Diffusion functional MRI with isotropic b-tensor encoding

Motivation: Diffusion fMRI (dfMRI) has the potential to overcome some of the limitations of BOLD fMRI. However, acquisitions with linear diffusion encoding are sensitive to the underlying fibre orientations and may therefore give variable sensitivity, particularly in white matter. Goal(s): To assess the utility of isotropic b-tensor encoding in a diffusion fMRI acquisition (iso-dfMRI). Approach: We acquired iso-dfMRI data during a visual stimulation task. We compared this to dfMRI with linear diffusion encoding (dir-dfMRI) and to BOLD. Results: Iso-dfMRI detected activity in the visual system with a larger spatial extent than dir-dfMRI and was less dependent on underlying fibre orientations. Impact: We highlight the utility of isotropic b-tensor encoding dfMRI for detecting activity independently of underlying fibre arrangement. Thus, temporal resolution can be increased compared to acquiring multiple linear encoding directions and fMRI sensitivity in white matter boosted compared to BOLD.