Magnetization transfer ratio in mild cognitive impairment and dementia of Alzheimer's type

Almost half of the elderly subjects that are diagnosed with mild cognitive impairment (MCI) go on to develop dementia of Alzheimer's type (DAT) over a 5-year follow-up. MCI and DAT subjects show regional decreases in the volume of brain structures, which correlate with the cognitive decline among these groups. Volumetric changes are found more consistently in the DAT group than in the MCI group. Since not all MCI subjects demonstrate volumetric decline, we propose that the underlying changes in the structural integrity of the brain, measured using magnetization transfer ratio (MTR), may be used as an additional predictor for abnormal cognitive decline in the elderly. Magnetic resonance (MR) images were obtained in 15 DAT, MCI, and elderly control subjects. Using automatic tissue classification, the brain region of each MR volume was segmented into gray matter and white matter. Mean and standard error of the mean MTR measured within the gray matter was found to be significantly lower in the MCI (30.77 +/- 0.29; P = 0.037) and the DAT (29.37 +/- 0.41; P = 0.000) group compared to the control group (32.11 +/- 0.20). The MTR of white matter was significantly lower only in the DAT group. The gray matter volume was significantly lower (P = 0.000) in the DAT (387.29 +/- 26.04 cm(3)) group compared to controls (532.93 +/- 20.53 cm(3)) and MCI (464.64 +/- 16.93 cm(3)). No significant differences were found in the white matter volume between the three groups. We conclude that changes in MTR are measurable even in the absence of detectable volumetric changes in gray and white matter in the MCI group. Furthermore, MTR changes may present a novel MRI measure for the early diagnosis of dementia of Alzheimer's type. (C) 2002 Elsevier Science (USA).