US 6,147,494 AGranted

Magnetic resonance apparatus provided with force-optimized gradient coils

AssigneeU.S. Philips Corporation

InventorCornelis L. G. Ham

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Abstract

The gradient coil system in a conventional MRI apparatus is optimized in respect of the shielding effect by the shielding coil of the system. Consequently, the system generally is not optimized in respect of the Lorentz forces occurring in the system, resulting in noise of a level such that it is annoying to the users. In order to avoid such noise, the system can be force-optimized. Because the shielding effect is partly lost in that case, however, eddy currents and hence disturbing noise would occur again. However, if the eddy currents are made to occur in acoustically insulated eddy current conductors which also have a large time constant for the decay of the eddy currents, the adverse effects of these eddy currents are adequately counteracted and the disturbing noise is reduced to an adequate extent. Particularly, the (cold) radiation shields of a cryogenic magnet system, arranged in vacuum, can be used as eddy current conductors. The vacuum then constitutes the acoustic insulation.

Claims16

Dependent claims

A magnetic resonance apparatus comprising:

a coil system for generating a steady magnetic field in a measuring space of the apparatus,
a gradient coil system which is arranged within the coil system for generating the steady magnetic field and serves to generate a magnetic gradient field in the measuring space of the apparatus, the gradient coil system including an inner coil and an enclosing shielding coil for shielding the environment from the gradient field generated by the inner coil, and the gradient coil system being optimized so as to provide internal compensation of Lorentz forces exerted on the turns of the gradient coil system by the steady magnetic field,
at least one eddy current conductor which is arranged in intermediate space between the coil system for generating the steady magnetic field and the gradient coil system, the at least one eddy current conductor having a time constant for eddy currents greater than the pulse duration of the gradient pulses to be applied to the gradient coil system, and
means for acoustic insulation of the at least one eddy current conductor.

1 more element

Dependencies are inferred from the claim text.