1. From the Departments of Radiology (M.C.K., M.A.v.B.) and Neurology (M.D.F.), Leiden University Medical Center, the Netherlands; the Department of Chronic Disease and Environmental Epidemiology, National Institute of Public Health and the Environment, Bilthoven, The Netherlands (L.J.L.); and the Laboratory of Epidemiology, Demography and Biometry, National Institute on Aging, National Institutes of Health, Bethesda, Md (L.J.L.).