EFFECTS OF OSMOTICALLY DRIVEN CELL-VOLUME CHANGES ON DIFFUSION-WEIGHTED IMAGING OF THE RAT OPTIC-NERVE

The apparent diffusion coefficient (ADC) of the rat optic nerve was me asured in vitro, using magnetic resonance imaging, to determine the ef fects of changes in cellular volume fraction on the diffusion of tissu e water, Nerve ADC was determined under conditions of cell membrane de polarization and (i) increased intracellular volume, (ii) decreased in tracellular volume, and (iii) negligible volume change. Depolarization alone had little affect on ADC, whereas volume changes produced stron g, reversible effects, Increased cell volume decreased ADC and vice ve rsa. These results are consistent with the view that changes in the ex tracellular space are the major source of ADC changes in brain tissue.