchange and cross-relaxation, that these filters suppress the effects of exchange on the diffusional decay in that frequent case where one of the participating spin pools is immobile and exhibits a short T2. We demonstrate the performance of this experiment in an agarose/water gel. We posit that this new experiment has advantages over other approaches hitherto used, such as that consisting of measuring separately the magnetization exchange rate, if suitable by Goldman-Shen type experiments, and then correcting for exchange effects within the framework of a two-site exchange model. We also propose experiments based on selective decoupling and applicable in systems with no large T2 difference between the different spin pools. Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.

  17. Experimental separation of a frequency spin echo signal

    International Nuclear Information System (INIS)

    Bun'kov, Yu.M.; Dmitriev, V.V.

    1981-01-01

    To study systems with bound nuclear-electron precession CsMnF 2 antiferromagnetic light-plane monocrystal was investigated. Crystal orientation was carried out by roentgenoscopy. Measurements were performed at helium temperatures in the 500-700 MHz frequency range. A NMR pulsed spectrometer with generators of both resonance and doubled frequency was used to produce an echo signal (to study by the parametric echo method). It was shown that the theory of the formation of a frequency modulated echo (FM echo) did not fully describe the properties of the echo signals in systems with dynamic frequency shift (DFS). An intense spin echo signal, which formation was apparently connected with other nonlinear properties of the systems with nuclear-electron precession, was observed. The spin echo signal in magnetics with DFS, which properties correspond to notions of the frequency mechanism of echo formation, was experimentally separated. As a result of the investigations it had been possible to settle contradictions between the theory of FM echo formation and the experimental results for the last 9 years. It turned out that the mechanism of FM echo formation in the magnetics with bound nuclear-electron precession was effective only at large delay times between the pulses. In the range of small delays the FM echo is ''jammed'' by a gigantic echo signal of a nature different from that of the traditional FM signal. The constant of gigantic echo intensity drop at increasing delay between the pulses weakly depends on spin-spin relaxation time [ru

  18. Single-shot echo-planar imaging of multiple sclerosis: effects of varying echo time

    International Nuclear Information System (INIS)

    Wolansky, L.J.; Chong, S.; Liu, W.C.; Kang, E.; Simpson, S.W.; Karimi, S.; Akbari, H.

    1999-01-01

    Our aim was to determine the relative merits of short and long echo times (TE) with single-shot echo-planar imaging for imaging cerebral lesions such as multiple sclerosis. We examined seven patients with clinically definite multiple sclerosis were imaged at 1.5 T. Patients were scanned with spin-echo, single-shot echo-planar imaging, using TEs of 45, 75, 105, and 135 ms. Region of interest (ROI) measurements were performed on 36 lesions at or above the level of the corona radiata. The mean image contrast (IC) was highest (231.1) for a TE of 45 ms, followed by 75 ms (218.9), 105 ms (217.9), and 135 ms (191.6). When mean contrast-to-noise ratios (C/N) were compared, the value was again highest (29.7) for TE 45 ms, followed by 75 ms (28.9), 105 ms (28.5), and 135 ms (26.3). In a lesion-by-lesion comparison, TE 45 ms had the highest IC and C/N in the largest number of cases (50 % and 47.2 %, respectively). IC and C/N for TE 45 ms were superior to those of 75 ms in 64 % and 58 %, respectively. These results support the use of relatively short TEs for single-shot echo-planar imaging in the setting of cerebral lesions such as multiple sclerosis. (orig.) (orig.)

  19. Wavelet-LMS algorithm-based echo cancellers

    Science.gov (United States)

    Seetharaman, Lalith K.; Rao, Sathyanarayana S.

    2002-12-01

    This paper presents Echo Cancellers based on the Wavelet-LMS Algorithm. The performance of the Least Mean Square Algorithm in Wavelet transform domain is observed and its application in Echo cancellation is analyzed. The Widrow-Hoff Least Mean Square Algorithm is most widely used algorithm for Adaptive filters that function as Echo Cancellers. The present day communication signals are widely non-stationary in nature and some errors crop up when Least Mean Square Algorithm is used for the Echo Cancellers handling such signals. The analysis of non-stationary signals often involves a compromise between how well transitions or discontinuities can be located. The multi-scale or multi-resolution of signal analysis, which is the essence of wavelet transform, makes Wavelets popular in non-stationary signal analysis. In this paper, we present a Wavelet-LMS algorithm wherein the wavelet coefficients of a signal are modified adaptively using the Least Mean Square Algorithm and then reconstructed to give an Echo-free signal. The Echo Canceller based on this Algorithm is found to have a better convergence and a comparatively lesser MSE (Mean Square error).

  20. Recalls API

    Data.gov (United States)

    US Consumer Product Safety Commission — CPSC provides accessibility to recalls via a recall database. The information is publicly available to consumers and businesses as well as software and application...

  1. Quantitative comparison between a multiecho sequence and a single-echo sequence for susceptibility-weighted phase imaging.

    Science.gov (United States)

    Gilbert, Guillaume; Savard, Geneviève; Bard, Céline; Beaudoin, Gilles

    2012-06-01

    The aim of this study was to investigate the benefits arising from the use of a multiecho sequence for susceptibility-weighted phase imaging using a quantitative comparison with a standard single-echo acquisition. Four healthy adult volunteers were imaged on a clinical 3-T system using a protocol comprising two different three-dimensional susceptibility-weighted gradient-echo sequences: a standard single-echo sequence and a multiecho sequence. Both sequences were repeated twice in order to evaluate the local noise contribution by a subtraction of the two acquisitions. For the multiecho sequence, the phase information from each echo was independently unwrapped, and the background field contribution was removed using either homodyne filtering or the projection onto dipole fields method. The phase information from all echoes was then combined using a weighted linear regression. R2 maps were also calculated from the multiecho acquisitions. The noise standard deviation in the reconstructed phase images was evaluated for six manually segmented regions of interest (frontal white matter, posterior white matter, globus pallidus, putamen, caudate nucleus and lateral ventricle). The use of the multiecho sequence for susceptibility-weighted phase imaging led to a reduction of the noise standard deviation for all subjects and all regions of interest investigated in comparison to the reference single-echo acquisition. On average, the noise reduction ranged from 18.4% for the globus pallidus to 47.9% for the lateral ventricle. In addition, the amount of noise reduction was found to be strongly inversely correlated to the estimated R2 value (R=-0.92). In conclusion, the use of a multiecho sequence is an effective way to decrease the noise contribution in susceptibility-weighted phase images, while preserving both contrast and acquisition time. The proposed approach additionally permits the calculation of R2 maps. Copyright © 2012 Elsevier Inc. All rights reserved.

  2. Are forward and backward recall the same? A dual-task study of digit recall.

    Science.gov (United States)

    St Clair-Thompson, Helen L; Allen, Richard J

    2013-05-01

    There is some debate surrounding the cognitive resources underlying backward digit recall. Some researchers consider it to differ from forward digit recall due to the involvement of executive control, while others suggest that backward recall involves visuospatial resources. Five experiments therefore investigated the role of executive-attentional and visuospatial resources in both forward and backward digit recall. In the first, participants completed visuospatial 0-back and 2-back tasks during the encoding of information to be remembered. The concurrent tasks did not differentially disrupt performance on backward digit recall, relative to forward digit recall. Experiment 2 shifted concurrent load to the recall phase instead and, in this case, revealed a larger effect of both tasks on backward recall, relative to forwards recall, suggesting that backward recall may draw on additional resources during the recall phase and that these resources are visuospatial in nature. Experiments 3 and 4 then further investigated the role of visual processes in forward and backward recall using dynamic visual noise (DVN). In Experiment 3, DVN was presented during encoding of information to be remembered and had no effect upon performance. However, in Experiment 4, it was presented during the recall phase, and the results provided evidence of a role for visual imagery in backward digit recall. These results were replicated in Experiment 5, in which the same list length was used for forward and backward recall tasks. The findings are discussed in terms of both theoretical and practical implications.

  3. Recalls API

    Data.gov (United States)

    General Services Administration — This Recalls API allows you to tap into a list of (1) drug and food safety recalls from the Food and Drug Administration, Food Safety and Inspection Service, and...

  4. Imaging and histological features of central subchondral osteophytes in racehorses with metacarpophalangeal joint osteoarthritis.

    Science.gov (United States)

    Olive, J; D'Anjou, M A; Girard, C; Laverty, S; Theoret, C L

    2009-12-01

    Marginal osteophytes represent a well known component of osteoarthritis in man and animals. Conversely, central subchondral osteophytes (COs), which are commonly present in human knees with osteoarthritis, have not been reported in horses. To describe and compare computed radiography (CR), single-slice computed tomography (CT), 1.5 Tesla magnetic resonance imaging (MRI), and histological features of COs in equine metacarpophalangeal joints with macroscopic evidence of naturally-occurring osteoarthritis. MRI sequences (sagittal spoiled gradient recalled echo [SPGR] with fat saturation, sagittal T2-weighted fast spin echo with fat saturation [T2-FS], dorsal and transverse T1-weighted gradient-recalled echo [GRE], and sagittal T2*-weighted gradient echo with fast imaging employing steady state acquisition [FIESTA]), as well as transverse and reformatted sagittal CTI and 4 computed radiographic (CR) views of 20 paired metacarpophalangeal joints were acquired ex vivo. Following macroscopic evaluation, samples were harvested in predetermined sites of the metacarpal condyle for subsequent histology. The prevalence and detection level of COs was determined for each imaging modality. Abnormalities consistent with COs were clearly depicted on MRI, using the SPGR sequence, in 7/20 (35%) joints. They were identified as a focal hypointense protuberance from the subchondral plate into the cartilage, at the palmarodistal aspect (n=7) and/or at the very dorsal aspect (n=2) of the metacarpal condyle. COs were visible but less obvious in 5 of the 7 joints using FIESTA and reformatted sagittal CT, and were not identifiable on T2-FS, T1-GRE or CR. Microscopically, they consisted of dense bone protruding into the calcified cartilage and disrupting the tidemarks, and they were consistently associated with overlying cartilage defects. Subchondral osteophytes are a feature of osteoarthritis of equine metacarpophalangeal joints and they may be diagnosed using 1.5 Tesla MRI and CT. Central

  5. Correction for Eddy Current-Induced Echo-Shifting Effect in Partial-Fourier Diffusion Tensor Imaging.

    Science.gov (United States)

    Truong, Trong-Kha; Song, Allen W; Chen, Nan-Kuei

    2015-01-01

    In most diffusion tensor imaging (DTI) studies, images are acquired with either a partial-Fourier or a parallel partial-Fourier echo-planar imaging (EPI) sequence, in order to shorten the echo time and increase the signal-to-noise ratio (SNR). However, eddy currents induced by the diffusion-sensitizing gradients can often lead to a shift of the echo in k-space, resulting in three distinct types of artifacts in partial-Fourier DTI. Here, we present an improved DTI acquisition and reconstruction scheme, capable of generating high-quality and high-SNR DTI data without eddy current-induced artifacts. This new scheme consists of three components, respectively, addressing the three distinct types of artifacts. First, a k-space energy-anchored DTI sequence is designed to recover eddy current-induced signal loss (i.e., Type 1 artifact). Second, a multischeme partial-Fourier reconstruction is used to eliminate artificial signal elevation (i.e., Type 2 artifact) associated with the conventional partial-Fourier reconstruction. Third, a signal intensity correction is applied to remove artificial signal modulations due to eddy current-induced erroneous T2(∗) -weighting (i.e., Type 3 artifact). These systematic improvements will greatly increase the consistency and accuracy of DTI measurements, expanding the utility of DTI in translational applications where quantitative robustness is much needed.

  6. Cognitive Factors Affecting Free Recall, Cued Recall, and Recognition Tasks in Alzheimer’s Disease

    Directory of Open Access Journals (Sweden)

    Takashi Yamagishi

    2012-07-01

    Full Text Available Background/Aims: Our aim was to identify cognitive factors affecting free recall, cued recall, and recognition tasks in patients with Alzheimer’s disease (AD. Subjects: We recruited 349 consecutive AD patients who attended a memory clinic. Methods: Each patient was assessed using the Alzheimer’s Disease Assessment Scale (ADAS and the extended 3-word recall test. In this task, each patient was asked to freely recall 3 previously presented words. If patients could not recall 1 or more of the target words, the examiner cued their recall by providing the category of the target word and then provided a forced-choice recognition of the target word with 2 distracters. The patients were divided into groups according to the results of the free recall, cued recall, and recognition tasks. Multivariate logistic regression analysis for repeated measures was carried out to evaluate the net effects of cognitive factors on the free recall, cued recall, and recognition tasks after controlling for the effects of age and recent memory deficit. Results: Performance on the ADAS Orientation task was found to be related to performance on the free and cued recall tasks, performance on the ADAS Following Commands task was found to be related to performance on the cued recall task, and performance on the ADAS Ideational Praxis task was found to be related to performance on the free recall, cued recall, and recognition tasks. Conclusion: The extended 3-word recall test reflects deficits in a wider range of memory and other cognitive processes, including memory retention after interference, divided attention, and executive functions, compared with word-list recall tasks. The characteristics of the extended 3-word recall test may be advantageous for evaluating patients’ memory impairments in daily living.

  7. Reconstruction strategy for echo planar spectroscopy and its application to partially undersampled imaging

    DEFF Research Database (Denmark)

    Hanson, L G; Schaumburg, K; Paulson, O B

    2000-01-01

    The most commonly encountered form of echo planar spectroscopy involves oscillating gradients in one spatial dimension during readout. Data are consequently not sampled on a Cartesian grid. A fast gridding algorithm applicable to this particular situation is presented. The method is optimal, i.......e., it performs as well as the full discrete Fourier transform for band limited signals while allowing for use of the fast Fourier transform. The method is demonstrated for reconstruction of data that are partially undersampled in the time domain. The advantages of undersampling are lower hardware requirements...

  8. Drug recall: An incubus for pharmaceutical companies and most serious drug recall of history.

    Science.gov (United States)

    Nagaich, Upendra; Sadhna, Divya

    2015-01-01

    There has been an increasing trend in the number of prescribed and over-the-counter drug recall over the last few years. The recall is usually due to company's discovery, customer's complaint or Food and Drug Administration (FDA) observation. The process of recall involves a planned specific course of action, which addresses the depth of recall, need for public warning, and the extent of effectiveness checks for the recall. The FDA review and/or recommend changes to the firm's recall strategy, as appropriate. The critical recall information list includes the identity of the product; summary of the failure; amount of product produced in the distribution chain and direct account. Product recalls clashes thousands of companies every year affecting: sales, testing customer relationships and disrupting supply chains. Drug recall is incubus for pharmaceutical companies. It effects the reputation of the company. The reason for the recall can be divided into two categories: manufacturing affined and safety/efficacy affined. It is essential to follow all the guidelines related to drug development and manufacturing procedure so as to minimize drug recall.

  9. Improving parallel imaging by jointly reconstructing multi-contrast data.

    Science.gov (United States)

    Bilgic, Berkin; Kim, Tae Hyung; Liao, Congyu; Manhard, Mary Kate; Wald, Lawrence L; Haldar, Justin P; Setsompop, Kawin

    2018-08-01

    To develop parallel imaging techniques that simultaneously exploit coil sensitivity encoding, image phase prior information, similarities across multiple images, and complementary k-space sampling for highly accelerated data acquisition. We introduce joint virtual coil (JVC)-generalized autocalibrating partially parallel acquisitions (GRAPPA) to jointly reconstruct data acquired with different contrast preparations, and show its application in 2D, 3D, and simultaneous multi-slice (SMS) acquisitions. We extend the joint parallel imaging concept to exploit limited support and smooth phase constraints through Joint (J-) LORAKS formulation. J-LORAKS allows joint parallel imaging from limited autocalibration signal region, as well as permitting partial Fourier sampling and calibrationless reconstruction. We demonstrate highly accelerated 2D balanced steady-state free precession with phase cycling, SMS multi-echo spin echo, 3D multi-echo magnetization-prepared rapid gradient echo, and multi-echo gradient recalled echo acquisitions in vivo. Compared to conventional GRAPPA, proposed joint acquisition/reconstruction techniques provide more than 2-fold reduction in reconstruction error. JVC-GRAPPA takes advantage of additional spatial encoding from phase information and image similarity, and employs different sampling patterns across acquisitions. J-LORAKS achieves a more parsimonious low-rank representation of local k-space by considering multiple images as additional coils. Both approaches provide dramatic improvement in artifact and noise mitigation over conventional single-contrast parallel imaging reconstruction. Magn Reson Med 80:619-632, 2018. © 2018 International Society for Magnetic Resonance in Medicine. © 2018 International Society for Magnetic Resonance in Medicine.

  10. Electric Dipole Echoes and Noise-Induced Coherence

    International Nuclear Information System (INIS)

    Mestayer, J.J.; Zhao, W.; Lancaster, J.C.; Dunning, F.B.; Yoshida, S.; Reinhold, Carlos O.; Burgdorfer, J.

    2007-01-01

    The generation of echoes in the electric dipole moment of a Rydberg wavepacket precessing in an external electric field by reversal of the field is described. When the wavepacket experiences reversible dephasing, large echoes are observed pointing to strong refocusing of the wavepacket. The presence of irreversible dephasing leads to a reduction in the size of the echoes. The effect of irreversible dynamics on echoes is investigated using artificially synthesized noise. Methods to determine the decoherence rate are discussed

  11. Beam echoes in the presence of coupling

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Axel [Case Western Reserve U.

    2017-10-03

    Transverse beam echoes could provide a new technique of measuring diusion characteristics orders of magnitude faster than the current methods; however, their interaction with many accelerator parameters is poorly understood. Using a program written in C, we explored the relationship between coupling and echo strength. We found that echoes could be generated in both dimensions, even with a dipole kick in only one dimension. We found that the echo eects are not destroyed even when there is strong coupling, falling o only at extremely high coupling values. We found that at intermediate values of skew quadrupole strength, the decoherence time of the beam is greatly increased, causing a destruction of the echo eects. We found that this is caused by a narrowing of the tune width of the particles. Results from this study will help to provide recommendations to IOTA (Integrable Optics Test Accelerator) for their upcoming echo experiment.

  12. Minimum weight protection - Gradient method; Protection de poids minimum - Methode du gradient

    Energy Technology Data Exchange (ETDEWEB)

    Danon, R.

    1958-12-15

    After having recalled that, when considering a mobile installation, total weight has a crucial importance, and that, in the case of a nuclear reactor, a non neglectable part of weight is that of protection, this note presents an iterative method which results, for a given protection, to a configuration with a minimum weight. After a description of the problem, the author presents the theoretical formulation of the gradient method as it is applied to the concerned case. This application is then discussed, as well as its validity in terms of convergence and uniqueness. Its actual application is then reported, and possibilities of practical applications are evoked.

  13. X-ray echoes from gamma-ray bursts

    International Nuclear Information System (INIS)

    Dermer, C.D.; Hurley, K.C.; Hartmann, D.H.

    1991-01-01

    The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum of the primary burst emission. The expected temporal and spectral signatures of the echo and a search for such echoes are described, and implications for gamma-ray burst models are discussed. 35 refs

  14. Parallel imaging enhanced MR colonography using a phantom model.

    LENUS (Irish Health Repository)

    Morrin, Martina M

    2008-09-01

    To compare various Array Spatial and Sensitivity Encoding Technique (ASSET)-enhanced T2W SSFSE (single shot fast spin echo) and T1-weighted (T1W) 3D SPGR (spoiled gradient recalled echo) sequences for polyp detection and image quality at MR colonography (MRC) in a phantom model. Limitations of MRC using standard 3D SPGR T1W imaging include the long breath-hold required to cover the entire colon within one acquisition and the relatively low spatial resolution due to the long acquisition time. Parallel imaging using ASSET-enhanced T2W SSFSE and 3D T1W SPGR imaging results in much shorter imaging times, which allows for increased spatial resolution.

  15. Free Recall Shows Similar Reactivation Behavior as Recognition & Cued Recall

    OpenAIRE

    Tarnow, Eugen

    2016-01-01

    I find that the total retrieval time in word free recall increases linearly with the total number of items recalled. Measured slopes, the time to retrieve an additional item, vary from 1.4-4.5 seconds per item depending upon presentation rate, subject age and whether there is a delay after list presentation or not. These times to retrieve an additional item obey a second linear relationship as a function of the recall probability averaged over the experiment, explicitly independent of subject...

  16. Cerebral staging of lung cancer: is one single contrast-enhanced T1-weighted three-dimensional gradient-echo sequence sufficient?

    Energy Technology Data Exchange (ETDEWEB)

    Ohana, Mickael; Jeung, Mi-Young; Roy, Catherine [Nouvel Hopital Civil-Hopitaux Universitaires de Strasbourg, Service de Radiologie B/Radiology Department, Strasbourg (France); Bazille, Gauthier [Clinique Saint Anne-Groupe Radiologique MIM, Strasbourg (France)

    2014-08-15

    Gadolinium-enhanced magnetic resonance imaging (MRI) is the gold standard for cerebral staging in thoracic oncology. We hypothesize that a minimalist examination, consisting of a single contrast-enhanced T1-weighted three-dimensional gradient-echo sequence (CE 3D-GRE), would be sufficient for the cerebral staging of nonsymptomatic lung cancer patients. Seventy nonsymptomatic patients (50 % men; 62 years ± 10.2) referred for cerebral staging of a lung cancer were retrospectively included. All underwent a standard 3 T MRI examination with T1, FLAIR, T2* GRE, diffusion, and CE 3D-GRE sequences, for a total examination time of 20 min. The sole CE 3D-GRE (acquisition time: 6 min) was extracted and blindly interpreted by two radiologists in search of brain metastases. Hemorrhagic features of potential lesions and relevant incidental findings were also noted. Discrepant cases were reviewed by a third reader. The full MRI examination and follow-up studies were used as a reference to calculate sensitivity and specificity of the sole CE 3D-GRE. Thirty-eight point six percent (27 out of 70) of the patients had brain metastases. Performances and reader's agreement with the sole CE 3D-GRE sequence were excellent for the diagnosis of brain metastases (sensitivity = 96.3 %, specificity = 100 %, κ = 0.91) and incidental findings (sensitivity = 85.7 %, specificity = 100 %, κ = 0.62) but insufficient for the identification of hemorrhages within the metastases (sensitivity = 33.3 %, specificity = 85.7 %, κ = 0.47). In the specific case of lung cancer, cerebral staging in nonsymptomatic patients can be efficiently achieved with a minimalistic protocol consisting of a single CE 3D-GRE sequence, completed if positive with a T2* sequence for hemorrhagic assessment, thus halving appointment delays. (orig.)

  17. Magnetic resonance imaging of the sacroiliac joints in patients with suspected spondyloarthritis. Comparison of turbo spin-echo and gradient-echo sequences for the detection of structural alterations; MRT-Bildgebung der Sakroiliakalgelenke bei Verdacht auf Spondyloarthritis. Vergleich von Turbospinecho- und Gradientenechosequenzen zum Nachweis struktureller Veraenderungen

    Energy Technology Data Exchange (ETDEWEB)

    Dornia, C.; Hoffstetter, P. [Universitaetsklinikum Regensburg (Germany). Inst. fuer Roentgendiagnostik; Asklepios Klinikum, Bad Abbach (Germany). Inst. fuer Roentgendiagnostik; Fleck, M. [Universitaetsklinikum Regensburg (Germany). Klinik fuer Innere Medizin I; Asklepios Klinikum, Bad Abbach (Germany). Klinik fuer Rheumatologie und Klinische Immunologie; Hartung, W. [Asklepios Klinikum, Bad Abbach (Germany). Klinik fuer Rheumatologie und Klinische Immunologie; Niessen, C.; Stroszczynski, C. [Universitaetsklinikum Regensburg (Germany). Inst. fuer Roentgendiagnostik

    2015-02-15

    Magnetic resonance imaging (MRI) is the method of choice for the evaluation of spondyloarthritis (SpA). According to the guidelines of the Assessment of Spondyloarthritis International Society (ASAS) and Outcome Measures in Rheumatology (OMERACT), MRI findings in SpA of the spine and the sacroiliac joints (SIJ) are classified as inflammatory and structural alterations. Modern gradient-echo sequences (GRE) are recommended for optimized detection of structural alterations of the SIJ. We assess the benefit of GRE in the detection of structural alterations of the SIJ in comparison to conventional turbo spin-echo sequences (TSE). Retrospective study of 114 patients who received MRI of the SIJ for the evaluation of SpA. Structural alterations of the SIJ were assessed by two blinded readers separately for T1 TSE and T2{sup *} GRE. The findings were classified according to a previously published chronicity score separately for both sides and sequences. Interobserver reliability was calculated with Cohen's Kappa, and the significance of findings was assessed with the Wilcoxon test. P-values < 0.05 were required for statistical significance. 68 of 114 (60%) patients showed SpA-typical findings of the SIJ. The average chronicity score for GRE (score 3.3) was significantly higher than for TSE (score 2.6), p=0.001. The Kappa-values for the interobserver reliability were 0.86-0.90 without any statistically significant differences between both sides and sequences. Both T1 TSE and T2{sup *} GRE showed a high interobserver reliability in the detection of structural alterations in patients with SpA. However, T2{sup *} GRE detected significantly more structural alterations than T1 TSE and should be an integral part of a modern MRI protocol for the diagnostic workup of patients with suspected SpA.

  18. Cognitive Factors Affecting Free Recall, Cued Recall, and Recognition Tasks in Alzheimer’s Disease

    OpenAIRE

    Takashi Yamagishi; Takuya Sato; Atsushi Sato; Toru Imamura

    2012-01-01

    Background/Aims: Our aim was to identify cognitive factors affecting free recall, cued recall, and recognition tasks in patients with Alzheimer’s disease (AD). Subjects: We recruited 349 consecutive AD patients who attended a memory clinic. Methods: Each patient was assessed using the Alzheimer’s Disease Assessment Scale (ADAS) and the extended 3-word recall test. In this task, each patient was asked to freely recall 3 previously presented words. If patients could not recall 1 or more of the ...

  19. A magnetic gradient induced force in NMR restricted diffusion experiments

    International Nuclear Information System (INIS)

    Ghadirian, Bahman; Stait-Gardner, Tim; Castillo, Reynaldo; Price, William S.

    2014-01-01

    We predict that the phase cancellation of a precessing magnetisation field carried by a diffusing species in a bounded geometry under certain nuclear magnetic resonance pulsed magnetic field gradient sequences results in a small force over typically micrometre length scales. Our calculations reveal that the total magnetisation energy in a pore under the influence of a pulsed gradient will be distance-dependent thus resulting in a force acting on the boundary. It is shown that this effect of the magnetisation of diffusing particles will appear as either an attractive or repulsive force depending on the geometry of the pore and magnetic properties of the material. A detailed analysis is performed for the case of a pulsed gradient spin-echo experiment on parallel planes. It is shown that the force decays exponentially in terms of the spin-spin relaxation. The proof is based on classical electrodynamics. An application of this effect to soft matter is suggested

  20. Free Recall Curves: Nothing but Rehearsing Some Items More or Recalling Them Sooner?

    Science.gov (United States)

    Brodie, Delbert A.; Prytulak, Lubomir S.

    1975-01-01

    The hypothesis that free recall curves reflecting effects of serial position, presentation time and delay of recall are attributable to subjects' pattern of rehearsal was explored. Experiments varied the patterns of rehearsal to examine the effects on recall. (CHK)

  1. MEASUREMENT OF TRANSVERSE ECHOES IN RHIC

    International Nuclear Information System (INIS)

    FISCHER, W.; SATOGATA, T.; TOMAS, R.

    2005-01-01

    Beam echoes are a very sensitive method to measure diffusion, and longitudinal echo measurements were performed in a number of machines. In RHIC, for the first time, a transverse beam echo was observed after applying a dipole kick followed by a quadrupole .kick. After application of the dipole kick, the dipole moment decohered completely due to lattice nonlinearities. When a quadrupole kick is applied at time τ after the dipole kick, the beam re-cohered at time 2τ thus showing an echo response. We describe the experimental setup and measurement results. In the measurements the dipole and quadrupole kick amplitudes, amplitude dependent tune shift, and the time between dipole and quadrupole kick were varied. In addition, measurements were taken with gold bunches of different intensities. These should exhibit different transverse diffusion rates due to intra-beam scattering

  2. Time-resolved Femtosecond Photon Echo Probes Bimodal Solvent Dynamics

    NARCIS (Netherlands)

    Pshenichnikov, M.S; Duppen, K.; Wiersma, D. A.

    1995-01-01

    We report on time-resolved femtosecond photon echo experiments of a dye molecule in a polar solution. The photon echo is time resolved by mixing the echo with a femtosecond gate pulse in a nonlinear crystal. It is shown that the temporal profile of the photon echo allows separation of the

  3. Gravitational wave sources: reflections and echoes

    Science.gov (United States)

    Price, Richard H.; Khanna, Gaurav

    2017-11-01

    The recent detection of gravitational waves has generated interest in alternatives to the black hole interpretation of sources. A subset of such alternatives involves a prediction of gravitational wave ‘echoes’. We consider two aspects of possible echoes: first, general features of echoes coming from spacetime reflecting conditions. We find that the detailed nature of such echoes does not bear any clear relationship to quasi-normal frequencies. Second, we point out the pitfalls in the analysis of local reflecting ‘walls’ near the horizon of rapidly rotating black holes.

  4. Gravitational wave sources: reflections and echoes

    International Nuclear Information System (INIS)

    Price, Richard H; Khanna, Gaurav

    2017-01-01

    The recent detection of gravitational waves has generated interest in alternatives to the black hole interpretation of sources. A subset of such alternatives involves a prediction of gravitational wave ‘echoes’. We consider two aspects of possible echoes: first, general features of echoes coming from spacetime reflecting conditions. We find that the detailed nature of such echoes does not bear any clear relationship to quasi-normal frequencies. Second, we point out the pitfalls in the analysis of local reflecting ‘walls’ near the horizon of rapidly rotating black holes. (paper)

  5. Sparse adaptive filters for echo cancellation

    CERN Document Server

    Paleologu, Constantin

    2011-01-01

    Adaptive filters with a large number of coefficients are usually involved in both network and acoustic echo cancellation. Consequently, it is important to improve the convergence rate and tracking of the conventional algorithms used for these applications. This can be achieved by exploiting the sparseness character of the echo paths. Identification of sparse impulse responses was addressed mainly in the last decade with the development of the so-called ``proportionate''-type algorithms. The goal of this book is to present the most important sparse adaptive filters developed for echo cancellati

  6. Vertical structure of the vhf backscattering region in the equatorial electrojet and the gradient drift instability

    International Nuclear Information System (INIS)

    Fejer, B.G.; Farley, D.T.; Balsley, B.B.; Woodman, R.F.

