Method for setting the current through shim coils and gradient coils in a nuclear magnetic resonance apparatus

摘要

For calculating the magnetic field inhomogeneity, a gradient echo sequence or a spin echo sequence having a non-central 180 DEG radio-frequency pulse is first carried out. The nuclear magnetic resonance signal thus acquired is Fourier-transformed and the phase curve of the nuclear spins in a given region is identified. This is multiply repeated in different projections. The phase curves that are obtained are analyzed with a fit method and the coefficients of the spherical, harmonic functions describing the field distribution are identified therefrom. The current to be supplied to the individual shim coils and an offset current for the gradient coils can thus be calculated.