Relaxometry and brain myelin quantification with synthetic MRI in MS subtypes and their associations with spinal cord atrophy

•Synthetic MR was able to quantify differences on MVF, R1, R2 and PD between patients with MS and CS.•Intracranial MVF has a greater impact on spinal cord volume loss compared to BPF or total brain lesion load.•MUCCA was associated with supratentorial demyelination as a result of diffuse disease activity.•Alterations in R1, R2 and PD in adjacent infratentorial ROIs were associated with spinal cord atrophy.