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MEDICAL DEVICES AND ACCESSORIES
DEVELOPED
FOR USE IN THE MR ENVIRONMENT AND
INTERVENTIONAL MRI PROCEDURES
Frank G. Shellock, Ph.D.
Adjunct Clinical Professor of Radiology, University of Southern California
Founder, Institute for Magnetic Resonance
Safety, Education, and Research
The
increasing capabilities of magnetic resonance (MR) studies to impact
medical diagnosis and prognosis has dramatically increased the number
of MR procedures performed worldwide. Many more patients, especially
those in high-risk or special population groups, are undergoing MR examinations
for an ever-widening spectrum of medical indications.
Additionally,
as Jolesz et al. have stated, continuous progress has been made to expand the
use of MRI beyond diagnosis into intervention. This has resulted in the
development and performance of innovative procedures that include
percutaneous biopsy (e.g., breast, bone, brain, abdominal), endoscopic
surgery of the abdomen, spine, and sinuses, open brain surgery, and MR-guided
monitoring of thermal therapies (i.e., laser-induced, RF-induced, and
cryomediated procedures).
Various vendors and
manufacturers, prompted by recommendations and requests from MR healthcare
professionals, have recognized the need for developing specialized medical
devices, equipment, accessories, and instruments necessary for use in the MR
environment and for interventional MRI procedures. Accordingly, there are now
numerous patient support devices and accessories that have been developed and
which have undergone thorough evaluation to assess and verify appropriate use
in the MR environment or during interventional MRI procedures.
In consideration of the many devices and accessories that are
commercially-available for safe use during MRI procedures, it is surprising
that incidents and accidents related to ferromagnetic projectiles, excessive
heating of devices, and other problems continue to occur. These have resulted
in at least one fatality, several injuries, substantial damage to MR systems,
and down-time (i.e., loss of revenue) for MRI centers.
Therefore, the intent of this article is to review the various devices and
accessories that are specifically designed for use in the MR environment or
for interventional MRI procedures, with the hope that this information will
help prompt MR healthcare professionals to recognize the many products that
exist and which are essential to ensure patient safety. In addition, these
devices and accessories may help to create a more efficient or more profitable
MR center.
Non-Magnetic Oxygen & Gas
Cylinders. According to Chaljub et al.,
accidents related to ferromagnetic oxygen tanks and other gas cylinders that
become projectiles may be increasing. Therefore, MR facilities should devise
an appropriate policy for delivery of oxygen or other gases to patients
undergoing MR procedures. The use of non-magnetic (usually aluminum) oxygen
and other gas cylinders is one means of maintaining a risk free MR
environment with regard to this equipment (Figure 1).
Figure 1. Non-magnetic
oxygen tanks of various sizes (Magmedix, Gardner, MA).
It should be noted that nonmagnetic tanks must
be prominently labeled to avoid confusion with magnetic cylinders.
Furthermore, all healthcare workers that work in and around the MR
environment must be informed regarding the fact that only nonmagnetic oxygen
and other gas cylinders are allowed into the MR system room.
Nonmagnetic
oxygen regulators, flow meters, cylinder carts, cylinder stands, cylinder
holders for wheelchairs, and suction devices are also commercially available
to provide safe respiratory support of patients in the MR environment.
Patient Comfort Devices. Certain patients who undergo MRI
procedures experience emotional distress that can range from mild anxiety to
a full-blown panic attack. Patient
distress contributes to adverse outcomes for the MRI procedure that includes
unintentional exacerbation of patient anxiety, a compromise in the quality and,
thus, the diagnostic power of the imaging study, and decreased efficiency of
the imaging facility due to delayed, cancelled or prematurely terminated
studies.
Fortunately,
there are a variety of techniques that can help minimize these problems for
patients. For example, special systems can be used during MRI procedures to
manage the anxious patient such as MR-compatible headphones to provide music
to the patient (which also reduce gradient magnetic field-induced noise) and
MR-compatible video systems that provide a visual distraction to the patient.
