The American College of Radiology White Paper on MR Safety (Kanal E, Borgstede JP, Barkovich AJ, et al. AJR 2002;178:1335-1347) and the review and commentary on it -- including the Special Report by William Bernstein, ACHA, AIA, which appeared on diagnosticimaging.com -- have made significant strides in establishing standards for MR facility design that support crucial safety protocols.

While the white paper succeeds in defining both operational and physical organization for an MR facility, many hospitals and diagnostic imaging practices may have a difficult time putting some of the design controls into practice. Real-world application of the standards will likely be significantly affected by a number of factors outside of the immediate MR suite.

PLANNING AN MR SUITE

Probably the single greatest influence on the design and layout of an MR suite is the magnet itself. The 5-gauss line represents the absolute minimum perimeter around a magnet for all nonscreened and unobserved personnel (staff, patients, visitors, etc.). This minimum exclusion zone extends in all directions around the magnet. Particular attention should be paid to securing the spaces above, below, and outside of a magnet room, including the roof of the building, as applicable.

Actively shielded magnets can dramatically reduce the reach of the fringe field and the volume of the exclusion zone. But active shielding can fail, creating a "bloom field," which may be substantially larger than the magnetic field during normal operation. It is up to each facility to weigh the risks of this failure mode and plan accordingly. MR manufacturers advise that the exclusion zone be extended to enclose the 5-gauss line during a bloom condition, although this recommendation is often disregarded.

The only sure way to contain an otherwise far-reaching magnetic field is through the use of magnetic shielding. In contrast to the ease of installation of a standard radio-frequency shield, electromagnetic shielding for high-field magnets requires tons of steel plating fabricated into a box that encloses the magnet room to dampen the reach of the magnetic field. The logistics and costs associated with magnetic shielding can be daunting.

PHYSICAL DESIGN TO SUPPORT SAFETY

Safety is the primary concern when designing for a new magnet. After a specific magnet has been identified for an imaging suite, the facility must be evaluated for its ability to support the safety protocols for that magnet. The magnetic strength, bore size, and field distribution combined with the functions adjacent to the MR suite will often immediately indicate whether there is a need for magnetic shielding in a particular location.

If a facility elects not to follow the manufacturer's recommendation and not extend the exclusion zone for an actively shielded magnet to the full reach of the 5-gauss line in a bloom situation, the location of the MR suite should be chosen with full consideration of adjacent functions and populations. Given the risks of magnetic field interference with pacemakers, for example, locating an actively shielded magnet immediately adjacent to (including directly above or below) a cardiac unit or catheterization lab would be ill-advised.

Although it is not recognized in the American College of Radiology's white paper, one design effort that may facilitate safety protocols in an MR suite is adding a secured door before the patient enters the dressing/holding area. With this configuration, the patient questionnaire and interview screen occur prior to patient admission to the dressing/holding area. Physical screenings can be conducted within the holding area, as appropriate. This effectively turns the dressing/holding area into a zone III area.

OPERATIONAL CONSIDERATIONS

While life-safety considerations are paramount, MR equipment and facilities represent an enormous financial and operational investment. Planning efforts should yield designs that respect indirect patient care issues as well as the importance of maximized operational time and acknowledge the rapid growth of radiological imaging.

• While it is crucial for the MR staff to have direct visual supervision of all personnel within the suite at all times, bringing patients through the control room introduces patient confidentiality conflicts. While the standard does not recommend this configuration, Figure 1 in the American College of Radiology's White Paper depicts such a conflict.
• Unless your imaging suite is assured a measured flow of patients, it is wise to provide adequate seating and bathrooms within the zone III area to prevent exit and reentry of previously screened individuals.
• Extending beyond the exclusion zone is a broader magnetic field that can disrupt CTs, computer monitors, and other sensitive equipment. After the life-safety issues have been resolved, a proposed site for an MR scanner should be evaluated for potential interference with existing and prospective facilities.
• Installation of a first MR should anticipate a possible second, or even third, magnet. Because of many magnets' sensitivity to vibration and the reach of their moving-metal sensitivity, it would be necessary -- and probably very expensive -- to shut down a magnet during the weeks required for construction of an unanticipated addition. During the design for a first MR, consider and plan for future additions. The incremental cost is minor when compared with the prospect of taking a valuable imaging resource offline for weeks at a time.

The increasing use and power of modern MRs present clinicians and researchers with the ability to generate diagnostic images faster and with greater resolution than ever before realized. The increased power, active shielding, and reduced scan times have made these units more effective, easier to site, and capable of supporting larger patient volumes. These advances do not, however, mitigate the hazards of powerful magnetic fields and the planning and operational considerations they warrant.

For patient supervision, facility planning, and, most important, patient and staff safety, MR suites must be very carefully planned. Design solutions alone cannot assure facility safety, but they can dramatically affect the implementation of safety protocols, as well as the long-range operability of an imaging suite.

Robert Paul Junk, AIA, is a principal of Junk Architects (www.junkarchitects.com), an architecture and design firm in Kansas City, MO.

Tobias Gilk is an associate architect with Junk Architects and has served as project manager/project architect for many radiological renovations.

Junk Architects, PC is a design firm specializing in medical projects. The authors can be reached at 816/472-7722 (phone) or 816/472-1822 (fax).