What is a PET-CT scan?

A PET-CT scan combines:

  • a CT (computerised tomography) scan, which uses X-rays and a computer to create pictures of the structures inside your body
  • a PET (positron emission tomography) scan, which creates three-dimensional (3D) pictures of inside your body and can show how well organs and tissues are working

Combining the two scans produces detailed pictures, which we can use to make a more accurate diagnosis. We perform a PET-CT scan on the same scanner all in one appointment.

How does a PET-CT scan work?

The CT scan takes X-rays from all around your body and uses them to build up a 3D picture.

The PET scan involves injecting a small amount of a radioactive sugar into a vein, usually in your arm. This substance is called a radioactive tracer. It travels through your body and the cells absorb the sugar for energy.

The scanner detects the radioactive tracer as it collects in different parts of your body. We can then see any areas where cells are more active than normal. Cancer cells tend to use more energy than normal cells and absorb more of the sugar. The same applies to areas of infection or inflammation (swelling). These areas show up brighter on the scan.

A computer then combines the two different scans. This gives us detailed information, which we use to develop an individual treatment plan.

Why might I have a PET-CT scan?

We can carry out a PET-CT scan to:

  • find out the size of a cancer and whether it has spread (that is, the stage of a cancer)
  • plan radiotherapy
  • show how well a cancer treatment, such as chemotherapy or radiotherapy, is working
  • check whether cancer has returned after treatment
  • identify areas of infection or inflammation

How can I prepare for a PET-CT scan?

If you have a PET-CT scan, you need to stop eating for six hours before your appointment. You can drink plain (unflavoured) water during this time. The preparation is slightly different if you have diabetes. Please contact us for more details.

You can keep taking any regular medicines, unless your consultant who is referring you for the scan tells you otherwise. Try to avoid any strenuous exercise or physical activity during the 24 hours before your appointment.

The area around the scanner is quite big and most people with claustrophobia (a fear of enclosed spaces) cope without problems. If you are severely claustrophobic, please tell our department in advance. We can then take extra steps to make sure that you are comfortable.

What happens during the PET-CT scan?

You have a PET-CT scan as an outpatient procedure. This means that you do not need to stay in hospital overnight.

On the day of your appointment, a member of staff asks you a few questions about your medical history. This information can help the radiologist, who reports the results of the scan.

We inject a small amount of the radioactive tracer into a vein in your arm or hand. You then relax in a chair for 1 to 2 hours. This allows the radioactive tracer to travel through your body. During this time, you can read, listen to music or use your smart phone, laptop or tablet.

Just before the scan, we ask you to visit the toilet and empty your bladder. This is to ensure your comfort and give a better view of your pelvic area (the area below your bellybutton).

We ask to lie on your back on the scanning bed. This bed is moved into the scanner, which is a large machine shaped like a doughnut. The machine takes pictures of your body as the bed slides slowly backwards and forwards through the scanner.

It is important to keep still during the scan, so that we can get the best quality pictures. The scan usually takes 20 to 30 minutes and the entire procedure lasts about 2.5 hours. Having the scan is painless. Our medical team can see and talk to you throughout the procedure.

What happens after the PET-CT scan?

After the PET-CT scan, you can go home and start eating and drinking normally again. There are no side effects.

Only a very small amount of radiation is used in a PET-CT scan. The radioactive tracer that we inject quickly becomes less radioactive over time. It should pass out of your body naturally within a few hours. If you drink plenty of fluids after your scan, this can help to flush the substance out of your system.

As a precaution, we recommend that you avoid close contact with pregnant women or children under 5 years old for at least 6 hours after your scan.

You do not get the results at the time of your scan because a specialist radiologist needs to interpret the pictures. Our team of radiologists report the results to your consultant within 2 working days. Your consultant can then explain the results to you at your next appointment.

How can I be referred for a PET-CT scan?

To refer you for a PET-CT scan, your consultant can download a referral form from here

Your consultant can either:

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If you have any questions or would like to book an appointment with a specialist, please complete this form online or call 020 3944 0568.