THURSDAY, Sept. 27, 2001 (HealthDayNews) -- A metal detector at the entrance to a magnetic resonance imaging (MRI) examination room could be a simple solution for preventing injury and death, a researcher says.
In June, a 6-year old cancer patient at a hospital in New York died after an MRI's massive magnet turned an oxygen tank into a ballistic missile, shattering the child's skull. Even if training to prevent such accidents is extensive, it's not enough, the researcher says. Using metal detectors adds an extra layer of protection.
"After I read what happened in New York, I started to think about what we could do, systematically, to reduce the risk of future MRI accidents," says Dr. Christopher Landrigan, research director of in-patient pediatric service at Children's Hospital in Boston.
MRIs use powerful magnets to direct radio waves at protons in the center of hydrogen atoms, a molecular constituent of water. An MRI image shows differences in the water content and distribution in various body tissues.
But the MRI magnet can wreak havoc with metal objects. A survey done in 1999 showed that 24 of 46 MRI facilities reported accidents when the magnet attracted such things as paper clips, sandbags with metal filings, a vacuum cleaner, and even a wheelchair, Landrigan says.
The so-called "missile effect" of MRIs is well known, Landrigan adds, and clinics have precise warnings about the possible dangers of iron-containing objects around the machines.
The magnetic field an MRI generates is 30,000 times stronger than that of the earth, capable of accelerating an object the size of an oxygen canister to dozens of feet per second.
"Generally, an MRI is a very safe diagnostic procedure, and incidents with metal objects being pulled in the machines are very rare -- on a percentage basis," Landrigan says. "But given the frequency which MRIs are done around the country, there are a fair number of incidents."
"The problem is not a lack of knowledge about MRI's dangers," he adds. "The problem is that there are many people who can be involved in the process. For instance, if a patient needs to be anesthetized for an MRI, there will be an anesthetist. And there may be support people who may or may not be trained. Or there could be nurses from elsewhere in the hospital who lack training in MRI procedures. Moreover, there are maintenance personnel, who usually are trained, but given turnover and other employment issues, the assurance of adequate training is a real challenge."
Metal detectors would prevent most metal objects from getting into an MRI examination room, Landrigan says. They cost between $2,000 and $5,500, and could be covered by the savings realized from a reduction in liability insurance, he adds.
The idea appears as a research letter in today's issue of the New England Journal of Medicine.
An international expert on MRI safety says the concept has been discussed in the past, and discarded. He says detectors are inadequate and create a false sense of security.
"The idea of using metal detectors was pretty well abandoned years ago" because they're not reliable, says Frank Shellock, an international expert on MRI safety who has written four textbooks on the subject. "Metal detectors do not offer the level of sensitivity necessary for identifying problematic metal objects --either because they miss the objects because of the speed you're going through the detectors or they give off false alarms."
Shellock, an adjunct clinical professor of radiology at the
University of Southern California
who has investigated MRI accidents for 15 years, says the detectors can lead people to think there's no metal around when there actually is. (Some patients have been injured because they had tiny iron filings in their eyelids for years, and never knew about them.)
Turnover of employees is also not a problem, Shellock insists, adding that education should be stronger.
"During orientation for every employee, the best idea is to give them education about the MRI area; that the magnet is always on and that there are always inherent risks," he says.
Landrigan acknowledges in his letter that metal detectors alone won't solve the problem. For instance, they probably won't catch implants made of metal, like aneurysm clips or pacemakers.
But having them would be "an inexpensive, simple and potentially lifesaving addition," he writes.
What To Do
For more on how MRIs work, visit How Stuff Works. You can also try the Food and Drug Administration to learn about problems with the attraction of the devices.
Simply Physics has a few pictures of what can get sucked into MRIs.
