共查询到19条相似文献,搜索用时 15 毫秒
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Effect of flip angle on the accuracy and repeatability of hepatic proton density fat fraction estimation by complex data‐based,T1‐independent,T2*‐corrected,spectrum‐modeled MRI 下载免费PDF全文
Benjamin L. Johnson MD Michael E. Schroeder MBA Tanya Wolfson MA Anthony C. Gamst PhD Gavin Hamilton PhD Masoud Shiehmorteza MD Rohit Loomba MD MHSc Jeffrey B. Schwimmer MD Scott Reeder MD PhD Michael S. Middleton MD PhD Claude B. Sirlin MD 《Journal of magnetic resonance imaging : JMRI》2014,39(2):440-447
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PURPOSE: To improve the immunity of the proton resonance frequency shift (PRFS) method of MRI temperature mapping against magnetic field disturbances. Since PRFS is a phase-sensitive method, it misinterprets magnetic field disturbances as artifact temperature changes. If not corrected, the resulting temperature artifacts can completely obscure the true temperature estimation, especially if the temperature elevations are small. MATERIALS AND METHODS: Since the fat protons experience the same magnetic field disturbances as the water protons, but no temperature-related frequency shift, the fat signal has been used for correcting PRFS temperature maps for the disturbances. A simple correction method is proposed that has either better compensation capability than the phase correction methods previously reported or higher spatial and temporal resolution than the spectroscopic correction methods previously reported. The evaluated method is based on the utilization of several gradient and spin echoes acquired within one repetition interval with water- and fat-selective scans. RESULTS: In a series of phantom experiments, the improved method is shown to enable the reconstruction of accurate temperature maps in spite of interscan motion, suboptimal fat-water separation, and a wide range of magnetic field disturbances. CONCLUSION: Our approach can be used for the guidance of thermal therapies involving tissues containing fat or surrounded by fat. 相似文献
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目的 比较3.0 T和1.5 T MR最小二乘法估计和不对称回波迭代分解水和脂肪成像(IDEAL-IQ)序列质子密度脂肪分数(PDFF)和铁含量(R2*)测量值的异同。 方法 于2019年12月选取佛山市第一人民医院健康志愿者20名[其中男性13名、女性7名,年龄(23.7±2.5)岁]并用不同脂肪含量的塑料试管模型进行前瞻性研究,分别在3.0 T(A组)和1.5 T(B组)2台 MRI设备上应用IDEAL-IQ序列进行扫描。在自动生成的FatFrac图和R2*图上自动勾画感兴趣区(ROI),分别测量模型、健康志愿者的肝脏和皮下脂肪的PDFF、R2*值。符合正态分布的计量资料采用配对样本t检验(方差齐)和Mann-Whitney U检验(方差不齐)进行比较。 结果 模型A1组和B1组PDFF的测量平均值分别为(20.59±14.39)%和(21.89±14.95)%,差异无统计学意义(Z=−1.550,P=0.121);A1组和B1组R2*的测量平均值分别为(84.86±116.43) Hz和(43.61±54.59) Hz,差异有统计学意义(Z=−3.448,P=0.001)。健康志愿者3.0 T和1.5 T MRI肝脏、皮下脂肪PDFF测量平均值分别为(3.33±2.95) %和(4.39±2.80) %、(81.78±6.33) %和(81.54±5.53) %,差异均无统计学意义(Z=−1.867、t=−0.301,均P>0.05);A组肝脏、皮下脂肪的R2*测量平均值为(52.42±12.22) Hz、(50.88±10.32) Hz,分别高于对应的B组[(32.73±5.62) Hz、(39.41±9.11) Hz],且差异均有统计学意义(Z=−3.920、t=4.372,均P<0.001)。 结论 基于IDEAL-IQ序列的3.0 T和1.5 T MR模型、健康志愿者肝脏和皮下脂肪的PDFF测量值的差异无统计学意义,但3.0 T MRI的PDFF测量值可能比1.5 T MRI更接近临床实际情况;2种场强获得的R2*值的差异有统计学意义,其影响因素需进一步研究。 相似文献
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Correction of phase errors in quantitative water–fat imaging using a monopolar time‐interleaved multi‐echo gradient echo sequence 下载免费PDF全文
Stefan Ruschke Holger Eggers Hendrik Kooijman Maximilian N. Diefenbach Thomas Baum Axel Haase Ernst J. Rummeny Houchun H. Hu Dimitrios C. Karampinos 《Magnetic resonance in medicine》2017,78(3):984-996
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Actual flip-angle imaging in the pulsed steady state: a method for rapid three-dimensional mapping of the transmitted radiofrequency field. 总被引:2,自引:0,他引:2
Vasily L Yarnykh 《Magnetic resonance in medicine》2007,57(1):192-200
A new method has been developed for fast image-based measurements of the transmitted radiofrequency (RF) field. The method employs an actual flip-angle imaging (AFI) pulse sequence that consists of two identical RF pulses followed by two delays of different duration (TR(1) < TR(2)). After each pulse, a gradient-echo (GRE) signal is acquired. It has been shown theoretically and experimentally that if delays TR(1) and TR(2) are sufficiently short and the transverse magnetization is completely spoiled, the ratio r = S(2)/S(1) of signal intensities S(1) and S(2), acquired at the beginning of the time intervals TR(1) and TR(2), depends on the flip angle (FA) of applied pulses as r = (1 + n * cos(FA))/(n + cos(FA)), where n = TR(2)/TR(1). The method allows fast 3D implementation and provides accurate B(1) measurements that are highly insensitive to T(1). The unique feature of the AFI method is that it uses a pulsed steady-state signal acquisition. This overcomes the limitation of previous methods that required long relaxation delays between sequence repetitions. The method has been shown to be useful for time-efficient whole-body B(1) mapping and correction of T(1) maps obtained using a variable FA technique in the presence of nonuniform RF excitation. 相似文献
