MODEL RELEASED. Person about to undergo a nuclear magnetic resonance (NMR) scan. NMR imaging (also called magnetic resonance imaging) is a diagnostic technique that is able to differentiate between various tissues in the body. Unlike CT scanning NMR imaging does not rely on potentially harmful X-rays, but depends on the physical behaviour of atomic particles (protons) in body tissues that are subjected to a strong magnetic field. When the magnetic field is interrupted by brief bursts of radio waves, the protons themselves behave as small radio-transmitters, supplying signals from which an image is ultimately constructed.