MATERIALS AND METHODS: The Investigators will include 7 healthy males aged 45-75 in our study. The participants will receive a careful medical examination, including a neurological examination, as part of the inclusion process. The subjects also have an MRI scan of the brain. PET/CT scans with [11C]donepezil are conducted. Six subjects will receive two PET/CT scans - once for the upper abdominal region and once for the head region two evaluate dynamic binding characteristics of the tracer in internal organ. Additionally, one single subject will receive 5 consecutive whole body PET scans to estimate radioactive dosimetry of this tracer.