Involving staff from clinical, operational, and facility
disciplines
By Tobias Gilk, M.Arch., associate architect with Junk Architects, PC
Nearly everyone who works around magnetic resonance imaging (MRI) has heard
the stories and seen the pictures1 of preventable accidents in the MRI suite:
the unscreened patient who made it into the room with a spinal shunt or on a
gurney made largely of steel, only to be caught in the magnetic attraction of
the MRI and launched into the large electromagnet.
Many experts in the realm of MRI safety believe that a principal factor in
the failure to proactively address safety issues in the MR suite is a profound
underestimation of the risks. The Food and Drug Administration’s (FDA’s)
Manufacturer and User Facility Device Experience Database (MAUDE)2 catalogues
accidents and incidents involving FDA-approved devices.
Despite mandatory reporting requirements, it is believed that fewer than 10%
of MRI accidents are reported (even with a doubling of MRI safety incident
reports in the 12 months ending mid-2006 from the previous one-year period).
This gross underreporting denies imaging providers the information they need to
make effective decisions regarding accident prevention and serves to stigmatize
those who admit to having had (or are discovered to have had) MRI safety
mishaps.
Upon entering the confines of the MRI suite, rules of safety are
imperceptibly changed by the powerful magnetic fields and invisible
radiofrequency (RF) waves. Though magnetic energies have not been demonstrated
to have adverse biological effects, lifesaving medical devices such as
pacemakers and nerve stimulators can malfunction in close proximity to MRI
magnets, with potentially fatal results.
Ubiquitous health care appliances, such as medical gas cylinders,
wheelchairs, or gurneys can be launched, homing in on the center of the MRI,
attracted by the far-reaching magnetic field.
Safety in the MRI suite is both vitally important and unusually challenging
to implement because of the invisibility of the threats coupled with the
increasingly common presence of objects that MRIs can act upon with disastrous
results.
An Interdisciplinary Approach to MRI Safety
Because of the numerous threats to safety and operations, effective mitigation
of hazards in the MRI suite often depends on collaborative problem solving
among clinicians, management, and facility designers. By combining the
strengths of the varied perspectives, building-in defenses against accidents
and supporting best practice procedures are made easier. Problems or solutions
readily apparent to one discipline may not even occur to another.
A well-rounded project team would likely include the organizational and
departmental management, MR technologists, radiologists, infection control,
anesthesiology, vendor representatives, and experienced MRI design
professionals.
| Tip: When
assembling a team to coordinate the installation of new MRI equipment, include
internal expertise from radiology management and clinical disciplines. Bring on
planning and design expertise as early as possible to inform project
development.
|
Those facilities developed without this sort of interdisciplinary approach—
likely a significant proportion of today’s MRI providers—often are frustrated
in their attempts to improve any operational parameters, including safety and
throughput, because obstacles were unintentionally erected in the path of
optimal procedures. Copy-and-paste policies and procedures or suite layouts
that do not address the issues unique to a given facility’s MRI equipment,
patients, referring physicians, patient load, staffing, and clinical practice
further impair an organization’s ability to deliver effective and efficient
care.
The hazards in the MRI suite are most accurately divided into three
families— operational, clinical, and facility design— though interventions to
mitigate any single hazard should include solutions from each group.
Sidebar 1. Descriptions of the American College of Radiology’s Four
Zones
| ACR Zones | Occupants | Hazards |
| Zone I | General Public | Negligible MRI hazards |
| Zone II | Unscreened MRI patients | Immediately
outside area(s) of hazard |
| Zone III | Screened MRI patients/personnel |
Potential biostimulation interference, access to magnet room |
| Zone IV | Screened MRI patients under constant direct
supervision of trained MR personnel | Biostimulation
interference, RF heating, missile effect, cryogens |
|
Facility Design
An effectively-composed MRI suite provides both a literal and figurative
foundation for best practice procedures. As a fundamental starting point for a
practice, facilities should be laid out to identify the four zones of
successive hazards and access restrictions, as defined in the American College
of Radiology’s (ACR’s) White Paper on MR Safety. The four-zone model
prescribes integrated strategies for screening personnel and objects to control
access to those areas with immediate access to the MRI. (See Sidebar 1, above,
for a description of the ACR’s four zones.)
