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1.
Jiang Du Atsushi M. Takahashi Mark Bydder Christine B. Chung Graeme M. Bydder 《Magnetic resonance in medicine》2009,62(2):527-531
Short T2 species such as the Achilles tendon and cortical bone cannot be imaged with conventional MR sequences. They have a much broader absorption lineshape than long T2 species, therefore they are more sensitive to an appropriately placed off‐resonance irradiation. In this work, a technique termed ultrashort TE (UTE) with off‐resonance saturation contrast (UTE‐OSC) is proposed to image short T2 species. A high power saturation pulse was placed +1 to +2 kHz off the water peak to preferentially saturate signals from short T2 species, leaving long T2 water and fat signals largely unaffected. The subtraction of UTE images with and without an off‐resonance saturation pulse effectively suppresses long T2 water and fat signals, creating high contrast for short T2 species. The UTE‐OSC technique was validated on a phantom, and applied to bone samples and healthy volunteers on a clinical 3T scanner. High‐contrast images of the Achilles tendon and cortical bone were generated with a high contrast‐to‐noise ratio (CNR) of the order of 12 to 20 between short T2 and long T2 species within a total scan time of 4 to 10 min. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc. 相似文献
2.
Catherine D.G. Hines MS Huanzhou Yu PhD Ann Shimakawa MSE Charles A. McKenzie PhD Jean H. Brittain PhD Scott B. Reeder MD PhD 《Journal of magnetic resonance imaging : JMRI》2009,30(5):1215-1222
Purpose:
To validate a T1‐independent, T2*‐corrected fat quantification technique that uses accurate spectral modeling of fat using a homogeneous fat‐water‐SPIO phantom over physiologically expected ranges of fat percentage and T2* decay in the presence of iron overload.Materials and Methods:
A homogeneous gel phantom consisting of vials with known fat‐fractions and iron concentrations is described. Fat‐fraction imaging was performed using a multiecho chemical shift‐based fat‐water separation method (IDEAL), and various reconstructions were performed to determine the impact of T2* correction and accurate spectral modeling. Conventional two‐point Dixon (in‐phase/out‐of‐phase) imaging and MR spectroscopy were performed for comparison with known fat‐fractions.Results:
The best agreement with known fat‐fractions over the full range of iron concentrations was found when T2* correction and accurate spectral modeling were used. Conventional two‐point Dixon imaging grossly underestimated fat‐fraction for all T2* values, but particularly at higher iron concentrations.Conclusion:
This work demonstrates the necessity of T2* correction and accurate spectral modeling of fat to accurately quantify fat using MRI. J. Magn. Reson. Imaging 2009;30:1215–1222. © 2009 Wiley‐Liss, Inc. 相似文献3.
Richard Kijowski MD Michael A. Woods MD Kenneth S. Lee MD Kuya Takimi BS Huanzhou Yu PhD Ann Shimakawa MSE Jean H. Brittain PhD Scott B. Reeder MD PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(2):436-442
Purpose
To evaluate and quantify improvements in the quality of fat suppression for fast spin‐echo imaging of the knee using multipeak fat spectral modeling and IDEAL fat‐water separation.Materials and Methods
T1‐weighted and T2‐weighted fast spin‐echo sequences with IDEAL fat‐water separation and two frequency‐selective fat‐saturation methods (fat‐selective saturation and fat‐selective partial inversion) were performed on 10 knees of five asymptomatic volunteers. The IDEAL images were reconstructed using a conventional single‐peak method and precalibrated and self‐calibrated multipeak methods that more accurately model the NMR spectrum of fat. The signal‐to‐noise ratio (SNR) was measured in various tissues for all sequences. Student t‐tests were used to compare SNR values.Results
Precalibrated and self‐calibrated multipeak IDEAL had significantly greater suppression of signal (P < 0.05) within subcutaneous fat and bone marrow than fat‐selective saturation, fat‐selective partial inversion, and single‐peak IDEAL for both T1‐weighted and T2‐weighted fast spin‐echo sequences. For T1‐weighted fast spin‐echo sequences, the improvement in the suppression of signal within subcutaneous fat and bone marrow for multipeak IDEAL ranged between 65% when compared to fat‐selective partial inversion to 86% when compared to fat‐selectivesaturation. For T2‐weighted fast spin‐echo sequences, the improvement for multipeak IDEAL ranged between 21% when compared to fat‐selective partial inversion to 81% when compared to fat‐selective saturation.Conclusion
Multipeak IDEAL fat‐water separation provides improved fat suppression for T1‐weighted and T2‐weighted fast spin‐echo imaging of the knee when compared to single‐peak IDEAL and two widely used frequency‐selected fat‐saturation methods. J. Magn. Reson. Imaging 2009;29:436–442. © 2009 Wiley‐Liss, Inc. 相似文献4.
