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 is an even smaller particle called a proton. Protons are very sensitive to magnetic fields.
MRI scanners use powerful magnets
When the powerful magnets that are used in magnetic resonance imaging (MRI) 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.
The MRI scanner sends radio signals to certain areas of the body which ‘snap’ the protons out of position. When 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, just as millions of pixels can create images, so the radio signals of millions of protons can be collected together and combined to create a detailed image of the inside of the body.
