Abstract: For recording the nuclear magnetic resonance in selected areas of a body for the purpose of representing body cross-sections in the form of images (NMR tomography), wherein the nuclear spins of a selected type present in the area of one plane of the body are subjected to a superimposed gradient field varying in the selected cross-sectional plane, and selectively excited, the excitation of the nuclear spins is effected by application of a pulse sequence which induces the nuclear spins to supply at one stage a number of chronologically successive induction signals. The induction signals corresponding to each other in chronolical sequence are then processed to obtain separate sets of image signals so that by one single measurement a sequence of cross-sectional images is obtained which differ from each other by the intensity of the excited nuclear spins which varies according to the relaxation times T.sub.1 or T.sub.2.

Abstract: For the purpose of limiting NMR spectroscopy to a selected area of a body the said area is prepared by applying first a homogeneous magnetic field passing through the entire body and superimposing thereafter upon the said magnetic field a first magnetic field of identical orientation whose strength varies in a first sense (first field gradient), exciting thereafter all the selected nuclear spins present within the body and in addition, selectively, only the nuclear spins present in a first body plane containing the volume element and extending vertically to the said first field gradient so that the selected nuclear spins contained in this body plane are returned to the direction of the homogeneous magnetic field while the nuclear spins outside this plane receive an orientation differing from the sense of the homogeneous magnetic field.

Abstract: In NMR tomography, the nuclear spins of a selected type present in a selected area of a body are selectively excited by applying first a selection gradient field and exciting thereafter the nuclear spins by a HF signal which initially effects a rotation of the nuclear spins situated in a selected plane by an angle .alpha. of less than 90.degree., then a rotation of all selected nuclear spins by 90.degree. and finally again a rotation of the nuclear spins contained in the selected plane by an angle of 90.degree.-.alpha.. As a result thereof, the nuclear spins contained in the selected area have resumed at the end of this excitation their original orientation determined by a homogeneous magnetic field, while nuclear spins located outside this area lie within a plane extending almost vertically thereto. Thereafter, a measuring gradient field may be switched on without disturbing the orientation of the nuclear spins contained in the selected area.