Zero-shell diffusion MRI: Focus on microstructure by decoupling fiber orientations

In brain dMRI, microstructure parameters of fiber fascicles, such as compartment fractions, exchange, diffusivities, relaxation rates, and structural disorder, are highly sought after. They can be accessed by sampling multiple diffusion weightings, b-tensor shapes, diffusion and/or echo times. Yet most scan time is spent oversampling the fiber orientation distribution function – because factoring it out nominally requires rotational invariants like the spherical mean. We show how to measure multiple inequivalent combinations of (b, \, ), while spending single gradient directions per unique combination. We recover signal’s rotational invariants for each one and use them for biophysical modeling of white and gray matter.