Magnetic resonance imaging of multiple sclerosis lesions. Measuring outcome in treatment trials.

Magnetic resonance-based measures of disease activity and progression are now routinely used in definitive phase III treatment trials of multiple sclerosis as important secondary outcome measures because they provide quantitative and objective confirmation of the primary clinical outcome measures. Magnetic resonance-based activity measures can also be used as an efficient mechanism for screening therapies in phase I and II trials. In this review I consider the natural history of multiple sclerosis lesions and the relationships between magnetic resonance measures and clinical observations of disease as the basis for the use of magnetic resonance markers in current and future treatment trials.