Magnetic Resonance Positron Emission Tomography (MR PET) is a medical imaging specialty that involves the use of MRI (Magnetic Resonance Imaging) and positron-emitting radiopharmaceuticals (also known as radioactive medicines or tracer medicines) for diagnostic imaging (scans) and research. While MR PET scans involve radiation exposure (like with nuclear medicine scans), by utilising MRI the exposure is limited as much as possible.

Why does my child need a MR PET scan?

MR PET combines the use of MRI and tracer medicines to provide images that can see inside the body.

MR PET scans are performed for many different reasons, including: 

• for early detection, treatment, and management of diseases
• to see how different organs in the body are functioning 
• to look at the shape or structure of parts of the body 

MR PET scans are often performed on the whole body, and are also commonly used to assess to the function of the brain. The majority of scans performed at RCH involve the administration of a radioactive glucose (¹⁸FDG).

Preparing your child for their appointment

Preparation for a MR PET scan can depend on the type of scan required but usually requires fasting due to the type of tracer administered, and if sedation or general anaesthesia is required. Fasting will consist of no food or drink containing sugar for 6 hours prior to the MR PET appointment. This is to ensure the radioactive glucose administered is seen in the areas of the body that are required. Water can usually be continued throughout the appointment. If fasting is required, you will be informed of this in your individual preparation instructions at the time of booking. Most patients can continue their usual medications (if they do not contain any sugar) on the day of the MR PET scan, however please check with the MR PET staff prior to the appointment.

For some ideas on how to prepare your child for the procedure, and tips on distracting them and helping them stay calm during the procedure, see our fact sheet Reducing your child's discomfort during procedures. 

It may be helpful to your child if the procedure is explained to them before they come in for their important. Explain that: 

• the scans are painless
• a parent or carer can stay with the child during the scan

Most children can watch a movie while having their scans, and you are welcome to bring in your child's favourite movie or TV show to keep your child occupied and distracted during the scan. 

Specialist staff from Child Life Therapy may also be of benefit for your child. The Child Life Therapist engages families in imaging-specific education and medical play, as well as providing distraction and support during procedures. Child Life Therapist’s also run a Mock MRI clinic which allows patients undergoing awake MRIs to learn about what is required, and to experience a simulated MRI prior to their actual MRI booking. Appointments for Child Life Therapist support can be made in advance via Medical Imaging or your referring doctor.

What to expect during a MR PET scan

Before the procedure

Preparation for a MR PET examination depends on the type of scan your child is having, and your child’s individual needs. Most scans require fasting for the actual imaging sequences, and others require fasting for sedation or general anaesthesia – please confirm with your individual instructions at the time of booking. Distraction techniques are utilised for all scans for all age patients in MR PET.

All MR PET scans require an administration of a radioactive tracer which is given intravenously (IV). If your child requires this via an injection, topical anaesthesia will be applied to the injection site to make it numb – this can be in the form of a cream or via Coolsense^® – a hand-held device that uses cryotherapy to numb the area. Cream usually takes over 45 minutes to work, so you will be asked to attend the department earlier than your scheduled appointment time. You will be advised if you need to do this when you are given your appointment.

All people entering the MRI room need to fill out a MRI questionnaire before the scan. It asks about their medical history and helps the MRI staff ensure the safety of all persons in the MRI room. It is very important that this questionnaire is filled in accurately.

The MRI magnet may affect some medical devices that have been implanted inside your child’s or your body. These include older style pacemakers, implanted defibrillators, various nerve stimulators, infusion pumps and embolisation coils. In general, all body piercings and other jewellery must be removed, due to the metal in the piercing affecting the quality of the scan.

Your child may be asked to change into a hospital gown before their scan. If they would prefer not to wear the hospital gown, wearing a plain T-shirt and shorts or leggings may be OK, however articles of clothing will have to be removed if they contain metal, decoration, or glitter as they will affect the pictures.

