Arezza Nico J J, Santini Tales, Omer Mohammad, Baron Corey A
Department of Medical Biophysics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.
Centre for Functional and Metabolic Mapping (CFMM), Robarts Research Institute, Western University, London, ON, Canada.
Front Neurosci. 2023 Mar 7;17:1074730. doi: 10.3389/fnins.2023.1074730. eCollection 2023.
Water diffusion anisotropy MRI is sensitive to microstructural changes in the brain that are hallmarks of various neurological conditions. However, conventional metrics like fractional anisotropy are confounded by neuron fiber orientation dispersion, and the relatively low resolution of diffusion-weighted MRI gives rise to significant free water partial volume effects in many brain regions that are adjacent to cerebrospinal fluid. Microscopic fractional anisotropy is a recent metric that can report water diffusion anisotropy independent of neuron fiber orientation dispersion but is still susceptible to free water contamination. In this paper, we present a free water elimination (FWE) technique to estimate microscopic fractional anisotropy and other related diffusion indices by implementing a signal representation in which the MRI signal within a voxel is assumed to come from two distinct sources: a tissue compartment and a free water compartment. A two-part algorithm is proposed to rapidly fit a set of diffusion-weighted MRI volumes containing both linear- and spherical-tensor encoding acquisitions to the representation. Simulations and acquisitions with four healthy volunteers indicated that the FWE method may be a feasible technique for measuring microscopic fractional anisotropy and other indices with greater specificity to neural tissue characteristics than conventional methods.
水分子扩散各向异性磁共振成像对大脑微观结构变化敏感，而这些变化是各种神经疾病的特征。然而，像分数各向异性这样的传统指标会受到神经元纤维方向离散的干扰，并且扩散加权磁共振成像相对较低的分辨率在许多与脑脊液相邻的脑区会产生显著的自由水部分容积效应。微观分数各向异性是一种新的指标，它可以报告与神经元纤维方向离散无关的水分子扩散各向异性，但仍然容易受到自由水污染的影响。在本文中，我们提出了一种自由水消除（FWE）技术，通过实现一种信号表示来估计微观分数各向异性和其他相关扩散指数，在这种表示中，体素内的磁共振信号被假定来自两个不同的源：一个组织部分和一个自由水部分。我们提出了一种两部分算法，用于快速将一组包含线性和球形张量编码采集的扩散加权磁共振成像体积拟合到该表示中。对四名健康志愿者的模拟和采集结果表明，FWE方法可能是一种可行的技术，用于测量微观分数各向异性和其他指数，与传统方法相比，对神经组织特征具有更高的特异性。
