Find out about having a PET scan what it is, how you have it and what happens afterwards.
PET stands for positron emission tomography. This type of scan can show how body tissues are working, as well as what they look like.
Not everybody who has cancer will need to have a PET scan. Other types of tests and scans may be more suitable.
You’ll usually have a PET scan in the x-ray radiology department as an outpatient. These scanners tend to be only in the major cancer hospitals. So you might have to travel to another hospital to have one.
A radiographer operates the scanner. It usually takes between 30 and 60 minutes.
Why you might have a PET scan
A PET scan can help to:
- show up a cancer
- find out the stage of a cancer, so doctors know how big it is and whether it has spread
- show whether a lump is cancer or not
- show whether a cancer has spread to other parts of the body
- decide the best treatment for your cancer
PET scans can also show how well a cancer drug is working.
After you have had treatment for cancer, a CT scan may show that there are still some signs of the cancer left. But this may not be active disease. It could be scar tissue left over from cancer killed off by your treatment. A PET scan can show whether this tissue is active cancer or not.
PET scans are sometimes used to look for cancer in the lymph nodes in the centre of the chest.
Preparing for your PET scan
For most PET scans, you need to stop eating for about 6 hours beforehand. You can usually drink water during this time. You might have instructions not to do any strenuous exercise for 24 hours before the scan.
Call the number on your appointment letter if not eating is a problem for you, for example if you’re diabetic. You might need to adapt your diet and sugar control and your appointment time could change.
Some people feel claustrophobic when they‘re having a scan. Contact the department staff before your test if you’re likely to feel like this. They can take extra care to make sure you’re comfortable and that you understand what’s going on. And your doctor can arrange to give you medicine to help you relax, if needed.
At the hospital
Your radiographer might ask you to change into a hospital gown. You have to remove any jewellery and other metal objects such as hair clips. Metal interferes with the images produced by the scanner.
You have an injection of a dye called a radiotracer about an hour before the scan. You have this into your arm through a small plastic tube called a cannula.
Then you rest and avoid moving too much. This allows the drug to spread through your body and travel to places where glucose is used for energy, like your brain.
In the scanning room
Your radiographer takes you into the scanning room. The PET machine is large and shaped like a doughnut.
You have most scans lying down on the machine couch on your back.
Once you’re in the right position, your radiographer leaves the room. They can see you on a TV screen or through a window from the control room. You can talk to each other through an intercom.
Having the PET scan
The couch slowly slides backwards and forwards through the scanner. The machine takes pictures as you move through it. The scan is painless but can be uncomfortable because you have to stay still. Tell your radiographer if you’re getting stiff and need to move.
It’s not particularly noisy but you’ll hear a constant background noise. When it’s over, your radiographer will come back into the room and lower the couch so you can get up.
Voiceover: PET and PET-CT scans help to diagnose and stage some cancers. They can also help your doctor decide which treatment you need and whether your treatment is working. PET and PET-CT scans show slightly different things but the process of having them is the same.
Radiographer: Okay, so first of all I’d like you to get changed.
Voiceover: For some scans you should not eat for 4 to 6 hours beforehand, for others there is no preparation. Your appointment card will give you details of what you need to do. One you have changed into your gown the radiographer will weigh and measure you. Then you have an injection of a very small amount of a radioactive drug called a tracer. This is what shows up on the scan. The drug is usually a form of glucose.
Radiographer: Right, I am starting now. Does that feel okay?
Girl: Yeah, that’s fine.
Radiographer: Is it comfortable?
Radiographer: Right, that’s all in now. I am going to take the needle away, because we don’t need that any more.
Voiceover: After the injection you rest for about an hour. This allows the tracer to spread through your body. The scan shows up cancer because they use glucose in a different way from normal tissue. When you are ready for the scan the radiographer helps you lie on the couch in the correct position.
Radiographer: I am just going to pop this under your knee, just to help your back stay comfortable. You’re going to move in and out of the scanner. Nothing is going to touch you or anything like that. You must keep very still. Close your eyes, because this light is quite bright.
Voiceover: Once you are in position and comfortable the radiographer will leave the room. You need to lie as still as possible while you are having the scan. You won’t feel anything but it can be difficult to lie still for up to an hour. If you begin to feel unwell or want some help you will be able to get the radiographers attention.
Radiographer: Are you okay in there, Charlotte?
Voiceover: The radiographer control the scan from a separate room, but they will be able to hear and see you all the time you are having the scan and will check you are okay.
Radiographer: We won’t be long now. Okay, that’s all done now; we will get you out of there. Are you okay? Good. You can pop your arms down now.
Voiceover: Once the scan is finished you can go home. As a precaution you should avoid contact with pregnant women and small babies for six hours after your scan. Your specialist will give you the results usually within a couple of weeks.
After your PET scan
Your radiographer removes the tube from your arm before you go home.
You can then eat and drink normally.
You need someone to take you home if you’ve had medicine to help you relax. You won’t be able to drive for the rest of the day, as you might be drowsy.
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.
A PET scan is a safe test for most people. But like all medical tests it has some risks. Your doctor and radiographer make sure the benefits of having the test outweigh these risks.
Pregnant women should only have the scan in an emergency. There’s a risk that the radiation could harm the baby. Contact the department as soon as you can before the scan if you are, or think you might be, pregnant.
Contact the department if you are breastfeeding. They will let you know if you need to stop breastfeeding for a length of time after the radioactive injection. You might need to store enough milk for one feed.
The radiation in the radioactive tracer is very small. Drinking plenty of fluids after your scan helps to flush the drug out of your system.
We have more information on tests, treatment and support if you have been diagnosed with cancer.