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Embedded metal in humans could pose a risk

放大字体  缩小字体 发布日期:2017-02-10 来源:Regina Leader-Post 浏览次数:1038


We humans are made of flesh and bone, but some of us carry around embedded metal, too. Stents or shunts, surgical screws, piercings, implanted electrodes, permanent makeup, are among a long list of possibilities. What does all that metal mean if a doctor suggests you should get a diagnostic scan using magnetic resonance imaging, commonly called an MRI?

Cautionary Tales

The machines use powerful magnets to produce detailed images of soft tissue, organs and joints. metal is a problem in the rooms wher MRIs are housed. A six-year old boy from New York State died in 2001 when an oxygen tank flew across the room and struck him in the head when the magnet was turned on. In another incident, a metal worker who had a metal sliver in his eye lost his vision when the magnet caused the shard to move, severing his optic nerve.

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.

"There are thousands of incidents a year of minor injuries," says Dr. Jerry Froelich, of the University of Minnesota., speaking of MRI-related reported events.

Stronger Magnets Magnify Concerns

So, who should stay out of an MRI? Figuring out the answer to that question is a complicated business and a moving target, given the fast changing field of medical devices. "... 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.

Scientists are using increasingly powerful magnets as they strive for greater detail in the images the machines make. The stronger the magnet, though, the more important the issue of embedded metal becomes.

Less Safe Than In Past

When the devices were first developed in the 1970s, the chief fear was about shrapnel. Unlike old lead bullets, which were toxic but not magnetic, modern bullets are made of steel, which is very magnetic.

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. Even makeup and hairspray may contain tiny bits of metal.

MRI's Not For Everyone

People who have some implanted devices cannot undergo MRI scans, though decisions are made on a case-by-case basis. 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, says Dr. Anish Kirpalani, codirector 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 but the metal potentially could distort the imagery.

Disclose Details

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.

"... 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.

The bigger and darker the tattoo, the greater the likelihood it will heat up in an MRI.
"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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