PET or PET-CT scan

A PET scan uses a low dose of radiation to check the activity of cells in different parts of the body. You may have a PET scan and a CT scan together. This is called a PET-CT scan.

What is a PET or PET-CT scan?

A PET scan uses a low dose of radiation to check the activity of cells in different parts of the body. It can give more detailed information about cancer or abnormal areas seen on x-rays, CT scans or MRI scans. It may help doctors find out:

  • whether a lump is cancerous (malignant) or non-cancerous (benign)
  • whether cancer has spread to other parts of the body
  • how well treatment is working
  • whether abnormal areas remaining after treatment are scar tissue or active cancer cells.

PET scans are not always suitable for everyone. Your cancer doctor or specialist nurse can tell you whether a PET scan may be helpful for you.

You may have a PET scan and a CT scan together. This is called a PET-CT scan.

These scans are not available at all hospitals. You may have to travel to a specialist centre to have one.

Before a PET scan

You will get an appointment letter telling you whether you need to do anything before the scan. You will usually be asked not to eat for a few hours before. But you may be able to drink. If not eating before the scan is a problem for you, call the number on your appointment letter.

If you are pregnant or breastfeeding, you should call the scanning department before the scan for advice.

At the scanning department, you may be asked to change into a hospital gown. The department staff may also ask you to remove any jewellery or objects containing metal. This includes:

  • piercings
  • hair clips
  • zips
  • your bra.

This is because the metal in these objects can affect the picture made by the scanner.

About 1 hour before the scan, the radiographer will inject a small amount of a radioactive substance through a cannula into a vein in your hand or arm. This substance is called a tracer. While you wait to have the scan, the radiographer will encourage you to drink water. This helps move the tracer around your body.

Very rarely, some people are allergic to the tracer. This can make them feel breathless, sweaty or weak. Tell the radiographer straight away if you feel unwell.

Having a PET scan

You have the scan in the x-ray or nuclear medicine department at the hospital. The person who does the scan is called a radiographer. The scan takes about 30 to 60 minutes. The scanner looks like a large, thick ring. You lie still on a narrow bed which moves slowly backwards and forwards through the ring.

After a PET scan

You can usually go home after the scan. The amount of radiation used is small. But the radiographer will advise you not to have close contact with pregnant people, babies and young children for 24 hours after the scan. After this, the radioactive substance will have been passed out in your urine (pee).

If you are travelling through an airport in the days following your scan, you should take your appointment letter with you. This is because some airport scanners may detect the small amounts of radiation in your body.

SPECT scan

This test is similar to a PET scan. It looks at blood flow through the brain.

Before the scan, you have an injection of a radioactive substance, usually in your arm. This substance travels in the blood to the brain. The PET scan then takes pictures (scans) of the brain.

Date reviewed

Reviewed: 24 January 2022
Next review: 24 July 2024
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