Is a pet scan of the brain accurate?

PET is reliable: Pet scans are used in a number of clinical and research applications. When used to measure the metabolic activity of brain region in comparison to other brain regions, in the research evaluation of dementia-yes; when used to evaluate hypermetabolism of suspected tumors vs. Normal brain-yes; when used to measure cerebral blood flow/metabolism in research/clinically-yes. It is often combined with ct.

Varies: The accuracy of the test is variable depending on which pathologic process you are evaluating in the brain (epilepsy, dementia, differentiating a recurring malignant tumor from post-radiation changes, etc).

Looking for what?: It depends on what is being looked for. Pet/ct looks at the metabolism. Or the function of the area scanned (brain in this case), using different radioactive drugs, or tracers. The most common is f-18 fdg, an analog of glucose, which images glucose consumption. Other radiotracers look at protein synthesis or for evidence of the plaques that are associated with alzheimer's.

Depends..: Depends on the tracer and the pathology you are looking for. There are different PET tracers which can be used. FDG (glucose) is the most common pet agent and can be used to evaluate brain tumors or dementia however due to significant glucose utilization by the normal brain, evaluation can be somewhat limited. Other tracers such as florbetapir can be used to evaluate for dementia.