Estimation and comparison of brainstem fiber orientation via diffusion MRI tractography and polarization sensitive OCT

dMRI-based tractography methods reconstruct neural pathways but often lack detailed microstructural information due to limited spatial resolution. To address this, we compared fiber orientation distributions in the human brainstem obtained through Constrained Spherical Deconvolution tractography and polarization-sensitive OCT (PS-OCT). While dMRI data were acquired using a 7T MRI scanner, PS-OCT offered high-resolution optic axis maps by leveraging the birefringence of myelinated fibers. We analyzed three brainstem specimens representing different stages of neurodegeneration. Preliminary results revealed strong agreement between the two modalities in regions with coherent fiber structures, while PS-OCT captured finer angular details in areas with complex architecture. These findings suggest that PS-OCT can enhance dMRI by validating and refining fiber orientation estimates, offering a promising complementary approach for advancing neuroimaging techniques used to study neurodegenerative diseases.