Evaluation of the perilesional normal-appearing white matter (NAWM) microenvironment in relapsing-remitting multiple sclerosis with quantitative T1rho magnetic resonance imaging.

Background: While conventional magnetic resonance imaging (MRI) in multiple sclerosis (MS) primarily evaluates focal lesions, the normal-appearing white matter (NAWM) encompasses brain tissue that appears radiologically normal but harbors subtle pathological changes that contribute to the overall disease burden. The aim of this study was to investigate the role of T1rho MRI in characterising distance-dependent microstructural changes in the perilesional NAWM in patients with relapsing-remitting multiple sclerosis (RRMS). Methods: T1rho and diffusion tensor imaging (DTI) images were acquired from 30 patients with RRMS and 30 age-matched healthy controls. A total of 217 non-contrast-enhancing MS lesions were identified, and five perilesional layers were delineated from the lesion margins. T1rho values in the intralesional and perilesional regions in MS patients and the corresponding normal white matter of controls were quantified and compared. Results: T1rho values progressively decreased from the lesional regions (111.82±27.58 ms) to the perilesional layer 5 (78.06±4.76 ms) (P value <0.05). Significant correlations were found between T1rho values and mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) in the perilesional areas, with a pattern of progressively lower correlation coefficients (r, 0.23 to 0.73, P value <0.01) between T1rho values and the DTI metrics as the distance from the lesion increased. Conclusions: Our findings suggest that T1rho is a sensitive method for the detection of microstructural changes in the NAWM, and may provide valuable information about the spatial extent and severity of these changes.