More generally, frailty is associated directly with a cerebral impact on a cogntif or thymic status or indirectly with the cognitive or thymic impacts related with other components (nutritional or autonomy or walking poor status, comorbidities) 18F-Flurodeoxyglucose (18F-FDG) Positron Emission Tomography (PET), is routinely performed in follow-up cancer patients in most cases, including older patients, to detect neoplastic localizations on the whole body. It also accurately quantifies cerebral glycolytic metabolism when early brain recording is performed. Brain metabolism reflects the neuronal synaptic activity. It is generally decreased in particular brain areas due of neurodegenerative damage with a little or no symptom, of thymic involvement particular in depression or during accelerated cerebral aging of vascular origin. The impairment of the brain function of the elderly, as evidenced by 18F-FDG PET, is most often multifactorial, as frailty. Above all, brain changes are visualized with 18F-FDG PET much earlier than using neuropsychological tests, especially for cognitive impairment.