MR-guided Focused ultrasound (MRgFUS) for neuro-interventions is gaining popularity. However, the biological effects of low level exposure on the brain tissue are less understood. In this study, we used in-vivo MR diffusion kurtosis imaging (DKI) to measure water diffusion changes in vivo in rats at varying FUS exposure levels in the whole brain. Acoustic simulation and experimental data demonstrate more wide spread tissue diffusion changes and not just local changes with just a single exposure albeit for varied duration. Our results suggest that diffusion changes are mainly due to shearing forces exerted on the brain.