In vivo imaging of viscoelasticity and hardness of biological soft tissue using ultrasound.

组织弹性的变化与活体软组织的弥漫性疾病过程有关。这项研究的目的是基于超声测量的位移和应变来表征组织的弹性，当主要的心脏搏动或外部机械力作用于软组织时。提出了一个组织弹性的变化模型，它是由于内部应变张量的变化而引起的杨氏弹性模数或剪切弹性模数的变化。使用实时超声进行测量，并将从组织返回的RF回波信号序列数字化以估计局部组织位移。本文利用射频回波包络信号的时空导数来估计内部位移的二维分布，由此计算出内部应变张量的分量。组织模拟体模实验表明，应变张量分量的二维场可以估计出8 mm×8 mm的空间分辨率。重建了基于应变图像的相对剪切模量值分布。在活体软组织实验中，如活体肝脏，相对剪切模数在弹性较小的区域较大。软组织的弹性可以用从接收到的射频回波信号中观察到的局部应变张量计算出的相对剪切模量来表征。

Changes in tissue elasticity are related to diffuse disease processes of living soft tissue. The goal of this study is to characterize tissue elasticity based on ultrasonic measurement of displacement and strain when the primary cardiac pulsation or the external mechanical force is applied to the soft tissue. A model is presented for the changes in tissue elasticity as a change of internal strain tensor, which results in variation in the Young's or shear modulus of elasticity. Mesurements are performed using real-time ultrasound and the sequences of RF echo signal returned from tissue are digitized to estimate local tissue displacement. In this paper the 2-dimensional distribution of internal displacement is estimated using the spatio-temporal derivative of RF echo envelope signals, from which components of internal strain tensor are computed. Experiments on tissue mimicking phantoms indicate that 2-dimensional fields of components of strain tensor can be estimated with the spatial resolution of 8mm*8mm. The distribution of the relative shear modulus based on strain images is reconstructed. In experiments with living soft tissue, such as liver in vivo, the relative shear modulus is large in less elastic regions. The elasticity of soft tissue can be characterized as the relative shear modulus computed from the local strain tenpor observed in the received RF echo signals.