Alan, Aluminum, Copper, or Steel, can all be used for the shielding envelope.
The wiring method can be EMT,IMC,RMC,HCFC or aluminum within the walls, but is typically aluminum flex or MC above the ceiling.
There MUST, be a dielectric separation from the metallic raceways inside the room and the grounded raceways outside the room, we accomplish this with carflex from the filters to junction boxes for the building wiring servicing the room.
The single point ground bonds everything back together and to the buildings earth system at the RF filter location.
The redundant grounding per 517.13 will become common at the single point grounding provision.
In reality, it is a moot point because I have never heard of any patient being attached to electrical equipment while inside the room, much less the magnet.
The receptacles are many times outside the patient vicinity as defined in NFPA 99 and NEC article 517, this in itself changes the rules for the space as far as the room meeting other requirements of both codes.
I have even been involved in some MRI's with no receptacles in the magnet room at all, house keeping used receptacles immediately outside the space.
In the event of a Code Blue situation, the patient would be removed from the magnet room where the respondents would treat the patient, so there would be no need for receptacles in this space for that issue.