(a)-(c) compares different plots which aim to summarize WM degeneration
with age. (a) Cerebral WM volume (cm3) vs. age, as calculated by
FreeSurfer during cortical reconstruction. r = −0.4097, moderate
correlation. (b) WM skeleton average of mean diffusion (MD, mm2/s)
vs. age, as calculated from conventional DTI without FWE. r = 0.4503, moderate
correlation. (c) WM skeleton average free water fraction f vs.
age. r = 0.6052, strong correlation. (d) Significant positive association of
free water fraction f with age in WM voxels. Color scale
denotes the age-related difference in intravoxel free water percentage per year.
The increase is more apparent in anterior regions than posterior regions.
Abbreviations: DTI, diffusion tensor imaging; FWE, free water elimination; MD,
mean diffusivity; WM, white matter.