Magnetization transfer imaging for in vivo detection of microstructural tissue changes in aging and dementia: a short literature review.

Magnetization-transfer imaging (MTI), a magnetic resonance imaging acquisition protocol, can detect microstructural brain tissue changes by assessing the magnetization exchange between tissue water and protons bound to macromolecules. This short literature review summarizes results of previous MTI studies in normal aging, cerebral small vessel disease, and Alzheimer's disease (AD). During normal aging, the magnetization transfer ratio (MTR), a measure for the magnitude of magnetization transfer between macromolecular and water protons, declines in normal appearing brain tissue and associations between lower MTR and executive dysfunction have been described. In AD, MTR changes follow a disease-specific temporo-parietal pattern, independent of cortical atrophy. The differential diagnostic contribution beyond atrophy seems to be modest and the independent effect of MTR alterations as predictors of conversion from mild cognitive impairment to AD needs to be explored. MTR correlates well with global cognitive measures like the Mini-Mental State Examination, and MTR decreases rapidly over time in AD. Longitudinal studies are needed to determine the clinical relevance of global and regional MTI measures in normal aging and neurodegenerative disease. Moreover, correlative MTI-histopathologic postmortem studies are warranted to determine the full spectrum of tissue destruction underlying MTR lowering apart from demyelination.