Magnetization transfer imaging to monitor the evolution of individual multiple sclerosis lesions

In multiple sclerosis (MS), conventional magnetic resonance imaging (MRI) is very sensitive in detecting new lesion formation and changes of lesion sizes over time. However, it lacks specificity to the heterogeneous pathological substrates of the MS lesions. This might explain the lack of correlation between MRI findings and the development of disability in MS. Magnetization transfer (MT) imaging is promising for a more accurate monitoring of the evolution of MS. MT changes indicate a reduced capacity of the macromolecules in brain tissue to exchange magnetization with the surrounding water molecules, thus reflecting matrix disorganization. The analysis of MT changes can be performed on a regional basis, thus obtaining information about individual lesions or discrete areas of the normal- appearing white matter, or on a more global basis, using MT histograms, thus estimating the amount and severity of microscopic and macroscopic disease burden in MS. The present review will summarize the major contributions given by MT for the understanding of how individual MS lesions evolve. Monitoring individual lesion evolution may be relevant not only for the understanding of the disease pathophysiology, but also as a new approach for assessing treatment efficacy in MS.