    1974-01-01

    Radar measurements made with high spatial resolution and large dynamic range at the Jicamarca Radar Observatory near the time of reversal of the electrojet current provide further proof that the gradient drift instability is in fact responsible for the type-2 irregularities. Echoes are received over a much wider range of altitudes at night than during the day, partly because of the change in character of the background electron density profile and partly because of recombination effects, which can be important during the day. One must be cautious, particularly at night, in associating the mean Doppler shift of oblique radar echoes with the maximum east--west electron drift velocity

  7. Mock ECHO: A Simulation-Based Medical Education Method.

    Science.gov (United States)

    Fowler, Rebecca C; Katzman, Joanna G; Comerci, George D; Shelley, Brian M; Duhigg, Daniel; Olivas, Cynthia; Arnold, Thomas; Kalishman, Summers; Monnette, Rebecca; Arora, Sanjeev

    2018-04-16

    This study was designed to develop a deeper understanding of the learning and social processes that take place during the simulation-based medical education for practicing providers as part of the Project ECHO® model, known as Mock ECHO training. The ECHO model is utilized to expand access to care of common and complex diseases by supporting the education of primary care providers with an interprofessional team of specialists via videoconferencing networks. Mock ECHO trainings are conducted through a train the trainer model targeted at leaders replicating the ECHO model at their organizations. Trainers conduct simulated teleECHO clinics while participants gain skills to improve communication and self-efficacy. Three focus groups, conducted between May 2015 and January 2016 with a total of 26 participants, were deductively analyzed to identify common themes related to simulation-based medical education and interdisciplinary education. Principal themes generated from the analysis included (a) the role of empathy in community development, (b) the value of training tools as guides for learning, (c) Mock ECHO design components to optimize learning, (d) the role of interdisciplinary education to build community and improve care delivery, (e) improving care integration through collaboration, and (f) development of soft skills to facilitate learning. Mock ECHO trainings offer clinicians the freedom to learn in a noncritical environment while emphasizing real-time multidirectional feedback and encouraging knowledge and skill transfer. The success of the ECHO model depends on training interprofessional healthcare providers in behaviors needed to lead a teleECHO clinic and to collaborate in the educational process. While building a community of practice, Mock ECHO provides a safe opportunity for a diverse group of clinician experts to practice learned skills and receive feedback from coparticipants and facilitators.

  8. Observation of Gravitationally Induced Vertical Striation of Polarized Ultracold Neutrons by Spin-Echo Spectroscopy.

    Science.gov (United States)

    Afach, S; Ayres, N J; Ban, G; Bison, G; Bodek, K; Chowdhuri, Z; Daum, M; Fertl, M; Franke, B; Griffith, W C; Grujić, Z D; Harris, P G; Heil, W; Hélaine, V; Kasprzak, M; Kermaidic, Y; Kirch, K; Knowles, P; Koch, H-C; Komposch, S; Kozela, A; Krempel, J; Lauss, B; Lefort, T; Lemière, Y; Mtchedlishvili, A; Musgrave, M; Naviliat-Cuncic, O; Pendlebury, J M; Piegsa, F M; Pignol, G; Plonka-Spehr, C; Prashanth, P N; Quéméner, G; Rawlik, M; Rebreyend, D; Ries, D; Roccia, S; Rozpedzik, D; Schmidt-Wellenburg, P; Severijns, N; Thorne, J A; Weis, A; Wursten, E; Wyszynski, G; Zejma, J; Zenner, J; Zsigmond, G

    2015-10-16

    We describe a spin-echo method for ultracold neutrons (UCNs) confined in a precession chamber and exposed to a |B0|=1  μT magnetic field. We have demonstrated that the analysis of UCN spin-echo resonance signals in combination with knowledge of the ambient magnetic field provides an excellent method by which to reconstruct the energy spectrum of a confined ensemble of neutrons. The method takes advantage of the relative dephasing of spins arising from a gravitationally induced striation of stored UCNs of different energies, and also permits an improved determination of the vertical magnetic-field gradient with an exceptional accuracy of 1.1  pT/cm. This novel combination of a well-known nuclear resonance method and gravitationally induced vertical striation is unique in the realm of nuclear and particle physics and should prove to be invaluable for the assessment of systematic effects in precision experiments such as searches for an electric dipole moment of the neutron or the measurement of the neutron lifetime.

  9. Wiener variable step size and gradient spectral variance smoothing for double-talk-robust acoustic echo cancellation and acoustic feedback cancellation

    DEFF Research Database (Denmark)

    Gil-Cacho, Jose M.; Van Waterschoot, Toon; Moonen, Marc

    2014-01-01

    Double-talk (DT)-robust acoustic echo cancellation (AEC) and acoustic feedback cancellation (AFC) are needed in speech communication systems, e.g., in hands-free communication systems and hearing aids. In this paper, we derive a practical and computationally efficient algorithm based...... model and in colored non-stationary noise....

  10. The effect of strong pitch angle scattering on the use of artificial auroral streaks for echo detection - Echo 5

    International Nuclear Information System (INIS)

    Swanson, R.L.; Steffen, J.E.; Winckler, J.R.

    1986-01-01

    During the Echo 5 experiment launched 13 November 1979 from the Poker Flat Research Range (Fairbanks, Alaska), a 0.75 A, 37 keV electron beam was injected both up and down the field line to test the use of optical and X-ray methods to detect the beam as it interacted with the atmosphere below the rocket for both the downward injections (markers) and the upward injected electrons which mirrored at the Southern Hemisphere and returned echoes. The artificial auroral streaks created by the markers were easily visible on the ground TV system but the large intensity of photons produced around the rocket masked any response to the markers by the on-board photometers and X-ray detectors. No echoes were detected with any of the detection systems although the power in some of the upward injections was 7.6 times the power in a detected downward injection thus setting an upper limit on the loss-cone echo flux. The magnitude of the bounce averaged pitch angle diffusion coefficient necessary to explain the lack of observable echoes was found to be 4 x 10 -4 S -1 . It was found that an equatorial wave electric field of 11 mVm -1 would account for the lack of echoes. Such fields should cause strong pitch angle scattering of up to 10 keV natural electrons and thus be consistent with the presence of diffuse aurora on the Echo 5 trajectory. (author)

  11. Recall Latencies, Confidence, and Output Positions of True and False Memories: Implications for Recall and Metamemory Theories

    Science.gov (United States)

    Jou, Jerwen

    2008-01-01

    Recall latency, recall accuracy rate, and recall confidence were examined in free recall as a function of recall output serial position using a modified Deese-Roediger-McDermott paradigm to test a strength-based theory against the dual-retrieval process theory of recall output sequence. The strength theory predicts the item output sequence to be…

  12. Time Limits : Effects on Recall

    OpenAIRE

    Hirano, Kinue

    2000-01-01

    This study investigates the effects of differing time limits and the level of language proficiency on the written recalls of 66 Japanese EFL undergraduates. Results showed that different time limits affected total recall, but not main ideas recalled. Regardless of proficiency level, the 20-minute group (Group 2) recalled a greater number of idea units than the 8-minute group (Group 1). However, no significant difference was found between Groups 1 and 2 regarding the recall of main ideas, alth...

  13. Writing superiority in cued recall

    Directory of Open Access Journals (Sweden)

    Carina eFueller

    2013-10-01

    Full Text Available In list learning paradigms with free recall, written recall has been found to be less susceptible to intrusions of related concepts than spoken recall when the list items had been visually presented. This effect has been ascribed to the use of stored orthographic representations from the study phase during written recall (Kellogg, 2001. In other memory retrieval paradigms, either better recall for modality-congruent items or an input-independent writing superiority effect have been found (Grabowski, 2005. In a series of four experiments using a paired associate (PA learning paradigm we tested (a whether output modality effects on verbal recall can be replicated in a paradigm that does not involve the rejection of semantically related intrusion words, (b whether a possible superiority for written recall was due to a slower response onset for writing as compared to speaking in immediate recall, and (c whether the performance in PA word recall was correlated with performance in an additional episodic memory task. We found better written recall in the first half of the recall phase, irrespective of the modality in which the material was presented upon encoding. An explanation based on longer response latencies for writing and hence more time for retrieval could be ruled out by showing that the effect persisted in delayed response versions of the task. Although there was some evidence that stored additional episodic information may contribute to the successful retrieval of associate words, this evidence was only found in the immediate response experiments and hence is most likely independent from the observed output modality effect. In sum, our results from a PA learning paradigm suggest that superior performance for written versus spoken recall cannot be (solely explained in terms of additional access to stored orthographic representations from the encoding phase. Our findings rather suggest a general writing-superiority effect at the time of memory

  14. Image correction during large and rapid B(0) variations in an open MRI system with permanent magnets using navigator echoes and phase compensation.

    Science.gov (United States)

    Li, Jianqi; Wang, Yi; Jiang, Yu; Xie, Haibin; Li, Gengying

    2009-09-01

    An open permanent magnet system with vertical B(0) field and without self-shielding can be quite susceptible to perturbations from external magnetic sources. B(0) variation in such a system located close to a subway station was measured to be greater than 0.7 microT by both MRI and a fluxgate magnetometer. This B(0) variation caused image artifacts. A navigator echo approach that monitored and compensated the view-to-view variation in magnetic resonance signal phase was developed to correct for image artifacts. Human brain imaging experiments using a multislice gradient-echo sequence demonstrated that the ghosting and blurring artifacts associated with B(0) variations were effectively removed using the navigator method.

  15. Echo-Interleaved-Spiral MR Imaging

    International Nuclear Information System (INIS)

    Rosenthal, Shirrie; Azhari, Haim; Montag, Avram

    1998-01-01

    Interleaved-Spiral imaging is an efficient method for MRI fast scans. However, images suffer from blurring and artifacts due to field inhomogeneities and the long readout times. In this paper, we combine interleaved-spirals with spin-echo for 3D scans. The refocusing RF-pulses (echoes) refocus off-resonance spins, thus allowing longer acquisition times per excitation, by limiting inhomogeneity effects. The total number of excitations for a 3D scan is reduced by half. The 3D Fourier transform of an object is divided into pairs of slices, one slice is scanned in an outgoing interleaved-spiral, initiated after a 90 degree pulse has been applied. The second slice is scanned in an ingoing interleaved-spiral, after a 180 degree pulse has been applied, thus reaching the slice origin at the echo time. (authors)

  16. Prediction of low birth weight: the placental T2* estimated by MRI versus the uterine artery pulsatility index

    DEFF Research Database (Denmark)

    Sinding, Marianne Munk; Peters, David Alberg; Frøkjær, Jens Brøndum

    (MRI) variable T2* reflects the placental oxygenation and thereby placental function. Therefore, we aimed to evaluate the performance of placental T2* in the prediction of low birth weight using the uterine artery (UtA) pulsatility index (PI) as gold standard. Methods: The study population......CONTROL ID: 2516296 ABSTRACT FINAL ID: P22.05 TITLE: Prediction of low birth weight: the placental T2* estimated by MRI versus the uterine artery pulsatility index AUTHORS (FIRST NAME, LAST NAME): Marianne Sinding1, David Peters2, Jens B. Frøkjær3, 4, Ole B. Christiansen1, 4, Astrid Petersen5...... had an EFW T2* was measured by MRI at 1.5T. A gradient recalled echo MRI sequence with readout at 16 echo times was used, and the placental T2* value was obtained by fitting the signal intensity as a function of the echo times...

  17. Acoustic noise reduction in T 1- and proton-density-weighted turbo spin-echo imaging.

    Science.gov (United States)

    Ott, Martin; Blaimer, Martin; Breuer, Felix; Grodzki, David; Heismann, Björn; Jakob, Peter

    2016-02-01

    To reduce acoustic noise levels in T 1-weighted and proton-density-weighted turbo spin-echo (TSE) sequences, which typically reach acoustic noise levels up to 100 dB(A) in clinical practice. Five acoustic noise reduction strategies were combined: (1) gradient ramps and shapes were changed from trapezoidal to triangular, (2) variable-encoding-time imaging was implemented to relax the phase-encoding gradient timing, (3) RF pulses were adapted to avoid the need for reversing the polarity of the slice-rewinding gradient, (4) readout bandwidth was increased to provide more time for gradient activity on other axes, (5) the number of slices per TR was reduced to limit the total gradient activity per unit time. We evaluated the influence of each measure on the acoustic noise level, and conducted in vivo measurements on a healthy volunteer. Sound recordings were taken for comparison. An overall acoustic noise reduction of up to 16.8 dB(A) was obtained by the proposed strategies (1-4) and the acquisition of half the number of slices per TR only. Image quality in terms of SNR and CNR was found to be preserved. The proposed measures in this study allowed a threefold reduction in the acoustic perception of T 1-weighted and proton-density-weighted TSE sequences compared to a standard TSE-acquisition. This could be achieved without visible degradation of image quality, showing the potential to improve patient comfort and scan acceptability.

  18. Time Delay Estimation Algoritms for Echo Cancellation

    Directory of Open Access Journals (Sweden)

    Kirill Sakhnov

    2011-01-01

    Full Text Available The following case study describes how to eliminate echo in a VoIP network using delay estimation algorithms. It is known that echo with long transmission delays becomes more noticeable to users. Thus, time delay estimation, as a part of echo cancellation, is an important topic during transmission of voice signals over packetswitching telecommunication systems. An echo delay problem associated with IP-based transport networks is discussed in the following text. The paper introduces the comparative study of time delay estimation algorithm, used for estimation of the true time delay between two speech signals. Experimental results of MATLab simulations that describe the performance of several methods based on cross-correlation, normalized crosscorrelation and generalized cross-correlation are also presented in the paper.

  19. Rapid flow imaging method

    International Nuclear Information System (INIS)

    Pelc, N.J.; Spritzer, C.E.; Lee, J.N.

    1988-01-01

    A rapid, phase-contrast, MR imaging method of imaging flow has been implemented. The method, called VIGRE (velocity imaging with gradient recalled echoes), consists of two interleaved, narrow flip angle, gradient-recalled acquisitions. One is flow compensated while the second has a specified flow encoding (both peak velocity and direction) that causes signals to contain additional phase in proportion to velocity in the specified direction. Complex image data from the first acquisition are used as a phase reference for the second, yielding immunity from phase accumulation due to causes other than motion. Images with pixel values equal to MΔΘ where M is the magnitude of the flow compensated image and ΔΘ is the phase difference at the pixel, are produced. The magnitude weighting provides additional vessel contrast, suppresses background noise, maintains the flow direction information, and still allows quantitative data to be retrieved. The method has been validated with phantoms and is undergoing initial clinical evaluation. Early results are extremely encouraging

  20. summarytable.PNG | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  1. Resources.PNG | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  2. Custom Search | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  3. Watershed Statistics | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  4. Does an Adolescent’s Accuracy of Recall Improve with a Second 24-h Dietary Recall?

    Directory of Open Access Journals (Sweden)

    Deborah A. Kerr

    2015-05-01

    Full Text Available The multiple-pass 24-h dietary recall is used in most national dietary surveys. Our purpose was to assess if adolescents’ accuracy of recall improved when a 5-step multiple-pass 24-h recall was repeated. Participants (n = 24, were Chinese-American youths aged between 11 and 15 years and lived in a supervised environment as part of a metabolic feeding study. The 24-h recalls were conducted on two occasions during the first five days of the study. The four steps (quick list; forgotten foods; time and eating occasion; detailed description of the food/beverage of the 24-h recall were assessed for matches by category. Differences were observed in the matching for the time and occasion step (p < 0.01, detailed description (p < 0.05 and portion size matching (p < 0.05. Omission rates were higher for the second recall (p < 0.05 quick list; p < 0.01 forgotten foods. The adolescents over-estimated energy intake on the first (11.3% ± 22.5%; p < 0.05 and second recall (10.1% ± 20.8% compared with the known food and beverage items. These results suggest that the adolescents’ accuracy to recall food items declined with a second 24-h recall when repeated over two non-consecutive days.

  5. Large individual differences in free recall

    OpenAIRE

    Tarnow, Eugen

    2016-01-01

    Using single factor ANOVA I show that there are large individual differences in free recall ({\\eta} ranges from 0.09-0.26) including the total recall, the balance between recency and primacy, and the initial recall (subsequent recalls show smaller individual differences). All three memory properties are relatively uncorrelated. The variance in the initial position may be a measure of executive control and is correlated with total recall (the smaller the variation, the larger the recall).

  6. CUTLASS HF radar observations of high-velocity E-region echoes

    Directory of Open Access Journals (Sweden)

    M. V. Uspensky

    Full Text Available A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ion-acoustic speed of 400 ms1 , while the other group had significantly larger velocities, of the order of 700 ms1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ~700 ms1 echoes originated from larger heights and distances of 500–700 km, while all ~400 ms1 echoes came from lower heights and from farther distances; 700–1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong ( ~70 mVm1 and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.

    Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; polar ionosphere

  7. Age and gender specific normal values of left ventricular mass, volume and function for gradient echo magnetic resonance imaging: a cross sectional study

    Directory of Open Access Journals (Sweden)

    Allansdotter-Johnsson Ase

    2009-01-01

    Full Text Available Abstract Background Knowledge about age-specific normal values for left ventricular mass (LVM, end-diastolic volume (EDV, end-systolic volume (ESV, stroke volume (SV and ejection fraction (EF by cardiac magnetic resonance imaging (CMR is of importance to differentiate between health and disease and to assess the severity of disease. The aims of the study were to determine age and gender specific normal reference values and to explore the normal physiological variation of these parameters from adolescence to late adulthood, in a cross sectional study. Methods Gradient echo CMR was performed at 1.5 T in 96 healthy volunteers (11–81 years, 50 male. Gender-specific analysis of parameters was undertaken in both absolute values and adjusted for body surface area (BSA. Results Age and gender specific normal ranges for LV volumes, mass and function are presented from the second through the eighth decade of life. LVM, ESV and EDV rose during adolescence and declined in adulthood. SV and EF decreased with age. Compared to adult females, adult males had higher BSA-adjusted values of EDV (p = 0.006 and ESV (p Conclusion LV volumes, mass and function vary over a broad age range in healthy individuals. LV volumes and mass both rise in adolescence and decline with age. EF showed a rapid decline in adolescence compared to changes throughout adulthood. These findings demonstrate the need for age and gender specific normal ranges for clinical use.

  8. Theory and optical design of x-ray echo spectrometers

    Science.gov (United States)

    Shvyd'ko, Yuri

    2017-08-01

    X-ray echo spectroscopy, a space-domain counterpart of neutron spin echo, is a recently proposed inelastic x-ray scattering (IXS) technique. X-ray echo spectroscopy relies on imaging IXS spectra and does not require x-ray monochromatization. Due to this, the echo-type IXS spectrometers are broadband, and thus have a potential to simultaneously provide dramatically increased signal strength, reduced measurement times, and higher resolution compared to the traditional narrow-band scanning-type IXS spectrometers. The theory of x-ray echo spectrometers presented earlier [Yu. Shvyd'ko, Phys. Rev. Lett. 116, 080801 (2016), 10.1103/PhysRevLett.116.080801] is developed here further with a focus on questions of practical importance, which could facilitate optical design and assessment of the feasibility and performance of the echo spectrometers. Among others, the following questions are addressed: spectral resolution, refocusing condition, echo spectrometer tolerances, refocusing condition adjustment, effective beam size on the sample, spectral window of imaging and scanning range, impact of the secondary source size on the spectral resolution, angular dispersive optics, focusing and collimating optics, and detector's spatial resolution. Examples of optical designs and characteristics of echo spectrometers with 1-meV and 0.1-meV resolutions are presented.

  9. Constrained optimization for position calibration of an NMR field camera.

    Science.gov (United States)

    Chang, Paul; Nassirpour, Sahar; Eschelbach, Martin; Scheffler, Klaus; Henning, Anke

    2018-07-01

    Knowledge of the positions of field probes in an NMR field camera is necessary for monitoring the B 0 field. The typical method of estimating these positions is by switching the gradients with known strengths and calculating the positions using the phases of the FIDs. We investigated improving the accuracy of estimating the probe positions and analyzed the effect of inaccurate estimations on field monitoring. The field probe positions were estimated by 1) assuming ideal gradient fields, 2) using measured gradient fields (including nonlinearities), and 3) using measured gradient fields with relative position constraints. The fields measured with the NMR field camera were compared to fields acquired using a dual-echo gradient recalled echo B 0 mapping sequence. Comparisons were done for shim fields from second- to fourth-order shim terms. The position estimation was the most accurate when relative position constraints were used in conjunction with measured (nonlinear) gradient fields. The effect of more accurate position estimates was seen when compared to fields measured using a B 0 mapping sequence (up to 10%-15% more accurate for some shim fields). The models acquired from the field camera are sensitive to noise due to the low number of spatial sample points. Position estimation of field probes in an NMR camera can be improved using relative position constraints and nonlinear gradient fields. Magn Reson Med 80:380-390, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  10. Echo-Interleaved-Spiral MR Imaging

    Energy Technology Data Exchange (ETDEWEB)

    Rosenthal, Shirrie; Azhari, Haim [Department of Biomedical Engineering, Technion, Israel Institute of Technology, Haifa 32000 (Israel); Montag, Avram [Elscint Ltd., MRI division, Haifa (Israel)

    1999-12-31

    Interleaved-Spiral imaging is an efficient method for MRI fast scans. However, images suffer from blurring and artifacts due to field inhomogeneities and the long readout times. In this paper, we combine interleaved-spirals with spin-echo for 3D scans. The refocusing RF-pulses (echoes) refocus off-resonance spins, thus allowing longer acquisition times per excitation, by limiting inhomogeneity effects. The total number of excitations for a 3D scan is reduced by half. The 3D Fourier transform of an object is divided into pairs of slices, one slice is scanned in an outgoing interleaved-spiral, initiated after a 90 degree pulse has been applied. The second slice is scanned in an ingoing interleaved-spiral, after a 180 degree pulse has been applied, thus reaching the slice origin at the echo time. (authors) 4 refs., 3 figs.

  11. Echo phenomena in a plasma

    International Nuclear Information System (INIS)

    Pavlenko, V.N.

    1983-01-01

    The mechanism of echo phenomenon in different plasma media: laboratory and cosmic plasma, metals and semiconductors is analyzed to get a more comprehensive idea on collective processes in a plasma and for practical applications in radiophysics and plasma diagnostics. The echo phenomenon permitted to confirm a reversible nature of the Landau damping, to prove the fact that the information on perturbation is conserved in a plasma (as non-damping oscillations of the distribution function) even after disappearing of the macroscopic field. The dependence of the diffusion coefficient on the velocity is measured, microturbulences in a plasma are investigated. New ways of the plasma wave conversion are suggested, as well as ''lightning'' of super-critical plasma layers and regions of plasma non-transparency. Prospective advantages of using echo for studying the mechanisms of charged particle interaction with the surface bounding a plasma are revealed

  12. Vertical structure of the VHF backscattering region in the equatorial electrojet and the gradient drift instability

    International Nuclear Information System (INIS)

    Fejer, B.G.; Farley, D.T.; Balsley, B.B.; Woodman, R.F.

    1975-01-01

    Radar measurements made with high spatial resolution and large dynamic range at the Jicamarca Radar Observatory near the time of reversal of the electrojet current provide further proof that the gradient drift instability is in fact responsible for the type 2 irregularities. Echoes are received over a much wider range of altitudes at night than during the day partly because of the change in character of the background electron density profile and partly because of recombination effects, which can be important during the day. It is also shown that one must be cautious, particularly at night, in associating the mean Doppler shift of oblique radar echoes with the maximum east-west electron drift velocity

  13. Multi-site study of diffusion metric variability: effects of site, vendor, field strength, and echo time on regions-of-interest and histogram-bin analyses.

    Science.gov (United States)

    Helmer, K G; Chou, M-C; Preciado, R I; Gimi, B; Rollins, N K; Song, A; Turner, J; Mori, S

    2016-02-27

    It is now common for magnetic-resonance-imaging (MRI) based multi-site trials to include diffusion-weighted imaging (DWI) as part of the protocol. It is also common for these sites to possess MR scanners of different manufacturers, different software and hardware, and different software licenses. These differences mean that scanners may not be able to acquire data with the same number of gradient amplitude values and number of available gradient directions. Variability can also occur in achievable b-values and minimum echo times. The challenge of a multi-site study then, is to create a common protocol by understanding and then minimizing the effects of scanner variability and identifying reliable and accurate diffusion metrics. This study describes the effect of site, scanner vendor, field strength, and TE on two diffusion metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA) using two common analyses (region-of-interest and mean-bin value of whole brain histograms). The goal of the study was to identify sources of variability in diffusion-sensitized imaging and their influence on commonly reported metrics. The results demonstrate that the site, vendor, field strength, and echo time all contribute to variability in FA and MD, though to different extent. We conclude that characterization of the variability of DTI metrics due to site, vendor, field strength, and echo time is a worthwhile step in the construction of multi-center trials.

  14. Method of T2 spectrum inversion with conjugate gradient algorithm from NMR data

    International Nuclear Information System (INIS)

    Li Pengju; Shi Shangming; Song Yanjie

    2010-01-01

    Based on the optimization techniques, the T 2 spectrum inversion method of conjugate gradient that is easy to realize non-negativity constraint of T2 spectrum is proposed. The method transforms the linear mixed-determined problem of T2 spectrum inversion into the typical optimization problem of searching the minimum of objective function by building up the objective function according to the basic idea of geophysics modeling. The optimization problem above is solved with the conjugate gradient algorithm that has quick convergence rate and quadratic termination. The method has been applied to the inversion of noise free echo train generated from artificial spectrum, artificial echo train with signal-to-noise ratio (SNR)=25 and NMR experimental data of drilling core. The comparison between the inversion results of this paper and artificial spectrum or the result of software imported in NMR laboratory shows that the method can correctly invert T 2 spectrum from artificial NMR relaxation data even though SNR=25 and that inversion T 2 spectrum with good continuity and smoothness from core NMR experimental data accords perfectly with that of laboratory software imported, and moreover,the absolute error between the NMR porosity computed from T 2 spectrum and helium (He) porosity in laboratory is 0.65%. (authors)

  15. Meteor head echoes - observations and models

    Directory of Open Access Journals (Sweden)

    A. Pellinen-Wannberg

    2005-01-01

    Full Text Available Meteor head echoes - instantaneous echoes moving with the velocities of the meteors - have been recorded since 1947. Despite many attempts, this phenomenon did not receive a comprehensive theory for over 4 decades. The High Power and Large Aperture (HPLA features, combined with present signal processing and data storage capabilities of incoherent scatter radars, may give an explanation for the old riddle. The meteoroid passage through the radar beam can be followed with simultaneous spatial-time resolution of about 100m-ms class. The current views of the meteor head echo process will be presented and discussed. These will be related to various EISCAT observations, such as dual-frequency target sizes, altitude distributions and vector velocities.

  16. Characteristics of spondylotic myelopathy on 3D driven-equilibrium fast spin echo and 2D fast spin echo magnetic resonance imaging: a retrospective cross-sectional study.

    Science.gov (United States)

    Abdulhadi, Mike A; Perno, Joseph R; Melhem, Elias R; Nucifora, Paolo G P

    2014-01-01

    In patients with spinal stenosis, magnetic resonance imaging of the cervical spine can be improved by using 3D driven-equilibrium fast spin echo sequences to provide a high-resolution assessment of osseous and ligamentous structures. However, it is not yet clear whether 3D driven-equilibrium fast spin echo sequences adequately evaluate the spinal cord itself. As a result, they are generally supplemented by additional 2D fast spin echo sequences, adding time to the examination and potential discomfort to the patient. Here we investigate the hypothesis that in patients with spinal stenosis and spondylotic myelopathy, 3D driven-equilibrium fast spin echo sequences can characterize cord lesions equally well as 2D fast spin echo sequences. We performed a retrospective analysis of 30 adult patients with spondylotic myelopathy who had been examined with both 3D driven-equilibrium fast spin echo sequences and 2D fast spin echo sequences at the same scanning session. The two sequences were inspected separately for each patient, and visible cord lesions were manually traced. We found no significant differences between 3D driven-equilibrium fast spin echo and 2D fast spin echo sequences in the mean number, mean area, or mean transverse dimensions of spondylotic cord lesions. Nevertheless, the mean contrast-to-noise ratio of cord lesions was decreased on 3D driven-equilibrium fast spin echo sequences compared to 2D fast spin echo sequences. These findings suggest that 3D driven-equilibrium fast spin echo sequences do not need supplemental 2D fast spin echo sequences for the diagnosis of spondylotic myelopathy, but they may be less well suited for quantitative signal measurements in the spinal cord.

  17. ECHO Data Partners Join Forces to Federate Access to Resources

    Science.gov (United States)

    Kendall, J.; Macie, M.

    2003-12-01

    During the past year the NASA's Earth Science Data and Information System (ESDIS) project has been collaborating with various Earth science data and client providers to design and implement the EOS Clearinghouse (ECHO). ECHO is an open, interoperable metadata clearinghouse and order broker system. ECHO functions as a repository of information intended to streamline access to digital data and services provided by NASA's Earth Science Enterprise and the extended Earth science community. In a unique partnership, ECHO data providers are working to extend their services in the digital era, to reflect current trends in scientific and educational communications. The multi-organization, inter-disciplinary content of ECHO provides a valuable new service to a growing number of Earth science applications and interdisciplinary research efforts. As such, ECHO is expected to attract a wide audience. In this poster, we highlight the contributions of current ECHO data partners and provide information for prospective data partners on how the project supports the incorporation of new collections and effective long-term asset management that is directly under the control of the organizations who contribute resources to ECHO.

  18. Ultrafast bold fMRI using single-shot spin-echo echo planar imaging

    Directory of Open Access Journals (Sweden)

    Boujraf Said

    2009-01-01

    Full Text Available The choice of imaging parameters for functional MRI can have an impact on the accuracy of functional localization by affecting the image quality and the degree of blood oxygenation-dependent (BOLD contrast achieved. By improving sampling efficiency, parallel acquisition techniques such as sensitivity encoding (SENSE have been used to shorten readout trains in single-shot (SS echo planar imaging (EPI. This has been applied to susceptibility artifact reduction and improving spatial resolution. SENSE together with single-shot spin-echo (SS-SE imaging may also reduce off-resonance artifacts. The goal of this work was to investigate the BOLD response of a SENSE-adapted SE-EPI on a three Tesla scanner. Whole-brain fMRI studies of seven healthy right hand-dominant volunteers were carried out in a three Tesla scanner. fMRI was performed using an SS-SE EPI sequence with SENSE. The data was processed using statistical parametric mapping. Both, group and individual subject data analyses were performed. Individual average percentage and maximal percentage signal changes attributed to the BOLD effect in M1 were calculated for all the subjects as a function of echo time. Corresponding activation maps and the sizes of the activated clusters were also calculated. Our results show that susceptibility artifacts were reduced with the use of SENSE; and the acquired BOLD images were free of the typical quadrature artifacts of SS-EPI. Such measures are crucial at high field strengths. SS SE-EPI with SENSE offers further benefits in this regard and is more specific for oxygenation changes in the microvasculature bed. Functional brain activity can be investigated with the help of single-shot spin echo EPI using SENSE at high magnetic fields.

  19. Recalling and forgetting dreams: theta and alpha oscillations during sleep predict subsequent dream recall.

    Science.gov (United States)

    Marzano, Cristina; Ferrara, Michele; Mauro, Federica; Moroni, Fabio; Gorgoni, Maurizio; Tempesta, Daniela; Cipolli, Carlo; De Gennaro, Luigi

    2011-05-04

    Under the assumption that dream recall is a peculiar form of declarative memory, we have hypothesized that (1) the encoding of dream contents during sleep should share some electrophysiological mechanisms with the encoding of episodic memories of the awake brain and (2) recalling a dream(s) after awakening from non-rapid eye movement (NREM) and rapid eye movement (REM) sleep should be associated with different brain oscillations. Here, we report that cortical brain oscillations of human sleep are predictive of successful dream recall. In particular, after morning awakening from REM sleep, a higher frontal 5-7 Hz (theta) activity was associated with successful dream recall. This finding mirrors the increase in frontal theta activity during successful encoding of episodic memories in wakefulness. Moreover, in keeping with the different EEG background, a different predictive relationship was found after awakening from stage 2 NREM sleep. Specifically, a lower 8-12 Hz (alpha) oscillatory activity of the right temporal area was associated with a successful dream recall. These findings provide the first evidence of univocal cortical electroencephalographic correlates of dream recall, suggesting that the neurophysiological mechanisms underlying the encoding and recall of episodic memories may remain the same across different states of consciousness.