Ananth J. Madhuranthakam PhD Huanzhou Yu PhD Ann Shimakawa MS Reed F. Busse PhD Martin P. Smith MD Scott B. Reeder MD PhD Neil M. Rofsky MD Jean H. Brittain PhD Charles A. McKenzie PhD 《Journal of magnetic resonance imaging : JMRI》2010,32(3):745-751
Purpose:
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.Materials and Methods:
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.Results:
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.Conclusion:
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. © 2010 Wiley‐Liss, Inc. 相似文献5.
Huanzhou Yu Ann Shimakawa Charles A. McKenzie Ethan Brodsky Jean H. Brittain Scott B. Reeder 《Magnetic resonance in medicine》2008,60(5):1122-1134
Multiecho chemical shift–based water‐fat separation methods are seeing increasing clinical use due to their ability to estimate and correct for field inhomogeneities. Previous chemical shift‐based water‐fat separation methods used a relatively simple signal model that assumes both water and fat have a single resonant frequency. However, it is well known that fat has several spectral peaks. This inaccuracy in the signal model results in two undesired effects. First, water and fat are incompletely separated. Second, methods designed to estimate T in the presence of fat incorrectly estimate the T decay in tissues containing fat. In this work, a more accurate multifrequency model of fat is included in the iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (IDEAL) water‐fat separation and simultaneous T estimation techniques. The fat spectrum can be assumed to be constant in all subjects and measured a priori using MR spectroscopy. Alternatively, the fat spectrum can be estimated directly from the data using novel spectrum self‐calibration algorithms. The improvement in water‐fat separation and T estimation is demonstrated in a variety of in vivo applications, including knee, ankle, spine, breast, and abdominal scans. Magn Reson Med 60:1122–1134, 2008. © 2008 Wiley‐Liss, Inc. 相似文献
6.
Allison Grayev MD Ann Shimakawa PhD Joseph Cousins MD PhD Patrick Turski MD Jean Brittain PhD Scott Reeder MD PhD 《Journal of magnetic resonance imaging : JMRI》2009,29(6):1367-1374
Purpose
To implement IDEAL (iterative decomposition of water and fat using echo asymmetry and least squares estimation) water‐fat separation with 3D time‐of‐flight (TOF) magnetic resonance angiography (MRA) of intracranial vessels for improved background suppression by providing uniform and robust separation of fat signal that appears bright on conventional TOF‐MRA.Materials and Methods
IDEAL TOF‐MRA and conventional TOF‐MRA were performed in volunteers and patients undergoing routine brain MRI/MRA on a 3T magnet. Images were reviewed by two radiologists and graded based on vessel visibility and image quality.Results
IDEAL TOF‐MRA demonstrated statistically significant improvement in vessel visibility when compared to conventional TOF‐MRA in both volunteer and clinical patients using an image quality grading system. Overall image quality was 3.87 (out of 4) for IDEAL versus 3.55 for conventional TOF imaging (P = 0.02). Visualization of the ophthalmic artery was 3.53 for IDEAL versus 1.97 for conventional TOF imaging (P < 0.00005) and visualization of the superficial temporal artery was 3.92 for IDEAL imaging versus 1.97 for conventional TOF imaging (P < 0.00005).Conclusion
By providing uniform suppression of fat, IDEAL TOF‐MRA provides improved background suppression with improved image quality when compared to conventional TOF‐MRA methods. J. Magn. Reson. Imaging 2009;29:1367–1374. © 2009 Wiley‐Liss, Inc. 相似文献7.
