1 Department of Radiology and Nuclear Medicine, Amsterdam University Medical Center, Vrije Universiteit, Amsterdam 1081 HV, Netherlands.
2 Department of Radiology and Nuclear Medicine, Amsterdam University Medical Center, Vrije Universiteit, Amsterdam 1081 HV, Netherlands; Queen Square Institute of Neurology and Centre for Medical Image Computing, University College London, London, UK. Electronic address: f.barkhof@amsterdamumc.nl.