MRI MEASUREMENTS OF WATER DIFFUSION AND CEREBRAL PERFUSION - THEIR RELATIONSHIP IN A RAT MODEL OF FOCAL CEREBRAL-ISCHEMIA

The aim of this study was to examine the quantitative relationship bet ween changes in apparent diffusion coefficient (ADC) and transverse re laxivity (Delta R(2)) measurements of relative perfusion deficits wit hin the gradients of a focal ischemic insult. Sixty minutes after perm anent occlusion of the middle cerebral artery, rats (n = 7) were subje cted to spin echo diffusion-weighted scans followed by fast low-angle shot (FLASH) perfusion-sensitive scans. Diffusion-weighted images show ed clear ischemic lesions in the affected basal ganglia and cortex. Is chemic deficits were demonstrated as a decrease in first-pass transit of injected boluses of gadodiamide. ADC maps were generated and region s of interest (ROIs) were obtained to span the range of ADC reductions from the lesion center or core to the periphery or penumbra. Correspo nding ROIs from the bolus injection images were used to calculate perf usion indexes relative to contralateral levels as ratios of Delta R(2) integrals and ratios of Delta R(2)* peak values. In all animals, the degree of ADC reductions was related to the degree of Delta R(2) per fusion deficits, ranging from severe ischemia in the core of the lesio n to intermediate and moderate changes toward the lesion periphery. In the ischemic periphery, ADC reductions were linearly correlated with Delta R(2) peak ratios. However, no significant correlation was found between ADC reductions and Delta R(2) integral ratios. These data su ggest that magnetic resonance measurements of ADC and Delta R(2) peak ratios can be used to quantitatively assess the variable gradients in focal ischemia, including potentiallyn critical areas at risk in the ischemic periphery.