Zhang L Zhong X Wang L Chen H Wang YA Yeh J Yang L Mao H 《Journal of magnetic resonance imaging : JMRI》2011,33(1):194-202
Purpose
To obtain positive contrast based on T1 weighting from magnetic iron oxide nanoparticle (IONP) using ultrashort echo time (UTE) imaging and investigate quantitative relationship between positive contrast and the core size and concentration of IONPs.Materials and Methods
Solutions of IONPs with different core sizes and concentrations were prepared. T1 and T2 relaxation times of IONPs were measured using the inversion recovery turbo spin echo (TSE) and multi‐echo spin echo sequences at 3 Tesla. T1‐weighted UTE gradient echo and T2‐weighted TSE sequences were used to image IONP samples. U87MG glioblastoma cells bound with arginine‐glycine‐aspartic acid (RGD) peptide and IONP conjugates were scanned using UTE, T1 and T2‐weighted sequences.Results
Positive contrast was obtained by UTE imaging from IONPs with different core sizes and concentrations. The relative‐contrast‐to‐water ratio of UTE images was three to four times higher than those of T2‐weighted TSE images. The signal intensity increases as the function of the core size and concentration. Positive contrast was also evident in cell samples bound with RGD‐IONPs.Conclusion
UTE imaging allows for imaging of IONPs and IONP bound tumor cells with positive contrast and provides contrast enhancement and potential quantification of IONPs in molecular imaging applications. J. Magn. Reson. Imaging 2011;33:194–202. © 2010 Wiley‐Liss, Inc. 相似文献8.
Dimitrios C. Karampinos Ph.D. Huanzhou Yu Ann Shimakawa Thomas M. Link Sharmila Majumdar 《Magnetic resonance in medicine》2011,66(5):1312-1326
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 T1 between muscle and fat, which can cause significant overestimation in the fat fraction. This T1 bias effect is usually reduced by using small flip angles. T1‐correction can be performed by using at least two different flip angles and fitting for T1 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 T1‐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 T1‐independent for the first flip angle and the fat signal is assumed to be T1‐independent for the second flip angle, has superior noise performance to the use of equal small flip angles (no T1 estimation required) and the use of large flip angles (T1 estimation required). Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. 相似文献
9.
Takatoshi Aoki MD Yoshiko Yamashita MD Hodaka Oki MD Hiroyuki Takahashi MD Yoshiko Hayashida MD Kazuyoshi Saito MD Yoshiya Tanaka MD Yukunori Korogi MD 《Journal of magnetic resonance imaging : JMRI》2013,37(3):733-738
Purpose:
To compare fat‐suppressed magnetic resonance imaging (MRI) quality using iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (IDEAL) with that using chemical shift selective fat‐suppressed T1‐weighted spin‐echo (CHESS) images for evaluating rheumatoid arthritis (RA) lesions of the hand and finger at 3T.Materials and Methods:
MRI was performed in eight healthy volunteers and eight RA patients with a 3.0T MR system (Signa HDxt GE healthcare) using an eight‐channel knee coil. FS‐CHESS‐T1‐SE and IDEAL imaging were acquired in the coronal planes covering the entire structure of the bilateral hands with a slice thickness of 2 mm. In the RA patients both images were obtained after intravenous gadolinium administration. Image quality was evaluated on a five‐point scale (1 = excellent to 5 = very poor). Synovitis and bone marrow contrast uptake on MR images were reviewed by two musculoskeletal radiologists using the Rheumatoid Arthritis MRI Scoring System (RAMRIS) of the Outcome Measures in Rheumatoid Arthritis Clinical Trials (OMERACT) group.Results:
IDEAL showed uniform FS unaffected by magnetic field inhomogeneity and challenging geometry of hand and fingers, while CHESS‐T1‐SE often showed FS failure within the first metacarpal joint, tip of the finger, and ulnar aspect of the wrist joint. Overall image quality was significantly better with IDEAL than CHESS‐T1‐SE images (4.43 vs. 3.43, P < 0.01). Interobserver agreement (κ value) for synovitis and bone marrow contrast uptake was good to excellent with IDEAL (0.74–0.91, 0.62–0.89, respectively).Conclusion:
IDEAL could compensate for the effects of field inhomogeneities, providing uniform FS of the hand and finger than did the CHESS‐T1‐SE sequence. J. Magn. Reson. Imaging 2013;37:733–738. © 2012 Wiley Periodicals, Inc. 相似文献10.
