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AJNR - American Journal of Neuroradiology

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Diffusion Changes in the Aging Human Brain

Terry Chun^a, Christopher G. Filippi^a, Robert D. Zimmerman^a and Aziz M. Ulu^,a

^a From the Weill Medical College of Cornell University—New York Presbyterian Hospital, Department of Radiology, 1300 York Avenue, New York, New York.

View larger version (15K): [in a new window]   FIG 1. Whole-brain–diffusion-constant distribution map (diffusion histogram) from a healthy volunteer. The data (dots) are fitted with a triple gaussian function to accommodate the two-compartment nature of the data and the mixing between two compartments (solid curve). The brain tissue compartment has a narrow distribution of values around its mean. The second and third compartments have broader distributions. The mean of the brain tissue pixel distribution (also mode of the entire distribution) is recognized as a mean diffusion constant for the entire brain (BDav). The distribution width () of the brain tissue compartment is also recorded. FIG 2. BDav histograms from an 86-year-old subject with age-appropriate atrophy. The thicker curve is the Dav histogram from three slices through the lateral ventricles. The tissue peak (around 0.75 x 10–5 cm2/s) and the CSF peak (around 3.2 x 10–5 cm2/s) are well separated. The thinner curve is the whole-brain Dav histogram. The location of the tissue peaks in both histograms did not change, demonstrating that the tissue peak is truly free of CSF contamination. The histograms are scaled so that the tissue peaks are the same height

View larger version (12K): [in a new window]   FIG 3. The brain diffusion constants (circles) measured from distribution maps are plotted against age of the subjects. A linear fit to the data (solid line) is also shown (BDav = 0.717 + 0.000421 x Age, r = 0.383, P < .05). Age dependency of the data is minimal. FIG 4. The diffusion constants determined from ROI measurements of the periventricular white matter (circles) are plotted against age of the subjects. There is a significant increase with respect to age. A linear fit to the data (solid line) is also shown (Dav = 0.718 + 0.000876 x Age, r = 0.406, P < .015)

View larger version (12K): [in a new window]   FIG 5. The diffusion constants measured from the thalamus (circles) by using ROIs are plotted against age of the subjects. Data do not show age dependency. A linear fit to data (solid line) is also shown (Dav = 0.734 + 0.000301 x Age, r = 0.174, P > .29). FIG 6. The distribution width () of the brain diffusion constants measured from distribution maps (circles) are plotted against age of the subjects. Data do not show age dependency. A linear fit to the data (solid line) is also shown ( = 0.163 + 0.000227 x Age, r = 0.274, P > .10).