Open access superconducting MRI magnet having an apparatus for reducing magnetic hysteresis in superconducting MRI systems

摘要

A MRI superconducting magnet having an open access frame with spaced parallel end plates, a superconducting coil assembly associated with each end plate, and gradient coils associated with each end plate includes an apparatus for minimizing hysteresis. The apparatus for minimizing hysteresis comprises a layer of nonferromagnetic conducting material interposed between the gradient coils and end plates. The interposed layer carries eddy currents induced by time varying magnetic fields produced by the gradient coils, thereby minimizing AC eddy current hysteresis from the end plates. The layer preferably has a thickness of at least one skin depth at the frequency associated with the time varying magnetic field. In another embodiment, each end plate has a plurality of slits formed therein for eliminating eddy currents in the end plates.