What a PET scan is:
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 have here.. 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.
PET scans are now often combined with CT scans to create more detailed pictures. This is called a PET-CT scan.
What a PET scan shows:
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 scar 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.
What having a PET scan involves:
For some PET scans you may be told not to eat for 4 to 6 hours before your appointment time and only drink water. You may be asked not to do any strenuous exercise for 24 hours before. For other scans there will be no preparation at all. Your appointment letter will 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. If you are diabetic, let the scanning department know a few days before your scan 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 does not make you feel unwell. 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. Occasionally, it can show up areas of infection or inflammation.
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 known 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.
Possible risks from a PET scan:
Although having a radioactive injection may sound dangerous, you only have a small amount of radiation given to you. The radiation goes away (decays) very quickly and it does not make you feel unwell. Drinking plenty after the scan will help flush the drug out of your system. Before having any test, doctors make sure the benefits outweigh any possible risks.
Although the amount of radiation is small, your doctor will recommend that you do not have long periods of close contact with pregnant women, babies and young children for the rest of the day. If you are pregnant or breast feeding, you must phone the department where you are due to have the scan for advice. They will let you know if you need to stop breast feeding for a length of time after having the radioactive injection. You may need to store enough expressed milk for at least one feed. If you are pregnant, you are unlikely to have a PET scan. This is because the radioactive drug could cross the placenta and affect the baby.
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.
Getting your results:
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 needs the results urgently, they make a note of this on the scan request form and the results will be ready sooner. 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 or specialist nurse to check if they are back.
PET SCAN