Miller Renee, Kolipaka Arunark, Nash Martyn P, Young Alistair A
Department of Anatomy and Medical Imaging, University of Auckland, New Zealand.
Auckland Bioengineering Institute, University of Auckland, New Zealand.
NMR Biomed. 2018 Oct;31(10):e3848. doi: 10.1002/nbm.3848. Epub 2017 Nov 6.
Although magnetic resonance elastography (MRE) has been used to estimate isotropic stiffness in the heart, myocardium is known to have anisotropic properties. This study investigated the determinability of global transversely isotropic material parameters using MRE and finite-element modeling (FEM). A FEM-based material parameter identification method, using a displacement-matching objective function, was evaluated in a gel phantom and simulations of a left ventricular (LV) geometry with a histology-derived fiber field. Material parameter estimation was performed in the presence of Gaussian noise. Parameter sweeps were analyzed and characteristics of the Hessian matrix at the optimal solution were used to evaluate the determinability of each constitutive parameter. Four out of five material stiffness parameters (Young's modulii E and E , shear modulus G and damping coefficient s), which describe a transversely isotropic linear elastic material, were well determined from the MRE displacement field using an iterative FEM inversion method. However, the remaining parameter, Poisson's ratio, was less identifiable. In conclusion, Young's modulii, shear modulii and damping can theoretically be well determined from MRE data, but Poisson's ratio is not as well determined and could be set to a reasonable value for biological tissue (close to 0.5).
尽管磁共振弹性成像（MRE）已被用于估计心脏的各向同性硬度，但已知心肌具有各向异性特性。本研究使用MRE和有限元建模（FEM）研究了全局横向各向同性材料参数的可确定性。在凝胶体模以及具有组织学衍生纤维场的左心室（LV）几何结构模拟中，评估了一种基于FEM的材料参数识别方法，该方法使用位移匹配目标函数。在存在高斯噪声的情况下进行材料参数估计。分析参数扫描，并使用最优解处的海森矩阵特征来评估每个本构参数的可确定性。使用迭代FEM反演方法从MRE位移场中很好地确定了描述横向各向同性线性弹性材料的五个材料刚度参数中的四个（杨氏模量E和E、剪切模量G和阻尼系数s）。然而，其余参数泊松比的可识别性较差。总之，理论上可以从MRE数据中很好地确定杨氏模量、剪切模量和阻尼，但泊松比的确定效果不佳，可以将其设定为生物组织的合理值（接近0.5）。
