Ultra-high-field MR imaging in multiple sclerosis

In multiple sclerosis (MS), MRI is the most important paraclinical tool used to inform diagnosis and for monitoring disease evolution, either natural or modified by treatment. The increased availability of ultra-high-field magnets (7 Tesla or higher) gives rise to questions about the main benefits of and challenges for their use in patients with MS. The main advantages of ultra-highfield MRI are the improved signal-to-noise ratio, greater chemical shift dispersion, and improved contrast due to magnetic susceptibility variations, which lead to increased sensitivity to the heterogeneous pathological substrates of the disease. At present, ultra-high-field MRI is mainly used to improve our understanding of MS pathogenesis. This review discusses the main achievements that have so far come from the use of these scanners, which are: better visualisation of white matter lesions and their morphological characteristics; an improvement in the ability to visualise grey matter lesions and their exact location; the quantification of 'novel' metabolites which may have a role in axonal degeneration; and greater sensitivity to iron accumulation. The application of ultra-high-field systems in standard clinical practice is still some way off since their role in the diagnostic work-up of patients at presentation with clinically isolated syndromes, or in monitoring disease progression or treatment response in patients with definite MS, needs to be established. Additional challenges remain in the development of morphological, quantitative and functional imaging methods at these field strengths, techniques which may ultimately lead to novel biomarkers for monitoring disease evolution and treatment response.