Burman Ingeberg Marius, Van Houten Elijah, Zwanenburg Jaco J M
Translational Neuroimaging Group, Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands.
Department of Mechanical Engineering, Université de Sherbrooke, Sherbrooke, Canada.
NMR Biomed. 2025 Jul;38(7):e70073. doi: 10.1002/nbm.70073.
Intrinsic MR elastography (iMRE) leverages brain pulsations that arise from cerebral arterial pulsations to reconstruct the mechanical properties of the brain. While iMRE has shown much potential recently, the technique was demonstrated for a viscoelastic brain model only, which suffered from data-model mismatch at the low actuation frequencies of the arterial pulsations. This work aims to address those limitations by considering the porous nature of brain tissue, where both a poroelastic and a poroviscoelastic model are assessed and compared. As a secondary goal, the influence of two driving frequencies on the material properties is investigated by looking at the 1 Hz and 2 Hz components of the motion data. The poroelastic and poroviscoelastic properties of the brain were reconstructed using a subzone-based nonlinear inversion scheme, using displacement measurements of eight healthy subjects from a previous study at 7 T MRI. The performance of each model was evaluated by assessing consistency of spatial distributions, repeatability through repeated scans, and left-right symmetry. The poroelastic model yielded mean storage moduli of 6.08 ± 0.87 and 32.01 ± 11.92 Pa, and the poroviscoelastic model yielded 5.32 ± 0.87 and 26.15 ± 8.02 Pa for the 1- and 2-Hz motion components, respectively. Among the mechanical properties of interest, the storage modulus was the most consistent, with low limits of agreement of (upper/lower) 15.0%/-22.2% for the poroelastic model and 10.9%/-18.5% for the poroviscoelastic model, relative to the whole-brain mean. It was also highly symmetric, with a mean whole-brain symmetry ratio of 0.99 across subjects for both models. Mechanical properties related to fluid flow demonstrated less consistency. The 2-Hz motion component was found to contain considerable information as it reflected the frequency-related stiffening associated with porous media, highlighting its relevance for use in multifrequency mechanical characterization. Both models demonstrated good performance, with the poroviscoelastic model in general showing the highest consistency in terms of test-retest repeatability. Future work aims to improve the models by addressing current assumptions on the boundary conditions of the pressure field.
内在磁共振弹性成像（iMRE）利用由脑动脉搏动产生的脑搏动来重建脑的力学特性。虽然iMRE最近已显示出很大潜力，但该技术仅在粘弹性脑模型中得到验证，在动脉搏动的低驱动频率下存在数据与模型不匹配的问题。这项工作旨在通过考虑脑组织的多孔性质来解决这些局限性，其中评估并比较了多孔弹性模型和多孔粘弹性模型。作为次要目标，通过查看运动数据的1Hz和2Hz分量，研究了两个驱动频率对材料特性的影响。使用基于子区域的非线性反演方案，利用先前在7T MRI研究中八名健康受试者的位移测量值，重建了脑的多孔弹性和多孔粘弹性特性。通过评估空间分布的一致性、重复扫描的可重复性以及左右对称性来评估每个模型的性能。对于1Hz和2Hz运动分量，多孔弹性模型的平均储能模量分别为6.08±0.87和32.01±11.92Pa，多孔粘弹性模型分别为5.32±0.87和26.15±8.02Pa。在所关注的力学特性中，储能模量最一致，相对于全脑平均值，多孔弹性模型的一致性下限（上限/下限）为15.0%/-22.2%，多孔粘弹性模型为10.9%/-18.5%。它也具有高度对称性，两个模型在受试者中的全脑平均对称比均为0.99。与流体流动相关的力学特性表现出较低的一致性。发现2Hz运动分量包含相当多的信息，因为它反映了与多孔介质相关的频率相关硬化，突出了其在多频力学表征中的相关性。两个模型都表现出良好的性能，多孔粘弹性模型在重测可重复性方面总体显示出最高的一致性。未来的工作旨在通过解决当前关于压力场边界条件的假设来改进模型。
