What you’ll be able to do after this lesson
- Describe what each of the four ACR zones is, and what changes about your obligations as you cross each boundary
- Explain who may enter Zone III and Zone IV, and under whose supervision
- Distinguish Level 1 MR personnel, Level 2 MR personnel and non-MR personnel — and say which of those you are today
- Recognise the three access-control failures that cause most MR incidents, and name the control that prevents each
The one fact the whole system is built on
The magnet is always on.
Not “on during working hours”. Not “off overnight”. Not “off because the console is shut down”, and not reliably off even after a quench. A superconducting magnet holds its field continuously for its entire installed life, and the only thing standing between that field and a hazard is a door, a policy, and a person doing their job.
Every zone rule that follows is an attempt to make that fact survive contact with a busy department, a night shift, a fire alarm, a new porter, and a cleaner with a floor buffer.
The four zones
The zone model comes from the ACR Manual on MR Safety and is the framework most departments in the US, UK, Australia and New Zealand build their local policy around. Learn it as a sequence of gates, each one narrower than the last.
Zone I — freely accessible. Everywhere the general public can walk without any MR-specific control: car park, main corridors, the hospital foyer. No screening, no field hazard.
Zone II — the interface. Reception, changing rooms, the subwait. This is where patients are greeted, screened, gowned and interviewed. Patients here are under the general supervision of MR personnel but are not yet in the controlled area. Zone II is where most of the safety work of a shift actually happens, because it is where screening happens.
Zone III — the controlled access area. The control room, equipment room and the corridor immediately outside the scanner room. Free access here by unscreened people or ferromagnetic objects can cause serious injury, so Zone III must be physically restricted — locked doors, badge access, or an equivalent control — and supervised by Level 2 MR personnel. The ACR Manual on MR Safety (2026) states it directly: the MR Controlled Access Area is “the locally defined area around the MR system that contains the MR Environment (including its static magnetic field) to which access is limited to authorized personnel”, and “any entrance to Zone III providing direct access to Zone IV should be restricted by access control cards, badges, or other technology”. Areas where the field exceeds the MR Environment contour form part of that hazard area even where they are not directly contiguous with Zone IV.
Zone IV — the scanner room. The magnet room itself, and it contains the MR Projectile Area. Only screened people enter, only under the direct supervision of Level 2 MR personnel, and nothing ferromagnetic goes in. Ever.
A useful mental test: at each boundary, ask what have I now taken responsibility for? At the Zone II boundary you take responsibility for the accuracy of a screening conversation. At the Zone III boundary you take responsibility for who is on the other side of a door. At the Zone IV boundary you take responsibility for every object on a person’s body and every item on the trolley.
Who counts as what
The personnel tiers matter more than they look, because they determine who may supervise whom.
- Non-MR personnel — anyone who has not completed MR safety education, or who does not work in the MR environment regularly. This includes doctors, ward nurses, porters, cleaners, engineers, students and the patient’s relatives. They must be screened and continuously escorted in Zones III and IV. Never left alone. Not for a minute.
- Level 1 MR personnel — have completed minimal safety education sufficient to ensure their own safety in the MR environment. They do not supervise others.
- Level 2 MR personnel — more extensively trained across the broader aspects of MR safety: RF heating, projectile risk, cryogen hazards, implant management. Level 2 personnel supervise Zone III and Zone IV access.
Above the operational tiers sits the governance structure you will meet properly in lesson 12: the MR Medical Director (MRMD) who owns the risk–benefit decision, the MR Safety Officer (MRSO) who runs day-to-day safety, and the MR Safety Expert (MRSE) who provides the physics and engineering input. The MRMD may delegate a function; the responsibility does not transfer with it.
If you are a first-year trainee, you are almost certainly Level 1. That is not a limitation to feel bad about — it is a statement about who is accountable when a decision goes wrong. You do not clear implants alone. You do not escort alone. You raise the flag and hand it up.
The three failures
Read enough incident reports and the same three shapes recur.
The propped door. Someone wedges the Zone IV door open — for a trolley, for ventilation, for a delivery — and the physical control that the entire model depends on ceases to exist. A door that is not closed is not a control. If you find one propped, close it and say so.
