A heterogenous, time harmonic, nearly incompressible transverse isotropic finite element brain simulation platform for MR elastography.
A heterogenous, time harmonic, nearly incompressible transverse isotropic finite element brain simulation platform for MR elastography.
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DOI：
10.1088/1361-6560/ab9a84
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发表时间：
2021-02-26
影响因子：
3.5
通讯作者：
中科院分区：
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在这项研究中，我们描述了一个异质的，几乎不可压缩的，横观各向同性（NITI）有限元（FE）模型的数值实现，用于纤维软组织的MR弹性成像的关键优势。MR弹性成像（MRE）根据组织反应的假设力学模型，从MR测量的谐波运动场估计异质性分布。目前的MRE属性估计方法通常假设各向同性属性，这导致当存在各向异性时由模型-数据失配引起的不一致。在这项研究中，我们使用的NITI模型参数化的基础剪切模量，剪切各向异性，拉伸各向异性，和各向同性的体积模量，它描述了对齐的纤维结构的组织的力学行为。属性和纤维方向的异质性在FE高斯点的水平上实现，这使得高分辨率的扩散张量成像（DTI）数据可以很容易地纳入模型。所得到的代码进行了验证，对解析解和商业有限元软件包，并适合纳入非线性反演MRE算法。从解剖、DTI和MRE图像数据中生成具有异质性和各向异性纤维束的脑组织中的MRE模拟，其产生与实验MRE类似的波场，允许在真实情况和基础机械行为已知的现实环境中调查MRE反演性能。两个建立各向同性反演算法-非线性反演（NLI）和局部直接反演（LDI）-被施加到模拟MRE数据。这两种算法在简单的各向同性同质的情况下表现良好，但是，异质性造成大量的文物在LDI所产生的违反当地的同质性假设。NLI能够在存在测量噪声的情况下恢复精确的非均匀位移场。各向同性NLI反演的模拟各向异性数据（使用NITI模型生成）产生的各向同性的机械性能与（不希望的）依赖于波场的地图。局部各向异性也造成波场相关的误差为7%，在附近的各向同性结构，相比之下，在各向异性结构的10%。
In this study, we describe numerical implementation of a heterogenous, nearly incompressible, transverse isotropic (NITI) finite element (FE) model with key advantages for use in MR elastography of fibrous soft tissue. MR elastography (MRE) estimates heterogenous property distributions from MR-measured harmonic motion fields based on assumed mechanical models of tissue response. Current MRE property estimation methods usually assume isotropic properties, which cause inconsistencies arising from model-data mismatch when anisotropy is present. In this study, we use a NITI model parameterized by a base shear modulus, shear anisotropy, tensile anisotropy, and an isotropic bulk modulus, which describes the mechanical behavior of tissues with aligned fiber structures well. Property and fiber direction heterogeneity are implemented at the level of FE Gauss points, which allows high-resolution diffusion tensor imaging (DTI) data to be incorporated easily into the model. The resulting code was validated against analytical solutions and a commercial FEM package, and is suitable for incorporation into nonlinear inversion MRE algorithms. Simulations of MRE in brain tissue with heterogeneous properties and anisotropic fiber tracts, which produced wavefields similar to experimental MRE, were generated from anatomical, DTI and MRE image data, allowing investigation of MRE inversion performance in a realistic setting where the ground truth and underlying mechanical behavior are known. Two established isotropic inversion algorithms – nonlinear inversion (NLI) and local direct inversion (LDI) – were applied to simulated MRE data. Both algorithms performed well in simple isotropic homogenous cases; however, heterogeneity cased substantial artifacts in LDI arising from violation of local homogeneity assumptions. NLI was able to recover accurate heterogenous displacement fields in the presence of measurement noise. Isotropic NLI inversion of simulated anisotropic data (generated using the NITI model) produced maps of isotropic mechanical properties with (undesirable) dependence on the wavefield. Local anisotropy also caused wavefield-dependent errors of 7% in nearby isotropic structures, compared to 10% in the anisotropic structures.
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影响因子：
5.7
作者：
Jenkinson, M;Bannister, P;Smith, S
通讯作者：
Smith, S
影响因子：
4.2
作者：
Hiscox LV;Johnson CL;McGarry MDJ;Perrins M;Littlejohn A;van Beek EJR;Roberts N;Starr JM
通讯作者：
Starr JM
影响因子：
2.7
作者：
Itskov, M;Aksel, N
通讯作者：
Aksel, N
影响因子：
3.5
作者：
Chatelin, Simon;Charpentier, Isabelle;Vappou, Jonathan
通讯作者：
Vappou, Jonathan
DOI：
10.1016/j.jmbbm.2016.03.005
发表时间：
2016-06-01
影响因子：
3.9
作者：
Anderson, Aaron T.;Van Houten, Elijah E. W.;Johnson, Curtis L.
通讯作者：
Johnson, Curtis L.