The effect of aging on the apparent diffusion coefficient of normal-appearing white matter

OBJECTIVE. The purpose of our study was to test the hypothesis that the app arent diffusion coefficient (ADC) of normal-appearing white matter increase s with advancing age. SUBJECTS AND METHODS, We selected 38 patients with normal MR imaging findin gs from 332 patients undergoing clinical MR imaging, Diffusion-weighted MR imaging was performed with diffusion gradients applied in three orthogonal directions, For each patient, the average ADC on trace-weighted diffusion i mages of white matter at prespecified regions of interest and at the thalam us were compared with the patient's age. RESULTS. For the white matter, ADC sorted by patient age in decades increas ed with advancing age. Patients at least 60 years old had significantly hig her ADC (0.769 +/- 0.019 mm(2)/sec x 10(-3)) than patients less than 60 yea rs old (0.740 +/- 0.013 mm(2)/sec x 10(-3)) (p < 0.001). Comparison of indi vidual white matter ADC and age showed a significant increase with advancin g age (p < 0.0001). For the thalamus, the average ADC among patients at lea st 60 years old (0.766 +/- 0.015 mm(2)/sec x 10(-3)) exceeded the average A DC for patients less than 60 years old (0.745 +/- 0.022 mm(2)/sec x 10(-3)) (p < 0.05). However, comparison of individual thalamic ADC and patient age s, although showing a trend to higher ADC with increasing age, did not reac h statistical significance (p = 0.06). CONCLUSION. Advancing age is associated with a small but statistically sign ificant increase of water diffusibility in human white matter. A similar tr end was present in the thalamus, These increases may reflect mild structura l changes associated with normal aging.