  20. Understanding the dynamics of correct and error responses in free recall: evidence from externalized free recall.

    Science.gov (United States)

    Unsworth, Nash; Brewer, Gene A; Spillers, Gregory J

    2010-06-01

    The dynamics of correct and error responses in a variant of delayed free recall were examined in the present study. In the externalized free recall paradigm, participants were presented with lists of words and were instructed to subsequently recall not only the words that they could remember from the most recently presented list, but also any other words that came to mind during the recall period. Externalized free recall is useful for elucidating both sampling and postretrieval editing processes, thereby yielding more accurate estimates of the total number of error responses, which are typically sampled and subsequently edited during free recall. The results indicated that the participants generally sampled correct items early in the recall period and then transitioned to sampling more erroneous responses. Furthermore, the participants generally terminated their search after sampling too many errors. An examination of editing processes suggested that the participants were quite good at identifying errors, but this varied systematically on the basis of a number of factors. The results from the present study are framed in terms of generate-edit models of free recall.

  1. Compound cueing in free recall

    Science.gov (United States)

    Lohnas, Lynn J.; Kahana, Michael J.

    2013-01-01

    According to the retrieved context theory of episodic memory, the cue for recall of an item is a weighted sum of recently activated cognitive states, including previously recalled and studied items as well as their associations. We show that this theory predicts there should be compound cueing in free recall. Specifically, the temporal contiguity effect should be greater when the two most recently recalled items were studied in contiguous list positions. A meta-analysis of published free recall experiments demonstrates evidence for compound cueing in both conditional response probabilities and inter-response times. To help rule out a rehearsal-based account of these compound cueing effects, we conducted an experiment with immediate, delayed and continual-distractor free recall conditions. Consistent with retrieved context theory but not with a rehearsal-based account, compound cueing was present in all conditions, and was not significantly influenced by the presence of interitem distractors. PMID:23957364

  2. Compound cuing in free recall.

    Science.gov (United States)

    Lohnas, Lynn J; Kahana, Michael J

    2014-01-01

    According to the retrieved context theory of episodic memory, the cue for recall of an item is a weighted sum of recently activated cognitive states, including previously recalled and studied items as well as their associations. We show that this theory predicts there should be compound cuing in free recall. Specifically, the temporal contiguity effect should be greater when the 2 most recently recalled items were studied in contiguous list positions. A meta-analysis of published free recall experiments demonstrates evidence for compound cuing in both conditional response probabilities and interresponse times. To help rule out a rehearsal-based account of these compound cuing effects, we conducted an experiment with immediate, delayed, and continual-distractor free recall conditions. Consistent with retrieved context theory but not with a rehearsal-based account, compound cuing was present in all conditions, and was not significantly influenced by the presence of interitem distractors.

  3. Practice makes perfect in memory recall

    OpenAIRE

    Romani, Sandro; Katkov, Mikhail; Tsodyks, Misha

    2016-01-01

    A large variability in performance is observed when participants recall briefly presented lists of words. The sources of such variability are not known. Our analysis of a large data set of free recall revealed a small fraction of participants that reached an extremely high performance, including many trials with the recall of complete lists. Moreover, some of them developed a number of consistent input-position-dependent recall strategies, in particular recalling words consecutively (?chainin...

  4. Comparative study of interventricular phase difference and pressure gradient in cases of isolated ventricular septal defect

    Energy Technology Data Exchange (ETDEWEB)

    Elhaddad, SH; Moustafa, H; Ziada, G; Seleem, Z; Elsabban, KH; Mahmoud, F [Nuclear medicine department and pediatric cardiology department Faculty of medicine, Cairo university, Cairo, (Egypt)

    1995-10-01

    One hundred and fifty patients with isolated VSD were evaluated by radionuclide MUGA study and Echo-Doppler. Difference between phase angle of the right and left ventricles as detected by MUGA had been divided into main four groups according to pressure gradient between the two ventricles : group I (with pressure gradient {<=}30 mmHg and phase difference 80.10 degree{+-}34.1), group III (with pressure gradient > 70 mmHg and phase difference -0.5 degree {+-} 8.4). It has been found that there was a significant difference between the 4 groups as regards right - to - left ventricular phase difference (P<0.0001). There was significant delay in emptying of right ventricle in groups with pressure gradient < 50 mmHg. Regression analysis revealed inverse correlation between right -to- left ventricular phase difference with changes in pressure gradient (r= 0.81). Similarly, significant correlation had been found between right -to-left ventricular phase difference in relation Qp/Qs (r=0.85); conclusion: interventricular phase difference can be used to evaluate interventricular pressure gradient in cases of isolated VSD. 4 figs., 2 tabs.

  5. Erroneous and Veridical Recall Are Not Two Sides of the Same Coin: Evidence From Semantic Distraction in Free Recall

    Science.gov (United States)

    2015-01-01

    Two experiments examined the extent to which erroneous recall blocks veridical recall using, as a vehicle for study, the disruptive impact of distractors that are semantically similar to a list of words presented for free recall. Instructing participants to avoid erroneous recall of to-be-ignored spoken distractors attenuated their recall but this did not influence the disruptive effect of those distractors on veridical recall (Experiment 1). Using an externalized output-editing procedure—whereby participants recalled all items that came to mind and identified those that were erroneous—the usual between-sequences semantic similarity effect on erroneous and veridical recall was replicated but the relationship between the rate of erroneous and veridical recall was weak (Experiment 2). The results suggest that forgetting is not due to veridical recall being blocked by similar events. PMID:25938326

  6. Predicting Free Recalls

    Science.gov (United States)

    Laming, Donald

    2006-01-01

    This article reports some calculations on free-recall data from B. Murdock and J. Metcalfe (1978), with vocal rehearsal during the presentation of a list. Given the sequence of vocalizations, with the stimuli inserted in their proper places, it is possible to predict the subsequent sequence of recalls--the predictions taking the form of a…

  7. The Usefulness of Fast-Spin-Echo T2-Weighted MR Imaging in Nutcracker Syndrome: a Case Report

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Heong Leng; Chen, Matt Chiung Yu; Wu, Cgek Siung; Fu, Kuo An; Lin, Cheng Hao [Yuan' s General Hospital, Kaohsiung (China); Weng, Mei Jui; Liang, Huei Lung; Pan, Huay Ben [National Yang-Ming University, Taipei (Korea, Republic of)

    2010-06-15

    Nutcracker syndrome occurs when the left renal vein (LRV) is compressed between the superior mesenteric artery and the aorta, and this syndrome is often characterized by venous hypertension and related pathologies. However, invasive studies such as phlebography and measuring the reno-caval pressure gradient should be performed to identify venous hypertension. Here we present a case of Nutcracker syndrome where the LRV and intra-renal varicosities appeared homogeneously hyperintense on magnetic resonance (MR) fast-spin-echo T2- weighted imaging, which suggested markedly stagnant intravenous blood flow and the presence of venous hypertension. The patient was diagnosed and treated without obtaining the reno-caval pressure gradient. The discomfort of the patient lessened after treatment. Furthermore, on follow-up evaluation, the LRV displayed a signal void, and this was suggestive of a restoration of the normal LRV flow and a decrease in LRV pressure.

  8. Conversational Memory Employing Cued and Free Recall.

    Science.gov (United States)

    Benoit, Pamela J.; Benoit, William L.

    1988-01-01

    Tests two hypotheses: (1) that cued recall elicits significantly more conversational information than free recall; and (2) that conversational interactants recall more of their partner's utterances than their own. Finds cued recall produced significantly higher amounts of remembering than free recall. (MS)

  9. Utility of dual echo T2-weighted turbo spin echo MR imaging for differentiation of solid, malignant hepatic lesions from nonsolid, benign hepatic lesions

    International Nuclear Information System (INIS)

    Yang, Dal Mo; Yoon, Myung Hwan; Kim, Hak Soo; Lee, Eun Joo; Kim, Jong Ho; Kim, Hyung Sik; Chung, Jin Woo

    1999-01-01

    To evaluate the additive value of multiphasic contrast-enhanced dynamic MR imaging as a supplement to dual-echo T2-weighted TSE MR imaging for the differentiation of solid, malignant hepatic lesions from nonsolid, benign hepatic lesions. Two radiologists retrospectively reviewed dual-echo T2-weighted TSE MR images and gadolinium-enhanced MR images in 51 patients with hepatic lesions (28 malignant, 69 benign). For the differentiation of malignant from benign lesions, as seen on dual-echo T2-weighted TSE MR images, we evaluated sensitivity, specificity, and accuracy, and compared with the results with those for dual echo T2-weighted MR images plus multiphasic contrast-enhanced dynamic MR images. In addition, Az values for dual echo T2-weighted MR images were compared with those for dual echo T2-weighted MR images plus multiphasic contrast-enhanced dynamic MR images. For the differentiation of malignant from benign hepatic lesions, as seen on dual-echo T2-weighted TSE images, sensitivity, specificity, and accuracy were 80.0%, 97.5%, and 93.9%, respectively, for lesions less than 3cm in diameter, and 92.3%, 95.0%, and 93.5%, respectively, for those that were 3cm or larger. The results for dual-echo T2-weighted MR imaging plus multiphasic contrast-enhanced dynamic MR imaging were 86.7%, 100.0%, and 97.3%, respectively, for lesions less than 3cm, and 92.3%, 100.0%, and 95.7%, respectively for those that were 3cm or larger. There were no significant differences in sensitivity, specificity, or accuracy between the results obtained using dual-echo T2-weighted MR imaging and those obtained with dual-echo T2-weighted MR imaging plus multiphasic contrast-enhanced dynamic MR imaging. Nor were these statistically significant differences in Az values between the two groups. For the differentiation of solid, malignant hepatic lesions from nonsolid, benign hepatic lesions, there is no difference in accuracy between dual-echo T2-weighted TSE MR imaging and the additional use of

  10. Serial position curves in free recall.

    Science.gov (United States)

    Laming, Donald

    2010-01-01

    The scenario for free recall set out in Laming (2009) is developed to provide models for the serial position curves from 5 selected sets of data, for final free recall, and for multitrial free recall. The 5 sets of data reflect the effects of rate of presentation, length of list, delay of recall, and suppression of rehearsal. Each model accommodates the serial position curve for first recalls (where those data are available) as well as that for total recalls. Both curves are fit with the same parameter values, as also (with 1 exception) are all of the conditions compared within each experiment. The distributions of numbers of recalls are also examined and shown to have variances increased above what would be expected if successive recalls were independent. This is taken to signify that, in those experiments in which rehearsals were not recorded, the retrieval of words for possible recall follows the same pattern that is observed following overt rehearsal, namely, that retrieval consists of runs of consecutive elements from memory. Finally, 2 sets of data are examined that the present approach cannot accommodate. It is argued that the problem with these data derives from an interaction between the patterns of (covert) rehearsal and the parameters of list presentation.

  11. Age and gender specific normal values of left ventricular mass, volume and function for gradient echo magnetic resonance imaging: a cross sectional study

    International Nuclear Information System (INIS)

    Cain, Peter A; Ahl, Ragnhild; Hedstrom, Erik; Ugander, Martin; Allansdotter-Johnsson, Ase; Friberg, Peter; Arheden, Hakan

    2009-01-01

    Knowledge about age-specific normal values for left ventricular mass (LVM), end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV) and ejection fraction (EF) by cardiac magnetic resonance imaging (CMR) is of importance to differentiate between health and disease and to assess the severity of disease. The aims of the study were to determine age and gender specific normal reference values and to explore the normal physiological variation of these parameters from adolescence to late adulthood, in a cross sectional study. Gradient echo CMR was performed at 1.5 T in 96 healthy volunteers (11–81 years, 50 male). Gender-specific analysis of parameters was undertaken in both absolute values and adjusted for body surface area (BSA). Age and gender specific normal ranges for LV volumes, mass and function are presented from the second through the eighth decade of life. LVM, ESV and EDV rose during adolescence and declined in adulthood. SV and EF decreased with age. Compared to adult females, adult males had higher BSA-adjusted values of EDV (p = 0.006) and ESV (p < 0.001), similar SV (p = 0.51) and lower EF (p = 0.014). No gender differences were seen in the youngest, 11–15 year, age range. LV volumes, mass and function vary over a broad age range in healthy individuals. LV volumes and mass both rise in adolescence and decline with age. EF showed a rapid decline in adolescence compared to changes throughout adulthood. These findings demonstrate the need for age and gender specific normal ranges for clinical use

  12. T2*-based MR imaging (gradient echo or susceptibility-weighted imaging) in midline and off-midline intracranial germ cell tumors. A pilot study

    International Nuclear Information System (INIS)

    Morana, Giovanni; Tortora, Domenico; Severino, Mariasavina; Rossi, Andrea; Alves, Cesar Augusto; Finlay, Jonathan L.; Nozza, Paolo; Ravegnani, Marcello; Pavanello, Marco; Milanaccio, Claudia; Garre, Maria Luisa; Maghnie, Mohamad

    2018-01-01

    The role of T2*-based MR imaging in intracranial germ cell tumors (GCTs) has not been fully elucidated. The aim of this study was to evaluate the susceptibility-weighted imaging (SWI) or T2* gradient echo (GRE) features of germinomas and non-germinomatous germ cell tumors (NGGCTs) in midline and off-midline locations. We retrospectively evaluated all consecutive pediatric patients referred to our institution between 2005 and 2016, for newly diagnosed, treatment-naive intracranial GCT, who underwent MRI, including T2*-based MR imaging (T2* GRE sequences or SWI). Standard pre- and post-contrast T1- and T2-weighted imaging characteristics along with T2*-based MR imaging features of all lesions were evaluated. Diagnosis was performed in accordance with the SIOP CNS GCT protocol criteria. Twenty-four subjects met the inclusion criteria (17 males and 7 females). There were 17 patients with germinomas, including 5 basal ganglia primaries, and 7 patients with secreting NGGCT. All off-midline germinomas presented with SWI or GRE hypointensity; among midline GCT, all NGGCTs showed SWI or GRE hypointensity whereas all but one pure germinoma were isointense or hyperintense to normal parenchyma. A significant difference emerged on T2*-based MR imaging among midline germinomas, NGGCTs, and off-midline germinomas (p < 0.001). Assessment of the SWI or GRE characteristics of intracranial GCT may potentially assist in differentiating pure germinomas from NGGCT and in the characterization of basal ganglia involvement. T2*-based MR imaging is recommended in case of suspected intracranial GCT. (orig.)

  13. T2*-based MR imaging (gradient echo or susceptibility-weighted imaging) in midline and off-midline intracranial germ cell tumors. A pilot study

    Energy Technology Data Exchange (ETDEWEB)

    Morana, Giovanni; Tortora, Domenico; Severino, Mariasavina; Rossi, Andrea [Istituto Giannina Gaslini, Neuroradiology Unit, Genoa (Italy); Alves, Cesar Augusto [Hospital Das Clinicas, Radiology Department, Sao Paulo (Brazil); Finlay, Jonathan L. [Nationwide Children' s Hospital and The Ohio State University, Division of Hematology, Oncology and BMT, Columbus, OH (United States); Nozza, Paolo [Istituto Giannina Gaslini, Pathology Unit, Genoa (Italy); Ravegnani, Marcello; Pavanello, Marco [Istituto Giannina Gaslini, Neurosurgery Unit, Genoa (Italy); Milanaccio, Claudia; Garre, Maria Luisa [Istituto Giannina Gaslini, Neuro-oncology Unit, Genoa (Italy); Maghnie, Mohamad [Istituto Giannina Gaslini, University of Genova, Pediatric Endocrine Unit, Genoa (Italy)

    2018-01-15

    The role of T2*-based MR imaging in intracranial germ cell tumors (GCTs) has not been fully elucidated. The aim of this study was to evaluate the susceptibility-weighted imaging (SWI) or T2* gradient echo (GRE) features of germinomas and non-germinomatous germ cell tumors (NGGCTs) in midline and off-midline locations. We retrospectively evaluated all consecutive pediatric patients referred to our institution between 2005 and 2016, for newly diagnosed, treatment-naive intracranial GCT, who underwent MRI, including T2*-based MR imaging (T2* GRE sequences or SWI). Standard pre- and post-contrast T1- and T2-weighted imaging characteristics along with T2*-based MR imaging features of all lesions were evaluated. Diagnosis was performed in accordance with the SIOP CNS GCT protocol criteria. Twenty-four subjects met the inclusion criteria (17 males and 7 females). There were 17 patients with germinomas, including 5 basal ganglia primaries, and 7 patients with secreting NGGCT. All off-midline germinomas presented with SWI or GRE hypointensity; among midline GCT, all NGGCTs showed SWI or GRE hypointensity whereas all but one pure germinoma were isointense or hyperintense to normal parenchyma. A significant difference emerged on T2*-based MR imaging among midline germinomas, NGGCTs, and off-midline germinomas (p < 0.001). Assessment of the SWI or GRE characteristics of intracranial GCT may potentially assist in differentiating pure germinomas from NGGCT and in the characterization of basal ganglia involvement. T2*-based MR imaging is recommended in case of suspected intracranial GCT. (orig.)

  14. Age differences in recall and predicting recall of action events and words.

    Science.gov (United States)

    McDonald-Miszczak, L; Hubley, A M; Hultsch, D F

    1996-03-01

    Age differences in recall and prediction of recall were examined with different memory tasks. We asked 36 younger (19-28 yrs) and 36 older (60-81 yrs) women to provide both global and item-by-item predictions of their recall, and then to recall either (a) Subject Performance Tasks (SPTs), (b) verb-noun word-pairs memorized in list-like fashion (Word-Pairs), or (c) nonsense verb-noun word-pairs (Nonsense-Pairs) over three experimental trials. Based on previous research, we hypothesized that these tasks would vary in relative difficulty and flexibility of encoding. The results indicated that (a) age differences in global predictions (task specific self-efficacy) and recall performance across trials were minimized with SPT as compared with verbal materials, (b) global predictions were higher and more accurate for SPT as compared to verbal materials, and (c) item-by-item predictions were most accurate for materials encoded with the most flexibility (Nonsense Pairs). The results suggest that SPTs may provide some level of environmental support to reduce age differences in performance and task-specific self-efficacy, but that memory monitoring may depend on specific characteristics of the stimuli (i.e., flexibility of encoding) rather than their verbal or nonverbal nature.

  15. Compound Cuing in Free Recall

    Science.gov (United States)

    Lohnas, Lynn J.; Kahana, Michael J.

    2014-01-01

    According to the retrieved context theory of episodic memory, the cue for recall of an item is a weighted sum of recently activated cognitive states, including previously recalled and studied items as well as their associations. We show that this theory predicts there should be compound cuing in free recall. Specifically, the temporal contiguity…

  16. Revival of silenced echo and quantum memory for light

    Energy Technology Data Exchange (ETDEWEB)

    Damon, V; Bonarota, M; Louchet-Chauvet, A; Chaneliere, T; Le Gouet, J-L, E-mail: jean-louis.legouet@lac.u-psud.fr [Laboratoire Aime Cotton, CNRS-UPR 3321, Univ. Paris-Sud, Bat. 505, 91405 Orsay cedex (France)

    2011-09-15

    We propose an original quantum memory protocol. It belongs to the class of rephasing processes and is closely related to two-pulse photon echo. It is known that the strong population inversion produced by the rephasing pulse prevents the plain two-pulse photon echo from serving as a quantum memory scheme. Indeed, gain and spontaneous emission generate prohibitive noise. A second {pi}-pulse can be used to simultaneously reverse the atomic phase and bring the atoms back into the ground state. Then a secondary echo is radiated from a non-inverted medium, avoiding contamination by gain and spontaneous emission noise. However, one must kill the primary echo, in order to preserve all the information for the secondary signal. In the present work, spatial phase mismatching is used to silence the standard two-pulse echo. An experimental demonstration is presented.

  17. Occupational exposure measurements of static and pulsed gradient magnetic fields in the vicinity of MRI scanners

    Energy Technology Data Exchange (ETDEWEB)

    Kaennaelae, Sami; Toivo, Tim; Jokela, Kari [STUK-Radiation and Nuclear Safety Authority, PO Box 14, 00881 Helsinki (Finland); Alanko, Tommi [Finnish Institute of Occupational Health, New Technologies and Risks, Topeliuksenkatu 41a A, 00250 Helsinki (Finland)], E-mail: sami.kannala@stuk.fi

    2009-04-07

    Recent advances in magnetic resonance imaging (MRI) have increased occupational exposure to magnetic fields. In this study, we examined the assessment of occupational exposure to gradient magnetic fields and time-varying magnetic fields generated by motion in non-homogeneous static magnetic fields of MRI scanners. These magnetic field components can be measured simultaneously with an induction coil setup that detects the time rate of change of magnetic flux density (dB/dt). The setup developed was used to measure the field components around two MRI units (1 T open and 3 T conventional). The measured values can be compared with dB/dt reference levels derived from magnetic flux density reference levels given by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The measured motion-induced dB/dt values were above the dB/dt reference levels for both MRI units. The measured values for the gradient fields (echo planar imaging (EPI) and fast field echo (FFE) sequences) also exceeded the dB/dt reference levels in positions where the medical staff may have access during interventional procedures. The highest motion-induced dB/dt values were 0.7 T s{sup -1} for the 1 T scanner and 3 T s{sup -1} for the 3 T scanner when only the static field was present. Even higher values (6.5 T s{sup -1}) were measured for simultaneous exposure to motion-induced and gradient fields in the vicinity of the 3 T scanner.

  18. Feasibility study of 2D thick-slice MR digital subtraction angiography

    International Nuclear Information System (INIS)

    Ishimori, Yoshiyuki; Takeuchi, Miho; Higashimura, Kyouji; Komuro, Hiroyuki

    2000-01-01

    Conditions required to perform contrast MR digital subtraction angiography using a two-dimensional thick-slice high-speed gradient echo were investigated. The conditions in the phantom experiment included: slice profile, flip angle, imaging matrix, fat suppression, duration of IR pulse and frequency selectivity, flip angle of IR pulse and inversion time. Based on the results of the experiment, 2D thick-slice MRDSA was performed in volunteers. Under TR/TE=5.3-9/1.3-1.8 ms conditions, the requirements were a slice thick enough to include the target region, a flip angle of 10 degrees, and a phase matrix of 96 or more. Fat suppression was required for adipose-tissue-rich regions, such as the abdomen. The optimal conditions for applying the IR preparation pulse of the IR prepped fast gradient recalled echo as spectrally selective inversion recovery appeared to be: duration of IR pulse =20 ms, flip angle =100 degrees, and inversion time =40 ms. The authors concluded that it was feasible to perform 2D thick-slice MRDSA with time resolution within 1 second. (K.H.)

  19. Fast MR imaging for evaluating the pancreaticobiliary system

    International Nuclear Information System (INIS)

    Takehara, Yasuo

    1999-01-01

    Due to physiological movement clinical MR applications for abdominal organs got off to a very slow start compared to MR imaging of other organs. However, with recent cutting-edge hardware technologies such as high performance gradient systems and phased-array capability, as well as software innovations including short TR fast spoiled gradient recalled acquisition in the steady state (GRASS), snapshot imaging such as single shot fast spin echo sequence (SSFSE) and echo planar imaging (EPI), scan times have been further reduced to make breath-hold imaging clinically viable and to enable semi-fluoroscopic, kinematic imaging recognition. The elimination of physiological motion has contributed to the significant improvement in image quality, or more specifically, the physiological motion that had long been problematic has been turned into a source of physiological information about pancreaticobiliary pathologies. In this article, the author reviewed the current status of fast MR technologies for examining pancreaticobiliary pathologies, stressing the functional and physiological aspects of the corresponding anatomy. The technologies included secretin MRCP, which became a powerful tool when combined with kinematic imaging

  20. Practice makes perfect in memory recall.

    Science.gov (United States)

    Romani, Sandro; Katkov, Mikhail; Tsodyks, Misha

    2016-04-01

    A large variability in performance is observed when participants recall briefly presented lists of words. The sources of such variability are not known. Our analysis of a large data set of free recall revealed a small fraction of participants that reached an extremely high performance, including many trials with the recall of complete lists. Moreover, some of them developed a number of consistent input-position-dependent recall strategies, in particular recalling words consecutively ("chaining") or in groups of consecutively presented words ("chunking"). The time course of acquisition and particular choice of positional grouping were variable among participants. Our results show that acquiring positional strategies plays a crucial role in improvement of recall performance. © 2016 Romani et al.; Published by Cold Spring Harbor Laboratory Press.

  1. Multi-site Study of Diffusion Metric Variability: Characterizing the Effects of Site, Vendor, Field Strength, and Echo Time using the Histogram Distance

    Science.gov (United States)

    Helmer, K. G.; Chou, M-C.; Preciado, R. I.; Gimi, B.; Rollins, N. K.; Song, A.; Turner, J.; Mori, S.

    2016-01-01

    MRI-based multi-site trials now routinely include some form of diffusion-weighted imaging (DWI) in their protocol. These studies can include data originating from scanners built by different vendors, each with their own set of unique protocol restrictions, including restrictions on the number of available gradient directions, whether an externally-generated list of gradient directions can be used, and restrictions on the echo time (TE). One challenge of multi-site studies is to create a common imaging protocol that will result in a reliable and accurate set of diffusion metrics. The present study describes the effect of site, scanner vendor, field strength, and TE on two common metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA). We have shown in earlier work that ROI metrics and the mean of MD and FA histograms are not sufficiently sensitive for use in site characterization. Here we use the distance between whole brain histograms of FA and MD to investigate within- and between-site effects. We concluded that the variability of DTI metrics due to site, vendor, field strength, and echo time could influence the results in multi-center trials and that histogram distance is sensitive metrics for each of these variables. PMID:27350723

  2. Multi-site Study of Diffusion Metric Variability: Characterizing the Effects of Site, Vendor, Field Strength, and Echo Time using the Histogram Distance.

    Science.gov (United States)

    Helmer, K G; Chou, M-C; Preciado, R I; Gimi, B; Rollins, N K; Song, A; Turner, J; Mori, S

    2016-02-27

    MRI-based multi-site trials now routinely include some form of diffusion-weighted imaging (DWI) in their protocol. These studies can include data originating from scanners built by different vendors, each with their own set of unique protocol restrictions, including restrictions on the number of available gradient directions, whether an externally-generated list of gradient directions can be used, and restrictions on the echo time (TE). One challenge of multi-site studies is to create a common imaging protocol that will result in a reliable and accurate set of diffusion metrics. The present study describes the effect of site, scanner vendor, field strength, and TE on two common metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA). We have shown in earlier work that ROI metrics and the mean of MD and FA histograms are not sufficiently sensitive for use in site characterization. Here we use the distance between whole brain histograms of FA and MD to investigate within- and between-site effects. We concluded that the variability of DTI metrics due to site, vendor, field strength, and echo time could influence the results in multi-center trials and that histogram distance is sensitive metrics for each of these variables.

  3. Mobile Bay.pdf | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  4. Report Environmental Violations | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  5. DWDashboard_Year.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  6. dashboard_3.PNG | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  7. ExampleDFR.PNG | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  8. monperload_1.PNG | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  9. monperload_2.PNG | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  10. Dischargers_Example.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  11. dashboard_1.PNG | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  12. dashboard_2.PNG | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  13. monperload_3.PNG | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  14. Denuncie violaciones ambientales | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  15. Custom Search Help | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  16. Watershed Statistics Help | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  17. Water Pollution Search | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  18. Erroneous and Veridical Recall Are Not Two Sides of the Same Coin: Evidence From Semantic Distraction in Free Recall

    OpenAIRE

    Marsh, John E.; Hughes, Robert W.; S?rqvist, Patrik; Beaman, C. Philip; Jones, Dylan M.

    2015-01-01

    Two experiments examined the extent to which erroneous recall blocks veridical recall using, as a vehicle for study, the disruptive impact of distractors that are semantically similar to a list of words presented for free recall. Instructing participants to avoid erroneous recall of to-be-ignored spoken distractors attenuated their recall but this did not influence the disruptive effect of those distractors on veridical recall (Experiment 1). Using an externalized output-editing procedure?whe...

  19. Erroneous and Veridical Recall Are Not Two Sides of the Same Coin: Evidence from Semantic Distraction in Free Recall

    Science.gov (United States)

    Marsh, John E.; Hughes, Robert W.; Sörqvist, Patrik; Beaman, C. Philip; Jones, Dylan M.

    2015-01-01

    Two experiments examined the extent to which erroneous recall blocks veridical recall using, as a vehicle for study, the disruptive impact of distractors that are semantically similar to a list of words presented for free recall. Instructing participants to avoid erroneous recall of to-be-ignored spoken distractors attenuated their recall but this…

  20. Duel frequency echo data acquisition system for sea-floor classification

    Digital Repository Service at National Institute of Oceanography (India)

    Navelkar, G.S.; Desai, R.G.P.; Chakraborty, B.

    An echo data acquisition system is designed to digitize echo signal from a single beam shipboard echo-sounder for use in sea-floor classification studies using a 12 bit analog to digital (A/D) card with a maximum sampling frequency of 1 MHz. Both 33...

  1. Variations in the occurrence of SuperDARN F region echoes

    Directory of Open Access Journals (Sweden)

    M. Ghezelbash

    2014-02-01

    Full Text Available The occurrence of F region ionospheric echoes observed by a number of SuperDARN HF radars is analyzed statistically in order to infer solar cycle, seasonal, and diurnal trends. The major focus is on Saskatoon radar data for 1994–2012. The distribution of the echo occurrence rate is presented in terms of month of observation and magnetic local time. Clear repetitive patterns are identified during periods of solar maximum and solar minimum. For years near solar maximum, echoes are most frequent near midnight during winter. For years near solar minimum, echoes occur more frequently near noon during winter, near dusk and dawn during equinoxes and near midnight during summer. Similar features are identified for the Hankasalmi and Prince George radars in the northern hemisphere and the Bruny Island TIGER radar in the southern hemisphere. Echo occurrence for the entire SuperDARN network demonstrates patterns similar to patterns in the echo occurrence for the Saskatoon radar and for other radars considered individually. In terms of the solar cycle, the occurrence rate of nightside echoes is shown to increase by a factor of at least 3 toward solar maximum while occurrence of the near-noon echoes does not significantly change with the exception of a clear depression during the declining phase of the solar cycle.

  2. Fast spin echo MRI techniques. Contrast characteristics and clinical potential. Techniques d'IRM en fast spin echo. Caracteristiques de contraste et potentiels cliniques

    Energy Technology Data Exchange (ETDEWEB)

    Melki, P.; Mulkern, R.V.; Dacher, J.N.; Helenon, O.; Higuchi, N. (Harvard Medical School, Boston, MA (United States)); Oshio, K.; Jolesz, F. (Keio Univ., Tokyo (Japan)); Pourcelot, L. (Hopital Bretonneau, 37 - Tours (France)); Einstein, S. (General Electric Medical System, Milwaukee, WI (United States))

    1993-03-01

    Based on partial RF echo planar principles, Fast Spin Echo techniques (FSE) were implemented on high field systems. These methods produce image quality and contrast which resemble to conventional spin echo (SE) techniques. By reducing acquisition times by factors between 1.4 and 16 over SE methods, FSE allows for several imaging options usually prohibitive with conventional spin echo (SE) sequences. These include fast scans (especially breathold acquisitions); improved T2 contrast with longer TR intervals; increased spatial resolution with the use of larger image matrices and/or smaller fields of view; and 3D volume imaging with a 3D multislab FSE technique. Contrast features of FSE techniques are directly comparable to those of multiple echo SE sequences using the same echo spacing than FSE methods. However, essential contrast differences existing between the FSE sequences and their routine asymmetric dual SE counterpart can be identified. Decreased magnetic susceptibility effects and increased fat signal present within T2 weighted images compared to conventional dual SE images are due to the use of shorter echo spacings employed in FSE sequences. Off-resonance irradiation inherent to the use of a large number of radio frequency pulses in shown to results in dramatic magnetization contrast transfer effects in FSE images acquired in multislice mode.

