Magnetic resonance imaging safety can be analogized to a three-legged stool. Anything less than an equal development of three distinct domains — clinical safety, operational safety, and physical safety – makes for a very precarious position.

All the attention in the world spent checking the relative MR safety of implants, or the thermodynamic stability of a contrast agent (examples of clinical safety) does nothing to enhance either of the other domains. Similarly, subject screening protocols, appointment of an MR safety officer, or staff training regimens (examples of operational safety) are also necessary, but insufficient alone, to comprise an MR safety program. In this article, we look at the third domain, physical safety, and some of its most important constituent parts.

ACR 4-Zone – avoiding danger in the MR suite
Broadly, one of the most important elements of physical MR safety is popularly known as the 4-Zone. In a nutshell, it states that any person should be under increasing security, or have greater and greater levels of safety knowledge, as they proceed through areas with greater proximity/access to the MR equipment.

The 4-Zone concept, originally published in the earliest of the American College of Radiology’s (ACR) Guidance Documents on MR Safety, is codified in the Facilities Guidelines Institute Guidelines for Design and Construction of Healthcare Facilities hospital building code. Versions of the FGI code have been adopted by more than 20 States as their licensure standard, and the 2010 edition is the default standard for Joint Commission accredited hospitals. Even the Joint Commission’s own Diagnostic Imaging Standards, released in December of 2013 and rescinded – pending a rewrite – a few months later, contained a version of the 4-Zone concept.

Fundamentally, the 4-Zone concept is intended to keep dangerous materials and untrained persons away from the room containing the MR scanner (designated as Zone 4). It is implemented by selectively segregating persons as they arrive at the MR department, and allowing only those who must proceed towards the scanner to do so. Along the way, this person undergoes screening, both physical and clinical to make sure they aren’t bringing anything to the scanner room that could be potentially harmful, and that they don’t have any medical devices or embedded foreign material that could pose a threat to them in a powerful magnetic field.

Integral to this model is access restrictions. Once a subject has been successfully screened, she is allowed to pass a secured entrance. This locked door can be secured by a conventional physical key system or by an RFID card; however, combination lock systems are NOT recommended due to the frequency which combinations are often distributed.

Situational awareness – design guidelines for MR suite safety
Another essential component for physical safety is that of situational awareness. Yes, the technologist is certainly capable of moving himself around such that they can see the patient/visitor wherever they might be in the controlled access portion of the MR suite (Zone 3), but the fact is that the majority of the time the technologist will be positioned at the operator’s console. It is from this position that the technologist should be able to see the approach to the entrance to the scanner room (Zone 4), as well as any patient holding /preparation areas within Zone 3 that aren’t otherwise staffed.

The suite should be laid out such that from the console the technologist has direct line-of-sight to these critical areas. In the absence of direct sight lines, facilities should deploy closed-circuit video monitoring, or other indirect means of facilitating the technologist’s awareness of their immediate surroundings and key points of access.

Similar principles apply to the view from the console into the scanner room, itself. Unless specific conditions prevent the use of a conventional RF shielded window through which the technologist can view the inside of the scanner room, windows are preferable to the fixed view of a video camera and ‘virtual window’ video monitoring system. That isn’t to say that video monitoring can’t be used to augment direct line-of-sight monitoring of the scanner room, but rather that, from a safety standpoint, it isn’t the preferred method.

The above elements of situational awareness should be thought of as additional to the ability to observe the patient in the scanner. Occasionally MR suites are laid out in such a way that the patient table of the scanner is perpendicular to the view angle from the operator’s console. For bore format scanners this often means that the technologist cannot see the part of the patient inside the scanner, greatly diminishing his or her ability to supervise the exam and the patient’s condition (respiration, coloration, expression…).

Classifying ferromagnetic materials
Given the widely known examples of ferromagnetic objects photographed while stuck to scanners, another key element to physical safety in the suite is the appropriate use of properly tested and labeled equipment. In 2005, the American Society for Testing and Materials International released new criteria for identifying the safety of objects in and around MR scanners. This system allowed objects to be classified based on their potential risk, as summarized below.

MR Safe: This designation is very restrictive (and, as a result, there are very few devices that have it). In essence, an object with this label must present zero risk in the MR environment, regardless of magnetic field strength, RF frequency / energy used, or the time-varying magnetic fields. Objects with this label must be non-magnetic, non-electrically conductive, and non-RF reactive. This leaves a small palate of possible materials, including silicone, glass, and some plastics and ceramics. While many homegrown “MR Safe” labels persist, properly labeled “MR Safe” objects are quite rare.

