Conventional magnetic resonance imaging (cMRI) has greatly improved our ability to diagnose multiple sclerosis (MS) and to monitor its evolution, either natural or modified by treatment. cMRI-derived measures have indeed shown several advantages over clinical assessment, including their more objective nature and increased sensitivity to MS-related changes. Nevertheless, the magnitude of the relationship between cMRI measures of disease activity or burden and the clinical manifestations of the disease is weak. Several factors are likely to be responsible for this clinical/MRI discrepancy, including the poor specificity of dual-echo scans with regard to the heterogeneous pathological substrates of individual lesions and the inability of T2-weighted images to delineate tissue damage occurring in the normal-appearing white matter (NAWM) and grey matter (GM).
Recently, several non-conventional MRI techniques have been developed and applied in an attempt to improve our understanding of the evolution of MS. These techniques, including magnetization transfer (MT) MRI, diffusion tensor (DT) MRI, and proton MR spectroscopy (1H-MRS) may provide quantitative information about MS micro- and macroscopic lesion burdens with a higher pathological specificity to the most destructive aspects of the disease (i.e., severe demyelination and axonal loss) than cMRI. In addition, their application in longitudinal studies is progressively improving our ability to monitor reparative mechanisms, such as resolution of edema, remyelination, reactive gliosis and recovery from sublethal axonal injury. Finally, functional MRI (fMRI) holds substantial promise to define the role of adaptive cortical reorganization with the potential to limit the clinical consequences of irreversible MS tissue injury.