  3. Experienced Sensory Modalities in Dream Recall

    OpenAIRE

    岡田, 斉

    2000-01-01

    The purpose of the present study is to survey the frequency of visual, auditory, kinaesthetic, cutaneous, organic, gustatory, and olfactory experience in dream recall. A total of 1267 undergraduate students completed a dream recall frequency questionnaire, which contained a question about dream recall frequency and about recall frequency of seven sensory modalities. Results showed that seven sensory modalities were divided into two groups; normally perceived sensory modalities in dreaming, wh...

  4. Feasibility of Imaging Tissue Electrical Conductivity by Switching Field Gradients with MRI.

    Science.gov (United States)

    Gibbs, Eric; Liu, Chunlei

    2015-12-01

    Tissue conductivity is a biophysical marker of tissue structure and physiology. Present methods of measuring tissue conductivity are limited. Electrical impedance tomography, and magnetic resonance electrical impedance tomography rely on passing external current through the object being imaged, which prevents its use in most human imaging. Recently, the RF field used for MR excitation has been used to non-invasively measure tissue conductivity. This technique is promising, but conductivity at higher frequencies is less sensitive to tissue structure. Measuring tissue conductivity non-invasively at low frequencies remains elusive. It has been proposed that eddy currents generated during the rise and decay of gradient pulses could act as a current source to map low-frequency conductivity. This work centers on a gradient echo pulse sequence that uses large gradients prior to excitation to create eddy currents. The electric and magnetic fields during a gradient pulse are simulated by a finite-difference time-domain simulation. The sequence is also tested with a phantom and an animal MRI scanner equipped with gradients of high gradient strengths and slew rate. The simulation demonstrates that eddy currents in materials with conductivity similar to biological tissue decay with a half-life on the order of nanoseconds and any eddy currents generated prior to excitation decay completely before influencing the RF signal. Gradient-induced eddy currents can influence phase accumulation after excitation but the effect is too small to image. The animal scanner images show no measurable phase accumulation. Measuring low-frequency conductivity by gradient-induced eddy currents is presently unfeasible.

  5. Robust water fat separated dual-echo MRI by phase-sensitive reconstruction.

    Science.gov (United States)

    Romu, Thobias; Dahlström, Nils; Leinhard, Olof Dahlqvist; Borga, Magnus

    2017-09-01

    The purpose of this work was to develop and evaluate a robust water-fat separation method for T1-weighted symmetric two-point Dixon data. A method for water-fat separation by phase unwrapping of the opposite-phase images by phase-sensitive reconstruction (PSR) is introduced. PSR consists of three steps; (1), identification of clusters of tissue voxels; (2), unwrapping of the phase in each cluster by solving Poisson's equation; and (3), finding the correct sign of each unwrapped opposite-phase cluster, so that the water-fat images are assigned the correct identities. Robustness was evaluated by counting the number of water-fat swap artifacts in a total of 733 image volumes. The method was also compared to commercial software. In the water-fat separated image volumes, the PSR method failed to unwrap the phase of one cluster and misclassified 10. One swap was observed in areas affected by motion and was constricted to the affected area. Twenty swaps were observed surrounding susceptibility artifacts, none of which spread outside the artifact affected regions. The PSR method had fewer swaps when compared to commercial software. The PSR method can robustly produce water-fat separated whole-body images based on symmetric two-echo spoiled gradient echo images, under both ideal conditions and in the presence of common artifacts. Magn Reson Med 78:1208-1216, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  6. Relaxation parameter estimation and comparison of NLS and LLS methods for DCE MRI in the cervix

    DEFF Research Database (Denmark)

    Mariager, Christian; Kallehauge, Jesper; Tanderup, Kari

    Dynamic Contrast Enhanced (DCE) MRI is a promising tool for tumor treatment planning. However, prior knowledge of the T1 value within each tumor voxel is needed to utilize this technique. Therefore, a T1 relaxation measurement is performed before the DCE experiment to establish a baseline, before...... any injection of contrast agent. This T1 relaxation measurement is often performed using a variable flip angle spoiled gradient recalled echo (SPGR) sequence. T1 can then be estimated using either a linear least squares (LLS) or a non-linear least squares (NLS) fitting algorithm....

  7. Reexposure Breeds Recall: Effects of Experience on 9-Month-Olds' Ordered Recall.

    Science.gov (United States)

    Bauer, Patricia J.; Wiebe, Sandra A.; Waters, Jennie M.; Bangston, Stephanie K.

    2001-01-01

    Two experiments using deferred imitation tested whether multiple experiences were necessary, or merely facilitative, of 9-month-olds' long-term recall. Found that infants did not demonstrate recall of a multi-step sequence experienced one, two, or three times a month earlier. However, when re-exposed to the experience 1 week after the initial…

  8. Ultrasound pulse-echo measurements on rough surfaces with linear array transducers

    DEFF Research Database (Denmark)

    Sjøj, Sidsel M. N.; Blanco, Esther N.; Wilhjelm, Jens E.

    2012-01-01

    The echo from planar surfaces with rms roughness, Rq, in the range from 0-155 μm was measured with a clinical linear array transducer at different angles of incidence at 6 MHz and 12 MHz. The echo-pulse from the surfaces was isolated with an equal sized window and the power of the echo-pulse was ......The echo from planar surfaces with rms roughness, Rq, in the range from 0-155 μm was measured with a clinical linear array transducer at different angles of incidence at 6 MHz and 12 MHz. The echo-pulse from the surfaces was isolated with an equal sized window and the power of the echo......-pulse was calculated. The power of the echo from the smooth surface (Rq = 0) is highly angle-dependent due to a high degree of specular reflection. Within the angular range considered here, -10° to 10°, the variation spans a range of 18 dB at both 6 MHz and 12 MHz. When roughness increases, the angle......-dependence decreases, as the echo process gradually changes from pure reflection to being predominantly governed by backscattering. The power of the echoes from the two roughest surfaces (Rq = 115 μm and 155 μm) are largely independent of angle at both 6 MHz and 12 MHz with a variation of 2 dB in the angular range...

  9. Recalling taboo and nontaboo words.

    Science.gov (United States)

    Jay, Timothy; Caldwell-Harris, Catherine; King, Krista

    2008-01-01

    People remember emotional and taboo words better than neutral words. It is well known that words that are processed at a deep (i.e., semantic) level are recalled better than words processed at a shallow (i.e., purely visual) level. To determine how depth of processing influences recall of emotional and taboo words, a levels of processing paradigm was used. Whether this effect holds for emotional and taboo words has not been previously investigated. Two experiments demonstrated that taboo and emotional words benefit less from deep processing than do neutral words. This is consistent with the proposal that memories for taboo and emotional words are a function of the arousal level they evoke, even under shallow encoding conditions. Recall was higher for taboo words, even when taboo words were cued to be recalled after neutral and emotional words. The superiority of taboo word recall is consistent with cognitive neuroscience and brain imaging research.

  10. The architecture of dynamic reservoir in the echo state network

    Science.gov (United States)

    Cui, Hongyan; Liu, Xiang; Li, Lixiang

    2012-09-01

    Echo state network (ESN) has recently attracted increasing interests because of its superior capability in modeling nonlinear dynamic systems. In the conventional echo state network model, its dynamic reservoir (DR) has a random and sparse topology, which is far from the real biological neural networks from both structural and functional perspectives. We hereby propose three novel types of echo state networks with new dynamic reservoir topologies based on complex network theory, i.e., with a small-world topology, a scale-free topology, and a mixture of small-world and scale-free topologies, respectively. We then analyze the relationship between the dynamic reservoir structure and its prediction capability. We utilize two commonly used time series to evaluate the prediction performance of the three proposed echo state networks and compare them to the conventional model. We also use independent and identically distributed time series to analyze the short-term memory and prediction precision of these echo state networks. Furthermore, we study the ratio of scale-free topology and the small-world topology in the mixed-topology network, and examine its influence on the performance of the echo state networks. Our simulation results show that the proposed echo state network models have better prediction capabilities, a wider spectral radius, but retain almost the same short-term memory capacity as compared to the conventional echo state network model. We also find that the smaller the ratio of the scale-free topology over the small-world topology, the better the memory capacities.

  11. Electric Dipole Echoes in Rydberg Atoms

    International Nuclear Information System (INIS)

    Yoshida, S.; Reinhold, C. O.; Burgdoerfer, J.; Zhao, W.; Mestayer, J. J.; Lancaster, J. C.; Dunning, F. B.

    2007-01-01

    We report the first observation of echoes in the electric dipole moment of an ensemble of Rydberg atoms precessing in an external electric field F. Rapid reversal of the field direction is shown to play a role similar to that of a π pulse in NMR in rephasing a dephased ensemble of electric dipoles resulting in the buildup of an echo. The mechanisms responsible for this are discussed with the aid of classical trajectory Monte Carlo simulations

  12. Examining the Relationship between Free Recall and Immediate Serial Recall: The Effect of Concurrent Task Performance

    Science.gov (United States)

    Bhatarah, Parveen; Ward, Geoff; Tan, Lydia

    2006-01-01

    In 3 experiments, participants saw lists of 16 words for free recall with or without a 6-digit immediate serial recall (ISR) task after each word. Free recall was performed under standard visual silent and spoken-aloud conditions (Experiment 1), overt rehearsal conditions (Experiment 2), and fixed rehearsal conditions (Experiment 3). The authors…

  13. No counterpart of visual perceptual echoes in the auditory system.

    Directory of Open Access Journals (Sweden)

    Barkın İlhan

    Full Text Available It has been previously demonstrated by our group that a visual stimulus made of dynamically changing luminance evokes an echo or reverberation at ~10 Hz, lasting up to a second. In this study we aimed to reveal whether similar echoes also exist in the auditory modality. A dynamically changing auditory stimulus equivalent to the visual stimulus was designed and employed in two separate series of experiments, and the presence of reverberations was analyzed based on reverse correlations between stimulus sequences and EEG epochs. The first experiment directly compared visual and auditory stimuli: while previous findings of ~10 Hz visual echoes were verified, no similar echo was found in the auditory modality regardless of frequency. In the second experiment, we tested if auditory sequences would influence the visual echoes when they were congruent or incongruent with the visual sequences. However, the results in that case similarly did not reveal any auditory echoes, nor any change in the characteristics of visual echoes as a function of audio-visual congruence. The negative findings from these experiments suggest that brain oscillations do not equivalently affect early sensory processes in the visual and auditory modalities, and that alpha (8-13 Hz oscillations play a special role in vision.

  14. Fast spin echo MRI techniques. Contrast characteristics and clinical potential

    International Nuclear Information System (INIS)

    Melki, P.; Mulkern, R.V.; Dacher, J.N.; Helenon, O.; Higuchi, N.; Oshio, K.; Jolesz, F.; Pourcelot, L.; Einstein, S.

    1993-01-01

    Based on partial RF echo planar principles, Fast Spin Echo techniques (FSE) were implemented on high field systems. These methods produce image quality and contrast which resemble to conventional spin echo (SE) techniques. By reducing acquisition times by factors between 1.4 and 16 over SE methods, FSE allows for several imaging options usually prohibitive with conventional spin echo (SE) sequences. These include fast scans (especially breathold acquisitions); improved T2 contrast with longer TR intervals; increased spatial resolution with the use of larger image matrices and/or smaller fields of view; and 3D volume imaging with a 3D multislab FSE technique. Contrast features of FSE techniques are directly comparable to those of multiple echo SE sequences using the same echo spacing than FSE methods. However, essential contrast differences existing between the FSE sequences and their routine asymmetric dual SE counterpart can be identified. Decreased magnetic susceptibility effects and increased fat signal present within T2 weighted images compared to conventional dual SE images are due to the use of shorter echo spacings employed in FSE sequences. Off-resonance irradiation inherent to the use of a large number of radio frequency pulses in shown to results in dramatic magnetization contrast transfer effects in FSE images acquired in multislice mode

  15. Echo project

    DEFF Research Database (Denmark)

    Gfader, Verina; Carson, Rebecca; Kraus, Chris

    2016-01-01

    team to both present the printed matter in the format of running a book stall, and stage a discursive event at the Classroom. Echo reverberates some of the encounters and debates there, with new commissioned chapters propelling a ongoing correspondence across urban environs: An essay on the General...... mothers and demonology (Kathy Acker’s property deals in the UK), and more; and future materials formalized as poster texts . . ....

  16. Subjective Organization Calculator for Free Recall

    Directory of Open Access Journals (Sweden)

    Olesya Senkova

    2015-11-01

    Full Text Available The free recall measure has an advantage over other memory measures because the free recall measure can provide organization measures, which can reveal the strategies participants used to maximize recall. For instance, even when a study list does not show a clear organizational scheme, recall outputs are often far from random, evidenced by participants recalling the same two or more items together repeatedly across multiple test trials. Unfortunately, computing organizational measures is laborious. The present article introduces a calculator to compute subjective organization (SO measures. The calculator is based on a popular platform accessible to most researchers and is designed to compute commonly used SO measures for each participant.

  17. Time-resolved echo-shared parallel MRA of the lung: observer preference study of image quality in comparison with non-echo-shared sequences

    International Nuclear Information System (INIS)

    Fink, C.; Puderbach, M.; Zaporozhan, J.; Plathow, C.; Kauczor, H.-U.; Ley, S.

    2005-01-01

    The aim of this study was to evaluate the image quality of time-resolved echo-shared parallel MRA of the lung. The pulmonary vasculature of nine patients (seven females, two males; median age: 44 years) with pulmonary disease was examined using a time-resolved MRA sequence combining echo sharing with parallel imaging (time-resolved echo-shared angiography technique, or TREAT). The sharpness of the vessel borders, conspicuousness of peripheral lung vessels, artifact level, and overall image quality of TREAT was assessed independently by four readers in a side-by-side comparison with non-echo-shared time-resolved parallel MRA data (pMRA) previously acquired in the same patients. Furthermore, the SNR of pulmonary arteries (PA) and veins (PV) achieved with both pulse sequences was compared. The mean voxel size of TREAT MRA was decreased by 24% compared with the non-echo-shared MRA. Regarding the sharpness of the vessel borders, conspicuousness of peripheral lung vessels, and overall image quality the TREAT sequence was rated superior in 75-76% of all cases. If the TREAT images were preferred over the pMRA images, the advantage was rated as major in 61-71% of all cases. The level of artifacts was not increased with the TREAT sequence. The mean interobserver agreement for all categories ranged between fair (artifact level) and good (overall image quality). The maximum SNR of TREAT did not differ from non-echo-shared parallel MRA (PA: TREAT: 273±45; pMRA: 280±71; PV: TREAT: 273±33; pMRA: 258±62). TREAT achieves a higher spatial resolution than non-echo-shared parallel MRA which is also perceived as an improved image quality. (orig.)

  18. Detecting deep venous thrombosis with limited flip angle gradient refocused MR imaging

    International Nuclear Information System (INIS)

    Spritzer, C.E.; Sussman, S.K.; Herfkens, R.J.; Blinder, R.A.; Saeed, M.; Vogler, J.A.; Baker, M.E.

    1987-01-01

    This study was undertaken to determine if limited flip angle gradient refocused MR pulse sequences (GRASS) could be used to accurately diagnose deep venous thrombosis (DVT). Sixteen patients (17 extremities) with possible DVT were prospectively evaluated with MR imaging and venography. Typical imaging parameters included a 16-msec echo time, 33-msec repetition time, 30 0 flip angle, and section thickness of 2 nex. MR imaging correctly disclosed the presence (nine cases) or absence (eight cases) of DVT. In one study, GRASS images overestimated the extent of clot due to slow venous blood flow. Subsequently the flip angle was varied to distinguish between venous thrombus and slow flow. When this technique was used, no false-positive studies occurred in the remaining patients. MR gradient refocused imaging appears to be an accurate aid for the diagnosis of DVT

  19. Recalling what was where when seeing nothing there

    OpenAIRE

    Staudte, Maria; Altmann, Gerry T. M.

    2016-01-01

    So-called ?looks-at-nothing? have previously been used to show that recalling what also elicits the recall of where this was. Here, we present evidence from an eye-tracking study which shows that disrupting looks to ?there? does not disrupt recalling what was there, nor do (anticipatory) looks to ?there? facilitate recalling what was there. Therefore, our results suggest that recalling where does not recall what.

  20. Note Taking and Recall

    Science.gov (United States)

    Fisher, Judith L.; Harris, Mary B.

    1974-01-01

    To study the effect of note taking and opportunity for review on subsequent recall, 88 college students were randomly assigned to five treatment groups utilizing different note taking and review combinations. No treatment effects were found, although quality of notes was positively correlated with free recall an multiple-choice measures.…

  1. Three-dimensional susceptibility-weighted imaging and two-dimensional T2*-weighted gradient-echo imaging of intratumoral hemorrhages in pediatric diffuse intrinsic pontine glioma

    International Nuclear Information System (INIS)

    Loebel, Ulrike; Sedlacik, Jan; Sabin, Noah D.; Hillenbrand, Claudia M.; Patay, Zoltan; Kocak, Mehmet; Broniscer, Alberto

    2010-01-01

    We compared the sensitivity and specificity of T2*-weighted gradient-echo imaging (T2*-GRE) and susceptibility-weighted imaging (SWI) in determining prevalence and cumulative incidence of intratumoral hemorrhages in children with diffuse intrinsic pontine glioma (DIPG) undergoing antiangiogenic and radiation therapy. Patients were recruited from an institutional review board-approved prospective phase I trial of vandetanib administered in combination with radiation therapy. Patient consent was obtained before enrollment. Consecutive T2*-GRE and SWI exams of 17 patients (F/M: 9/8; age 3-17 years) were evaluated. Two reviewers (R1 and R2) determined the number and size of hemorrhages at baseline and multiple follow-ups (92 scans, mean 5.4/patient). Statistical analyses were performed using descriptive statistics, graphical tools, and mixed-effects Poisson regression models. Prevalence of hemorrhages at diagnosis was 41% and 47%; the cumulative incidences of hemorrhages at 6 months by T2*-GRE and SWI were 82% and 88%, respectively. Hemorrhages were mostly petechial; 9.7% of lesions on T2*-GRE and 5.2% on SWI were hematomas (>5 mm). SWI identified significantly more hemorrhages than T2*-GRE did. Lesions were missed or misinterpreted in 36/39 (R1/R2) scans by T2*-GRE and 9/3 scans (R1/R2) by SWI. Hemorrhages had no clinically significant neurological correlates in patients. SWI is more sensitive than T2*-GRE in detecting hemorrhages and differentiating them from calcification, necrosis, and artifacts. Also, petechial hemorrhages are more common in DIPG at diagnosis than previously believed and their number increases during the course of treatment; hematomas are rare. (orig.)

  2. Closed-form expressions for flip angle variation that maximize total signal in T1-weighted rapid gradient echo MRI.

    Science.gov (United States)

    Drobnitzky, Matthias; Klose, Uwe

    2017-03-01

    Magnetization-prepared rapid gradient-echo (MPRAGE) sequences are commonly employed for T1-weighted structural brain imaging. Following a contrast preparation radiofrequency (RF) pulse, the data acquisition proceeds under nonequilibrium conditions of the relaxing longitudinal magnetization. Variation of the flip angle can be used to maximize total available signal. Simulated annealing or greedy algorithms have so far been published to numerically solve this problem, with signal-to-noise ratios optimized for clinical imaging scenarios by adhering to a predefined shape of the signal evolution. We propose an unconstrained optimization of the MPRAGE experiment that employs techniques from resource allocation theory. A new dynamic programming solution is introduced that yields closed-form expressions for optimal flip angle variation. Flip angle series are proposed that maximize total transverse magnetization (Mxy) for a range of physiologic T1 values. A 3D MPRAGE sequence is modified to allow for a controlled variation of the excitation angle. Experiments employing a T1 contrast phantom are performed at 3T. 1D acquisitions without phase encoding permit measurement of the temporal development of Mxy. Image mean signal and standard deviation for reference flip angle trains are compared in 2D measurements. Signal profiles at sharp phantom edges are acquired to access image blurring related to nonuniform Mxy development. A novel closed-form expression for flip angle variation is found that constitutes the optimal policy to reach maximum total signal. It numerically equals previously published results of other authors when evaluated under their simplifying assumptions. Longitudinal magnetization (Mz) is exhaustively used without causing abrupt changes in the measured MR signal, which is a prerequisite for artifact free images. Phantom experiments at 3T verify the expected benefit for total accumulated k-space signal when compared with published flip angle series. Describing

  3. The EChO science case

    DEFF Research Database (Denmark)

    Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul

    2015-01-01

    in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? How do planetary....... The mission can target super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300–3000 K) of F to M-type host stars. The EChO core science would be delivered by a three-tier survey. The EChO Chemical Census: This is a broad survey of a few...

  4. J-NSE: Neutron spin echo spectrometer

    Directory of Open Access Journals (Sweden)

    Olaf Holderer

    2015-08-01

    Full Text Available Neutron Spin-Echo (NSE spectroscopy is well known as the only neutron scattering technique that achieves energy resolution of several neV. By using the spin precession of polarized neutrons in magnetic field one can measure tiny velocity changes of the individual neutron during the scattering process. Contrary to other inelastic neutron scattering techniques, NSE measures the intermediate scattering function S(Q,t in reciprocal space and time directly. The Neutron Spin-Echo spectrometer J-NSE, operated by JCNS, Forschungszentrum Jülich at the Heinz Maier-Leibnitz Zentrum (MLZ in Garching, covers a time range (2 ps to 200 ns on length scales accessible by small angle scattering technique. Along with conventional NSE spectroscopy that allows bulk measurements in transmission mode, J-NSE offers a new possibility - gracing incidence spin echo spectroscopy (GINSENS, developed to be used as "push-button" option in order to resolve the depth dependent near surface dynamics.

  5. Murdock free recall data: The initial recall search identifies the context by the location of the least remembered item and produces only better remembered items in proportion to the total recall difference.

    OpenAIRE

    Tarnow, Dr. Eugen

    2009-01-01

    The curious free recall data of Murdock (1962) shows an additional surprise that seems to have gone undetected until now: the probability of guessing an item in the initial recall is not identical to the overall free recall curve. Initial recall of an item is well correlated with the total recall of that item using a straight line but with an unexpected offset. The offset varies with the presentation rate and the total number of list items but in each case it is the same as the total recall ...

  6. Echo Shaping Using Sums of Damped Complex Sinusoids

    DEFF Research Database (Denmark)

    Putnam, Lance Jonathan

    2015-01-01

    Feedback delay lines are the basis of myriad audio effects and reverberation schemes. The feedback delay line, by itself, is limited to producing an infinite sequence of exponentially decaying echoes. We introduce a new type of linear time-invariant echo effect whose impulse response is a general...

  7. Examining the Effect of Interference on Short-term Memory Recall of Arabic Abstract and Concrete Words Using Free, Cued, and Serial Recall Paradigms

    Directory of Open Access Journals (Sweden)

    Ahmed Mohammed Saleh Alduais

    2015-12-01

    Full Text Available Purpose: To see if there is a correlation between interference and short-term memory recall and to examine interference as a factor affecting memory recalling of Arabic and abstract words through free, cued, and serial recall tasks. Method: Four groups of undergraduates in King Saud University, Saudi Arabia participated in this study. The first group consisted of 9 undergraduates who were trained to perform three types of recall for 20 Arabic abstract and concrete words. The second, third and fourth groups consisted of 27 undergraduates where each group was trained only to perform one recall type: free recall, cued recall and serial recall respectively. Interference (short-term memory interruption was the independent variable and a number of recalled abstract and concrete words was the dependent variable. The used materials in this study were: abstract and concrete words classification form based on four factors was distributed to the participants (concreteness, imageability, meaningfulness, and age of acquisition, three oral recall forms, three written recall forms, and observation sheets for each type of recall. Also, three methods were used: auditory, visual, and written methods. Results: Findings indicated that interference effect on short-term memory recall of Arabic abstract and concrete words was not significant especially in the case of free and serial recall paradigms. The difference between the total number of recalled Arabic abstract and concrete words was also very slight. One other the hand, we came to the conclusion that Pearson’s correlation between interference at these memory recall paradigms (M: 1.66, SD= .47 and the short-term memory recall (M: 1.75, SD= .43 supported the research hypothesis that those participants with oral interruptions tended to recall slightly less Arabic abstract and concrete words, whereas those participants with no oral interruptions would tend to recall slightly more Arabic abstract and concrete

  8. The electron capture in 163Ho experiment - ECHo

    Science.gov (United States)

    Gastaldo, L.; Blaum, K.; Chrysalidis, K.; Day Goodacre, T.; Domula, A.; Door, M.; Dorrer, H.; Düllmann, Ch. E.; Eberhardt, K.; Eliseev, S.; Enss, C.; Faessler, A.; Filianin, P.; Fleischmann, A.; Fonnesu, D.; Gamer, L.; Haas, R.; Hassel, C.; Hengstler, D.; Jochum, J.; Johnston, K.; Kebschull, U.; Kempf, S.; Kieck, T.; Köster, U.; Lahiri, S.; Maiti, M.; Mantegazzini, F.; Marsh, B.; Neroutsos, P.; Novikov, Yu. N.; Ranitzsch, P. C. O.; Rothe, S.; Rischka, A.; Saenz, A.; Sander, O.; Schneider, F.; Scholl, S.; Schüssler, R. X.; Schweiger, Ch.; Simkovic, F.; Stora, T.; Szücs, Z.; Türler, A.; Veinhard, M.; Weber, M.; Wegner, M.; Wendt, K.; Zuber, K.

    2017-06-01

    Neutrinos, and in particular their tiny but non-vanishing masses, can be considered one of the doors towards physics beyond the Standard Model. Precision measurements of the kinematics of weak interactions, in particular of the 3H β-decay and the 163Ho electron capture (EC), represent the only model independent approach to determine the absolute scale of neutrino masses. The electron capture in 163Ho experiment, ECHo, is designed to reach sub-eV sensitivity on the electron neutrino mass by means of the analysis of the calorimetrically measured electron capture spectrum of the nuclide 163Ho. The maximum energy available for this decay, about 2.8 keV, constrains the type of detectors that can be used. Arrays of low temperature metallic magnetic calorimeters (MMCs) are being developed to measure the 163Ho EC spectrum with energy resolution below 3 eV FWHM and with a time resolution below 1 μs. To achieve the sub-eV sensitivity on the electron neutrino mass, together with the detector optimization, the availability of large ultra-pure 163Ho samples, the identification and suppression of background sources as well as the precise parametrization of the 163Ho EC spectrum are of utmost importance. The high-energy resolution 163Ho spectra measured with the first MMC prototypes with ion-implanted 163Ho set the basis for the ECHo experiment. We describe the conceptual design of ECHo and motivate the strategies we have adopted to carry on the present medium scale experiment, ECHo-1K. In this experiment, the use of 1 kBq 163Ho will allow to reach a neutrino mass sensitivity below 10 eV/ c 2. We then discuss how the results being achieved in ECHo-1k will guide the design of the next stage of the ECHo experiment, ECHo-1M, where a source of the order of 1 MBq 163Ho embedded in large MMCs arrays will allow to reach sub-eV sensitivity on the electron neutrino mass.

  9. Trends in Non-prescription Drug Recalls in Japan.

    Science.gov (United States)

    Yamamoto, Chikoto; Ishida, Takuya; Osawa, Takashi; Naito, Takafumi; Kawakami, Junichi

    2016-01-01

    Recalls of non-prescription drugs can contribute to preventing harm to human health, however, they also interrupt the supply of medicines to the market. The aim of the present study was to investigate the trends in non-prescription drug recalls in Japan. Class I, II, and III recalls reported from April 2009 to March 2014 were obtained from the websites of the Ministry of Health, Labour and Welfare and the Pharmaceuticals and Medical Devices Agency. Each drug recall was classified according to year, dosage form, therapeutic category, and reasons for the recall. The trends over the 5 year period were assessed for each class. A total of 220 recalls were reported in the 5-year study period. The numbers of drug recalls were 21, 16, 80, 58, and 45 in 2009, 2010, 2011, 2012, and 2013, respectively. The drugs recalled consisted of 177 internal medications, 35 topical agents, and 8 others. Drug recalls were observed in 12 therapeutic categories of drug effects. The largest number of recalls was for Chinese herbal medicines and crude drugs. Of all the drug recalls in 2011, Chinese herbal medicines and crude drugs produced by one manufacturer accounted for 84%. Slightly more than half (54%) of drug recalls were due to a violation of the regulations. One manufacturer recalled many drugs because of non-compliance with the standard regulations for manufacturing drugs after 2011. In conclusion, non-prescription drug recalls can occur for any drug regardless of the dosage form and therapeutic category.

