Healthcare Business Unit, Hitachi, Ltd., Taito-ku, Tokyo, Japan.
Department of Diagnostic Imaging, Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido, Japan.
Magn Reson Med. 2021 Sep;86(3):1369-1382. doi: 10.1002/mrm.28806. Epub 2021 Apr 23.
Cerebrospinal fluid (CSF) plays an important role in the clearance system of the brain. Recently, low b-value diffusion tensor imaging (low-b DTI) has been reported to be useful in the observation of CSF flow; however, the precise flow property observed by low-b DTI has not been fully investigated. Accordingly, a mathematical framework of low-b DTI is proposed for investigating CSF and clarifying its pseudorandom flow.
The framework will show that the limit of the diffusion tensor as b-value decreases to zero approximately represents the covariance of the velocity distribution of the CSF's pseudorandom flow.
The low b-value diffusion tensor (DT ) of whole-brain CSF was obtained using diffusion-weighted echo-planar imaging. Seven healthy volunteers were scanned for intersubject analysis; three of the volunteers was consecutively scanned for repeatability analysis. Obtained DT was visually assessed by ellipsoid-representation map and was statistically evaluated by calculating mean diffusivity (MD) and fractional anisotropy (FA) in regions of interest (ROIs) representing intensive pseudorandom flow.
Obtained DT consistently shows large and anisotropic diffusivity in some segments of CSF, typically the ROIs around the foramen of Monro, the aqueduct, the prepontine cistern, the middle cerebral artery, and the Sylvian fissure throughout the study. The statistical analysis shows high repeatability and consistently high MD and FA in all the ROIs for all the volunteers.
From the viewpoint of the proposed framework, the high and anisotropic DT in the ROIs indicates large covariance of velocity distribution, which represents intensive pseudorandom flows of CSF.
脑脊液（CSF）在大脑清除系统中起着重要作用。最近，低 b 值扩散张量成像（low-b DTI）已被报道可用于观察 CSF 流动；然而，低 b 值 DTI 观察到的精确流动性质尚未得到充分研究。因此，提出了一种低 b 值扩散张量成像的数学框架，用于研究 CSF 并阐明其伪随机流动。
该框架将表明，当 b 值降低到零时，扩散张量的极限大约代表 CSF 伪随机流动速度分布的协方差。
使用扩散加权回波平面成像获得全脑 CSF 的低 b 值扩散张量（DT）。对 7 名健康志愿者进行了扫描以进行受试者间分析；其中 3 名志愿者连续扫描以进行可重复性分析。通过椭圆表示图对获得的 DT 进行视觉评估，并通过计算代表密集伪随机流动的感兴趣区域（ROI）中的平均扩散系数（MD）和各向异性分数（FA）对其进行统计学评估。
在 CSF 的某些区域，通常是 Monro 孔、导水管、脑桥前池、大脑中动脉和大脑外侧裂周围的 ROI，获得的 DT 始终显示出较大的各向异性扩散性。在整个研究中，统计分析显示所有志愿者的所有 ROI 都具有高度的可重复性和一致的高 MD 和 FA。
从提出的框架的角度来看，ROI 中高且各向异性的 DT 表示速度分布的大协方差，这代表 CSF 的密集伪随机流动。
