This page explains about 18F-DOPA PET scans at UCLH and what to expect when your child comes to have this procedure.
What is a PET scan?
A positron emission tomography (PET) scan gives very detailed, three-dimensional images of the body.
It works by injecting a substance called an isotope called 18-F-DOPA so you may hear the scan referred to by this name. A PET scan is regarded as the ‘gold standard’ for diagnosing the focal form of hyperinsulinism.
PET scanning is a relatively new technology. Some hospitals in the UK have PET scanners, but currently we do not have one at Great Ormond Street Hospital (GOSH). The nearest hospital with a PET scanner is University College London Hospital (UCLH).
Why does my child need a PET scan?
Cells in the pancreas called beta cells release insulin to regulate blood glucose level. In hyperinsulinism, the beta cells produce too much insulin lowering the blood glucose level to a dangerous level. Blood glucose is vital for all systems in the body to function properly, but especially the brain.
With this scan, the doctors are trying to find out whether the beta cells in one area of the pancreas (focal) are producing too much insulin or whether beta cells spread throughout the pancreas (diffuse) are responsible. The treatment recommended by the doctors depends on the results of the scan. The focal lesion is very tiny and cannot be seen by other X-ray techniques.
If you are pregnant or think you could be pregnant, please let us know at least two days before your child is due to have the scan. There is a risk that the isotope given to your child could harm your unborn baby.
What happens before the PET scan?
Your child will need to be prepared for the scan in various ways. Firstly, if they are currently on total parenteral nutrition (TPN), this will be stopped and replaced with an intravenous glucose drip two days before the scan is scheduled. If your child is feeding by mouth as well as by TPN, this will continue.
They will also need to stop taking diazoxide, chlorothiazide, glucagon and octreotide medicines two days before the scan. These medicines reduce insulin secretion so need to be stopped so the scan can pick up the beta cells that are overproducing insulin.
The nurses will insert a cannula (thin, plastic tube) into a vein in your child’s hand or foot the day before the scan is scheduled. The cannula will be used to inject the isotope. If your child has a double lumen central venous catheter, this can be used to inject the isotope so your child will not need a cannula.
The day of the scan
On the morning of the scan, the nurses will pass a naso-gastric tube so that the sedation medicine can be given easily. Your child will not need to get undressed for the scan. However, they should wear clothes without any metal, such as zips, buttons or fasteners, as this interferes with the scan.
Your child will need to ‘fast’ or stop eating and drinking before the sedation as it can be dangerous for liquid to be breathed into the lungs while under sedation. The nurses will discuss the precise times after which your child should not eat or drink anything. They will have an intravenous dextrose infusion from this fasting time until your child is back at GOSH. It will also help if you can keep your child awake during the morning so that the sedation is more effective.
At midday, an ambulance will take you and your child to UCLH for the scan. Unfortunately, as space is limited in the ambulance, only one parent will be able to travel with your child. They will be accompanied by a nurse and in some cases a doctor. If your child’s other parent also wants to go to UCLH, it is a short walk of about 15 minutes away from GOSH. Taxis are also available – often outside the main reception at GOSH – or you can call them from the free phone in reception or we can organise one for you.
What to take with you
Parents who have been to UCLH with their child suggest taking a favourite toy, soother or blanket with you. It is also a good idea to take a spare set of clothes and nappies if your child is using them.
Your child will be admitted to the general children’s ward – called T11 south. The sedation medicine will be given through your child’s nasogastric tube about an hour before the scan is due to start. Once sedation is given, your child will go down to the scanner on a trolley.
Once your child is sleepy, the scan will start. You will be asked to leave the scanning room and sit in the waiting room opposite while the isotope is being injected. After the injection, two adults will be allowed to stay for the majority of the scan.
Your child's intravenous dextrose infusion will continue during the scan – we will take regular blood glucose measurements as well as observing their heart rate and oxygen saturation levels.
After the scan, your child will return to the children’s ward to recover from the sedation and start eating and drinking again. When they have recovered, they will be transferred back to GOSH in an ambulance as before.
TPN and other medications can recommence immediately.
Are there any risks?
There are no side effects to the scan. The isotope that we inject will not interfere with any medicines your child is taking. The isotope contains a very small amount of radioactivity, similar to the amount we receive from natural background radiation in about six months. This is not a danger to your child as the isotope becomes inactive in the hours following the scan. However, it is necessary to take some precautions for the first 24 hours after the scan, while the isotope is leaving your child’s body. These are explained in the next section.
There is a risk that the isotope could harm an unborn baby so, if you are pregnant or think you could be pregnant, please let us know at least two days before your child is due to have the scan.
After the scan
For the first 24 hours after the scan:
Your child should drink plenty of fluids. This will allow the isotope to pass out through their body as quickly as possible.
If your child is toilet-trained, they should go to the toilet as often as possible. Hand washing afterwards is very important.
If your child is in nappies, you should change them frequently and dispose of the dirty nappy in an outside bin. Wash your hands thoroughly after nappy changing.
If you are pregnant or think you could be pregnant, you should avoid contact with your child’s bodily fluids, such as urine (wee), faeces (poo) and vomit.
Your child should continue to take any medicines as usual. The isotope will not affect them in any way.
Getting the results of the scan
The doctors will interpret the results from the scan and discuss them with your consultant at GOSH as soon as possible. Your consultant will then explain the plan of treatment for your child and when it is likely to start.
Please note this is a generic GOSH information sheet. If you have specific questions about how this relates to your child, please ask your doctor. Please note this information may not necessarily reflect treatment at other hospitals.