  10. The EChO science case

    Science.gov (United States)

    Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul; Hartogh, Paul; Isaak, Kate; Linder, Martin; Lovis, Christophe; Micela, Giusi; Ollivier, Marc; Puig, Ludovic; Ribas, Ignasi; Snellen, Ignas; Swinyard, Bruce; Allard, France; Barstow, Joanna; Cho, James; Coustenis, Athena; Cockell, Charles; Correia, Alexandre; Decin, Leen; de Kok, Remco; Deroo, Pieter; Encrenaz, Therese; Forget, Francois; Glasse, Alistair; Griffith, Caitlin; Guillot, Tristan; Koskinen, Tommi; Lammer, Helmut; Leconte, Jeremy; Maxted, Pierre; Mueller-Wodarg, Ingo; Nelson, Richard; North, Chris; Pallé, Enric; Pagano, Isabella; Piccioni, Guseppe; Pinfield, David; Selsis, Franck; Sozzetti, Alessandro; Stixrude, Lars; Tennyson, Jonathan; Turrini, Diego; Zapatero-Osorio, Mariarosa; Beaulieu, Jean-Philippe; Grodent, Denis; Guedel, Manuel; Luz, David; Nørgaard-Nielsen, Hans Ulrik; Ray, Tom; Rickman, Hans; Selig, Avri; Swain, Mark; Banaszkiewicz, Marek; Barlow, Mike; Bowles, Neil; Branduardi-Raymont, Graziella; du Foresto, Vincent Coudé; Gerard, Jean-Claude; Gizon, Laurent; Hornstrup, Allan; Jarchow, Christopher; Kerschbaum, Franz; Kovacs, Géza; Lagage, Pierre-Olivier; Lim, Tanya; Lopez-Morales, Mercedes; Malaguti, Giuseppe; Pace, Emanuele; Pascale, Enzo; Vandenbussche, Bart; Wright, Gillian; Ramos Zapata, Gonzalo; Adriani, Alberto; Azzollini, Ruymán; Balado, Ana; Bryson, Ian; Burston, Raymond; Colomé, Josep; Crook, Martin; Di Giorgio, Anna; Griffin, Matt; Hoogeveen, Ruud; Ottensamer, Roland; Irshad, Ranah; Middleton, Kevin; Morgante, Gianluca; Pinsard, Frederic; Rataj, Mirek; Reess, Jean-Michel; Savini, Giorgio; Schrader, Jan-Rutger; Stamper, Richard; Winter, Berend; Abe, L.; Abreu, M.; Achilleos, N.; Ade, P.; Adybekian, V.; Affer, L.; Agnor, C.; Agundez, M.; Alard, C.; Alcala, J.; Allende Prieto, C.; Alonso Floriano, F. J.; Altieri, F.; Alvarez Iglesias, C. A.; Amado, P.; Andersen, A.; Aylward, A.; Baffa, C.; Bakos, G.; Ballerini, P.; Banaszkiewicz, M.; Barber, R. J.; Barrado, D.; Barton, E. J.; Batista, V.; Bellucci, G.; Belmonte Avilés, J. A.; Berry, D.; Bézard, B.; Biondi, D.; Błęcka, M.; Boisse, I.; Bonfond, B.; Bordé, P.; Börner, P.; Bouy, H.; Brown, L.; Buchhave, L.; Budaj, J.; Bulgarelli, A.; Burleigh, M.; Cabral, A.; Capria, M. T.; Cassan, A.; Cavarroc, C.; Cecchi-Pestellini, C.; Cerulli, R.; Chadney, J.; Chamberlain, S.; Charnoz, S.; Christian Jessen, N.; Ciaravella, A.; Claret, A.; Claudi, R.; Coates, A.; Cole, R.; Collura, A.; Cordier, D.; Covino, E.; Danielski, C.; Damasso, M.; Deeg, H. J.; Delgado-Mena, E.; Del Vecchio, C.; Demangeon, O.; De Sio, A.; De Wit, J.; Dobrijévic, M.; Doel, P.; Dominic, C.; Dorfi, E.; Eales, S.; Eiroa, C.; Espinoza Contreras, M.; Esposito, M.; Eymet, V.; Fabrizio, N.; Fernández, M.; Femenía Castella, B.; Figueira, P.; Filacchione, G.; Fletcher, L.; Focardi, M.; Fossey, S.; Fouqué, P.; Frith, J.; Galand, M.; Gambicorti, L.; Gaulme, P.; García López, R. J.; Garcia-Piquer, A.; Gear, W.; Gerard, J.-C.; Gesa, L.; Giani, E.; Gianotti, F.; Gillon, M.; Giro, E.; Giuranna, M.; Gomez, H.; Gomez-Leal, I.; Gonzalez Hernandez, J.; González Merino, B.; Graczyk, R.; Grassi, D.; Guardia, J.; Guio, P.; Gustin, J.; Hargrave, P.; Haigh, J.; Hébrard, E.; Heiter, U.; Heredero, R. L.; Herrero, E.; Hersant, F.; Heyrovsky, D.; Hollis, M.; Hubert, B.; Hueso, R.; Israelian, G.; Iro, N.; Irwin, P.; Jacquemoud, S.; Jones, G.; Jones, H.; Justtanont, K.; Kehoe, T.; Kerschbaum, F.; Kerins, E.; Kervella, P.; Kipping, D.; Koskinen, T.; Krupp, N.; Lahav, O.; Laken, B.; Lanza, N.; Lellouch, E.; Leto, G.; Licandro Goldaracena, J.; Lithgow-Bertelloni, C.; Liu, S. J.; Lo Cicero, U.; Lodieu, N.; Lognonné, P.; Lopez-Puertas, M.; Lopez-Valverde, M. A.; Lundgaard Rasmussen, I.; Luntzer, A.; Machado, P.; MacTavish, C.; Maggio, A.; Maillard, J.-P.; Magnes, W.; Maldonado, J.; Mall, U.; Marquette, J.-B.; Mauskopf, P.; Massi, F.; Maurin, A.-S.; Medvedev, A.; Michaut, C.; Miles-Paez, P.; Montalto, M.; Montañés Rodríguez, P.; Monteiro, M.; Montes, D.; Morais, H.; Morales, J. C.; Morales-Calderón, M.; Morello, G.; Moro Martín, A.; Moses, J.; Moya Bedon, A.; Murgas Alcaino, F.; Oliva, E.; Orton, G.; Palla, F.; Pancrazzi, M.; Pantin, E.; Parmentier, V.; Parviainen, H.; Peña Ramírez, K. Y.; Peralta, J.; Perez-Hoyos, S.; Petrov, R.; Pezzuto, S.; Pietrzak, R.; Pilat-Lohinger, E.; Piskunov, N.; Prinja, R.; Prisinzano, L.; Polichtchouk, I.; Poretti, E.; Radioti, A.; Ramos, A. A.; Rank-Lüftinger, T.; Read, P.; Readorn, K.; Rebolo López, R.; Rebordão, J.; Rengel, M.; Rezac, L.; Rocchetto, M.; Rodler, F.; Sánchez Béjar, V. J.; Sanchez Lavega, A.; Sanromá, E.; Santos, N.; Sanz Forcada, J.; Scandariato, G.; Schmider, F.-X.; Scholz, A.; Scuderi, S.; Sethenadh, J.; Shore, S.; Showman, A.; Sicardy, B.; Sitek, P.; Smith, A.; Soret, L.; Sousa, S.; Stiepen, A.; Stolarski, M.; Strazzulla, G.; Tabernero, H. M.; Tanga, P.; Tecsa, M.; Temple, J.; Terenzi, L.; Tessenyi, M.; Testi, L.; Thompson, S.; Thrastarson, H.; Tingley, B. W.; Trifoglio, M.; Martín Torres, J.; Tozzi, A.; Turrini, D.; Varley, R.; Vakili, F.; de Val-Borro, M.; Valdivieso, M. L.; Venot, O.; Villaver, E.; Vinatier, S.; Viti, S.; Waldmann, I.; Waltham, D.; Ward-Thompson, D.; Waters, R.; Watkins, C.; Watson, D.; Wawer, P.; Wawrzaszk, A.; White, G.; Widemann, T.; Winek, W.; Wiśniowski, T.; Yelle, R.; Yung, Y.; Yurchenko, S. N.

    2015-12-01

    The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population. We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, and new populations of planets with masses between that of the Earth and Neptune—all unknown in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? How do planetary systems work and what causes the exceptional diversity observed as compared to the Solar System? The EChO (Exoplanet Characterisation Observatory) space mission was conceived to take up the challenge to explain this diversity in terms of formation, evolution, internal structure and planet and atmospheric composition. This requires in-depth spectroscopic knowledge of the atmospheres of a large and well-defined planet sample for which precise physical, chemical and dynamical information can be obtained. In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample within its 4-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allows us to measure atmospheric signals from the planet at levels of at least 10-4 relative to the star. This can only be achieved in conjunction with a carefully designed stable payload and satellite platform. It is also necessary to provide broad instantaneous wavelength coverage to detect as many molecular species as possible, to probe the thermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellar photosphere. This requires wavelength

  11. 21 CFR 7.42 - Recall strategy.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Recall strategy. 7.42 Section 7.42 Food and Drugs....42 Recall strategy. (a) General. (1) A recall strategy that takes into account the following factors... in the market-place. (v) Continued availability of essential products. (2) The Food and Drug...

  12. Recall in extensive form games

    OpenAIRE

    Klaus Ritzberger

    1999-01-01

    This paper considers characterizations of perfect recall in extensive form games. It is shown that perfect recall can be expressed in terms of choices without any reference to infomation sets. When information sets are taken into account, it is decomposable into an ordering of information sets and that players do not forget what they knew nor what they did. Thus, if information sets are partially ordered, then perfect recall is implied by the player's inability to refine her information from ...

  13. Examining the relationship between free recall and immediate serial recall: the effects of list length and output order.

    Science.gov (United States)

    Ward, Geoff; Tan, Lydia; Grenfell-Essam, Rachel

    2010-09-01

    In 4 experiments, participants were presented with lists of between 1 and 15 words for tests of immediate memory. For all tasks, participants tended to initiate recall with the first word on the list for short lists. As the list length was increased, so there was a decreased tendency to start with the first list item; and, when free to do so, participants showed an increased tendency to start with one of the last 4 list items. In all tasks, the start position strongly influenced the shape of the resultant serial position curves: When recall started at Serial Position 1, elevated recall of early list items was observed; when recall started toward the end of the list, there were extended recency effects. These results occurred under immediate free recall (IFR) and different variants of immediate serial recall (ISR) and reconstruction of order (RoO) tasks. We argue that these findings have implications for the relationship between IFR and ISR and between rehearsal and recall. (c) 2010 APA, all rights reserved).

  14. Unusual Radar Echo from the Wake of Meteor Fireball in Nearly

    Directory of Open Access Journals (Sweden)

    Young-Sook Lee

    2018-06-01

    Full Text Available The summer polar lower thermosphere (90–100 km has an interesting connection to meteors, adjacent to the mesopause region attaining the lowest temperature in summer. Meteors supply condensation nuclei for charged ice particles causing polar mesospheric summer echoes (PMSE. We report the observation of meteor trail with nearly horizontal transit at high speed (20–50 km/s, and at last with re-enhanced echo power followed by diffusive echoes. Changes in phase difference between radar receivers aligned in meridional and zonal directions are used to determine variations in horizontal displacements and speeds with respect to time by taking advantage of radar interferometric analysis. The actual transit of echo target is observed along the straight pathway vertically and horizontally extended as much as a distance of at least 24 km and at most 29 km. The meteor trail initially has a signature similar to ‘head echoes’, with travel speeds from 20 – 50 km/s. It subsequently transforms into a different type of echo target including specular echo and then finally the power reenhanced. The reenhancement of echo power is followed by fume-like diffusive echoes, indicating sudden release of plasma as like explosive process probably involved. We discuss a possible role of meteor-triggered secondary plasma trail, such as fireball embedded with electrical discharge that continuously varies the power and transit speed.

  15. Practice Makes Perfect in Memory Recall

    Science.gov (United States)

    Romani, Sandro; Katkov, Mikhail; Tsodyks, Misha

    2016-01-01

    A large variability in performance is observed when participants recall briefly presented lists of words. The sources of such variability are not known. Our analysis of a large data set of free recall revealed a small fraction of participants that reached an extremely high performance, including many trials with the recall of complete lists.…

  16. Puget Sound Watershed.pdf | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  17. Hierarchy of Loading Calculations | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  18. eff-date-range.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  19. PWS_Dashboard_2.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  20. eff-hover-chart.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  1. PWS_Dashboard_1.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  2. eff-toggle-chart.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  3. Analyze Trends: State Hazardous Waste Dashboard | ECHO ...

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  4. Custom Search Results Help | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  5. Technical Users Background Document | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  6. Product Recall Policies and Their Improvement in Korea

    Directory of Open Access Journals (Sweden)

    Huh Kyungok

    2016-12-01

    Full Text Available This article aims to investigate recall policies for product safety in Korea and make suggestions for future improvements. Problematic issues in current recall policies are reviewed and analyzed. Based on survey results and previous studies, this article discusses the consumer perception of a recall. Consumers tend to regard a recall as a signal of poor quality. Furthermore, regulatory differences and weak penalties remain as obstacles to improving the recall system. Suggestions for the betterment of recall policies are derived from consultations with an expert panel and the application of other appropriate methods. At first, despite an increasing number of recall cases in Korea, it turns out that consumers are not highly sensitive to recalls, although their perceptions are mostly negative. Secondly, regulatory inconsistencies and difference problems are primarily attributable to the existence of many separate rules and regulations by product category. Thirdly, the information concerning recalls is limited, which creates an inefficient environment in which manufacturers are reluctant to voluntarily recall a defective product and consumer participation rates are too low. Therefore, the government should induce consumers to have more positive perceptions of recalls whilst concurrently reinforcing the related rules and regulations in accordance with international standards.

  7. Black hole ringdown echoes and howls

    Science.gov (United States)

    Nakano, Hiroyuki; Sago, Norichika; Tagoshi, Hideyuki; Tanaka, Takahiro

    2017-07-01

    Recently the possibility of detecting echoes of ringdown gravitational waves from binary black hole mergers was shown. The presence of echoes is expected if the black hole is surrounded by a mirror that reflects gravitational waves near the horizon. Here, we present slightly more sophisticated templates motivated by a waveform which is obtained by solving the linear perturbation equation around a Kerr black hole with a complete reflecting boundary condition in the stationary traveling wave approximation. We estimate that the proposed template can bring about a 10% improvement in the signal-to-noise ratio.

  8. Evolution of entanglement under echo dynamics

    International Nuclear Information System (INIS)

    Prosen, Tomaz; Znidaric, Marko; Seligman, Thomas H.

    2003-01-01

    Echo dynamics and fidelity are often used to discuss stability in quantum-information processing and quantum chaos. Yet fidelity yields no information about entanglement, the characteristic property of quantum mechanics. We study the evolution of entanglement in echo dynamics. We find qualitatively different behavior between integrable and chaotic systems on one hand and between random and coherent initial states for integrable systems on the other. For the latter the evolution of entanglement is given by a classical time scale. Analytic results are illustrated numerically in a Jaynes-Cummings model

  9. Autogenic training and dream recall.

    Science.gov (United States)

    Schredl, M; Doll, E

    1997-06-01

    The present study has investigated the relationship between Autogenic Training and dream recall for 112 participants in 16 beginning courses of 10 wk. Analyses confirmed the hypothesis that learning and practicing this relaxation technique enhanced dream recall.

  10. Intrusions in story recall: when over-learned information interferes with episodic memory recall. Evidence from Alzheimer's disease.

    Science.gov (United States)

    De Anna, Francesca; Attali, Eve; Freynet, Laurence; Foubert, Lucie; Laurent, Aurore; Dubois, Bruno; Dalla Barba, Gianfranco

    2008-03-01

    Patients with Alzheimer's disease (AD) suffer from distortions of memory. Among such distortions, intrusions in memory tests are frequently observed. In this study we describe the performance of a group of mild AD patients and a group of normal controls on the recall of three different types of stories: a previously unknown story, a well-known fairy-tale (Cinderella), and a modified well-known fairy-tale (Little Red Riding Hood is not eaten by the wolf). The aim of our study was to test the hypothesis that in patients who tend to produce intrusions, over-learned information interferes with episodic recall, i.e., the retrieval of specific, unique past episodes. AD patients produced significantly more intrusions in the recall of the modified fairy-tale compared to the recall of the two other stories. Intrusions in the recall of the modified fairy-tale always consisted of elements of the original version of the story. We suggest that in AD patients intrusions may be traced back to the interference of strongly represented, over-learned information in episodic memory recall.

  11. Comparison of Echo 7 field line length measurements to magnetospheric model predictions

    International Nuclear Information System (INIS)

    Nemzek, R.J.; Winckler, J.R.; Malcolm, P.R.

    1992-01-01

    The Echo 7 sounding rocket experiment injected electron beams on central tail field lines near L = 6.5. Numerous injections returned to the payload as conjugate echoes after mirroring in the southern hemisphere. The authors compare field line lengths calculated from measured conjugate echo bounce times and energies to predictions made by integrating electron trajectories through various magnetospheric models: the Olson-Pfitzer Quiet and Dynamic models and the Tsyganenko-Usmanov model. Although Kp at launch was 3-, quiet time magnetic models est fit the echo measurements. Geosynchronous satellite magnetometer measurements near the Echo 7 field lies during the flight were best modeled by the Olson-Pfitzer Dynamic Model and the Tsyganenko-Usmanov model for Kp = 3. The discrepancy between the models that best fit the Echo 7 data and those that fit the satellite data was most likely due to uncertainties in the small-scale configuration of the magnetospheric models. The field line length measured by the conjugate echoes showed some temporal variation in the magnetic field, also indicated by the satellite magnetometers. This demonstrates the utility an Echo-style experiment could have in substorm studies

  12. Investigating the Group-Level Impact of Advanced Dual-Echo fMRI Combinations

    Directory of Open Access Journals (Sweden)

    Adam Kettinger

    2016-12-01

    Full Text Available Multi-echo fMRI data acquisition has been widely investigated and suggested to optimize sensitivity for detecting the BOLD signal. Several methods have also been proposed for the combination of data with different echo times. The aim of the present study was to investigate how these advance echo combination methods provide advantages over the simple averaging of echoes when state-of-the-art group-level random-effect analyses are performed. Both resting-state and task-based dual-echo fMRI data were collected from 27 healthy adult individuals (14 male, mean age = 25.75 years using standard echo-planar acquisition methods at 3T. Both resting-state and task-based data were subjected to a standard image pre-processing pipeline. Subsequently the two echoes were combined as a weighted average, using four different strategies for calculating the weights: (1 simple arithmetic averaging, (2 BOLD sensitivity weighting, (3 temporal-signal-to-noise ratio weighting and (4 temporal BOLD sensitivity weighting. Our results clearly show that the simple averaging of data with the different echoes is sufficient. Advanced echo combination methods may provide advantages on a single-subject level but when considering random-effects group level statistics they provide no benefit regarding sensitivity (i.e. group-level t-values compared to the simple echo-averaging approach. One possible reason for the lack of clear advantages may be that apart from increasing the average BOLD sensitivity at the single-subject level, the advanced weighted averaging methods also inflate the inter-subject variance. As the echo combination methods provide very similar results, the recommendation is to choose between them depending on the availability of time for collecting additional resting-state data or whether subject-level or group-level analyses are planned.

  13. Visual Perceptual Echo Reflects Learning of Regularities in Rapid Luminance Sequences.

    Science.gov (United States)

    Chang, Acer Y-C; Schwartzman, David J; VanRullen, Rufin; Kanai, Ryota; Seth, Anil K

    2017-08-30

    A novel neural signature of active visual processing has recently been described in the form of the "perceptual echo", in which the cross-correlation between a sequence of randomly fluctuating luminance values and occipital electrophysiological signals exhibits a long-lasting periodic (∼100 ms cycle) reverberation of the input stimulus (VanRullen and Macdonald, 2012). As yet, however, the mechanisms underlying the perceptual echo and its function remain unknown. Reasoning that natural visual signals often contain temporally predictable, though nonperiodic features, we hypothesized that the perceptual echo may reflect a periodic process associated with regularity learning. To test this hypothesis, we presented subjects with successive repetitions of a rapid nonperiodic luminance sequence, and examined the effects on the perceptual echo, finding that echo amplitude linearly increased with the number of presentations of a given luminance sequence. These data suggest that the perceptual echo reflects a neural signature of regularity learning.Furthermore, when a set of repeated sequences was followed by a sequence with inverted luminance polarities, the echo amplitude decreased to the same level evoked by a novel stimulus sequence. Crucially, when the original stimulus sequence was re-presented, the echo amplitude returned to a level consistent with the number of presentations of this sequence, indicating that the visual system retained sequence-specific information, for many seconds, even in the presence of intervening visual input. Altogether, our results reveal a previously undiscovered regularity learning mechanism within the human visual system, reflected by the perceptual echo. SIGNIFICANCE STATEMENT How the brain encodes and learns fast-changing but nonperiodic visual input remains unknown, even though such visual input characterizes natural scenes. We investigated whether the phenomenon of "perceptual echo" might index such learning. The perceptual echo is a

  14. A computational model for biosonar echoes from foliage.

    Directory of Open Access Journals (Sweden)

    Chen Ming

    Full Text Available Since many bat species thrive in densely vegetated habitats, echoes from foliage are likely to be of prime importance to the animals' sensory ecology, be it as clutter that masks prey echoes or as sources of information about the environment. To better understand the characteristics of foliage echoes, a new model for the process that generates these signals has been developed. This model takes leaf size and orientation into account by representing the leaves as circular disks of varying diameter. The two added leaf parameters are of potential importance to the sensory ecology of bats, e.g., with respect to landmark recognition and flight guidance along vegetation contours. The full model is specified by a total of three parameters: leaf density, average leaf size, and average leaf orientation. It assumes that all leaf parameters are independently and identically distributed. Leaf positions were drawn from a uniform probability density function, sizes and orientations each from a Gaussian probability function. The model was found to reproduce the first-order amplitude statistics of measured example echoes and showed time-variant echo properties that depended on foliage parameters. Parameter estimation experiments using lasso regression have demonstrated that a single foliage parameter can be estimated with high accuracy if the other two parameters are known a priori. If only one parameter is known a priori, the other two can still be estimated, but with a reduced accuracy. Lasso regression did not support simultaneous estimation of all three parameters. Nevertheless, these results demonstrate that foliage echoes contain accessible information on foliage type and orientation that could play a role in supporting sensory tasks such as landmark identification and contour following in echolocating bats.

  15. Semi-Supervised Bayesian Classification of Materials with Impact-Echo Signals

    Directory of Open Access Journals (Sweden)

    Jorge Igual

    2015-05-01

    Full Text Available The detection and identification of internal defects in a material require the use of some technology that translates the hidden interior damages into observable signals with different signature-defect correspondences. We apply impact-echo techniques for this purpose. The materials are classified according to their defective status (homogeneous, one defect or multiple defects and kind of defect (hole or crack, passing through or not. Every specimen is impacted by a hammer, and the spectrum of the propagated wave is recorded. This spectrum is the input data to a Bayesian classifier that is based on the modeling of the conditional probabilities with a mixture of Gaussians. The parameters of the Gaussian mixtures and the class probabilities are estimated using an extended expectation-maximization algorithm. The advantage of our proposal is that it is flexible, since it obtains good results for a wide range of models even under little supervision; e.g., it obtains a harmonic average of precision and recall value of 92.38% given only a 10% supervision ratio. We test the method with real specimens made of aluminum alloy. The results show that the algorithm works very well. This technique could be applied in many industrial problems, such as the optimization of the marble cutting process.

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

    Science.gov (United States)

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

    2014-09-01

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

  17. Ultrashort Echo Time Magnetic Resonance Imaging of the Lung Using a High-Relaxivity T1 Blood-Pool Contrast Agent

    Directory of Open Access Journals (Sweden)

    Joris Tchouala Nofiele

    2014-10-01

    Full Text Available The lung remains one of the most challenging organs to image using magnetic resonance imaging (MRI due to intrinsic rapid signal decay. However, unlike conventional modalities such as computed tomography, MRI does not involve radiation and can provide functional and morphologic information on a regional basis. Here we demonstrate proof of concept for a new MRI approach to achieve substantial gains in a signal to noise ratio (SNR in the lung parenchyma: contrast-enhanced ultrashort echo time (UTE imaging following intravenous injection of a high-relaxivity blood-pool manganese porphyrin T1 contrast agent. The new contrast agent increased relative enhancement of the lung parenchyma by over 10-fold compared to gadolinium diethylene triamine pentaacetic acid (Gd-DTPA, and the use of UTE boosted the SNR by a factor of 4 over conventional T1-weighted gradient echo acquisitions. The new agent also maintains steady enhancement over at least 60 minutes, thus providing a long time window for obtaining high-resolution, high-quality images and the ability to measure a number of physiologic parameters.

  18. Echo questions as a means of building coherence in conversational discourse

    Directory of Open Access Journals (Sweden)

    Strelchenko Natalia

    2017-06-01

    Full Text Available The study focuses on the cognitive-communicative characteristics of echo questions in English conversational discourse. Drawing on van Dijk's sociocognitive (mental model theory and cognitive discourse analysis, the paper suggests viewing echo questions as a means of building/updating a mental context model of a communicative situation. As discourse comprehension presupposes building its coherent mental model, echo questions resolving misunderstanding are regarded as an instrument for increasing coherence in conversational discourse. Based on the mental model theory, the study offers a typology of misunderstandings corrected by echo questions.

  19. Orienting task effects on text recall in adulthood.

    Science.gov (United States)

    Simon, E W; Dixon, R A; Nowak, C A; Hultsch, D F

    1982-09-01

    This investigation examined the effects of orienting task-controlled processing on the text recall of younger (18 to 32 years), middle-aged (39 to 51 years), and older (59 to 76 years) adults. The participants were presented with a 500-word narrative text. Three groups performed orienting tasks (syntactic, stylistic, advice) within an incidental memory paradigm. A fourth group was asked for intentional recall. Analysis indicated a significant age by orienting task interaction. Younger adults recalled more propositions when recall was intentional or when it was preceded by a deep-orienting task than when it was preceded by a shallow-orienting task. Middle-aged and older adults recalled more propositions when recall was intentional than when it was incidental, regardless of the depth of the orienting task. There were no significant differences in intentional recall. In addition, a significant age x orienting task x propositional level interaction indicated that younger adults recalled more of the main ideas of the text following deep processing, whereas the middle-aged and older adults recalled more of these ideas following intentional processing.

  20. Pictorial Detail and Recall in Adults and Children.

    Science.gov (United States)

    Ritchey, Gary H.

    1982-01-01

    Specific comparisons for a categorized set of items indicated that recall of detailed drawings and outlines was superior to recall of words. For an uncategorized set, outlines were recalled significantly better than pictures and both were recalled better than words. (Author/PN)

  1. A new phase coding method using a slice selection gradient for high speed flow velocity meaurements in NMR tomography

    International Nuclear Information System (INIS)

    Oh, C.H.; Cho, Z.H.; California Univ., Irvine

    1986-01-01

    A new phase coding method using a selection gradient for high speed NMR flow velocity measurements is introduced and discussed. To establish a phase-velocity relationship of flow under the slice selection gradient and spin-echo RF pulse, the Bloch equation was numerically solved under the assumption that only one directional flow exists, i.e. in the direction of slice selection. Details of the numerical solution of the Bloch equation and techniques related to the numerical computations are also given. Finally, using the numerical calculation, high speed flow velocity measurement was attempted and found to be in good agreement with other complementary controlled measurements. (author)

  2. Is scanning in probed order recall articulatory?

    Science.gov (United States)

    Farrell, Simon; Lelièvre, Anna

    2009-09-01

    We consider how theories of serial recall might apply to other short-term memory tasks involving recall of order. In particular, we consider the possibility that when participants are cued to recall an item at an arbitrary position in a sequence, they covertly serially recall the list up to the cued position. One question is whether such "scanning" is articulatory in nature. Two experiments are presented in which the syllabic length of words preceding and following target positions were manipulated, to test the prediction of an articulatory-based mechanism that time to recall an item at a particular position will depend on the number of preceding long words. Although latency was dependent on target position, no word length effects on latency were observed. Additionally, the effects of word length on accuracy replicate recent demonstrations in serial recall that recall accuracy is dependent on the word length of all list items, not just that of target items, in line with distinctiveness assumptions. It is concluded that if scanning does occur, it is not carried out by covert or overt articulation.

  3. Hemorrhagic Transformation After Large Cerebral Infarction in Rats Pretreated With Dabigatran or Warfarin.

    Science.gov (United States)

    Kwon, Il; An, Sunho; Kim, Jayoung; Yang, Seung-Hee; Yoo, Joonsang; Baek, Jang-Hyun; Nam, Hyo Suk; Kim, Young Dae; Lee, Hye Sun; Choi, Hyun-Jung; Heo, Ji Hoe

    2017-10-01

    It is uncertain whether hemorrhagic transformation (HT) after large cerebral infarction is less frequent in dabigatran users than warfarin users. We compared the occurrence of HT after large cerebral infarction among rats pretreated with dabigatran, warfarin, or placebo. This was a triple-blind, randomized, and placebo-controlled experiment. After treatment with warfarin (0.2 mg/kg), dabigatran (20 mg/kg), or saline for 7 days, Wistar rats were subjected to transient middle cerebral artery occlusion. As the primary outcome, HT was determined by gradient-recalled echo imaging. For the secondary outcome, intracranial hemorrhage was assessed via gradient-recalled echo imaging in surviving rats and via autopsy for dead rats. Of 62 rats, there were 33 deaths (53.2%, 17 technical reasons). Of the intention-to-treat population, 33 rats underwent brain imaging. HT was less frequent in the dabigatran group than the warfarin group (placebo 2/14 [14%], dabigatran 0/10 [0%], and warfarin 9/9 [100%]; dabigatran versus warfarin; P warfarin group (19/29 [65.5%]; P =0.003), but not in the dabigatran group (6/19 [31.6%]; P =0.420). Mortality was significantly higher in the warfarin group than the dabigatran group (79.3% versus 47.4%; P =0.022), but not related to the hemorrhage frequency. The risk of HT after a large cerebral infarction was significantly increased in rats pretreated with warfarin than those with dabigatran. However, the results here may not have an exact clinical translation. © 2017 American Heart Association, Inc.

  4. MANAGEMENT OF UNSAFE FOOD RECALL

    Directory of Open Access Journals (Sweden)

    Justyna Górna

    2016-06-01

    Full Text Available The aim of this paper is to present the essence of eff ective management to recall unsafe food. The implementation of the development is refl ected in its individual parts. Legal requirements oblige companies to take immediate action when an available product poses a threat to the consumer’s health or life. These actions imply blocking of a suspicious batch or a possible product recall, as well as eff ective communication with supervisory authorities and consumers, if a product has already been available to them. The scope of these regulations is scrupulously listed in private safety standards and food quality, such as BRC, IFS, or in an international norm ISO 22000. The article emphasized the importance of the traceability system to ensure eff ective recall, also analysed the results of the research into the causes and evaluated the eff ectiveness of the food recall.

  5. Recall versus familiarity when recall fails for words and scenes: the differential roles of the hippocampus, perirhinal cortex, and category-specific cortical regions.

    Science.gov (United States)

    Ryals, Anthony J; Cleary, Anne M; Seger, Carol A

    2013-01-25

    This fMRI study examined recall and familiarity for words and scenes using the novel recognition without cued recall (RWCR) paradigm. Subjects performed a cued recall task in which half of the test cues resembled studied items (and thus were familiar) and half did not. Subjects also judged the familiarity of the cue itself. RWCR is the finding that, among cues for which recall fails, subjects generally rate cues that resemble studied items as more familiar than cues that do not. For words, left and right hippocampal activity increased when recall succeeded relative to when it failed. When recall failed, right hippocampal activity was decreased for familiar relative to unfamiliar cues. In contrast, right Prc activity increased for familiar cues for which recall failed relative to both familiar cues for which recall succeeded and to unfamiliar cues. For scenes, left hippocampal activity increased when recall succeeded relative to when it failed but did not differentiate familiar from unfamiliar cues when recall failed. In contrast, right Prc activity increased for familiar relative to unfamiliar cues when recall failed. Category-specific cortical regions showed effects unique to their respective stimulus types: The visual word form area (VWFA) showed effects for recall vs. familiarity specific to words, and the parahippocampal place area (PPA) showed effects for recall vs. familiarity specific to scenes. In both cases, these effects were such that there was increased activity occurring during recall relative to when recall failed, and decreased activity occurring for familiar relative to unfamiliar cues when recall failed. Copyright © 2012 Elsevier B.V. All rights reserved.

  6. Recall versus familiarity when recall fails for words and scenes: The differential roles of the hippocampus, perirhinal cortex, and category-specific cortical regions☆

    Science.gov (United States)

    Ryals, Anthony J.; Cleary, Anne M.; Seger, Carol A.

    2013-01-01

    This fMRI study examined recall and familiarity for words and scenes using the novel recognition without cued recall (RWCR) paradigm. Subjects performed a cued recall task in which half of the test cues resembled studied items (and thus were familiar) and half did not. Subjects also judged the familiarity of the cue itself. RWCR is the finding that, among cues for which recall fails, subjects generally rate cues that resemble studied items as more familiar than cues that do not. For words, left and right hippocampal activity increased when recall succeeded relative to when it failed. When recall failed, right hippocampal activity was decreased for familiar relative to unfamiliar cues. In contrast, right Prc activity increased for familiar cues for which recall failed relative to both familiar cues for which recall succeeded and to unfamiliar cues. For scenes, left hippocampal activity increased when recall succeeded relative to when it failed but did not differentiate familiar from unfamiliar cues when recall failed. In contrast, right Prc activity increased for familiar relative to unfamiliar cues when recall failed. Category-specific cortical regions showed effects unique to their respective stimulus types: The visual word form area (VWFA) showed effects for recall vs. familiarity specific to words, and the parahippocampal place area (PPA) showed effects for recall vs. familiarity specific to scenes. In both cases, these effects were such that there was increased activity occurring during recall relative to when recall failed, and decreased activity occurring for familiar relative to unfamiliar cues when recall failed. PMID:23142268

  7. MR-based field-of-view extension in MR/PET: B0 homogenization using gradient enhancement (HUGE).

    Science.gov (United States)

    Blumhagen, Jan O; Ladebeck, Ralf; Fenchel, Matthias; Scheffler, Klaus

    2013-10-01

    In whole-body MR/PET, the human attenuation correction can be based on the MR data. However, an MR-based field-of-view (FoV) is limited due to physical restrictions such as B0 inhomogeneities and gradient nonlinearities. Therefore, for large patients, the MR image and the attenuation map might be truncated and the attenuation correction might be biased. The aim of this work is to explore extending the MR FoV through B0 homogenization using gradient enhancement in which an optimal readout gradient field is determined to locally compensate B0 inhomogeneities and gradient nonlinearities. A spin-echo-based sequence was developed that computes an optimal gradient for certain regions of interest, for example, the patient's arms. A significant distortion reduction was achieved outside the normal MR-based FoV. This FoV extension was achieved without any hardware modifications. In-plane distortions in a transaxially extended FoV of up to 600 mm were analyzed in phantom studies. In vivo measurements of the patient's arms lying outside the normal specified FoV were compared with and without the use of B0 homogenization using gradient enhancement. In summary, we designed a sequence that provides data for reducing the image distortions due to B0 inhomogeneities and gradient nonlinearities and used the data to extend the MR FoV. Copyright © 2011 Wiley Periodicals, Inc.