MR Conditional: Any object constructed with metal, or containing wires/batteries, or with any electrically conductive elements must be minimally identified as MR Conditional. This means that virtually every device/appliance used in the MR suite that is intended to be able to safely go into the scanner room — from fire extinguishers to wheelchairs — should be designated MR Conditional. Unlike MR Safe, MR Conditional imposes restrictions on what constitutes safe use. These limitations can include field strength, magnetic spatial gradient, RF energy, and time-varying magnetic field. This means that two different objects with MR Conditional labels may not be appropriate for safe use under the same conditions.

Particularly if an MR suite has more than one scanner, it is important that MR Conditional equipment not only be categorized and labeled as such, but also that the specific conditions for safe use be identified on the equipment. It may be that a device is known to be safe/functional at 1.5T, but not at 3.0T. For a site that has MR systems with different field strengths, or magnetic spatial gradients, or gradient coil capabilities, it is essential that the MR Conditional conditions for each piece of equipment be readily available to the department staff.

MR Unsafe:
As the name suggests, some materials/objects demonstrate overt ferromagnetic properties that make them unsafe near the scanner. Many crash carts are made of steel and would give an entirely unintended meaning to ‘crash’ if they were brought into the scanner room.

That means equipment in the suite should be appropriately tested, and conspicuously labeled, so that department staff can immediately recognize the safety characteristics of materials within the controlled access area (a principle that should be extended to equipment known to be brought into the suite, such as ventilators or anesthesia equipment).

Despite our best efforts to screen patients/ visitors and restrict the access of untested equipment, every provider knows that there are always opportunities for things to slip through the process. Whether through deception or ignorance, potentially dangerous ferromagnetic materials regularly find their way into suites without the knowledge of the technologists. One of the newest tools to thwarting this risk is the use of ferromagnetic detection systems, required for many through the FGI codes.

Ferromagnetic protection systems
Ferromagnetic Detection Systems are quickly gaining popularity as useful tools to enhance the security and safety around MR suites as it pertains to ferromagnetic materials. Historically, the introduction of ferrous materials to an MR has resulted in problems from imaging issues, to more serious situations such as severe damage to the equipment or even serious harm to a patient or staff.

While ferromagnetic detection systems provide an opportunity to enhance the security and safety around an MR suite, both the type of technology chosen and the manner that the ferromagnetic detection system is implemented drive the overall benefits derived from an installation.

There are two different classes of ferromagnetic detectors, mass screeners intended to screen the subject all at once, and targeted or localized screeners, that detect in a focal area. We will begin by discussing the different applications of mass screeners — where and how they can be integrated into a suite.

Mass screeners
There are several ways that mass ferromagnetic detection systems may be implemented. The first is as a prescreen device to help check the individual concurrent with the screening process (prior to bringing the patient into the controlled access area).Essentially, a facility would take a patient through all the normal screening procedures and, as an additional step in the screening procedure, would have a patient pass through a highly sensitive ferromagnetic detection system intended to detect anything from larger ferrous objects (e.g. pocket knives, or cell phones) to smaller objects (e.g. nail clippers, jewelry, or hairpins).

The second application involves the use of a ferromagnetic detection system as a screener at the entryway to the MRI suite. This application can help catch elements missed in the conventional patient screening, and materials being brought to the suite by persons who have circumvented the screening process, altogether, such as transport personnel, respiratory/anesthesia (or other clinical personnel), or even housekeeping staff. Particularly in retrofit situations, there are often limitations with this type of application that are dependent upon where it is employed at the entryway of the controlled access portion of the suite (Zone 3), or at the doorway to the scanner room (Zone 4), and the specific technology utilized in the ferromagnetic detection system which is employed.

An entryway application involves utilizing a ferromagnetic detection system to monitor and screen individuals and items attempting to enter an MR suite, or scanner room. Therefore, it is very common for the ferromagnetic detection system to be mounted at the door jamb of the entry point to Zone 3 or Zone 4. Depending on the layout and operation of an MR suite, it may not be practical to provide the entryway mass screener at the entrance to Zone 3, even though this is the preferred location. In nearly all situations, however, a solution can be found in which the FMDS is placed at the entrance to either Zone 3 or Zone 4.

A third application would be a combination of prescreen and entryway screening systems. Utilizing both applications ensures that patients have been thoroughly screened prior to entering the suite. It also ensures that the magnet room itself has additional protection from anyone that may enter the suite, including those previously identified as likely getting around the standard screening process.
Depending on the sitting conditions, including the location and swing direction of the door, selecting a proper product and installation location for an entryway application requires some careful consideration. Doors, even RF shielded doors at the entrance to Zone 4, contain ferrous material, which can lead to unintended positive indications on a ferromagnetic detection system if the door is in motion as someone passes through the system. The obvious solution would be to use a ferrous-free door, but unfortunately. Even an aluminum (or other non-ferromagnetic material) door would create a phenomena known as “eddy currents” when it opened or closed, which would trigger a sufficiently sensitive FMDS.

