The Projectile (Missile) Effect
The signature MRI danger
Any ferromagnetic object brought near the magnet is pulled in as a lethal projectile — steel oxygen cylinders, laryngoscopes, scissors, pens, drip stands, ordinary infusion pumps and monitors. Deaths have occurred. Defence: rigorous screening, MR-safe/conditional equipment only, aluminium gas cylinders, and never taking unchecked kit into Zone IV.
RF Heating, Burns & Cryogen Quench
RF-induced heating & burns
- RF energy heats looped cables, ECG leads & pulse-oximeter fibres → skin burns
- Remove unnecessary wires; avoid coils/loops; insulate leads from skin; keep cables straight
Cryogen quench
- Sudden boil-off of liquid helium (accidental or via the emergency quench button) vents huge volumes of cold gas
- Risk of O₂ displacement / asphyxiation, frostbite & rapid room-pressure rise — evacuate; use only in a true emergency (e.g. a person pinned by a projectile, fire)
Acoustic Noise, Gadolinium & Interference
| Hazard | Detail & mitigation |
|---|---|
| Acoustic noise | Gradient switching is very loud (can exceed 100 dB) → hearing protection for the patient (ear plugs/defenders) and staff |
| Gadolinium contrast | Risk of anaphylaxis; nephrogenic systemic fibrosis (NSF) in severe renal impairment — check renal function |
| Monitoring interference | ECG is distorted (magnetohydrodynamic effect elevates the T-wave); pulse-oximetry artefact; equipment can also degrade the image — use MR-conditional monitors |
| Limited access | The patient is deep in a dim bore, out of easy reach during the scan — plan for it |