A tensor model and measures of microscopic anisotropy for double-wave-vector diffusion-weighting experiments with long mixing times
A tensor model and measures of microscopic anisotropy for double-wave-vector diffusion-weighting experiments with long mixing times
复制标题
DOI：
10.1016/j.jmr.2009.09.015
复制
发表时间：
2010-01-01
影响因子：
2.2
通讯作者：
Finsterbusch, Juergen
中科院分区：
文献类型：
--
作者：
Lawrenz, Marco;Koch, Martin A.;Finsterbusch, Juergen
在单个实验中连续应用两个扩散加权周期的实验，即所谓的双波矢量（DWV）扩散加权实验，是在微观水平上研究材料或组织结构的有前途的工具，例如。确定细胞或隔室的大小或检测孔或细胞的各向异性。然而，迄今为止，旨在研究两种扩散权重之间长混合时间的微观各向异性的实验的理论描述仅限于某些波矢量方向、特定的孔隙形状和宏观各向同性样品。在这里，更详细地重新研究了完全受限扩散的信号方程。获得涉及四阶张量方法的任意波矢量方向、孔隙或细胞形状以及孔隙或细胞的方向分布的信号行为的一般描述。从这些方程中，导出了微观各向异性的旋转不变测量（称为 MA），该测量产生的信息与标准扩散张量采集的（宏观）各向异性测量的信息互补。此外，还导出了具有各向同性取向分布的任意细胞形状的详细角度调制。使用蒙特卡罗算法对 MR 信号进行数值模拟证实了理论考虑。扩展的理论描述和引入可靠的微观各向异性测量可能有助于提高相应实验的适用性和可靠性。 (C) 2009 Elsevier Inc. 保留所有权利。
Experiments with two diffusion-weighting periods applied successively in a single experiment, so-called double-wave-vector (DWV) diffusion-weighting experiments, are a promising tool for the investigation of material or tissue structure on a microscopic level, e.g. to determine cell or compartment sizes or to detect Pore or cell anisotropy. However, the theoretical descriptions presented so far for experiments that aim to investigate the microscopic anisotropy with a long mixing time between the two diffusion weightings, are limited to certain wave vector orientations, specific pore shapes, and macroscopically isotropic samples. Here, the signal equations for fully restricted diffusion are re-investigated in more detail. A general description of the signal behavior for arbitrary wave vector directions, pore or cell shapes, and orientation distributions of the pores or cells is obtained that involves a fourth-order tensor approach. From these equations, a rotationally invariant measure of the microscopic anisotropy, termed MA, is derived that yields information complementary to that of the (macroscopic) anisotropy measures of standard diffusion-tensor acquisitions. Furthermore, the detailed angular modulation for arbitrary cell shapes with an isotropic orientation distribution is derived. Numerical simulations of the MR signal with a Monte-Carlo algorithms confirm the theoretical considerations. The extended theoretical description and the introduction of a reliable measure of the microscopic anisotropy may help to improve the applicability and reliability of corresponding experiments. (C) 2009 Elsevier Inc. All rights reserved.