Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, United States of America. Author to whom any correspondence should be addressed.
Phys Med Biol. 2019 Mar 12;64(6):065010. doi: 10.1088/1361-6560/ab0290.
Intrinsic activation MR elastography (IA-MRE) is a novel technique which seeks to estimate brain mechanical properties non-invasively and without external mechanical drivers. The method eliminates actuation hardware and patient discomfort while capitalizing on the brain's intrinsic low frequency motion. This study explores low frequency actuation (1 Hz) MR elastography in phantoms and analyzes performance of non-linear inversion (NLI) of viscoelastic and poroelastic mechanical models as a framework for assessing clinical results from IA-MRE. We present results from four gelatin phantoms and report stiffness resolution of 6 mm (two measurement voxels) with a stiffness contrast ratio of 4.21 relative to the background and 9 mm (three measurement voxels) with a lower stiffness contrast ratio of near 1.77. Stiffness edge resolution was also evaluated using edge spread and line spread functions and yielded a stiffness edge response distance of 9 mm. The intraclass correlation coefficient was high (0.93) between mechanical testing and poroelastic estimates, although quantitative agreement was affected by model-data mismatch. Viscoelastic MRE at low frequencies has issues with non-uniqueness due to small inertial forces, and performed worse than poroelastic MRE in terms of inclusion detection and consistency with mechanical testing. These results present the first evaluation of MR elastography using displacement measurements from an actuation frequency less than 5 Hz and support the validity of brain IA-MRE to recover spatially resolved stiffness changes. They provide a baseline of performance in terms of standard metrics for future animal and human brain stiffness studies and analyses based on intrinsic motion.
内禀激活磁共振弹性成像（IA-MRE）是一种新的技术，旨在无创且无需外部机械驱动器的情况下估计脑的机械特性。该方法消除了驱动硬件和患者不适，同时利用大脑固有的低频运动。本研究探索了在体模中的低频激励（1Hz）磁共振弹性成像，并分析了粘弹性和多孔弹性力学模型的非线性反演（NLI）的性能，作为评估 IA-MRE 临床结果的框架。我们提出了四个明胶体模的结果，并报告了 6mm（两个测量体素）的刚度分辨率，与背景相比刚度对比度比为 4.21，9mm（三个测量体素）的刚度对比度比接近 1.77 时的分辨率较低。还使用边缘扩散和线扩散函数评估了刚度边缘分辨率，得出刚度边缘响应距离为 9mm。力学测试和多孔弹性估计之间的组内相关系数很高（0.93），尽管定量一致性受到模型与数据不匹配的影响。由于惯性力较小，低频粘弹性 MRE 存在非唯一性问题，在检测包含物和与力学测试一致性方面，表现不如多孔弹性 MRE。这些结果首次评估了使用低于 5Hz 的激励频率的位移测量进行的磁共振弹性成像，支持使用大脑 IA-MRE 恢复空间分辨的刚度变化的有效性。它们为未来基于内在运动的动物和人脑刚度研究和分析提供了标准指标的性能基准。
