METHOD OF EXCITING A SAMPLE FOR NMR TOMOGRAPHY

摘要

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 T2 this time can be reduced by a -90 DEG pulse 12 that coincides with the center of the last spin echo 9 with appropriate application of the gradient fields. This -90 DEG 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.