Generally speaking, we’re all introduced to shielding from the point of view of ionizing radiation. The very first thing we need to clarify is that MRI shielding is not one type of shielding, but is two separate types. RF shielding is most typically made from copper foil, stretched over conjoined frames, or thin sheets of steel clamped together at the joints.
Particularly in new construction, magnetic shielding can often be avoided by simply making the MRI scanner room slightly larger. By contrast, in MRI the RF shielding is designed to keep stray radiofrequency energies out of the scanner room! There is a false notion that squeezing the dimensions of a new MRI scanner room saves construction dollars, but we have repeatedly seen MRI scanner rooms reduced in size (saving $10,000 in construction cost), only to wind up so small that they need passive magnetic shielding to contain the 5 gauss line (adding $20,000 or more back into the construction cost).
The shielding material and means of assembly should be determined early on in the design process, because there are consequences to the design of the building to most effectively integrate the RF shield type in with the suite construction.

In X-ray (and nuclear medicine, and radiation therapy), the shielding is designed to keep the ionizing radiation from leaving the room. Unlike RF shields, which need to wrap the entire room of an MRI scanner, passive magnetic shielding can be applied to discreet areas. If the concern is only the penetration of the magnetic field through an end-wall of the MRI scanner room, it is possible to apply magnetic shielding to just that wall, though the introduction of magnetic shielding will distort the otherwise symmetrical magnetic file and may necessitate shielding to ‘return’ on the side walls a short distance in order to contain the reshaped field.
When it comes to radio isotopes for nuclear medicine, or even the gargantuan shielding needs for radiation therapy or proton beam facilities, these are essentially magnifications of that initial model of ‘containment’. It is with this basic principle engrained that many of us are first introduced to MRI shielding, so it’s perfectly understandable that we get it horribly wrong. Magnetic shielding can also be used (though with limited and variable effectiveness) in a manner similar to RF shielding.
Obviously thousands of pounds of passive magnetic shielding runs counter to this objective.

Clear and consistent MR images require RF shielding all the way around the room… floor, ceiling, every wall, window, and door.
Copper, our preferred RF shield material, is also invisible to magnetic energies, though the thinness of galvanized steel sheets typically used for RF shielding means that it, too, is ineffective for containing magnetic energies. One of the problems with magnetic shielding is that MRI scanners operate best with no magnetic materials in the immediate vicinity.
Sometimes insuring the proper operation of an MRI scanner may require magnetic shielding even if there isn’t a concern with magnetic field containment.

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