[From nuclear magnetic resonance to magnetic resonance imaging].

Magnetic resonance imaging is based upon the phenomenon of nuclear magnetic resonance. The patient is placed in a magnet the provides a strong magnetic field inducing a net magnetization due to hydrogen nuclei inside biological tissues. The image is formed from the localized measurement of this magnetization by means of radio-frequency waves. The contrast is a function of the number of hydrogen nuclei and of the time characteristics T1 and T2 of the return to equilibrium. Many other parameters can be measured by this method and the permanent improvement of the technique will extend further the field of its medical application.