Time course of ADCw changes in ischemic stroke:: Beyond the human eye!

Background and Purpose-Using newly developed computerized image analysis, we studied the heterogeneity of apparent diffusion coefficient of water (ADC(w)) values in human ischemic stroke within LQ hours of onset. Methods-Echo-planar trace diffusion-weighted images from 9 patients with focal cortical ischemic stroke were obtained within 10 hours of symptom onset. An Iterative Self-Organizing Data Analysis (ISODATA) clustering algorithm was implemented to segment different tissue types with a series of DW images. ADC(w) maps were calculated from 4 DW images on a pixel-by-pixel basis. The segmented zones within the lesion were characterized as low, pseudonormal, or high, expressed as a ratio of the mean+/-SD of ADC(w) of contralateral noninvolved tissue. Results-The average ADC(w) in the ischemic stroke region within 10 hours of onset was significantly depressed compared with homologous contralateral tissue (626.6+/-76.8 versus 842.9+/-60.4x10(-6) mm(2)/s; P<0.0001). Nevertheless, ISODATA segmentation yielded multiple zones within the stroke region that were characterized as low, pseudonormal, and high. The mean proportion of low:pseudonormal:high was 72%:20%:8%. Conclusions-Despite low average ADC(w), computer-assisted segmentation of DW MRI detected heterogeneous zones within ischemic lesions corresponding to low, pseudonormal, and high ADC(w) not visible to the human eye. This supports acute elevation of ADC(w) in human ischemic stroke and, accordingly, different temporal rates of tissue evolution toward infarction.