Contribution of residual BOLD susceptibility-induced local field gradients in diffusion fMRI
Aso T, Urayama S, Le Behan D, Hanakawa T, Fukuyama N
Kyoto University Graduate School of Medicine
A transient decrease of water diffusion has been reported during activation of visual cortex using a MRI sequence sensitized to diffusion by a monopolar pair of gradient pulses. However, this sequence could be contaminated by BOLD susceptibility-induced background field gradients. Diffusion fMRI acquisitions were made at 3T from a monopolar sequence and from a bipolar sequence immune to background gradients. The signal increase during activation at b=1200 s/mm2 was similar for both the monopolar and bipolar sequences suggesting susceptibility effects in the monopolar sequence were not significant. By contrast, the signal change at b=2400 s/mm2 was significantly lower for the monopolar sequence, suggesting that BOLD induced background gradients were significantly reducing the local b value and the diffusion activation effect.