Method and apparatus for compensating for drift in magnetic field strength in superconducting magnets

A magnetic resonance imaging (MRI) system comprising:

• a cylindrical superconducting magnet assembly having a longitudinal axis;
• a cylindrical vacuum vessel (OVC) having a bore tube therein, that contains the superconducting magnet assembly, said OVC having a bore tube therein that is rotationally symmetrical about the longitudinal axis;
• a gradient coil assembly situated within the bore tube of the OVC, said gradient coil assembly having a coil assembly bore therein;
• said superconducting magnet assembly being configured to produce a magnetic field in an imaging region within said bore tube of said gradient coil assembly, said magnetic field in said imaging region exhibiting a field property that is subject to drift due to heating that occurs during operation of said MRI system;
• compensating material situated at a radial position, relative to said longitudinal axis, between the imaging region and the superconducting magnet assembly at a location that is subject to heating over a range of temperatures due to said heating that occurs during said operation of the MRI system;
• said compensating material being adjustable between two magnetic phases thereof in response to an applied physical characteristic;
• and
• an adjustment device configured to selectively apply the physical characteristic to the compensation material so as to change the compensating material from a first magnetization to a second magnetization, and thereby compensate said drift.