Quantitative susceptibility mapping captures chronic multiple sclerosis rim lesions with greater myelin damage: Comparison with high-pass filtered phase MRI

Abstract

Background Chronic active MS lesions with paramagnetic rim can be identified by high-pass filtered (HPF) phase imaging or quantitative susceptibility mapping (QSM). Purpose The objective was to compare the ability of HPF and QSM to identify MS lesions with greater myelin damage and to distinguish MS patients with increased clinical disability. Material and Methods Eighty-six patients were scanned with gradient echo sequence for lesion rim detection and FAST-T2 sequence for myelin water fraction (MWF) mapping. Chronic lesions were classified based on the presence/absence of rim on HPF and QSM images (HPF rim+/QSM rim+, HPF rim+/QSM rim-, HPF rim-/QSM rim+, HPF rim-/QSM rim-). A lesion-level linear mixed-effects model with MWF as outcome was used to compare myelin damage among the lesion groups. A multivariate patient-level linear regression model was fit to establish the association between Expanded Disease Status Scale (EDSS) and the number of rim lesions (zero vs. one or more). Results Of 2229 lesions, 96 (8.8%) were HPF rim+/QSM rim+, 211 (9.5%) were HPF rim+/QSM rim-, and the remainder had no rim. Adjusting for other factors, HPF rim+/QSM rim+ lesions had on average significantly lower MWF than both HPF rim+/QSM rim- (p<0.001) and HPF rim-/QSM rim- (p<0.001) lesions, while the MWF difference between HPF rim+/QSM rim- and HPF rim-/QSM rim- lesions was not statistically significant (p=0.309). Having at least one QSM rim+ lesion was associated with an increase in EDSS compared to having no QSM rim+ lesions, holding all other factors constant (p=0.026). The relationship between having one or more HPF rim+ lesions vs. having no HPF rim+ lesions and EDSS was not statistically significant. Conclusion QSM identifies chronic MS lesions with paramagnetic rim that on average have greater myelin damage. QSM may be a valuable tool for studying the impact of rim lesions on clinical disability in MS.