MR and Iontophoretic Diffusion Measurements in Brain

描述（由申请人提供）： 扩散是脑组织细胞外（EC）和细胞内（IC）区室的重要转运机制。这些复杂环境的物理性质可以由两个参数来概括：体积分数决定了扩散分子可进入的脑体积的比例，而曲折度描述了环境相对于无障碍介质施加的阻碍。扩散加权磁共振（DW-MR）检测EC和IC信号的复杂混合物。实时离子电渗（RTI）方法也可用于测量扩散，但仅在EC空间中。这两种方法都已用于研究病理条件，如缺血，并通常发现在受损组织中扩散较慢。机制仍在讨论中。 我们将测量一个小的阴离子，六氟锑酸盐（SbF 6-）的扩散，以帮助DW-MR测量的解释。SbF 6-可被DW-MR和RTI检测到，并且不易穿过细胞膜。在RTI方法的帮助下，将有可能分离EC和IC隔室的扩散性质。有三个具体目标： 目的1：检验SbF 6-在DW-MR和RTI中测量的扩散性质相同的假设。将在7特斯拉下优化氟敏感DW-MR序列，以可靠地检测作为水替代物的SbF 6-阴离子。将使用两种方法在稀释琼脂糖凝胶中测量扩散，以确定其对应程度。 目标二：测试在正常条件下和在模拟缺血中细胞体积变化的低渗应激期间乌龟小脑中EC和IC扩散参数之间是否存在差异。将通过DW-MR测量EC扩散并与RTI进行比较。DW-MR测量将持续几个小时，促进细胞外SbF 6-逐渐进入细胞。这将允许分离EC和IC扩散性质。 目的3：在离体厚切片缺血模型中测量EC和IC扩散。目标2中开发的方法将用于确定大鼠新皮层厚（1000（m））切片中预期扩散降低的特征和起源（EC、IC或两者）。

DESCRIPTION (provided by applicant): Diffusion is an important transport mechanism in both the extracellular (EC) and intracellular (IC) compartments of brain tissue. The physical properties of these complex environments can be summarized by two parameters: the volume fraction determines the proportion of the brain volume accessible to diffusing molecules and the tortuosity describes the hindrance imposed by the environment relative to an obstacle free medium. Diffusion-weighted magnetic resonance (DW-MR) detects a complicated mixture of the EC and IC signals. The Real-Time Iontophoresis (RTI) method also can be used to measure diffusion but only in the EC space. Both methods have been used to study pathological conditions such as ischemia, and generally found slower diffusion in the compromised tissue. The mechanisms are still debated. We will measure diffusion of a small anion, hexafluoroantimonate (SbF6-), to aid in the interpretation of the DW-MR measurements. SbF6- can be detected by both DW-MR and RTI, and does not easily cross cellular membranes. With help from the RTI method, it will be possible to separate the diffusion properties of the EC and IC compartments. There are three specific aims: Aim 1: Test the hypothesis that the measured diffusion properties of SbF6- are the same in DW-MR and RTI. A fluorine-sensitive DW-MR sequence will be optimized at 7 Tesla to reliably detect the SbF6- anion acting as a water substitute. The diffusion will be measured in a diluted agarose gel using both methods to establish the degree of their correspondence. Aim 2: Test whether differences exist between the EC and IC diffusion parameters in the turtle cerebellum under normal conditions and during hypoosmotic stress mimicking cell volume changes in ischemia. The EC diffusion will be measured by DW-MR and compared with RTI. The DW-MR measurement will then continue for several hours, facilitating gradual entry of extracellular SbF6- into cells. This will allow separation of the EC and IC diffusion properties. Aim 3: Measure EC and IC diffusion in a thick-slice in vitro model of ischemia. The method developed in Aim 2 will be applied to determine the characteristics and origins (EC, IC, or both) of the expected diffusion decrease in the thick (1000 (m) slices of rat neocortex.