Getting into the Room: The MRI Environment & Implants, Pacemakers, etc.
Scott B Reeder1
1Radiology, University of Wisconsin, Madison, WI, United States

Synopsis

With the increasing number of implanted metallic devices in patients, as well as non-medical implants such as shrapnel or body piercings, MRI safety screening becomes more essential than ever. This presents an increasing challenge to ensure that patients undergoing this potentially lifesaving diagnostic exam can be performed in the safest manner and avoid injury to the patient. It is for this reason that it is essential that institutions develop standardized procedures that can address the existing and increasing number of metallic implants in a systematic way to ensure the safety of our patients.

Highlights

  • Metallic implants are increasingly common in patients undergoing MRI exams.
  • Rigorous and standardized safety screening is an essential part of delivering safe MRI care to our patients.
  • Whenever possible, the origin of metallic implants should be ascertained and manufacturer’s guidelines and/or should be followed for that specific implant.
  • In many circumstances, the identity of metallic implants may be unknown, including non-medical implants. There may be sufficient information, however, to categorize the implant into a general class of implant that guidance on whether an implant is safe or do, or under certain circumstances.
  • Institutions should develop standardized procedures for MRI in patients with implants of uncertain identity, in order to mitigate risk, while recognizing the need for potentially lifesaving diagnostic MRI exams.
  • Implanted electronic devices such as cardiac pacemakers are increasingly prevalent and pose an additional burden on the MRI staff to ensure the safe use of MRI in our patients.
  • The prevalence of metallic implants including IEDs will continue to grow and necessitates standardized institutional procedures to image patients safely through a standardized process.

Introduction

In this lecture, I will review one of the most important and growing safety related issues in MRI: MRI in patients with metallic implants. There is a large and growing number of metallic implants, including orthopedic hardware, and vascular, biliary, and GI stents, as well as a growing number of implanted electronic devices such as neurostimulators, insulin pumps, cardiac pacemakers, defibrillators, etc. Many of these devices can go into the MRI environment safely under certain conditions, while others are strictly contraindicated and pose a major safety hazard to the patient. Identifying the specific make and model implants prior to a patient entering the MRI environment is critical to maintain a safe environment. Further, patients often present with incomplete information, insufficient to accurately identify the specific implant prior to the MRI exam, which poses a significant challenge for patients who need an MRI exam as part of a lifesaving treatment. In this talk, we will review some of the standard approaches to appropriate MRI safety screening, and focus on how to address the common scenario where patients present with a metallic implant of unknown origin.

MRI Safety Screening

MRI safety screening procedures prior to patients entering the MRI environment is a critical step used universally at MRI facilities. This step is necessary to identify a variety of safety issues including metallic implants, contraindications to contrast agents, claustrophobia, etc. In this lecture, we will focus on metallic implants. Safety screening occurs at multiple levels, often at the time a referring physician orders an MRI with “hard stops” in the ordering system to identify known implanted devices such as cardiac implanted electronic devices (CIEDs). This provides a convenient pathway to quickly identify such patients who can be worked up by staff in the MRI department prior to the patient arrival in the MRI department. Regardless, a complete safety screening procedure should be in place at your institution and geared to identify any metallic implants.
Increasingly, safety screening is also being performed prior to the patient exam through online patient portals, which also provides a convenient manner for patients to list any potential contraindications or safety issues prior to arriving at the MRI suite. This is also a helpful way for the MRI safety staff to investigate any potential metallic implants of concern. Finally, it should be noted that it is always essential to perform a thorough safety screening review immediately prior to the MRI exam, in the event that a procedure was performed between the initial safety screening and the day of the MRI exam. Some institutions also perform a last minute “timeout” at the MRI suite door, prior to entering zone IV, to ensure that no metallic implants enter the MRI environment, such as keys, cell phones, etc. This lecture will focus on the specifics of MRI safety screening relevant to metallic implants.

