Nuclear Magnetic Resonance
MRI is based on a physical phenomenon known as nuclear magnetic resonance, which may be summarised as follows:
Certain atomic nuclei, when placed in a strong static magnetic field, will absorb and subsequent re-emit radiowaves of a specific frequency. This resonance frequency is dependent on the nuclear species and the strength of the applied field.
Thus, unlike most medical imaging modalities, MRI does not use ionising radiation, but instead uses a combination of magnetic fields and radiowaves.
It is therefore generally regarded as a safer imaging technique. However, there is a very significant hazard in that the very powerful magnet used can turn ferrous objects into deadly projectiles. This requires careful safety precautions around MRI scanners.
