PET Scan: About This Test

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Patient lying in doughnut-shaped PET scan machine, with images of scan on computer screen.

What is it?

A PET scan is a test that uses a doughnut-shaped special type of camera and a radioactive substance called a "tracer" to look at organs in the body. PET stands for positron emission tomography.

During the test, the tracer liquid is put into a vein in your arm. It moves through your body and collects in the specific organ or tissue. The tracer gives off tiny positively charged particles (positrons). As you lie in the "hole" of the machine, the camera records the positrons and turns the recording into pictures on a computer.

A computed tomography (CT) scan is often done at the same time as a PET scan.

Why is this test done?

A PET scan is often used to look for cancer and find heart and brain disorders.

How do you prepare for the test?

  • Tell your doctor ALL the medicines, vitamins, supplements, and herbal remedies you take. Some may increase the risk of problems during your test. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it.
  • Don't drink caffeine for 24 hours before a PET scan of your heart.
  • Don't do any exercise or other strenuous activity for at least 48 hours before this test.
  • Don't eat or drink (except water) for at least 6 hours before this test.
  • If you are breastfeeding, you may want to pump enough breast milk before the test to get through 1 to 2 days of feeding. The radioactive tracer used in this test can get into your breast milk and is not good for the baby.
  • Tell your doctor if you get nervous in tight spaces. You may get a medicine to help you relax. If you think you'll get this medicine, be sure you have someone to take you home.

How is the test done?

  • A radioactive tracer will be given in a vein (I.V.). You may need to wait 30 to 60 minutes for the tracer to move through your body. During this time, you will need to avoid moving and talking.
  • You will lie on a table that is attached to a PET scanner.
  • The table will pass slowly through the PET scanner, which is shaped like a doughnut. The scanner picks up signals from the tracer in your body. It is very important to lie still while each scan is being done.

How long does the test take?

The test will take 1 to 3 hours.

How does having a PET scan feel?

You will not feel pain during the test. The table you lie on may be hard and the room may be cool. It may be difficult to lie still during the test.

You may feel a quick sting or pinch when the I.V. is put in your arm. The tracer is unlikely to cause any side effects. If you don't feel well during or after the test, tell the person who is doing the test.

You may feel nervous inside the PET scanner.

What are the risks of a PET scan?

Allergic reactions to the tracer are very rare.

In rare cases, some soreness or swelling may develop at the I.V. site where the radioactive tracer was put in. Apply a moist, warm compress to your arm.

Anytime you're exposed to radiation, there's a small chance of damage to cells or tissue. That's the case even with the low-level radioactive tracer used for this test. But the chance of damage is very low compared with the benefits of the test.

What happens after the test?

  • You will probably be able to go home right away.
  • You can go back to your usual activities right away.
  • In rare cases, some soreness or swelling may develop at the I.V. site where the radioactive tracer was put in. Apply a moist, warm compress to your arm.
  • The radioactive tracer used in this test can get into your breast milk. Do not breastfeed your baby for 1 or 2 days after this test. During this time, you can give your baby breast milk you stored before the test, or you can give formula. Discard the breast milk you pump in the 1 or 2 days after the test.
  • Most of the tracer will leave your body through your urine or stool within a day. So be sure to flush the toilet right after you use it, and wash your hands well with soap and water. The amount of radiation in the tracer is very small. This means it isn't a risk for people to be around you after the test.
  • After the test, drink lots of fluids for the next 24 hours to help flush the tracer out of your body.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

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The Health Encyclopedia contains general health information. Not all treatments or services described are covered benefits for Kaiser Permanente members or offered as services by Kaiser Permanente. For a list of covered benefits, please refer to your Evidence of Coverage or Summary Plan Description. For recommended treatments, please consult with your health care provider.