Metallic Implants of Known Origin

Ideally, patients have detailed documentation in their medical records listing all relevant details of any implanted metallic devices, sufficient to determine whether or not patients are safe to enter the MRI scanner. In general, implants can be categorized into three general categories including MRI safe, MRI unsafe, and MRI conditional. The first two categories are self-explanatory. The third category, “MRI conditional”, implies that patients with such devices can undergo MRI safely, so long as the MRI exam is performed under specific conditions. Conditions may include a particular field strength and RF mode (eg. normal mode) to avoid excessive heating from RF deposition. Details about specific implants can be found at multiple resources including the manufacturer websites and packet inserts, as well as resources such as mrisafety.com and the American College of Radiology.
An important consideration is whether or not the particular metallic implant may interfere with the diagnostic quality of the scan. For example, an embolization coil that is be considered MRI safe or conditional may generate a large artifact that renders the exam non-diagnostic for the specific clinical or research question. In situations where this is strongly suspected or known a priori, consideration for cancelling the MRI exam should be made.
The ability to identify the specific make and model of metallic implants is the best way to ensure the safe use of MRI in patients with metallic implants. Therefore, it is incumbent upon those physicians performing procedures such as the implantation of stents, pacemakers, etc., to provide accurate documentation within the medical records as to the specific implant placed inside the patient. As providers of MRI, you are strongly encouraged to work with your referring physicians to ensure that they perform sufficiently detailed documentation to ensure that their patients have the safest access to MRI exams in the future.

Metallic Implants of Unknown Origin

Despite all efforts to identify the specific details of metallic implants, inevitably there are many circumstances where this is not possible. This includes situations where medical records are not available from other institutions, incomplete documentation about the specifics needed to identify the type of implant, as well as nonmedical implanted devices such as metallic shrapnel or cosmetic implants. Further, depending on the acuity of the urgency of the MRI exam, there may be insufficient time to obtain medical records for potentially lifesaving diagnostic procedures, eg. stroke MRI protocol. A risk-benefit analysis must be performed based on incomplete information. In many clinical situations, it may be to the patient’s significant detriment to deny the patient the MRI exam. This is an evolving topic, but I would strongly urge you to develop institutional guidelines on how to address this challenge. The following principles should be considered for scanning patients with metallic implants of uncertain identity:
  1. Good faith attempts should always be made to obtain written documentation of the specifics of any metallic implant placed by a physician.
  2. In circumstances where the identity of the metallic implant is known but there are no published literature on the specific implants, standardized approaches to MRI in patients with that implant may be useful and can be developed based on the approach described below.
  3. Published MRI safety guidelines should be followed as closely as possible, for example ACR MRI Safety Guidelines (JMRI 2020 51(2): 331-338).
  4. The need to obtain diagnostic information may outweigh the potential risk of injury. The standardized approach at your institution should be taken to mitigate this uncertainty as much as possible.
  5. The use of informed consent is a challenging, given that the risk of injury is unknown with an unknown implant. The use of informed consent should be determined at an institutional level.
  6. A successful prior MRI exam is not sufficient to “clear” any metallic implant of unknown identity. This principle applies broadly to MRI safety practices.
  7. Consideration should be given to limiting scanning to 1.5T and/or normal mode in patients with unknown implants. Please note, however, that some implants, particularly those with long strands of wire that can act as an antenna, may be less safe at 1.5T than higher field strengths.
  8. A standardized approach should be taken at your institution to avoid radiologist “shopping” in order to approve a patient for an MRI exam.
  9. The use of radiography or CT to identify the nature and identity of metallic implants is highly appropriate in many circumstances. For example, the make and model of CIEDs can usually be determined from a chest radiograph. Screening for metallic implants in unconscious patients who require an emergent MRI, using whole body radiography, is highly appropriate as an effective way to exclude or the identify specific implants such as GI clips and other stents, to determine their MRI safety.
  10. Hand magnets may be helpful to identify ferromagnetic materials that should not enter the MRI environment, eg. jewelry, but the lack of obvious torque with a hand magnet does not ensure a safe MRI exam, ie: this is helpful way to identify MRI unsafe superficial implants, but is not sufficient to classify metal as safe.
  11. In certain circumstances, consideration for alternative diagnostic methods such as CT should be considered, depending on the specific clinical question and the potential risk from the metallic implant.
  12. Individuals accompanying a patient into the MRI suite, eg. parent, should not enter zone 4 if they have a metallic implant of unknown identity.
  13. In general, subjects considered for research MRI exams who have metallic implants of unknown origin should not enter the MRI environment unless specific procedures have been taken to mitigate this risk, and such risk mitigation is approved under an appropriate IRB-approved protocol.
In most real-world circumstances some information about the metallic implant of unknown identify is often available. For example, patients often know the general class of implant (e.g. stent, pacemaker) as well as the general time frame of when the implant was placed but are often not be aware of the specific make and model. If the medical records are not available or are inadequate to identify the specific implant, the availability of general category of implant may be very helpful. General classes of implant may be adequate to determine the general safety of the implant, if an entire class of implant is known to be safe, or conversely if some implants in a general class are known to be unsafe. For example, in the United States, intrauterine devices (IUDs) are generally considered to be MRI safe and those patients with an IUD placed in the United States generally undergo MRI without knowing the specific make and model. However, some IUDs placed in other countries may have ferromagnetic materials that would be considered MRI unsafe. Thus, understanding the date and type of implant, as well as the origin of the implant, may be sufficient to categorize an implant as safe based on its category and specific details. Commonly encountered classes of implants and scenarios commonly encountered include:
  1. Intrauterine devices (IUDs).
  2. Orthopedic hardware.
  3. Coronary artery stents, as well as vascular, biliary, and GI stents.
  4. Cardiac valves.
  5. IVC filters and non-neuro embolization coils.
  6. Neuro-embolization coils.
  7. Shrapnel, nonmedical metallic foreign bodies.
  8. Unresponsive patients with inadequate medical records needed to confirm the absence of metallic implants.
  9. Otolaryngology implants including scleral buckles, ocular implants, cochlear implants, middle ear prosthesis.
  10. Metallic piercings, tattoos, and other metallic cosmetic materials/devices.
A systematic approach can be generated for each of the above categories in order to determine a safety procedure that mitigates risk to the patient. Comprehensive guidelines for all of these categories will not be discussed in this lecture due to time constraints, but illustrative examples will be shown. Each of these categories will require periodic review and updates and new devices in these categories are introduced into the market.

