Magnetic resonance elastography in nonlinear viscoelastic materials under load.
Magnetic resonance elastography in nonlinear viscoelastic materials under load.
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DOI：
10.1007/s10237-018-1072-1
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发表时间：
2019-03
影响因子：
3.5
通讯作者：
Nordsletten D
中科院分区：
文献类型：
--
作者：
Capilnasiu A;Hadjicharalambous M;Fovargue D;Patel D;Holub O;Bilston L;Screen H;Sinkus R;Nordsletten D
软组织力学特性的表征是转化和临床研究中越来越感兴趣的主题。磁共振弹性成像（MRE）已被用于在这种情况下，在体内非侵入性地评估组织的机械性能。通常情况下，这些分析依赖于线性粘弹性波动方程，从测量的波动力学评估材料性能。但是，某些组织（例如呼吸期间的肝脏、心动周期期间的心脏或乳房检查期间的外部压缩）中发生的变形可能会产生加载偏倚，从而使MRE测量中的组织硬度解释复杂化。在本文中，它是如何结合知识的材料的流变学和加载状态可以用来消除加载偏差，使解释的内在（卸载）刚度特性。方程推导出利用摄动理论和柯西的运动方程，以证明在非线性粘弹性材料的周期性稳态波动行为的加载状态的影响。这些方程说明了加载偏差如何产生明显的材料硬化、软化和各向异性。MRE变形的敏感性在实验体模中得到证明，显示出高达两倍的加载偏差。从一个无偏刚度的Pa在卸载状态下，偏置刚度增加到9767.5 - 1949.9 Pa的负载下的34%的单轴压缩。集成到一个新的MRE重建的幻影加载和流变学的知识，它表明，它是可能的，以消除固有的材料特性，从MRE数据的加载偏差。在幻影中介绍和展示的框架说明了一种途径，可以被翻译和应用于复杂变形组织中的MRE。这将有助于采用弹性成像更好地评估软组织中的材料特性。
Characterisation of soft tissue mechanical properties is a topic of increasing interest in translational and clinical research. Magnetic resonance elastography (MRE) has been used in this context to assess the mechanical properties of tissues in vivo noninvasively. Typically, these analyses rely on linear viscoelastic wave equations to assess material properties from measured wave dynamics. However, deformations that occur in some tissues (e.g. liver during respiration, heart during the cardiac cycle, or external compression during a breast exam) can yield loading bias, complicating the interpretation of tissue stiffness from MRE measurements. In this paper, it is shown how combined knowledge of a material’s rheology and loading state can be used to eliminate loading bias and enable interpretation of intrinsic (unloaded) stiffness properties. Equations are derived utilising perturbation theory and Cauchy’s equations of motion to demonstrate the impact of loading state on periodic steady-state wave behaviour in nonlinear viscoelastic materials. These equations demonstrate how loading bias yields apparent material stiffening, softening and anisotropy. MRE sensitivity to deformation is demonstrated in an experimental phantom, showing a loading bias of up to twofold. From an unbiased stiffness of Pa in unloaded state, the biased stiffness increases to 9767.5 1949.9 Pa under a load of 34% uniaxial compression. Integrating knowledge of phantom loading and rheology into a novel MRE reconstruction, it is shown that it is possible to characterise intrinsic material characteristics, eliminating the loading bias from MRE data. The framework introduced and demonstrated in phantoms illustrates a pathway that can be translated and applied to MRE in complex deforming tissues. This would contribute to a better assessment of material properties in soft tissues employing elastography.
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