Differential progression of magnetization transfer imaging changes depending on severity of cerebral hypoxic-ischemic injury.

We hypothesized that magnetic resonance magnetization transfer (MT) imaging would be sensitive for detecting cerebral ischemic injury in white matter of neonatal brain. We compared the progression of changes in T(2) and the MT ratio (MTR) after cerebral hypoxic-ischemic insults of differing severity in neonatal rats. Magnetization transfer imaging parameters were first optimized, and then MTR and T(2) maps were acquired at various times after a mild (rather selective white matter) or substantial insult produced by unilateral cerebral hypoxia-ischemia. Depending on insult severity, time after insult, and region (e.g., subcortical white matter or cortex), cerebral hypoxia-ischemia produced reductions in MTR and an increase in T(2). The exception was acutely at 1 to 5 h at which time points MTR was reduced ipsilaterally in white matter, whereas T(2) was not affected significantly. Progression of imaging changes differed in rats grouped according to whether gross damage was present after chronic recovery. Behavioral changes were generally associated with chronic reductions in MTR and gross brain damage. Magnetization transfer imaging was capable of early detection of hypoxic-ischemic injury and particularly sensitive for identifying the progression of cerebral injury in white matter. Magnetization transfer ratio has potential for assisting with early diagnosis and treatment assessment for infants affected by perinatal hypoxia-ischemia.