Abstract: In particular with 3D tomography, it is necessary to acquire a large number of individual spectra. Therefore it is advisable to reduce the time needed for the acquisition of a single spectrum without loosing too much in signal-to-noise ratio. To a significant extent, this time is determined by the relaxation time of the spins. Prior to each excitation a significant quantity of these spins have to return into their equilibrium (z-direction of the homogeneous magnetic field) in order to create a usable signal with the next excitation. For spins with long relaxation times T.sub.2 this time can be reduced by a -90.degree. pulse 12 that coincides with the center of the last spin echo 9 with appropriate application of the gradient fields. This -90.degree. pulse returns the x-y magnetization that exists in the x-y plane into the z-direction. The diagnostic relevance can be significantly increased by such a procedure.

Abstract: The use of longer 180.degree. pulse sequences for the generation of spin echos is made possible according to the invention during NMR tomography using the 2d-Fourier transformation process in that the phase coding gradient between each pair of 180.degree. pulses is switched on in such a manner that the dephasing caused between each pair of 180.degree. pulses by the phase coding gradient is twice as great as the dephasing caused before the beginning of the first 180.degree. pulse by the phase coding gradient. The mirror images which appear otherwise when using the known 180.degree. pulse sequences, e.g. the Carr-Purcell-Gill-Meiboom pulse sequence, are avoided by this measure.

Abstract: The use of longer 180.degree. pulse sequences for the generation of spin echos is made possible according to the invention during NMR tomography using the 2d-Fourier transformation process in that the phase position and, thus, the sense of rotation of the 180.degree. pulses is reversed after every two pulses. The mirror images which appear otherwise when using the known 180.degree. pulse sequences, e.g. the Carr-Purcell-Gill-Meiboom pulse sequence, are avoided by this measure.