A procedure that combines the pictures from a positron emission tomography (PET) scan and a computed tomography (CT) scan. The PET and CT scans are done at the same time with the same machine. The combined scans give more detailed pictures of areas inside the body than either scan gives by itself. A positron emission tomography-computed tomography scan may be used to help diagnose disease, such as cancer, plan treatment, or find out how well treatment is working. Also called PET-CT scan.