Low MT ratio in hippocampus of amnestic MCI patients who will progress to AD

Dear Sirs, Patients with mild cognitive impairment (MCI) progress to Alzheimer disease (AD) with an annual rate between 6.8 and 8.1 %. Conversion from MCI to AD is notoriously difficult to predict and a significant proportion of patients remain stable or even improve over time. In this con- text, a specific type of MCI, termed amnestic MCI (aMCI), is assumed to represent an intermediary predementia stage of AD. Magnetization transfer (MT) imaging provides a unique MR contrast based on the exchange of magnetization macromolecules, which is usually evaluated through computation of the MT ratio. In AD patients, the MT ratio decreases in the hippocampus and temporal lobe before the occurrence of regional atrophy and is correlated with clinical severity and disease duration. Moreover, MT ratio appears to be capable of tracking progression of microstructural changes of regional gray matter in AD [4]. In addition, progression of aMCI to AD has been associ- ated with a reduction in MT ratio in hippocampal, temporal and frontal regions that can precede significant volume changes. We previously reported that MT ratio values in the hippocampus and amygdala of aMCI patients were between those of healthy subjects and mild AD patients