Ann Shimakawa

General Electric, Fairfield, California, United States

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Publications (94)305.55 Total impact

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    ABSTRACT: To develop and validate clinically a single-shot fast spin echo (SSFSE) sequence utilizing variable flip angle refocusing pulses to shorten acquisition times via reductions in specific absorption rate (SAR) and improve image quality. A variable refocusing flip angle SSFSE sequence (vrfSSFSE) was designed and implemented, with simulations and volunteer scans performed to determine suitable flip angle modulation parameters. With Institutional Review Board (IRB) approval/informed consent, patients referred for 3T abdominal magnetic resonance imaging (MRI) were scanned with conventional SSFSE and either half-Fourier (n = 25) or full-Fourier vrfSSFSE (n = 50). Two blinded radiologists semiquantitatively scored images on a scale from -2 to 2 for contrast, noise, sharpness, artifacts, cardiac motion-related signal loss, and the ability to evaluate the pancreas and kidneys. vrfSSFSE demonstrated significantly increased speed (∼2-fold, P < 0.0001). Significant improvements in image quality parameters with full-Fourier vrfSSFSE included increased contrast, sharpness, and visualization of pancreatic and renal structures with higher bandwidth technique (mean scores 0.37, 0.83, 0.62, and 0.31, respectively, P ≤ 0.001), and decreased image noise and improved visualization of renal structures when used with an equal bandwidth technique (mean scores 0.96 and 0.35, respectively, P < 0.001). Increased cardiac motion-related signal loss with full-Fourier vrfSSFSE was seen in the pancreas but not the kidney. vrfSSFSE increases speed at 3T over conventional SSFSE via reduced SAR, and when combined with full-Fourier acquisition can improve image quality, although with some increased sensitivity to cardiac motion-related signal loss. J. Magn. Reson. Imaging 2015. © 2015 Wiley Periodicals, Inc.
    Journal of Magnetic Resonance Imaging 06/2015; DOI:10.1002/jmri.24941 · 3.21 Impact Factor
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    ABSTRACT: To evaluate free-breathing chemical shift-encoded (CSE) magnetic resonance imaging (MRI) for quantification of hepatic proton density fat-fraction (PDFF). A secondary purpose was to evaluate hepatic R2* values measured using free-breathing quantitative CSE-MRI. Fifty patients (mean age, 56 years) were prospectively recruited and underwent the following four acquisitions to measure PDFF and R2*; 1) conventional breath-hold CSE-MRI (BH-CSE); 2) respiratory-gated CSE-MRI using respiratory bellows (BL-CSE); 3) respiratory-gated CSE-MRI using navigator echoes (NV-CSE); and 4) single voxel MR spectroscopy (MRS) as the reference standard for PDFF. Image quality was evaluated by two radiologists. MRI-PDFF measured from the three CSE-MRI methods were compared with MRS-PDFF using linear regression. The PDFF and R2* values were compared using two one-sided t-test to evaluate statistical equivalence. There was no significant difference in the image quality scores among the three CSE-MRI methods for either PDFF (P = 1.000) or R2* maps (P = 0.359-1.000). Correlation coefficients (95% confidence interval [CI]) for the PDFF comparisons were 0.98 (0.96-0.99) for BH-, 0.99 (0.97-0.99) for BL-, and 0.99 (0.98-0.99) for NV-CSE. The statistical equivalence test revealed that the mean difference in PDFF and R2* between any two of the three CSE-MRI methods was less than ±1 percentage point (pp) and ±5 s(-1) , respectively (P < 0.046). Respiratory-gated CSE-MRI with respiratory bellows or navigator echo are feasible methods to quantify liver PDFF and R2* and are as valid as the standard breath-hold technique. J. Magn. Reson. Imaging 2015. © 2015 Wiley Periodicals, Inc.
