PET/CT is a diagnostic imaging study that combines the best features of positron emission tomography (PET) and computed tomography (CT). In PET, a small amount of a sugar called fluorodeoxyglucose (FDG) is purified and injected into a vein. Under the controlled conditions of the study, the FDG goes to diseased cells in different amounts than to healthy cells. The FDG produces gamma rays, which are similar to x-rays. These are recorded on a ring of detectors. A computer processes the information to pinpoint areas of disease.

CT is related to a regular x-ray exam, but the x-rays are recorded on a ring of detectors rather than film. A computer processes the information into very detailed images of the body. The combined PET/CT study takes advantage of the strengths of both exams. The PET portion provides for very sensitive detection of disease. It also has the ability to measure the metabolism of diseased tissue in order to gauge the severity of the disease, and to detect any change in the disease over time.

The CT portion provides for very precise localization of structures in the body. It also allows for accurate determination of the size and shape of normal structures and lesions. Together, PET and CT provide a more accurate way to diagnose and follow disease. As an added bonus, the combined exam takes less time to perform than both exams performed separately. Also, by performing both exams at one time, only one preparation and one exam visit is needed.