Special Considerations

There are many circumstances that necessitate additional considerations. For example, external fixator devices often present a special challenge. The main concern with external orthopedic fixators is the creation of current loops between the patient and external fixation devices in the MR environment. Scanning patients with external fixator devices may be feasible, depending on where the external fixation devices lies in the MRI environment. For example, a brain MRI with an external fixator in the lower leg may be feasible if the fixator is not ferromagnetic and is outside the magnet. For implants where there is a small but real potential for heating, the risk-benefit ratio will change depending on the level of consciousness of the patient. A fully alert patient may be able to report any heating to the MRI operator, and thus abort the MRI prior to any significant injury. However, a patient with impaired consciousness or under general anesthesia would be unable to report any heating and serious burns may be possible.
Patients often present to medical attention and are unable to provide adequate medical history, for example in a patient who is unconscious. Without updated medical records, it may not be possible to determine whether there are any metallic implants, medical or nonmedical, that make it safe for the patient to undergo MRI. In such circumstances whole body radiography may be appropriate to exclude any metallic devices, and if any are found, to identify the type of implant. All scenarios such as this should be considered as part of developing guidelines for scanning patients with metallic implants of unknown origin.

Pacemakers and Implanted Electronic Devices

Historically, MRI has been strictly contraindicated in patients with cardiac implanted electronic devices (CIEDs) due to concerns for torque on ferromagnetic devices, heating, and other adverse interactions within the MRI environment. However, two major developments have occurred in the past several years. First, many of the CIED manufacturers have developed regulatory body-approved MRI conditional devices. Typically, this implies imaging at 1.5T and in a reduced SAR mode. Second, there is a large and growing body of evidence that legacy CIEDs, i.e. those devices not approved as MRI conditional, can still be scanned safely in the MRI environment, so long as certain procedures are performed. As a result of numerous studies (eg. Heart Rhythm Society Guidelines, 2017, Heart Rhythm, 14(7), e97-e153), the use of MRI in patients with legacy CIEDs is rapidly growing and is now approved for payment by many payers. Specific details for MRI safety are rapidly being developed in the literature and are increasingly becoming commonplace.
In addition to cardiac IEDs, an increasing number of other implanted electronic devices such as neurostimulators, insulin pumps, and analgesia pumps are increasingly common in patients requiring MRI exams. In general, the specific origin of all implanted electronic devices must be known prior to MRI. No IED should ever undergo MRI without knowing the make and model of the implant and manufacturing guidelines should be followed. A detailed description of procedures for CIEDs and other IEDs is beyond the scope of this talk.

Summary

With the increasing number of implanted metallic devices in patients, as well as non-medical implants such as shrapnel or body piercings, MRI safety screening becomes more essential than ever. This presents an increasing challenge to ensure that patients undergoing this potentially lifesaving diagnostic exam can be performed in the safest manner and avoid injury to the patient. It is for this reason that it is essential that institutions develop standardized procedures that can address the existing and increasing number of metallic implants in a systematic way to ensure the safety of our patients.

Acknowledgements

No acknowledgement found.

References

No reference found.
Proc. Intl. Soc. Mag. Reson. Med. 28 (2020)