This page tells you about PET scans. There is information about
What is a PET scan
PET stands for Positron Emission Tomography. A PET scan can show how body tissues are working, as well as what they look like. It can help to diagnose and stage a cancer. This helps your doctor decide which treatment you need and whether your treatment is working. A PET scan can also sometimes tell if an area in the body is scar tissue or an active cancer.
Having a PET scan
For some PET scans you should not eat and should drink only water for 4 to 6 hours beforehand. For other scans there is no preparation. Your appointment card should give you details about what you need to do.
First the radiographer gives you an injection of a very small amount of a radioactive drug (tracer) into your bloodstream. After the injection you rest for about an hour. You then go into the scanning room and lie on your back on a narrow bed. The bed moves through the scanner. The scan can take up to an hour.
The radiographer controls the scan from outside the room. They can see and talk to you. It is important to lie as still as possible. It shouldn’t be at all painful. If you begin to feel unwell or want some help, you have a buzzer to call the staff.
PET scans are very safe. The amount of radiation you have is small and it goes away (decays) very quickly. But it is best not to have close contact with pregnant women, babies and young children for a few hours after the scan.
It can take up to a couple of weeks to get the results. The scanning department sends the report to your specialist who gives you the results.
PET stands for Positron Emission Tomography. This type of scan can show how body tissues are working, as well as what they look like. PET scanners are very expensive and only a few hospitals in the UK have one. This means that you may have to travel to another hospital for your scan. Not everybody who has cancer will need to have a PET scan. Other types of tests and scans may be more suitable.
A PET scan can help to
- Show up a cancer
- Find out the stage of a cancer
- 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
- Show how well cancer drug treatment is working
- Show the difference between scar tissue and active cancer tissue
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 fibrous tissue left over from cancer killed off by your treatment. A PET scan can show whether this tissue is active cancer or not.
In lung cancer, PET scans are sometimes used to look for cancer in the lymph nodes in the centre of the chest. Or to show whether the cancer has spread to other areas. This can help your specialist to decide whether it is possible to remove the cancer with surgery.
For some PET scans you may need to eat nothing for 4 to 6 hours before your appointment time and only drink water. For other scans there will be no preparation at all. Your appointment card should give you details about what you need to do to prepare for your scan. Unless you are told otherwise, always take any prescribed medications as usual. Let your doctor know if you are diabetic as you may need to adapt your diet and sugar control routine a little.
With a PET scan you have an injection of a very small amount of a radioactive drug (tracer) first. The amount of radiation is very small and no more than you have during a normal X-ray. It only stays in the body for a few hours. Depending on which drug you have, the radioactive drug will travel to particular parts of your body. The most common drug is fluorine 18, also known as FDG-18. This is a radioactive version of glucose.
When FDG-18 is injected into your body it travels to places where glucose is used for energy. It shows up cancers because they use glucose in a different way from normal tissue. And it will show up changes in tissues that use glucose as their main source of energy - for example, the brain or heart muscle.
After you have the injection you rest for about an hour. This allows the radioactive tracer to spread through the body. The scan itself can take up to an hour. The scan produces an image of the radioactive tracer in the body. It is important that you lie as still as possible while the scan is being done. It shouldn’t be at all painful. If you begin to feel unwell or want some help, you will have a buzzer that you can press to get attention. The staff doing the scan will be able to see you at all times.
There are no side effects of this type of scan. But it can be a bit boring waiting around and some people find it difficult to lie still for an hour. To help with the boredom some centres have a CD player that you can use whilst lying down in the scanner. So you may want to bring along some of your favourite CD’s to listen to. You may be able to bring a friend to sit with you while you are waiting to have the scan. But it is always best to ring and check if this is possible before you go.
After your scan you should feel fine and will be able to go back to your normal diet and activities.
This video shows you what happens when you have a PET scan:
View a transcript of the video showing what happens when you have a PET scan. (Opens in a new window)
For the patient, PET scans are very safe. You have a radioactive injection, but this is a small amount and the radiation goes away (decays) very quickly.
These days, some doctors tell PET scan patients that they should not have close contact with pregnant women, babies and young children for a few hours after their scan. 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 that 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.
PET scans can diagnose and stage many types of cancer. But there is a lack of high quality research into how well it works for certain types of cancer. A UK review of PET scanning by the Department of Health in 2005 reported strong evidence that routine PET scanning works well for
- Staging non-small cell lung cancer
- Staging non Hodgkin’s lymphoma and Hodgkin’s lymphoma
- Staging and evaluating bowel cancer that had come back
There is growing evidence for using it to look at
The use of PET scanning in these and other cancers needs more research.
As with other scans, PET scans are not right every single time. But they do greatly increase the certainty of a diagnosis and help doctors decide on the best treatment for you.
Not every hospital in the UK has PET 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.
It can take time for test results to come through, sometimes a couple of weeks. Usually, the scan is examined by a specialist in radiology or nuclear medicine and a report is typed up. The report is then sent to your specialist, who gives the results to you.
Understandably, waiting for results can make you anxious. If your doctor needed the results urgently, it would have been noted on the scan request form and the results will be ready quickly. Try to remember to ask your doctor how long you should expect to wait for the results when you are first asked to go for the test. If it is not an emergency, and you have not heard a couple of weeks after your test, ring your doctor's secretary to check if they are back.
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