MRI scan
MRI (magnetic resonance imaging) scanners build up detailed pictures by using a strong magnetic field to read the signal sent out by the water molecules within the body. Computer systems and radio waves help with this but no X-rays are used. MRI scans are not suitable for everyone and your doctor will decide if an MRI scan would be helpful in your case.
Who shouldn’t have an MRI scan?
The strong magnetic fields used in MRI scans make them unsuitable for some patients.
You may not be able to have an MRI scan if you have a pacemaker, as the magnetic field interferes with the internal workings of the pacemaker and may stop it from working.
Patients with reprogrammable shunts in their heads may have to be scanned in a specialist centre where the shunt can be reprogrammed safely following the scan if necessary.
Other metallic implants may prevent you from having an MRI scan, such as:
- aneurysm clips on blood vessels in the brain
- artificial heart valves
- cochlear implants
- neurostimulators.
An MRI scan may not be advisable in the first trimester of pregnancy unless there are special circumstances.
MRI scans are perfectly safe for breast-feeding mothers. However, if you require an injection of contrast medium (dye) you should not breastfeed for 48 hours following the injection.
Preparing for an MRI scan
Usually there is no preparation required for an MRI scan. You can eat and drink normally before and after the scan. Some patients who are having an abdominal scan will be required not to eat or drink for four hours before the scan. If you are required to fast, full instructions will be given to you in advance.
For some patients an injection of contrast medium (dye) may be given into a vein. A very small number of patients may be allergic to this.
When you come for your appointment it is advisable to wear clothing without metal fastenings. Alternatively, you will be provided with a hospital gown or pyjamas. You will not be allowed to take or wear anything metallic or with magnetic strips into the scan room, except a wedding band. You may wear your spectacles, but they will be taken off immediately before your scan.
During an MRI scan
The scan is not painful. However, you will have to lie still for up to one hour on a table. The radiographers will do their best to make you comfortable.
The scanner produces a variety of loud noises. These noises are caused by magnetic coils that switch on and off during the scan. These coils measure the signal coming from your body in order to make the images that are used for your diagnosis. You will be given ear defenders or earplugs to help to reduce this. The level of noise can be reduced but this makes the scan take a little longer. Please let the radiographer know if you are particularly sensitive to noise.
Although the scanner is open at both ends, some people may find it slightly claustrophobic. If you are worried about this please speak to your radiographer. There are several methods available which can make the scan easier for you.
After an MRI scan
Unless you have received a bowel relaxant you may leave the hospital immediately after your MRI scan. You may go to the toilet and eat and drink as normal. There are no side affects to the MRI scan itself.
The scan will be carefully interpreted by a radiologist and a report will be sent to your doctor who will let you know the result.