Rat Brain Diffusion Tensor MR Imaging ; evaluation of anisotropic diffusion process determination factors

扩散张量（DT）磁共振成像已被提出作为一个有吸引力的非侵入性的工具，用于评估生物组织中的微结构和生理状态，通过测量水分子的扩散过程。水分子的随机位移（即扩散）通过介质中的结构和生理因素进行修改。在脑白色物质中，水分子的扩散率在三维空间的所有方向上是不相同的，并且由于其特有的有序的微观和宏观特征（诸如髓鞘、轴突和纤维束）而在成像体素尺度上是各向异性的。扩散过程用椭圆体来表示。通过估计椭球的性质，可以获得有关白色物质的生理和结构（包括组织病理学）的定量信息。到出生后年龄，各向异性减小。这种皮质灰质的各向异性在成年大鼠中很低。通过比较胚胎晚期至生后晚期大鼠大脑皮质灰质的各向异性变化与组织病理学变化，可以揭示各向异性扩散过程的决定因素及其贡献。本研究包括建立大鼠脑弥散张量磁共振体外成像技术，建立弥散张量计算和映射工具，以及估计Sprague-Dawley大鼠脑皮质的免疫组织化学特征，探讨大鼠胚胎晚期至胚胎晚期大脑皮质灰质各向异性变化与组织病理学变化的关系。出生后期

Diffusion-tensor (DT) MR imaging has been proposed as an attractive noninvasive tool for evaluating microstructural and physiological states in biological tissues by measuring the diffusion process of water molecules. Random displacements of water molecules (i.e. diffusion) are modified by stuctural and physiological factors in a medium. In brain white matter, diffusivity of water molecules is not the same in all directions of three dimensional space and is anisotropic at an imaging voxel scale due to its characteristic ordered microscopic and macroscopic features such as myelin sheath, axon, and fiber tract. The diffusion process is graphically expressed as an ellipsoid. By estimating properties of the ellipsoid, useful quantitative physiological and structural (including histopathological) information about white matter can be obtainedDuring late embryonic and early postnatal stage, high anisotropy is observed in rat brain gray matter. By later postnatal ages, the anisotropy, decreases. This anisotropy of the cortical gray matter is low in adult rats. By comparison between the anisotropic changes and the histopathological changes in the rat cortical gray matter from late embryonic stage to late postnatal stage, determination factors and their contribution to anisotropic diffusion process can be revealed. This seems to be essential for evaluating information derived from diffusion tensor MR imagingThis study includes development of rat brain diffusion MR in vitro imaging technique, creation of diffusion tensor calculation and mapping tools, and estimation of immunohistochemical featres of Sprague-Dawley rat brain cortex, to evaluate relationship between the anisotropic changes and the histopathological changes in the rat cortical gray matter from late embryonic stage to late postnatal stage