COMPARISON OF DIFFUSION-WEIGHTED MRI WITH CHANGES IN CELL-VOLUME IN ARAT MODEL OF BRAIN INJURY

The precise mechanisms that underlie acute changes in tissue water dif fusion following cerebral ischemia or related insults such as glutamat e exposure remain unexplained, but it has been suggested that these ma y he caused by cell swelling due to water uptake. This study was under taken to compare the changes observed in diffusion-weighted MR images with changes in the cellular volume measured by electrical impedance i n a model of N-methyl-D-aspartate-induced brain injury in perinatal ra ts. The results show that the temporal course of the intensity changes in the diffusion-weighted images parallelled the progressive shrinkag e of the extracellular space measured from the electrical impedance. A fter administration of the N-methyl-D-aspartate antagonist MK-801 the signal enhancement in the images was reversed, which paralleled the no rmalization of the extracellular space observed by the impedance measu rements. It was estimated that the extracellular space decreased from 24 to 12% while the apparent diffusion coefficient of water decreased from 0.89 X 10(-9) in normal tissue to 0.42 X 10(-9) m(2)/s in tissue exposed to N-methyl-D-aspartate. These data indicate that changes in t issue water diffusion are related to changes in cell volume.