Regional magnetization transfer ratio changes in mild cognitive impairment.

Reduction in temporal lobe volume is consistently found in dementia of Alzheimer's type (DAT). However, due to the lack of a consistent association between brain volume and cognitive decline in mild cognitive impairment (MCI), volumetric measures are not a reliable predictor for the progression of the disease. In our study, we hypothesized that changes in the magnetization transfer ratio (MTR) may reflect underlying brain pathology in the absence of quantifiable volumetric changes. Such a measure may be used as a predictor for abnormal cognitive decline in elderly subjects. The study was carried out on 15 normal elderly controls, 11 subjects with DAT, and 12 subjects with MCI. We used MTRs with magnetic resonance imaging (MRI) to detect tissue changes in the four lobes of each hemisphere, and compared that to the volumetric changes in the same regions. Our results indicate that the MTR of both temporal lobes is significantly reduced in subjects with MCI in the absence of significant volumetric changes. In comparison, DAT subjects have significantly reduced temporal lobe volumes and MTR. We conclude that changes in MTR have the potential to mark the progression of MCI to DAT, before volumetric changes are detected on conventional MRI scans.