Isidor I Rabi’s right hand man, Polykarp Kush, prepared a conceptual design in which the use of a caesium atomic beam was envisaged. In a famous paper written in 1937, Rabi described the fundamental theory for magnetic resonance experiments. F Bloch had the idea independently to use magnetic resonance by employing an oscillating magnetic field. The first successful experiments to detect magnetic resonance in matter by electromagnetic effects were carried out independently by Bloch at Stanford, E M Purcell at Harvard and E Zavoisky in the former USSR. Whole body magnetic resonance imaging appeared on the scene about 1980. Nuclear magnetic resonance (NMR), initially conceived as a means to study the magnetic behaviour of matter, with time has become an indispensable medical technique. The NMR allows in fact the position of nuclei-bearing magnetic moments to be identified as a result of the presence of their characteristic absorption spectrum.