EVALUATION OF EXTRACELLULAR AND INTRACELLULAR APPARENT DIFFUSION IN NORMAL AND GLOBALLY ISCHEMIC RAT-BRAIN VIA F-19 NMR

The biophysical mechanism(s) underlying diffusion-weighted MRI contras t following brain injury remains to be elucidated. Although it is gene rally accepted that water apparent diffusion coefficient (ADC) decreas es after brain injury, it is unknown whether this is associated with a decrease in intracellular or extracellular water displacement, or bot h. To address this question, 2-[F-19]luoro-2-deoxyglucose-6-phosphate (PFDG-6P) was employed as a compartment-specific marker in normal and globally ischemic rat brain. Through judicious choice of routes of adm inistration, 2FDG-6P was confined to the intra-or extracellular space, There was no statistical difference between intra-and extracellular 2 FDG-6P ADCs in normal or in globally ischemic brain (P > 0.16), sugges ting that water ADCs in both compartments are similar. However, ischem ia did result in a 40% ADC decrease in both compartments (P < 0.001), Assuming that 2FDG-6P reflects water motion, this study shows that wat er ADC decreases in both spaces after ischemia, with the reduction of intracellular water motion being the primary source of diffusion-weigh ted contrast.