Positron emission tomography (PET) scan

A PET scan is a nuclear medicine imaging test. It uses a form of radioactive sugar to create 3D colour images to see how your body’s cells are working.

PET uses a radioactive material (radiopharmaceutical) made up of a radioactive isotope that is attached to a material used in the body, usually sugar (glucose). It travels through the body and gathers in cells that are using a lot of energy, such as cancer cells. The radioactive material gives off tiny positively charged particles (positrons). A camera records the positrons and turns the recording into pictures on a computer.

Why a PET scan is done

A PET scan may be done to:

  • help diagnose certain cancers
  • see how far the cancer has spread (staging)
  • find out if cancer treatment is working or as part of follow-up
  • check if cancer has come back (recurred) after treatment or spread to other parts of the body
  • help diagnose non-cancerous conditions

Combined PET-CT scanning joins a PET scan and a computed tomography (CT) scan into one test. It may provide a more complete image of a tumour’s location, growth or spread than either test alone.

Getting ready for a PET scan

Before you have any nuclear medicine test, it is important to tell the nuclear staff if you are breastfeeding or pregnant or think you may be pregnant.

Tell the nuclear medicine staff if you have diabetes. They may ask you to adjust your normal dose of diabetes medicine.

Before the scan, you may be told to:

  • not eat or drink anything for 4 to 6 hours
  • avoid tobacco, caffeine, alcohol or vigorous exercise for 24 hours

You may be told to not wear clothes with metal zippers, belts or buttons on the day of the scan. Or you may change into a gown for the test. If you are wearing glasses, jewellery or objects that could interfere with the test, you will be asked to take them off.

Check with the nuclear medicine department to see if there is anything else you need to do before the test.

How a PET scan is done

A PET scan is usually done as an outpatient procedure in the nuclear medicine department of a hospital or specialized PET scan centre. This means that you don’t stay overnight. The test takes 45 minutes to 2 hours, depending on whether a single organ or the whole body is scanned.

The nuclear medicine staff will ask you if you’ve recently had surgery, a biopsy or cancer therapy (such as chemotherapy or radiation therapy). They may also check your blood sugar level before the test.

The radioactive material is injected into a vein in your hand or arm. It needs about 1 hour to travel throughout your body and get absorbed by the cells.

You will be asked to urinate just before the scan. Depending on the area being studied, a urinary bladder catheter or medicine (diuretic) may be used to help get rid of urine.

For the scan, you will sit or lie down on the exam table and will be asked to stay very still. The exam table moves through the PET scanner, which is shaped like a large doughnut. Detectors in the scanner pick up the signal from the radioactive material in the body. A computer analyzes the patterns and creates 3D colour images of the area being scanned.

If you’re having a PET-CT scan, you will have one scan after the other during the same hospital visit.

After a PET scan

The radioactive material passes out of the body through urine or stool (feces). It may take a few hours or days to completely pass out of the body. Drink lots of fluids after the test to help flush it out.

Side effects

The dose of x-rays or radioactive materials used in nuclear medicine imaging can be different for every test. The dose depends on the type of procedure and body part being examined. In general, the dose of radioactive material given during a PET scan is small and you are exposed to low levels of radiation during the test. The benefits of having a PET scan outweigh the risk of exposure to the small amount of radiation received during the scan.

Allergic reactions to the radioactive material may occur, but they are extremely rare.

What the results mean

PET scans detect areas of activity (like cell growth) in the body. More radioactive material collects in cancer cells than normal cells and will appear brighter on the image.

Not all cancers show up on a PET scan. PET scan results are often used with other imaging and lab test results. Other tests are often needed to find out whether an area that collected a lot of radioactive material is non-cancerous (benign) or cancerous (malignant). Recent surgery, chemotherapy and radiation therapy and some medicines may affect the test results.

What happens if the results are abnormal

Your doctor may recommend more tests, procedures, follow-up care or treatment.

Special considerations for children

Preparing children before a test or procedure can help lower their anxiety, increase their cooperation and develop their coping skills. This includes explaining to children what will happen during the test, such as what they will see, feel and hear.

Preparing a child for a PET scan depends on the age and experience of the child. Find out more about helping your child cope with tests and treatments.

Expert review and references

Medical disclaimer

The information that the Canadian Cancer Society provides does not replace your relationship with your doctor. The information is for your general use, so be sure to talk to a qualified healthcare professional before making medical decisions or if you have questions about your health.

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