RF Shielding (Faraday Cage)
Required for MRI installs to prevent external radiofrequency from entering the magnet room. The magnet's receive coils detect the very weak NMR signal from the patient; ambient RF (FM radio, cell signal, hospital communications, fluorescent lighting, switching power supplies) corrupts the signal as image-quality artifact (zipper artifact, banding, herringbone). Materials: copper mesh or galvanized-steel panels. Typical attenuation: ~100 dB at the relevant Larmor frequencies.
Construction
- Wall / ceiling / floor RF panels — copper or galvanized-steel sheet, soldered or RF-gasketed at all seams.
- Door with RF-gasket seal — fingerstock or knife-edge gasket; door is the most-common failure point.
- Observation window with RF-attenuating glass (laminated or wire-mesh).
- Penetration panels for cables, conduits, plumbing, HVAC ductwork — RF-filtered penetrations rated to maintain attenuation.
- Filter panel for incoming electrical and signal lines.
Failure modes
- Door gasket wear → RF leak → image artifacts. Most common service issue; gaskets are consumables on a multi-year cycle.
- Penetration-panel deterioration — gaskets age, RF filters degrade.
- Physical damage from construction — drilling for new conduit, mounting hardware, or HVAC modifications can compromise the cage. Must be re-tested after any room modification.
- Adjacent-room RF source intrusion — new wireless infrastructure (Wi-Fi, cellular DAS, hospital communications) can pierce a marginal cage.
Survey + maintenance
- Annual RF leakage survey is part of MRI PM. Calibrated spectrum analyzer + signal generator measure attenuation across the relevant frequency band.
- Post-modification re-survey — any room construction, even outside the magnet room, that involves the cage walls requires re-verification.
- Door gasket inspection at every service visit.
Refurb / relocation gotchas
- Existing rooms rarely have intact 100 dB attenuation; most refurb installs need cage refurbishment or replacement.
- 3T installs into former 1.5T rooms — frequency band differs (Larmor frequency scales with field), and existing cage may underperform at 3T target frequencies.
- Cage replacement is a multi-day construction project requiring access to all six surfaces of the room.