    Journal of Magnetic Resonance Imaging 04/2015; 42(5). DOI:10.1002/jmri.24896 · 3.21 Impact Factor
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    Journal of Cardiovascular Magnetic Resonance 02/2015; 17(1). DOI:10.1186/1532-429X-17-S1-Q36 · 4.56 Impact Factor
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    ABSTRACT: To develop and evaluate a free-breathing chemical-shift-encoded (CSE) spoiled gradient-recalled echo (SPGR) technique for whole-heart water-fat imaging at 3 Tesla (T). We developed a three-dimensional (3D) multi-echo SPGR pulse sequence with electrocardiographic gating and navigator echoes and evaluated its performance at 3T in healthy volunteers (N = 6) and patients (N = 20). CSE-SPGR, 3D SPGR, and 3D balanced-SSFP with chemical fat saturation were compared in six healthy subjects with images evaluated for overall image quality, level of residual artifacts, and quality of fat suppression. A similar scoring system was used for the patient datasets. Images of diagnostic quality were acquired in all but one subject. CSE-SPGR performed similarly to SPGR with fat saturation, although it provided a more uniform fat suppression over the whole field of view. Balanced-SSFP performed worse than SPGR-based methods. In patients, CSE-SPGR produced excellent fat suppression near metal. Overall image quality was either good (7/20) or excellent (12/20) in all but one patient. There were significant artifacts in 5/20 clinical cases. CSE-SPGR is a promising technique for whole-heart water-fat imaging during free-breathing. The robust fat suppression in the water-only image could improve assessment of complex morphology at 3T and in the presence of off-resonance, with additional information contained in the fat-only image. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 09/2014; 72(3). DOI:10.1002/mrm.24982 · 3.57 Impact Factor
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    ABSTRACT: To compare the image quality of three techniques and diagnostic performance in detecting implant rupture. The study included 161 implants for the evaluation of image quality, composed of water-saturated short TI inversion recovery (herein called "water-sat STIR"), three-point Dixon techniques (herein called "Dixon"), and short TI inversion recovery fast spin-echo with iterative decomposition of silicone and water using least-squares approximation (herein called "STIR IDEAL") and included 41 implants for the evaluation of diagnostic performance in detecting rupture, composed of water-sat STIR and STIR IDEAL. Six image quality categories were evaluated and three classifications were used: normal implant, possible rupture, and definite rupture. Statistically significant differences were noted for the image quality categories (p<0.001). STIR IDEAL was superior or equal to water-sat STIR in all image quality categories except artifact effects and superior to Dixon in all categories. Water-sat STIR performed the poorest for water suppression uniformity. The sensitivity and specificity in detecting implant rupture of STIR-IDEAL were 81.8 % and 77.8 % and the difference between two techniques was not statistically significant. STIR-IDEAL is a useful silicone-specific imaging technique demonstrating more robust water suppression and equivalent diagnostic accuracy for detecting implant rupture, than water-sat STIR, at the cost of longer scan time and an increase in minor motion artifacts.