Design guidelines for a ferromagnetic detection system
In order for a mass screener ferromagnetic detection system to be effective, the users and site designers can consider several options. The first and most ideal option is to layout the suite with the implementation of a ferromagnetic detection system planned into the site layout. In an ideal situation, the planners would be able to create an entryway hall or partition wall that leads to the magnet room. An entryway that extends several feet away from the entrance allows patients and staff to pass through the entry way prior to opening the magnet room door, which will limit the possibility of false positives generated by door motion. As many sites are in existence and many others lack the space needed to implement such an option, a second option of proper training and safety protocols can be utilized to avoid the potential of incidental alarms from door movement. For example, as part of the protocols for entering the room, staff can first open the door prior to allowing patients to pass through the room. Once the door is open and no longer in motion, it would be possible for individual to pass through the ferromagnetic detection system for an appropriate screening without any interference from door motion.

The direction of door swing creates additional challenges when implementing a FMDS. The previous suggestions address the typical issues experienced with in-swing door applications (in which the door swings into the scanner room), but out-swing door applications tend to be more challenging. One solution is to install the ferromagnetic detection system on the face of the door jamb just inside the MR room. When a ferromagnetic detection system is placed on the jamb or walls immediately outside the MR room, the staff and a patient have a more time to respond to a positive alarm before entering the room. This is not the case when the ferromagnetic system is located inside the MR scanner room. Typically, a person will take an additional step or two before being able to respond to a positive alarm, which will place a person well within the suite. Depending on the size of the room and location of the MR within the room, the possibility of an accident could greatly increase. For this reason, siting FMDS within the scanner room is typically strongly discouraged.

Focal screeners
It is important to consider the FMDS technology being implemented in an effort to develop an optimal screening process for a given situation. While mass screeners are excellent tools for ambulatory patients, non-ambulatory patients represent a unique situation. Non-ambulatory patients, which are transported to the MR via stretcher or wheelchair, cannot easily be screened by a mass screener, wall mount or portable entryway ferromagnetic detection systems. In these instances, a focal handheld ferromagnetic system offers a distinct advantage. A handheld system allows staff to screen the patient and to discern if there is ferromagnetic material on the individual (versus the transport equipment or ancillary equipment carried on the transport equipment). Particularly in a hospital setting where there are a significant proportion of non-ambulatory patients, the coordinated and combined use of both mass

FMDS and focal FMDS screening typically represents the best option to provide safety screening to all persons entering the MI area.

Implementing ferromagnetic safety protocols
There are many things to consider when implementing a FMDS as part of a facility’s safety protocols. Users must identify the goals of implementing an FMDS. For example, is the focus on patient screening, protecting the scanner or a combination of screen and protection? The ideal solution would be a multiple system approach. One system would be positioned near patient changing rooms. This system would be extremely sensitive and would be setup to detect small ferrous objects. A second system would be positioned at the entryway to the suite. This system would be set up to detect ferrous objects that could do serious damage to the scanner or could be responsible for bodily injury to a patient. Additionally, users must consider the various technologies and identify the technology that will yield the best results.

In order to maximize the advantages of a FMDS, proper planning and technology selection are a must. A knowledgeable FMDS distributor or manufacturer will be able to support the user in identifying the optimal products and implementation of those products for the specific application.

Conclusion
A truly safe MR environment will balance the operational, clinical, and physical elements of safety. For many practitioners, however, the physical elements of MR safety are not the recurring daily concerns that the other two domains are. It is only natural, then, that physical safety considerations may slowly drift from thought. The risk of this, of course, is that as the regulatory, accreditation and best practice standards evolve, providers may one day realize that their protection protocols have become lopsided. Poor physical safety preparations have left them vulnerable to accidents and injuries that they might otherwise have been able to prevent.

About the authors:
Tobias Gilk is a former member of the ACR’s MRI Safety Committee, and contributing author for the 2007 ACR Guidance Document on MR Safe Practices. He presently serves as Senior Vice President of RAD-Planning, a radiology architectural and design consulting firm, and principal of his own consulting firm, Gilk Radiology Consultants.

Joel Kellogg is the manager of Technical Engineering and Consulting with ETS-Lindgren. Since joining ETS-Lindgren in 1998, he has been involved in the company’s magnetic resonance imaging (MRI) products and services, including surveys and engineered solutions for vibration, acoustic, EMI and RF.