Magnetic fringe field from the magnet can extend outside the room based on the set of magnetic field. The magnetic shielding which can be calculated based on the equipment and surrounding requirement, Shielding contains the field strength without the periphery of the room, thereby It can reduce the image quality issues due to moving magnetic permeable items around the MRI. Frank Shields uses passive shielding using magnets permeable mentioned on the walls, floors & ceiling partially or fully based on the site requirements. The final aim is to contain the 5 gauss line in a safe limit around the magnet.
Shielding refers to the magnetic field outside the magnet bore. Passive shielding is the placement of heavy ferromagnetic plating in the walls or floor of the magnet room or even the magnet itself. This concentrates magnetic flux lines, reducing the fringe field beyond the shielding.
Passive shielding (see also Faraday cage) significantly eases the problems of siting a MR Image in a confined space. Ferromagnetic objects are less prone to being attracted to the magnet, ancillary electronic equipment, credit cards and computer disks can be brought closer to the magnet and the MRI safety limit for pacemaker wearers (the 5 gauss line = 0.5 mT) is reduced from, typically, 10 m to 2 m from the magnet. A passive shield for a whole-body MRI magnet weights many tons. An alternative method of controlling stray field is active shielding.
Magnetic Shielding :