    Magnetic Resonance Imaging 07/2013; 31(9). DOI:10.1016/j.mri.2013.05.011 · 2.09 Impact Factor
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    ABSTRACT: Purpose: To compare lumbar muscle fat-signal fractions derived from three-dimensional dual gradient-echo magnetic resonance (MR) imaging and multiple gradient-echo MR imaging with fractions from single-voxel MR spectroscopy in patients with low back pain. Materials and methods: This prospective study had institutional review board approval, and written informed consent was obtained from all study participants. Fifty-six patients (32 women; mean age, 52 years ± 15 [standard deviation]; age range, 20-79 years) with low back pain underwent standard 1.5-T MR imaging, which was supplemented by dual-echo MR imaging, multi-echo MR imaging, and MR spectroscopy to quantify fatty degeneration of bilateral lumbar multifidus muscles in a region of interest at the intervertebral level of L4 through L5. Fat-signal fractions were determined from signal intensities on fat- and water-only images from both imaging data sets (dual-echo and multi-echo fat-signal fractions without T2* correction) or directly obtained, with additional T2* correction, from multi-echo MR imaging. The results were compared with MR spectroscopic fractions. The Student t test and Bland-Altman plots were used to quantify agreement between fat-signal fractions derived from imaging and from spectroscopy. Results: In total, 102 spectroscopic measurements were obtained bilaterally (46 of 56) or unilaterally (10 of 56). Mean spectroscopic fat-signal fraction was 19.6 ± 11.4 (range, 5.4-63.5). Correlation between spectroscopic and all imaging-based fat-signal fractions was statistically significant (R(2) = 0.87-0.92; all P < .001). Mean dual-echo fat-signal fractions not corrected for T2* and multi-echo fat-signal fractions corrected for T2* significantly differed from spectroscopic fractions (both P < .01), but mean multi-echo fractions not corrected for T2* did not (P = .11). There was a small measurement bias of 0.5% (95% limits of agreement: -6.0%, 7.2%) compared with spectroscopic fractions. Conclusion: Large-volume image-based (dual-echo and multi-echo MR imaging) and spectroscopic fat-signal fractions agree well, thus allowing fast and accurate quantification of muscle fat content in patients with low back pain.
    Radiology 11/2012; 266(2). DOI:10.1148/radiol.12120399 · 6.87 Impact Factor
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    ABSTRACT: Chemical shift-based water/fat separation methods have been emerging due to the growing clinical need for fat quantification in different body organs. Accurate quantification of proton-density fat fraction requires the assessment of many confounding factors, including the need of modeling the presence of multiple peaks in the fat spectrum. Most recent quantitative chemical shift-based water/fat separation approaches rely on a multipeak fat spectrum with precalibrated peak locations and precalibrated or self-calibrated peak relative amplitudes. However, water/fat susceptibility differences can induce fat spectrum resonance shifts depending on the shape and orientation of the fatty inclusions. The effect is of particular interest in the skeletal muscle due to the anisotropic arrangement of extracellular lipids. In this work, the effect of susceptibility-induced fat resonance shift on the fat fraction is characterized in a conventional complex-based chemical shift-based water/fat separation approach that does not model the susceptibility-induced fat resonance shift. A novel algorithm is then proposed to quantify the resonance shift in a complex-based chemical shift-based water/fat separation approach that considers the fat resonance shift in the signal model, aiming to extract information about the orientation/geometry of lipids. The technique is validated in a phantom and preliminary in vivo results are shown in the calf musculature of healthy and diabetic subjects. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 11/2012; 68(5):1495-505. DOI:10.1002/mrm.24157 · 3.57 Impact Factor
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    Diego Hernando · Karl K Vigen · Ann Shimakawa · Scott B Reeder ·
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    ABSTRACT: R₂ mapping has important applications in MRI, including functional imaging, tracking of super-paramagnetic particles, and measurement of tissue iron levels. However, R₂ measurements can be confounded by several effects, particularly the presence of fat and macroscopic B₀ field variations. Fat introduces additional modulations in the signal. Macroscopic field variations introduce additional dephasing that results in accelerated signal decay. These effects produce systematic errors in the resulting R₂ maps and make the estimated R₂ values dependent on the acquisition parameters. In this study, we develop a complex-reconstruction, confounder-corrected R₂ mapping technique, which addresses the presence of fat and macroscopic field variations for both 2D and 3D acquisitions. This technique extends previous chemical shift-encoded methods for R₂, fat and water mapping by measuring and correcting for the effect of macroscopic field variations in the acquired signal. The proposed method is tested on several 2D and 3D phantom and in vivo liver, cardiac, and brain datasets.
