Apparent diffusion coefficient and MR relaxation during osmotic manipulation in isolated turtle cerebellum

The apparent diffusion coefficient (ADC) and relaxation times of water were measured by magnetic resonance imaging (MRI) in the isolated turtle cerebe llum during osmotic cell volume manipulation. The aim was to study effects of cell volume changes, a factor in ischemia and spreading depression, in i solation from considerations of blood flow and metabolism. Cerebella were s uperfused at 12-14 degrees C with solutions ranging from 50-200% normal osm olarity. Hypotonic solutions, which are known to cause cell swelling, led t o reductions of ADC and increases of T-2, while hypertonic solutions had th e opposite effect. This supports the concept that ADC varies with the extra cellular space fraction and, combined with published data on extracellular ion diffusion, is consistent with fast or slow exchange models with effecti ve diffusion coefficients that are approximately 1.7 times lower in intrace llular than in extracellular space. Spin-spin relaxation can be affected by osmotic disturbance, though such changes are not seen in all pathologies t hat cause cell swelling. (C) 2000 Wiley-Liss, Inc.