ABSTRACT Objective Differentiating remyelinated from demyelinated lesions in MS remains challenging without histological confirmation. This study introduces the T 1 ‐to‐PD 2 ratio (TPR) imaging approach and evaluates its ability to characterize MS lesions alongside other quantitative MRI (qMRI) metrics. Methods Thirty individuals with MS (mean age: 47.5 ± 11.5 years) underwent 3 T MRI using 3D gradient‐echo qMRI sequences to generate quantitative maps of T 1 , proton density (PD), T 2 *, quantitative susceptibility mapping (QSM), magnetization transfer ratio (MTR), and MT saturation index (MTsat). TPR images were derived from B 1 ‐corrected T 1 and PD maps. White matter hyperintense lesions on T 2 ‐weighted FLAIR were classified as hyper‐, hypo‐, or iso‐intense relative to normal‐appearing white matter on TPR. Lesion‐specific qMRI values were analyzed, and simulated signal intensities based on empirical T 1 and PD values were used to illustrate TPR contrast. Statistical analyses included Wilcoxon rank‐sum tests and Spearman correlations ( p < 0.05). Results We found that hyperintense lesions on TPR exhibited significantly higher T 1 (1566 ms), PD (0.96 a.u.), and T 2 * (92 ms) values but lower MTR (37.3%) and MTsat (1.57%) compared to hypointense lesions (1085 ms; 0.88 a.u.; 64 ms; 46%; 2.48%, respectively). QSM values varied across lesion types. Interpretation In summary, TPR imaging visually differentiates MS lesions into hyper‐, hypo‐, and iso‐intense categories, whereas all lesions appear hyperintense on FLAIR. Hyperintense TPR lesions correspond to increased water and reduced myelin content, as confirmed by quantitative T 1 , PD, and MT metrics, consistent with demyelination. In contrast, hypointense lesions may reflect tissue changes associated with repair processes such as remyelination.
Wright et al. (Sun,) studied this question.