EVOLUTION OF PHOTOCHEMICALLY INDUCED FOCAL CEREBRAL-ISCHEMIA IN THE RAT - MAGNETIC-RESONANCE-IMAGING AND HISTOLOGY

Background and Purpose Magnetic resonance imaging (MRI) is increasingl y used to study the pathophysiological evolution of cerebral ischemia in humans and animals. We have investigated photochemically induced (r ose bengal) focal cerebral ischemia, a relatively noninvasive. reprodu cible model for stroke, and compared the evolution of the ischemic res ponse in vivo and postmortem with MRI and histology, respectively. Met hods MR images weighted for T-2, diffusion, and T-2 and parallel hist ological sections stained with cresyl fast violet (CFV) and for glial fibrillary acid protein were obtained from 34 adult male Hooded Lister rats at seven time points (3.75 to 196 hours) after bilateral ischemi a induction. From CFV histology, lesion volumes and cell counts were c alculated; from diffusion-weighted and T-2-weighted images, and lesion volumes were determined. Results Both MRI and histology revealed a we ll-defined lesion at 3.75 hours after irradiation and a consistent pat tern of temporal evolution; lesion apparent diffusion coefficients dec reased significantly by 3.75 hours, increased significantly by day 2, and correlated strikingly with the decline in lesion CFV-positive cell numbers. After day 2, astrocytes and connective tissue cells invaded the infarct. Throughout the time course, lesion volumes determined in vivo and postmortem (after shrinkage correction) agreed well. Conclusi ons MRI changes quantitatively reflect histopathology, revealing repro ducible primary and secondary damage characteristics noninvasively. Th ese changes essentially replicate those reported for other animal stro ke models and clinically, emphasizing the value both of MRI and the ph otochemically induced focal cerebral ischemia model in stroke research .