Temporal profile of magnetic resonance imaging changes following forebrain ischemia in the gerbil.

Quantitative T2 magnetic resonance (MR) imaging was used to examine gerbil brains 1, 3, 10, and 30 days after 5 min forebrain ischemia. T2 was increased in the dorsal-lateral striatum 1 and 3 days post-ischemia, and in the hippocampus 3 days post-ischemia. T2 was normal 10 days post-ischemia, and decreased in the hippocampus and dorsal-lateral striatum 30 days post-ischemia. Neuronal counts in the dorsal-lateral striatum and CA1 hippocampal region were uniformly decreased 30 days post-ischemia. The increase in T2 shortly after ischemia is attributed to brain edema localized to regions where neuronal injury developed. The late decrease in T2 may be due to decreased water in gliotic tissue, or to ferritin-positive microglia, following forebrain ischemia. Tissue atrophy at later times gave enlarged ventricles on MR images.