Acute focal cerebral ischemia in rats studied by diffusion-weighted magnetic resonance imaging - An experimental study

BACKGROUND Temporary occlusion of the cerebral artery is occasionally repeated during neurosurgical operations, but the safety of such a procedure remains to be studied further. METHOD We studied early changes and reversibility of focal cerebral ischemia and the cumulative effects of repeated ischemic insults in rats using magnetic resonance imaging (MRI). RESULTS Diffusion-weighted magnetic resonance images (DWI) and determination of signal intensity ratio (SIR) proved to be a valuable measure of studying early changes and reversibility of transient focal cerebral ischemia and cumulative adverse effects of repeated ischemic insults. DWIs showed marked intensity changes shortly after focal cerebral ischemia, while T-2-weighted images failed to show hyperintensities until 2.5 hours after the onset of permanent ischemia. The critical period of ischemia in this model was SO minutes. However, 20 minutes ischemia, when repeated twice with 60 minutes reperfusion in between, showed irreversible damage. CONCLUSION Repeated insults of focal regional cerebral ischemia may cause irreversible tissue damage even if each ischemic period is less than the critical one.