MR Hazard Summary

Introduction

Limitations: This MRI Hazard Primer only provides highlights and generalities ; those directly involved in MRI operations and safety should consider the "Sources" listed below

Outline

• Five Types of MR Hazards
• What Makes These Hazards Tricky?
• Recommendations Under Consideration
• Open Issues and Next Steps
• Addendum
• References

Five Types of MR Hazards

1. Projectile effect (magnetic material pulled toward the magnet bore)
   • Oxygen bottles, scissors, IV poles, patient lifts, traction weights, pens, stethoscopes, and hair barrettes
   • Hairpins near a 1.5 Tesla MR magnet can reach speeds of 40mph
2. Twisting (magnetic objects aligning parallel with the field - torque)
   • Magnetic cochlear implants and cerebral aneurysm clips twist within the body causing damage
   • Magnetic components rip loose from their foundation on equipment causing device failure or patient injury
3. Burns (generally caused by the use of electrically conductive material inside the bore)
   • Looped ECG leads, pulse oximeter cables, and MR accessories (e.g., RF coil leads) in contact with a patient under sedation can cause full thickness burns
   • While rare in occurrence, tattoos or tattooed eye-liner containing iron oxide have heated to cause minor burns
   • Skin burns at the sites where the pulse oximeter sensor touches and ECG electrode sites
   • Skin burns from contacting the bore of the magnet.
   • Inadvertent overly high settings for extremity exams have caused ignition of special cuffs/sleeves
4. Image artifacts (subtle changes to MRI image due to various factors)
   • RF emissions from equipment picked up by the MR RF receiver as noise)
   • All metals produce signal voids. Signal voids can mask pathology or be misinterpreted as pathology
5. Device malfunction (electronics or mechanics affected)
   • Devices with analog gauges, electric motors, transformers, relays, and switches can be affected by the static magnetic field.
   • Devices that use magnetization to attach to a patient (e.g., some dental devices) and some implants that are electrically, magnetically, or mechanically activated can be affected by the static magnetic field.
   • A PCA pump reversed flow, despite presenting normal displays to the user - a one-way valve stopped flow blood into the IV bag. A similar incident occurred with an insulin infusion pump.
   • A ventilator delivered inadequate inspiratory pressure.- Pacemakers can pace at the wrong point in the cycle and rapid pacing can occur due to RF field interactions.
   • ECG waveforms can be distorted (e.g., increased T-wave or ST segment) due to the static magnetic field interactions, and ECG signals can be misinterpreted (e.g., missed complexes) due to the gradient magnetic field interactions

What Makes These Hazards Tricky?

1. Large invisible magnetic fields that extend in 3 dimensions
2. It is impossible to tell by looking at an MR system whether it is "ON" or not
3. Many objects that don't appear to contain iron (or ferromagnetic/hazardous material)
• For example, sandbags - some contain ferrous materials even though one would not think so.
4. Labeling on devices or in documentation can be confusing
   • "MR safe" and "MR compatible" are specific to a particular MR environment. The terms are not intended to be used without further specifying the particular MR environment where the devices have been tested and found safe and compatible for.
• "MR safe" and "MR compatible" may not be with more powerful MRIs.
5. Combination of complacency, workarounds for speed, and diffuse responsibility
6. If you need to emergently shut off the MRI , there are hazards and $20,000-$500,000 cost
7. Equipment and consumables that are "safe" 99% of the time become "unsafe" near MRI
8. People and equipment who are "new" to MRI suite (more interventions and surgeries)
9. It is difficult and inaccurate to make "simple" lists of unsafe materials
   • In general, magnetic materials can become projectiles or twist in the bore (e.g., high carbon steel alloys, pure iron); and all metals conduct so they all can become hot or interfere with imaging in the bore. However, to be complete, you run more risks by compiling simple lists than diligently identifying and labeling items appropriate to enter the MR room and the bore.

Recommendations Under Consideration

REDESIGN:

1. use hand-held magnet to generally screen patient and other items (limited effectiveness)
2. identify and mark the 5 Gauss line
3. hang posters reminding patients and providers of hazards of all types in plain English
4. consider providing the patient with an MR compatible alarm device to alert staff

TRAINING:

1. initial and refresher training on MRI safety considerations for all personnel related to MRI, including emergency, transport, maintenance, housekeeping, and security
2. add conceptual and some practical training to radiology residents and fellows

PROCEDURAL:

