Positron emission tomography, tuh MOG ruh fee (PET), is a technique used to produce images of the chemical activity of the brain and other body tissues. PET enables scientists to observe chemical changes in specific regions of a person's brain while the person performs various tasks, such as listening, thinking, or moving an arm or leg. Scientists use PET to compare the brain processes of healthy people and people with diseases of the brain. Research is being done to see if it is possible to use these comparisons to identify abnormalities that underlie various brain disorders. These disorders include such mental illnesses as bipolar disorder and schizophrenia, as well as such conditions as Alzheimer's disease, cerebral palsy, epilepsy, and stroke. PET also helps doctors diagnose certain other disorders, including heart disease and cancer.