    Magnetic Resonance in Medicine 09/2012; 68(3):830-40. DOI:10.1002/mrm.23306 · 3.57 Impact Factor
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    ABSTRACT: To develop a robust T(2) -weighted volumetric imaging technique with uniform water-silicone separation and simultaneous fat suppression for rapid assessment of breast implants in a single acquisition. A three-dimensional (3D) fast spin echo sequence that uses variable refocusing flip angles was combined with a three-point chemical-shift technique (IDEAL) and short tau inversion recovery (STIR). Phase shifts of -π/6, +π/2, and +7π/6 between water and silicone were used for IDEAL processing. For comparison, two-dimensional images using 2D-FSE-IDEAL with STIR were also acquired in axial, coronal, and sagittal orientations. Near-isotropic (true spatial resolution-0.9 × 1.3 × 2.0 mm(3) ) volumetric breast images with uniform water-silicone separation and simultaneous fat suppression were acquired successfully in clinically feasible scan times (7:00-10:00 min). The 2D images were acquired with the same in-plane resolution (0.9 × 1.3 mm(2) ), but the slice thickness was increased to 6 mm with a slice gap of 1 mm for complete coverage of the implants in a reasonable scan time, which varied between 18:00 and 22:30 min. The single volumetric acquisition with uniform water and silicone separation enables images to be reformatted into any orientation. This allows comprehensive assessment of breast implant integrity in less than 10 min of total examination time.
    Journal of Magnetic Resonance Imaging 05/2012; 35(5):1216-21. DOI:10.1002/jmri.22872 · 3.21 Impact Factor
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    ABSTRACT: To show the feasibility of assessing the spatial distribution of skeletal muscle adipose tissue using chemical shift-based water/fat separation and to characterize differences in calf intermuscular adipose tissue (IMAT) compartmentalization in patients with type 2 diabetes mellitus (T2DM) compared to healthy age-matched controls. A chemical shift-based water/fat separation approach using a multiecho 3D spoiled gradient echo sequence was applied in a study of 64 patients, including 35 healthy controls and 29 subjects with T2DM. Masks were defined based on manual segmentations to compute fat volume within different compartments, including regions of subcutaneous adipose tissue (SAT) and six muscular regions. IMAT was divided into two compartments representing fat within the muscular regions (intraMF) and fat between the muscular regions (interMF). Two-sample Student's t-tests were used to compare fat volumes between the two groups. The subjects with T2DM had a lower volume of SAT compared to the healthy controls (P = 4 × 10(-5) ). There was no statistically significant difference in the IMAT volume between the two groups. However, the intraMF volume normalized by the IMAT volume was higher in the diabetics compared to the controls (P = 0.006). Chemical shift-based water/fat separation enables the quantification of fat volume within localized muscle regions, showing that the IMAT regional distribution is significantly different in T2DM compared to normal controls.
    Journal of Magnetic Resonance Imaging 04/2012; 35(4):899-907. DOI:10.1002/jmri.23512 · 3.21 Impact Factor
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    ABSTRACT: Fat suppression is an essential part of routine MRI scanning. Multiecho chemical-shift based water-fat separation methods estimate and correct for Bo field inhomogeneity. However, they must contend with the intrinsic challenge of water-fat ambiguity that can result in water-fat swapping. This problem arises because the signals from two chemical species, when both are modeled as a single discrete spectral peak, may appear indistinguishable in the presence of Bo off-resonance. In conventional methods, the water-fat ambiguity is typically removed by enforcing field map smoothness using region growing based algorithms. In reality, the fat spectrum has multiple spectral peaks. Using this spectral complexity, we introduce a novel concept that identifies water and fat for multiecho acquisitions by exploiting the spectral differences between water and fat. A fat likelihood map is produced to indicate if a pixel is likely to be water-dominant or fat-dominant by comparing the fitting residuals of two different signal models. The fat likelihood analysis and field map smoothness provide complementary information, and we designed an algorithm (Fat Likelihood Analysis for Multiecho Signals) to exploit both mechanisms. It is demonstrated in a wide variety of data that the Fat Likelihood Analysis for Multiecho Signals algorithm offers highly robust water-fat separation for 6-echo acquisitions, particularly in some previously challenging applications.
