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MR Hazard Summary
Lori King, Joe DeRosier, and John Gosbee**
- VA National Center for Patient Safety
INTRODUCTION
Rationale: This magnetic resonance (MR) Hazard Primer is inspired by:
- close calls formally and informally reported within VA medical centers,
- MR events in the public press and FDA’s Manufacturer and User Facility Device Experience (MAUDE) database,
- the fact that MR hazards are complex and not obvious,
- the increasing amount of procedures and even surgeries performed within MR suites, and
- MR systems with more powerful magnets being marketed to facilities
Limitations: This MRI Hazard Primer only provides highlights and generalities and deals primarily with issues pertaining to use of medical devices in the MR environment; those persons directly involved in MR operations and MR safety should consider the References and Web Resources listed below for more comprehensive information.
FIVE TYPES OF MR HAZARDS
- Projectile effect (also called missile effect; magnetic material pulled – often violently - toward the magnet bore)
- While this phenomenon is generally associated with ferromagnetic materials, magnetic materials that are not ferromagnetic (e.g., diamagnetic and paramagnetic materials) can also be pulled into the magnet bore. The force on magnetic materials that are not ferromagnetic is just of smaller magnitude than the force on ferromagnetic materials.
- Objects that have become projectiles in VA facilities: oxygen cylinder, IV pole, transport stretcher, traction weight, floor buffer, wheelchair, file cabinet, drill, and patient walker. Other items that have been reported to become projectiles in the MR environment include patient lifts, stethoscopes, infusion pumps, pulse oximeters, tools, laundry carts, scissors, pens, hair barrettes and more.
- Paper clips and hairpins near a 1.5 Tesla (T) MR magnet can reach speeds of 40 mph.
- The projectile effect can be and has been fatal, can cause significant equipment damage and therefore can be costly, can cause a quench of the magnet (release of the magnet’s cryogen), and can result in downtime for MR facilities.
- The average cost of a projectile incident in VA is $43,172. The financial and marketing costs of lawsuits must also be considered.
- Twisting (also known as torque; magnetic objects aligning parallel with the MR system’s magnetic field)
- Magnetic cochlear implants and cerebral aneurysm clips can twist within the body causing damage. This can be fatal.
- Magnetic components can rip loose from their foundation on equipment causing device failure or patient injury.
- Burns (generally caused by heating of electrically conductive material inside the bore of the magnet)
- Looped and unlooped electrocardiogram (ECG) leads, pulse oximeter cables, and MR accessories (e.g., radio frequency (RF) coil leads) in contact with a patient under sedation can cause full thickness burns, some requiring plastic surgery.
- Skin burns have resulted at sites where pulse oximeter sensors and ECG electrodes have touched the patient’s skin.
- Patients have received skin burns from contact with the magnet’s RF coils or the bore of the magnet.
- Skin burns have resulted from conductive loops formed with the patient’s body (e.g., patient’s finger touched their thigh; patient’s arms were crossed; patient’s thighs were touching).
- While rare in occurrence, tattoos or tattooed eye-liner containing iron oxide have heated to cause minor burns.
- Image artifacts (changes to MRI images due to various factors)
- RF emissions from equipment picked up by the MR RF receiver can result in image artifacts (e.g., decrease in contrast, stripes on image).
- The presence of metals near the imaging site (e.g., mascara, metal biopsy needles) can produce image artifacts (e.g., signal voids, distortion of image). Signal voids, for instance, can mask pathology or be misinterpreted as pathology.
- Terminology used to describe whether a device is suitable for the MR environment has changed and can cause confusion. New terminology ( MR Safe , MR Conditional , and MR Unsafe , as defined in the American Society of Testing and Materials (ASTM) Standard F2503-05) has replaced old MR terminology (MR safe and MR compatible, as defined in the 1997 FDA's MRI Working Group report on medical device interactions with MR systems). (See References for both of these documents.)
- The new MR Safe and the old MR safe terms have very different meanings. MR Safe (the new labeling, as defined in ASTM F2503-05) indicates that the device is safe - period; it poses no risks in any MR environment. MR safe (the old labeling) meant that the device was safe for use in a particular MR environment. Bringing a device with an old marking of MR safe into the MR environment and expecting it to be MR Safe (according to ASTM F2503-05) could have catastrophic results. Hence, ensure devices and equipment are labeled according to the new terminology laid out by ASTM F2503-05. Devices with icons (as laid out in ASTM F2503-05 and shown below) indicate new terminology is being used.
- The term MR Unsafe (according to ASTM F2503-05) indicates the device would be unsafe in any MR environment.
- The term MR Conditional (according to ASTM F2503-05) indicates that the device poses no known hazards in a specified MR environment (specific field strength, spatial gradient, RF pulse limitations, and specific absorption rate). In other words, the safety of the device is conditional upon a specific MR environment; MR Conditional devices may not be MR Conditional with more powerful or upgraded MR systems.
- MR Conditional data is not easily extrapolated. Just because a device is MR Conditional for a 1.5 T system doesn’t mean it will be MR Conditional for a 3 T system, and vice-versa.
MR Safe
or
MR Conditional
MR Unsafe
NOTE: Symbols may also appear in black and white.
- It is difficult and inaccurate to make "simple" lists of unsafe materials.
- In general, ferromagnetic materials (e.g., high carbon steel alloys, pure iron) can become projectiles or twist in the bore, and all metals are conductors so they all can become hot or interfere with imaging in the bore. However, you run more risks by compiling “simple” lists than diligently identifying and labeling items appropriate to enter the MR scan room and the bore.
- New 3 Tesla systems have been introduced.
