Magnetization Transfer Ratio Tractometry in Multiple Sclerosis

Nikola Stikov¹, Antonio Giorgio², Jennifer S.W. Campbell¹, Erin L. Mazerolle¹, Nicola De Stefano², G Bruce Pike¹

MR tractometry is a promising new application of diffusion tractography that associates quantitative MRI biomarkers to specific white matter pathways. One such biomarker is the magnetization transfer ratio (MTR), which is sensitive to the myelin content in brain white matter and is used to evaluate the level of demyelination in neurodegenerative diseases such as multiple sclerosis (MS). Computing the MTR along fiber tracts can help us identify the level of myelination of different fibers in the brain, as well as understand the patterns of (de)myelination in normal-appearing white matter in MS patients and healthy controls. We performed MTR tractometry on three healthy controls and six relapsing-remitting MS patients, three of which had lesions in the cortico-spinal tract. Whole brain tractometry demonstrated fiber MTR differences between controls and patients, whereas ROI-based analyses distinguished between the two patient subgroups. We conclude that scoring and grouping fibers by their average MTR score gives insight in the tract-specific pattern of demyelination in MS.