MagneticMagnetic Resonance Imaging (MRI) resonanceResonance imaging is a beautiful example of how the magnetic properties of the human body may be used to generate images of body parts that have abundant hydrogen atoms surrounded in a favorable environment, where they may readily change their orientation. Each protonProton, the nucleus of a hydrogen atom, behaves like a spinning top with a magnetic field. When this proton (or hydrogen atom) is embedded in a medium like water, body tissues, ligaments, etc., it may easily change its orientation by emitting a special electronic signal that carries information about the nature of the surrounding medium (tissue, flesh, etc.). If the hydrogen atom or the proton is surrounded by teeth bone and other similar media, it takes much longer time to change its orientation and therefore does not emit a useful electronic signalSignal. Detail of magnetic resonance technique is discussed in this chapter.