Rapid acquisition of multifrequency, multislice and multidirectional MR elastography data with a fractionally encoded gradient echo sequence
Rapid acquisition of multifrequency, multislice and multidirectional MR elastography data with a fractionally encoded gradient echo sequence
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DOI：
10.1002/nbm.2958
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发表时间：
2013-10-01
影响因子：
2.9
通讯作者：
Sinkus, Ralph
中科院分区：
文献类型：
--
作者：
Garteiser, Philippe;Sahebjavaher, Ramin S.;Sinkus, Ralph
在MR弹性成像（MRE）中，使用与外部施加的周期性机械激励同步的运动编码梯度对周期性组织运动进行相位编码。传统的方法导致扫描时间延长，以获得高质量的相位图像，从而限制了磁共振成像在临床上的广泛应用。对于实际的扫描时间，研究人员一直依赖于一维或二维运动编码，低相位采样和有限数量的切片，以及伪影倾向，单次激发，回波平面成像（EPI）读出。在这里，我们介绍了一种快速的多片脉冲序列能够三维运动编码，也适合于同时编码运动与多个频率分量。该序列基于梯度回波（GRE）序列，并利用分数编码的原理。该GRE MRE脉冲序列经验证能够在不到一分钟的时间内采集大量各向同性体素的完整三维运动编码。该序列适用于单频和多频MRE实验。在均质石蜡体模中，eXtreme序列产生的储能模量值与常规方法获得的储能模量值相似，尽管方差显著降低（GRE MRE为7.11 +/- 0.26 kPa，而常规自旋回波EPI序列为7.16 +/- 1.33 kPa）。GRE MRE序列获得了比等效自旋回波EPI序列更好的相噪比（匹配相同的采集时间）在石蜡体模和肝脏中的体内数据中（在肝脏实验中，X、Y和Z分量分别为59.62 +/- 11.89与27.86 +/- 3.81、61.49 +/- 14.16与24.78 +/- 2.48和58.23 +/- 10.39与23.48 +/- 2.91）。在单频或多频实验中使用的GRE MRE之间的相噪比相似（28 Hz时为75.39 +/- 14.93对比86.13 +/- 18.25，56 Hz时为71.52 +/- 24.74对比86.96 +/- 30.53，84 Hz时为95.60 +/- 36.96对比61.35 +/- 26.25，分别）。版权所有（C）2013约翰威利父子有限公司
In MR elastography (MRE), periodic tissue motion is phase encoded using motion-encoding gradients synchronized to an externally applied periodic mechanical excitation. Conventional methods result in extended scan time for quality phase images, thus limiting the broad application of MRE in the clinic. For practical scan times, researchers have been relying on one-dimensional or two-dimensional motion-encoding, low-phase sampling and a limited number of slices, and artifact-prone, single-shot, echo planar imaging (EPI) readout. Here, we introduce a rapid multislice pulse sequence capable of three-dimensional motion encoding that is also suitable for simultaneously encoding motion with multiple frequency components. This sequence is based on a gradient-recalled echo (GRE) sequence and exploits the principles of fractional encoding. This GRE MRE pulse sequence was validated as capable of acquiring full three-dimensional motion encoding of isotropic voxels in a large volume within less than a minute. This sequence is suitable for monofrequency and multifrequency MRE experiments. In homogeneous paraffin phantoms, the eXpresso sequence yielded similar storage modulus values as those obtained with conventional methods, although with markedly reduced variances (7.11 +/- 0.26 kPa for GRE MRE versus 7.16 +/- 1.33 kPa for the conventional spin-echo EPI sequence). The GRE MRE sequence obtained better phase-to-noise ratios than the equivalent spin-echo EPI sequence (matched for identical acquisition time) in both paraffin phantoms and in vivo data in the liver (59.62 +/- 11.89 versus 27.86 +/- 3.81, 61.49 +/- 14.16 versus 24.78 +/- 2.48 and 58.23 +/- 10.39 versus 23.48 +/- 2.91 in the X, Y and Z components, respectively, in the case of liver experiments). Phase-to-noise ratios were similar between GRE MRE used in monofrequency or multifrequency experiments (75.39 +/- 14.93 versus 86.13 +/- 18.25 at 28 Hz, 71.52 +/- 24.74 versus 86.96 +/- 30.53 at 56 Hz and 95.60 +/- 36.96 versus 61.35 +/- 26.25 at 84 Hz, respectively). Copyright (C) 2013 John Wiley & Sons, Ltd.