A positron emission tomography (PET) scan is an imaging test that helps reveal how your tissues and organs are functioning.
Among its many functions, PET can measure blood flow, oxygen intake, how your body uses glucose (sugar), and the speed by which a cell replicates. By identifying abnormalities in cellular metabolism, a PET scan can detect the early onset of a disease well before other imaging tests. A PET scan is useful in revealing or evaluating several conditions, including many cancers, heart disease and brain disorders.
A PET scan uses a radioactive drug (tracer) to show this activity. The tracer may be injected, swallowed or inhaled, depending on which organ or tissue is being studied. The tracer collects in areas of your body that have higher levels of chemical activity, which often correspond to areas of disease. On a PET scan, these areas show up as bright spots.
PET differs from CT and MRI in that it examines the function, rather than the structure, of living cells. CT and MRI are used to detect damage caused by a disease, and PET looks at how your body responds to a disease. PET scans are often done in conjunction with CT scans or MRI scans to create special views. In some cases you may have the combined scan in the same machine during the same appointment.
If the drug is injected, you may briefly feel a cold sensation moving up your arm. During the scan you’ll need to lie very still so that the images aren’t blurred. The test is painless, but if you’re afraid of enclosed spaces, you may feel some anxiety while in the scanner.The scanner itself does not emit radiation, and because the amount of radiation you’re exposed to is small, the risk of negative effects from it is low. The drug half-life (the time it will be in your system) is short. Some of the agents have a half-life of two minutes or two hours. In most cases, the drug will be in and out of your system within a day. But the tracer might cause a rare major allergic reaction or, if you are pregnant or breast-feeding, expose your baby to radiation.