Jiang Du Michael Carl Eric Diaz Atsushi Takahashi Eric Han Nikolaus M. Szeverenyi Christine B. Chung Graeme M. Bydder 《Magnetic resonance in medicine》2010,64(3):834-842
In this study, we report the use of a novel ultrashort echo time T1rhoT1 sequence that combines a spin‐lock preparation pulse with a two‐dimensional ultrashort echo time sequence of a nominal echo time 8 μsec. The ultrashort echo time‐T1rho sequence was employed to quantify T1rho in short T2 tissues including the Achilles tendon and the meniscus. T1rho dispersion was investigated by varying the spin‐lock field strength. Preliminary results on six cadaveric ankle specimens and five healthy volunteers show that the ultrashort echo time‐T1rho sequence provides high signal and contrast for both the Achilles tendon and the meniscus. The mean T1rho of the Achilles tendon ranged from 3.06 ± 0.51 msec for healthy volunteers to 5.22 ± 0.58 msec for cadaveric specimens. T1rho increased to 8.99 ± 0.24 msec in one specimen with tendon degeneration. A mean T1rho of 7.98 ± 1.43 msec was observed in the meniscus of the healthy volunteers. There was significant T1rho dispersion in both the Achilles tendon and the meniscus. Mean T1rho increased from 2.06 ± 0.23 to 7.85 ± 0.74 msec in normal Achilles tendon and from 7.08 ± 0.64 to 13.42 ± 0.93 msec in normal meniscus when the spin‐lock field was increased from 250 to 1,000 Hz. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
11.
Madhuranthakam AJ Smith MP Yu H Shimakawa A Reeder SB Rofsky NM McKenzie CA Brittain JH 《Journal of magnetic resonance imaging : JMRI》2012,35(5):1216-1221
Purpose:
To develop a robust T2‐weighted volumetric imaging technique with uniform water‐silicone separation and simultaneous fat suppression for rapid assessment of breast implants in a single acquisition.Materials and Methods:
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.Results:
Near‐isotropic (true spatial resolution—0.9 × 1.3 × 2.0 mm3) 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 mm2), 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.Conclusion:
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. J. Magn. Reson. Imaging 2012;35:1216‐1221. © 2012 Wiley Periodicals, Inc.12.
Jiang Du Atsushi M. Takahashi Won C. Bae Christine B. Chung Graeme M. Bydder 《Magnetic resonance in medicine》2010,63(2):447-455
Imaging of short‐T2 species requires not only a short echo time but also efficient suppression of long‐T2 species in order to maximize the short‐T2 contrast and dynamic range. This paper introduces a method of long‐T2 suppression using two long adiabatic inversion pulses. The first adiabatic inversion pulse inverts the magnetization of long‐T2 water and the second one inverts that of fat. Short‐T2 species experience a significant transverse relaxation during the long adiabatic inversion process and are minimally affected by the inversion pulses. Data acquisition with a short echo time of 8 μs starts following a time delay of inversion time (TI1) for the inverted water magnetization to reach a null point and a time delay of TI2 for the inverted fat magnetization to reach a null point. The suppression of long‐T2 species depends on proper combination of TI1, TI2, and pulse repetition time. It is insensitive to radiofrequency inhomogeneities because of the adiabatic inversion pulses. The feasibility of this dual inversion recovery ultrashort echo time technique was demonstrated on phantoms, cadaveric specimens, and healthy volunteers, using a clinical 3‐T scanner. High image contrast was achieved for the deep radial and calcified layers of articular cartilage, cortical bone, and the Achilles tendon. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
13.
