Intracellular water preexchange lifetime in neurons and astrocytes

PurposeTo determine the intracellular water preexchange lifetime, (i), the average residence time of water, in the intracellular milieu of neurons and astrocytes. The preexchange lifetime is important for modeling a variety of MR data sets, including relaxation, diffusion-sensitive, and dynamic contrast-enhanced data sets. MethodsHerein, (i) in neurons and astrocytes is determined in a microbead-adherent, cultured cell system. In concert with thin-slice selection, rapid flow of extracellular media suppresses extracellular signal, allowing determination of the transcytolemmal-exchange-dominated, intracellular T-1. With this knowledge, and that of the intracellular T-1 in the absence of exchange, (i) can be derived. ResultsUnder normal culture conditions, (i) for neurons is 0.750.05 s versus 0.57 +/- 0.03 s for astrocytes. Both neuronal and astrocytic (i)s decrease within 30min after the onset of oxygen-glucose deprivation, with the astrocytic (i) showing a substantially greater decrease than the neuronal (i). ConclusionsGiven an approximate intra- to extracellular volume ratio of 4:1 in the brain, these data imply that, under normal physiological conditions, an MR experimental characteristic time of less than 0.012 s is required for a nonexchanging, two-compartment (intra- and extracellular) model to be valid for MR studies. This characteristic time shortens significantly (i.e., 0.004 s) under injury conditions. Magn Reson Med 79:1616-1627, 2018. (c) 2017 International Society for Magnetic Resonance in Medicine.