|
Tip: Maintain copies of MRI safety reference materials on site to assist
in defining best practice procedures for four-zone access and screening
protocols. These access controls are vital even beyond the confines of the
magnet room itself. Unlike conventional X-ray or CT scanners, where a lead
shield contains the threat within the examination room, magnetism from an MRI
machine can penetrate all standard forms of building construction, including
concrete, and impose hazards in areas outside the room, the radiology
department, and sometimes outside the building. The strength and polar
orientation of the magnet used in the MR scanner may project the physical
hazards into adjacent spaces, even areas above and below the magnet. In some
facilities, rooms outside the MRI suite, even rooftops, may require access
restrictions to protect unscreened persons from exposure to the
risks. |
|
Tip: Identify the extent of the 5-Gauss magnetic field, including areas
above and below the MRI, and control access to these Zone III areas, even
outside the confines of the MRI suite.
|
Contemporary superconducting magnets, the most common type used in clinical
MRI equipment, are enabled through the use of liquid helium. This cryogenic
liquid, though nontoxic and chemically inert, can present significant hazards
that facility design can mitigate. Contained within what amounts to a large
thermos bottle surrounding the magnet, the liquid helium is maintained at
roughly –450º F. In certain failure modes, the liquid helium can boil off and
vent at near-explosive pressure. If the ducting system fails, a room can be
flooded with helium gas at hundreds of degrees below zero, potentially
entrapping and asphyxiating anyone inside the room. Manufacturers of MRI
systems today require both active and passive pressure venting systems to
protect against such a risk.
|
Tip: Evaluate current cryogen pressure relief and exhaust requirements
from your MRI vendor. In addition, inspect cryogen vent systems, including the
quench pipe, at least annually for obstructions or wear.
|
When informed by the specifics of the practice, suite design and layout
significantly contributes to the efficacy of both clinical and operational
measures by crystallizing best practice procedures with the spaces, equipment,
and accommodations required of each. This can be done through the appropriate
design and placement of facilities, such as private HIPAA–compliant patient
interview areas for clinical screenings, access controls, and sightlines.
Facility planners and clinicians should consider the facility ramifications
of such divergent issues as sedation/anesthesia, infection control,
image-guided/interventional procedures, emergent scan needs, and bariatric
patients early in the process.
Despite what is known about the risks to patients, staff, and imaging
equipment, the invisible nature of the hazards in the MRI suite allows us to
slip into complacency far too easily. Many MRI providers believe that they can
squeak by with just the special MRI fire extinguisher and the probability that
an accident won’t happen to them. But surveys of technologists and radiology
managers illuminate the dark side of this probability; given enough patient
scans over the course of months and years, sooner or later, nearly every MRI
facility will have a serious accident if it fails to implement appropriate
protections.
Those that proactively protect against such an event can greatly diminish
their liability exposure and help to assure the safety of patients and staff in
the MRI suite.
To ensure that you are effectively evaluating all the MRI safety risks, see
page 12 of the online version of this issue for a checklist of questions.
Sidebar 2. Device-Marking Terminology
MR Safe: The device is safe for use in an MR environment, without
exception, regardless of magnet strength and any other field conditions.
MR Conditional: The device is safe for use in a specified MR
environment under specified conditions; however, it may not be safe to use in
MR environments that don’t match the specified conditions.
MR Unsafe: The device is not safe to use in any MR environment.
Source: ECRI: What’s new in MR safety: The latest on the safe use of
equipment in the magnetic resonance environment. Health Devices
34:333–350, Oct. 2005.
|
Operational
Frequent injuries in the MRI suite, equipment damage, and interrupted patient
throughput are caused by the introduction of ferromagnetic materials into the
magnet room. Objects with significant iron or steel content can be sucked into
the MRI at speeds of up to 40 miles per hour. Unlike the hazards for CT or
conventional X-ray technologies, the magnetic fields for clinical MRI are
present for virtually all systems. This means that safety is not only a concern
during imaging, but protocols for protecting staff and equipment must be in
place and enforced 24 hours a day.
