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What is a PET-CT scan

A PET-CT scan combines a CT scan and a PET scan into one scan. A CT scan takes pictures from all around your body and a computer puts them together. A PET scan uses a very small amount of a radioactive drug to show where cells are active in the body.

A PET-CT scan allows your doctor to see any changes in the activity of cells and know exactly where the changes are happening. It helps your doctor to diagnose and stage a cancer. This helps doctors to decide which treatment you need and also see whether it is working. These scans can sometimes tell the difference between scar tissue and an active cancer.

Having a PET-CT scan

Your doctor or radiographer will give you instructions about preparing for your scan. Usually you should not have anything to eat for 6 hours beforehand. An hour before the test the radiographer puts a small tube (cannula) into one of the veins in your arm or the back of your hand. Then they give you the radioactive drug (tracer) as an injection through the tube. You lie down to have the injection and for at least one hour afterwards.

For the scan, you lie on your back on a narrow bed that moves through the scanner. The radiographer controls the scan from outside the room. They can see and talk to you. You need to lie as still as possible for 30 to 60 minutes while you have the scan. It shouldn’t be at all painful. If you feel unwell or want some help, you press a buzzer to call the staff.

Once the scan is over you can go home straight away. You need to stay some distance from children for the rest of the day so you don’t expose them to any radiation, although the dose is extremely small.

The results

It usually takes a couple of weeks to get the results. The scanning department sends the report to your specialist who gives you the results.

 

CR PDF Icon You can view and print the quick guide for this page about PET-CT scans.

 

 

What a PET-CT scan is

A PET-CT scan combines a CT scan and a PET scan into one scan to give more detailed information about your cancer.

A CT scan takes pictures from all around your body and uses a computer to put them together. There is detailed information about CT scans in our section about cancer tests.

A PET scan uses a very small amount of an injected radioactive drug to show where cells are active in the body. There is detailed information about PET scans in the cancer tests section.

These scanners tend to be in the major cancer hospitals. So you may have to travel to another hospital if you need to have one. Not everybody who has cancer will need one. Other types of tests and scans may be more suitable.

Below is a 360° photograph of a PET-CT scanning room. Use the arrows to move the picture and look around the room. If you can't see the photograph, you can download the Adobe Flash Player from the Adobe website.

 

 

How a PET-CT scan works

A PET-CT scan takes CT pictures of the structures of your body. At the same time, a mildly radioactive drug shows up areas of your body where the cells are more active than normal. The scanner combines both of these types of information. This allows your doctor to see any changes in the activity of cells and know exactly where the changes are happening.

 

What doctors use PET-CT for

In 2012 the Royal College of Radiologists and the Royal College of Physicians reviewed the research about PET-CT scans. They looked at the research evidence to show when PET-CT scans can help people with cancer. Based on this evidence, they published UK guidelines about when doctors use PET-CT scans. If you would like to, you can read this report on this link. It is written for doctors so it is not in plain English.

PET-CT scans are used for many types of cancer and are generally thought to be more accurate in diagnosing cancer than PET scans alone.  From the research, we know that in some cancers PET-CT scans can help to

  •  Diagnose cancer
  •  Stage a cancer
  •  Make decisions about whether you can have surgery to remove your cancer
  •  Make decisions about which is the best treatment for your cancer
  •  Show how well the treatment is working
  •  Show the difference between scar tissue and active cancer tissue
  •  Check whether your cancer has come back
  •  Find the place in the body where your cancer first started to grow (primary cancer)

After you have had treatment for cancer, a scan may show that there are still some signs of the cancer left. But this may not be active cancer. It could be scar tissue left over from cancer killed off by your treatment. A PET-CT scan can sometimes show whether this tissue is active cancer or not.

 

What having a PET-CT scan involves

Your doctor or the scanning department will give you instructions on how to prepare for your scan. You should not normally have anything to eat for 6 hours beforehand. You can usually drink as much as you like, but you must avoid milk and sugary drinks. Unless you are told otherwise, you should carry on taking any medicines prescribed for you by your doctor.

When you arrive, check in with the receptionist so the radiographers know you are there. Then you usually take a seat in the waiting room until someone calls you for your scan and shows you to the preparation room. You will be asked to change into a hospital gown and take off all your jewellery and any other metallic objects. Your doctor may want you to take a dose of diazepam (Valium) to relax the muscles around your neck and shoulders. This can give clearer pictures on the scan.

You will have a small tube (cannula) put into one of the veins in the back of your hand or arm. Then you have the radioactive drug (tracer) as an injection through the tube. You lie down to have the tube put in and have the radioactive tracer and for at least one hour afterwards. You will be ready for your scan when your body has absorbed the radioactive drug. You then go to the toilet to empty your bladder. Then you go into the scanning room.

You lie on your back on the scanning bed and the bed moves through the scanner. This can feel strange. The scan takes between 30 and 90 minutes, depending on which parts of your body are scanned. The scan is not particularly noisy but the computers and air conditioning make a constant background noise. You need to stay as still as you can during the scan. You can talk to the scan operator through an intercom if you need to.

Some people feel a bit claustrophobic ('closed in') when they are having a scan. If you think you are likely to feel this way, tell the radiographers before the day of your appointment.

The video below shows you what happens when you have a PET scan or a PET-CT scan:

View a transcript of the video showing you what what happens when you have a PET-CT scan. (opens in a new window)

 

After the scan

Once the scan is over you will be able to go home straight away. You can eat and drink what you like. It is best not to be close to children for the rest of the day. This is to avoid exposing them to any radiation, although the dose is extremely small and it is just to be on the safe side. If you have had diazepam (Valium) you must not drive for the rest of the day, as it makes you drowsy.

 

Possible risks of a PET-CT scan

PET-CT scans are very safe. You have a radioactive injection (tracer) and the CT scan uses radiation. But the amount of radiation in the tracer is small. You are exposed to some radiation when you have the CT scan so doctors only do these scans if they are necessary. But the benefit of the scan, in finding out about your cancer, outweighs any potential risk from the radiation.

You should not usually have a PET-CT scan if you are pregnant, as there is a risk that the radiation could harm the baby. If your doctors think it is essential for you to have the scan, they will tell the staff in the scanning department and the dose of radiation will normally be reduced. You should not bring babies, young children or anyone who is pregnant to the scanning department.

If you are breast feeding, you have to express enough milk beforehand to get your baby through the first 6 hours after the scan. This isn't because there will be radiation in the milk. It is because the mother shouldn't be holding the baby closely during the time the radiation is in her body. Some doctors recommend you get someone else to feed the baby for 24 hours, although it is safe for you to express more milk for those feeds from 6 hours after the scan.

If you have had diazepam (Valium) as part of your scan you may be drowsy afterwards and it is best if someone can go home with you.

 

The results

It can take time for test results to come through. Usually, a specialist in radiology or nuclear medicine examines the scan and has a report typed up. The scan department sends the report to your specialist, who gives you the results.

Understandably, waiting for results can make you anxious. It usually takes a couple of weeks. If your doctor needed the results urgently, they would note that on the scan request form and the results will be ready sooner. Remember to ask how long you should expect to wait for the results when the doctor first asks you to go for the test. If it is not an emergency, and you have not heard a couple of weeks after your scan, ring your doctor's secretary to check if the results are back.

 

PET-CT scans in the UK

Not every hospital in the UK has PET-CT scanning facilities so you may need to travel to another hospital to have one. Some scanners are in mobile units so that you may have the scan in a mobile unit parked at the hospital.

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Updated: 29 August 2013