Multimodal quantitative MRI assessment of cortical damage in relapsing-remitting multiple sclerosis

Purpose: To investigate magnetization transfer ratio (MTR), T₁ relaxation time, and proton density (PD) as indicators of gray matter damage in relapsing-remitting multiple sclerosis (RRMS), reflecting different aspects of microstructural damage and as imaging correlates of clinical disability. We aimed to determine which of these parameters may optimally quantify cortical damage, and serve as an imaging surrogate of clinical disability. In this study, cortical values of MTR, a surrogate for demyelination in MS, of PD, reflecting replacement of neural tissue by water, and of T₁, indicating a complex array of microstructural changes, were assessed in a group of RRMS patients in comparison to healthy controls (HC). Materials and Methods: 22 RRMS patients with varying disease duration (4.0 ± 6.54 years) and 10 HC received quantitative 3T magnetic resonance imaging (MRI) with MTR, T₁, and PD mapping. We tested for differences in cortical measurements between patients and HC. Additionally, correlation with disability as quantified by the Expanded Disability Status Scale was investigated. Results: Cortical parameter values were significantly altered in the RRMS group, with increased values of T₁ (P = 0.008) and PD (P = 0.028) and reduced values of MTR (P = 0.043). Only cortical T₁ was correlated with clinical disability measurements (P = 0.001, r = 0.65). Receiver operating characteristic analysis demonstrated the best discriminatory power for T₁ (area under the curve 0.79, PD: 0.75, MTR 0.73). Conclusion: Out of the parameters studied, cortical T₁ is best suited to detect cortical damage as an imaging surrogate of clinical disability in RRMS. J. Magn. Reson. Imaging 2016;44:1600–1607.