Department of Chemistry, Campus Box 1134, Washington University School of Medicine, St. Louis, MO 63110, USA.
NMR Biomed. 2010 Aug;23(7):725-33. doi: 10.1002/nbm.1530.
As a result of the technical challenges associated with distinguishing the MR signals arising from intracellular and extracellular water, a variety of endogenous and exogenous MR-detectable molecules and ions have been employed as compartment-specific reporters of water motion. Although these reporter molecules and ions do not have the same apparent diffusion coefficients (ADCs) as water, their ADCs are assumed to be directly related to the ADC of the water in which they are solvated. This approach has been used to probe motion in the intra- and extracellular space of cultured cells and intact tissue. Despite potential interpretative challenges with the use of reporter molecules or ions and the wide variety used, the following conclusions are consistent considering all studies: (i) the apparent free diffusive motion in the intracellular space is approximately one-half of that in dilute aqueous solution; (ii) ADCs for intracellular and extracellular water are similar; (iii) the intracellular ADC decreases in association with brain injury. These findings provide support for the hypothesis that the overall brain water ADC decrease that accompanies brain injury is driven primarily by a decrease in the ADC of intracellular water. We review the studies supporting these conclusions, and interpret them in the context of explaining the decrease in overall brain water ADC that accompanies brain injury.
由于区分细胞内和细胞外水的磁共振（MR）信号存在技术挑战，因此已经采用了多种内源性和外源性可被 MR 检测到的分子和离子作为水运动的特定隔室报告物。尽管这些报告分子和离子的表观扩散系数（ADC）与水不同，但它们的 ADC 被认为与它们所处的溶剂的 ADC 直接相关。这种方法已被用于探测培养细胞和完整组织的细胞内和细胞外空间的运动。尽管使用报告分子或离子存在潜在的解释性挑战，而且使用的种类繁多，但考虑到所有研究，以下结论是一致的：（i）细胞内空间中的表观自由扩散运动大约是稀水溶液中的一半；（ii）细胞内水和细胞外水的 ADC 相似；（iii）细胞内 ADC 随脑损伤而降低。这些发现为以下假说提供了支持，即伴随脑损伤的脑水 ADC 总体降低主要是由细胞内水 ADC 的降低驱动的。我们回顾了支持这些结论的研究，并在解释伴随脑损伤的脑水 ADC 总体降低的背景下对其进行了解释。