The escorted person who stopped being escorted. A relative is walked in, then the technologist turns to the console, and the relative wanders back for a coat. An anaesthetist steps out and returns with their own equipment. Escorting is continuous, not an event at the threshold.
The person who was screened last time. Ward staff, engineers, cleaners and radiologists who “come in all the time” accumulate exemptions informally. Their pockets change daily. So does their implant status — a colleague can acquire a pacemaker between one visit and the next. Screening is per entry, not per person.
None of these are exotic. They are all ordinary, reasonable-seeming shortcuts taken by competent people under time pressure, which is exactly why the answer is a system rather than vigilance.
When the boundary must be crossed anyway
Real departments have emergencies, and the zone model has an answer for each.
A patient arresting in Zone IV is removed from Zone IV and resuscitated outside it. The crash team and their trolley never enter the magnet room. Rehearse this — the ACR Manual recommends mock-code drills precisely because the instinct to run towards a collapsed patient is stronger than the memory of a policy.
A fire brings people with air cylinders, axes and breathing apparatus. Your local policy should specify how the fire service is briefed and who meets them; MR-conditional firefighting equipment exists for exactly this reason.
Ward or theatre transfers arrive with infusion pumps, oxygen cylinders, monitoring and a trolley — each of which must be assessed as an object, not waved through because it came with a patient.
In all three, the principle is identical: bring the patient out to the equipment rather than the equipment in to the patient, unless that equipment is labelled for the MR environment and your local policy permits it.
At the console
It is 19:40. Your list is running late, and a cardiology registrar you know well appears at the Zone III door wanting to look at images on the console for a patient he is admitting. He is in scrubs, has been in the room before, and is visibly in a hurry.
The correct action is not dramatic. He is non-MR personnel. He gets screened — the same form, the same questions, the same pocket check — and he is escorted, continuously, for as long as he is inside. If you cannot escort him because you are scanning, he waits, or he views the images somewhere outside Zone III. “He’s a doctor” is not a screening category. “He’s been in before” is the sentence that appears in incident reports.
Second scenario, same evening: a porter arrives to collect the previous patient’s bed and is already halfway through the Zone III door with it. Stop at the door, not at the bore. Beds, cylinders, drip stands and wheelchairs are the classic projectile class, and the fact that a piece of equipment lives in the hospital does not make it MR conditional. Check the label, or swap it for the department’s own MR-conditional equipment.
Check yourself
Walk your own department in your head, from the main corridor to the bore. Where exactly is the Zone III boundary — is it a door with a lock, or a line on a floor plan nobody can see? Who could walk through it right now unchallenged? Then answer the harder one: if you found that door propped open at 21:00 with no one around, what would you actually do, and who would you tell?
This is a private prompt. Nothing you write is stored or assessed.
Key takeaways
- The static field is always on. Every zone control exists because that fact cannot be switched off.
- Zone I is public; Zone II is the screening interface; Zone III is physically restricted and supervised by Level 2 MR personnel; Zone IV is the scanner room and contains the MR Projectile Area.
- Non-MR personnel — including clinicians, porters and relatives — must be screened and continuously escorted in Zones III and IV. Level 2 personnel supervise; Level 1 personnel do not.
- Most access failures are ordinary shortcuts: a propped door, an escort that lapsed, a familiar face who was not screened this time.
- In an arrest, the patient leaves Zone IV. The resuscitation team does not enter it.
- Zone definitions and personnel duties vary between the ACR Manual, MHRA guidance and your own department. Check the current edition and your local policy.
References
- ACR Manual on MR Safety, 2026 edition. American College of Radiology https://www.acr.org/Clinical-Resources/Clinical-Tools-and-Reference/Radiology-Safety/MR-Safety
- Pedrosa I, et al. American College of Radiology Manual on MR Safety: 2024 Update and Revisions. Radiology, 2025 https://pubs.rsna.org/doi/10.1148/radiol.241405
- MHRA. Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use, 5th edition (July 2026) https://www.gov.uk/government/publications/safety-guidelines-for-magnetic-resonance-imaging-equipment-in-clinical-use
- highyieldmri.com — MRI Screening, Patient Prep and Positioning