| 摘要 |
Magnetic resonance apparatus includes a magnet system for generating a steady magnetic field in a measuring space, which steady magnetic field is oriented mainly parallel to one of the axes of an orthogonal coordinate system, a gradient system with gradient coil systems and with a controlled source for supplying the gradient coil systems with excitation currents with a predetermined variation in time. The gradient coil systems include a number of linear gradient coil systems, each of which is arranged to generate a main gradient field which is dependent on the location of the field in the measuring space in such a manner that a magnetic field formed by superposition of one of the main gradient fields on the steady magnetic field can be described, as a function of the coordinates of the coordinate system, as a series containing first-order terms and higher-order terms, the first-order terms having predetermined coefficients which are equal to zero for two of the coordinates. The gradient system is arranged so that at least a part of the second-order terms of the series describing the magnetic field formed by superposition of the magnetic fields generated by the gradient system on the steady magnetic field have predetermined coefficients. The undesirable effects of concomitant gradient fields can thus be counteracted.
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