Functional magnetic resonance imaging (fMRI)
This page explains about functional magnetic resonance imaging (fMRI) and what to expect when your child comes to Great Ormond Street Hospital (GOSH) to have this procedure.
Functional magnetic resonance imaging (fMRI) has an established role in evaluating patients for epilepsy surgery.
It can be helpful when results from standard diagnostic methods, such as clinical information, electroencephalography (EEG) and MRI are insufficient to identify where seizures start in the brain in relation to eloquent parts of the brain responsible for function.
What is an MRI scan?
An MRI (magnetic resonance imaging) scan uses a magnetic field rather than X-rays to take pictures of your child’s body. The MRI scanner is a hollow machine with a tube running horizontally through its middle. Your child will lie on a bed that slides into the tube. MRI scans are used to get detailed pictures of the size and shape of part of your child’s body. The information from the scan is then used to plan your child’s treatment.
What is a functional MRI scan and why does my child need one?
The main difference between a normal MRI scan and a functional MRI scan is the results that can be obtained. Whereas a normal MRI scan gives pictures of the structure of the brain, a functional MRI scan shows which parts of the brain are activated when certain tasks are carried out such as language, memory and movement.
Functional MRI (fMRI) evaluates blood flow in the brain called the blood oxygenation level dependent (BOLD) contrast technique. This means that brain activity can be picked up by the MRI scanner because of tiny chemical changes in the blood.
This particular type of scan can be extremely useful when planning brain surgery as the areas of the brain used for important functions such as language, memory and movement can be identified beforehand. This means that the operation can be planned to preserve as much of these areas as possible.
Are there any alternatives?
Other types of imaging can show the structure of the brain, but they cannot show which areas of the brain are used for particular tasks. The only other test that can be used to build up a complete picture is invasive monitoring, which can allow the epilepsy team to carry out ‘functional brain mapping’. This mapping allows the team to check exactly which areas of the brain your child needs for essential tasks, like movement or speech.
Invasive monitoring involves an operation to place electrodes, in strips or grids, directly over the surface of your child’s brain. These electrodes are then connected to an EEG machine so that technicians can record your child’s brain activity over several days. The fMRI scan is not at all invasive and does not require an anaesthetic.
Are there any risks?
There are no risks associated with fMRI scans. They are painless and generally quick with no lasting effects. The scanner does not touch your child during the scan.
All types of MRI scan are unsuitable for people with any metal inside them (pacemakers, surgical clips or metallic implants) because the scanner emits a strong magnetic field. Your child should wear clothes without zips or metal poppers for the scan, otherwise he or she will need to change into a gown.
Before the scan starts, the nurse or radiographer will check you or your child do not have a pacemaker, metal implants or clips, dental braces, a history of metal fragments in the eyes or any allergies. We will ask you to sign a form to confirm this. You will also need to leave metallic objects like jewellery, watches, keys, pens or cards with metallic strips like bank cards and train tickets in the lockers outside the scanner room.
Your child will need to keep his or her head very still for the scan, so we may use some sandbags to help.
What does the fMRI scan involve?
When you arrive at the hospital, you should report to the MRI department.
You are welcome to stay with your child during the scan, but if you are in the first three months of pregnancy, you should let us know before the scan. If your daughter is 12 years old or older, we will ask her about her periods and any possibility she could be pregnant.
Your child will need to lie on the bed for the scan. When your child is in the correct position, the radiographer will move the bed inside the scanner and then go into the control room. The scanner will make a continuous knocking sound throughout the scan, which can be quite loud, but we will give your child ear protectors to minimise any discomfort.
The radiographer will warn your child when a loud noise is due by talking to him or her through an intercom. During the scan, your child will be asked to do certain things, such as answering questions or tapping one finger.
The scan can take up to two hours. When the scan has finished, the radiographer will move the bed out of the scanner and your child can get up and leave.
What happens afterwards?
The radiologist (doctor specialising in scans) along with members of the epilepsy team will analyse the results of the scan in time for your child’s next appointment.