This recently-developed technique involves placing the person in a strong magnetic field that aligns or ‘polarizes’, the protons (positively-charged atomic particles) in his or her tissues. When the magnetic field is switched off the protons return to their normal positions; as they do so they emit tiny pulses of electromagnetic energy that can be detected and imaged. Bone does not respond to the magnetic field and is therefore almost invisible on an NMR scan – the opposite of conventional X-rays. The technique is in its early stages of development, but is believed to be risk-free and is already producing images as clear as, and even more informative than, conventional X-rays and CT scans. However, each imaging technique has its own particular advantages and it is unlikely that one will completely supplant the others.