Multispectral analysis of the temporal evolution of cerebral ischemia in the rat brain

A major difficulty in staging and predicting ischemic brain injury by magne tic resonance (MR) imaging is the time-varying nature of the MR parameters within the ischemic lesion. A new multispectral (MS) approach is described to characterize cerebral ischemia in a time-independent fashion. MS analysi s of five MR parameters (mean diffusivity, diffusion anisotropy, T2, proton density, and perfusion) was employed to characterize the progression of is chemic lesion in the rat brain following 60 minutes of transient focal isch emia. k-Means (KM) and fuzzy c-means (FCM) classification methods were empl oyed to define the acute and subacute ischemic lesion. KM produced an estim ate of lesion volume that was highly correlated with postmortem infarct vol ume, independent of the age of the lesion. Overall classification rates for KM exceeded FCM at acute and subacute time points as follows: KM, 90.5%, 9 4.4%, and 95.9%; FCM, 82.4%, 90.6%, and 82.6% (for 45 minutes, 180 minutes, and 24-120 hours post MCAO groups). MS analysis also offers a formal metho d of combining diffusion and perfusion parameters to provide an estimate of the ischemic penumbra (KM classification rate = 70.3%). (C) 2000 Wiley-Lis s, Inc.