What is a PET scan?

Positron emission tomography (PET) is an imaging test that shows how your tissues and organs are functioning. PET uses a radioactive drug to show this activity. This scan can sometimes detect a disease before it shows up on other imaging tests.

The tracer can be injected, swallowed, or inhaled, depending on the organ or tissue being studied. The tracer collects in areas of your body that have higher levels of chemical activity, which often correspond to areas of disease.

PET is useful in revealing or evaluating several conditions, including many cancers, heart disease, and brain disorders.

Why do healthcare providers use PET scans?

Your healthcare provider may order a PET scan to check for signs of:

• Cancer, including breast, lung, and thyroid cancer;
• Coronary artery disease, heart attack, or other heart problems;
• Brain disorders, such as brain tumors, epilepsy, dementia, and Alzheimer's disease;

What does a PET scan show?

A PET scan can:

• Measure vital functions, such as blood flow, oxygen use, and blood sugar (glucose) metabolism;
• Identify organs and tissues that aren't working as they should;
• Detect cancerous tumor cells to help assess the spread of cancer (metastasis);
• Evaluate the effectiveness of a treatment plan and help your provider adjust treatment, if needed;

What are the indications for a PET scan?

Cancer

Cancer cells show up as bright spots on PET scans because they have a higher metabolic rate than normal cells. PET can be helpful in:

• Detecting cancer;
• Revealing if your cancer has spread;
• Checking if cancer treatment is working;
• Finding a cancer recurrence;

PET should be interpreted cautiously because noncancerous conditions can look like cancer, and some cancers don't show up on PET. Many types of solid tumors appear on PET scans, including

• Brain;
• Cervical;
• Colorectal;
• Esophageal;
• Head and neck;
• Lung;
• Lymphoma;
• Melanoma;
• Pancreatic;
• Prostate;
• Thyroid;

Heart disease

PET can reveal areas of decreased blood flow in the heart. This information can help you and your doctor decide, for example, if you might benefit from a procedure to open blocked heart arteries (angioplasty) or coronary artery bypass grafting.

Brain disorders

PET can be used to evaluate certain brain disorders, such as tumors, Alzheimer's disease, and seizures.

What should I expect during a PET scan?

The following steps occur during a PET scan:

• You receive an IV injection of a radiotracer that contains a safe amount of radioactive medication. The most commonly used radiotracer is fluorodeoxyglucose;
• You sit in a chair for about an hour while the radiotracer circulates in your bloodstream. Too much activity can send the radiotracer to areas of your body that your provider isn’t testing. You won’t be able to feel the radiotracer;
• In about an hour, your organs and tissues absorb the radiotracer;
• You may also receive an IV injection of a contrast agent;
• You lie on an examination table that slides into and out of the scanner;
• During the scan, you must lie still. Any movement can blur the images;
• You will hear buzzing and clicking sounds as the scanner takes images;
• Tell your provider if being in a closed space makes you anxious. You may be able to take a mild sedative to help you relax during the procedure;
• A radiology technician will review the scans before you leave to make sure the images are clear;

How long does a PET scan take?

The entire PET process takes about two hours. Your body can take up to 60 minutes to absorb the injected radiotracer. During this time, you will need to sit quietly and limit your movement. The PET scan itself takes about 45 minutes. After the scan, you’ll need to wait while the technologist reviews the scans to make sure the images are clear.

Are there any risks associated with a PET scan?

The amount of radiation in the radioactive tracer is very small. It doesn’t stay in your body for long. You should drink plenty of water after a PET scan to help flush the radioactive medication from your body. In general, PET scans are safe and rarely cause problems. Exceptions include:

• Pregnant or breastfeeding women shouldn't have a PET scan. The radiation can be harmful to an unborn baby and can pass to the infant in breast milk;
• Some people have an allergic reaction to PET radiotracers or contrast dyes. Your medical team can give you medication to quickly slow and stop this reaction;
• People with diabetes may not absorb the sugar in the radiotracer, which can affect the scan results. Your provider will offer suggestions for altering your diet and medications before the test;

PET Scan Results

Images from a PET scan show the bright spots where the radioactive tracer has collected. These spots reveal higher levels of chemical activity and details about how your tissues and organs are functioning. A radiologist—a doctor specially trained to interpret scan images—will report the results to your doctor.

The radiologist may also compare your PET images with images from other tests you’ve recently had, such as computed tomography (CT) or magnetic resonance imaging (MRI). The images may also be combined to provide more details about your condition.