During the procedure

You and your child will be invited into an interview room by a MRI technologist and a PET technologist where the procedure will be explained. Your child will have their height and weight recorded, and the MRI questionnaire will be finalised together with a few other PET questions.

Following administration of the radioactive tracer, there is often a length of time required for the tracer to localise – uptake time – of around 30-60mins. During this time you and your child can usually watch a movie from our list, or bring a favourite in for us to play for them.

Following this uptake time the staff will take you and your child into the MR PET scanner. For all examinations, a family member or carer is encouraged to stay with your child to help them feel comfortable about the procedure and to help them to keep still. The MR PET scanner is like a big square box with a tunnel through the middle. During the scan your child will have to lie very still in the tunnel, usually on their back. The MR PET machine makes some loud knocking noises which change during the study. It is generally only the noises made by the machine that people are aware of during the imaging but occasionally they may feel a little warm.

The table your child will lie on is quite narrow and foam cushions and soft straps are used to help your child remain safe and to remain still during their scan.

Depending on the examination some extra pads may be placed around or over your child’s body. They can watch their chosen movie and see around the room through mirrors that are positioned above their head, and they can hear and talk to the technologists performing the scan through headphones and a microphone. The scan time will vary depending on which or how many parts of the body are being examined, but will usually take 45-90 minutes.

After the scan

Usually you will be able to leave straight after the completion of the scan sequences, unless your child has had sedation or general anaesthesia. If your child had sedation or general anaesthesia, they will be required to remain under the care of the department or recovery nurse until they have recovered appropriately.

MR PET scans have many pictures with great detail that often take a long time for the Nuclear Medicine Specialist and Radiologist to review and report on. A report will be prepared by these Specialists and sent to your referring doctor. The report is usually available within a week but can be received earlier if required. If you have any questions about why your child needs a MR PET scan, or questions about the results of your scan, please speak to your doctor.

MR PET scan with sedation

Whether or not your child needs sedation depends on the type of scan they are having and their individual circumstances. In cases where a child is unable to remain still enough or they are very anxious or distressed, sedation may be required. Your child will be assessed to ensure that the sedation is suitable for them. This is often required for younger children but also for teenagers.

See our fact sheet Sedation for procedures.

MR PET scan with general anaesthetic

Some MR PET scans may need to be performed while your child is asleep under a general anaesthetic. This may be required if sedation will not be effective for your child and for them to achieve their scan. If your child does need a general anaesthetic for their scan, you will be given specific instructions for what to do before the scan, including fasting requirements. 

Key points to remember

• MR PET scans use a combination of MRI and tracer medicines to provide images and demonstrate the function of the organs inside the body.
• Most MR PET scans require fasting for the actual imaging sequences, and others require fasting for sedation.
• Your child will be lying on a scanning bed and has to keep very still during the procedure.
• Although the MR PET process can take a long time, you can remain with your child throughout their scan and they can watch a movie or listen to music during the uptake phase and scan.
• Sedation or general anaesthesia may be required for children who are unable to remain still enough to achieve their scan.
• The scans are painless, and if an injection is required your child can have numbing solution applied to the injection site. 
  

>For more information

• Kids Health Info fact sheet: Reducing your child's discomfort during procedures 
• Be Positive: A child's guide to hospital: MR PET    
  
• The Royal Children's Hospital: Okee in Medical Imaging app
• Child Life Therapy Service: Medical Imaging
• Kids Health Info fact sheet: Sedation for procedures
• Radiation fact sheet: Ionising Radiation and Health
• Talk to your doctor or the MR PET staff

Developed by The Royal Children's Hospital Medical Imaging and Day Surgery departments. We acknowledge the input of RCH consumers and carers.

Reviewed November 2018.

This information is awaiting routine review. Please always seek the most recent advice from a registered and practising clinician.

Kids Health Info is supported by The Royal Children’s Hospital Foundation. To donate, visit  www.rchfoundation.org.au.