TORONTO – We humans are made of flesh and bone, of cartilage, sinews, muscles and tendons.
But a surprising number of us carry around embedded metal as well. The potential list of metal bits is long: stents or shunts, surgical screws or plates, artificial joints or implanted electrodes, dental posts, body piercings or even so called permanent makeup, eyeliner or eyebrows that are tattooed on.
What does all that metal mean if a doctor suggests you should get a diagnostic scan using magnetic resonance imaging, more commonly referred to as an MRI? As the name suggests, the machines use powerful magnets to produce detailed images of soft tissue, organs and joints. Metal is a problem in the rooms where MRIs are housed.
In a highly publicized and tragic example of why, a six-year old boy from New York State died in 2001 from injuries incurred when an oxygen tank left in the testing room flew across the room and struck him in the head when the magnet was turned on. In another cautionary incident, a metal worker who had a metal sliver in his eye – the result of an old work accident – lost his vision when the magnet caused the shard to move, severing his optic nerve.
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Those stories are rare. But there are more common reports of minor incidents, such as people complaining of burns when their tattoos heated up while they were in an MRI. Why, you may ask. The inks used to draw the body art contain metals, which are embedded in the skin.
“There are thousands of incidents a year of minor injuries,” says Dr. Jerry Froelich, of the University of Minnesota, speaking of MRI-related events in the United States reported to the Food and Drug Administration.
“The major ones like an oxygen tank that kills somebody makes the news. But there are thousands of other ones that are reported or not reported that are minor instances that should not have occurred.”
So, who should stay out of an MRI?
It turns out that figuring out the answer to that question is a complicated business and a moving target, given the fast changing field of medical devices. People who administer MRI scans and the professional organizations that oversee the field of radiology give it serious and ongoing study.
“I do spend a lot of time reviewing paperwork to determine whether or not our research subjects are safe or not safe. And almost a day doesn’t go by that I don’t get a request from a researcher: ‘I have this patient with such and such and such. Are they safe?”‘ says Froelich, who is chair of the American College of Radiology’s MRI safety committee.
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In research, scientists like Froelich are using increasingly powerful magnets as they strive for greater detail in the images the machines make. They can currently capture neuron bundles in the brain and are trying to get to the point where they can see individual neurons.
“What we’re trying to do is if we can actually see deeper and deeper into the brain, we can better hopefully identify that which is causing traumatic brain injury or psychiatric diseases or certain problems we see,” he explains. “So that’s the reason for going stronger and stronger, because we know that we’re getting closer and closer to seeing what’s happening on a cellular level within the body.”
The stronger the magnet, though, the more important the issue of embedded metal becomes. “As we continue to go higher and higher in field strength and as we continue to try to look at smaller and smaller objects … we have greater concerns.”
When the devices were first developed in the 1970s, the chief fear was about shrapnel – metal lodged in bodies by bomb blasts or bullets. Unlike the lead bullets of the olden days, which were toxic but not magnetic, modern bullets are made of steel, which is very magnetic.
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Over time the concerns have expanded, as more metal is being used in surgeries, in implanted medical devices and in dentistry.
There are pacemakers and implanted defibrillators. Neurostimulators – electrodes implanted in the brain – and cochlear implants to give hearing to people who would otherwise be deaf. There are penile implants. Artificial joints. Prosthetic eyes. Intrauterine device or IUDs for birth control. Diabetic pumps.
Nicotine patches or dermal patches that deliver pain medication through the skin are sometimes backed with metal foil. Makeup and hair spray may contain tiny bits of metal and some MRI clinics will instruct patients not to use these produce the day of their scan.
People who have some implanted devices cannot undergo MRI scans, though decisions are made on a case-by-case basis. For instance while some new pacemakers are designated MRI-compatible, many of the devices cannot be put into an MRI.
Likewise ear implants, breast tissue expanders and certain types of older model surgical clips are considered contraindications for MRIs – it is unsafe for people with them to be put into the machines, says Dr. Anish Kirpalani, co-director of the MRI program at St. Michael’s Hospital in Toronto.
Some metal – the posts used to hold dental implants, for instance – aren’t a safety issue for the patient. But depending on how much metal there is and where it is in conjunction to the part of the body being scanned, the metal could distort the image being captured.
The metal that is problematic is known as ferromagnetic; it’s attracted to magnets. Kirpalani says his clinic has a regular handheld magnet and will use it at times to test whether something metal in or on a patient is likely to pose a problem.
He and Froelich describe detailed intake procedures where patients are asked myriad questions aimed at finding out whether they may have any embedded metal and whether they are safe to scan.
“In general we have a procedure in place to check these things and we have several checks and balances to make sure that things that we’re not familiar with are checked before the patient shows up in an MRI scanner,” Kirpalani says.
The goal is to get as much detail as possible. For example, people who have implanted devices are asked for specifics, down to model and manufacturer. People who have had operations of any sort are queried to see whether they might unknowingly have metal clips or pins implanted. When available, medical records are checked.
With detailed information, many people can be safely scanned. “But if they don’t have medical records and we don’t know what’s in them, then commonly they cannot have an MRI,” Froelich says.
People who have body piercings are asked if they can be removed. If they cannot, the clinic may decide to go through with the scan, but will offer an important caveat. “We will tell them that if they have any kind of heating issue or they experience any kind of sensation that they’re not comfortable with, we will stop the scan,” Kirpalani says.
The same advice is offered to people with tattoos. The bigger and darker the tattoo, the greater the likelihood it will heat up in an MRI – though Froelich notes the issue initially came to light when some women who had tattooed eyeliner complained the MRI made their eyelids flutter. Some MRI clinics get patients with tattoos to cover them with ice packs during the procedure.
“It’s important for somebody who’s having an MRI scan who has big tattoos to tell their doctor about it. Tell their doctor who’s requesting it and more importantly when they show up for an MRI scan they have to tell the intake staff and the technologist that they have this,” Kirpalani says.
In fact, if your doctor orders an MRI for you, you should be ready for a thorough intake process and come armed with as much information as possible about metal in and on your body.
“You need to be open,” Kirpalani says. “That’s one thing I would stress, that people disclose these kinds of things to us.”
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