The PET scan gives information on brain and body chemistry and function. The subject lies on a bed that slides in and out of the doughnut-shaped scanner. A catheter is placed in a vein in the arm and another is placed in an artery in the wrist or elbow area. The catheter in the arm is used for injecting a radioactive material that the scanner detects, and the other is used to collect blood samples. A custom-molded plastic mask is used to support the head and prevent it from moving during the procedure. The subject may be asked to perform various tasks during the PET scan or to lie quietly. The scan lasts about 2.5 hours.