Diffusion MRI (dMRI) is sensitive to neuronal alignment, yet its directional signal does not depend only on the fiber orientation distribution function (fODF). Current validation methods for measuring and modeling the ODF have major limitations. Small-angle X-ray scattering (SAXS) produces directly structural signal, specific to myelin’s repetitive structural arrangement. We apply 3D scanning SAXS on mouse brain sections, retrieve fODFs and compare against dMRI-derived axonal directionality. We also apply SAXS-tensor tomography to mouse spinal cord, produce tractography maps and correlate dMRI- and SAXS-TT-derived fODF parameters. These demonstrate SAXS’s potential for providing novel microstructural insights and structurally validating dMRI-derived fODFs.