There is even a virtual reality environment system that provides audio and
visual distraction to the patient
(Figure 2). A similar device is designed for use in fMRI procedures.
Figure 2. Specialized equipment
used to provide virtual reality environment and for fMRI studies (Resonance
Technology, Inc., Northridge, CA).
Monitoring
Equipment. In general, monitoring during an MRI examination is
indicated whenever a patient requires observations of vital physiologic
parameters due to an underlying health problem or whenever a patient is
unable to respond or alert the MRI technologist or other healthcare worker
regarding pain, respiratory problem, cardiac distress, or other difficulty
that might arise during the examination. In addition, a patient should be
monitored if there is a greater potential for a change in physiologic status
during the MR procedure.
In 1992, the Safety Committee of the
Society for Magnetic Resonance Imaging published guidelines and
recommendations concerning the monitoring of patients during MR procedures.
This information indicates that all patients undergoing MR procedures should,
at the very least, be visually and/or verbally (e.g., intercom system)
monitored, and that patients who are sedated, anesthetized, or are unable to
communicate should be physiologically monitored and supported by the
appropriate means.
Of note is
that guidelines issued by the Joint Commission on Accreditation of Healthcare
Organizations (JCAHO) indicate that patients that receive sedatives or
anesthetics require monitoring during the administration and recovery from
these medications.
Additionally, there must be policies and procedures implemented to
continue appropriate physiologic monitoring of the patient by trained
personnel after the MRI procedure is performed. This is especially needed for
a patient recovering from the effects of a sedative or general anesthesia.
Conventional monitoring equipment and
accessories were not designed to operate in the harsh magnetic resonance (MR)
environment where static, gradient, and radio frequency (RF) electromagnetic
fields can adversely effect or alter the operation of these devices. However,
various physiologic monitors and other patient support devices have been
developed or specially-modified to perform properly during MRI
procedures. Besides patient
monitoring, various support devices and accessories may be needed for use in
the high-risk patient to ensure safety. Many of these likewise have been
modified or designed to be safe to use in the MR environment or during
interventional MRI procedures.
Emergency-Related Equipment. Emergencies can and do happen in the MR environment. Therefore,
the development and regular practice of an emergency plan that addresses and
defines the activities, use of equipment, and other pertinent issues
pertaining to a medical or other emergency are important for patient safety
in the MR setting.
For example,
a specific plan needs to be developed for handling a patient if there is the
need to perform cardiopulmonary resuscitation in the event of a cardiac or
respiratory arrest. This includes having a means to immediately remove the
patient from the MR system to a place outside the MR environment to properly
conduct CPR, allowing the use of necessary equipment such as a cardiac
defibrillator. For this reason, it may be necessary to have a stand-by
nonmagnetic stretcher or gurney available that can be used to quickly
transfer the patient (especially for MR systems that do not have tables that
separate from the MR system or that quickly disengage).
Notably, the
healthcare professionals that are members of the Code Blue team, (i.e.,
responsible for establishing and maintaining the patient’s airway,
administering drugs, recording events, and conducting other emergency-related
duties) must be identified, trained in MR safety, and continuously practiced
in the performance of these critical activities relative to the MR
environment.
For
instances when it may not be possible to remove the patient from the MR
system room during an emergency, especially if the patient is experiencing a
respiratory or cardiac arrest, it is advisable to have various nonmagnetic
devices and accessories readily available including an oxygen cylinder, laryngoscope,
suction system, stethoscope, blood pressure manometer, and other similar
emergency equipment that is appropriate for the MR environment.
MR Contrast
Agent Injection Systems. The
controlled, power injection of MR contrast agents is gaining in popularity
for a variety of clinical applications including examinations of abdominal
organs, vascular anatomy, and dynamic MRI studies of the breast. Power
injectors must be able to operate in the MR environment without affecting
magnet homogeneity, degrading signal-to-noise, or causing artifacts. To date,
two devices are available for power delivery of MR contrast agents: the
Optistar MR Contrast Delivery System (Mallinckrodt, St. Louis, MO) and the
Spectris MR Injection System (Medrad, Inc., Indianola, PA).
