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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.

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