Tests and Treatments Positron Emission Tomography (PET) Scan Positron emission tomography (PET) scans provide two- and three-dimensional pictures of brain activity by measuring radioactive isotopes that are injected into the bloodstream. PET scans of the brain are used to detect or highlight tumors and diseased tissue, measure cellular and/or tissue metabolism, show blood flow, evaluate patients who have seizure disorders that do not respond to medical therapy and patients with certain memory disorders, and determine brain changes following injury or drug abuse, among other uses. PET may be ordered as a follow-up to a CT or MRI scan to give the physician a greater understanding of specific areas of the brain that may be involved with certain problems. Scans are conducted in a hospital or at a testing facility, on an outpatient basis. A low-level radioactive isotope, which binds to chemicals that flow to the brain, is injected into the bloodstream and can be traced as the brain performs different functions. The patient lies still while overhead sensors detect gamma rays in the body’s tissues. A computer processes the information and displays it on a video monitor or on film. Using different compounds, more than one brain function can be traced simultaneously. PET is painless and relatively risk-free. Length of test time depends on the part of the body to be scanned. PET scans are performed by skilled technicians at highly sophisticated medical facilities.