Sensitivity analysis of effective transverse shear viscoelastic and diffusional properties of myelinated white matter
Sensitivity analysis of effective transverse shear viscoelastic and diffusional properties of myelinated white matter
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DOI：
10.1088/1361-6560/aba0cc
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发表时间：
2020-06
影响因子：
3.5
通讯作者：
Dan Sullivan;Xuehai Wu;Nicolás. Gallo;Noel M. Naughton;J. Georgiadis;A. Pelegri
中科院分区：
文献类型：
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作者：
Dan Sullivan;Xuehai Wu;Nicolás. Gallo;Noel M. Naughton;J. Georgiadis;A. Pelegri
出于解释体内脑磁共振弹性成像（MRE）和弥散张量成像（DTI）联合使用的结果的需要，我们开发了一个计算框架来研究单频MRE和DTI指标对白色物质微观结构和细胞水平机械和弥散特性的敏感性。将白色物质建模为三相单向复合物，由被鞘（髓鞘）包围的平行圆柱形内含物（轴突）组成，并包埋在基质（神经胶质细胞加细胞外基质）中。只有二维力学和扩散的横向平面（垂直于轴突方向）被认为是均匀的（有效的）属性导出的周期性域包含一个单一的轴突。MRE问题的数值解与ABAQUS和采用先进的边界协调网格生成方案进行。基于线性粘弹性响应谐波剪切激励和稳态扩散在横向平面上，MRE度量（有效横向剪切存储和损耗模量）和DTI度量（有效径向扩散率）进行了系统的灵敏度分析的范围广泛的微观结构和内在（基于相位）的物理性能。所考虑的显微结构特性是纤维体积分数和髓鞘/轴突直径比。MRE和DTI指标对纤维体积分数和胶质相的固有粘弹性模量非常敏感。MRE度量是纤维体积分数的非线性函数，而有效扩散系数则与纤维体积分数呈线性关系。最后，稳态时MRE和DTI的横向度量对轴突直径不敏感。我们的研究结果与文献中有限的各向异性MRE和共配准DTI测量结果一致，主要是在胼胝体中。我们的结论是，各向同性MRE和DTI本构模型是很好的近似有髓鞘的白色物质的横向平面。本文提出的单向复合材料模型首次用于在单元水平上模拟MRE相关频率下的谐波剪应力。该模型可以扩展到3D，以通知MRE中的逆问题的解决方案，建立MRE指标的生物学基础，并将MRE/DTI与其他模态集成，以提高神经成像的特异性。
Motivated by the need to interpret the results from a combined use of in vivo brain Magnetic Resonance Elastography (MRE) and Diffusion Tensor Imaging (DTI), we developed a computational framework to study the sensitivity of single-frequency MRE and DTI metrics to white matter microstructure and cell-level mechanical and diffusional properties. White matter was modeled as a triphasic unidirectional composite, consisting of parallel cylindrical inclusions (axons) surrounded by sheaths (myelin), and embedded in a matrix (glial cells plus extracellular matrix). Only 2D mechanics and diffusion in the transverse plane (perpendicular to the axon direction) was considered, and homogenized (effective) properties were derived for a periodic domain containing a single axon. The numerical solutions of the MRE problem were performed with ABAQUS and by employing a sophisticated boundary-conforming grid generation scheme. Based on the linear viscoelastic response to harmonic shear excitation and steady-state diffusion in the transverse plane, a systematic sensitivity analysis of MRE metrics (effective transverse shear storage and loss moduli) and DTI metric (effective radial diffusivity) was performed for a wide range of microstructural and intrinsic (phase-based) physical properties. The microstructural properties considered were fiber volume fraction, and the myelin sheath/axon diameter ratio. The MRE and DTI metrics are very sensitive to the fiber volume fraction, and the intrinsic viscoelastic moduli of the glial phase. The MRE metrics are nonlinear functions of the fiber volume fraction, but the effective diffusion coefficient varies linearly with it. Finally, the transverse metrics of both MRE and DTI are insensitive to the axon diameter in steady state. Our results are consistent with the limited anisotropic MRE and co-registered DTI measurements, mainly in the corpus callosum, available in the literature. We conclude that isotropic MRE and DTI constitutive models are good approximations for myelinated white matter in the transverse plane. The unidirectional composite model presented here is used for the first time to model harmonic shear stress under MRE-relevant frequency on the cell level. This model can be extended to 3D in order to inform the solution of the inverse problem in MRE, establish the biological basis of MRE metrics, and integrate MRE/DTI with other modalities towards increasing the specificity of neuroimaging.