Estimation of Anisotropic Material Properties of Soft Tissue by MRI of Ultrasound-Induced Shear Waves
Estimation of Anisotropic Material Properties of Soft Tissue by MRI of Ultrasound-Induced Shear Waves
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DOI：
10.1115/1.4046127
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发表时间：
2020-03-01
影响因子：
1.7
通讯作者：
Bayly, Philip V.
中科院分区：
文献类型：
--
作者：
Guertler, Charlotte A.;Okamoto, Ruth J.;Bayly, Philip V.
本文介绍了一种新的方法来估计纤维软组织的各向异性力学性能成像剪切波引起的聚焦超声（FUS）和分析其方向依赖的速度。具有单一主导纤维方向的纤维材料可以在剪切模量和拉伸模量两者中表现出各向异性，反映了当在不同方向上施加载荷时材料响应的差异。剪切波在这种材料中的速度取决于波相对于主纤维方向的传播和偏振方向。在这项研究中，剪切波诱导肌肉组织（鸡胸肉）离体谐波振荡的振幅聚焦在一个圆柱形的组织样本的超声波束。通过旋转样品来改变纤维方向相对于激发方向的取向。磁共振弹性成像（MRE）用于可视化和测量由于超声诱导剪切波引起的全三维位移场。径向传播的“慢”和“快”剪切波的相位梯度（PG）提供了它们各自的波速和方向的局部估计。在不可压缩的，横向各向同性（TI），线性弹性材料的这些波的速度方程拟合到测量，以估计材料的剪切和拉伸模量。聚焦超声和磁共振成像的组合允许非侵入性的，但全面的，各向异性软组织的表征。
This paper describes a new method for estimating anisotropic mechanical properties of fibrous soft tissue by imaging shear waves induced by focused ultrasound (FUS) and analyzing their direction-dependent speeds. Fibrous materials with a single, dominant fiber direction may exhibit anisotropy in both shear and tensile moduli, reflecting differences in the response of the material when loads are applied in different directions. The speeds of shear waves in such materials depend on the propagation and polarization directions of the waves relative to the dominant fiber direction. In this study, shear waves were induced in muscle tissue (chicken breast) ex vivo by harmonically oscillating the amplitude of an ultrasound beam focused in a cylindrical tissue sample. The orientation of the fiber direction relative to the excitation direction was varied by rotating the sample. Magnetic resonance elastography (MRE) was used to visualize and measure the full 3D displacement field due to the ultrasound-induced shear waves. The phase gradient (PG) of radially propagating "slow" and "fast" shear waves provided local estimates of their respective wave speeds and directions. The equations for the speeds of these waves in an incompressible, transversely isotropic (TI), linear elastic material were fitted to measurements to estimate the shear and tensile moduli of the material. The combination of focused ultrasound and MR imaging allows noninvasive, but comprehensive, characterization of anisotropic soft tissue.