Tract-specific analysis of diffusion MRI at 3T detects cervical spinal cord aberrations in multiple sclerosis

In people with multiple sclerosis (MS), diffusion tensor imaging (DTI) applied in the spinal cord (SC) can reveal microstructural damage prior to significant symptom burden, yet lacks specificity. Diffusion tensor tractography goes beyond conventional DTI-derived microstructural indices and, though widely applied in the brain, has yet to be fully exploited in the SC of people with relapsing-remitting MS (pwRRMS). We sought to determine the course of streamlines within cervical SC white matter (WM) fiber tracts in 46 healthy controls (HCs) and 56 pwRRMS scanned at 3T and investigate whether tractography provides added value beyond conventional analyses. We extended conventional lesion load analysis by investigating lesion load specific to white matter columns and streamlines within white matter columns, and quantified diffusion features along streamlines within a column. We identified reduced fractional anisotropy (FA) within WM columns for females and older participants, though these findings were more limited in WM streamlines. We also determined no significant associations between clinical variables and either lesion load or microstructural indices as derived from streamlines. While tractography in the MS SC may have value for visualization purposes, we did not determine added benefit to applying tractography compared to conventional volume or voxel-based analyses.