    Magnetic Resonance in Medicine 04/2012; 67(4):1065-76. DOI:10.1002/mrm.23087 · 3.57 Impact Factor
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    ABSTRACT: To validate the utility and performance of a T 2 correction method for hepatic fat quantification in an animal model of both steatosis and iron overload. Mice with low (n = 6), medium (n = 6), and high (n = 8) levels of steatosis were sedated and imaged using a chemical shift-based fat-water separation method to obtain magnetic resonance imaging (MRI) fat-fraction measurements. Imaging was performed before and after each of two superparamagnetic iron oxide (SPIO) injections to create hepatic iron overload. Fat-fraction maps were reconstructed with and without T 2 correction. Fat-fraction with and without T 2 correction and T 2 measurements were compared after each injection. Liver tissue was harvested and imaging results were compared to triglyceride extraction and histology grading. Excellent correlation was seen between MRI fat-fraction and tissue-based fat quantification. Injections of SPIOs led to increases in R 2 (=1/T 2). Measured fat-fraction was unaffected by the presence of iron when T 2 correction was used, whereas measured fat-fraction dramatically increased without T 2 correction. Hepatic fat-fraction measured using a T 2-corrected chemical shift-based fat-water separation method was validated in an animal model of steatosis and iron overload. T 2 correction enables robust fat-fraction estimation in both the presence and absence of iron, and is necessary for accurate hepatic fat quantification.
    Journal of Magnetic Resonance Imaging 04/2012; 35(4):844-51. DOI:10.1002/jmri.22890 · 3.21 Impact Factor
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    ABSTRACT: MRI imaging of hepatic iron overload can be achieved by estimating T(2) values using multiple-echo sequences. The purpose of this work is to develop and clinically evaluate a weighted least squares algorithm based on T(2) Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation (IDEAL) technique for volumetric estimation of hepatic T(2) in the setting of iron overload. The weighted least squares T(2) IDEAL technique improves T(2) estimation by automatically decreasing the impact of later, noise-dominated echoes. The technique was evaluated in 37 patients with iron overload. Each patient underwent (i) a standard 2D multiple-echo gradient echo sequence for T(2) assessment with nonlinear exponential fitting, and (ii) a 3D T(2) IDEAL technique, with and without a weighted least squares fit. Regression and Bland-Altman analysis demonstrated strong correlation between conventional 2D and T(2) IDEAL estimation. In cases of severe iron overload, T(2) IDEAL without weighted least squares reconstruction resulted in a relative overestimation of T(2) compared with weighted least squares.
    Magnetic Resonance in Medicine 01/2012; 67(1):183-90. DOI:10.1002/mrm.22986 · 3.57 Impact Factor
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    ABSTRACT: Chemical shift-based water/fat separation, like iterative decomposition of water and fat with echo asymmetry and least-squares estimation, has been proposed for quantifying intermuscular adipose tissue. An important confounding factor in iterative decomposition of water and fat with echo asymmetry and least-squares estimation-based intermuscular adipose tissue quantification is the large difference in T(1) between muscle and fat, which can cause significant overestimation in the fat fraction. This T(1) bias effect is usually reduced by using small flip angles. T(1) -correction can be performed by using at least two different flip angles and fitting for T(1) of water and fat. In this work, a novel approach for the water/fat separation problem in a dual flip angle experiment is introduced and a new approach for the selection of the two flip angles, labeled as the unequal small flip angle approach, is developed, aiming to improve the noise efficiency of the T(1) -correction step relative to existing approaches. It is shown that the use of flip angles, selected such the muscle water signal is assumed to be T(1) -independent for the first flip angle and the fat signal is assumed to be T(1) -independent for the second flip angle, has superior noise performance to the use of equal small flip angles (no T(1) estimation required) and the use of large flip angles (T(1) estimation required).
