Time Course of ADC w Changes in Ischemic Stroke: Beyond the Human Eye!

Abstract

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 10 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±60.4×10 −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.