1. Department of Radiology, Leiden University Medical Centre, Leiden
2. Department of Chronic Disease and Environmental Epidemiology, National Institute of Public Health and the Environment, Bilthoven, the Netherlands
3. boratory 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