Scanning the Unscannable: MRI Safety for Patients with Implanted Medical Devices

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2019

By Matt Skoufalos

Historically, most conversations about patient safety in medical imaging have focused on how to limit their exposure to unnecessary ionizing radiation, the differences in treating pediatric and pregnant patients, or the importance of routine equipment maintenance and calibration. The bulk of those concerns have centered on modalities like computed tomography (CT) and X-ray, which employ ionizing (i.e., possibly harmful) radiation, but don’t necessarily apply to patients headed for ultrasound or magnetic resonance imaging (MRI) studies.

However, as the use of these modalities is expanded to a broader number of applications, a new wrinkle has emerged: how to safely image the growing number of patients with implanted medical devices and replacement joints.

These foreign bodies can interact differently with the energy fields produced by an MRI scanner, producing artifacts on the studies themselves, interfering with the normal operation of the implanted devices themselves, or possibly harming the patient by shifting them in the body. As the number of patients who receive a new hip or a stent or an insulin pump continues to climb, closer attention is starting to be paid to the composition of these materials and the effects of their interaction with imaging equipment.

At the simplest level, clinical sites can establish patient protocols around the use of MRI equipment, but for the most part, patients are responsible for self-disclosing what and whether they have an implanted device, said Chris Farischon, the 1.5T product systems product manager for Siemens Healthineers of Malvern, Pennsylvania.

“I was scanned at a site recently, and was given an iPad and 30 questions to run down, and they got very specific as far as what types of implants did I have,” Farischon said. “Based on that screening, the site may make a determination as to whether that patient can be scanned under MR.”

Before undergoing any medical imaging, a patient typically will change into a dressing gown, removing any clothing, jewelry, or accessories containing metal. Some sites may pass patients through metal detectors before scanning them, or may wand them with a handheld detector. But not every implanted device is made of a ferrous (iron-derived) metal, and some metals are safe to scan within certain energy thresholds.

“A lot of this is dependent on the type of implant that the patient has,” said Phillip Uptmor, Siemens Healthineers MR Clinical Product Manager for the Southeast Zone. “It’s also dependent on the hardware that you’re using to scan that patient. The [implant] manufacturers basically look at where the object is in the magnet, and how attractive it is to the magnetic field [of the MR unit].”

Also of concern is whether an implantable device is active, like a pacemaker, or passive, like a replacement knee. Some of these may interact adversely with the various energy sources at work in an MR scanner, while others may simply distort the image acquired in the study. The strength of the scanner (most devices are only cleared for use with 1.5-Tesla scanners, but the most powerful machines on the market can operate at nearly five times that strength) is another factor.

Given the perceived risks of patient injury and the expense involved in damaging some of the most expensive equipment in the hospital, most clinicians and technologists err on the side of caution, and are more likely not to image a patient with an implanted device than to send one through a potentially hazardous scan.

“I think medical communities have become very cautious,” Uptmor said. “You could very well have a patient show up that has an aneurysm clip, they don’t know that they have it, or they don’t know what the material is made of, and that clip could twist [during an MR study], and the patient could suffer serious injuries.”

There are some technological solutions to avoid the image distortion and artifact-generating side effects of scanning orthopedic implants, Farischon said. Siemens artifact reduction software Advanced WARP includes Slice Encoding for Metal Artifact Correction (SEMAC), which preserves soft tissue diagnostic quality in patients with metal implants, and its Implant Suite for the MAGNETOM Aera MR scanner enables diagnostic imaging for patients with MR-conditional (able to be scanned within certain parameters) implants.

Ultimately, it’s up to the individual sites, and sometimes the individual technologists and radiologists, to decide who gets a study and who doesn’t, and training and protocols in this area are decidedly uneven.

“Training until recently has been left to facilities, and facilities don’t always provide the best or most consistent training,” Uptmor said. “Historically outpatient centers are more cautious with implants due to staffing and resources; if an outpatient clinic isn’t sure, they just won’t perform the study.”

