Bouhrara M, et al. - Authors used magnetic resonance imaging of myelin to evaluate brain demyelination in aging, mild cognitive impairment (MCI), and dementia. Compared with old controls, MCI subjects showed decreased myelin water fraction (MWF). In Alzheimer's disease or vascular dementia, demyelination was greater. Decreased MWF was accompanied by decreased magnetization transfer ratio and increased relaxation times, though this was expected. Compared to the old subjects, young subjects showed greater myelin content. This was the first demonstration of myelin loss in MCI, Alzheimer's disease, and vascular dementia using a method that provided a quantitative magnetic resonance imaging-based measure of myelin. For the pathology of MCI and dementia, myelination could represent an important biomarker.