The invention concerns a system capable of generating a magnetic indication B.sub.o comprising gradients (Gx, Gy, Gz) in certain directions, transmitting ratio frequency wave pulse sequences (RF) perpendicular to B.sub.o in a range of adjustable frequencies, and detecting electromagnetic signals received from a body part (4). The method consists in: injecting a contrast product in said body part, capable of being temporarily fixed in an observed zone (1), and comprising and element capable of causing chemical displacement of a resonance frequency of water hydrogen protons; exciting said body part, using a radio frequency wave pulse sequence: in a range of frequencies adjusted on the basis of the magnetic induction B.sub.o and the chemical displacement for some of said waves: detecting the electromagnetic signals received in said body part, substantially corresponding to the magnetic resonance signals of the protons of the observed zone having undergone the chemical displacement.