Evaluation of exercised or cooled skeletal muscle on the basis of diffusion-weighted magnetic resonance imaging

In this study, we assessed the physiological changes after exercising or cooling skeletal muscles on the basis of the apparent diffusion coefficient (ADC) values in magnetic resonance (MR) diffusion-weighted images (DWIs). DWIs of the ankle dorsiflexors were acquired with a 1.5-T MR device before and after exercising (22 subjects) or cooling (19 subjects). The exercise comprised a 5-min walk with the ankles dorsiflexed and a 30-time ankle dorsiflexion. Cooling (0 degrees C) of the ankle dorsiflexors was performed for 30 min. ADC values were calculated as ADC1-reflecting diffusion and perfusion and ADC2-approximating the true diffusion coefficient of the ankle dorsiflexors before and after exercising or cooling. ADC1 and ADC2 significantly increased with exercise and decreased with cooling (P < 0.05). Considering both diffusion and perfusion, ADC values allowed us to evaluate the intramuscular changes induced by exercising or cooling in terms of the motion of water molecules and microcirculation.