Changes and variability of proton density and T1 relaxation times in early multiple sclerosis: MRI markers of neuronal damage in the cerebral cortex.

OBJECTIVES: Proton density (PD) and T1 relaxation time are promising quantitative MRI (qMRI) markers of neuronal damage in multiple sclerosis (MS). However, it is unknown whether cortical differences of these parameters between patients and controls exist in the early stages of disease. This study investigates cortical T1 and PD in early MS stages, hypothesizing that these are altered and display a high spatial variability. METHODS: Quantitative T1 and PD mapping was performed on 11 patients with clinically isolated syndrome (CIS)/early MS in remission and 11 healthy controls. The normal appearing cortical gray matter was extracted, lobar regions were identified, and mean values and standard deviations of both parameters were calculated within each region. RESULTS: Increased PD was detected in MS/CIS patients in the cerebral cortex as a whole and all subregions, indicating an increase of water content. Increase of PD variability reached significance in the whole cortex and in the frontal and parietal regions. Longer T1 relaxation times and increased variability were found in the cerebral cortex in all regions studied, indicating a change of microstructural tissue composition that is spatially heterogeneous. CONCLUSIONS: The data show spatially heterogeneous cortical involvement in early MS is reflected in T1 and PD qMRI. KEY POINTS: • Cortical involvement in early MS is reflected in T1/PD quantitative MRI. • The changes are spatially heterogeneous. • Cortical damage goes beyond increased water content.