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MRI proton density fat fraction is robust across the biologically plausible range of triglyceride spectra in adults with nonalcoholic steatohepatitis 下载免费PDF全文
Cheng William Hong MD MS Adrija Mamidipalli MBBS Jonathan C. Hooker BS Gavin Hamilton PhD Tanya Wolfson MA Dennis H. Chen BSE Soudabeh Fazeli Dehkordy MD MPH Michael S. Middleton MD PhD Scott B. Reeder MD PhD Rohit Loomba MD MHSc Claude B. Sirlin MD 《Journal of magnetic resonance imaging : JMRI》2018,47(4):995-1002
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Single‐slab 3D turbo/fast spin echo (SE) imaging with very long echo trains was recently introduced with slab selection using a highly selective excitation pulse and short, nonselective refocusing pulses with variable flip angles for high imaging efficiency. This technique, however, is vulnerable to image degradation in the presence of spatially varying B1 amplitudes. In this work we develop a B1 inhomogeneity‐reduced version of single‐slab 3D turbo/fast SE imaging based on the hypothesis that it is critical to achieve spatially uniform excitation. Slab selection was performed using composite adiabatic selective excitation wherein magnetization is tipped into the transverse plane by a nonselective adiabatic‐half‐passage pulse and then slab is selected by a pair of selective adiabatic‐full‐passage pulses. Simulations and experiments were performed to evaluate the proposed technique and demonstrated that this approach is a simple and efficient way to reduce B1 sensitivity in single‐slab 3D turbo/fast SE imaging with very long echo trains. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc. 相似文献
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Inter‐examination precision of magnitude‐based MRI for estimation of segmental hepatic proton density fat fraction in obese subjects 下载免费PDF全文
Lindsey M. Negrete BS Michael S. Middleton MD PhD Lisa Clark PhD Tanya Wolfson MA Anthony C. Gamst PhD Jessica Lam BS Chris Changchien BS Ivan M. Deyoung‐Dominguez BS Gavin Hamilton PhD Rohit Loomba MD MHSc Jeffrey Schwimmer MD Claude B. Sirlin MD 《Journal of magnetic resonance imaging : JMRI》2014,39(5):1265-1271
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Accuracy of multiecho magnitude‐based MRI (M‐MRI) for estimation of hepatic proton density fat fraction (PDFF) in children 下载免费PDF全文
Kevin A. Zand MD Amol Shah MD Elhamy Heba MD Tanya Wolfson MA Gavin Hamilton PhD Jessica Lam BS Joshua Chen BS Jonathan C. Hooker BS Anthony C. Gamst PhD Michael S. Middleton MD PhD Jeffrey B. Schwimmer MD Claude B. Sirlin MD 《Journal of magnetic resonance imaging : JMRI》2015,42(5):1223-1232
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Spatial distribution of MRI‐determined hepatic proton density fat fraction in adults with nonalcoholic fatty liver disease 下载免费PDF全文
Susanne Bonekamp DVM PhD An Tang MD Arian Mashhood MD Tanya Wolfson MA Christopher Changchien BS Michael S. Middleton MD PhD Lisa Clark MPH PhD Anthony Gamst PhD Rohit Loomba MD Claude B. Sirlin MD 《Journal of magnetic resonance imaging : JMRI》2014,39(6):1525-1532
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MRI‐determined liver proton density fat fraction,with MRS validation: Comparison of regions of interest sampling methods in patients with type 2 diabetes 下载免费PDF全文
Kim‐Nhien Vu MD Guillaume Gilbert PhD Marianne Chalut Miguel Chagnon MS Gabriel Chartrand BS An Tang MD MS 《Journal of magnetic resonance imaging : JMRI》2016,43(5):1090-1099
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Quantification of liver proton‐density fat fraction in 7.1T preclinical MR systems: Impact of the fitting technique 下载免费PDF全文
Christoph Mahlke MD Diego Hernando PhD Christina Jahn Antonio Cigliano PhD Till Ittermann PhD Anne Mössler PhD Marie‐Luise Kromrey MD Grazyna Domaska PhD Scott B. Reeder MD Jens‐Peter Kühn MD 《Journal of magnetic resonance imaging : JMRI》2016,44(6):1425-1431
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Charlie C. Park Catherine Hooker Jonathan C. Hooker Emily Bass William Haufe Alexandra Schlein Yesenia Covarrubias Elhamy Heba Mark Bydder Tanya Wolfson Anthony Gamst Rohit Loomba Jeffrey Schwimmer Diego Hernando Scott B. Reeder Michael Middleton Claude B. Sirlin Gavin Hamilton 《Journal of magnetic resonance imaging : JMRI》2019,49(1):229-238