MR Hazard Summary – AUGUST 2001 UPDATE
John Gosbee and Joe DeRosier
VA National Center for Patient Safety
734-930-5890 vaww.ncps.med.va.gov www.patientsafety.gov
Rationale: This magnetic resonance imaging (MR) Hazard
Primer is inspired by: 1) close calls formally and informally reported
within VA medical centers; 2) MR events in the public press and FDA MAUDE
database; 3) the fact that MR hazards are complex and not obvious; and
4) there is increasing amount of procedures and even surgeries provided
within MR suites
Limitations: This MRI Hazard Primer only provides highlights
and generalities; those directly involved in MRI operations and safety
should consider the “Sources” listed below
Sources: FDA Working Group Report and ECRI draft Primer
(see “References” section below for details); Discussions
with MR hazard experts at VA, FDA, ECRI, Marconi Medical Systems; Discussion
with MR technicians inside and outside the VA
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, work-arounds 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
NOTE: Most personnel dealing with an MRI-related event and MRI
safety experts agree the safety issues need to be dealt with as a systems
issue. That is, addressing one component of hazard reduction (e.g., training)
is an ineffective or a short-term fix.
REDESIGN:
a) use hand-held magnet to generally screen patient and other items (limited
effectiveness)
b) identify and mark the 5 Gauss line
c) hang posters reminding patients and providers of hazards of all types
in plain English
d) consider providing the patient with an MR compatible alarm device to
alert staff
TRAINING:
a) initial and refresher training on MRI safety considerations for all
personnel related to MRI, including emergency, transport, maintenance,
housekeeping, and security
b) add conceptual and some practical training to radiology residents and
fellows
Recommendations (cont.):
PROCEDURAL:
a) appoint an MRI safety officer responsible for assuring that procedures
are in effect and that they are carried out
b) carefully screen all personnel entering the MR environment for magnetic
or conductive objects in, on, or attached to their bodies
c) maintain a database of MRI-safe and compatible equipment
d) if you buy a new MRI or upgrade an existing system, make sure labels
of “safe” and “compatible” still apply
e) always assume the MRI magnet is “on” even if it appears
idle
f) 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
g) empower MRI tech to have control over access.
h) assume that blankets and clothes are hiding something missed during
screening
j) 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)
k) place sensors and cables as far away from RF coils as possible.
l) periodically check sensor sites on unconscious patients for heating.
m) 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:
a) all items purchased for use in or near MRI should have MRI compatibility
established for that particular MR environment. In addition,
b) use manufacturer-approved fiberoptic, carbon or graphite leads instead
of conductive leads on medical devices
c) 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:
a) Read the technical information about the device or
implant
b) Call the manufacturer of the device or implant
c) 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
CONTACT US!!!
Please notify NCPS if you have had close calls, you had discovered
unsafe materials that were a “surprise”, or especially if
you have discovered effective countermeasures
NCPS contact information: vaww.ncps.med.va.gov or www.patientsafety.gov
References:
1) FDA’s MRI Working Group report (1997) www.fda.gov/cdrh/ode/primerf6.html
2) ECRI. Use of equipment in the magnetic resonance (MR) environment.
Health Devices. Draft, under review, to be published December 2001. www.ecri.org
(contact Lori King)
3) American College of Radiology www.acr.org (navigate to accreditation
or standards)
4) Shellock FG. Magnetic resonance procedures: health effects and safety.
Boca Raton, FL: CRC Press, 2001
5) http://199.96.2.32/AHRAArticles/AHRAArticles.dll/Show?ID=272 -Very
good Example of RCA activities for MRI Adverse Events at Hospital outside
VHA
(Radiology Management Article)
Addendum:
1) Other Groups Provide Indirect Guidance
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 area4. 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.
|