Age-associated alterations in cortical gray and white matter signal intensity and gray to white matter contrast.

Prior studies have focused on patterns of brain atrophy with aging and age-associated cognitive decline. It is possible that changes in neural tissue properties could provide an important marker of more subtle changes compared to gross morphometry. However, little is known about how MRI tissue parameters are altered in aging. We created cortical surface models of 148 individuals and mapped regional gray and white matter T1-weighted signal intensities from 3D MPRAGE images to examine patterns of age-associated signal alterations. Gray matter intensity was decreased with aging with strongest effects in medial frontal, anterior cingulate, and inferior temporal regions. White matter signal intensity decreased with aging in superior and medial frontal, cingulum, and medial and lateral temporal regions. The gray/white ratio (GWR) was altered throughout a large portion of the cortical mantle, with strong changes in superior and inferior frontal, lateral parietal, and superior temporal and precuneus regions demonstrating decreased overall contrast. Statistical effects of contrast changes were stronger than those of cortical thinning. These results demonstrate that there are strong regional changes in neural tissue properties with aging and tissue intensity measures may serve as an important biomarker of degeneration.