  8. Effects of language dominance on item and order memory in free recall, serial recall and order reconstruction.

    Science.gov (United States)

    Francis, Wendy S; Baca, Yuzeth

    2014-01-01

    Spanish-English bilinguals (N = 144) performed free recall, serial recall and order reconstruction tasks in both English and Spanish. Long-term memory for both item and order information was worse in the less fluent language (L2) than in the more fluent language (L1). Item scores exhibited a stronger disadvantage for the L2 in serial recall than in free recall. Relative order scores were lower in the L2 for all three tasks, but adjusted scores for free and serial recall were equivalent across languages. Performance of English-speaking monolinguals (N = 72) was comparable to bilingual performance in the L1, except that monolinguals had higher adjusted order scores in free recall. Bilingual performance patterns in the L2 were consistent with the established effects of concurrent task performance on these memory tests, suggesting that the cognitive resources required for processing words in the L2 encroach on resources needed to commit item and order information to memory. These findings are also consistent with a model in which item memory is connected to the language system, order information is processed by separate mechanisms and attention can be allocated differentially to these two systems.

  9. Temporal-contextual processing in working memory: evidence from delayed cued recall and delayed free recall tests.

    Science.gov (United States)

    Loaiza, Vanessa M; McCabe, David P

    2012-02-01

    Three experiments are reported that addressed the nature of processing in working memory by investigating patterns of delayed cued recall and free recall of items initially studied during complex and simple span tasks. In Experiment 1, items initially studied during a complex span task (i.e., operation span) were more likely to be recalled after a delay in response to temporal-contextual cues, relative to items from subspan and supraspan list lengths in a simple span task (i.e., word span). In Experiment 2, items initially studied during operation span were more likely to be recalled from neighboring serial positions during delayed free recall than were items studied during word span trials. Experiment 3 demonstrated that the number of attentional refreshing opportunities strongly predicts episodic memory performance, regardless of whether the information is presented in a spaced or massed format in a modified operation span task. The results indicate that the content-context bindings created during complex span trials reflect attentional refreshing opportunities that are used to maintain items in working memory.

  10. Variable-flip-angle spin-echo imaging (VFSE)

    International Nuclear Information System (INIS)

    Kasai, Toshifumi; Sugimura, Kazuro; Kawamitsu, Hideaki; Yasui, Kiyoshi; Ishida, Tetsuya; Tsukamoto, Tetsuji.

    1990-01-01

    T 2 weighted imaging provides images with high object contrast for pathologic conditions in which the water content of tissues is increased. The authors predicted theoretical analysis of the effects of changing flip angle, and analyzed the effects in MR imaging of both phantoms and humans. Variable flip angle spin echo MR imaging (VFSE) with a 1,000/80 (repetition time msec/echo time msec) can obtain T 2 weighted image when flip angle is smaller than 80 degrees. VFSE with 40 to 60 degrees flip angle have higher contrast than other flip angle images. Signal to noise ratio (S/N) of VFSE are 55% at a 30 degree, 76% at a 45 degree, 92% at a 60 degree respectively as compared with conventional spin echo image (2000/80, flip angle 90 degree). VFSE is applicable to obtain T 2 weighted image reduced imaging time. (author)

  11. Classification of underwater target echoes based on auditory perception characteristics

    Science.gov (United States)

    Li, Xiukun; Meng, Xiangxia; Liu, Hang; Liu, Mingye

    2014-06-01

    In underwater target detection, the bottom reverberation has some of the same properties as the target echo, which has a great impact on the performance. It is essential to study the difference between target echo and reverberation. In this paper, based on the unique advantage of human listening ability on objects distinction, the Gammatone filter is taken as the auditory model. In addition, time-frequency perception features and auditory spectral features are extracted for active sonar target echo and bottom reverberation separation. The features of the experimental data have good concentration characteristics in the same class and have a large amount of differences between different classes, which shows that this method can effectively distinguish between the target echo and reverberation.

  12. Dynamic rayed aurora and enhanced ion-acoustic radar echoes

    Directory of Open Access Journals (Sweden)

    E. M. Blixt

    2005-01-01

    Full Text Available The generation mechanism for naturally enhanced ion-acoustic echoes is still debated. One important issue is how these enhancements are related to auroral activity. All events of enhanced ion-acoustic echoes observed simultaneously with the EISCAT Svalbard Radar (ESR and with high-resolution narrow field-of-view auroral imagers have been collected and studied. Characteristic of all the events is the appearance of very dynamic rayed aurora, and some of the intrinsic features of these auroral displays are identified. Several of these identified features are directly related to the presence of low energy (10-100eV precipitating electrons in addition to the higher energy population producing most of the associated light. The low energy contribution is vital for the formation of the enhanced ion-acoustic echoes. We argue that this type of aurora is sufficient for the generation of naturally enhanced ion-acoustic echoes. In one event two imagers were used to observe the auroral rays simultaneously, one from the radar site and one 7km away. The data from these imagers shows that the auroral rays and the strong backscattering filaments (where the enhanced echoes are produced are located on the same field line, which is in contrast to earlier statements in the litterature that they should be separated.

  13. Faraday rotation echo spectroscopy and detection of quantum fluctuations.

    Science.gov (United States)

    Chen, Shao-Wen; Liu, Ren-Bao

    2014-04-15

    Central spin decoherence is useful for detecting many-body physics in environments and moreover, the spin echo control can remove the effects of static thermal fluctuations so that the quantum fluctuations are revealed. The central spin decoherence approach, however, is feasible only in some special configurations and often requires uniform coupling between the central spin and individual spins in the baths, which are very challenging in experiments. Here, by making analogue between central spin decoherence and depolarization of photons, we propose a scheme of Faraday rotation echo spectroscopy (FRES) for studying quantum fluctuations in interacting spin systems. The echo control of the photon polarization is realized by flipping the polarization with a birefringence crystal. The FRES, similar to spin echo in magnetic resonance spectroscopy, can suppress the effects of the static magnetic fluctuations and therefore reveal dynamical magnetic fluctuations. We apply the scheme to a rare-earth compound LiHoF4 and calculate the echo signal, which is related to the quantum fluctuations of the system. We observe enhanced signals at the phase boundary. The FRES should be useful for studying quantum fluctuations in a broad range of spin systems, including cold atoms, quantum dots, solid-state impurities, and transparent magnetic materials.

  14. Avascular necrosis of the hip

    International Nuclear Information System (INIS)

    Lang, P.; Genant, H.K.; Lindquist, T.; Chafetz, N.; Steiger, P.; Sanny, J.; Rhodes, M.L.; Rothman, S.L.G.; Delamarter, R.; Kilgus, D.

    1988-01-01

    T1-weighted (repetition time [TR] = 450 msec, echo time [TE] = 20 msec), T2-weighted (TR = 1,800 msec, TE = 20 and 80 msec), and T2*-weighted gradient-echo gradient recalled acquisition in a steady state, TR = 70 msec, TE = 30 msec, theta = 15 0 ) MR images (General Electric Signa, 1.5 T) were generated in 11 patients with avascular necrosis of the hip. Three-dimensional MR image reconstruction was performed on an independent imaging system (IIS, Dimensional Medicine Inc). Pelvic and femoral bone contours were computed based on either the T1-weighted or the T2*-weighted images. Three-dimensional displays of necrotic zones and areas of granulation tissue were computed on the basis of the T2-weighted images. The tissues were simultaneously displayed in the three-dimensional images using different colors and transparencies. The three-dimensional MR images generated demonstrated the extent of the necrotic zone and adjacent granulation tissue and their position relative to the weight-bearing surface. They may soon prove to be useful in preoperative planning and intraoperative localization of complex surgical interventions in avascular necrosis of the hip

  15. Flow velocity change in the cortical vein during motor activation and its effect on functional brain MRI

    Energy Technology Data Exchange (ETDEWEB)

    Nakajima, Kazuhiro [Kyoto Prefectural Univ. of Medicine (Japan)

    1998-06-01

    On the brain functional magnetic resonance imaging (fMRI) using the gradient-recalled echo technique with clinical MR scanner, the activated areas nearly correspond with the cortical veins. This suggests that the fMRI signal mainly originates from the cortical veins. In this study, we analyzed the flow velocity in the cortical vein quantitatively during brain activation and resting status using 2 dimensional time-of-flight cine MR venography (2D-TOF-cine-MRV) and 2 dimensional phase contrast MRV (2D-PC-MRV) techniques, and demonstrated that the flow velocity increased in the cortical vein corresponding to the activated area during activation status. The increase of flow velocity was calculated to be about 20%. The reason for the increased flow velocity is probably due to the increased regional cerebral blood flow and volume in the activated area. We should be careful to analyze the data of the fMRI because the flow velocity affects the fMRI signal such as the inflow effect and the oblique flow effect. When using the gradient echo method, the effect of the flow velocity is one of the important factors of the fMRI signal. (author)

  16. TUW at the First Total Recall Track

    Science.gov (United States)

    2015-11-20

    TUW AT THE FIRST TOTAL RECALL TRACK MIHAI LUPU Abstract. For the first participation in the TREC Total Recall track, we set out to try some basic...significantly and consistently outperformed it. 1. Introduction As the organizers point out, the focus of the Total Recall Track is to evaluate methods to...TUW AT THE FIRST TOTAL RECALL TRACK 3 The only change we made was at a higher level. The Sofia ML library provides 5 more ML algorithms. The following

  17. Emotional discussions reduce memory recall.

    Science.gov (United States)

    Soleti, Emanuela; Wright, Daniel B; Curci, Antonietta

    2017-05-01

    People often discuss events they have seen and these discussions can influence later recollections. We investigated the effects of factual, emotional, and free retelling discussion on memory recollections of individuals who have witnessed an event. Participants were shown a video, made an initial individual recall, participated in one of the three retelling conditions (emotional versus factual versus free) or a control condition, and then recalled the event individually again. Participants in the factual and free retelling conditions reported more items not previously recalled than participants in the control condition did, while the emotional condition did not show the same advantage. Participants in all three retelling conditions failed to report more previously recalled items as compared with the control condition. Finally, a memory conformity effect was observed for all three retelling conditions. These findings suggest that eyewitnesses' discussions may influence the accuracy of subsequent memory reports, especially when these discussions are focused on emotional details and thoughts.

  18. Characterization of echoes: A Dyson-series representation of individual pulses

    Science.gov (United States)

    Correia, Miguel R.; Cardoso, Vitor

    2018-04-01

    The ability to detect and scrutinize gravitational waves from the merger and coalescence of compact binaries opens up the possibility to perform tests of fundamental physics. One such test concerns the dark nature of compact objects: are they really black holes? It was recently pointed out that the absence of horizons—while keeping the external geometry very close to that of General Relativity—would manifest itself in a series of echoes in gravitational wave signals. The observation of echoes by LIGO/Virgo or upcoming facilities would likely inform us on quantum gravity effects or unseen types of matter. Detection of such signals is in principle feasible with relatively simple tools but would benefit enormously from accurate templates. Here we analytically individualize each echo waveform and show that it can be written as a Dyson series, for arbitrary effective potential and boundary conditions. We further apply the formalism to explicitly determine the echoes of a simple toy model: the Dirac delta potential. Our results allow to read off a few known features of echoes and may find application in the modeling for data analysis.

  19. Effects of the timing and identity of retrieval cues in individual recall: an attempt to mimic cross-cueing in collaborative recall.

    Science.gov (United States)

    Andersson, Jan; Hitch, Graham; Meudell, Peter

    2006-01-01

    Inhibitory effects in collaborative recall have been attributed to cross-cueing among partners, in the same way that part-set cues are known to impair recall in individuals. However, studies of part-set cueing in individuals typically involve presenting cues visually at the start of recall, whereas cross-cueing in collaboration is likely to be spoken and distributed over time. In an attempt to bridge this gap, three experiments investigated effects of presenting spoken part-set or extra-list cues at different times during individual recall. Cues had an inhibitory effect on recollection in the early part of the recall period, especially when presented in immediate succession at the start of recall. There was no difference between the effects of part-set and extra-list cues under these presentation conditions. However, more inhibition was generated by part-set than extra-list cues when cue presentation was distributed throughout recall. These results are interpreted as suggesting that cues presented during recall disrupt memory in two ways, corresponding to either blocking or modifying retrieval processes. Implications for explaining and possibly ameliorating inhibitory effects in collaborative recall are discussed.

  20. A Pilot Study Assessing ECG versus ECHO Ventriculoventricular Optimization in Pediatric Resynchronization Patients.

    Science.gov (United States)

    Punn, Rajesh; Hanisch, Debra; Motonaga, Kara S; Rosenthal, David N; Ceresnak, Scott R; Dubin, Anne M

    2016-02-01

    Cardiac resynchronization therapy indications and management are well described in adults. Echocardiography (ECHO) has been used to optimize mechanical synchrony in these patients; however, there are issues with reproducibility and time intensity. Pediatric patients add challenges, with diverse substrates and limited capacity for cooperation. Electrocardiographic (ECG) methods to assess electrical synchrony are expeditious but have not been extensively studied in children. We sought to compare ECHO and ECG CRT optimization in children. Prospective, pediatric, single-center cross-over trial comparing ECHO and ECG optimization with CRT. Patients were assigned to undergo either ECHO or ECG optimization, followed for 6 months, and crossed-over to the other assignment for another 6 months. ECHO pulsed-wave tissue Doppler and 12-lead ECG were obtained for 5 VV delays. ECG optimization was defined as the shortest QRSD and ECHO optimization as the lowest dyssynchrony index. ECHOs/ECGs were interpreted by readers blinded to optimization technique. After each 6 month period, these data were collected: ejection fraction, velocimetry-derived cardiac index, quality of life, ECHO-derived stroke distance, M-mode dyssynchrony, study cost, and time. Outcomes for each optimization method were compared. From June 2012 to December 2013, 19 patients enrolled. Mean age was 9.1 ± 4.3 years; 14 (74%) had structural heart disease. The mean time for optimization was shorter using ECG than ECHO (9 ± 1 min vs. 68 ± 13 min, P cost for charges was $4,400 ± 700 less for ECG. No other outcome differed between groups. ECHO optimization of synchrony was not superior to ECG optimization in this pilot study. ECG optimization required less time and cost than ECHO optimization. © 2015 Wiley Periodicals, Inc.

  1. Velocities of Auroral Coherent Echoes At 12 and 144 Mhz

    Science.gov (United States)

    Koustov, A. V.; Danskin, D. W.; Makarevitch, R. A.; Uspensky, M. V.; Janhunen, P.; Nishitani, N.; Nozawa, N.; Lester, M.; Milan, S.

    Two Doppler coherent radar systems are currently working at Hankasalmi, Finland, the STARE and CUTLASS radars operating at 144 MHz and 12 MHz, respectively. The STARE beam 3 is nearly co-located with the CUTLASS beam 5 providing an opportunity for echo velocity comparison along the same direction but at significantly different radar frequencies. In this study we consider one event when STARE radar echoes are detected t the same ranges as CUTLASS radar echoes. The observations are complemented by EISCAT measurements of the ionospheric electric field and elec- tron density behavior at one range of 900 km. Two separate situations are studied; for the first one, CUTLASS observed F-region echoes (including the range of the EIS- CAT measurements) while for the second one CUTLASS observed E-region echoes. In both cases STARE E-region measurements were available. We show that F-region CUTLASS velocities agree well with the convection component along the CUTLASS radar beam while STARE velocities are sometimes smaller by a factor of 2-3. For the second case, STARE velocities are found to be either smaller or larger than CUTLASS velocities, depending on range. Plasma physics of E- and F-region irregularities is dis- cussed in attempt to explain inferred relationship between various velocities. Special attention is paid to ionospheric refraction that is important for the detection of 12-MHz echoes.

  2. Short term memory in echo state networks

    OpenAIRE

    Jaeger, H.

    2001-01-01

    The report investigates the short-term memory capacity of echo state recurrent neural networks. A quantitative measure MC of short-term memory capacity is introduced. The main result is that MC 5 N for networks with linear Output units and i.i.d. input, where N is network size. Conditions under which these maximal memory capacities are realized are described. Several theoretical and practical examples demonstrate how the short-term memory capacities of echo state networks can be exploited for...

  3. Three-dimensional MR imaging in the assessment of physeal growth arrest

    Energy Technology Data Exchange (ETDEWEB)

    Sailhan, Frederic; Chotel, Franck; Gollogly, Sohrab; Adam, Philippe; Berard, Jerome [Department of Orthopaedics, Hopital Bebrousse, 29 rue Soeur Bouvier, 69005, Lyon (France); Guibal, Anne-Laure; Guibaud, Laurent [Department of Radiology, Hopital Bebrousse, 29 rue Soeur Bouvier, 69005, Lyon (France)

    2004-09-01

    The purpose of this study is to describe an imaging method for identifying and characterising physeal growth arrest following physeal plate aggression. The authors describe the use of three-dimensional MRI performed with fat-suppressed three-dimensional spoiled gradient-recalled echo sequences followed by manual image reconstruction to create a 3D model of the physeal plate. This retrospective series reports the analysis of 33 bony physeal bridges in 28 children (mean age 10.5 years) with the use of fat-suppressed three-dimensional spoiled gradient-recalled echo imaging and 3D reconstructions from the source images. 3D reconstructions were obtained after the outlining was done manually on each source image. Files of all patients were reviewed for clinical data at the time of MRI, type of injury, age at MRI and bone bridge characteristics on reconstructions. Twenty-one (63%) of the 33 bridges were post-traumatic and were mostly situated in the lower extremities (19/21). The distal tibia was involved in 66% (14/21) of the cases. Bridges due to causes other than trauma were located in the lower extremities in 10/12 cases, and the distal femur represented 60% of these cases. Of the 28 patients, five presented with two bridges involving two different growth plates making a total of 33 physeal bone bars. The location and shape of each bridge was accurately identified in each patient, and in post-traumatic cases, 89% of bone bars were of Ogden type III (central) or I (peripheral). Reconstructions were obtained in 15 min and are easy to interpret. Volumes of the physeal bone bridge(s) and of the remaining normal physis were calculated. The bone bridging represented less than 1% to 47% of the total physeal plate volume. The precise shape and location of the bridge can be visualised on the 3D reconstructions. This information is useful in the surgical management of these deformities; as for the eight patients who underwent bone bar resection, an excellent correspondence was

  4. Three-dimensional MR imaging in the assessment of physeal growth arrest

    International Nuclear Information System (INIS)

    Sailhan, Frederic; Chotel, Franck; Gollogly, Sohrab; Adam, Philippe; Berard, Jerome; Guibal, Anne-Laure; Guibaud, Laurent

    2004-01-01

    The purpose of this study is to describe an imaging method for identifying and characterising physeal growth arrest following physeal plate aggression. The authors describe the use of three-dimensional MRI performed with fat-suppressed three-dimensional spoiled gradient-recalled echo sequences followed by manual image reconstruction to create a 3D model of the physeal plate. This retrospective series reports the analysis of 33 bony physeal bridges in 28 children (mean age 10.5 years) with the use of fat-suppressed three-dimensional spoiled gradient-recalled echo imaging and 3D reconstructions from the source images. 3D reconstructions were obtained after the outlining was done manually on each source image. Files of all patients were reviewed for clinical data at the time of MRI, type of injury, age at MRI and bone bridge characteristics on reconstructions. Twenty-one (63%) of the 33 bridges were post-traumatic and were mostly situated in the lower extremities (19/21). The distal tibia was involved in 66% (14/21) of the cases. Bridges due to causes other than trauma were located in the lower extremities in 10/12 cases, and the distal femur represented 60% of these cases. Of the 28 patients, five presented with two bridges involving two different growth plates making a total of 33 physeal bone bars. The location and shape of each bridge was accurately identified in each patient, and in post-traumatic cases, 89% of bone bars were of Ogden type III (central) or I (peripheral). Reconstructions were obtained in 15 min and are easy to interpret. Volumes of the physeal bone bridge(s) and of the remaining normal physis were calculated. The bone bridging represented less than 1% to 47% of the total physeal plate volume. The precise shape and location of the bridge can be visualised on the 3D reconstructions. This information is useful in the surgical management of these deformities; as for the eight patients who underwent bone bar resection, an excellent correspondence was

  5. Three-dimensional MR imaging in the assessment of physeal growth arrest.

    Science.gov (United States)

    Sailhan, Frédéric; Chotel, Franck; Guibal, Anne-Laure; Gollogly, Sohrab; Adam, Philippe; Bérard, Jérome; Guibaud, Laurent

    2004-09-01

    The purpose of this study is to describe an imaging method for identifying and characterising physeal growth arrest following physeal plate aggression. The authors describe the use of three-dimensional MRI performed with fat-suppressed three-dimensional spoiled gradient-recalled echo sequences followed by manual image reconstruction to create a 3D model of the physeal plate. This retrospective series reports the analysis of 33 bony physeal bridges in 28 children (mean age 10.5 years) with the use of fat-suppressed three-dimensional spoiled gradient-recalled echo imaging and 3D reconstructions from the source images. 3D reconstructions were obtained after the outlining was done manually on each source image. Files of all patients were reviewed for clinical data at the time of MRI, type of injury, age at MRI and bone bridge characteristics on reconstructions. Twenty-one (63%) of the 33 bridges were post-traumatic and were mostly situated in the lower extremities (19/21). The distal tibia was involved in 66% (14/21) of the cases. Bridges due to causes other than trauma were located in the lower extremities in 10/12 cases, and the distal femur represented 60% of these cases. Of the 28 patients, five presented with two bridges involving two different growth plates making a total of 33 physeal bone bars. The location and shape of each bridge was accurately identified in each patient, and in post-traumatic cases, 89% of bone bars were of Ogden type III (central) or I (peripheral). Reconstructions were obtained in 15 min and are easy to interpret. Volumes of the physeal bone bridge(s) and of the remaining normal physis were calculated. The bone bridging represented less than 1% to 47% of the total physeal plate volume. The precise shape and location of the bridge can be visualised on the 3D reconstructions. This information is useful in the surgical management of these deformities; as for the eight patients who underwent bone bar resection, an excellent correspondence was

  6. Relativistic electron dropout echoes induced by interplanetary shocks

    Science.gov (United States)

    Schiller, Q.; Kanekal, S. G.; Boyd, A. J.; Baker, D. N.; Blake, J. B.; Spence, H. E.

    2017-12-01

    Interplanetary shocks that impact Earth's magnetosphere can produce immediate and dramatic responses in the trapped relativistic electron population. One well-studied response is a prompt injection capable of transporting relativistic electrons deep into the magnetosphere and accelerating them to multi-MeV energies. The converse effect, electron dropout echoes, are observations of a sudden dropout of electron fluxes observed after the interplanetary shock arrival. Like the injection echo signatures, dropout echoes can also show clear energy dispersion signals. They are of particular interest because they have only recently been observed and their causal mechanism is not well understood. In the analysis presented here, we show observations of electron drift echo signatures from the Relativistic Electron-Proton Telescope (REPT) and Magnetic Electron and Ion Sensors (MagEIS) onboard NASA's Van Allen Probes mission, which show simultaneous prompt enhancements and dropouts within minutes of the associated with shock impact. We show that the observations associated with both enhancements and dropouts are explained by the inward motion caused by the electric field impulse induced by the interplanetary shock, and either energization to cause the enhancement, or lack of a seed population to cause the dropout.

  7. Sensitivity-encoded (SENSE) proton echo-planar spectroscopic imaging (PEPSI) in the human brain.

    Science.gov (United States)

    Lin, Fa-Hsuan; Tsai, Shang-Yueh; Otazo, Ricardo; Caprihan, Arvind; Wald, Lawrence L; Belliveau, John W; Posse, Stefan

    2007-02-01

    Magnetic resonance spectroscopic imaging (MRSI) provides spatially resolved metabolite information that is invaluable for both neuroscience studies and clinical applications. However, lengthy data acquisition times, which are a result of time-consuming phase encoding, represent a major challenge for MRSI. Fast MRSI pulse sequences that use echo-planar readout gradients, such as proton echo-planar spectroscopic imaging (PEPSI), are capable of fast spectral-spatial encoding and thus enable acceleration of image acquisition times. Combining PEPSI with recent advances in parallel MRI utilizing RF coil arrays can further accelerate MRSI data acquisition. Here we investigate the feasibility of ultrafast spectroscopic imaging at high field (3T and 4T) by combining PEPSI with sensitivity-encoded (SENSE) MRI using eight-channel head coil arrays. We show that the acquisition of single-average SENSE-PEPSI data at a short TE (15 ms) can be accelerated to 32 s or less, depending on the field strength, to obtain metabolic images of choline (Cho), creatine (Cre), N-acetyl-aspartate (NAA), and J-coupled metabolites (e.g., glutamate (Glu) and inositol (Ino)) with acceptable spectral quality and localization. The experimentally measured reductions in signal-to-noise ratio (SNR) and Cramer-Rao lower bounds (CRLBs) of metabolite resonances were well explained by both the g-factor and reduced measurement times. Thus, this technology is a promising means of reducing the scan times of 3D acquisitions and time-resolved 2D measurements. Copyright (c) 2007 Wiley-Liss, Inc.

  8. FIRST DIRECT EVIDENCE OF TWO STAGES IN FREE RECALL

    Directory of Open Access Journals (Sweden)

    Eugen Tarnow

    2015-12-01

    Full Text Available I find that exactly two stages can be seen directly in sequential free recall distributions. These distributions show that the first three recalls come from the emptying of working memory, recalls 6 and above come from a second stage and the 4th and 5th recalls are mixtures of the two.A discontinuity, a rounded step function, is shown to exist in the fitted linear slope of the recall distributions as the recall shifts from the emptying of working memory (positive slope to the second stage (negative slope. The discontinuity leads to a first estimate of the capacity of working memory at 4-4.5 items. The total recall is shown to be a linear combination of the content of working memory and items recalled in the second stage with 3.0-3.9 items coming from working memory, a second estimate of the capacity of working memory. A third, separate upper limit on the capacity of working memory is found (3.06 items, corresponding to the requirement that the content of working memory cannot exceed the total recall, item by item. This third limit is presumably the best limit on the average capacity of unchunked working memory.The second stage of recall is shown to be reactivation: The average times to retrieve additional items in free recall obey a linear relationship as a function of the recall probability which mimics recognition and cued recall, both mechanisms using reactivation (Tarnow, 2008.

  9. Polar mesosphere winter echoes during MaCWAVE

    Directory of Open Access Journals (Sweden)

    S. Kirkwood

    2006-07-01

    Full Text Available During the MaCWAVE winter campaign in January 2003, layers of enhanced echo power known as PMWE (Polar Mesosphere Winter Echoes were detected by the ESRAD 52 MHz radar on several occasions. The cause of these echoes is unclear and here we use observations by meteorological and sounding rockets and by lidar to test whether neutral turbulence or aerosol layers might be responsible. PMWE were detected within 30 min of meteorological rocket soundings (falling spheres on 5 separate days. The observations from the meteorological rockets show that, in most cases, conditions likely to be associated with neutral atmospheric turbulence are not observed at the heights of the PMWE. Observations by instrumented sounding rockets confirm low levels of turbulence and indicate considerable small-scale structure in charge density profiles. Comparison of falling sphere and lidar data, on the other hand, show that any contribution of aerosol scatter to the lidar signal at PMWE heights is less than the detection threshold of about 10%.

  10. Echo in a semibounded plasma confined by an inhomogeneous electrostatic potential

    International Nuclear Information System (INIS)

    Revenchuk, S.M.

    1997-01-01

    The effect of the shape of a confining potential (potential barrier) on linear and nonlinear echoes arising due to the reflection of charged particles by this potential is studied. The model of a plasma confined by a potential that is a monotonous power-law function of the space coordinate is used to study the problem. It is shown that a linear echo (the effect of a nonlocal reflection of waves) arises only for a square-law confining potential. The second-order nonlinear echo caused by two external perturbations with different frequencies can occur for potentials with both square-law and inverse power-law coordinate dependences: the frequency of this echo equals the difference of the frequencies of the externally applied perturbations. In the model considered, an echo at the frequency that is the sum of the frequencies of the external perturbations, which was predicted in the previous papers, does not occur

  11. Numerical modelling of so-called secondary ultrasonic echoes

    International Nuclear Information System (INIS)

    Langenberg, K.J.; Fellinger, P.; Hofmann, C.

    1994-01-01

    The formation of secondary ultrasonic echoes is discussed for a particularly simple testing situation. This discussion is based upon the intuitive visualization of elastic wave propagation as obtained with the numerical EFIT-Code (Elastodynamic Finite Integration Technique). The resulting travel times for the econdary echoes contain well-defined limits as they originate from the simple model of grazing incidence plane longitudinal wave mode conversion. (orig.) [de

  12. Detection of generalized synchronization using echo state networks

    Science.gov (United States)

    Ibáñez-Soria, D.; Garcia-Ojalvo, J.; Soria-Frisch, A.; Ruffini, G.

    2018-03-01

    Generalized synchronization between coupled dynamical systems is a phenomenon of relevance in applications that range from secure communications to physiological modelling. Here, we test the capabilities of reservoir computing and, in particular, echo state networks for the detection of generalized synchronization. A nonlinear dynamical system consisting of two coupled Rössler chaotic attractors is used to generate temporal series consisting of time-locked generalized synchronized sequences interleaved with unsynchronized ones. Correctly tuned, echo state networks are able to efficiently discriminate between unsynchronized and synchronized sequences even in the presence of relatively high levels of noise. Compared to other state-of-the-art techniques of synchronization detection, the online capabilities of the proposed Echo State Network based methodology make it a promising choice for real-time applications aiming to monitor dynamical synchronization changes in continuous signals.

  13. An Improved Algorithm for Predicting Free Recalls

    Science.gov (United States)

    Laming, Donald

    2008-01-01

    Laming [Laming, D. (2006). "Predicting free recalls." "Journal of Experimental Psychology: Learning, Memory, and Cognition," 32, 1146-1163] has shown that, in a free-recall experiment in which the participants rehearsed out loud, entire sequences of recalls could be predicted, to a useful degree of precision, from the prior sequences of stimuli…

  14. 21 CFR 892.1560 - Ultrasonic pulsed echo imaging system.

    Science.gov (United States)

    2010-04-01

    ... system. (a) Identification. An ultrasonic pulsed echo imaging system is a device intended to project a... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Ultrasonic pulsed echo imaging system. 892.1560... receiver. This generic type of device may include signal analysis and display equipment, patient and...