Effective screening protocols should include more than only identifying
clinical contraindications; they also should interdict ferromagnetic threats
before they approach the MRI room. Recently, the FDA adopted the revised and
updated ASTM International testing and labeling criteria for object safety near
MRI magnets. Items within the MRI suite should be prospectively identified and
clearly labeled with the new icons MR Safe, MR Conditional, or MR
Unsafe so that there is no ambiguity about an object or device’s
suitability in (or near) the MRI room. (See Sidebar 2, above, for definitions
of MR Safe, MR Conditional, and MR Unsafe.) Facilities with
equipment labeled under the previous standards should determine the correct
current designation and identify each piece of equipment in the MRI suite using
the new nomenclature.
|
Tip: Label all portable equipment and devices within the MRI suite
(including those likely to be brought to the suite) using the current ASTM/FDA
criteria. Particularly for suites with different magnet types, ‘MR Conditional’
labeling should include specific parameters for safety.
As an adjunct to conventional screening practices used for identifying
potential missile threats, MR safety experts are now recommending the use of
ferromagnetic-only detectors specifically developed for use in MRI facilities.
These devices identify only ferromagnetic objects that can be attracted to MRI
machines and, unlike conventional metal detectors, do not alarm on aluminum,
titanium, brass, or other metals that aren’t magnetically attracted.
|
|
Tip: MRI facilities may wish to consider siting ferromagnetic detection
systems to augment conventional screening. Ferromagnetic detection systems are
made available by several manufacturers in the U.S. and pricing varies on the
detector size, sensitivity, and format.
|
Clinical
MRI is touted as a safe modality because magnetism is non-ionizing and does not
carry the risks associated with examinations using conventional radiography,
computed tomography (CT) scans, or nuclear medicine devices. However, the
magnetic energy can present serious risks to persons with implants and medical
devices. (See Sidebar 3 on page 12 of the online version of this issue for a
partial list of devices and appliances that should trigger additional safety
questions.) Despite recent advances in pacemaker technology, no implanted
pacemaker device has yet been approved by the FDA as safe for MR examination.
For those implants, prostheses, and devices that have been identified as
conditionally safe to be scanned, manufacturer guidelines must be followed
precisely for issues such as field strength, gradients, RF deposition,
sequences, and coils.
It also is important to note that MRI safety protocols for implants and
medical devices are not always linear. Simply because a particular
configuration was tested safe under specific conditions at a magnetic field
strength of 3.0 Tesla, for example, does not mean that the device or scan is
comparably safe under other conditions, including at a lower magnetic field
strength. Some scans safe at 3.0 Tesla may be extremely hazardous when
performed at 1.5 Tesla or lower field strengths. It is for this reason that
manufacturer guidance is to be followed precisely for scanning patients with
conditionally safe devices or implants.
|
Tip: Prospectively identify the safety parameters of every implant,
prosthesis, and device before admitting persons into the controlled access
portions of the MRI suite. Maintain current reference materials and resources
to assess the safety of devices.
|
References
- NessAiver M.: DANGER! Flying Objects. Simply Physics. http://simplyphysics.com/
flying_objects.html (accessed Nov. 13, 2006).
- Food and Drug Administration: Manufacturer and User Facility Device
Experience
Database (MAUDE). http://www.fda.gov/cdrh/maude.html (accessed Nov. 13, 2006).
- American College of Radiology: ACR White Paper on Magnetic Resonance (MR)
Safety. http://www.acr.org/s_acr/bin.asp?TrackID= & S I D = 1
& D I D = 1 2 1 8 3 & C I D =1848&VID=2&DOC=File.PDF (accessed Nov. 13,
2006).
Source: Joint Commission Perspectives on Patient Safety, March
2006, Volume 6, Issue 3
http://www.jcrinc.com/33/