MRI DIFFUSION MAPPING OF REVERSIBLE AND IRREVERSIBLE ISCHEMIC-INJURY IN FOCAL BRAIN ISCHEMIA

The reduction of the apparent diffusion coefficient (ADC) of water sho rtly after a focal ischemic insult is thought to reflect intracellular water accumulation (cytotoxic edema) related to high-energy metabolis m failure and loss of ion homeostasis. We attempted to clarify whether varying ranges of ADC measurements in ischemic brain tissue can be us ed to differentiate between reversible and irreversible ischemic lesio ns before reperfusion in a temporary ischemia model. We induced 45 min utes of temporary ischemia in 12 rats using the middle cerebral artery suture occlusion method. Regional changes of ADC values were serially measured in seven regions of interest in each hemisphere and evaluate d by Delta ADC, defined as the difference between ADC value in an isch emic region and that in a contralateral homologous region. We acquired dynamic contrast-enhanced perfusion images 2 minutes before and after reperfusion to document reduced perfusion and its restoration. We con firmed the infarct area by 2,3,5-triphenyltetra-zolium chloride staini ng 24 hours after occlusion and correlated this with the MRI studies. Recovery of initially reduced ADC values occurred only in ischemic reg ions where Delta ADC values were not below -0.25 X 10(-5) cm(2)/sec. A lthough the extent of infarction at postmortem examination varied in r egions with moderately decreased prereperfusion ADC values, more than 70% of regions of interest with slight declines of prereperfusion ADC values exhibited no infarction. ADC values progressively decreased aft er reperfusion in regions that initially had severely decreased prerep erfusion ADC values, and postmortem examination always demonstrated in farction in such regions. These results suggest that measurement of De lta ADC can provide information that will enable the clinician to disc riminate between irreversible and potentially reversible ischemic regi ons before reperfusion is performed.