    Magnetic Resonance in Medicine 11/2011; 66(5):1312-26. DOI:10.1002/mrm.22925 · 3.57 Impact Factor
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    ABSTRACT: Multipoint water-fat separation techniques rely on different water-fat phase shifts generated at multiple echo times to decompose water and fat. Therefore, these methods require complex source images and allow unambiguous separation of water and fat signals. However, complex-based water-fat separation methods are sensitive to phase errors in the source images, which may lead to clinically important errors. An alternative approach to quantify fat is through "magnitude-based" methods that acquire multiecho magnitude images. Magnitude-based methods are insensitive to phase errors, but cannot estimate fat-fraction greater than 50%. In this work, we introduce a water-fat separation approach that combines the strengths of both complex and magnitude reconstruction algorithms. A magnitude-based reconstruction is applied after complex-based water-fat separation to removes the effect of phase errors. The results from the two reconstructions are then combined. We demonstrate that using this hybrid method, 0-100% fat-fraction can be estimated with improved accuracy at low fat-fractions.
    Magnetic Resonance in Medicine 07/2011; 66(1):199-206. DOI:10.1002/mrm.22840 · 3.57 Impact Factor
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    ABSTRACT: To propose a new noncontrast-enhanced flow-independent angiography sequence based on balanced steady-state free precession (bSSFP) that produces reliable vessel contrast despite the reduced blood flow in the extremities. The proposed technique addresses a variety of factors that can compromise the exam success including insufficient background suppression, field inhomogeneity, and large volumetric coverage requirements. A bSSFP sequence yields reduced signal from venous blood when long repetition times are used. Complex-sum bSSFP acquisitions decrease the sensitivity to field inhomogeneity but retain phase information, so that data can be processed with the Iterative Decomposition of Water and Fat with Echo Asymmetry and Least-Squares Estimation (IDEAL) method for robust fat suppression. Meanwhile, frequent magnetization preparation coupled with parallel imaging reduces the muscle and long-T(1) fluid signals without compromising scan efficiency. In vivo flow-independent peripheral angiograms with reliable background suppression and high spatial resolution are produced. Comparisons with phase-sensitive bSSFP angiograms (that yield out-of-phase fat and water signals, and exploit this phase difference to suppress fat) demonstrate enhanced vessel depiction with the proposed technique due to reduced partial-volume effects and improved venous suppression. Magnetization-prepared complex-sum bSSFP with IDEAL fat/water separation can create reliable flow-independent angiographic contrast in the lower extremities.
    Journal of Magnetic Resonance Imaging 04/2011; 33(4):931-9. DOI:10.1002/jmri.22479 · 3.21 Impact Factor

  • Journal of Magnetic Resonance Imaging 01/2011; 35. · 3.21 Impact Factor
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    ABSTRACT: Coronary wall cardiovascular magnetic resonance (CMR) is a promising noninvasive approach to assess subclinical atherosclerosis, but data are limited in subjects over 60 years old, who are at increased risk. The purpose of the study was to evaluate coronary wall CMR in an asymptomatic older cohort. Cross-sectional images of the proximal right coronary artery (RCA) were acquired using spiral black-blood coronary CMR (0.7 mm resolution) in 223 older, community-based patients without a history of cardiovascular disease (age 60-72 years old, 38% female). Coronary measurements (total vessel area, lumen area, wall area, and wall thickness) had small intra- and inter-observer variabilities (r = 0.93~0.99, all p < 0.0001), though one-third of these older subjects had suboptimal image quality. Increased coronary wall thickness correlated with increased coronary vessel area (p < 0.0001), consistent with positive remodeling. On multivariate analysis, type 2 diabetes was the only risk factor associated with increased coronary wall area and thickness (p = 0.03 and p = 0.007, respectively). Coronary wall CMR measures were also associated with coronary calcification (p = 0.01-0.03). Right coronary wall CMR in asymptomatic older subjects showed increased coronary atherosclerosis in subjects with type 2 diabetes as well as coronary calcification. Coronary wall CMR may contribute to the noninvasive assessment of subclinical coronary atherosclerosis in older, at-risk patient groups.
