PET scan
A PET scan uses a mildly radioactive drug to show up areas of your body where cells are more active than normal. It can help doctors work out whether tissue is active cancer or not.
Why you might have it
PET scans might be useful for some people with high grade non-Hodgkin lymphoma. Your doctor can tell you whether it may be helpful in your case. They are useful for staging some types of lymphoma and seeing how well treatment has worked.
PET scans can show the difference between tissues that are actively growing (like cancer) and an old injury or scar. So it can also show if swollen lymph nodes after treatment are scar tissue or lymphoma that has not responded to treatment.
How you have it
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.
Preparing for your PET scan
Check your appointment letter for instructions on how to prepare for this test. You should follow the information given in your appointment letter. Some hospitals may have slightly different instructions.
For most PET scans, you need to stop eating for about 4 to 6 hours beforehand. You can usually drink unflavoured water during this time. They will tell you if you need to stop any regular medication you are taking.
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 your appointment time could change.
It is important to tell the scanning staff beforehand if you are pregnant or think you might be pregnant. Or you are breastfeeding.
You might have instructions not to do any strenuous exercise for around 12 to 24 hours before the scan.
Some people feel claustrophobic or closed in when they are having a scan. Contact the PET scanning 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. Your doctor can arrange to give you medicine to help you relax, if needed.
What happens
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 injection through a small plastic tube called a cannula in your arm.
You need to rest and avoid moving too much during this hour. This allows the drug to spread through your body and travel to places where glucose is used for energy, like your brain.
When you arrive
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 do hear a constant background noise.
When it’s over, your radiographer comes back into the room and lowers 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: Ok 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 ok?
Girl: Yeah that’s fine
Radiographer: Is it comfortable?
Girl: Yeah
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 ok in there Charlotte?
Girl: Yeah
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 ok
Radiographer: We won’t be long now. Ok that’s all done now; we will get you out of there. Are you ok? Good. You can pop your arms down now
Voiceover: One 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 cannula from your arm before you go home. You can then eat and drink normally.
The radiation in the radioactive tracer is very small. Drinking plenty of fluids after your scan helps to flush the radioactive tracer out of your system.
The radioactive tracer gives off very small levels of radiation that go away very quickly. As a precaution, you should avoid close contact with pregnant women, babies and young children for the rest of the day. Your radiographer will give you more information about this. Speak to them if you have any questions. Some hospitals may have different instructions.
If you’ve had medicine to help you relax (sedation), you need someone to take you home and stay overnight. If you've had sedation, for the next 24 hours, you also shouldn’t:
- drive
- drink alcohol
- operate heavy machinery
- sign any legally binding documents
If you are travelling abroad within a week of your PET scan, it's a good idea to take your appointment letter with you. This is because most airports have sensitive radiation monitors. This may pick up a trace of radiation left in your body following your test.
Getting your results
Your scan will be looked at by a specialist doctor and you should get your results within 1 or 2 weeks. You won't get any results at the time of the scan.
Waiting for test results can make you anxious. Ask your doctor or nurse how long it will take to get them. Contact them if you haven’t heard anything after a couple of weeks.
You might have the contact details for a specialist nurse. You can contact them for information and support if you need to. It may help to talk to a close friend or relative about how you feel.
For support and information, you can call the Cancer Research UK information nurses on freephone 0808 800 4040. The lines are open from 9am to 5pm, Monday to Friday.
Contact the doctor that arranged the test if you haven't heard anything after a couple of weeks.
Possible risks
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.
Some of the possible risks include:
Pregnancy
Pregnant women should only have the scan in an emergency. There’s a risk that the radiation could harm the developing baby. Contact the department beforehand if you're pregnant or think you might be pregnant.
Breastfeeding
If you're breastfeeding, let the department know a few days before your appointment. They will let you know if you need to stop breastfeeding for a length of time after having the radioactive tracer. You might need to store enough expressed milk for at least one feed.
Bruising and swelling
You might get a small bruise around the area where they put the 
in. There is a risk that the radioactive tracer will leak outside the vein, this is rare. If this does happen, it can cause swelling and pain in your arm.
Allergic reaction
Rarely, people have an allergic reaction to the radioactive tracer. This most often starts with weakness, sweating and difficulty breathing. Tell your radiographer immediately if you feel unwell.
Radiation
Exposure to radiation from the radioactive tracer during a PET scan slightly increases your risk of developing cancer in the future. Talk to your doctor if this worries you.
