Despite MRI’s coarse resolution, diffusion MRI (dMRI) enables probing cellular microstructure. Advanced dMRI acquisition and biophysical modeling can provide microstructural metrics related to disease processes, and spherical harmonics (SH)-based orientation distribution function (ODF). Yet, these still need structural validation, and a gold standard for quantifying microstructure, particularly fiber dispersion, is missing. X-ray scattering directly probes tissue microstructure, exploiting the ~17nm myelin repeat distance, and can also represent ODF in a SH basis. Here, we show good correspondence between SH coefficients from dMRI and X-ray scattering on a mouse brain, with analysis on human samples and histological validation to follow.