PET-CT scan | Cancer Research UK
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What is a PET-CT scan

A PET-CT scan combines a CT scan and a PET scan into one to give more detailed information. A CT scan takes a series of X-rays from all around your body and a computer puts them together. A PET scan uses a very small amount of radioactive drug to show how body tissues are working.

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 appointment letter will give you details about how to prepare for your scan. Usually you should not have anything to eat for about 6 hours beforehand. You can normally drink water during this time. You may be told not to do any strenuous exercise for 24 hours before the test.

About 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 need to lie down and rest 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 can speak to the staff through an intercom.

Once the scan is over you can go home straight away. The amount of radiation from the drug is small and goes away (decays) very quickly. But it is best not to have close contact with pregnant women and young children for the rest of the day. Drinking plenty after the scan will help flush the drug out of your system. 

If you are pregnant or breast feeding, you should contact the department before your scan for advice.

The results

The scanning department sends the report to your specialist who gives you the results. This may take up to a couple of weeks, depending on why you are having the scan. Contact your doctor or specialist nurse if you have not heard anything after this time.
 

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What a PET-CT scan is

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

A CT scan takes a series of X-rays from all around your body and uses a computer to put them together. A PET scan uses a very small amount of radioactive drug to show how body tissues are working.

We have more information about having a CT scan or PET scan.

PET-CT 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 uses X-rays to take 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

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.  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
  •  Find the place in the body where you cancer first started to grow (primary cancer)
  •  Check whether your cancer has come back
  •  Show the difference between scar tissue and active cancer tissue

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

The scanning department will give you instructions on how to prepare for your scan. These are normally written in your appointment letter. Generally, you should not have anything to eat for about 6 hours beforehand. You can usually only drink water during this time. You may be told not to do any strenuous exercise for 24 hours before the scan. Unless you are told otherwise, you should carry on taking any medicines prescribed for you by your doctor. If you are diabetic, you should contact the department a couple of days before your appointment. You may need to adapt your diet and sugar control routine a little.

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. You can take a friend or relative, but they will usually not be allowed to go into the scanning room with you. The radiographer may ask you to change into a hospital gown. You will need to take off all your jewellery and any other metallic objects. They 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 need to rest for about an hour afterwards. This allows the drug to spread through your body and into your tissues. Before your scan begins, you will go to the toilet to empty your bladder.

In the scanning room, you lie on your back on the narrow bed. The radiographer will help you to get comfortable and make sure you are in the right position. The bed gently moves through the scanner. The scan takes between 30 to 60 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 and go back to normal activities. Although the amount of radiation from the radioactive drug is very small, it is best not to have long periods of close contact with pregnant women, babies and young children for the rest of the day. 

If you have had diazepam (Valium) you must not drive for the rest of the day, as it makes you drowsy. You will need someone to take you home from the hospital.

If you are travelling abroad within a few days of your scan, it may be a good idea to take your appointment letter with you to show that you have had a scan. Most airports have sensitive radiation monitors which may pick up the trace of radiation following your test.

 

Possible risks of a PET-CT scan

During a PET-CT scan you are exposed to radiation from the X-rays and the radioactive drug. The radiation in the radioactive tracer is very small, and goes away (decays) very quickly. It does not make you feel unwell. Drinking plenty after the scan helps flush the drug out of your system. The radiation from the CT part of the scan is also kept to the minimum necessary. The risk of the radiation causing any problems in the future is very small. Doctors only do these scans if they are necessary. They make sure the benefit of having the scan outweighs any possible risks.

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, let the department know a few days before your appointment. They will let you know if you need to stop breast feeding for a length of time after having the radioactive drug. You may need to store enough expressed milk for at least one feed.

 

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 scanning department sends the report to your specialist, who gives you the results.

Understandably, waiting for results can make you anxious. It usually takes up to a couple of weeks. If your doctor needs the results urgently, they make a note of this on the scan request form and the results are 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 or specialist nurse to check if the results are back.

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Updated: 29 April 2015