How MRI works
MRI relies on the way that hydrogen atoms, which make up nearly two-thirds of the human body, absorb and then give off magnetic energy at radio frequencies. The nuclei of these hydrogen atoms are like tiny spinning magnets, and so they respond to changes in magnetic fields. Computerised images are calculated from variations in how this energy is absorbed and emitted across the body. As very little energy is involved, the normal biochemistry of the body is completely unaffected.