PET/CT scans

A PET/CT scan is a nuclear medicine test combining a PET scan and a CT scan. Pictures of different parts of your body can be produced to help find out how your body is working.

What is nuclear medicine?

Nuclear medicine helps doctors to check how well different parts of your body are working. A small amount of a radioactive substance (tracer) is given, usually by injection into a vein.

The tracer gives off gamma rays, so we can measure the distribution of that tracer in your body. This measurement is usually taken with a gamma camera (a large machine for detecting radioactivity), although occasionally, measurement of blood samples may be needed.

Is there any risk from the radiation?

The amount of radiation involved is small, and is similar to the amount used in some x-ray procedures. The benefits of the scan far outweigh any possible risk from the radiation.

What is positron emission tomography (PET)?

PET is a medical imaging technique in which a radioactive tracer is injected into a vein. The most commonly used tracer in PET is FDG (fluoro-deoxy-glucose), which is a radioactive form of glucose. The scan shows how the body breaks down and uses glucose. Abnormal cells use glucose differently and this will show up on the scan.

A CT (Computerised Tomography) scan uses X-rays to produce images of the body. By combining PET and CT, we are able to provide important information about many conditions affecting the different organs of your body. This will help your doctor to plan appropriate treatment for you.

What preparation do I need?

You should not have anything to eat for six hours before your appointment. During this time you can drink as much water, black unsweetened coffee or tea and diet coke as you like. You do not need to have a full bladder for your scan. You can continue to take any medication that has been prescribed for you by your doctor. It is also safe for you to take 'over the counter' medicines.

What happens when I arrive for my scan?

When you arrive for your scan you will be taken to a preparation room. We will ask you to change into a hospital gown and remove all your jewellery and any other metallic objects. A member of our staff will explain the procedure and will also ask a few questions about your health. If you have any questions this is a good opportunity to ask them.

Some patients may be prescribed diazepam. The diazepam will relax the muscles around your neck and shoulders to provide clearer information. If diazepam has been requested we will give it to you soon after arrival.

How is the radioactive tracer given?

The tracer is given as an injection. However, we cannot use skin-tunnelled catheters or any other intravenous device that cannot be removed immediately after the injection.

We will usually insert a cannula into one of your veins about 15 minutes before we want to give you the radioactive tracer. We will ask you to lie down to have the cannula inserted, while the radioactive tracer is given and for at least one hour following this. The cannula will be removed as soon as the tracer has been given.

Your scan

When the radioactive tracer has been absorbed by your body, you are ready for your scan. Before your scan you will be asked to go to the toilet to empty your bladder. In the scanning room you will be asked to lie on your back on the scanning bed.

You will be scanned with your arms raised above your head. Occasionally we may also scan you with your arms by your sides. The bed will move through the scanner and collect images for between 30 and 90 minutes, depending on which parts of your body we need to look at.

The scan is not particularly noisy although there is a constant background noise caused by the computers and air conditioning and this will make it difficult for you to listen to any music during the scan. You will not be aware of anything other than the scanning couch moving every few minutes.

It is essential that you stay still during the whole of the scan. There is a two-way microphone between the scanner and the control room and we will be able to hear you and respond if you have any queries.

Further information is available by watching this video of what to expect when having a PET scan.

Are there any side effects?

The tracer that we inject will not produce any side effects. You can continue with your usual daily activities. In particular it will not make you drowsy and so will not prevent you from driving a car. However, if you have been given diazepam you MUST NOT drive for the rest of the day.

What happens after my PET/CT scan?

Once the scan is completed you will be able to leave the department immediately. You will be able to eat and drink what you like. You may go anywhere you wish but we ask you to avoid prolonged close contact with children for the rest of the day. This is to avoid exposing children to unnecessary radiation.