A Magnetic Resonance Imaging (MRI) system is disclosed. The MRI system
includes a cryogenic magnet assembly with a cryogenic vessel housing a
superconducting magnet. Disposed radially inboard of the cryogenic magnet
assembly are a gradient coil module and a plurality of room temperature
steel rings proximate to the gradient coil module. A field of view is
defined by at least the superconducting magnet, the gradient coil module,
and the plurality of room temperature steel rings. In response to the
superconducting magnet being energized, the room temperature steel rings
create high order harmonics that serve to expand the magnetic field
homogeneity FOV, and low order harmonics that tend to degrade the
magnetic field homogeneity within the FOV. The low order harmonics are
compensated for by the cryogenic magnet assembly.