- Devices previously labeled MR Conditional (according to ASTM F2503-05) may no longer be MR Conditional with these newer, more powerful systems since many claims for MR Conditional were established with 1.5 T systems. Further, even upgrades to the same system could render a previously MR Conditional device unsafe in the upgraded environment.
- Projectile incidents are more likely to occur and ferromagnetic implanted objects are more likely to move or rotate with these stronger magnets. Close calls that you may have had in the past with 1.5 T MR systems could translate into major incidents with 3 T MR systems.
- Benefits of costly interventions might be difficult to envision because there are only scattered and relatively infrequent reports of death or serious injury; however, incident data is under-reported. Many near misses that don’t cause injury to the patient or staff go unreported.
RECOMMENDATIONS
NOTE: Most personnel dealing with an MR-related event and MR safety experts agree that safety issues need to be dealt with as systems issues. That is, simply addressing only one component of hazard reduction (e.g., training) is an ineffective or a short-term fix.
REDESIGN :
a. identify and physically mark the 5 Gauss line that identifies the MR environment, and do not allow any equipment past this line, unless it is proven to be suitable for your particular MR environment b. hang posters reminding patients and providers of the hazards in the MR environment in plain English. Ensure that items used to hang the posters are suitable for the MR environment. c. design MR suites for safety
- consider installing ferromagnetic detectors. Note however, that the detectors should only supplement screening patients; they should never take the place of screening. And, while they will detect a ferromagnetic oxygen cylinder, they
f. have patients don hospital-provided gowns, acceptable for the MR environment, and provide them with lockers for their belongings
g. use a hand-held magnet to screen objects on or accompanying patients and other items that need to be brought into the MR environment. Note that this has limited effectiveness; for example, ferromagnetic springs within a pillow have gone undetected with a hand-held magnet.
h. maintain a database of MR Safe and MR Conditional equipment (according to ASTM F2503-05) and label devices appropriately
i. if you buy a new MRI or upgrade an existing system, make sure the label of MR Conditional still applies
j. do not make assumptions about implants, devices, or equipment (e.g., sand bags that actually contain iron). Err on the side of caution, assuming materials are not suitable for the MR environment unless they are proven to be so. If you do not know if your implants, devices or equipment are MR Conditional, MR Safe, or MR Unsafe, you can take three steps: a. Read the technical information about the device or implant b. Call the manufacturer of the device or implant and obtain information regarding the suitability of the device in the MR environment in writing c. Call the manufacturer of the MR system
k. assume that blankets and clothes are hiding something missed during screening (e.g., oxygen cylinder, sandbag)
l. don't loop conductive leads or cables, don't allow cables to cross over one another, don't let cables touch the magnet bore and if possible, don't let cables touch the patient (other than where they have to)
m. place sensors and cables as far away as possible from RF coils and the magnet bore
n. remove all unnecessary conductors from inside the magnet bore
o. do not let the patient contact the magnet bore; provide insulation between the two if needed
p. periodically check sensor sites on unconscious patients for heating
q. don't inadvertently make the patient's tissue a loop (e.g., don't position the patient's hand so that a finger touches their thigh)
r. periodically check sedated patients for heating at sensor sites
s. conduct codes outside the MR environment (i.e., move the patient out of the MR scan room)
t. report not only serous incidents but also close calls to NCPS. Report serious incidents to FDA as well.
u. ensure cryogen vent systems are adequately designed, as minimum design requirements have been revised by some MR system suppliers, and inspect the cryogen vents at least annually
PURCHASING :
a. all items purchased for use in or near the MR environment should be suitable for your particular MR environment b. use manufacturer-approved fiber optic, carbon fiber or graphite leads instead of conductive leads on medical devices c. use manufacturer-approved large surface area, low impedance ECG electrodes d. purchase sand bags that really contain sand and pillows without magnetic springs for use within or near the MR system e. consider providing the patient with an alarm device suitable for the MR environment to alert staff
THE BOTTOM LINE
The MR environment presents many challenges for safety. Responsibility for hazard reduction and patient/provider protection is shared among FDA, manufacturer, radiology management, MRI technicians, nurses, transport personnel, patients, family members, and more. While it is impossible to eliminate risk in the MR environment, addressing the various components of hazard reduction - redesign, procedural, purchasing, and training - will work toward mitigation of the risks. Considering the actual costs of incidents, along with the financial and marketing costs of lawsuits, it relatively easy to make a case for MR safety.
REFERENCES
- Kanal et al. ACR guidance document for MR safe practices: 2007. AJR 2007 June; 188:1-27.
- ECRI Institute. What’s new in MR safety. Health Devices 2005 Oct; 34(10):333-
- American Society of Testing and Materials (ASTM) International. Standard practice for marking medical devices and other items for safety in the magnetic resonance environment. ASTM F2503-05. 2005.
- ECRI Institute. The safe use of equipment in the magnetic resonance environment. Health Devices 2001 Dec; 30(12), 421-444.
- FDA's MRI working group report (1997). www.fda.gov/cdrh/ode/primerf6.html
- Shellock FG. Magnetic resonance procedures: health effects and safety. Boca Raton, FL: CRC Press, 2001.
Patient Death Illustrates the importance of Adhering to Safety Precautions in Magnetic Resonance Environments
ECRI Institute free (no subscription required) Hazard article, “Patient Death Illustrates the Importance of Adhering to Safety Precautions in Magnetic Resonance Environments” outlining recommendations for preventing the projectile effect. (2001)
MRI Safety: Everyone’s Job
Good example of RCA activities based upon an MR close call at a facility outside of VHA (2001).
A Primer on Medical Device Interations with Magnetic Resonance Imaging Systems
FDA’s CDRH Magnetic Resonance Working Group report (1997): A Primer on Medical Device Interactions with Magnetic Resonance Imaging Systems