MRI
Compatible Ventilators. Devices used for ventilation of patients typically contain
mechanical switches, microprocessors, and ferromagnetic components that may
be adversely affected by the electromagnetic fields used by MR systems.
Ventilators that are activated by high-pressure oxygen and controlled by use
of fluidics (i.e., no requirements for electricity) may still have
ferromagnetic parts that can malfunction as a result of interference from MR
systems.
MR-compatible
ventilators have been modified or specially designed for use during MRI
procedures that are performed in adult as well as neonatal patients. These
devices tend to be constructed from non-ferromagnetic materials and have
undergone pre-clinical evaluations to ensure that they operate properly in
the MR environment, without producing artifacts on MR images. There are at
least two sources of respirators for patients that require respiratory
support in the MR environment. These devices have been tested in association
with MR systems operating at 1.5-Tesla or less
(Figure 3).
Figure 3. The Omni-Vent Series D Ventilator used for respiratory
support of patients in the MR environment (Magmedix, Garner, MA).
Basic
Patient Management Accessories and Equipment.
All new and existing MR facilities should be prepared to
handle patients and everyday situations (e.g., maintenance) in the MR
environment by obtaining a selection of nonmagnetic or other suitable
accessories or equipment. For example, useful items for an out-patient
facility include nonmagnetic equipment such as a wheelchair (one or more),
stretcher or gurney, step stool, IV pole, laundry cart, stethoscope, blood
pressure manometer, storage or utility care, fire extinguisher, and custodial
cart (Figures 4 and 5).
Figure 4. Examples
of nonmagnetic devices and accessories developed or modified for use in the
MR environment.
Figure 5. Non-magnetic
custodial cart (the wheels, casters, and bucket handle are all nonmagnetic).
A nonmagnetic mop handle and mop head clamp should be used with this
equipment.
MR facilities that handle both out-patients and in-patients should
additionally consider obtaining a nonmagnetic patient slider board,
physiologic monitoring equipment (e.g., fiber-optic pulse oximeter),
nonmagnetic oxygen tank (including nonmagnetic regulator, cart or stand),
portable suction, Mayo stand, and other devices and accessories.
Of
note is that MR centers should have a sufficient number of nonmagnetic oxygen
tanks and fire extinguishers in the immediate and general area to prevent
responding emergency staff members from introducing ferromagnetic objects
into the MR environment. In fact, some hospital-based MR centers have
nonmagnetic oxygen tanks and fire extinguishers used throughout their
buildings to prevent projectile accidents.
Biopsy
Needles, Biopsy Guns, and Tissue Markers. Interventional MRI
has been used to guide tissue biopsy and apply markers with encouraging results.
Obviously, the performance of these specialized procedures requires tools
that are compatible with MR systems. Many conventional biopsy needles, biopsy
guns, and tissue markers have been evaluated with respect to compatibility
with MR procedures, not only to determine ferromagnetic qualities but also to
characterize imaging artifacts. The results have indicated that most of these
are not useful for MRI-guided biopsy procedures due to the presence of
excessive ferromagnetism and associated imaging artifacts that limit or
obscure the area of interest. Fortunately, several biopsy needles and biopsy
guns have been constructed out of nonferromagnetic materials specifically for
use in interventional MRI procedures. These are now commercially available from
various vendors.
The placement of a marking clip or wire
enables the accurate localization of the surgical excision site and is a
useful surrogate target, even if the entire lesion is removed and there is a
subsequent need for wire localization prior to surgery. Marking clips and wires have been
specially designed for use in interventional MRI procedures.
Surgical
Instruments. Interventional MRI procedures
have evolved into clinically viable techniques for a variety of minimally
invasive surgical and therapeutic applications. Besides the typical MRI
safety concerns, there are possible hazards in the interventional MRI
environment related to the instrumentation and accessory equipment that must
be addressed to ensure the safety of MR healthcare practitioners and
patients. Surgical instruments are an obvious necessity for interventional
MRI procedures. However, many of these instruments are made from metallic
materials that can create substantial problems in association with
interventional MRI procedures.
