Comparing the macromolecular-to-free pool size ratio and the magnetization transfer ratio for the assessment of myelin injury in early multiple sclerosis

Background: The selective inversion recovery quantitative magnetization transfer imaging-derived macromolecular-to-free pool size ratio (PSR) and the magnetization transfer imaging-derived magnetization transfer ratio (MTR) are both indirect indicators of myelin integrity. However, it remains unknown whether the two measures perform equally in clinical studies. Objectives: To compare the accuracy and effect size (ES) of PSR and MTR in assessing white matter (WM) injury in the brain of people with multiple sclerosis (PwMS). Methods: MTR and PSR were measured in lesions and normal-appearing white matter (NAWM) of 40 PwMS and in the normal white matter (NWM) of 16 healthy controls (HCs). Results: In total, 231 T 2 -lesions, 257 chronic black holes (cBHs), 450 regions of interest (ROIs) in NAWM proximal (pNAWM) and distant (dNAWM) to lesions of PwMS, and 150 NWM ROIs of HCs were assessed. PSR was more accurate ( p ⩽ 0.046) and had higher ES ( p < 0.001) than MTR in differentiating T 2 -lesions from pNAWM, dNAWM, or NWM. PSR was more accurate ( p = 0.006) than MTR in differentiating cBHs from NWM and showed higher ES ( p = 0.003) when comparing cBHs with pNAWM and dNAWM. Conclusions: PSR has greater accuracy and ES than MTR in distinguishing WM areas with different degrees of tissue injury.