Generalized diffusion spectrum magnetic resonance imaging (GDSI) for model-free reconstruction of the ensemble average propagator

Diffusion spectrum MRI (DSI) provides model-free estimation of the diffusion ensemble average propagator (EAP) and orientation distribution function (ODF) but requires the diffusion data to be acquired on a Cartesian q-space grid. This study proposes a generalized DSI (GDSI) framework to recover the EAP from commonly acquired multi-shell diffusion MRI data.. The EAP is directly calculated in a preferable coordinate system by multiplying the sampling density corrected q-space signals by a discrete Fourier transform matrix, without any need for gridding. The model-free EAP is demonstrated as a way to map diffusion patterns in brain regions where the tissue microstructure is not as well characterized as in white matter. Scalar metrics derived from the EAP provide new diffusion image contrasts that differentiate tissue types and infer axonal microstructure. GDSI formulates the ODF reconstruction as a linear system that elucidates the contribution and combination of q-space signals to a diffusion ODF. The model-free diffusion ODF allows estimation and comparison of fiber orientations from both the model-free and model-based methods on the same multi-shell data.

Tian Q, Yang G, Leuze CW, Rokem A, Edlow BL, McNab JA. Generalized diffusion spectrum magnetic resonance imaging (GDSI) for model-free reconstruction of the ensemble average propagator. NeuroImage, 2019: 10.1016/j.neuroimage.2019.01.038.