PET Scan

By Medically reviewed by hellodoktor


What is PET Scan?

A positron emission tomography (PET) scan is an imaging test that uses a very small dose of a radioactive chemical, called a radiotracer, to help doctors see how the organs and tissues are working. PET scans are used most often to detect cancer, heart problems, brain disorders and other central nervous system disorders.

Why is PET Scan performed?

The purpose of PET Scan is to diagnose certain health conditions, to plan treatment, to find out how an existing condition is developing, and to see how effective a treatment is.

PET scans are often used with CT or MRI scans to help make a diagnosis or to get more data about a health condition and the progress of any treatment.

While an MRI or CT scan shows how part of the body looks, a PET scan can reveal how it is functioning.

PET scans are commonly used to investigate a number of conditions.

  • Epilepsy: It can reveal which part of the brain the epilepsy is affecting. This can help doctors decide on the most suitable treatment, and it can be useful if surgery is necessary.
  • Alzheimer’s disease: PET scans can help diagnose Alzheimer’s disease by measuring the uptake of sugar in specific parts of the brain. Brain cells that are affected by Alzheimer’s tend to use glucose more slowly than normal cells.
  • Cancer: PET scans can reveal the presence and stage of a cancer, show whether and where it has spread, and help doctors decide on treatment. A PET scan can give an idea of how well chemotherapy is working, and it can detect a recurring tumor sooner than other techniques.
  • Heart disease: A PET scan can help detect which parts of the heart have been damaged or scarred, and it can help identify circulation problems in the working of the heart. This information can help plan treatment options for heart disease.
  • Medical research: Researchers can learn vital information by using PET scans, especially about the workings of the brain.


What should I know before receiving PET Scan?

PET Scan is generally considered a safe procedure for most people. You shouldn’t experience any side effects after having a PET scan.

Any exposure to radiation carries a very small risk of potential tissue damage that could lead to cancer at a later date.

But the amount of radiation you’re exposed to in a standard PET scan is small – about the same as the amount you get from natural sources, such as the sun, over 3 years.

The radiotracer becomes quickly less radioactive over time and will usually be passed out of your body naturally within a few hours.

The CT component of a PET-CT scan also involves exposure to a small amount of additional radiation, but the risk of this causing any problems in the future is still very small.


How to prepare for PET Scan?

Your doctor will provide you with complete instructions for how to prepare for your PET scan. Tell your doctor about any prescription, over-the-counter (OTC), or supplemental medications you’re taking.

You may be asked to refrain from strenuous physical activity, such as exercise, in the 24 to 48 hours preceding the test.

Twenty-four hours before your appointment, you’ll be asked to stick to a low-carbohydrate, no-sugar diet. Foods and beverages you should avoid include:

  • Cereal
  • Pasta
  • Bread
  • Rice
  • Milk and yogurt, whether dairy or nondairy
  • Fruit and fruit juices
  • Alcohol
  • Caffeinated beverages
  • Candy, including chewing gum and mints

Foods you can eat include meat, tofu, nuts, and nonstarchy vegetables.

If you’re receiving anesthesia for the procedure, don’t eat or drink anything the entire morning of your PET scan. Drink only a few sips of water if you need to take any medications.

If you’re not receiving anesthesia, you’ll still want to refrain from eating anything for six hours before your scan. Remember to avoid chewing gum or sucking on hard candy, cough drops, or mints.

You’ll be able to drink water, however, and take any medications as recommended.

You may be asked to change into a hospital gown. Because metal can interfere with the testing equipment, you’ll also need to remove any jewelry you’re wearing, including body piercing jewelry. However, medical devices such as pacemakers and artificial hips won’t affect your results.

Other considerations

You should also tell your doctor about any medical conditions you have.

If you’re pregnant or believe you could be pregnant, tell your doctor. The test may be unsafe for your baby.

If you’re breastfeeding, you may need to pump and store your breastmilk 24 hours prior to the procedure, as you won’t be able to breastfeed for 24 hours after the test.

If you have diabetes, you’ll get special instructions for test preparation because fasting beforehand could affect your blood sugar levels. You’ll likely be told to take your normal dose of insulin and eat a light meal four hours before you’re scheduled to receive your scan.

What happens during PET Scan?

The scan usually takes up to 30 minutes.

Before the scan, you’ll get tracers through a vein in your arm, through a solution you drink, or in a gas you inhale. Your body needs time to absorb the tracers, so you’ll wait about an hour before the scan begins. How long it takes for your body to fully absorb the tracer will depend on the area of the body being scanned.

While you wait, you’ll want to limit any movement, relax, and try to stay warm. If you’re undergoing a brain scan, you’ll want to avoid television, music, and reading.

Next, you’ll undergo the scan. This involves lying on a narrow table attached to a PET machine, which looks like a giant letter “O.” The table glides slowly into the machine so that the scan can be conducted.

You’ll need to lie still during the scan. The technician will let you know when it is that you need to remain still. You may be asked to hold your breath for several seconds. You’ll hear buzzing and clicking noises during the test.

When all the necessary images have been recorded, you’ll slide out of the machine. The test is then complete.

What happens after PET Scan?

The results of your scan won’t usually be available on the same day. They’ll be sent to your specialist to be discussed at your next appointment.

After the test, you can go about your day unless your doctor gives you other instructions. However, because radioactive material will remain in your body for about 12 hours, you’ll want to limit your contact with both pregnant women and infants during this time.

Drink plenty of fluids after the test to help flush the tracers out of your system. Generally, all tracers leave your body after two days.

If you have any questions about the PET Scan, please consult with your doctor to better understand your instructions.

Explanation of results

What do my results mean?

A PET scan shows bright areas where there’s heavy activity in your cells, which may be a sign of disease. To get a more complete picture of what’s going on, your doctor may compare your PET scan with results from other imaging you’ve had. You can get results within 24 hours, but it depends on where you have the scan done.

A radiologist or other physician who has specialized training in nuclear medicine will interpret the images and send a report to your referring physician.

If your physician has ordered a diagnostic CT, a radiologist with specialized training in interpreting CT exams will report the findings of the CT and forward a report to your referring physician.

Depending on the laboratory and hospital, the normal range for PET Scan may vary. Please discuss with your doctor any questions you may have about your test results.


Hello Health Group does not provide medical advice, diagnosis or treatment.


Review Date: October 9, 2018 | Last Modified: September 12, 2019

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