Diagnostic Imaging Online
April 21, 2004

Metal detector promises increased safety in MR suites

Automatic scanning technology may help screen ferromagnetic objects, but common sense has no substitute

A system to detect objects that can turn into projectiles in the magnetic field of an MR scanner could prevent accidents causing personal injury and equipment damage. A specialized metal detector being marketed by ETS-Lindgren that can be mounted in the doorway leading to an MR suite allows staff and patients to be scanned automatically. An alarm sounds when the device detects ferromagnetic metal, but not MR-compatible objects, such as an aluminum oxygen tank.

Although rare, accidents involving metal objects pulled into the bore of an MR scanner can be devastating. In July 2001, a six-year-old child was killed by a metal oxygen tank erroneously brought into the MR suite of Westchester Medical Centre in Valhalla, NY. More common are accidents that damage the scanner itself. Even minor ones involving relatively small objects can require thousands of dollars worth of repairs and lost time.

Tobias Gilk, an associate architect for Junk Architects, which specializes in planning and designing MR suites, welcomes the introduction of a metal detector that could help prevent such accidents, but he noted that remarkably effective low-tech solutions exist that are not always applied. Some need little more than common sense.

"At one facility I visited, the door from the magnet room entered directly into the patient holding area," he said. "The tech did not have a view of the magnet room door, so there was no way of seeing who was entering the suite."

Administrators recognized the need for improved safety after a hospital worker walked through the door pushing a steel gurney with an oxygen cylinder mounted underneath. An MR tech and the worker wrestled the gurney into the holding room before it could be pulled into the magnet.

"While a ferromagnetic detector could have helped avoid this incident, the more reliable solution would have been a window from the control room into the holding area," Gilk said. "Installing an access control on the door to the MR suite would allow the tech to prevent dangerous equipment from getting near the magnet.

Although architectural designs cannot by themselves create a safe environment, neither can metal detectors alone, a point echoed by Benjamin D. Turner, vice president of sales and marketing at ETS-Lindgren. The company developed the Ferromagnetic Detection System in collaboration with U.K.-based Qinetiq.

"The system is intended not to replace whatever safety measures are in place, but to augment them," Turner said. "It's to prevent the infrequent accident from happening."

The detector is operating at clinical sites in the U.K., and preparations are under way to install it at several U.S. hospitals. ETS-Lindgren wants feedback from clinical sites to determine whether any fine-tuning is needed before launching a major marketing campaign later this year. Engineers may consider changing the size, appearance, or sound of the alarm, for example.

Turner emphasizes the need to use the detector as part of a comprehensive effort to prevent accidents. Getting sites to take the problem seriously could be a major challenge. On his visits to MR facilities, Gilk preaches the importance of safety and the ability of his firm to conduct a safety audit to uncover problems. Some administrators question the need for such an audit; others question the legal wisdom of doing one.

"Sometimes I sense the sentiment, Well, if it was a real problem, then why hasn't an accident happened here before?" Gilk said. "I suppose it's more rational than the other answer that, on the advice of attorneys, the facilities decline audits because of the fear that 'institutional knowledge' (of a potentially dangerous situation) would worsen their position were they to be sued over an accident."

The need for vigilance will only increase as more MR scanners are installed outside radiology departments, in areas where staff are less aware of the dangers that high-power magnetic fields present. The increasing popularity of 3T systems raises the stakes further, as the higher field strength draws metal objects faster with a more powerful impact than if they were drawn into a 1.5T magnet. This increases the potential for serious injury and the cost of repairing the scanner.

-- By Greg Freiherr