QUANTITATION OF DIFFUSION EFFECTS IN MR IMAGING OF BRAIN

大脑 MR 成像中扩散效应的量化

• 批准号: 2269990
• 负责人: JIANHUI ZHONG
• 金额: $ 10.74万
• 依托单位: YALE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-05-01 至 1999-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/2269990
• 关键词: animal tissue; biological fluid transport; brain circulation; brain disorder diagnosis; cell water; computer simulation; diagnosis design /evaluation; diagnosis quality /standard; diffusion; generalized seizures; gerbil /jird; laboratory mouse; laboratory rat; magnetic resonance imaging; membrane permeability; nuclear magnetic resonance spectroscopy; phantom model; stroke; technology /technique

This study aims to better understand the information provided by diffusion weighted magnetic resonance imaging (MRI) in tissues. As extensive uses of diffusion-weighted imaging (DWI) techniques evolve, it is essential to develop a greater understanding of the factors that affect diffusion in tissues. The specific issues we will address are: (l) Quantitative determination of the magnitude and time course of changes in water diffusion coefficient that happen during pathological occurrences such as stroke and seizure, using animal models we have developed. Diffusion- weighted imaging will be obtained with time resolution on order of seconds, and during the acute stages of stroke and seizure; (2) Quantitative evaluation of different mechanisms responsible for the alteration of apparent water diffusion coefficient (ADC), including changes in restriction of water diffusion during pathological changes, cytosolic streaming motion, and variations of local magnetic field gradient due to susceptibility difference caused by oxyhemoglobin/ deoxyhemoglobin conversion. We will use specifically designed experiments in simple phantoms, perfused cells, freshly excised tissues, and animal models to address each of these; (3) Develop a model for water diffusion in heterogeneous systems such as tissues based on a clear understanding and quantitative evaluation of each individual mechanism that affects water diffusion. Our own preliminary observation of reduction in ADC during seizure has highlighted the need to quantitatively validate the hypotheses concerning ADC reduction in ischemia that have been suggested by other researchers. Since ischemia and seizure represent two quite different biological conditions (blood flow, oxygenation, and energy status, etc), close comparison of the two models and quantitative studies of individual mechanisms should facilitate improved understanding of the ADC changes in both. We will use NMR spectroscopic and imaging methods based on relaxation and diffusion measurements to quantify water transport among diffusion barriers and across cell membranes or capillary walls of finite permeability. We will use numerical analysis and computer simulations to quantify diffusion among barriers of different shapes, sizes, and different boundary conditions. We will use the NMR q-space concepts developed by Callaghan (1991) to study microstructure and dynamics beyond the resolution of conventional MRI. The q-space imaging is based on the pulsed gradient spin-echo (PGSE) method first developed by Stejeskal and Tanner (1965), and it can be used to characterize water displacement profiles which reflect, if analyzed appropriately, the autocorrelation function of compartment dimensions as well as the relative number and sizes of differently diffusing compartments. These new methods are potentially very powerful at providing new insights into diffusion in heterogeneous compartmented systems such as tissue, but to date their use has been restricted largely to inanimate samples. We will perform experiments on our 2T and 7T scanners both of which are equipped with high strength, shielded magnetic field gradients. A further significance of this work is that it would evaluate the value of the q-space imaging technique for biological samples.

这项研究旨在更好地了解扩散提供的信息 组织中的加权磁共振成像（MRI）。作为广泛用途 扩散加权成像（DWI）技术的发展，至关重要 对影响扩散的因素有更深入的了解 组织。我们将要解决的具体问题是：（l）定量 确定水变化的大小和时间过程 在病理发生期间发生的扩散系数，例如 中风和癫痫发作，使用我们开发的动物模型。扩散- 加权成像将通过时间分辨率以 秒，在中风和癫痫发作的急性阶段； （2） 对负责的不同机制的定量评估 改变表观水扩散系数（ADC），包括 病理变化期间水扩散限制的变化， 胞质流运动和局部磁场的变化 梯度是由于氧气蛋白/敏感性差异而引起的 脱氧血红蛋白的转化。我们将使用专门设计的实验 在简单的幻影中，灌注细胞，新鲜切除的组织和动物 解决这些模型； （3）开发水扩散模型 在异质系统（例如组织）中，基于清晰的理解 以及对影响的每个单独机制的定量评估 水扩散。我们自己对ADC减少的初步观察 在癫痫发作期间，强调了需要定量验证 有关缺血的ADC减少的假设 由其他研究人员。由于缺血和癫痫发作代表了两个 不同的生物条件（血流，氧合和能量 状态等），两种模型和定量研究的密切比较 个体机制应有助于提高对 ADC两者都在变化。我们将使用NMR光谱和成像方法 基于放松和扩散测量以量化水的运输 在扩散屏障以及跨细胞膜或毛细管壁之间 有限的渗透性。我们将使用数值分析和计算机 模拟以量化不同形状障碍之间的扩散， 尺寸和不同的边界条件。我们将使用NMR Q空间 Callaghan（1991）开发的概念用于研究微观结构和 超出传统MRI解决的动力。 Q空间成像是 基于脉冲梯度旋转回波（PGSE）方法最初开发的 Stejeskal和Tanner（1965），可以用来表征水 位移曲线，如果适当分析，则反映 隔室维度以及相对的自相关功能 不同扩散室的数量和尺寸。这些新方法 在提供扩散的新见解方面可能非常有力 异构隔室系统（例如组织），但至今 已被限制在很大程度上是无生命的样品。我们将表演 我们的2T和7T扫描仪的实验都配备了高 强度，屏蔽磁场梯度。进一步的意义 这项工作是它将评估Q空间成像的价值 生物样品的技术。