Irreversible regional cerebral ischemia: serial MR imaging and proton MR spectroscopy in a nonhuman primate model.

PURPOSE To delineate the changes in proton MR spectroscopy and imaging that occur with acute, irreversible ischemia of the basal ganglia of a baboon. MATERIALS AND METHODS The M1 segments of the middle cerebral arteries of six adult male baboons were occluded by endovascular means with microcatheters and N-butyl cyanoacrylate adhesive. Cerebral blood flow measurements were taken with positron emission tomography or radioactive microsphere techniques. Serial spatially localized proton MR spectroscopy of the basal ganglia and MR imaging of the brain were performed. The distribution of ischemic and infarcted tissue was demonstrated by histopathologic techniques or triphenyltetrazolium chloride staining. RESULTS Radioactive microsphere or positron emission tomography measurements demonstrated no significant cerebral blood flow within the basal ganglia after occlusion of the middle cerebral artery. Proton MR spectroscopy of the basal ganglia demonstrated increasing cerebral lactate and decreasing N-acetyl aspartate within 30 minutes of middle cerebral artery occlusion. Changes in the MR imaging signal intensity of the basal ganglia were observed as early as 3.1 hours on T2-weighted, 3.3 hours on T1-weighted, and 6.1 hours on spin density-weighted images. The distribution of these changes correlated well with the histopathologic features of ischemia and infarction that were seen throughout the basal ganglia. CONCLUSION Changes in MR imaging signal intensity corresponded to ischemia and infarction in our baboon model of acute irreversible ischemia of the basal ganglia. Increasing cerebral lactate and decreasing N-acetyl aspartate preceded changes in MR imaging signal intensity.