1. appoint an MRI safety officer responsible for assuring that procedures are in effect and that they are carried out
2. carefully screen all personnel entering the MR environment for magnetic or conductive objects in, on, or attached to their bodies
3. maintain a database of MRI-safe and compatible equipment
4. if you buy a new MRI or upgrade an existing system, make sure labels of "safe" and "compatible" still apply
5. always assume the MRI magnet is "on" even if it appears idle
6. do not make assumptions about equipment (e.g., sand bags that actually contain iron). Err on the side of caution, assuming materials are not safe or compatible unless they are proven to be so
7. empower MRI tech to have control over access.
8. assume that blankets and clothes are hiding something missed during screening
9. 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)
10. place sensors and cables as far away from RF coils as possible.
11. periodically check sensor sites on unconscious patients for heating.
12. don't inadvertently make the patient's tissue a loop (e.g., don't position the patient's hand so that a finger touches the thigh)

PURCHASING:

1. all items purchased for use in or near MRI should have MRI compatibility established for that particular MR environment. In addition,
2. use manufacturer-approved fiber optic, carbon or graphite leads instead of conductive leads on medical devices
3. purchase sand bags that really contain sand for use at or near MRI

Open Issues and Next Steps

1. Responsibility for hazard reduction and patient/provider protection is shared among FDA, manufacturer, radiology management, MRI technicians, nurses and transport personnel, and patients and family members
2. If you do not know if your devices or implants are safe or compatible for your SPECIFIC MRI machine, you can take three steps:
   1. Read the technical information about the device or implant
   2. Call the manufacturer of the device or implant
   3. Call the manufacturer of the MRI machine
3. Benefits of costly interventions might be suspect because there are only scattered and relatively infrequent reports of death or serious injury - but underreporting of any adverse event is widely known
4. A working group of MR and patient safety experts from VA, other agencies, and some MRI manufacturers will convene to discuss the above issues and see how we all can develop understandable, effective, and usable recommendations

Addendum

American College of Radiology: PATIENT AND PERSONNEL SAFETY GUIDELINES

Safety guidelines, practices, and policies shall be written, enforced, documented, and reviewed at least annually by the supervising physician. These guidelines take into consideration potential interactions of the magnetic field with ferromagnetic objects in the environment of the scanner. They also consider potential hazards posed by objects implanted within the patient as well as within other individuals in the area 4 . Patient and personnel safety information should be maintained on site.

2) Terms are confusing - but the distinction is often important

a) ferromagnetic vs. magnetic: magnetic materials that are not ferromagnetic (e.g., diamagnetic and paramagnetic materials) can also be pulled into the bore. The force on magnetic materials that are not ferromagnetic is of smaller magnitude than the force on ferromagnetic materials - this is generally why we hear of the projectile effect being associated with ferromagnetic materials; however, just stating ferromagnetic would be inaccurate

b) safe vs. compatible: objects and devices that are not magnetically attracted, may not be "safe" in all instances - some compatible devices can be affected by the microwave or magnetic field - some compatible metals can still make a circuit and cause burns in certain situations. Also, - some MR compatible devices have restrictions to their compatibility. For instance, a device can be MR compatible but have certain gauss line restrictions (for instance, it may say can be used up to the 150 G line) or pulse sequence limitations (for instance, it may say which pulse sequences can/cannot be used). These restrictions must be adhered to for safe use in the MR environment

3) Why newer systems may add to the confusion

New 3 Tesla systems have been introduced - devices previously MR safe or compatible may not longer be with these new systems since many claims for compatibility were established with 1.5 T systems. Further, even upgrades to the same system could render previously safe or compatible devices unsafe or not compatible in the upgraded environment.

References

1. FDA's MRI Working Group report (1997)
2. ECRI. Use of equipment in the magnetic resonance (MR) environment. Health Devices. Draft, under review, to be published December 2001. (contact Lori King)
3. American College of Radiology (navigate to accreditation or standards)
4. Shellock FG. Magnetic resonance procedures: health effects and safety. Boca Raton, FL: CRC Press, 2001

Links

Flying Objects!

Vivid examples of what can happen when you bring metal objects near an MRI. Several interesting pictures of chairs and oxygen tanks that fly into the MR machinery.

VA National Center for Patient Safety Internet

NCPS Internet home available to the public.

American College of Radiology

Navigate to accreditation or standards

Diagnostic imaging online magazine

News article: Metal detector promises increased safety in MR suites.

ECRI. Use of equipment in the magnetic resonance (MR) environment. Health Devices.

Draft, under review, to be published December 2001.(contact Lori King)

FDA's MRI Working Group report (1997)

A Primer on Medical Device Interactions with Magnetic Resonance Imaging Systems

MRI Safety: Everyone's job by John D. Kerr

Very good Example of RCA activities for MRI Adverse Events at Hospital outside VHA

NE Wisconsin MRI Center MR Safety Precautions

Listing of many common metal implants and their MR compatibility.

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