COMBINED PERFUSION AND DIFFUSION-WEIGHTED MAGNETIC-RESONANCE-IMAGING IN A RAT MODEL OF REVERSIBLE MIDDLE CEREBRAL-ARTERY OCCLUSION

Background and Purpose Diffusion-weighted imaging and dynamic first-pa ss bolus tracking of susceptibility contrast agents (perfusion imaging ) are two new magnetic resonance imaging techniques that offer the pos sibility of early diagnosis of stroke. The present study was performed to evaluate the diagnostic information derived from these two methods in a rat model of temporary focal ischemia. Methods Fifteen male Wist ar rats were assigned to 45 (n=7) or 120 minutes (n=8) of middle cereb ral artery occlusion followed by reperfusion using the intraluminal fi lament technique. The diffusion-weighted images were collected, and ar eas of hyperintensity were compared with histologically assessed arl-a s of ischemic injury. The magnetic resonance perfusion image series we re postprocessed to produce topographic maps reflecting the maximum re duction in the signal obtained during the first passage of the contras t agent and the time delay between the arrival of the bolus and the po int of maximum contrast-agent effect. Results Hyperintensity in diffus ion-weighted images was demonstrated after 30 minutes of middle cerebr al artery occlusion and was mainly expressed in the lateral caudoputam en and parts of the lower frontoparietal cortex. Reperfusion after 45 minutes of occlusion reduced the area of hyperintensity from 24.2% to 9.9% of hemispheric area. In the group with 120 minutes of occlusion, the hyperintense area increased from 24.4% to 29.1%. Relative to the n onischemic hemisphere, the changes in the topographic maps of maximum signal reduction occurred in the lateral caudoputamen and adjacent low er neocortical areas. Increased time delay to maximum effect, however, was seen also in the upper frontoparietal cortex. Conclusions Hyperin tensity in diffusion-weighted images was reversible after 45 minutes b ut not after 120 minutes of middle cerebral artery occlusion. Analysis of the signal-reduction and time-delay parametric maps demonstrated r egions of different perfusion changes in the ischemic hemisphere.