Purpose
To integrate water‐fat–resolved spiral gradient‐echo imaging with off‐resonance correction into a clinical MR scanner and to evaluate its basic feasibility and performance.Materials and Methods
Three‐point chemical shift imaging was implemented with forward and strongly T2*‐weighted reverse spiral sampling and with off‐resonance correction after water–fat separation. It was applied in a volunteer study on single breathhold abdominal imaging, which included a brief comparison with Cartesian sampling.Results
Water‐fat–resolved, off‐resonance–corrected forward and reverse three‐dimensional interleaved spiral imaging was found to be feasible on a clinical MR scanner with only minor changes to the existing data acquisition and reconstruction, and to provide good image quality. Three‐point chemical shift encoded data thus support both, water–fat separation and off‐resonance correction with high accuracy.Conclusion
The combination of chemical shift encoding and appropriate postprocessing could pave the way for water‐fat–resolved spiral imaging in clinical applications. J. Magn. Reson. Imaging 2010;32:1262–1267. © 2010 Wiley‐Liss, Inc. 相似文献14.
Reeder SB McKenzie CA Pineda AR Yu H Shimakawa A Brau AC Hargreaves BA Gold GE Brittain JH 《Journal of magnetic resonance imaging : JMRI》2007,25(3):644-652
Purpose
To combine gradient‐echo (GRE) imaging with a multipoint water–fat separation method known as “iterative decomposition of water and fat with echo asymmetry and least squares estimation” (IDEAL) for uniform water–fat separation. Robust fat suppression is necessary for many GRE imaging applications; unfortunately, uniform fat suppression is challenging in the presence of B0 inhomogeneities. These challenges are addressed with the IDEAL technique.Materials and Methods
Echo shifts for three‐point IDEAL were chosen to optimize noise performance of the water–fat estimation, which is dependent on the relative proportion of water and fat within a voxel. Phantom experiments were performed to validate theoretical SNR predictions. Theoretical echo combinations that maximize noise performance are discussed, and examples of clinical applications at 1.5T and 3.0T are shown.Results
The measured SNR performance validated theoretical predictions and demonstrated improved image quality compared to unoptimized echo combinations. Clinical examples of the liver, breast, heart, knee, and ankle are shown, including the combination of IDEAL with parallel imaging. Excellent water–fat separation was achieved in all cases. The utility of recombining water and fat images into “in‐phase,” “out‐of‐phase,” and “fat signal fraction” images is also discussed.Conclusion
IDEAL‐SPGR provides robust water–fat separation with optimized SNR performance at both 1.5T and 3.0T with multicoil acquisitions and parallel imaging in multiple regions of the body. J. Magn. Reson. Imaging 2007;25:644–652. © 2007 Wiley‐Liss, Inc. 相似文献15.
