Diffusion Imaging in Gray Matter

描述(申请人提供)：扩散张量成像(DTI)对神经组织中扩散各向异性(DA)的微观变化敏感，作为一种无创评估神经组织结构状态的方法，已引起基础神经科学研究和临床应用的极大兴趣。然而，标准的DTI方法，包括它的高角度分辨率(HARDI)扩展，其利用单对脉冲场梯度(SPFG)，是基于在成像分辨率的尺度上显示宏观DA的体素组成的存在。对于包含白质(WM)纤维束的体素来说，通常是这种情况，因此WM中的DTI已成为DTI研究和应用的主要焦点。然而，灰质(GM)的情况并非如此，它在微观上是不均匀的，但在体素的空间尺度上缺乏结构一致性，从而表现出宏观的DA。这严重限制了我们利用MRI对扩散的敏感性来研究GM微观结构的能力，GM微观结构是一个具有重要临床意义的组织。最近，一组新的基于双脉冲梯度(DPFG)的磁共振方法被理论研究并在简单的实验中得到验证，该方法对宏观上均匀的体素中的微观DA表现出敏感性。这些研究主要应用于具有微孔的材料，反映了这些方法发展出来的对多孔材料的关注。然而，尽管我们假设这些方法对GM的研究具有巨大的潜力，但这种组织的巨大复杂性使得对GM的dPFG方法的研究几乎不可能进行分析。因此，这项建议的目标是利用我们最近开发的扩散模拟平台(DiffSim)，结合我们最近开发的dPFG理论框架，来研究dPFG方法检测和量化灰质结构参数和变化的能力，并开发将这些方法应用于临床的实验技术。

DESCRIPTION (provided by applicant): Diffusion tensor imaging (DTI), with its sensitivity to microscopic variations in diffusion anisotropy (DA) in neural tissues, has generated great interest in both basic neuroscience research and clinical applications as a method that offers the potential for the non-invasive assessment of the status of neural tissue architecture. However, the standard DTI methodology, including its high angular resolution (HARDI) extensions, which utilizes a single pair of pulsed field gradients (sPFG), are predicated on the existence of voxel compositions that exhibit a macroscopic DA on the scale of the imaging resolution. This is often the case with voxels containing bundles of white matter (WM) fibers and thus DTI in WM has become a major focus of DTI research and applications. However, this is not the case in gray matter (GM) which is microscopically heterogeneous but lacks the structural coherence on the spatial scale of voxels to exhibit macroscopic DA. This has severely limited our ability to utilize the sensitivity of MRI to diffusion in the investigation of GM microstructure, which is a tissue of significant clinical interest. Recently, a novel set of MR methods based upon the double pulsed field gradient (dPFG) pairs have been investigated theoretically and verified in simple experiments to exhibit sensitivity to microscopic DA in voxels that are macroscopically homogeneous. These studies have primarily been applied to materials with microscopic pores, reflecting the focus on porous materials from which these methods developed. However, while we hypothesize that these methods have great potential for the study of GM, the great complexity of this tissue makes investigation of dPFG methods in GM nearly impossible to do analytically. Thus the goal of this proposal is to utilize our recently developed diffusion simulation platform (DiffSim), in conjunction with our recently developed theoretical framework for dPFG, to investigate the ability of dPFG methods to detect and quantitate gray matter architectural parameters and changes, and develop experimental techniques for applying these methods clinically.