Swelling of slow water diffusion pool precedes hemodynamic response during activation of human visual cortex
Le Bihan D, Urayama S, Aso T, Hanakawa T, Fukuyama H
Kyoto University Graduate School of Medicine
A transient decrease of water diffusion has been reported during activation of visual cortex. We have investigated its temporal relationship with activation. At 3T activation of visual cortex was detected in our 6 subjects through a diffusion-weighted signal increase. Using a diffusion biexponential model the diffusion signal time course was converted into a slow diffusion pool swelling time course. The diffusion-derived time courses showed no initial dip, but a post-stimulus undershoot was present. Although the diffusion-derived and the BOLD time courses were similar in shape, the BOLD time course always lagged behind the diffusion-derived time course during the activation period with an average of 2.4 +/- 0.7s. Diffusion-sensitized MRI might provide a quantitative access to an early and direct physiological surrogate of cortical activation.