A nuclear magnetic resonance signal is collected from a target by using a special pulse sequence which is repeated and, between various repetitions, the relative temporal ratio of signal collection and excitation events is changed. The pulse sequence consists e.g. of the following actions: a target zone is first excited with a so-called 90.degree. pulse followed by coupling of magnetic field gradients in a manner that re-excitation of the target with a 180.degree. pulse serves to generate a so-called spin echo, which is stored and during which at least one magnetic field gradient is turned on. If the purpose is to image a three-dimensional target, e.g. the first excitation event can be effected by using so-called selective excitation and by using a gradient pulse orthogonal to the direction of a read gradient for phase encoding a nuclear system. Phase encoding can also be made in directions orthogonal to said read gradient and to each other to produce this way a complete three-dimensional local distribution of the chemical spectrum of a target.