“I think it’s a really big issue right now, and there is a huge effort to ensure MRI techs are properly trained and equipped to handle conditional devices in the MR environment,” he said.

The issue is one that will only become more relevant to resolve as clinical applications for MRI continue to expand, and the patient population for them with it. Imaging more and different (and aging) patients means more of them will have implanted medical devices, which necessitates that procedures around safe scanning must improve.

“We have to get better at it than we have been,” said radiology consultant Tobias Gilk. “Unfortunately for patients with devices, every technological innovation of MR only serves to increase the risk factors. We want to use MR for a greater variety of examination types, a greater variety of patient types, and we’re doing it on magnets that are stronger, faster, more powerful.”

“All of these inputs are incrementally ratcheting up the relative risk, and we really need to have a more comprehensive strategy as to how we’re going to not simply play catch-up, which we’ve been playing for the past 20 years, and get ahead of changes in the marketplace,” he said.

According to Gilk, the biggest holdup in resolving the issue is the lack of a comprehensive dialogue between the manufacturers of MR systems and those of medical devices.

“When a set of MR conditions may appear to be absurdly restrictive, is that restrictive nature really a safety issue, or really a liability management issue on the part of the manufacturer, or a limitation of how the device was tested?” Gilk said.

“They may say, ‘This is too risky, we want to cancel this patient,’ or they may say, ‘We’ll do the exam in this super-restrictive mode, and therefore we’re going to limit the amount of clinical information that we’re going to get from this scan, so we compromise the effectiveness of the MR scan,’” he said.

Gilk believes that the more those changes are made to existing imaging protocols to accommodate patients with implanted devices, the greater the chance that their exams will take more time, throwing scheduling and workflow out of whack, or making the studies less effective or less efficient to provide.

“There are all kinds of downstream consequences to these events,” he said.

Gilk would like to see product support documentation that focuses less on insulating manufacturers from legal risk and more on supporting technologists in safely scanning patients with technical complications.

“Unless you can match up magnet information with vendor implant information, the people in the middle are left being the Rosetta Stone, trying to bridge the gap,” Gilk said. “That gap can be fairly small and easy to bridge, or it can be enormous. It’s really the MR techs and the radiologists who have to say, ‘Yes, I feel comfortable imaging this patient.’”

Until device-makers resolve that disconnect, traversing that gulf is the responsibility of clinical care providers, who must digest the information from both sets of manufacturers in the context of each individual patient. Further complicating matters, clinicians that call either camp for advice on the interaction of specific devices with one another, are only allowed to receive FDA-approved guidance from the manufacturers. If their questions fall outside that guidance, vendors may simply decline to answer.

“Even if the exam that the site wants to do is much safer in the grand scheme of things, the manufacturer can’t say so to the customer because it’s a medical use that has not been vetted and approved by the FDA,” Gilk said. “It’s not only just a question of not wanting the liability; it’s also a question of the way that our system is set up. Readily knowable truths about risk can’t be communicated to the providers because of the way that the FDA regulates product information.”

“Providers are clamoring for information on these systems, and the two people they would turn to for help are legally prevented from providing them with that assistance,” he said. “The immediate solution is improving the skills of the clinical personnel.”

The chief agency credentialing health care professionals in safe MR operation is the American Board of Magnetic Resonance Safety (ABMRS), an independent, not-for-profit organization founded in 2014 by radiologist Emanuel Kanal of the University of Pittsburgh Medical Center. ABMRS provides Magnetic Resonance Safety Certified (MRSC) credentials for professionals charged with overseeing the safety of magnetic resonance sites in three job areas: Magnetic Resonance Medical Director/Physician (MRMD), Magnetic Resonance Safety Officer (MRSO), and Magnetic Resonance Safety Expert (MRSE).

