Evaluating R1 and T1w/T2w as myelin-sensitive measures compared to macromolecular proton fraction

Motivation: In vivo myelin mapping of the human brain holds great research significance due to the critical role that myelin health plays in both normal and neuropathological conditions. Goal(s): To quantitatively assess the relationship and concordance between MRI-based myelin-sensitive metrics, which are not well understood in current literature. Approach: Using the macromolecular proton fraction (MPF) as a standard myelin marker, we compared the longitudinal relaxation rate (R1) and T1w/T2w image ratio and their reliability across tissue types. Results: We show that R1 corresponds well with MPF across the brain while T1w/T2w is reasonably reliable in only limited areas. Impact: By quantitatively comparing R1 and T1w/T2w with more established myelin marker MPF, we highlight their varying levels of concordance across tissue types, which informs future studies planning to use R1 or T1w/T2w as myelin proxies in the brain.