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MRI – 4 Zone Safety Boundaries

Due to the powerful magnetic field, many Magnetic Resonance Imaging (MRI) facilities and hospitals restrict access to the MR Suite by establishing four conceptual zones around the MR scanner. Each boundary zone in this four-zone safety system is defined by its purpose and distance from the MR scanner. Since the magnetic field extends in three dimensions, some zones may extend into other areas or floors of the facility.

Zone One consists of all areas freely accessible to the general public. This zone includes the entrance to the MR facility and the magnet poses no hazards in these areas.

Zone Two acts as a buffer between Zone One and the more restrictive Zone Three. Here, patients are under the general supervision of MR personnel. Normally, these areas are also safe from all magnetic field hazards. Zone Two may include the reception area, dressing room and interview room.

Access to Zone Three should be restricted by a physical barrier. Only approved MR personnel and patients that have undergone a medical questionnaire and interview are allowed inside Zone Three. The MR control room and/or computer room are located within Zone Three.

Zone Four is strictly the area within the walls of the MR scanner room, sometimes called the magnet room. Access into the MR scanner room should only be available by passing through Zone Three. Zone Four is sometimes considered to be inside of

Zone Three because it does not have a direct entrance to unrestricted areas.
Zone Three and Zone Four are sometimes collectively referred to as the MR Suite. Inside the MR Suite is an invisible boundary defined by the magnetic field’s five Gauss line. The five Gauss line is the point at which the magnetic field begins to affect electromagnetic devices, such as pacemakers.

Because the magnetic field extends in all directions, the five Gauss line can also extend to areas outside of the MR Suite, including other floors, if the magnetic field is large enough. Magnetic fields cannot be seen or felt, so the five Gauss line is sometimes marked on floors or walls for safety. Marking the five Gauss line is particularly important when it extends beyond the walls of the MR scanner room.

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