Superconducting gradient shield coils

摘要

An examination region (12) is defined within the bore of a superconducting magnet assembly (10). An RF coil (22) and gradient magnetic field coils (14) are disposed within the bore of the superconducting magnet assembly around the examination region. The superconducting magnet includes a hollow, cylindrical vacuum vessel (40). An annular, liquid helium holding low temperature reservoir (60) extends centrally through the vacuum vessel, but is sealed therefrom such that liquid helium is not drawn into the vacuum. A plurality of annular superconducting magnets (56) are received in the low temperature reservoir immersed in the liquid helium. A first cold shield (44) and a second cold shield (50) are mounted in the vacuum vessel surrounding the low temperature reservoir. A main magnetic field shield coil (66) is disposed in the low temperature reservoir outside of the annular superconducting magnets for canceling the magnetic field generated by the annular magnets surrounding the magnet. A gradient shield coil (70) is mounted in low temperature reservoir inside the annular superconducting magnets to cancel magnetic fields generated by the gradient magnetic field coils in the region beyond the gradient shield coil. The gradient shield coil is electromagnetically coupled to the gradient field coils to be driven by magnetic fields emanating therefrom. Optionally, the gradient shield coil can be constructed of a higher temperature superconducting material and disposed in association with one of the cold shields.