Functional imaging is now widely used to support the diagnosis of dementia, depending on the pattern of cerebral glucose metabolism certain causes of dementia can exclude or support the diagnosis. Anatomic imaging such as CT or MR has limited the ability to distinguish patterns of dementia, since atrophy and other changes are usually late sings of the disease. Similar preparation to a whole body PET/CT scan is applied, the patient should be fasting for at least 4 hours from solid food; drugs that alter the biodistribution of FDG in CNS such as barbiturates or benzodiazepines should be stopped for 48 hours (a list of medications should be provided before scheduling an appointment). The patient will be sitting in a quite, semi-dark room and will be asked not to talk, keeping their eyes open to ensure standardized distribution of the tracer before the study. Imaging will commence 30 minutes after receiving the injection; the length of the exam is 15 minutes.