Histogram-based characterization of healthy and ischemic brain tissues using multiparametric MR imaging including apparent diffusion coefficient mapsand relaxometry

Decreased, renormalized, or increased values of the calculated apparent dif fusion coefficient (ADC) are observed in stroke models. A quantitative desc ription of corresponding tissue states using ADC values may be extended to include true relaxation times. A histogram-based segmentation is well suite d for characterizing tissues according to specific parameter combinations i rrespective of the heterogeneity found for human healthy and ischemic brain tissues. In a new approach, navigated diffusion-weighted images and ADC ma ps were incorporated into voxel-based parameter sets of relaxation times (T -1, T-2), and T-1- or T-2-weighted images, followed by a supervised histogr am-based analysis. Healthy tissues were segmented by incorporating T-1 rela xation into the data set, ischemic regions by combining T-2- or diffusion-w eighted images with ADC maps. Mean values of healthy and pathologic tissues were determined, spatial distributions of the parameter vectors were visua lized using color-encoded overlays. One to six days after stroke, ischemic regions exhibited reduced relative mean ADC values. Magn Reson Med 43:52-61 , 2000, (C) 2000 Wiley-Liss, Inc.