Meier Christian, Dreher Wolfgang, Leibfritz Dieter
Universität Bremen, Fachbereich 2 (Chemie), Bremen, Germany.
Magn Reson Med. 2003 Sep;50(3):510-4. doi: 10.1002/mrm.10558.
Diffusion-weighted single-voxel (1)H spectroscopic measurements were performed on rat brain tissue in vivo and postmortem. Diffusion weighting was achieved by varying the diffusion time from 23 ms to 1.18 sec via the mixing time in a stimulated echo sequence. A series of constant gradient (cg-) experiments of eight effective gradient strengths q(2)(q(2) = gamma(2)delta(2)g(2)) from 24.2 x 10(3) to 490.2 x 10(3) mm(-2) was performed, resulting in a maximum attenuation factor of b = 580,000 s/mm(2). A fit of three exponential terms was found to be appropriate to represent the attenuation signal over the whole b-range. The behavior of the slowest decaying component can be fully understood in terms of a long time limit of a modified Kärger formalism for a two-compartment system. This allowed estimation of the transmembrane water exchange rate: the intracellular exchange time was determined to be 622 +/- 29 ms and 578 +/- 20 ms in vivo and postmortem, respectively.
在活体和死后的大鼠脑组织上进行了扩散加权单像素（1）H光谱测量。通过在受激回波序列中改变混合时间，将扩散时间从23毫秒变化到1.18秒来实现扩散加权。进行了一系列具有八个有效梯度强度q(2)（q(2)=γ(2)δ(2)g(2)）的恒定梯度（cg-）实验，范围从24.2×10(3)到490.2×10(3)mm(-2)，得到的最大衰减因子b = 580,000 s/mm(2)。发现用三个指数项拟合可适当地表示整个b范围内的衰减信号。根据两室系统的改进卡尔格形式主义的长时间极限，可以充分理解最慢衰减成分的行为。这使得能够估计跨膜水交换率：在活体和死后，细胞内交换时间分别确定为622±29毫秒和578±20毫秒。
