4881035 Magnetic structural arrangement of an installation for nuclear magnetic resonance tomography with superconducting background field coils and normal-conducting gradient coils

Abstract

Magnetic structural arrangement of an installation for nuclear magnetic resonance tomography with superconducting background field coils and normally conducting gradient coils. The magnetic structural arrangement contains superconducting coils cooled by a cryogenic medium for generating a homogeneous magnetic background field, normally conducting coils within the inner space bounded by the background field coils for developing magnetic field gradients, and at least one cooled radiation shield of an electrically and thermally conducting material which is disposed between the gradient coils and the background field coils. In such a structural arrangement the danger exists that eddy currents set up in the radiation shield distort the gradient fields and/or these gradient fields generate undesired heat in the region of the background field coils. To solve this problem, on the side of the background field coils facing the inner space, a tubular shielding structure is disposed which at least contains superconducting material of the second kind and is thermally coupled to the cryogenic medium of the background field coils, and the radiation shield is designed to suppress eddy currents induced in it at least by the gradient coils. The shielding structure can be formed, in particular, of several pre-fabricated shield elements. The magnetic structural arrangement is intended for installations for nuclear magnetic resonance tomography.