PET-CT scan

A PET-CT scan combines a CT scan and a PET scan into one scan.

A CT scan takes pictures from all around your body and uses a computer to put them together. There is detailed information about CT scans in our section about cancer tests.

A PET scan uses a very small amount of an injected radioactive drug to show where cells are active in the body. There is detailed information about PET scans in the cancer tests section.

These 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.

A PET-CT scan takes CT 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.

A PET-CT scan can give important information about your cancer. It can help to

• Diagnose a cancer
• Stage a cancer
• Show whether a lump is cancer or not
• Show whether a cancer has spread to other parts of the body
• Help your doctors decide on the best treatment for your cancer
• Show how well your treatment is working
• 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.

Your doctor or the scanning department will give you instructions on how to prepare for your scan. You should not normally have anything to eat for 6 hours beforehand. You can usually drink as much as you like, but you must avoid milk and sugary drinks. Unless you are told otherwise, you should carry on taking any medicines prescribed for you by your doctor.

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 and shows you to the preparation room. You will be asked to change into a hospital gown and take off all your jewellery and any other metallic objects. Your doctor 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 lie down to have the tube put in and have the radioactive tracer and for at least one hour afterwards. You will be ready for your scan when your body has absorbed the radioactive drug. You then go to the toilet to empty your bladder. Then you go into the scanning room.

You lie on your back on the scanning bed and the bed moves through the scanner. This can feel strange. The scan takes between 30 and 90 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.

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.

Once the scan is over you will be able to go home straight away. You can eat and drink what you like. It is best not to be close to children for the rest of the day. This is to avoid exposing them to any radiation, although the dose is extremely small and it is just to be on the safe side. If you have had diazepam (Valium) you must not drive for the rest of the day, as it makes you drowsy.

PET-CT scans are very safe. You have a radioactive injection and the scan uses radiation. But the amount of radiation is small, the same as when you have an X-ray. The benefit of the scan, in finding out about your cancer, outweighs any potential risk from the radiation. The radioactive drug does not have any side effects.

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, 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 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.

If you have had diazepam (Valium) as part of your scan you may be drowsy afterwards and it is best if someone can go home with you.

PET-CT scans can diagnose and stage many types of cancer and are generally thought to be more accurate in diagnosing cancer than PET scans alone.

From research, we know that they can help to

• Check whether people with lung cancer can have surgery
• Monitor people with lung cancer for recurrence
• Determine the stage of Hodgkin's lymphoma and non Hodgkin's lymphoma
• Check whether people with bowel cancer which has spread to the liver can have surgery
• Check whether people with cancer of the food pipe (oesophageal cancer) can have surgery

There is some evidence that PET-CT scans can help to measure the stage of sarcomas and also cancers of the brain and spinal cord, thyroid, testes and skin (melanoma).

There is some evidence that they can help to find head and neck cancers or breast cancer, or unknown primary cancer.

It is not clear how helpful PET-CT scans may be in helping doctors to make decisions about treatment. We don't know yet whether they can increase cure rates or survival for most types of cancer.

Using PET-CT scanning in these and other cancers needs more research.

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

Understandably, waiting for results can make you anxious. It usually takes a couple of weeks. If your doctor needed the results urgently, they would note that on the scan request form and the results will be 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 to check if the results are back.

Not every hospital in the UK has PET-CT 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.