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Magnetic Resonance Imaging (MRI)

What is it?

MRI stands for 'magnetic resonance image'. It is a special type of scan. In the spine it is used to look at the nerves and discs, which don't show up on normal x-rays. It shows these structures better than a CT scan, and can also look at the spine in more directions than a CT scan can.

How is it done?

It is performed in a very specialised scanning machine. The test is done by a radiographer (an x-ray technician). A radiologist (a doctor who is an x-ray specialist) supervises the test and then reads the scans. The MRI machine is like a CT scanner as you lie on a table that slides in and out of a narrow tunnel. The machine uses a very strong magnetic field and radio waves rather than normal x-rays. This means there is no radiation and the test is very safe.

What are the risks?

Because it uses a magnet, there are some people that cannot have an MRI. These include people with pacemakers, metal aneurysm clips in their brain, and particles of metal in their eye. People who have worked with metal such as with welding or grinding may need to have an x-ray of their eyes to make sure there are no metal fragments there. Precautions sometimes need to be taken if people have had heart, brain or eye surgery. Hearing aids and dentures may need to be removed.

The tunnel in the machine is quite small. This is a problem for large people and those who are claustrophobic. If you suffer from severe claustrophobia you can be given sedation to calm you before the test. This can be either tablets or an injection. If any of the above problems apply to you, you need to contact the Radiology Department before the scan, as well as tell the radiographer when you arrive.

What will happen during the test?

You will be asked to change into a gown. You must leave your watch, jewellery, keys, purse or wallet and credit cards outside the scan room, as the magnet may affect your watch and erase your credit cards! You will then lie on the scan table and move into the tunnel. You will need to lie as still as possible. While the machine is scanning it makes a loud humming and knocking noise. You can choose to wear headphones and listen to music during the scan. Sometimes a special magnetic dye (not iodine like for other scans) is injected into a vein through a needle in the back of your hand for the scan. The scan usually takes about half an hour. When they are finished, the scans will be reported and then sent to your doctor.