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PET scan

4-minute read

What is a PET scan?

A PET (positron emission tomography) scan is an imaging test that uses radioactive material to diagnose a variety of diseases. Doctors use it to find tumours, diagnose heart disease, brain disorders and other conditions. A PET scan provides a picture of the body working, not just a picture of its structure, like some other scans.

How do PET scans work?

If you have a PET scan, you’ll be given an injection of a small amount of short-acting radioactive liquid, known as a tracer. The one most commonly used is FDG (fluorodeoxyglucose). FDG is a simple sugar — it’s glucose that has been radiolabelled, and it gives off energy in the body, which can be seen by the scanner.

The rate that the sugar is taken up by the body’s tissues provides an indication of how active the tissue is. For example, cancer cells grow quickly, which needs a lot of energy, and hence a lot of sugar. This increased uptake of sugar makes them show up as bright hot spots on the scan.

Healthy tissue also uses more sugar than unhealthy tissue, so an area where there is little tracer may indicate unhealthy tissue or reduced blood flow.

When is a PET scan done?

PET scans can be used for many purposes, including:

  • finding tumours
  • monitoring the spread or recurrence of cancer
  • monitoring a tumour’s response to treatment
  • diagnosing and evaluating heart disease
  • in refractory epilepsy — to assess whether a person is suitable for surgery

How do I prepare for a PET scan?

The scan usually takes about 15 to 20 minutes but you can expect to be in the PET imaging department for between 2 and 3 hours.

Before the scan, you should:

  • ask about any food and drink restrictions before your scan
  • bring any previous x-ray or radiology images you have
  • let staff know if you’re breastfeeding, or if you are (or might be) pregnant
  • tell them if you have diabetes
  • tell them if you are likely to feel anxious about being in a closed space

How is a PET scan performed?

After arriving at the hospital or radiology centre, you will change into a gown and remove all metal and jewellery items. Staff will insert an intravenous line into a vein on the back of your hand or arm. Your blood sugar levels will be checked and then the radioactive tracer will be injected into your vein through the intravenous line.

You may then need to rest quietly in a bed or chair for 90 minutes. For some scans you may need to drink some contrast material. You will be able to empty your bladder before the scans.

The PET scanner has a flat bed which slides into a round opening. Once in the PET scanner, you will be asked to remain as still as possible, while the scans are being done. You can tell the staff if you get stiff or uncomfortable, or if you are feeling claustrophobic.

The scan usually does not take more than 20 minutes.

After the scanning, staff will check the images. They will remove your intravenous line. After the test you should drink plenty of water to flush out the radioactive tracer. If you are breastfeeding, you will be given specific instructions.

A specialist will examine the scans and write a report for your doctor, who will explain the results to you.

Are there any risks of having a PET scan?

PET scans are very safe. There are no side effects associated with the radioactive tracers, which only remain in your body for a short time. In addition, the dose of radiation is very small — similar to several years’ worth of natural radiation from the environment. Allergic reactions are very rare and usually minor.

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Last reviewed: February 2022

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