Abstract: A system of coils is disclosed for the production of imaging by nuclear magnetic resonance of gradients Gx and Gy. The system of coils is disposed on the outer surface of a straight cylinder of revolution of axis Oz and radius R. The coils include four patterns of conductor wires which are pairwise symmetrical with respect to a center O and pairwise symmetrical with respect to the vertical plane xOy. Each pattern has three arcs participating in the production of the gradient which is required. That is, two outward arcs are located close to the center O at respective distances h.sub.1 and h.sub.2 from plane xOy and a return arc is spaced further from the center O and is located at a distance H.sub.3 from the plane xOy. Each arc has three section a, b and c, with the two end sections a and c having the same length being traversed by a current which has one-half the intensity of the current passing through the central section b.

Abstract: System of coils for producing additional fields in a magnet having pole pieces for producing images by nuclear magnetic resonance. For producing gradients Gx=(.differential.Bz/.differential.x) and Gy=(.differential.Bz/.differential.y), it comprises two layers of orthogonal windings, one on each pole piece. For producing the gradient Gz=(.differential.Bz/.differential.z), it has two systems of windings of circular symmetry and axis Oz, located on the inner facing faces of the pole pieces and traversed by currents whose direction changes between the individual pole pieces.

Abstract: Process for the generation and processing of signals for obtaining a nuclear magnetic resonance image, which is free from distortions, from an inhomogeneous polarization field B=Bo+E(x,y,z) using known 2D,FT and 3D,FT image coding methods involving the application of a 90.degree. radiofrequency pulse in plane xOy, then a phase coding during time .tau. followed by frequency coding by applying, along Ox, a reading gradient during the acquisition of the free precession signal, which is then made to undergo Fourier transformations with respect to time and with respect to the gradient or gradients applied.During a second series of sequences involving the successive application of the same gradients, the free precession system is subject to a second 180.degree. radiofrequency pulse at the start of establishing each reading gradient.