    Journal of Cardiovascular Magnetic Resonance 12/2010; 12(1):75. DOI:10.1186/1532-429X-12-75 · 4.56 Impact Factor
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    ABSTRACT: To develop a robust 3D fast spin echo (FSE) T2-weighted imaging method with uniform water and fat separation in a single acquisition, amenable to high-quality multiplanar reformations. The Iterative Decomposition of water and fat with Echo Asymmetry and Least squares estimation (IDEAL) method was integrated with modulated refocusing flip angle 3D-FSE. Echoes required for IDEAL processing were acquired by shifting the readout gradient with respect to the Carr-Purcell-Meiboom-Gill echo. To reduce the scan time, an alternative data acquisition using two gradient echoes per repetition was implemented. Using the latter approach, a total of four gradient echoes were acquired in two repetitions and used in the modified IDEAL reconstruction. 3D-FSE T2-weighted images with uniform water–fat separation were successfully acquired in various anatomies including breast, abdomen, knee, and ankle in clinically feasible scan times, ranging from 5:30–8:30 minutes. Using water-only and fat-only images, in-phase and out-of-phase images were reconstructed. 3D-FSE-IDEAL provides volumetric T2-weighted images with uniform water and fat separation in a single acquisition. High-resolution images with multiple contrasts can be reformatted to any orientation from a single acquisition. This could potentially replace 2D-FSE acquisitions with and without fat suppression and in multiple planes, thus improving overall imaging efficiency. J. Magn. Reson. Imaging 2010;32:745–751.
    Journal of Magnetic Resonance Imaging 09/2010; 32(3):745 - 751. DOI:10.1002/jmri.22282 · 3.21 Impact Factor
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    ABSTRACT: To address phase and amplitude errors for multi-point water-fat separation with "bipolar" acquisitions, which efficiently collect all echoes with alternating read-out gradient polarities in one repetition. With the bipolar acquisitions, eddy currents and other system nonidealities can induce inconsistent phase errors between echoes, disrupting water-fat separation. Previous studies have addressed phase correction in the read-out direction. However, the bipolar acquisitions may be subject to spatially high order phase errors as well as an amplitude modulation in the read-out direction. A method to correct for the 2D phase and amplitude errors is introduced. Low resolution reference data with reversed gradient polarities are collected. From the pair of low-resolution data collected with opposite gradient polarities, the two-dimensional phase errors are estimated and corrected. The pair of data are then combined for water-fat separation. We demonstrate that the proposed method can effectively remove the high order errors with phantom and in vivo experiments, including obliquely oriented scans. For bipolar multi-echo acquisitions, uniform water-fat separation can be achieved by removing high order phase errors with the proposed method.
    Journal of Magnetic Resonance Imaging 05/2010; 31(5):1264-71. DOI:10.1002/jmri.22111 · 3.21 Impact Factor

Publication Stats

4k Citations
305.55 Total Impact Points


  • 1987-2008
    • General Electric
      Fairfield, California, United States
    • University of Utah
      • Department of Radiology
      Salt Lake City, Utah, United States
  • 2007
    • University of Wisconsin, Madison
      • Department of Medical Physics
      Madison, MS, United States
  • 2006
    • Leiden University
      Leyden, South Holland, Netherlands
  • 2005
    • Applied Science Laboratories
      Bedford, Massachusetts, United States
  • 1991-2000
    • University of California, San Francisco
      • Division of Hospital Medicine
      San Francisco, California, United States
  • 1999
    • University of Wisconsin - Milwaukee
      Milwaukee, Wisconsin, United States
  • 1988
    • Duke University Medical Center
      • Department of Radiology
      Durham, North Carolina, United States