The interventional MRI
safety issues that exist for a surgical instrument include unwanted movement
caused by magnetic field interactions (e.g., the missile effect,
translational attraction, torque), heating generated by RF power deposition,
and artifacts associated with the use of the instrument, if it is in the
imaging area of interest during its intended use. To address these various
problems, surgical instruments have been developed that do not present a
hazard or additional risk to the MR healthcare practitioner or patient in the
interventional MRI environment ( Figure
6).
Figure 6. MR-compatible surgical
instruments (Aesculap, Center Valley, PA).
REFERENCES
Chaljub G, et al. Projectile
cylinder accidents resulting from the presence of ferromagnetic nitrous oxide
or oxygen tanks in the MR suite. American Journal of Roentgenology
2001;177:27-30.
Food and Drug
Administration, Guidance for the Submission Of Premarket Notifications for
Magnetic Resonance Diagnostic Devices, Document issued on: November 14,
1998.
http://www.fda.gov/cdrh/ode/95.html
http://www.MRIsafety.com
Holshouser B, Hinshaw DB, Shellock FG. Sedation,
anesthesia, and physiologic monitoring during MRI. Journal of Magnetic
Resonance Imaging, 3: 553-558, 1993.
Jolesz FA, et al. Compatible instrumentation for
intraoperative MRI: expanding resources. Journal of Magnetic Resonance
Imaging, 1998;8:8-11.
Kanal
E, Shellock FG. Policies, guidelines, and recommendations for MR imaging
safety and patient management. Patient
monitoring during MR
examinations. Journal of Magnetic
Resonance Imaging, 1992;2: 247-248.
Keeler EK, et al.
Accessory equipment considerations with respect to MRI compatibility. Journal
of Magnetic Resonance Imaging, 1998;8:12-18.
Shellock FG. Magnetic
Resonance Procedures: Health Effects and Safety. CRC Press, Boca Raton, FL,
2001.
Shellock FG. Guide
to MR Procedures and Metallic Objects: Update 2001. Seventh Edition,
Lippincott Williams & Wilkins Healthcare, Philadelphia, 2001.
Shellock FG. Reference
Manual for Magnetic Resonance Safety: 2002 Edition. Amirsys, Inc., Salt Lake
City, Utah, 2002.
Shellock
FG. Surgical instruments for interventional MRI procedures: assessment of MR
safety. Journal of Magnetic Resonance Imaging, 2001;13:152-157.
Shellock FG, Crues JV.
Commentary: MR safety and the American College of Radiology White Paper.
American Journal of Roentgenology, 2002;178:1349-1352.
Shellock FG, Shellock VJ. Metallic marking clips used
after stereotactic breast biopsy: ex vivo testing of ferromagnetism, heating,
and artifacts associated with MRI. American Journal of Roentgenology,
1999,72:1417-1419.
FIGURE LEGENDS
Figure 1. Non-magnetic
oxygen tanks of various sizes (Magmedix, Gardner, MA).
Figure 2. Specialized equipment used to
provide virtual reality environment and for fMRI studies (Resonance
Technology, Inc., Northridge, CA).
Figure 3. The
Omni-Vent Series D Ventilator used for respiratory support of patients in the
MR environment (Magmedix, Garner, MA).
Figure 4. Examples of nonmagnetic devices
and accessories developed or modified for use in the MR environment.
Figure 5. Non-magnetic
custodial cart (the wheels, casters, and bucket handle are all nonmagnetic).
A nonmagnetic mop handle and mophead clamp should be used with this
equipment.
Figure 6. MR-compatible surgical
instruments (Aesculap, Center Valley, PA).
*
Excerpted from article on DiagnosticImaging.com with permission of Shellock
R&D Services Inc. and Frank G. Shellock, Ph.D.
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