  15. Veridical and false recall in adults who stutter.

    Science.gov (United States)

    Byrd, Courtney T; Sheng, Li; Ratner, Nan Bernstein; Gkalitsiou, Zoi

    2015-02-01

    This study used a false memory paradigm to explore the veridical and false recall of adults who stutter. Twelve adults who stutter and 12 age-matched typically fluent peers listened to and then verbally recalled lists of words that consisted of either semantic or phonological associates or an equal number of semantic and phonological associates (i.e., hybrid condition) of a single, unpresented critical "lure" word. Three parameters of recall performance were measured across these 3 conditions: (a) number of accurately recalled words, (b) order of recall (primacy vs. recency effect), and (c) number of critical lures produced (i.e., false memories). Significant group differences were noted in recall accuracy specific to list type and also list position as well as relative to critical lure productions. Results suggest that certain basic memory processes (i.e., recency effect) and the processing of gist semantic information are largely intact in adults who stutter, but recall of verbatim phonological information and subvocal rehearsal may be deficient.

  16. Proton T2 Relaxation effect of superparamagnetic iron oxide on fast spin echo sequence. Influence of echo number (even or odd) of effective TE

    International Nuclear Information System (INIS)

    Tsuchihashi, Toshio; Maki, Toshio; Kitagawa, Matsuo; Suzuki, Takeshi; Fujita, Isao

    1999-01-01

    The T 2 relaxation effect of the fast spin echo sequence (FSE) was investigated using superparamagnetic iron oxide (SPIO) particles. When even echoes were used as the effective TE of FSE, the signal intensity ratio [signal intensity of FSE/signal intensity of conventional spin echo sequence (CSE)] of FSE and CSE increased, whereas the T 2 relaxation effect of SPIO with FSE was reduced. However, when odd echoes were used, neither signal intensity changed, and weakening of the T 2 relaxation effect, considered a problem with FSE, was reduced. This phenomenon was not observed when the refocusing flip angle was changed to 30 and 60 degrees. However, it was observed when the refocusing flip angle was 120 and 150 degrees. Thus, this phenomenon can be considered to be related to oscillation in longitudinal magnetization when using the Carr-Purcell-Meiboom-Gill (CPMG) technique. (author)

  17. Parallel electric fields detected via conjugate electron echoes during the Echo 7 sounding rocket flight

    Science.gov (United States)

    Nemzek, R. J.; Winckler, J. R.

    1991-01-01

    Electron detectors on the Echo 7 active sounding rocket experiment measured 'conjugate echoes' resulting from artificial electron beam injections. Analysis of the drift motion of the electrons after a complete bounce leads to measurements of the magnetospheric convection electric field mapped to ionospheric altitudes. The magnetospheric field was highly variable, changing by tens of mV/m on time scales of as little as hundreds of millisec. While the smallest-scale magnetospheric field irregularities were mapped out by ionospheric conductivity, larger-scale features were enhanced by up to 50 mV/m in the ionosphere. The mismatch between magnetospheric and ionspheric convection fields indicates a violation of the equipotential field line condition. The parallel fields occurred in regions roughly 10 km across and probably supported a total potential drop of 10-100 V.

  18. Layer disturbances and the radio-echo free zone in ice sheets

    Directory of Open Access Journals (Sweden)

    R. Drews

    2009-08-01

    Full Text Available Radio-echo sounding of the Antarctic and Greenlandic ice sheets often reveals a layer in the lowest hundreds of meters above bedrock more or less free of radio echoes, known as the echo-free zone (EFZ. The cause of this feature is unclear, so far lacking direct evidence for its origin. We compare echoes around the EPICA drill site in Dronning Maud Land, Antarctica, with the dielectric properties, crystal orientation fabrics and optical stratigraphy of the EPICA-DML ice core. We find that echoes disappear in the depth range where the dielectric contrast is blurred, and where the coherency of the layers in the ice core is lost due to disturbances caused by the ice flow. At the drill site, the EFZ onset at ~2100 m marks a boundary, below which the ice core may have experienced flow induced disturbances on various scales. The onset may indicate changing rheology which needs to be accounted for in the modeling of ice sheet dynamics.

  19. Recalled emotions and risk judgments

    Directory of Open Access Journals (Sweden)

    Shosh Shahrabani

    2009-08-01

    Full Text Available The current study is based on a field study of the 2006 Israel-Lebanon war that was conducted in two waves, the first two weeks after the end of the war, and the second 18 months later (2008. The purpose of the study was to examine recalled emotions and perceived risks induced by manipulation using a short videoclip that recalled the sounds of the alarms and the sights of the missile attacks during the war. Before filling in the study questionnaire in 2008, the experimental group watched a short videoclip recalling the events of the war. The control group did not watch the video before filling in the questionnaire. Using the data provided by questionnaires, we analyzed the effect of recalled emotions on perceived risks in two different regions in Israel: the northern region, which was under missile attack daily during the war, and the central region, which was not under missile attacks. The videoclip had a strong effect on the level of recalled emotions in both regions, but it did not affect risk judgments. The results of the analytical framework in the northern region support both the valence approach, in which negative emotion increases pessimism about risk (Johnson and Tversky, 1983, and the modified appraisal tendency theory, which implies different effects for different emotions (Lerner and Keltner, 2000. The current study emphasizes the effects of recalled emotion in the context of the 2006 Israel-Lebanon war on perceived risks among those in the northern region who were under direct attack compared to those who were not directly exposed to the war. Understanding people's responses to stressful events is crucial, not only when these events take place but also over time, since media-induced emotions can influence appraisals and decisions regarding public policies.

  20. Water Quality Indicators Data Review | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  1. Civil Enforcement Case Report Data Dictionary | ECHO | US ...

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  2. Water Pollution Search Criteria Help | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  3. DW_Dashboard_CalendarView.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  4. TRI DMR Dashboard Top Industries_Chemicals.png | ECHO ...

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  5. Hypoxia Task Force Scope and Methodology | ECHO | US ...

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  6. HF Radar Sea-echo from Shallow Water

    Directory of Open Access Journals (Sweden)

    Josh Kohut

    2008-08-01

    Full Text Available HF radar systems are widely and routinely used for the measurement of ocean surface currents and waves. Analysis methods presently in use are based on the assumption of infinite water depth, and may therefore be inadequate close to shore where the radar echo is strongest. In this paper, we treat the situation when the radar echo is returned from ocean waves that interact with the ocean floor. Simulations are described which demonstrate the effect of shallow water on radar sea-echo. These are used to investigate limits on the existing theory and to define water depths at which shallow-water effects become significant. The second-order spectral energy increases relative to the first-order as the water depth decreases, resulting in spectral saturation when the waveheight exceeds a limit defined by the radar transmit frequency. This effect is particularly marked for lower radar transmit frequencies. The saturation limit on waveheight is less for shallow water. Shallow water affects second-order spectra (which gives wave information far more than first-order (which gives information on current velocities, the latter being significantly affected only for the lowest radar transmit frequencies for extremely shallow water. We describe analysis of radar echo from shallow water measured by a Rutgers University HF radar system to give ocean wave spectral estimates. Radar-derived wave height, period and direction are compared with simultaneous shallow-water in-situ measurements.

  7. HST Archival Imaging of the Light Echoes of SN 1987A

    Science.gov (United States)

    Lawrence, S. S.; Hayon, M.; Sugerman, B. E. K.; Crotts, A. P. S.

    2002-12-01

    We have undertaken a search for light echo signals from Supernova 1987A that have been serendipitously recorded in images taken near the 30 Doradus region of the Large Magellanic Cloud by HST. We used the MAST interface to create a database of the 1282 WF/PC, WFPC2 and STIS images taken within 15 arcminutes of the supernova, between 1992 April and 2002 June. These 1282 images are grouped into 125 distinct epochs and pointings, with each epoch containing between 1 and 42 separate exposures. Sorting this database with various programs, aided by the STScI Visual Target Tuner, we have identified 63 pairs of WFPC2 imaging epochs that are not centered on the supernova but that have a significant amount of spatial overlap between their fields of view. These image data were downloaded from the public archive, cleaned of cosmic rays, and blinked to search for light echoes at radii larger than 2 arcminutes from the supernova. Our search to date has focused on those pairs of epochs with the largest degree of overlap. Of 16 pairs of epochs scanned to date, we have detected 3 strong light echoes and one faint, tentative echo signal. We will present direct and difference images of these and any further echoes, as well as the 3-D geometric, photometric and color properties of the echoing dust structures. In addition, a set of 20 epochs of WF/PC and WFPC2 imaging centered on SN 1987A remain to be searched for echoes within 2 arcminutes of the supernova. We will discuss our plans to integrate the high spatial-resolution HST snapshots of the echoes with our extensive, well-time-sampled, ground-based imaging data. We gratefully acknowledge the support of this undergraduate research project through an HST Archival Research Grant (HST-AR-09209.01-A).

  8. Anatomical details of the brainstem and cranial nerves visualized by high resolution readout-segmented multi-shot echo-planar diffusion-weighted images using unidirectional MPG at 3T

    International Nuclear Information System (INIS)

    Naganawa, Shinji; Yamazaki, Masahiro; Kawai, Hisashi; Sone, Michihiko; Nakashima, Tsutomu; Isoda, Haruo

    2011-01-01

    We compared diffusion-weighted imaging (DWI) with readout-segmented multi-shot echo-planar imaging (rs-EPI) and single-shot EPI, both using unidirectional motion-probing gradient, in 10 patients for visualization of the anatomical structures in the brainstem. DWI by rs-EPI was significantly better than DWI by single-shot EPI for visualizing the medial longitudinal fasciculus, lateral lemniscus, corticospinal tract, and seventh/eighth cranial nerves and offered significantly less distortion of the brainstem. (author)

  9. Collision-induced stimulated photon echoes in ‘strong’ magnetic field

    Science.gov (United States)

    Reshetov, V. A.

    2018-05-01

    Collision-induced stimulated photon echoes formed in a gaseous medium on the transition with the angular momentum change Ja=0 → Jb=1 under the action of ‘strong’ longitudinal magnetic field, when the echo pulse becomes unpolarized, are considered with an account of elastic depolarizing collisions. In the case of narrow spectral line the explicit expressions for the echo polarization density matrix and the degree of polarization are obtained. In the case of broad spectral line the results of the numeric calculations reproduce qualitatively the curve obtained in the experiments with ytterbium vapor.

  10. 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

  11. Improved sensitivity and specificity for resting state and task fMRI with multiband multi-echo EPI compared to multi-echo EPI at 7T.

    NARCIS (Netherlands)

    Boyacioglu, R.; Schulz, J.; Koopmans, P.J.; Barth, M.; Norris, David Gordon

    2015-01-01

    A multiband multi-echo (MBME) sequence is implemented and compared to a matched standard multi-echo (ME) protocol to investigate the potential improvement in sensitivity and spatial specificity at 7 T for resting state and task fMRI. ME acquisition is attractive because BOLD sensitivity is less

  12. ECHO Services: Foundational Middleware for a Science Cyberinfrastructure

    Science.gov (United States)

    Burnett, Michael

    2005-01-01

    This viewgraph presentation describes ECHO, an interoperability middleware solution. It uses open, XML-based APIs, and supports net-centric architectures and solutions. ECHO has a set of interoperable registries for both data (metadata) and services, and provides user accounts and a common infrastructure for the registries. It is built upon a layered architecture with extensible infrastructure for supporting community unique protocols. It has been operational since November, 2002 and it available as open source.

  13. Echoing Sentiments: Art and Melancholy in the Work of Pleshette DeArmitt

    Directory of Open Access Journals (Sweden)

    Michael Naas

    2015-12-01

    Full Text Available During those first few days, those first few weeks, truth be told, still today, something in me has wanted simply to echo the sentiments of others. That’s because I myself didn’t know exactly what to say and, truth be told, I still don’t know today. But it’s also because others, including and especially some of the people here today, beginning with my co-panelists and, perhaps especially, early on, Leigh Johnson, knew at the time just what had to be said and so expressed so well the sentiments that we all—that I at least—just wanted to echo. Just to echo, that’s what I wanted to do, because by echoing the sentiments of others I would be able to protect myself just a bit longer, I thought, though also, I self-justified, by echoing others I would be able to give back in some way to Pleshette herself, who showed us in her work that Echo does not simply repeat but initiates even when it looks or sounds as if she is not, Echo who gives back even when it sounds as if she has nothing to give, Echo who not only has her own Narcissus but her own narcissism—which Pleshette would have been the first to tell us is not only not a bad thing but a necessary one, and perhaps just what is needed for a new thinking of empathy, of mourning, and, perhaps, as I will try to say, of the ephemeral.

  14. Experimental observation of fluid echoes in a non-neutral plasma

    International Nuclear Information System (INIS)

    Yu, Jonathan H.; Driscoll, C. Fred

    2002-01-01

    Experimental observation of a nonlinear fluid echo is presented which demonstrates the reversible nature of spatial Landau damping, and that non-neutral plasmas behave as nearly ideal 2D fluids. These experiments are performed on UCSD's CamV Penning-Malmberg trap with magnetized electron plasmas. An initial m i =2 diocotron wave is excited, and the received wall signal damps away in about 5 wave periods. The density perturbation filaments are observed to wrap up as the wave is spatially Landau damped. An m t =4 'tickler' wave is then excited, and this wave also Landau damps. The echo consists of a spontaneous appearance of a third m e =2 wave after the responses to the first two waves have inviscidly damped away. The appearance time of the echo agrees with theory, and data suggests the echo is destroyed at least partly due to saturation

  15. Hepatic fat quantification: a prospective comparison of magnetic resonance spectroscopy and analysis methods for chemical-shift gradient echo magnetic resonance imaging with histologic assessment as the reference standard.

    Science.gov (United States)

    Kang, Bo-Kyeong; Yu, Eun Sil; Lee, Seung Soo; Lee, Youngjoo; Kim, Namkug; Sirlin, Claude B; Cho, Eun Yoon; Yeom, Suk Keu; Byun, Jae Ho; Park, Seong Ho; Lee, Moon-Gyu

    2012-06-01

    The aims of this study were to assess the confounding effects of hepatic iron deposition, inflammation, and fibrosis on hepatic steatosis (HS) evaluation by magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) and to assess the accuracies of MRI and MRS for HS evaluation, using histology as the reference standard. In this institutional review board-approved prospective study, 56 patients gave informed consents and underwent chemical-shift MRI and MRS of the liver on a 1.5-T magnetic resonance scanner. To estimate MRI fat fraction (FF), 4 analysis methods were used (dual-echo, triple-echo, multiecho, and multi-interference), and MRS FF was calculated with T2 correction. Degrees of HS, iron deposition, inflammation, and fibrosis were analyzed in liver resection (n = 37) and biopsy (n = 19) specimens. The confounding effects of histology on fat quantification were assessed by multiple linear regression analysis. Using the histologic degree of HS as the reference standard, the accuracies of each method in estimating HS and diagnosing an HS of 5% or greater were determined by linear regression and receiver operating characteristic analyses. Iron deposition significantly confounded estimations of FF by the dual-echo (P hepatic fat, with coexisting histologic abnormalities having no confounding effects.

  16. Time efficient whole-brain coverage with MR Fingerprinting using slice-interleaved echo-planar-imaging.

    Science.gov (United States)

    Rieger, Benedikt; Akçakaya, Mehmet; Pariente, José C; Llufriu, Sara; Martinez-Heras, Eloy; Weingärtner, Sebastian; Schad, Lothar R

    2018-04-27

    Magnetic resonance fingerprinting (MRF) is a promising method for fast simultaneous quantification of multiple tissue parameters. The objective of this study is to improve the coverage of MRF based on echo-planar imaging (MRF-EPI) by using a slice-interleaved acquisition scheme. For this, the MRF-EPI is modified to acquire several slices in a randomized interleaved manner, increasing the effective repetition time of the spoiled gradient echo readout acquisition in each slice. Per-slice matching of the signal-trace to a precomputed dictionary allows the generation of T 1 and T 2 * maps with integrated B 1 + correction. Subsequent compensation for the coil sensitivity profile and normalization to the cerebrospinal fluid additionally allows for quantitative proton density (PD) mapping. Numerical simulations are performed to optimize the number of interleaved slices. Quantification accuracy is validated in phantom scans and feasibility is demonstrated in-vivo. Numerical simulations suggest the acquisition of four slices as a trade-off between quantification precision and scan-time. Phantom results indicate good agreement with reference measurements (Difference T 1 : -2.4 ± 1.1%, T 2 *: -0.5 ± 2.5%, PD: -0.5 ± 7.2%). In-vivo whole-brain coverage of T 1 , T 2 * and PD with 32 slices was acquired within 3:36 minutes, resulting in parameter maps of high visual quality and comparable performance with single-slice MRF-EPI at 4-fold scan-time reduction.

  17. Memory as a hologram: an analysis of learning and recall.

    Science.gov (United States)

    Franklin, Donald R J; Mewhort, D J K

    2015-03-01

    We present a holographic theory of human memory. According to the theory, a subject's vocabulary resides in a dynamic distributed representation-a hologram. Studying or recalling a word alters both the existing representation of that word in the hologram and all words associated with it. Recall is always prompted by a recall cue (either a start instruction or the word just recalled). Order of report is a joint function of the item and associative information residing in the hologram at the time the report is made. We apply the model to archival data involving simple free recall, learning in multitrial free recall, simple serial recall, and learning in multitrial serial recall. The model captures accuracy and order of report in both free and serial recall. It also captures learning and subjective organisation in multitrial free recall. We offer the model as an alternative to the short- and long-term account of memory postulated in the modal model. (PsycINFO Database Record (c) 2015 APA, all rights reserved).

  18. Monkeys Recall and Reproduce Simple Shapes from Memory

    OpenAIRE

    Basile, Benjamin M.; Hampton, Robert R.

    2013-01-01

    If you draw from memory a picture of the front of your childhood home, you will have demonstrated recall. You could also recognize this house upon seeing it. Unlike recognition, recall demonstrates memory for things that are not present. Recall is necessary for planning and imagining, and can increase the flexibility of navigation, social behavior, and other cognitive skills. Without recall, memory is more limited to recognition of the immediate environment. Amnesic patients are impaired on r...

  19. The value of 3D T1-weighted gradient-echo MR imaging for evaluation of the appendix during pregnancy: preliminary results

    Energy Technology Data Exchange (ETDEWEB)

    Jang, Kyung Mi; Kim, Seong Hyun; Choi, Dongil; Lee, Soon Jin; Rhim, Hyunchul; Park, Min Jung (Depts. of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan Univ. School of Medicine, Seoul (Korea, Republic of)), email: kshyun@skku.edu

    2011-10-15

    Background The use of oral contrast has been essential for the identification of a normal appendix on MR imaging during pregnancy. However, stool could be used as a positive oral contrast as it is characterized by a relatively high signal on T1-weighted imaging, and 3D T1-weighted gradient-echo (T1W-GRE) MR imaging has been used to evaluate 3 mm diameter intestines in fetuses. Purpose To evaluate the added value of 3D T1W-GRE MR imaging in combination with T2-weighted imaging (T2WI) compared to T2WI alone for evaluating the appendix during pregnancy. Material and Methods Eighteen consecutive pregnant patients who were clinically suspected of having acute appendicitis underwent appendix MR imaging which included T2WI with or without spectral presaturation attenuated inversion-recovery (SPAIR) fat suppression, and 3D T1W-GRE with SPAIR fat suppression. Two radiologists reviewed the two image sets (the T2WI set and the combined set of T2WI and 3D T1W-GRE images). Pathologic and clinical results served as the reference standard. The differences in the degree of visibility of the appendix and confidence scale for diagnosing acute appendicitis between two image sets were compared by using the paired Wilcoxon signed rank test. Results For both reviewers, the degree of visibility of the appendix using the combined T2WI and 3D T1W-GRE images was significantly higher than using T2WI alone (P < 0.01), and the confidence levels for acute appendicitis using combined T2WI and 3D T1W-GRE images were significantly different from those using T2WI alone (P < 0.01). In the 13 patients with a normal appendix, both reviewers showed improved confidence levels for appendicitis using combined T2WI and 3D T1W-GRE images than T2WI alone. Conclusion Adding 3D T1W-GRE images to T2WI is helpful for identification of the appendix, as compared to T2WI alone in pregnant women without ingestion of oral contrast material. This may improve diagnostic confidence for acute appendicitis in pregnant

  20. Usefulness of dual echo volumetric isotropic turbo spin echo acquisition (VISTA) in MR imaging of the temporomandibular joint

    International Nuclear Information System (INIS)

    Sugimori, Yuko; Tanaka, Shigeko; Naito, Yukari; Nishimura, Tetsuya; Yamamoto, Akira; Miki, Yukio; Ohfuji, Satoko; Katsumata, Yasutomo

    2013-01-01

    We investigated the ability to detect the articular disk and joint effusion of the temporomandibular joint (TMJ) of a method of dual echo volumetric isotropic turbo spin echo acquisition (DE-VISTA) additional fusion images (AFI). DE-VISTA was performed in the 26 TMJ of 13 volunteers and 26 TMJ of 13 patients. Two-dimensional (2D) dual echo turbo spin echo was performed in the 26 TMJ of 13 volunteers. On a workstation, we added proton density-weighted images (PDWI) and T 2 weighted images (T 2 WI) of the DE-VISTA per voxel to reconstruct DE-VISTA-AFI. Two radiologists reviewed these images visually and quantitatively. Visual evaluation of the articular disk was equivalent between DE-VISTA-AFI and 2D-PDWI. The sliding thin-slab multiplanar reformation (MPR) method of DE-VISTA-AFI could detect all articular disks. The ratio of contrast (CR) of adipose tissue by the articular disk to that of the articular disk itself was significantly higher in DE-VISTA-AFI than DE-VISTA-PDWI (P 2 WI but in only 3 of those joints in 2D-T 2 WI. The CR of joint effusion to adipose tissue on DE-VISTA-AFI did not differ significantly from that on DE-VISTA-PDWI. However, using DE-VISTA-T 2 WI in addition to DE-VISTA-PDWI, we could visually identify joint effusion on DE-VISTA-AFI that could not be identified on DE-VISTA-PDWI alone. DE-VISTA-AFI can depict the articular disk and a small amount of joint effusion by the required plane of MPR using the sliding thin-slab MPR method. (author)

  1. Rehearsal development as development of iterative recall processes.

    Science.gov (United States)

    Lehmann, Martin

    2015-01-01

    Although much is known about the critical importance of active verbal rehearsal for successful recall, knowledge about the mechanisms of rehearsal and their respective development in children is very limited. To be able to rehearse several items together, these items have to be available, or, if presented and rehearsed previously, retrieved from memory. Therefore, joint rehearsal of several items may itself be considered recall. Accordingly, by analyzing free recall, one cannot only gain insight into how recall and rehearsal unfold, but also into how principles that govern children's recall govern children's rehearsal. Over a period of three and a half years (beginning at grade 3) 54 children were longitudinally assessed seven times on several overt rehearsal free recall trials. A first set of analyses on recall revealed significant age-related increases in the primacy effect and an age-invariant recency effect. In the middle portion of the list, wave-shaped recall characteristics emerged and increased with age, indicating grouping of the list into subsequences. In a second set of analyses, overt rehearsal behavior was decomposed into distinct rehearsal sets. Analyses of these sets revealed that the distribution of rehearsals within each set resembled the serial position curves with one- or two-item primacy and recency effects and wave-shaped rehearsal patterns in between. In addition, rehearsal behavior throughout the list was characterized by a decreasing tendency to begin rehearsal sets with the first list item. This result parallels the phenomenon of beginning recall with the first item on short lists and with the last item on longer lists.

  2. Rehearsal development as development of iterative recall processes

    Directory of Open Access Journals (Sweden)

    Martin eLehmann

    2015-03-01

    Full Text Available Although much is known about the critical importance of active verbal rehearsal for successful recall, knowledge about the mechanisms of rehearsal and their respective development in children is very limited. To be able to rehearse several items together, these items have to be available, or, if presented and rehearsed previously, retrieved from memory. Therefore, joint rehearsal of several items may itself be considered recall. Accordingly, by analyzing free recall, one cannot only gain insight into how recall and rehearsal unfold, but also into how principles that govern children’s recall govern children’s rehearsal. Over a period of three and a half years (beginning at grade 3 54 children were longitudinally assessed seven times on several overt rehearsal free recall trials. A first set of analyses on recall revealed significant age-related increases in the primacy effect and an age-invariant recency effect. In the middle portion of the list, wave-shaped recall characteristics emerged and increased with age, indicating grouping of the list into subsequences. In a second set of analyses, overt rehearsal behavior was decomposed into distinct rehearsal sets. Analyses of these sets revealed that the distribution of rehearsals within each set resembled the serial position curves with one- or two-item primacy and recency effects and wave-shaped rehearsal patterns in between. In addition, rehearsal behavior throughout the list was characterized by a decreasing tendency to begin rehearsal sets with the first list item. This result parallels the phenomenon of beginning recall with the first item on short lists and with the last item on longer lists.

  3. Zonal asymmetry of daytime 150-km echoes observed by Equatorial Atmosphere Radar in Indonesia

    Directory of Open Access Journals (Sweden)

    T. Yokoyama

    2009-03-01

    Full Text Available Multi-beam observations of the daytime ionospheric E-region irregularities and the so-called 150-km echoes with the 47-MHz Equatorial Atmosphere Radar (EAR in West Sumatra, Indonesia (0.20° S, 100.32° E, 10.36° S dip latitude are presented. 150-km echoes have been frequently observed by the EAR, and their characteristics are basically the same as the equatorial ones, except for an intriguing zonal asymmetry; stronger echoes in lower altitudes in the east directions, and weaker echoes in higher altitudes in the west. The highest occurrence is seen at 5.7° east with respect to the magnetic meridian, and the altitude gradually increases as viewing from the east to west. Arc structures which return backscatter echoes are proposed to explain the asymmetry. While the strength of radar echoes below 105 km is uniform within the wide coverage of azimuthal directions, the upper E-region (105–120 km echoes also show a different type of zonal asymmetry, which should be generated by an essentially different mechanism from the lower E-region and 150-km echoes.

  4. Bias-Voltage Stabilizer for HVHF Amplifiers in VHF Pulse-Echo Measurement Systems.

    Science.gov (United States)

    Choi, Hojong; Park, Chulwoo; Kim, Jungsuk; Jung, Hayong

    2017-10-23

    The impact of high-voltage-high-frequency (HVHF) amplifiers on echo-signal quality is greater with very-high-frequency (VHF, ≥100 MHz) ultrasound transducers than with low-frequency (LF, ≤15 MHz) ultrasound transducers. Hence, the bias voltage of an HVHF amplifier must be stabilized to ensure stable echo-signal amplitudes. We propose a bias-voltage stabilizer circuit to maintain stable DC voltages over a wide input range, thus reducing the harmonic-distortion components of the echo signals in VHF pulse-echo measurement systems. To confirm the feasibility of the bias-voltage stabilizer, we measured and compared the deviations in the gain of the HVHF amplifier with and without a bias-voltage stabilizer. Between -13 and 26 dBm, the measured gain deviations of a HVHF amplifier with a bias-voltage stabilizer are less than that of an amplifier without a bias-voltage stabilizer. In order to confirm the feasibility of the bias-voltage stabilizer, we compared the pulse-echo responses of the amplifiers, which are typically used for the evaluation of transducers or electronic components used in pulse-echo measurement systems. From the responses, we observed that the amplitudes of the echo signals of a VHF transducer triggered by the HVHF amplifier with a bias-voltage stabilizer were higher than those of the transducer triggered by the HVHF amplifier alone. The second, third, and fourth harmonic-distortion components of the HVHF amplifier with the bias-voltage stabilizer were also lower than those of the HVHF amplifier alone. Hence, the proposed scheme is a promising method for stabilizing the bias voltage of an HVHF amplifier, and improving the echo-signal quality of VHF transducers.

  5. Workshop on neutron spin-echo

    Energy Technology Data Exchange (ETDEWEB)

    Aynajian, P.; Habicht, K.; Keller, Th.; Keimer, B.; Mezei, F.; Monkenbusch, M.; Allgaier, J.; Richter, D.; Fetters, L.J.; Muller, K.; Kreiling, S.; Dehnicke, K.; Greiner, A.; Ehlers, G.; Arbe, A.; Colmenero, J.; Richter, D.; Farago, B.; Monkenbusch, M.; Ohl, M.; Butzek, M.; Kozielewski, T.; Monkenbusch, M.; Richter, D.; Pappas, C.; Hillier, A.; Manuel, P.; Cywinski, R.; Bentley, P.; Alba, M.; Mezei, F.; Campbell, I.A.; Zimmermann, U.; Ellis, J.; Jobic, H.; Pickup, R.M.; Pappas, C.; Farago, B.; Cywinski, R.; Haussler, W.; Holderer, O.; Frielinghaus, H.; Byelov, D.; Monkenbusch, M.; Allgaier, J.; Richter, D.; Egger, H.; Hellweg, Th.; Malikova, N.; Cadene, A.; Marry, V.; Dubois, E.; Turq, P.; Gardner, J.S.; Ehlers, G.; Bramwell, St.S.; Grigoriev, S.; Kraan, W.; Rekveldt, T.; Bouwman, W.; Van Dijk, N.; Falus, P.; Vorobiev, A.; Major, J.; Felcher, G.P.; Te-velthuis, S.; Dosch, H.; Vorobiev, A.; Dridi, M.H.; Major, J.; Dosch, H.; Falus, P.; Felcher, G.P.; Te Velthuis, S.G.E.; Bleuel, M.; Broell, M.; Lang, E.; Littrell, K.; Gahler, R.; Lal, J.; Lauter, H.; Toperverg, B.; Lauter, V.; Jernenkov, M.; Stueber, S.; Enderle, M.; Janoschek, M.; Keller, Th.; Klimko, S.; Boeni, P.; Nagao, M.; Yamada, N.; Kawabata, Y.; Seto, H.; Takeda, T.; Yoshizawa, H.; Yoshida, K.; Yamaguchi, T.; Bellissent-Funel, M.C.; Longeville, St

    2005-07-01

    This document gathers the abstracts of most papers presented at the workshop. Neutron spin-echo (NSE) spectroscopy is a well established technique with a growing expert user community, the aim of the meeting was to discuss the latest achievements in neutron spin-echo science and instrumentation. One of the applications presented is the investigation on the microscopic scale of the dynamics of water in montmorillonite clays with Na{sup +} and Cs{sup +} ions in monolayer and bilayer states. The NSE technique has been used in the normal and resonance modes. NSE results show consistently slower dynamics (higher relaxation times) than both time-of-flight technique (TOF) and classical molecular dynamics simulations (MD). In the present TOF and NSE experiments, anisotropy of the water motion in the interlayer is almost impossible to detect, due to the use of powder samples and insufficient resolution. (A.C.)

  6. Accuracy of multiecho magnitude-based MRI (M-MRI) for estimation of hepatic proton density fat fraction (PDFF) in children.

    Science.gov (United States)

    Zand, Kevin A; Shah, Amol; Heba, Elhamy; Wolfson, Tanya; Hamilton, Gavin; Lam, Jessica; Chen, Joshua; Hooker, Jonathan C; Gamst, Anthony C; Middleton, Michael S; Schwimmer, Jeffrey B; Sirlin, Claude B

    2015-11-01

    To assess accuracy of magnitude-based magnetic resonance imaging (M-MRI) in children to estimate hepatic proton density fat fraction (PDFF) using two to six echoes, with magnetic resonance spectroscopy (MRS) -measured PDFF as a reference standard. This was an IRB-approved, HIPAA-compliant, single-center, cross-sectional, retrospective analysis of data collected prospectively between 2008 and 2013 in children with known or suspected nonalcoholic fatty liver disease (NAFLD). Two hundred eighty-six children (8-20 [mean 14.2 ± 2.5] years; 182 boys) underwent same-day MRS and M-MRI. Unenhanced two-dimensional axial spoiled gradient-recalled-echo images at six echo times were obtained at 3T after a single low-flip-angle (10°) excitation with ≥ 120-ms recovery time. Hepatic PDFF was estimated using the first two, three, four, five, and all six echoes. For each number of echoes, accuracy of M-MRI to estimate PDFF was assessed by linear regression with MRS-PDFF as reference standard. Accuracy metrics were regression intercept, slope, average bias, and R(2) . MRS-PDFF ranged from 0.2-40.4% (mean 13.1 ± 9.8%). Using three to six echoes, regression intercept, slope, and average bias were 0.46-0.96%, 0.99-1.01, and 0.57-0.89%, respectively. Using two echoes, these values were 2.98%, 0.97, and 2.72%, respectively. R(2) ranged 0.98-0.99 for all methods. Using three to six echoes, M-MRI has high accuracy for hepatic PDFF estimation in children. © 2015 Wiley Periodicals, Inc.

