CONTRAST MECHANISMS IN DIFFUSION WEIGHTED MRI OF BRAIN

该项目的总体目标是提供一个全面和 定量描述人脑中的水扩散， 用于解释在正常和 病理条件，并在扩散加权MR中产生对比 图像. 现在有令人信服的证据表明水的扩散变化 在各种正常和疾病中具有普遍意义和重要性 条件 我们的目标是明确地了解这些变化的基础 这发生在脑卒中、癫痫发作和 神经元激活 我们的目标是执行一系列详尽的 测量正常人脑中的水扩散特性。 这些 研究将利用收集整套 先进的回波平面成像技术在人类中的数据，以获得 测量组织水的表观扩散系数（ADC）， 扩散受到限制的程度，以及 扩散各向异性。 这些测量结果将用于推断 水舱的大小，它们之间的交换率， 脑组织的固有扩散系数。 改进的导航仪 还将实施回波方法，以实现高分辨率 无回波平面采集的弥散图像。 测量还将 是由组织的横向衰变的详细性质组成的 磁化，以允许分解成组件衰减率。 这些所谓的弛豫谱的各个分量的图像将 这些应该揭示空间上的相关信息， 不同水环境的程度和交换。 这些测量 将与ADC在大鼠脑模型中的详细研究相补充， 癫痫发作和电休克，其中相关电生理 将获得测量结果。 观察扩散的阈值 将建立在非常短暂的刺激之后的变化。 我们将 还可以进行离体制剂的高分辨率Q空间成像， 切除的大鼠视神经，进行不同的渗透操作， 评估水量变化和其他变化的影响;我们将 继续我们对水的广泛的计算机和理论建模 在限制和分隔系统中的扩散，以提供定量的 这些和其他临床观察结果的解释。 我们将从而 获得必要的信息来解释水的扩散行为， 大脑，以指导患者最佳使用MR成像技术 管理和开发组织水扩散模型， 充分解释了中风患者和其他 条件

The overall aims of this project are to provide a comprehensive and quantitative description of water diffusion in human brain which can be used to explain the variations in water diffusion that occur in normal and pathological conditions and that produce contrast in diffusion weighted MR images. There is now compelling evidence that water diffusion variations are of general interest and importance in a variety of normal and disease conditions. We aim specifically to understand the basis for the changes that occur in diffusion weighted imaging studies of stroke, seizure and neuronal activation. We aim to perform a series of exhaustive measurements of water diffusion properties in normal human brains. These studies will make use of the efficiency for collecting complete sets of data of advanced echo planar imaging techniques in humans to obtain measurements of the apparent diffusion coefficient (ADC) of tissue water, the degree to which diffusion is restricted, and assessments of the degree of diffusion anisotropy. These measurements will be used to infer the sizes of water compartments, the rates of exchange between them, and their intrinsic diffusion coefficients in brain tissues. Improved navigator echo methods will be implemented as well to permit high resolution diffusion images without echo planar acquisition. Measurements will also be made of the detailed nature of the transverse decay of tissue magnetization to permit the decomposition into component decay rates. Images of individual components of these so-called relaxation spectra will be produced and these should reveal correlative information on the spatial extent and exchange of different water environments. These measurements will be complemented with detailed studies of ADC in rat brain models of seizure and electroshock in which correlative electrophysiological measurements will be acquired. The threshold for observing diffusion changes following very brief stimulations will be established. We will also perform high resolution q space imaging of ex vivo preparations of excised rat optic nerve, subjected to different osmotic manipulations, to evaluate the effects of water volume shifts and other changes; and we will continue our extensive computer and theoretical modeling of water diffusion in restricted and compartmented systems to provide quantitative interpretations of these and other clinical observations. We will thereby obtain the information necessary to interpret water diffusion behavior in the brain, to guide the optimal use of MR imaging techniques in patient management and for developing models of tissue water diffusion to more fully explain the MRI changes seen in patients with stroke and other conditions.