2.1 ACR Safety Zones and Personnel

ACR Safety Zones and Personnel

The American College of Radiology (ACR) establishes standard safety guidelines to mitigate the substantial risks associated with the clinical magnetic resonance (MR) environment. Because the static magnetic field of an MRI scanner is invisible and constantly active, maintaining strict spatial control and personnel accountability is essential for preventing accidents. The ACR defines four distinct MR Safety Zones (Zones I, II, III, and IV) and two classes of trained MR Personnel (Level 1 and Level 2). Understanding these boundaries and roles is a primary requirement for the ARRT MRI registry and represents the core framework of daily clinical operations.

The Four ACR Safety Zones

The MR facility is structured in a series of progressive security barriers. As you move from Zone I to Zone IV, the magnetic field strength increases, the hazards become more severe, and the access controls become significantly more restrictive.

Zone I: General Public Access

Zone I includes all areas that are freely accessible to the general public without supervision or restriction. Because there are no magnetic fields or associated hazards in this zone, anyone can navigate it.

• Examples: Public hallways, the hospital lobby, external walkways, and waiting rooms located outside the department.
• Access Control: Completely unrestricted. No MR safety screening is required.
• Hazards: None.

Zone II: Transition and Screening Area

Zone II serves as the interface between the unrestricted public spaces of Zone I and the strictly controlled, potentially hazardous environments of Zone III and Zone IV. It is here that patients are greeted, safety screening is initiated, and initial clinical preparations are made.

• Examples: Patient registration desks, waiting areas specific to the MRI department, dressing rooms, and patient interview offices.
• Access Control: Semi-restricted. While patients are not yet exposed to strong magnetic fields, they must be supervised by MR personnel. It is in Zone II that patients complete the written MR safety screening questionnaire and verbally review it with staff to prevent them from wandering into higher-risk zones.
• Hazards: Minimal, but represents a critical zone for intercepting ferromagnetic materials.

Zone III: Restricted Access / Control Area

Zone III is a highly restricted area representing the boundary where the static magnetic field's fringe field poses physical danger to unscreened individuals. This zone is the final barrier before the magnet room itself.

• Examples: The MR control room/console area, equipment rooms, and adjacent hallways where the fringe field is present.
• Access Control: Strictly restricted. Access must be physically secured (typically via keypad locks, badge swipes, or double-door interlocks) to prevent unauthorized, unscreened individuals from entering. Only trained MR personnel can enter independently. All patients, visitors, and non-MR personnel must be escorted and directly supervised by Level 2 MR personnel.
• Hazards: Strong spatial gradient fields, potential projectile risks, and electromagnetic interference. The final, thorough screening review must occur before crossing from Zone II into Zone III.

Zone IV: The Magnet Room / Scanner Room

Zone IV is the magnet room itself, where the physical MRI scanner is located. This is the highest-hazard zone in the entire facility.

• Examples: The scanner room containing the gantry.
• Access Control: Extremely restricted. Access is limited strictly to Level 2 personnel and those under their direct, continuous visual line-of-sight supervision. The door to Zone IV must remain closed at all times except during entry/exit, and a lighted sign reading "The Magnet is On" must be visible outside the door.
• Hazards: The primary static magnetic field (B0) is always active—24 hours a day, 7 days a week, 365 days a year. There is an immediate risk of projectile accidents, implant malfunction, and severe RF heating.

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Comparison of ACR Safety Zones

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MR Personnel Classifications

To ensure safety within the restricted zones, the ACR classifies individuals based on their level of MR safety training.

Non-MR Personnel

This category includes any individual who has not completed formal MR safety training within the past 12 months.

• Who they are: Patients, patient family members, visitors, ward nurses, physicians from other departments, respiratory therapists, and untrained janitorial or maintenance staff.
• Safety Rule: Non-MR personnel must never enter Zone III or Zone IV unless they have been fully screened and are accompanied by a designated Level 2 MR staff member who maintains constant visual supervision.

Level 1 MR Personnel

Level 1 personnel are individuals who have undergone basic, introductory MR safety education. This training ensures they understand the unique hazards of the MR environment to keep themselves safe when working within or moving through Zone III.

• Who they are: Front desk receptionists, department aides, transport personnel, and designated environmental services staff.
• Safety Rule: Level 1 personnel can navigate Zone III independently without an escort. However, they are not authorized to supervise unscreened non-MR personnel in Zone III, and they cannot enter Zone IV without direct supervision from Level 2 staff.

Level 2 MR Personnel

Level 2 personnel have undergone comprehensive, advanced training regarding the physical hazards of MR technology, including static magnetic fields, radiofrequency energy, and time-varying gradient fields.

• Who they are: MRI technologists, radiologists, and MR Safety Officers (MRSO).
• Safety Rule: Level 2 personnel are responsible for final screening reviews, patient positioning, and maintaining safety within Zones III and IV. They must maintain direct visual control over all non-MR personnel in Zone IV.

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Critical Clinical Workflows

Emergency Code Situations

If a patient experiences cardiac or respiratory arrest inside the magnet room (Zone IV), a medical code must be called immediately. However, standard emergency response teams (comprising Non-MR Personnel) and their medical equipment (such as code carts, defibrillators, and oxygen cylinders) are highly ferromagnetic and represent lethal projectile hazards.

• Protocol: The Level 2 technologist must immediately evacuate the patient from Zone IV to a pre-designated resuscitation area in Zone II or outside the MR suite. All cardiopulmonary resuscitation (CPR), intubation, and defibrillation must be performed in this safe zone. The code team is not permitted to enter Zone IV.

Housekeeping and Maintenance

When routine cleaning or machine maintenance is required in Zone IV, the work must be coordinated with Level 2 staff.

• Protocol: Any tools, vacuum cleaners, floor buffers, or mop buckets brought into Zone IV must be verified as MR Safe or MR Conditional. The cleaning staff (if classified as Level 1 or Non-MR) must be under the direct supervision of a Level 2 technologist throughout their entire time in the magnet room.