The MRI Machine
The MRI machine is basically a large ring shaped magnet with a very high magnetic field strength. Electrical pulses are used to vary the direction and strength of the magnetic field. This causes magnetic realignment of atoms and molecules within the body. (Sounds dangerous? There have been no reports of any harm to patients from MRI over more than 20 years of use in medicine). Computer processing can recognise the changes in the atoms as typical of organs and other structures within the body, building up a picture of normal parts of your body and those affected by disease.
MRI is used for the investigation of the entire body: from slipped discs to brain tumours, from painful or injured joints to assessment of blood flow in blood vessels, from gynaecological problems to breast disease, from kidney transplants to the function of the heart and for the diagnosis and planning of treatment for cancer.
You lie usually on your back on a hard couch, not much wider than a bench while the radiographer prepares you for the examination. Often an open frame will be placed around a part of your body (your head, your abdomen or your legs for example).
The couch on which you are lying is then moved into the hole in the middle of the magnet. If we are examining your legs then much of your body is outside the magnet. Otherwise it will feel as if you are lying in a small tunnel perhaps a bit like the connection between the Soyuz Space craft and the space station.
Some may find this a little claustrophobic but we can help you cope with this. You can listen to music, wear special glasses to allow you to see more of the room or close your eyes and listen to the beat of the machine. Yes, the machine is noisy. As the magnetic field changes the noise may vary from a light tapping, through a pneumatic drill, to a massed band of children with sticks and dustbin lids! The noise only lasts a few minutes….it just seems longer!
To produce the pictures the machine will need to complete a number of "sequences" of noise of up to 5 minutes with quieter intervals where all you hear is the hum of electrical machinery. You might expect to be in the magnet for between 20 and 40 minutes.
Listen to the MRI machine
The following clip last approximately 20 seconds.
