Functional MRI (fMRI)
These notes give some information about functional MRI scan for language mapping.
MRI is a method for producing images of the brain. It involves placing the participant inside a large, powerful magnet which forms part of the brain scanner. In addition MRI can be used to determine which parts of the brain are active during different tasks – this is known as functional MRI or fMRI. When particular regions of the brain are active, they require more oxygen, which comes from red corpuscles in the blood. As a result, the flow of blood increases. This can be detected as changes in the echoes from brief pulses of radio waves. These changes can then be converted by a computer into 3D images. This enables us to determine which parts of the brain are active during different tasks.
As far as we know, this procedure poses no direct health risks. However, the Department of Health advises that certain people should NOT be scanned. Because the scanner magnet is very powerful, it can interfere with heart pacemakers and clips or other metal items which have been implanted into the body by a surgeon, or with body-piercing items. If you have had surgery which may have involved the use of metal items you should NOT take part. Note that only ferro-magnetic materials (eg steel) are likely to cause significant problems. Thus normal dental amalgam fillings do not prohibit you from being scanned, though a dental plate which contains metal would do so, and you would be asked to remove it. You will be asked to remove metal from your pockets (coins, keys), remove articles of clothing which have metal fasteners (belts, bras, etc), as well as most jewellery. Watches and credit cards should not be taken into the scanner since it can interfere with their operation. You will be asked to complete a Consent & Safety Information Form which asks about these and other matters to determine whether it is safe for you to be scanned.
In addition, you are asked to give the name and address of your Family Doctor. This is because there is a very small chance that the scan could reveal something which requires investigation by a doctor. If that happens, we would contact your doctor directly. By signing the consent form, you authorise us to do this.
To be scanned, you will lie on your back on a narrow bed on runners, on which you will be moved until your head is inside the magnet. The scanning process itself creates intermittent loud noises, and you must wear ear-plugs or sound-attenuating headphones. We are able to talk to you while you are in the scanner through an intercom. During the scan you will be able to alert the staff by activating an alarm and will then be removed from the scanner quickly. It is important that you keep your head as still as possible during the scan, and to help you with this, your head will be partially restrained with padded headrests. We shall ask you to relax your head and keep it still for a period that depends on the task you are performing but may be more than one hour, which may require some effort on your part. If this becomes unacceptably difficult or uncomfortable, you may demand to be removed from the scanner.
You will be asked to look at a screen through a small mirror (or other optical device) placed just above your eyes therefore you must be able to see the screen. If you need to wear contact lenses please make sure you wear them on the day of the scan. The details of the task will be explained to you just before the scan. Detailed instructions will be given just before the scan, and from time to time during it.
We usually allow 2 hours for this procedure although this may be shorter on the day. If you have any questions before the scan appointment please contact us as soon as possible.