Papazoglou Sebastian, Rump Jens, Braun Jürgen, Sack Ingolf
Institute of Radiology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
Magn Reson Med. 2006 Sep;56(3):489-97. doi: 10.1002/mrm.20993.
In vivo quantification of the anisotropic shear elasticity of soft tissue is an appealing objective of elastography techniques because elastic anisotropy can potentially provide specific information about structural alterations in diseased tissue. Here a method is introduced and applied to MR elastography (MRE) of skeletal muscle. With this method one can elucidate anisotropy by means of two shear moduli (one parallel and one perpendicular to the muscle fiber direction). The technique is based on group velocity inversion applied to bulk shear waves, which is achieved by an automatic analysis of wave-phase gradients on a spatiotemporal scale. The shear moduli are then accessed by analyzing the directional dependence of the shear wave speed using analytic expressions of group velocities in k-space, which are numerically mapped to real space. The method is demonstrated by MRE experiments on the biceps muscle of five volunteers, resulting in 5.5+/-0.9 kPa and 29.3+/-6.2 kPa (P<0.05) for the medians of the perpendicular and parallel shear moduli, respectively. The proposed technique combines fast steady-state free precession (SSFP) MRE experiments and fully automated processing of anisotropic wave data, and is thus an interesting MRI modality for aiding clinical diagnosis.
对软组织各向异性剪切弹性进行体内定量分析是弹性成像技术的一个诱人目标，因为弹性各向异性可能提供有关病变组织结构改变的特定信息。本文介绍了一种方法并将其应用于骨骼肌的磁共振弹性成像（MRE）。通过该方法，可以借助两个剪切模量（一个平行于肌纤维方向，一个垂直于肌纤维方向）来阐明各向异性。该技术基于应用于体剪切波的群速度反演，这是通过在时空尺度上对波相位梯度进行自动分析来实现的。然后，利用k空间中群速度的解析表达式，通过分析剪切波速度的方向依赖性来获取剪切模量，这些表达式在数值上被映射到实空间。通过对五名志愿者肱二头肌进行MRE实验验证了该方法，垂直和平行剪切模量的中位数分别为5.5±0.9 kPa和29.3±6.2 kPa（P<0.05）。所提出的技术结合了快速稳态自由进动（SSFP）MRE实验和各向异性波数据的全自动处理，因此是一种有助于临床诊断的有趣的MRI模式。
