The Magnetic Environment
Three fields
- Static magnetic field (typically 1.5–3 T) — always on, even when no scan is running; the source of the projectile hazard
- Gradient (switching) fields — the loud knocking noise; can induce currents
- Radiofrequency (RF) pulses — deposit energy → tissue/cable heating & burns
A difficult place to work
- Remote & isolated — far from theatre help
- Limited access to the patient inside a long, dim bore during scanning
- Unfamiliar equipment, cold room, noise, and image-degradation constraints
Remember
The magnet cannot be "switched off" for an emergency — de-energising means a costly, hazardous quench. Treat the field as permanently live.
The Four ACR Safety Zones
Increasing restriction from the public area to the magnet
Zone IFreely accessible public area — outside the MR environment
Zone IIReception / interview / screening — patients supervised but not yet in the controlled area
Zone IIIControl room & restricted access — MR-safety-screened personnel & patients only; strictly controlled entry
Zone IVThe scanner (magnet) room itself — the strong field; the highest-hazard zone
Ferromagnetic screening of every person and every item is mandatory before entering Zone III/IV — patients, staff, the anaesthetist, and all equipment. Screen for implants (pacemakers, cochlear implants, aneurysm clips, metallic foreign bodies), and remove all loose metal.