Scan using computed tomography to record the positrons (positively charged particles) emitted from a radiopharmaceutical and produce a cross-sectional image of metabolic activity in body tissues to determine the presence of disease. This is especially useful in scanning the brain and nervous system to diagnose disorders that involve abnormal tissue metabolism, such as schizophrenia, brain tumors, epilepsy, stroke, and Alzheimer disease. The images are produced using colors that indicate degrees of metabolism or blood flow. The highest rates appear red; lower rates appear yellow, then green; andthe lowest rates appear blue.