Diffusion anisotropy in subcortical white matter and cortical gray matter: Changes with aging and the role of CSF-suppression

Purpose: To determine the relevance of cerebrospinal fluid (CSF)-suppression for the measurement of diffusion anisotropy in well-localized areas of the brain, particularly the subcortical white matter (W-M) within the gyri and cortical gray matter (GM), in young and elderly subjects, and to assess the changes of water diffusivity in the brain with normal aging. Materials and Methods: Quantitative measures of anisotropy in 26 regions, including subcortical WM (i.e., in the gyri), cortical GM, major deep WM, and deep GM regions of young (21-25 years, N = 8) and elderly (61-74 years, N = 10) normal volunteers, were assessed with CSF-suppressed diffusion tensor imaging (DTI) relative to standard DTI. Results: CSF-suppressed DTI demonstrated significant increases in fractional anisotropy (FA) of 3-12% in the young and 2-14% in the elderly groups with the largest changes being in the subcortical WM of the gyri. Furthermore, FA decreased by 10-19% in the subcortical WM of the gyri of the elderly subjects relative to the young, primarily due to increases in the perpendicular diffusivity, lambda(3), with age. Conclusion: CSF-suppressed DTI yields more accurate measures of quantitative anisotropy in cortical and subcortical brain regions. Reductions of anisotropy with aging were predominantly observed in subcortical W-M of the gyri.