  7. Study of turbulent flow using Half-Fourier Echo-Planar imaging

    International Nuclear Information System (INIS)

    Rodriguez, A.O.

    2006-01-01

    The Echo-Planar Imaging technique combined with a partial Fourier acquisition method was used to obtain velocity images for liquid flows in a circular cross-section pipe at Reynolds number of up to 8000. This partial-Fourier imaging scheme is able to generate shorter echo times than the full-Fourier Echo-Planar Imaging methods, reducing the signal attenuation due to T2 * and flow. Velocity images along the z axis were acquired with a time-scale of 80 ms thus obtaining a real-time description of flow in both the laminar and turbulent regimes. Velocity values and velocity fluctuations were computed with the flow image data. A comparison plot of NMR velocity and bulk velocity and a plot of velocity fluctuations were calculated to investigate the feasibility of this imaging technique. Flow encoded Echo-Planar Imaging together with a reduced data acquisition method can provide us with a real-time technique to capture instantaneous images of the flow field for both laminar and turbulent regimes. (author)

  8. Collaborative recall of details of an emotional film.

    Science.gov (United States)

    Wessel, Ineke; Zandstra, Anna Roos E; Hengeveld, Hester M E; Moulds, Michelle L

    2015-01-01

    Collaborative inhibition refers to the phenomenon that when several people work together to produce a single memory report, they typically produce fewer items than when the unique items in the individual reports of the same number of participants are combined (i.e., nominal recall). Yet, apart from this negative effect, collaboration may be beneficial in that group members remove errors from a collaborative report. Collaborative inhibition studies on memory for emotional stimuli are scarce. Therefore, the present study examined both collaborative inhibition and collaborative error reduction in the recall of the details of emotional material in a laboratory setting. Female undergraduates (n = 111) viewed a film clip of a fatal accident and subsequently engaged in either collaborative (n = 57) or individual recall (n = 54) in groups of three. The results show that, across several detail categories, collaborating groups recalled fewer details than nominal groups. However, overall, nominal recall produced more errors than collaborative recall. The present results extend earlier findings on both collaborative inhibition and error reduction to the recall of affectively laden material. These findings may have implications for the applied fields of forensic and clinical psychology.

  9. A study of MRI gradient echo signals from discrete magnetic particles with considerations of several parameters in simulations.

    Science.gov (United States)

    Kokeny, Paul; Cheng, Yu-Chung N; Xie, He

    2018-05-01

    Modeling MRI signal behaviors in the presence of discrete magnetic particles is important, as magnetic particles appear in nanoparticle labeled cells, contrast agents, and other biological forms of iron. Currently, many models that take into account the discrete particle nature in a system have been used to predict magnitude signal decays in the form of R2* or R2' from one single voxel. Little work has been done for predicting phase signals. In addition, most calculations of phase signals rely on the assumption that a system containing discrete particles behaves as a continuous medium. In this work, numerical simulations are used to investigate MRI magnitude and phase signals from discrete particles, without diffusion effects. Factors such as particle size, number density, susceptibility, volume fraction, particle arrangements for their randomness, and field of view have been considered in simulations. The results are compared to either a ground truth model, theoretical work based on continuous mediums, or previous literature. Suitable parameters used to model particles in several voxels that lead to acceptable magnetic field distributions around particle surfaces and accurate MR signals are identified. The phase values as a function of echo time from a central voxel filled by particles can be significantly different from those of a continuous cubic medium. However, a completely random distribution of particles can lead to an R2' value which agrees with the prediction from the static dephasing theory. A sphere with a radius of at least 4 grid points used in simulations is found to be acceptable to generate MR signals equivalent from a larger sphere. Increasing number of particles with a fixed volume fraction in simulations reduces the resulting variance in the phase behavior, and converges to almost the same phase value for different particle numbers at each echo time. The variance of phase values is also reduced when increasing the number of particles in a fixed

  10. Comparison of INTAKE24 (an Online 24-h Dietary Recall Tool) with Interviewer-Led 24-h Recall in 11-24 Year-Old.

    Science.gov (United States)

    Bradley, Jennifer; Simpson, Emma; Poliakov, Ivan; Matthews, John N S; Olivier, Patrick; Adamson, Ashley J; Foster, Emma

    2016-06-09

    Online dietary assessment tools offer a convenient, low cost alternative to traditional dietary assessment methods such as weighed records and face-to-face interviewer-led 24-h recalls. INTAKE24 is an online multiple pass 24-h recall tool developed for use with 11-24 year-old. The aim of the study was to undertake a comparison of INTAKE24 (the test method) with interviewer-led multiple pass 24-h recalls (the comparison method) in 180 people aged 11-24 years. Each participant completed both an INTAKE24 24-h recall and an interviewer-led 24-h recall on the same day on four occasions over a one-month period. The daily energy and nutrient intakes reported in INTAKE24 were compared to those reported in the interviewer-led recall. Mean intakes reported using INTAKE24 were similar to the intakes reported in the interviewer-led recall for energy and macronutrients. INTAKE24 was found to underestimate energy intake by 1% on average compared to the interviewer-led recall with the limits of agreement ranging from minus 49% to plus 93%. Mean intakes of all macronutrients and micronutrients (except non-milk extrinsic sugars) were within 4% of the interviewer-led recall. Dietary assessment that utilises technology may offer a viable alternative and be more engaging than paper based methods, particularly for children and young adults.

  11. Examining the Relationship between Free Recall and Immediate Serial Recall: The Role of List Length, Strategy Use, and Test Expectancy

    Science.gov (United States)

    Grenfell-Essam, Rachel; Ward, Geoff

    2012-01-01

    Recent findings suggest that the immediate free recall (IFR) of short lists is similar to immediate serial recall (ISR). These findings were obtained using a methodology in which participants did not know the list length in advance of each list, and this uncertainty may have encouraged participants to adopt atypical recall strategies. Therefore,…

  12. 40 CFR 51.370 - Compliance with recall notices.

    Science.gov (United States)

    2010-07-01

    ... shall have an electronic means to identify recalled vehicles based on lists of VINs with unresolved... Requirements § 51.370 Compliance with recall notices. States shall establish methods to ensure that vehicles..., receive the required repairs. States shall require that owners of recalled vehicles have the necessary...

  13. Fast, three-dimensional, MR Imaging for polymer gel dosimetric applications involving high dose and steep dose gradients

    International Nuclear Information System (INIS)

    Sandilos, Panagiotis; Baras, Panagiotis; Georgiou, Evangelos; Dardoufas, Konstantinos; Karaiskos, Pantelis; Papagiannis, Panagiotis; Paschalis, Theodoros; Tatsis, Elias; Torrens, Michael; Vlahos, Lampros

    2006-01-01

    Polymer gels constitute water equivalent integrating detectors, which, combined with magnetic resonance imaging (MRI), can provide accurate three dimensional (3D) dose distributions in contemporary radiotherapy applications where the small field dimensions and steep dose gradients induce limitations to conventional dosimeters. One of the main obstacles for adapting the method for routine use in the clinical setting is the cost effectiveness of the MRI readout method. Currently, optimized Carr-Purcell-Meiboom-Gill (CPMG) multiple spin echo imaging pulse sequences are commonly used which however result in long imaging times. This work evaluates the efficiency of 3D, dual-echo, k-space segmented turbo spin echo (TSE) scanning sequences for accurate dosimetry with sub-millimetre spatial resolution in strenuous radiation therapy applications. PABIG polymer gel dosimeters were irradiated with an 192 Ir High Dose Rate brachytherapy source, the 4 mm and 8 mm collimator helmets of a gamma knife unit and a custom made x-knife collimator of 1 cm diameter. Profile and dose distribution measurements using TSE are benchmarked against corresponding findings obtained by the commonly used, but time consuming, CPMG sequence as well as treatment planning calculations, Monte Carlo (MC) simulations and film measurements. The implementation of a high Turbo factor was found to provide comparable accuracy, allowing a 64-fold MRI scan acceleration compared to conventional multi-echo sequences. The availability of TSE sequences in typical MRI installations greatly facilitates the introduction of polymer gel dosimetry in the clinical environment as a practicable tool for the determination of full 3D dose distributions in contemporary radiotherapy applications

  14. Fast, three-dimensional, MR Imaging for polymer gel dosimetric applications involving high dose and steep dose gradients

    Energy Technology Data Exchange (ETDEWEB)

    Sandilos, Panagiotis [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece); Baras, Panagiotis [Philips Hellas Medical Systems, 44 Kifissias Ave., Maroussi 151 25, Athens (Greece); Georgiou, Evangelos [Medical Physics Department, University of Athens, 75 Mikras Asias, 115 27 Athens (Greece); Dardoufas, Konstantinos [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece): Hygeia Hospital, Kiffisias Avenue and 4 Erythrou Stavrou, Marousi, 151 23 Athens (Greece); Karaiskos, Pantelis [Medical Physics Department, University of Athens, 75 Mikras Asias, 115 27 Athens (Greece): Hygeia Hospital, Kiffisias Avenue and 4 Erythrou Stavrou, Marousi, 151 23 Athens (Greece)]. E-mail: p.karaiskos@hygeia.gr; Papagiannis, Panagiotis [Physics Department, Nuclear and Particle Physics Section, University of Athens, Panepistimioupolis, Ilisia, 157 71 Athens (Greece); Paschalis, Theodoros [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece); Tatsis, Elias [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece); Torrens, Michael [Hygeia Hospital, Kiffisias Avenue and 4 Erythrou Stavrou, Marousi, 151 23 Athens (Greece); Vlahos, Lampros [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece)

    2006-12-20

    Polymer gels constitute water equivalent integrating detectors, which, combined with magnetic resonance imaging (MRI), can provide accurate three dimensional (3D) dose distributions in contemporary radiotherapy applications where the small field dimensions and steep dose gradients induce limitations to conventional dosimeters. One of the main obstacles for adapting the method for routine use in the clinical setting is the cost effectiveness of the MRI readout method. Currently, optimized Carr-Purcell-Meiboom-Gill (CPMG) multiple spin echo imaging pulse sequences are commonly used which however result in long imaging times. This work evaluates the efficiency of 3D, dual-echo, k-space segmented turbo spin echo (TSE) scanning sequences for accurate dosimetry with sub-millimetre spatial resolution in strenuous radiation therapy applications. PABIG polymer gel dosimeters were irradiated with an {sup 192}Ir High Dose Rate brachytherapy source, the 4 mm and 8 mm collimator helmets of a gamma knife unit and a custom made x-knife collimator of 1 cm diameter. Profile and dose distribution measurements using TSE are benchmarked against corresponding findings obtained by the commonly used, but time consuming, CPMG sequence as well as treatment planning calculations, Monte Carlo (MC) simulations and film measurements. The implementation of a high Turbo factor was found to provide comparable accuracy, allowing a 64-fold MRI scan acceleration compared to conventional multi-echo sequences. The availability of TSE sequences in typical MRI installations greatly facilitates the introduction of polymer gel dosimetry in the clinical environment as a practicable tool for the determination of full 3D dose distributions in contemporary radiotherapy applications.

  15. 9 CFR 381.311 - Recall procedure.

    Science.gov (United States)

    2010-01-01

    ... CERTIFICATION POULTRY PRODUCTS INSPECTION REGULATIONS Canning and Canned Products § 381.311 Recall procedure... 9 Animals and Animal Products 2 2010-01-01 2010-01-01 false Recall procedure. 381.311 Section 381.311 Animals and Animal Products FOOD SAFETY AND INSPECTION SERVICE, DEPARTMENT OF AGRICULTURE AGENCY...

  16. Recall initiation strategies must be controlled in training studies that use immediate free recall tasks to measure the components of working memory capacity across time.

    Science.gov (United States)

    Gibson, Bradley S; Gondoli, Dawn M; Johnson, Ann C; Robison, Matthew K

    2014-01-01

    There has been great interest in using working memory (WM) training regimens as an alternative treatment for ADHD, but it has recently been concluded that existing training regimens may not be optimally designed because they target the primary memory component but not the secondary component of WM capacity. This conclusion requires the ability to accurately measure changes in primary and secondary memory abilities over time. The immediate free recall task has been used in previous studies to measure these changes; however, one concern with these tasks is that the recall order required on training exercises may influence the recall strategy used during free recall, which may in turn influence the relative number of items recalled from primary and secondary memory. To address this issue, previous training studies have explicitly controlled recall strategy before and after training. However, the necessity of controlling for recall strategies has not been explicitly tested. The present study investigated the effects of forward-serial-order training on free recall performance under conditions in which recall strategy was not controlled using a sample of adolescents with ADHD. Unlike when recall order was controlled, the main findings showed selective improvement of the secondary memory component (as opposed to the primary memory component) when recall order was uncontrolled. This finding advances our understanding of WM training by highlighting the importance of controlling for recall strategies when free recall tasks are used to measure changes in the primary and secondary components of WM across time.

  17. Video context-dependent recall.

    Science.gov (United States)

    Smith, Steven M; Manzano, Isabel

    2010-02-01

    In two experiments, we used an effective new method for experimentally manipulating local and global contexts to examine context-dependent recall. The method included video-recorded scenes of real environments, with target words superimposed over the scenes. In Experiment 1, we used a within-subjects manipulation of video contexts and compared the effects of reinstatement of a global context (15 words per context) with effects of less overloaded context cues (1 and 3 words per context) on recall. The size of the reinstatement effects in Experiment 1 show how potently video contexts can cue recall. A strong effect of cue overload was also found; reinstatement effects were smaller, but still quite robust, in the 15 words per context condition. The powerful reinstatement effect was replicated for local contexts in Experiment 2, which included a no-contexts-reinstated group, a control condition used to determine whether reinstatement of half of the cues caused biased output interference for uncued targets. The video context method is a potent way to investigate context-dependent memory.

  18. Water Dashboard Help | ECHO | US EPA

    Science.gov (United States)

    The dashboards on the ECHO website are specialized to track both facility and agency performance as they relate to compliance with and enforcement of environmental standards under the Clean Water Act (CWA).

  19. Climatology and variability in the ECHO coupled GCM

    International Nuclear Information System (INIS)

    Latif, M.; Stockdale, T.; Wolff, J.; Burgers, G.; Maier-Reimer, E.; Junge, M.M.; Arpe, K.; Bengtsson, L.

    1993-01-01

    ECHO is a new global coupled ocean-atmosphere general circulation model (GCM), consisting of the Hamburg version of the European Centre atmospheric GCM (ECHAM) and the Hamburg Primitive Equation ocean GCM (HOPE). We performed a twenty year integration with ECHO. Climate drift is significant, but typical in the open oceans. Near the boundaries, however, SST errors are considerably larger. The coupled model simulates an irregular ENSO cycle in the tropical Pacific, with spatial patterns similar to those observed. The mechanism behind the model ENSO is related to the subsurface memory of the system, but stochastic forcing by the atmosphere seems to be also important. The variability, however, is somewhat weaker relative to observations. ECHO also simulates significant interannual variability in midlatitudes. Consistent with observations, variability over the North Pacific can be partly attributed to remote forcing from the tropics. In contract, the interannual variability over the North Atlantic appears to be generated locally. Indications for decadal-scale variability are also found over the North Atlantic. (orig.)

  20. Involuntary conscious memory facilitates cued recall performance: further evidence that chaining occurs during voluntary recall.

    Science.gov (United States)

    Mace, John H

    2009-01-01

    Recent studies have shown that conscious recollection of the past occurs spontaneously when subjects voluntarily recall their own past experiences or a list of previously studied words. Naturalistic diary studies and laboratory studies of this phenomenon, often called involuntary conscious memory (ICM), show that it occurs in 2 ways. One is direct ICM retrieval, which occurs when a cue spontaneously triggers a conscious memory; the other is chained ICM retrieval, which occurs when a retrieved conscious memory spontaneously triggers another. Laboratory studies investigating ICM show that chained ICM retrieval occurs on voluntary autobiographical memory tasks. The present results show that chained ICM retrieval also occurs on a voluntary word list memory task (cued recall). These results are among a handful suggesting that ICM retrieval routinely occurs during voluntary recall.

  1. Two-pulse and stimulated nuclear-quadrupole-resonance echoes in YAlO3:Pr3+

    International Nuclear Information System (INIS)

    Erickson, L.E.

    1991-01-01

    The dephasing of trivalent praseodymium dilute in yttrium aluminum oxide (YAlO 3 ) in the ground electronic state 3 H 4 state is evaluated using an optically detected method, to measure two-rf-pulse- and three-rf-pulse-stimulated nuclear quadrupole echoes. The magnitude of the echo is obtained by detecting the weak Raman optical field generated by the interaction of the magnetic moment of the echo and a light beam resonant with the 3 H 4 (0 cm 1 ) to 1 D 2 (16 374 cm -1 ) optical transition. This same light beam is used as an optical pump (37-ms duration) prior the rf-pulse sequence to increase the population difference of the hyperfine energy levels, thereby improving the echo signal. The light is turned off 9 ms before the rf-pulse sequence and remains off until the echo to avoid optical-pumping effects on the measured nuclear-quadrupole-resonance (NQR) echo lifetime. The dephasing time T 2 from two-pulse nuclear-quadrupole-echo measurement is found to be 366±29 μs

  2. A spin echo study of A15 intermetallic compounds

    International Nuclear Information System (INIS)

    Schoep, G.K.

    1976-01-01

    This thesis mainly concerns the measurement of spin-lattice relaxation times in intermetallic compounds of the bcc lattice structure, having the formula V 3 X (C = Pt, Ir, Os, Pd, Rh, Ni, Co, Au). When, in a spin echo experiment, a two-pulse sequence was applied, several quadrupolar echoes were observed. Special attention is given to the 'forbidden' echoes (absol.(Δm')GT1) in V 3 Au and V 3 Co. In relation to the V 3 X compounds, several characteristics are discussed including temperature dependence and concentration dependence of spin relaxation times, superconductivity and the importance of d-state electrons in determination of the spin relaxation times. Finally, the above characteristics were determined for 6 different samples of the vanadium-gold alloy, V 3 Au, specifically

  3. Histogram analysis of noise performance on fractional anisotropy brain MR image with different diffusion gradient numbers

    International Nuclear Information System (INIS)

    Chang, Yong Min; Kim, Yong Sun; Kang, Duk Sik; Lee, Young Joo; Sohn, Chul Ho; Woo, Seung Koo; Suh, Kyung Jin

    2005-01-01

    We wished to analyze, qualitatively and quantitatively, the noise performance of fractional anisotropy brain images along with the different diffusion gradient numbers by using the histogram method. Diffusion tensor images were acquired using a 3.0 T MR scanner from ten normal volunteers who had no neurological symptoms. The single-shot spin-echo EPI with a Stejskal-Tanner type diffusion gradient scheme was employed for the diffusion tensor measurement. With a b-valuee of 1000 s/mm 2 , the diffusion tensor images were obtained for 6, 11, 23, 35 and 47 diffusion gradient directions. FA images were generated for each DTI scheme. The histograms were then obtained at selected ROIs for the anatomical structures on the FA image. At the same ROI location, the mean FA value and the standard deviation of the mean FA value were calculated. The quality of the FA image was improved as the number of diffusion gradient directions increased by showing better contrast between the WM and GM. The histogram showed that the variance of FA values was reduced as the number of diffusion gradient directions increased. This histogram analysis was in good agreement with the result obtained using quantitative analysis. The image quality of the FA map was significantly improved as the number of diffusion gradient directions increased. The histogram analysis well demonstrated that the improvement in the FA images resulted from the reduction in the variance of the FA values included in the ROI

  4. Eye Movements and Overt Rehearsal in Word Recall

    Science.gov (United States)

    Geiselman, Ralph E.; Bellezza, Francis S.

    1977-01-01

    Rates of overt rehearsal and eye movement were compared to each other, and were also compared as predictors of immediate and delayed recall. Concludes that total looking time was the best predictor of long-term retention and that recall performance following overt rehearsal was different from recall performance following silent study. (Editor/RK)

  5. Recognition during recall failure: Semantic feature matching as a mechanism for recognition of semantic cues when recall fails.

    Science.gov (United States)

    Cleary, Anne M; Ryals, Anthony J; Wagner, Samantha R

    2016-01-01

    Research suggests that a feature-matching process underlies cue familiarity-detection when cued recall with graphemic cues fails. When a test cue (e.g., potchbork) overlaps in graphemic features with multiple unrecalled studied items (e.g., patchwork, pitchfork, pocketbook, pullcork), higher cue familiarity ratings are given during recall failure of all of the targets than when the cue overlaps in graphemic features with only one studied target and that target fails to be recalled (e.g., patchwork). The present study used semantic feature production norms (McRae et al., Behavior Research Methods, Instruments, & Computers, 37, 547-559, 2005) to examine whether the same holds true when the cues are semantic in nature (e.g., jaguar is used to cue cheetah). Indeed, test cues (e.g., cedar) that overlapped in semantic features (e.g., a_tree, has_bark, etc.) with four unretrieved studied items (e.g., birch, oak, pine, willow) received higher cue familiarity ratings during recall failure than test cues that overlapped in semantic features with only two (also unretrieved) studied items (e.g., birch, oak), which in turn received higher familiarity ratings during recall failure than cues that did not overlap in semantic features with any studied items. These findings suggest that the feature-matching theory of recognition during recall failure can accommodate recognition of semantic cues during recall failure, providing a potential mechanism for conceptually-based forms of cue recognition during target retrieval failure. They also provide converging evidence for the existence of the semantic features envisaged in feature-based models of semantic knowledge representation and for those more concretely specified by the production norms of McRae et al. (Behavior Research Methods, Instruments, & Computers, 37, 547-559, 2005).

  6. Significance of spin-echo intracardiac signal during cine cardiac MR imaging

    International Nuclear Information System (INIS)

    Feiglin, D.H.I.; O'Donnell, J.K.

    1987-01-01

    Thirty patient studies were performed using several multisection spin multi-echo pulse sequences (SEPS) formattable into the cine mode, with repetition time (TR)≤RR interval and 18 msec ≤ echo time (TE) ≤ 64 msec. Thirteen studies were performed in patients with various cardiomyopathies, ten in patients with cardiac tumors, and seven in healthy volunteers. The SEPS in the multi-echo acquisition format differentiated between tumor and stasis in terms of signal behavior. Healthy subjects may exhibit stasis of flow adjacent to the endocardium during the cardiac cycle

  7. Magnetic resonance imaging metallic artifact of commonly encountered surgical implants and foreign material.

    Science.gov (United States)

    Sutherland-Smith, James; Tilley, Brenda

    2012-01-01

    Magnetic resonance imaging (MRI) artifacts secondary to metallic implants and foreign bodies are well described. Herein, we provide quantitative data from veterinary implants including total hip arthroplasty implants, cranial cruciate repair implants, surgical screws, a skin staple, ligation clips, an identification microchip, ameroid constrictor, and potential foreign bodies including air gun and BB projectiles and a sewing needle. The objects were scanned in a gelatin phantom with plastic grid using standardized T2-weighted turbo-spin echo (TSE), T1-weighted spin echo, and T2*-weighted gradient recalled echo (GRE) image acquisitions at 1.5 T. Maximum linear dimensions and areas of signal voiding and grid distortion were calculated using a DICOM workstation for each sequence and object. Artifact severity was similar between the T2-weighted TSE and T1-weighted images, while the T2*-weighted images were most susceptible to artifact. Metal type influenced artifact size with the largest artifacts arising from steel objects followed by surgical stainless steel, titanium, and lead. For animals with metallic surgical implants or foreign bodies, the quantification of the artifact size will help guide clinicians on the viability of MRI. © 2012 Veterinary Radiology & Ultrasound.

  8. Assmentment of myocardial perfusion by magnetic resonance imaging: on the way to clinical application

    International Nuclear Information System (INIS)

    Fischer, S.E.; Lorenz, C.H.

    1997-01-01

    Magnetic resonance imaging detects the flow of contrast - enhanced blood and even allows the quantitative assessment of myocardial perfusion. The clinical application of this method is being held back by the difficulties in image evaluation and the limitation of standard techniques to the acquisition of a single slice per heart beat cycle. Recent developments in scanner hardware as well as in image acquisition techniques open up the possibility of assessing myocardial perfusion over the entire heart with a spatial resolution in the range of 2 mm. As an example of such a new scanning strategy, a segmented gradient-echo recalled echo planar imaging sequence with preceding saturation is discussed and results in a patient with an infarction are presented. The clinical use of perfusion assessment covering the entire heart for the diagnosis of coronary artery disease is enhanced by the flexibility of magnetic resonance imaging for the assessment of functional cardiac parameters. (orig.) [de

  9. Water Pollution Search Results Help - TRI | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  10. TRI DMR Dashboard Summary Table.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  11. TRI DMR Dashboard Top Industries Graph.png | ECHO | US ...

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  12. TRI DMR Dashboard Pie Chart.png | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  13. Peanut Product Recalls

    Data.gov (United States)

    U.S. Department of Health & Human Services — This list includes human and pet food subject to recall in the United States since January 2009 related to peanut products distributed by Peanut Corporation of...

  14. Comparison of INTAKE24 (an Online 24-h Dietary Recall Tool with Interviewer-Led 24-h Recall in 11–24 Year-Old

    Directory of Open Access Journals (Sweden)

    Jennifer Bradley

    2016-06-01

    Full Text Available Online dietary assessment tools offer a convenient, low cost alternative to traditional dietary assessment methods such as weighed records and face-to-face interviewer-led 24-h recalls. INTAKE24 is an online multiple pass 24-h recall tool developed for use with 11–24 year-old. The aim of the study was to undertake a comparison of INTAKE24 (the test method with interviewer-led multiple pass 24-h recalls (the comparison method in 180 people aged 11–24 years. Each participant completed both an INTAKE24 24-h recall and an interviewer-led 24-h recall on the same day on four occasions over a one-month period. The daily energy and nutrient intakes reported in INTAKE24 were compared to those reported in the interviewer-led recall. Mean intakes reported using INTAKE24 were similar to the intakes reported in the interviewer-led recall for energy and macronutrients. INTAKE24 was found to underestimate energy intake by 1% on average compared to the interviewer-led recall with the limits of agreement ranging from minus 49% to plus 93%. Mean intakes of all macronutrients and micronutrients (except non-milk extrinsic sugars were within 4% of the interviewer-led recall. Dietary assessment that utilises technology may offer a viable alternative and be more engaging than paper based methods, particularly for children and young adults.

  15. Contrast-enhanced Magnetic Resonance Imaging of Pelvic Bone Metastases at 3.0 T: Comparison Between 3-dimensional T1-weighted CAIPIRINHA-VIBE Sequence and 2-dimensional T1-weighted Turbo Spin-Echo Sequence.

    Science.gov (United States)

    Yoon, Min A; Hong, Suk-Joo; Lee, Kyu-Chong; Lee, Chang Hee

    2018-06-12

    This study aimed to compare 3-dimensional T1-weighted gradient-echo sequence (CAIPIRINHA-volumetric interpolated breath-hold examination [VIBE]) with 2-dimensional T1-weighted turbo spin-echo sequence for contrast-enhanced magnetic resonance imaging (MRI) of pelvic bone metastases at 3.0 T. Thirty-one contrast-enhanced MRIs of pelvic bone metastases were included. Two contrast-enhanced sequences were evaluated for the following parameters: overall image quality, sharpness of pelvic bone, iliac vessel clarity, artifact severity, and conspicuity and edge sharpness of the smallest metastases. Quantitative analysis was performed by calculating signal-to-noise ratio and contrast-to-noise ratio of the smallest metastases. Significant differences between the 2 sequences were assessed. CAIPIRINHA-VIBE had higher scores for overall image quality, pelvic bone sharpness, iliac vessel clarity, and edge sharpness of the metastatic lesions, and had less artifacts (all P 0.05). Our results suggest that CAIPIRINHA-VIBE may be superior to turbo spin-echo for contrast-enhanced MRI of pelvic bone metastases at 3.0 T.

  16. Recall from Semantic and Episodic Memory.

    Science.gov (United States)

    Gillund, Gary; Perlmutter, Marion

    Although research in episodic recall memory, comparing younger and older adults, favors the younger adults, findings in semantic memory research are less consistent. To examine age differences in semantic and episodic memory recall, 72 young adults (mean age, 20.8) and 72 older adults (mean age 71) completed three memory tests under varied…

  17. Optimizing Design Efficiency of Free Recall Events for fMRI

    OpenAIRE

    Öztekin, Ilke; Long, Nicole M.; Badre, David

    2010-01-01

    Free recall is a fundamental paradigm for studying memory retrieval in the context of minimal cue support. Accordingly, free recall has been extensively studied using behavioral methods. However, the neural mechanisms that support free recall have not been fully investigated due to technical challenges associated with probing individual recall events with neuroimaging methods. Of particular concern is the extent to which the uncontrolled latencies associated with recall events can confer suff...

  18. Pistachio Product Recalls

    Data.gov (United States)

    U.S. Department of Health & Human Services — This list includes food subject to recall in the United States since March 2009 related to pistachios distributed by Setton Pistachio of Terra Bella, Inc. The FDA...

  19. MRI before and after external beam intensity-modulated radiotherapy of patients with prostate cancer: The feasibility of monitoring of radiation-induced tissue changes using a dynamic contrast-enhanced inversion-prepared dual-contrast gradient echo sequence

    International Nuclear Information System (INIS)

    Franiel, Tobias; Luedemann, Lutz; Taupitz, Matthias; Boehmer, Dirk; Beyersdorff, Dirk

    2009-01-01

    Purpose: To identify and quantify suitable pharmacokinetic MRI parameters for monitoring tissue changes after external beam intensity-modulated radiotherapy of prostate cancer. Material and methods: Six patients with biopsy-proven prostate cancer (initial PSA, 6.0-81.4 ng/ml) underwent MRI at 1.5 T using a combined endorectal/body phased-array coil and a dynamic contrast-enhanced inversion-prepared dual-contrast gradient echo sequence (T1/T2*w; 1.65 s temporal resolution). MRI was performed before and immediately after radiotherapy, at 3 months and at 1 year. Perfusion, blood volume, mean transit time, delay, dispersion, interstitial volume, and extraction coefficient were calculated in prostate cancer and normal prostate for all four time points using a sequential 3-compartment model. Results: Prostate cancer and normal prostate tissue showed a statistically significant decrease in perfusion (p = 0.006, p = 0.001) and increase in extraction coefficient (p = 0.004, p 3 min, p = 0.028) and a smaller extraction coefficient (0.42 vs. 0.64, p = 0.028). Conclusions: Two pharmacokinetic parameters, perfusion and extraction coefficient, appear to be suitable candidates for monitoring the response to percutaneous intensity-modulated radiotherapy of prostate cancer.

  20. Stationary echo canceling in velocity estimation by time-domain cross-correlation

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt

    1993-01-01

    The application of stationary echo canceling to ultrasonic estimation of blood velocities using time-domain cross-correlation is investigated. Expressions are derived that show the influence from the echo canceler on the signals that enter the cross-correlation estimator. It is demonstrated...