Positron Emission Tomography (PET) - Computerised Tomography (CT)

The aim of this page is to answer some of the questions you may have about PET-CT scanning and to help you prepare your child for the scan. If you have any further questions or concerns, please contact the PET Imaging Centre on 020 7188 4988. They will be happy to speak with you about the procedure.

What is PET-CT scanning?

A PET-CT scan - Positron Emission Tomography coupled with Computerised Tomography - takes three dimensional images of your child’s body. This allows us to see if your child’s organs are working normally. Before your child has a PET-CT scan, we inject him or her with a small dose of a substance called a ‘tracer’ (usually a form of slightly radioactive sugar – the dose varies with the weight of your child). The tracer goes to the tissues which can then be seen by the scanner as a three dimensional image. PET-CT scans are different from other scans your child may have had, such as X-rays, diagnostic CT, ultrasound or MRI. This is because these scans show us what tissues look like, while PET-CT scans show us how the tissues are working.

What are the benefits of PET-CT scans?

PET-CT scans help us to get important information about a range of conditions that can affect the organs of a child. For example, they can help to tell us more about epilepsy, cancer and heart conditions. PET-CT scans help your child’s doctor to plan the best possible treatment.

Are there any alternatives?

Other imaging tests, such as a CT or MRI give different information than a PET-CT scan and are not considered an alternative. Your child has been referred for a PET-CT scan because your doctor feels it is the best way to get the information he/she needs to decide which treatment is best for your child.

Are there any risks associated with PET-CT scans?

Tracer injections
There have been no documented side-effects with tracer injections, such as sickness or feeling unwell.

All radiation carries a risk but the risk of radiation-induced cancer is much smaller than the natural risk of cancer. 1 in 3 people in the UK develop cancer, where as the additional risk of a fatal cancer associated with this type of imaging examination using radiation, is about 1 chance in 1000.

We always check that the PET-CT scan is the best way to get an answer to your child’s medical problem. And we always use the lowest possible radiation dose to get the scan your doctor needs. The amount of radiation your child will receive is equivalent to four years exposure to natural background radiation.

General anaesthetic
Any examination with general anaesthetic carries a slight risk. The level of risk depends on your child’s general health and the complexity of the procedure he or she is having. These risks will be discussed fully with you by the staff caring for your child. The Trust’s leaflet, Having an anaesthetic, gives more information about the risks and side-effects associated with having a general anaesthetic. If you do not have a copy, please ask us for one.

How co-operative will my child need to be?

PET-CT scanning is a relatively simple test but to get the best results some co-operation is needed from both the child and the parents or carers.

Parents and carers can stay with the child throughout the scan. However, exposure to radiation should be avoided if you are pregnant – please speak to the PET Centre staff about this before attending the appointment.

Asking for your consent

We want to involve you in all the decisions about your child’s care and treatment. If you decide to go ahead, you will be asked to sign a consent form on behalf of your child. This confirms that you agree to your child having the procedure and understand what it involves. You should receive the leaflet, Helping you decide: our consent policy, which gives you more information. If you do not, please ask us for one.

If your child is very young, has behavioural difficulties or is unable to lie still for the scan he/ she may need sedation or a general anaesthetic.

In this case:

  • we may ask your GP or hospital doctor to do some blood tests before the procedure
  • to make sure it is safe for your child to have the anaesthetic
  • he/she will need to stay in hospital longer – either for the day or overnight
  • you will be asked to sign a consent form to give us permission to do the procedure with an anaesthetic.

How can I prepare my child for the PET-CT scan?

Food and drink
We will ask you not to give your child anything to eat:

  1. for three hours before the scan – for a brain scan
  2. for six hours before the scan – for a body scan.

If your child is having a heart scan, he or she may have to go without food - it depends on the type of scan being performed. We will give you clear instructions in the appointment letter.

Unflavoured water can be given at anytime. This makes sure that your child does not get 19 dehydrated and also helps us to get the best scan possible. If however your child is having a general anaesthetic we will give you specific instructions.

If your child is having a body or a heart scan we suggest that he/she wears something loose and comfortable for the scan. As part of the exam includes a limited CT scan it is important that your child is not wearing any metal, including jewellery, watches, zips and bra hooks. We will provide a hospital gown.

Talk to your child
Preparing your child for the visit to hospital and the PET-CT scan will help him/her to understand what is happening. From a young age, children are keen to talk about what they know about hospitals. Talking to your child in advance will give him/her time to ask any questions or raise any concerns. Children tend to be more co-operative when they know what is happening to them. Use familiar words that your child will understand and give truthful, factual information. Explain that your child will meet doctors and nurses and that they should only have to stay in hospital for about half a day (or maybe overnight if they are having an anaesthetic). 

Will my child feel any pain?

The scan itself is not painful. However, a cannula (plastic tube) will be put in the back of his/ her hand or arm to give the tracer injection and any anaesthetic. We can make this as pain free as possible by using Emla cream. This cream temporarily numbs the skin and helps to reduce any discomfort when putting the cannula in.

What happens during your visit for the scan?

This depends on the type of scan, and will be fully explained to you and your child by ourstaff when you arrive.

General procedure

  • Emla cream will be put on the back of your child’s hand or arm (if this has not been done at home).
  • The imaging staff will explain the procedure in full and take a short medical history.
  • A nurse will then place a small cannula (plastic tube) in the most easily available vein (usually in the back of the hand or in the arm).
  • We will then move your child to a quiet room to have the tracer injection and to relax for up to 90mins before the scan. This period of time, called the ‘uptake period’, allows the tracer to circulate in the blood stream and go into the tissues – this helps us see them on the scan. If your child is having a brain scan he/she should not be distracted (by for example talking, music or games) during this period as these activities can affect the look of the scan.
  • If your child is having a body scan, this is not such a problem. He/she can watch a DVD or listen to music. However, it is still important that your child relaxes quietly so the tracer goes to the areas we need to do the scan, rather than his or her muscles.
  • Your child can also use the toilet if needed
  • After this period of relaxation, a nurse will position your child on the PET/CT scanner couch and make him or her as comfortable as possible. Your child will be asked to lie very still for the scan. You can stay with your child throughout the procedure although we do ask that you do not distract them and cause them to move their head or wriggle.
  • We may take pictures of all of your child’s body or just the part that we have been asked to examine.
  • Once the scan is completed you can give your child refreshments and either go home or recover on the ward (if he/she has had sedation or a general anaesthetic).

PET-CT brain scans

PET/CT brain scans are performed for children with a variety of conditions including epilepsy, brain tumours and movement disorders. The scan usually takes about 10 -15 minutes

  • If your child is suffering from epilepsy – it is important to tell the PET Centre doctors if your child has an epileptic fit during the period between the tracer injection and the scan. We will also do an EEG (electro-encephalogram) after the injection of the tracer to monitor brain activity – this will also spot any fits that cannot be seen by just watching your child. The doctors reporting the scan need to know if a fit has happened as this can change how they report the scan findings. Most children who suffer from epilepsy will be familiar with having an EEG
  • If your child has a brain tumour – it may be necessary to use two different radiotracers to look at brain tumours. If this is the case then two scans, one after the other, will be performed on the same day. We can deliver both injections through the same cannula so will only need one needle. The procedure is longer and a bit more complicated but staff will explain this to you and your child in more detail.
  • If your child has a movement disorder - it is usually necessary to give your child an anaesthetic for the scan so that they can remain still.

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