MRI magnetic field generator

An MRI magnetic field generator which comprises:

• first and second spaced magnetic structures having respective first and second ends that face one another and define an air gap therebetween,
• first and second pole pieces respectively positioned on said first and second ends of said first and second magnetic structures,
• first and second shim holders positioned between said first and second pole pieces, said first shim holder being positioned adjacent said first pole piece and including a first disk holder having a plurality of pits therein arranged in concentric circles and a first cover disk detachably connected to said first disk holder for covering said pits, and said second shim holder being positioned adjacent said second pole piece and including a second disk holder having pits therein arranged in concentric circles and a second cover disk detachably connected to said second disk holder for covering said pits,
• first and second gradient coils respectively positioned between said first shim holder and said first pole piece and said second shim holder and said second pole piece, and
• a plurality of magnetic pellets removably positionable in at least some of said pits of said first and second disk holders prior to positioning of said respective first and second shim holders between said first and second pole pieces and prior to attachment of said cover disks to said disk holders in order to adjust magnetic field intensity in said air gap.