Positron emission tomography (PET) is a test that uses a special type of camera and a tracer (radioactive chemical) to look at organs in the body.

During the test, the tracer liquid is put into a vein (intravenous, or IV) in your arm. The tracer moves through your body, where much of it collects in the specific organ or tissue. The tracer gives off tiny positively charged particles (positrons). The camera records the positrons and turns the recording into pictures on a computer.

PET scan pictures do not show as much detail as computed tomography (CT) scans or magnetic resonance imaging (MRI) because the pictures show only the location of the tracer. The PET picture may be matched with those from a CT scan to get more detailed information about where the tracer is located.

A PET scan is often used to find cancer, to check blood flow, or to see how organs are working.

See pictures of a PET scanner and PET scans of the brain.

Why It Is Done

A positron emission tomography (PET) scan is done to:

• Study the brain's blood flow and metabolic activity. A PET scan can help a doctor find nervous system problems, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, transient ischemic attack (TIA), amyotrophic lateral sclerosis (ALS), Huntington's disease, stroke, and schizophrenia.
• Find changes in the brain that may cause epilepsy.
• Find some cancers, especially lymphoma or cancers of the breast, brain, lung, colon, or prostate. In its early stages cancer may show up more clearly on a PET scan than on a CT scan or an MRI.
• See how advanced a cancer is and whether it has spread to another area of the body (metastasized). It is often necessary to do both CT and PET scans to evaluate cancer.
• Help a doctor choose the best treatment for cancer. PET scans may also be done to see whether surgery can be done to remove a tumor.
• Find poor blood flow to the heart, which may mean coronary artery disease.
• Find damaged heart tissue, especially after a heart attack.
• Help choose the best treatment, such as coronary artery bypass graft surgery, for a person with heart disease.

How To Prepare

Stop taking medicines and herbal remedies 24 hours before you have this test. If you take insulin to control diabetes, you may need to take less than your normal dose. Talk with your doctor about how much insulin you should take.

Do not smoke or drink caffeine or alcohol for 24 hours before this test.

Do not eat or drink for 8 hours before this test.

Tell your doctor if you are or might be pregnant or if you are breast-feeding.

Tell your doctor if you have a fear of enclosed spaces or have ever had a panic attack.

You may be asked to sign a consent form for this test. Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done or what the results mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?) .