The certification process is composed of formal examinations (one for each job), and certifications are valid for a decade. Since AMBRS began offering this in June 2015, more than 1,500 people have been certified. Manufacturers GE, Siemens and Philips have each provided grants to end-users to pay for half the cost of the ABRMS certification exam as well.

Even as device operators continue to gain relevant knowledge about how to safely scan patients with implanted medical devices, patients’ knowledge about their own implants remains a key hurdle. Addressing that oversight means asking manufacturers to maintain patient databases as a redundancy for physicians and health systems that may not be adequately tracking their patients in the same fashion.

“We’re past due for a persistent record that follows the patient,” Gilk said. “For hospital groups that have a uniform electronic health record (EHR), at least we can capture and retain that information for patient services received within the network. But anything out of network doesn’t get captured in the EHR unless someone jumps through flaming hoops of bureaucracy and technology.”

“Patients are notoriously poor historians,” he said, “and for the patient who has to get an MRI every other year, the idea that we don’t preserve that information from exam number one to exam two to exam three is just really frustrating, especially when we essentially ask the patient to regurgitate the same information for each exam. The way in which we collect and use MRI safety information associated with an individual patient could not have been engineered to be much worse than it is.”

One of the most promising approaches to addressing the knowledge gap in scanning patients with implanted devices is another project of Kanal’s, a data simulation application called MagnetVision. It’s the backbone of his MR safety course (in addition to being Chief of the Division of Emergency Radiology at the University of Pittsburgh Medical Center, Kanal is also its director of MR services, and a professor of radiology and neuroradiology there), and represents data collected from manufacturers of 19 different MR systems in clinical use today.

“The average radiologist does not understand some of the safety issues behind the modality, and certainly often does not understand the nuances behind the safety concerns regarding scanning a patient with a device, implant or foreign body,” Kanal said. “In MR, there are three different energy sources, and each has its own safety issues; where you are depositing that energy in this patient is not necessarily where the examination is centered.”

Although MRI does not involve ionizing radiation like an X-ray or computed tomography (CT) scan, the modality can have potential health effects on patients who are improperly scanned, including disrupting the normal function of their device, causing neurological or cardiac dysfunction, or even burning them. MagnetVision allows radiologists and technologists to simulate the effects of different MR machines on patients with different implanted devices by showing them where the energy fields created by the MR units would interact with their bodies in a given study.

“I’ve gone to the manufacturers of these devices and asked them to provide me with the 3D field plots of the strengths of different energies, and converted that to visible colors on the screen,” Kanal said. “Whichever of the MR scanners it models, you can call them up and it shows you the components and what they expose. You can create a photorealistic model of your patient, position the device, implant or foreign body to match where it would be in the patient in front of you, and then position that patient how you would in the MR scanner at your site, and it will show you what energies he will be exposed to, and where they will be initially deposited.”

By creating a visual guideline for each of the potential interactions between patient and devices – MagnetVision displays colored guidance from green to yellow to red to illustrate how safe the study would be to the patient – the application can define what technologists are trying to model with the push of a button. Kanal’s goal is to make it freely available to everyone working in the field, but to avoid legal liability stemming from its potential misuse, today MagnetVision is only provided to professionals who attend his safety courses, or those to whom he has personally taught the basics of MR safety and how to use the app.

“The two things that are driving me are certification and standardization,” Kanal said. “I take the science world of the physicist, and try to turn it into the language of the physician and the technologist.”

If patients are turned away from imaging studies due to the presence of implanted devices, the alternatives aren’t always ideal, he said. If a requested MRI study is unnecessarily cancelled, that patient may then be sent for a higher-risk or more invasive alternative scan.

“I believe that the lion’s share of mistakes we’re making in the U.S. MR industry today is cancelling people who could be safely scanned,” Kanal said. “I believe clinicians are being overly cautious, but the risk they’re limiting may be their own, and not necessarily that of their patient.”

“It’s easy to say no,” he said. “It takes knowledge, understanding, and a willingness to apply it to say yes.”

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