Scott B. Reeder Angel R. Pineda Zhifei Wen Ann Shimakawa Huanzhou Yu Jean H. Brittain Garry E. Gold Christopher H. Beaulieu Norbert J. Pelc 《Magnetic resonance in medicine》2005,54(3):636-644
Chemical shift based methods are often used to achieve uniform water–fat separation that is insensitive to Bo inhomogeneities. Many spin‐echo (SE) or fast SE (FSE) approaches acquire three echoes shifted symmetrically about the SE, creating time‐dependent phase shifts caused by water–fat chemical shift. This work demonstrates that symmetrically acquired echoes cause artifacts that degrade image quality. According to theory, the noise performance of any water–fat separation method is dependent on the proportion of water and fat within a voxel, and the position of echoes relative to the SE. To address this problem, we propose a method termed “iterative decomposition of water and fat with echo asymmetric and least‐squares estimation” (IDEAL). This technique combines asymmetrically acquired echoes with an iterative least‐squares decomposition algorithm to maximize noise performance. Theoretical calculations predict that the optimal echo combination occurs when the relative phase of the echoes is separated by 2π/3, with the middle echo centered at π/2+πk (k = any integer), i.e., (–π/6+πk, π/2+πk, 7π/6+πk). Only with these echo combinations can noise performance reach the maximum possible and be independent of the proportion of water and fat. Close agreement between theoretical and experimental results obtained from an oil–water phantom was observed, demonstrating that the iterative least‐squares decomposition method is an efficient estimator. Magn Reson Med, 2005. © 2005 Wiley‐Liss, Inc. 相似文献
16.
Zhiqiang Li Christian Graff Arthur F. Gmitro Scott W. Squire Ali Bilgin Eric K. Outwater Maria I. Altbach 《Magnetic resonance in medicine》2009,61(6):1415-1424
Three‐point Dixon methods have been investigated as a means to generate water and fat images without the effects of field inhomogeneities. Recently, an iterative algorithm (IDEAL, iterative decomposition of water and fat with echo asymmetry and least squares estimation) was combined with a gradient and spin‐echo acquisition strategy (IDEAL‐GRASE) to provide a time‐efficient method for lipid–water imaging with correction for the effects of field inhomogeneities. The method presented in this work combines IDEAL‐GRASE with radial data acquisition. Radial data sampling offers robustness to motion over Cartesian trajectories as well as the possibility of generating high‐resolution T2 maps in addition to the water and fat images. The radial IDEAL‐GRASE technique is demonstrated in phantoms and in vivo for various applications including abdominal, pelvic, and cardiac imaging. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc. 相似文献
17.
Donglai Huo Zhiqiang Li Eric Aboussouan John P. Karis James G. Pipe 《Magnetic resonance in medicine》2009,61(1):188-195
Suppression of the fat signal in MRI is very important for many clinical applications. Multi‐point water–fat separation methods, such as IDEAL (Iterative Decomposition of water and fat with Echo Asymmetry and Least‐squares estimation), can robustly separate water and fat signal, but inevitably increase scan time, making separated images more easily affected by patient motions. PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) and Turboprop techniques offer an effective approach to correct for motion artifacts. By combining these techniques together, we demonstrate that the new TP‐IDEAL method can provide reliable water–fat separation with robust motion correction. The Turboprop sequence was modified to acquire source images, and motion correction algorithms were adjusted to assure the registration between different echo images. Theoretical calculations were performed to predict the optimal shift and spacing of the gradient echoes. Phantom images were acquired, and results were compared with regular FSE‐IDEAL. Both T1‐ and T2‐weighted images of the human brain were used to demonstrate the effectiveness of motion correction. TP‐IDEAL images were also acquired for pelvis, knee, and foot, showing great potential of this technique for general clinical applications. Magn Reson Med 61:188–195, 2009. © 2008 Wiley‐Liss, Inc. 相似文献
18.
