MRI (magnetic resonance imaging) scanners use a strong magnetic field to build up detailed pictures of various parts of the body, by reading the signal sent out by the water molecules within it. 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 cannot have an MRI scan in this department if you have a pacemaker, as the magnetic field interferes with the internal workings of the pacemaker, and may stop it from working.
We do not scan patients with reprogrammable shunts in their heads. If you have a reprogrammable shunt, we will arrange for you 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.
Many of these are now MRI safe, but the department staff will need as many details as you can provide in order to check that the implant has been tested and is safe to scan. Please contact the department if you have any metallic/artificial implants so that these can be investigated prior to your scan. If you have any documentation, please bring it with you.
Pregnancy: MRI may not be advisable in the first trimester of pregnancy, unless there are special circumstances. Please contact the department if you think you may be pregnant.
Breastfeeding: MRI scans are perfectly safe for breastfeeding mothers. However, should you require an injection of contrast medium (dye), you should not breastfeed for 48 hours following the injection.
What happens when I come for an MRI scan?
Usually there is no preparation for MRI. 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 included in your appointment letter.
For some patients an injection of contrast medium (dye) may be given into a vein. This is not necessary in all circumstances, but can provide additional information. As with all medication, a very small number of patients may be allergic to contrast medium. Please inform the radiographer if you have any allergies.
When you come for your appointment it is advisable to wear clothing without metal fastenings. Alternatively, we can provide 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. A locker is provided for your valuables, however, you must give the key to a radiographer, as it is magnetic.
The scan is not painful. However, you will have to lie still for up to one hour on a table, which is quite hard. 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. These coils are switched on and off rapidly causing them to vibrate and produce the noise you hear. You will be given ear defenders or earplugs to help to reduce this. The level of noise can be reduced, however the scan will 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 the radiographer. There are several methods we can use to make the scan easier for you and we will discuss this with you at the time. The newer scanners are much shorter and wider than previously, have a light inside and a slight breeze flowing through them. We can play you music while you are in the scanner, you may bring a CD or tape with you or choose one from our collection.
What happens afterwards?
Unless you have received a bowel relaxant, you may leave the department immediately after your 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.