Diffusion- andT2-Weighted Increases in Magnetic Resonance Images of Immature Brain during Hypoxia–Ischemia: Transient Reversal Posthypoxia

Abstract

Hypoxic–ischemic changes in brain are detected earlier with diffusion-weighted (DW) than withT2-weighted magnetic resonance (MR) imaging techniques in adults, whereas the response in immature brain is not known. We investigated MR imaging changes prior to, during, and/or after 2 h of hypoxia–ischemia (right carotid artery occlusion+2 h of hypoxia) in 7-day-old rats anesthetized with isoflurane. In general, within the first 45 min of hypoxia–ischemia there were no changes in the DW orT2-weighted images. By the second hour of hypoxia–ischemia there were marked areas of increased intensity inboththeT2and the DW images, with cortex and striatum being affected prior to thalamus and hippocampus. The area of DW exceeded that ofT2hyperintensities. In the first hour after hypoxia–ischemia there was a transient recovery of hyperintensities on bothT2and DW images. Between 24 and 72 h the hyperintense area on DW images decreased, whereas that onT2-weighted images increased. The distribution of pathological damage assessed histologically correlated with the areas of hyperintensity on the MR images. In contrast to adult brain, early hypoxic–ischemic injury in immature brain is detected as an increase in intensity in both diffusion-and T2-weighted images, indicating a unique alteration in brain water dynamics in this neonatal model of hypoxia–ischemia. These imaging changes and alterations in brain water can rapidly but transiently reverse upon the start of normoxia and reperfusion, suggestive of secondary energy failure or delayed neuronal death.