This leaflet answers common questions about having an FDG PET-CT brain scan. If you would like further information, or have any worries, please do not hesitate to ask your nurse or doctor. In all cases, a doctor will explain the FDG PET-CT brain scan to you and answer any questions you may have.

What is a 18F-FDG PET-CT brain scan?

A positron emission tomography (PET) is a scan which involves injecting a radioactive substance called 18F-FDG, which will travel to areas in your body which take up a lot of sugar, like the brain. This is seen when the scanner takes pictures of the brain during the scan. As part of the procedure, a simple CT scan will be acquired before the PET scan.

How long will the appointment take?

Please allow an hour for your appointment.

How early should I arrive?

Please arrive 30 minutes before your appointment.

Do I need to bring anything with me?

Please bring any medication you take.

How should I prepare for the scan?

Please do not eat anything for 4 hours before your scan, you can only drink plain unflavoured water. If there is any reason this may be difficult, please contact the nuclear medicine department on 020 7830 2196 who can provide advice. Avoid strenuous exercise 24 hours before your appointment.

How should I dress?

Please wear comfortable clothing which allows your sleeves to be easily rolled up for the cannula to be inserted. You will not be required to undress.

What happens if I am diabetic?

The preparation may be different depending on how your diabetes is managed, please contact the nuclear medicine department on 020 7830 2196 who can provide advice.

What happens if my blood sugar level is too high?

To ensure we have a representative idea of your glucose uptake it’s important your blood sugar levels are within certain levels. If it is too high, we may have to reschedule the scan.

Where can I go for help?

If you require any additional help or translating services, please contact the nuclear medicine department on 0207 830 2196.

What happens when I come to the department?

  • A nuclear medicine technologist will explain the procedure and complete a questionnaire with you.
  • The technologist will measure your height and weight.
  • A trolley will be provided to place your personal belongings in; this will be with you all the time.
  • You will be taken to a resting bay which is a room containing a bed/couch which is where you will be injected with the radioactive tracer. 
  • A cannula will be inserted on your arm and the technologist will take a blood sample to check your blood glucose levels. Later this cannula will also be used to inject the radiotracer.
  • After the injection you will stay in the resting bay for 30 minutes, this is to allow your body to rest. We ask that you do not use any devices or read anything. If you are feeling cold, please ask for a blanket.
  • The 18F-FDG will be administered through the cannula, you will be asked to rest for an additional 30 minutes. This is to allow time for the radioactive tracer to circulate in your body. The 18F-FDG will naturally be taken up by the entire body, but we will only collect images of the brain.
  • Immediately before the scan, you will be asked if you need the toilet, please feel free to use the toilet during the 30-minute waiting period.
  • The scan will take 10 minutes. Your head will be positioned in a head support to keep it in the same position during the scan. It’s important to keep your head still to acquire the best pictures of your brain.

What can I do when I’m in the resting bay?

We would like you to feel relaxed, please let us know if you would like a blanket or water. We ask that you avoid reading, looking at your mobile phone or listening to music because it may impact the 18F-FDG uptake. We will also dim the lights so that you can have a proper rest period.

What will happen during the scan?

The nuclear medicine technologist will ask you to lie down on the scanning bed. You head will be positioned in a special support. The bed will then move into the correct position and the scan will begin. Please remain still throughout the scan. A technologist will be overseeing the scan the entire time to make sure you’re okay. If you would like to see the scanner beforehand, please let us know.

Can I bring someone with me?

If you need someone with you, they can sit in the waiting room with you. However, they won’t be able to stay with you in the resting bay or during the scan. Please do not bring anyone pregnant or children with you.

Is this scan dangerous?

No, the scan is not dangerous, but it uses a small amount of radioactive material.

What does everything look like?

This is the scanner room

This is the resting bay

Can I eat after the scan?

Yes, once your scan is completed you can continue with normal day-to-day activities.

What shall I do after the scan?

Please drink lots of water and maintain a one metre distance from any pregnant women and children aged less than five for the remaining hours of the day.

Scan side effects

Generally, patients do not experience any side effects. However, if anything concerns you, let a technologist know immediately.

When will I hear back about the results?

We aim to report the scan within one week.

Travelling to your appointment at the Royal Free Hospital

From Pond Street entrance

Enter the main doors and head towards WH Smith. Go past the lifts on your left, past the stairs on your right and after passing the double doors in front of you, the department is on your immediate left.

From Rowland Hill entrance

Walk down the corridor and turn left onto the main corridor, past the library on the left and the department is on the corridor on your right.