Fluoromisonidazole in a Rat Model of Ischemic Stroke

Background and Purpose—The ischemic penumbra is a major focus of stroke research. F-fluoromisonidazole (F-FMISO), a positron emission tomography (PET) marker of hypoxic cells, has shown promise as a technique to image the penumbra in humans. Our aim was to delineate the pattern of F-FMISO binding in a rat middle cerebral artery transient thread-occlusion model, and correlate this with tissue outcome at 24 hours. We hypothesized that the pattern of F-FMISO binding would mimic that seen in humans. Methods—Thirty-eight rats underwent 2 hours transient middle cerebral artery (MCA) occlusion, and then received F-FMISO at time points from 0.5 to 22 hours post-MCA occlusion and were killed 2 hours later. Autoradiographic assessment of F-FMISO binding and assessment (triphenyltetrazolium chloride) of the area of infarction were performed on tissue slices. Results—Until 1 hour after MCA occlusion, F-FMISO binding was increased in the entire MCA territory, with little or no infarction visible. Over the next 5 hours, the pattern of binding evolved to a small rim of intensely binding tissue surrounding the infarct core, which itself showed reduced binding compared with the contralateral hemisphere. By 24 hours, there was minimal accumulation of F-FMISO binding and a large area of infarction. Conclusions—The pattern of F-FMISO binding rats reproduced the pattern seen in humans, consistent with this tracer being a marker of the ischemic penumbra in both species. This technique may have application in studying the ischemic penumbra in animal models, and correlating this with similar studies in humans. (Stroke. 2004;35:000-000.)