How Does Water Diffusion in Human White Matter Change Following Ischemic Stroke?

Purpose: Temporal evolution of the water apparent diffusion coefficients (ADC) parallel (ADC∥) and perpendicular (ADC⊥) to the human white matter tract following ischemia has not been investigated systematically. We attempted to quantify the evolution of ADC∥ and ADC⊥ and examine whether it can be interpreted by a model of ischemic edema. Methods: We retrospectively selected 53 patients with ischemic lesions involving the posterior limb of the internal capsule (PLIC) and placed regions of interest in the right and left PLIC on ADC maps. We performed regression analysis of lesion-to-contralateral ratios of ADC∥ and ADC⊥ against the time (t=1-1600 h) from onset. We then fitted the estimated time courses of ADC∥ and ADC⊥ obtained from the analysis to a model of nerve tissue composed of cylinders (axons) and spheres corresponding to isotropic structures, particularly focal cytoplasmic swellings of glial cells and axons seen in ischemic white matter. Results: The evolution of ADC⊥ and ADC∥ differed. The estimated time course of ADC∥ in μm2•ms-1 was 0.64+0.88 exp (-0.24t) for 1