MRI (Magnetic Resonance Imaging) is a technique that has been used since the early 1980's to create an internal picture of parts of the body.
An MRI scanner uses strong magnetic fields and radio waves, meaning that there is no exposure to harmful forms of radiation.
MRI Scanner (courtesy Siemens UK)
During the procedure, you lie in a large cylinder shaped machine which produces a powerful magnetic field (between 10,000-30,000 times stronger than the Earth's). The scanner machine emits pulses of radio waves and as these pulses move though the body, they cause certain particles contained in your body's tissues to vibrate and spin.
In between the pulses of radio waves, the particles stop spinning and settle back into their original states and as they do so, they send out a small radio wave of their own. A specialized computer is able to detect these radio waves and use them to build a picture of the types of tissues present in the area of the body being scanned.
Different types of tissues emit differing strengths of radio waves so, for example, bones usually look dark on the scans while fatty tissues look much brighter. The MRI scan provides such a detailed picture of your body that is possible for your Consultant to locate even small growths or abnormalities in the area being scanned. As the MRI scan is like a very high-definition photograph of the internal structure of your body, if you need an operation, your Consultant can use your MRI scan to guide him to the correct area of the problem.
Because of the powerful magnetic fields used by the machine, MRI scanners can be quite noisy so you may be offered ear plugs or headphones to wear during the scan to make you more comfortable.