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Ferromagnetic equipment is strictly prohibited from entering which of the following magnetic resonance imaging (MRI) safety zones?
A. Zone I X
B. Zone II X
C. Zone IV ✔
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Magnetic resonance imaging (MRI) is a widely used diagnostic modality. Safety issues that should be considered specifically for the MRI suite include projectile injury, injury due to dislodged ferromagnetic implants, electric burns, anaphylaxis to contrast, and hearing loss.
All anesthesia providers need to be very familiar with the basic principles of MRI safety to help prevent lapses during an emergency. The magnet is always on, and large magnetic field gradients are always present surrounding the MRI scanner. All the equipment and monitors must be MRI compatible and used according to the manufacturer’s guidelines. The magnetic field in the MRI suite can draw nearby ferromagnetic objects at an alarming speed and force, creating a dangerous projectile that can seriously injure patients and staff and irreversibly damage the MRI scanner.
The American College of Radiology has defined MRI safety zones for facilities with MRI scanners. These are zones I through IV, with zone I safely outside the MRI environment and zone IV having the greatest magnetic field exposure and safety concerns (Figure 1). Zone IV is the scanner room and should only have MRI-compatible equipment for suction, physiological monitoring, and mechanical ventilation. This functions as a second anesthesia workstation. In case of a potentially life-threatening situation or emergency, the patient must be promptly transferred from zone IV to the primary anesthesia workstation in zone II so optimal care and additional help can be provided.
Figure 1. Safety zones of a magnetic resonance imaging (MRI) suite. © 2023 American Society of Anesthesiologists.
If an object is pulled into the magnet causing equipment damage or patient injury (eg, the patient is pinned by the projectile), the superconducting magnet can be shut down immediately. This process, called “quenching,” should only be performed by MRI technicians. The superconducting magnet of an MRI scanner operates at cryogenic temperatures and requires coolant (called cryogen) such as liquid helium to maintain the low temperature. The quenching process involves a rise in temperature of the superconducting magnet with the escape of cryogen into a venting system outside the MRI room. However, in rare circumstances, cryogen can escape into the MRI room and displace oxygen, which can cause cold injury and hypoxia.
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Date of last update: September 19, 2023
