1. Department of Radiology, Leiden University Medical Centre, Leiden, the Netherlands.
2. Department of Chronic Disease and Environmental Epidemiology, National Institute of Public Health and the Environment, Bilthoven, the Netherlands.
3. Laboratory of Epidemiology, Demography and Biometry, National Institute on Aging, National Institutes of Health, Bethesda, MD, USA.
4. Department of Neurology, Leiden University Medical Centre, Leiden, the Netherlands.