Characterizing spatial associations between deficits in white-matter fractional anisotropy, gray-matter density, and cortical metabolic activity in patients with mild cognitive impairment may provide insight into whether those changes occur due to age or disease process, and help in a better diagnosis of Alzheimer's disease, according to lead author and presenter Nathalie Martin, a research technologist in the department of radiology, and colleagues.
Ten patients with mild cognitive impairment (mean age, 78.5 years) were compared with 32 healthy individuals (mean age, 65.8 years). All received brain scans with MRI and FDG-PET.
Fractional anisotropy maps in each subject were coregistered to FDG-PET and aligned to a standard template. Gray-matter density maps also were obtained and coregistered. Regional correlations between fractional anisotropy, gray matter, and FDG uptake were examined across each participant's entire brain.
By comparing the images, the researchers found that patients with mild cognitive impairment showed unique components that were not seen among normal patients. The five largest components accounted for a variance of 65% in mildly cognitively impaired patients, compared with 29% in the normal group.
One discovery was that patients with mild cognitive impairment showed typical Alzheimer's patterns of reduced FDG uptake in the parietotemporal and frontal cortices of the brain, sparing primary sensorimotor and visual cortices.
The mild cognitive impairment group also had spatially differential involvement of white matter from FDG and gray matter not seen in the healthy control group.
While common functional and anatomical correlations across regions exist in normal controls and mildly cognitively impaired individuals, the greater variance in mild cognitive impairment suggests that the disease process introduces regional changes in imaging indices, Martin and colleagues concluded.