Magnetic Resonance Imaging (MRI) is a diagnostic scanning technique based on the principles of nuclear magnetic resonance. The term "nuclear" has long been dropped from the description of medical MR techniques because of its association with radiation and radioactivity. MRI uses no radioactivity or x rays which is why it is often described as being such a safe modality. The basic principles are as follows:

The human body is predominately made of water molecules which contain hydrogen protons.

When you are placed in a strong magnetic field the tiny magnetic fields of the hydrogen protons, which normally move around randomly, are aligned to the magnetic field.

A brief radio pulse is rapidly switched on and off. This makes the protons' magnetic fields spin round in unison and emit a weak radio signal. (This is happening at a microscopic level, you will feel nothing at all)

By altering the timing of the radio wave applications it is possible to produce images which show up the various body tissues as shades of grey. The contrast on MRI images is very good and the operator can change the parameters to give images that demonstate the anatomy of the area and also, in many cases, highlight common disease processes.

This contrast depends upon whether the hydrogen protons are linked to fat, muscle, water, etc. In certain anatomical areas the inherent contrast is poor and a small injection may be required to enhance the scan.

During the scan, the main magnetic field strength is altered using electromagnets. This causes a wide range of sounds during the scan procedure including banging, buzzing and rumbling noises. You will be offered ear protection during the scan and, in some centres, music is available.