Department of Radiology, University of Michigan, Ann Arbor, Michigan, USA.
NMR Biomed. 2023 Aug;36(8):e4925. doi: 10.1002/nbm.4925. Epub 2023 Apr 2.
This work aimed to demonstrate an essential phase shift for better quantifying and in human brain white matter (WM), and to further elucidate its origin related to the directional diffusivities from standard diffusion tensor imaging (DTI). was integrated into a proposed generalized transverse relaxation model for characterizing previously published and orientation dependence profiles in brain WM, and then comparisons were made with those without . It was theorized that anisotropic diffusivity direction was collinear with an axon fiber subject to all eigenvalues and eigenvectors from an apparent diffusion tensor. To corroborate the origin of , orientation dependences referenced by were compared with those referenced by the standard principal diffusivity direction at b-values of 1000 and 2500 (s/mm ). These orientation dependences were obtained from -weighted images (b = 0) of ultrahigh-resolution Connectome DTI datasets in the public domain. A normalized root-mean-square error ( ) and an -test were used for evaluating curve-fittings, and statistical significance was considered to be a p of 0.05 or less. A phase-shifted model resulted in significantly reduced compared with that without in quantifying various and profiles, both in vivo and ex vivo at multiple fields. The profiles based on manifested a right-shifted phase ( ) at two b-values, while those based on became free from . For all phase-shifted and profiles, generally depended on the directional diffusivities by , as predicted. In summary, a ubiquitous phase shift has been demonstrated as a prerequisite for better quantifying transverse relaxation orientation dependences in human brain WM. Furthermore, the origin of associated with the directional diffusivities from DTI has been elucidated. These findings could have a significant impact on interpretations of prior and datasets and on future research.
本研究旨在演示在人体大脑白质（WM）中进行更好的量化所必需的相位偏移，进一步阐明其起源与来自标准扩散张量成像（DTI）的各向异性扩散的方向有关。将相位偏移整合到一个提出的广义横向弛豫模型中，用于描述以前发表的和大脑 WM 中的方向依赖性分布，然后与没有相位偏移的进行比较。理论上认为各向异性扩散方向与轴突纤维共线，该纤维受到各向异性扩散张量的所有特征值和特征向量的影响。为了证实的起源，通过比较参考和参考的方向依赖性，来验证参考和参考的方向依赖性。在 b 值为 1000 和 2500（s/mm）时，从公共领域超高分辨率 Connectome DTI 数据集的加权图像（b = 0）中获得了这些方向依赖性。归一化均方根误差（ ）和 检验用于评估曲线拟合，统计显著性被认为是 p 值小于或等于 0.05。与没有相位偏移的相比，在量化各种和分布时，相位偏移模型显著降低了。在多个场中，体内和体外均如此。基于的分布在两个 b 值处表现出右移的相位（ ），而基于的分布则没有相位偏移。对于所有的相位偏移和分布，一般取决于各向异性扩散的方向，如预测的那样。总之，已经证明在人体大脑 WM 中进行更好的量化横向弛豫方向依赖性必需的普遍相位偏移。此外，已经阐明了与 DTI 的各向异性扩散有关的的起源。这些发现可能对先前和数据集的解释以及未来的研究产生重大影响。
