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MRI safety and gadolinium-based contrast
The MRI magnetic field is always on, so the hazards are metal objects that are attracted, heating from RF waves and implanted devices — and gadolinium is chosen from the low-risk (macrocyclic) group to avoid NSF and limit brain deposition.
Why it matters in the exam
MRI safety questions deal with three forces: the static field (B0) pulls ferromagnetic objects as "projectiles" and moves implants; RF waves heat tissue and can cause burns through loops of cables, wires or tattoos, measured by the SAR; and the gradients create loud noise — hence hearing protection — and peripheral nerve stimulation. The ACR divides the MRI environment into four zones: zone I public, zone II reception and screening, zone III controlled, and zone IV the magnet room. Everyone entering zone III completes a screening questionnaire.
Implants are labelled MR Safe, MR Conditional — allowed under the conditions set by the manufacturer — or MR Unsafe. An MR-conditional pacemaker is scanned under its conditions; an older pacemaker is sometimes possible in an experienced centre with a protocol. A metallic foreign body in the eye of a metal worker is a contraindication, and anyone with such a suspicion has orbital radiographs before the examination. An old ferromagnetic cerebral aneurysm clip is forbidden. MRI without contrast is allowed in pregnancy.
Gadolinium: the ACR groups the agents. Group II, with the lowest risk of NSF (nephrogenic systemic fibrosis), includes the macrocyclic agents gadobutrol, gadoterate and gadoteridol as well as gadobenate. With a group II agent, prior eGFR screening is optional; a group I agent (linear, such as gadodiamide) is contraindicated with eGFR below 30 or AKI. NSF is fibrosis of the skin and internal organs, almost only in patients with severe kidney disease. Gadolinium deposition in the brain — high T1 signal in the dentate nucleus and globus pallidus — is more common with linear agents and has not been shown to cause clinical harm; because of it the EMA restricted intravenous linear agents in 2017. Allergic-like reactions to gadolinium are rarer than to iodine, and treatment is the same.
Key points
- Static field — projectiles; RF — heating; gradients — noise.
- Four zones; screening before zone III.
- Eye foreign body — orbital radiographs first.
- Group II (macrocyclic agents and gadobenate) — negligible NSF risk.
- Gadolinium in pregnancy only when essential.
Summary table
| Hazard | Source | Example | Prevention |
|---|---|---|---|
| Projectile | Static field B0 | Oxygen cylinder, metal wheelchair | Screening questionnaire and zones |
| Burn | RF waves (SAR) | Cable loop, tattoo, metallic patches | Disconnect cables, padding, SAR limits |
| Noise and nerve stimulation | Gradients | Noise above 100 dB | Hearing protection |
| Implant | B0, RF, gradients | Old pacemaker, eye foreign body, ferromagnetic clip | Check the MR Safe, Conditional or Unsafe label |
| NSF | Gadolinium in severe kidney impairment | Group I agent with eGFR below 30 | Group II agent; low dose |
In the full version for subscribers
- A simple algorithm
- Memory aid
- Exam traps
- 5 review cards
- Enough for IMLE
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Sources
- ACR Manual on MR Safety, 2024 — MR environment zones; Screening; Implants and devices
- ACR Manual on Contrast Media, 2024 — Gadolinium-based contrast agents and nephrogenic systemic fibrosis; Gadolinium retention
- European Medicines Agency: Gadolinium-containing contrast agents, Article 31 referral, 2017 — Restriction of linear agents
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.