Recent imaging data in multiple sclerosis (MS) suggests that chronic-active lesions and inactive lesions can be differentiated based on the presence of paramagnetic rims on gradient-echo (GRE). At autopsy, chronic-active lesions show significant demyelination, oligodendrocyte loss, and outer rims of iron laden macrophages and activated microglia. Confirmation of the destructive nature of these lesions on MRI would provide in vivo evidence of their consequences. Further, evidence of local blood-brain barrier (BBB) breakdown in these lesions would provide further validation of their chronic-active state, along with suggesting a possible opportunity for therapeutic intervention.
We aimed to determine if white matter lesions (WMLs) with paramagnetic rims show greater alterations in multiple signal characteristics, including our novel metric for BBB breakdown, Magnetization prepared 2 rapid gradient echo (MP2RAGE) ΔT1 mapping.
MP2RAGE and GRE images of the brain were acquired on 36 participants with MS on a 7T MRI before and after contrast. GRE images were processed for R2* and quantitative susceptibility maps (QSM). MP2RAGE was processed for T1 mapping and all images were registered to the pre-contrast T1-weighted (T1-w) image. ΔT1 maps were created by subtracting pre and post-contrast T1 maps. All WMLs were masked on T1-w and masks were separately created for lesions with visible paramagnetic rims on QSM. T1, ΔT1, χ (from QSM), and R2* values were compared across lesion types using a linear mixed effects model and Wilcoxon rank sum testing.
Mean pre-contrast T1 was significantly higher in rimmed lesions (2.323, SE = 0.03964) compared to non-rimmed lesions (2.113, SE = 0.05791; p<0.001). Mean and median ΔT1 values were not significantly different in non-rimmed lesions versus rimmed lesions. Median pre-contrast χ values were significantly smaller in rimmed lesions (-0.00581, SE = 0.00277) versus non-rimmed lesions (-0.01298, SE = 0.003332; p = 0.011). Pre-contrast median R2* was significantly lower in rimmed lesions (24.55, SE = 0.8378) versus non-rimmed lesions (28.04, SE = 0.8919; p<0.001).
Elevated T1 and reduced χ and R2* in rimmed lesions in this study are confirmatory of greater demyelination and tissue destruction in this lesion subtype. The lack of significant difference in ΔT1 values suggests that there is no evidence of additional BBB breakdown in chronic-active lesions as measured on MRI.