During a magnetic resonance imaging (MRI) scan, you lie in a strong magnetic field and radio frequency waves are directed at your body. This produces detailed images of the inside of your body.
Most of the human body is made up of water molecules, which consist of hydrogen and oxygen atoms. At the centre of each hydrogen atom there is an even smaller particle called a proton. Protons are very sensitive to magnetic fields.
When the powerful magnets that are used in MRI scans are switched on, all the protons in your body are pulled towards the same direction, in the same way that a magnet can pull the needle of a compass.
Short bursts of radio waves are sent to certain areas of the body and pull the protons out of position. As this happens, each proton transmits a radio signal that provides information about its exact location in the body.
On its own, a single proton will not provide much useful information, in the same way that a single pixel on a computer screen is essentially just a coloured dot.
However, in the same way that millions of pixels can create images, the radio signals of millions of protons can be collected together and combined to create a detailed image of the inside of the body.