Venkata V. Chebrolu MS Huanzhou Yu PhD Angel R. Pineda PhD Charles A. McKenzie PhD Jean H. Brittain PhD Scott B. Reeder MD PhD 《Journal of magnetic resonance imaging : JMRI》2010,32(2):493-500
Purpose:
To model the theoretical signal‐to‐noise ratio (SNR) behavior of 3‐point chemical shift‐based water‐fat separation, using spectral modeling of fat, with experimental validation for spin‐echo and gradient‐echo imaging. The echo combination that achieves the best SNR performance for a given spectral model of fat was also investigated.Materials and Methods:
Cramér‐Rao bound analysis was used to calculate the best possible SNR performance for a given echo combination. Experimental validation in a fat‐water phantom was performed and compared with theory. In vivo scans were performed to compare fat separation with and with out spectral modeling of fat.Results:
Theoretical SNR calculations for methods that include spectral modeling of fat agree closely with experimental SNR measurements. Spectral modeling of fat more accurately separates fat and water signals, with only a slight decrease in the SNR performance of the water‐only image, although with a relatively large decrease in the fat SNR performance.Conclusion:
The optimal echo combination that provides the best SNR performance for water using spectral modeling of fat is very similar to previous optimizations that modeled fat as a single peak. Therefore, the optimal echo spacing commonly used for single fat peak models is adequate for most applications that use spectral modeling of fat. J. Magn. Reson. Imaging 2010;32:493–500. © 2010 Wiley‐Liss, Inc. 相似文献19.
Hines CD Frydrychowicz A Hamilton G Tudorascu DL Vigen KK Yu H McKenzie CA Sirlin CB Brittain JH Reeder SB 《Journal of magnetic resonance imaging : JMRI》2011,33(4):873-881
Purpose:
To determine the precision and accuracy of hepatic fat‐fraction measured with a chemical shift‐based MRI fat‐water separation method, using single‐voxel MR spectroscopy (MRS) as a reference standard.Materials and Methods:
In 42 patients, two repeated measurements were made using a T1‐independent, T‐corrected chemical shift‐based fat‐water separation method with multi‐peak spectral modeling of fat, and T2‐corrected single voxel MR spectroscopy. Precision was assessed through calculation of Bland‐Altman plots and concordance correlation intervals. Accuracy was assessed through linear regression between MRI and MRS. Sensitivity and specificity of MRI fat‐fractions for diagnosis of steatosis using MRS as a reference standard were also calculated.Results:
Statistical analysis demonstrated excellent precision of MRI and MRS fat‐fractions, indicated by 95% confidence intervals (units of absolute percent) of [?2.66%,2.64%] for single MRI ROI measurements, [?0.81%,0.80%] for averaged MRI ROI, and [?2.70%,2.87%] for single‐voxel MRS. Linear regression between MRI and MRS indicated that the MRI method is highly accurate. Sensitivity and specificity for detection of steatosis using averaged MRI ROI were 100% and 94%, respectively. The relationship between hepatic fat‐fraction and body mass index was examined.Conclusion:
Fat‐fraction measured with T1‐independent T‐corrected MRI and multi‐peak spectral modeling of fat is a highly precise and accurate method of quantifying hepatic steatosis. J. Magn. Reson. Imaging 2011;33:873–881. © 2011 Wiley‐Liss, Inc.20.
Purpose: To investigate various sources of bias in MRI‐based quantification of fat fraction (FF) and fatty acid composition (FAC) using chemical shift‐encoded techniques. Methods: Signals from various FFs and FACs and individual relaxation rates of all signal components were simulated. From these signals, FF and FAC parameters were estimated with and without correction for differences in individual relaxation rates. In addition, phantom experiments were conducted with various flip angles and number of echoes to validate the simulations. Results: As expected, T1 weighting resulted in an overestimation of the FF, but had much smaller impact on the FAC parameters. Differences in T2 values of the signal components resulted in overestimation of the FAC parameters in fat/water mixtures, whereas the estimation in pure oil was largely unaffected. This bias was corrected using a simplified signal model with different T2 values of water and fat, where the accuracy of the modeled T2 of water was critical. The results of the phantom experiment were in agreement with simulations. Conclusion: T1 weighting has only a minor effect on FAC quantification in both fat/water mixtures and pure oils. T2 weighting is mainly a concern in fat/water mixtures but may be corrected using a simplified model. Magn Reson Med 72:1320–1329, 2014. © 2013 Wiley Periodicals, Inc. 相似文献