HIGH-SPEED MR-IMAGING OF ISCHEMIC BRAIN INJURY FOLLOWING STENOSIS OF THE MIDDLE CEREBRAL-ARTERY

Magnetic susceptibility contrast-enhanced and diffusion-weighted echo planar magnetic resonance (MR) imaging was performed using a cat model of acute regional cerebral ischemia induced by partial stenosis of th e right middle cerebral artery (MCA). The imaging data were correlated with triphenyltetrazolium chloride (TTC)-stained histopathologic coro nal brain sections to determine the prognostic efficacy of high-speed MR imaging techniques in differentiating mild, moderate, and severe ce rebral hypoperfusion. Brains of animals without cortical injury on TTC staining were found to have a reduction in peak contrast enhancement of 32 +/- 6% (mean +/- SD) below control values with no significant ch ange in the apparent diffusion coefficient (ADC), determined from the diffusion-weighted MR images. In cases where moderate ischemic injury was observed in the TTC-stained sections, a 10-20% drop in the ADC was found over the 6-h study period, accompanied by a much wider variatio n in peak contrast enhancement. Finally, where TTC staining showed sev ere ischemic brain damage, a 40-50% drop in ADC and a reduction in pea k contrast enhancement effect of >95% were observed as early as 1 h fo llowing MCA stenosis. The significant correlation between imaging obse rvations and histologically confirmed cerebral ischemia indicates that magnetic susceptibility contrast-enhanced echo planar MR imaging is s ensitive to slight reductions in cerebral perfusion that fall below th e threshold for reliably detectable ischemia-induced alterations in AD C. First-pass perfusion-sensitive imaging may thus be diagnostically u seful in differentiating severely hypoperfused permanently injured tis sue from the mildly hypoperfused ischemic penumbra.