a compact whole - body open circular magnet system for mri purposes includes a protrusion overhanging the central homogeneous field region . the overhanging protrusion permits a reduction of the total magnet homogeneity requirements of the mri system . further reducing the radius of this protrusion increases access to a patient under examination but diminishes the homogeneity . active shimming means incorporated in a gradient coil can regain the original homogeneity while maintaining increased patient access .