U.S. Philips Corporation

Gerardus B Mulder

Johannes Adrianus Overweg

Gerardus Nerius Peeren

Tatjana Claasen-Vujcic

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.

Magnetic resonance apparatus

The apparatus comprises a magnet system which is rotationally symmetrically arranged about a central axis (9) and which comprises a superconducting inner coil system (1) for generating a steady magnetic field in a measurement space (5) within the magnet system, and also comprises an outer coil system (7) which is arranged so as to be coaxial with the inner coil system and which is electrically connected in series therewith in order to shield the environment from the magnetic field generated by the inner coil system. The magnet system can be bridged by of a superconducting persistent current switch (33) and comprises a superconducting shunt (37) which bridges a pan of the magnet system which is situated between first and second connection points (39, 41). In order to improve the shielding of the measurement space (5) from the effects of external magnetic fields, at least one turn of a coil (17) forming part of the magnet system is situated between at least one of the connection points (39, 41) and the nearest end of the inner coil system (1 ). The shielding effect can be further enhanced by utilizing more than one shunt (37, 53).

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Eindhoven, Netherlands

Gerardus B Mulder