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种有吸引力的无创工具，通过测量水分子的扩散过程来评估生物组织的微观结构和生理状态。水分子的随机位移（即扩散）受到介质中结构和生理因素的影响。在脑白质中，由于其具有髓鞘、轴突、纤维束等微观和宏观有序的特征，水分子的扩散率在三维空间的各个方向上并不相同，在成像体素尺度上具有各向异性。扩散过程用图形表示为椭球体。在胚胎晚期和出生后早期，大鼠脑灰质表现出高度的各向异性。在出生后较晚的年龄，各向异性减少。成年大鼠皮质灰质的这种各向异性较低。通过对胚胎晚期至出生后期大鼠皮层灰质各向异性变化和组织病理学变化的比较，揭示各向异性扩散过程的决定因素及其贡献。本研究包括大鼠脑弥散张量体外成像技术的发展，弥散张量计算和制图工具的创建，以及Sprague-Dawley大鼠脑皮层免疫组织化学特征的估计，以评估大鼠大脑皮层灰质各向异性变化与胚胎后期至出生后期组织病理学变化之间的关系

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