Magnetization transfer imaging to monitor clinical trials in multiple sclerosis.

Magnetization transfer imaging (MTI) is a sensitive magnetic resonance scanning technique for detecting disease activity and monitoring disease progression in multiple sclerosis (MS) patients. To date, MTI has not been used as an outcome measure in early phase and pivotal clinical trials. Magnetization transfer ratio, a quantitative measure of MT, can be used to follow the evolution of individual MS plaques as well as microscopic disease in normal-appearing white matter (NAWM). Volumetric whole brain MT ratios of every voxel in the brain can be expressed as a histogram, providing an estimate of cerebral atrophy and a global disease activity including "occult" disease in NAWM, thus providing a quantitative measure of a therapeutic response. This report will briefly focus on how MTI could be used to monitor a therapeutic response in a treatment trial and address some of the pitfalls/limitations of MTI that can be encountered even in a well-designed longitudinal study.