考虑剪切波声弹衰减的组织粘弹性非线性表征
Nonlinear Characterization of Tissue Viscoelasticity with Acoustoelastic Attenuation of Shear-Waves
摘要：
剪切波弹性成像（SWE）测量剪切波速（SWS），其与软组织的潜在剪切模量相关。SWE方法通常假设软组织粘弹性与机械载荷无关，然而，已知软组织具有随着预压缩而非线性变化的粘弹性。因此，仅通过SWS进行表征是不够的，其中非线性特性可被视为混杂因素，但也可用作额外的生物标记物。介质的粘弹性性质完全由其存储和损耗模量表征，这与SWS和剪切波衰减（SWA）有关。在这项工作中，我们研究SWA特性作为施加应变的函数来测量软组织中的非线性粘弹性参数。为了这个目的，我们施加增量准静态压缩的样品，同时测量SWS和SWA，从中我们获得存储和损耗模量估计非线性粘弹性参数作为应用应变的函数，使用声弹性（AE）理论。不同含油率的仿组织模型和离体猪肝实验结果表明了该方法的可行性。在这两个实验中，观察到SWA随着施加的应变而降低。对于离体肝脏中的10%压缩，剪切波衰减平均降低28%（93 Np/m），而SWS平均增加20%（0.26 m/s）。
英文摘要：
Shear-wave elastography (SWE) measures shear-wave speed (SWS), which is related to the underlying shear modulus of soft tissue. SWE methods generally assume that soft tissue viscoelasticity is independent of mechanical loading, however, soft tissues are known to have viscoelasticity changing nonlinearly with pre-compression. Hence, characterization by SWS alone is insufficient, where nonlinear properties can be seen as confounders but may also be utilized as additional bio-markers. The viscoelastic nature of a medium is fully characterized by its storage and loss moduli, which are related to SWS and shear-wave attenuation (SWA). In this work, we study SWA characteristics as a function of applied strain to measure nonlinear viscoelastic parameters in soft tissues. For this purpose, we apply incremental quasi-static compression on the samples while measuring SWS and SWA, from which we derive storage and loss moduli to estimate nonlinear viscoelastic parameters as a function of applied strain using acoustoelasticity (AE) theory. Results from tissue-mimicking phantoms with varying oil percentages and ex-vivo porcine liver experiments demonstrate the feasibility of the proposed approach. In both these experiments, SWA was observed to decrease with applied strain. For 10 % compression in ex-vivo livers, shear-wave attenuation decreased on average by 28 % (93 Np/m), while SWS increased on average by 20 % (0.26 m/s).
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