CORRELATION OF EARLY REDUCTION IN THE APPARENT DIFFUSION-COEFFICIENT OF WATER WITH BLOOD-FLOW REDUCTION DURING MIDDLE CEREBRAL-ARTERY OCCLUSION IN RATS

To determine the relationship between reductions in the apparent diffu sion coefficient of water (ADC) and in cerebral blood flow (CBF) durin g focal ischemia, we used diffusion-weighted magnetic resonance (D-MR) imaging and autoradiographic CBF analysis to examine rats subjected t o 30 or 90 min of permanent middle cerebral artery (MCA) occlusion, In the 30-min occlusion group (n = 10), the area with substantially redu ced ADC (15% or more below the contralateral level [ADC(15)]) correspo nded best to the area with CBF below 25 ml/100 g/min and was significa ntly smaller than the area with CBF below 50 ml/100 g/min (CBF50), a l evel associated with reduced protein synthesis and delayed necrosis (4 0 +/- 13% versus 74 +/- 8% of the ischemic hemisphere; P < 0.0001), In the 90-min occlusion group (n = 6), the ADC(15) area corresponded bes t to the CBF30 to CBF35 area and was again significantly smaller than the CBF50 area (54 +/- 13% versus 73 +/- 20%, P < 0.05), Thus, the are a of substantially reduced ADC at 30 and 90 min represents only 53% an d 74%, respectively, of the tissue at risk for infarction, These findi ngs indicate a potential limitation in using early D-MR imaging to pre dict stroke outcome.