Meier Christian, Dreher Wolfgang, Leibfritz Dieter
Universität Bremen, Fachbereich 2 (Chemie), Bremen, Germany.
Magn Reson Med. 2003 Sep;50(3):500-9. doi: 10.1002/mrm.10557.
This article examines the way in which microscopic tissue parameters affect the signal attenuation of diffusion-weighted MR experiments. The influence of transmembrane water flux on the signal decay is emphasized using the Kärger equations, which are modified with respect to the cellular boundary restrictions for intra- and extracellular diffusion. This analytical approach is extensively compared to Monte-Carlo simulations for a tissue model consisting of two compartments. It is shown that diffusion-weighted MR methods provide a unique tool for estimation of the intracellular exchange time. Restrictions of applicability to in vivo data are examined. It is shown that the intracellular exchange time strongly depends on the size of a cell, leading to an apparent diffusion time dependence for in vivo data. Hence, an analytical model of a two-compartment system with an averaged exchange time is inadequate for the interpretation of signal curves measured in vivo over large ranges of b-values. Furthermore, differences of multiexponential signal curves, as obtained by different methods of diffusion weighting, can be explained by the influence of transmembrane water flux.
本文研究了微观组织参数影响扩散加权磁共振实验信号衰减的方式。利用卡尔格方程强调了跨膜水通量对信号衰减的影响，该方程针对细胞内和细胞外扩散的细胞边界限制进行了修正。对于由两个隔室组成的组织模型，将这种分析方法与蒙特卡罗模拟进行了广泛比较。结果表明，扩散加权磁共振方法为估计细胞内交换时间提供了一种独特的工具。研究了其在体内数据应用中的局限性。结果表明，细胞内交换时间强烈依赖于细胞大小，导致体内数据出现明显的扩散时间依赖性。因此，具有平均交换时间的双隔室系统分析模型不足以解释在体内大范围b值下测量的信号曲线。此外，不同扩散加权方法获得的多指数信号曲线差异可以用跨膜水通量的影响来解释。
