Nuclear magnetic resonance (NMR) is the physical phenomenon in which magnetic nuclei in a magnetic field absorb, then re-emit electromagnetic radiation. This energy is of a specific resonance frequency that depends on the magnetic field strength, and the magnetic properties of the isotopes of the atoms. Many scientific techniques exploit the NMR phenomena to study molecular physics, crystals and non crystalline materials through NMR spectroscopy. NMR is also used for advanced medical imaging techniques, for example, magnetic resonance imaging (MRI).