Ferrous metal detector scrutinizes patients and staff seeking entry to MR suite

A metal detector specially designed for MR offers the imaging community a two-step process for protection against physical and financial damage.

One component of the FerrAlert, which was shown May 9 at the International Society for Magnetic Resonance in Medicine meeting, prescreens patients and staff for tiny objects that might cause image artifacts or compromise the scanner. FerrAlert Prescreen looks like a freestanding doorjamb and may be located in the dressing or interview room.

The other component stands guard at the door actually leading to the scanner. The sensor arrays making up FerrAlert Entry are mounted around this door. They pick up the kinds of objects that have in the past become formidable projectiles: wrenches, air tanks, floor buffers.

Together, the components offer a means to prevent injury to patients and staff, reduce downtime to repair equipment damaged by flying metal objects, and avoid image artifacts and consequent diagnostic errors. They are priced at $28,500.

Anna Srb, marketing manager for Kopp Development, the maker of FerrAlert, emphasizes that the product is only meant to supplement current safety procedures. Prescreen can pick up objects not mentioned during the interview process, and Entry can prevent the worst-case scenario.

"The patient sometimes will forget about something, or in an emergency situation, someone will run into the magnet room with a ferrous object," she said. "In either case, you will get a signal."

It was such an emergency situation that led to the death of a six-year-old child in July 2001, killed by a metal oxygen tank erroneously brought into an MR suite at Westchester Medical Centre in Valhalla, NY (DI SCAN 8/08/2001). Two years later, ETS-Lindgren unveiled a ferrous metal detector, called FerroGuard, designed to be mounted in the doorway leading to the MR suite (DI SCAN 1/28/04).

FerrAlert, which has been installed at eight sites in the U.S., operates in two parts. Patients, visitors, and staff seeking entry to the scanner room first pass through the Prescreen unit. An audiovisual alarm on a toaster-sized operator console goes off if a ferrous object passes through the device. Indicator lights along an icon representing the detector indicate the side and approximate height of the ferromagnetic object, helping the screener track it down and eliminate it.

FerrAlert Entry sensors installed in the doorway leading to the magnet room pick up large objects that could turn into potentially hazardous projectiles in the presence of a powerful magnetic field. As with the Prescreen component, the Entry sensors send signals to a small operator console that sounds an alarm when ferromagnetic objects are detected.

Neither component is affected by nonferrous metals such as aluminum or brass. Nor is either bothered by electromagnetic signals from other electronic equipment. Ferrous metals installed in the surrounding walls or positioned nearby have no effect on FerrAlert, according to Keith A. Kopp, inventor of the device. FerrAlert identifies the presence of these materials and then tunes them out.

The device is totally passive, emitting no radiation. It works by detecting disruptions in the ambient magnetic field, according to Kopp.

"This works on a principle not unlike the one that explains why a compass spins when you put a wrench near it," he said. "The wrench distorts the local magnetic field."

FerrAlert may be the first in a family of products based on this principle. A related device on Kopp's drawing board would be used to detect ferrous metal particles in the eyes of patients. Staff currently ask patients if they work with metal, for example, at a grinder's wheel. If the interview indicates that metal shavings or other particles may have gotten into the eye, patients typically are examined with x-ray to determine whether such particles might still be in the globe.

"The problem is that x-rays are not very good at picking up small particles, nor can they tell if they are ferrous," Kopp said.

The device he is designing now, a detector ring the patient could quickly duck into and out of, would answer those questions. Another device in the concept stage would be installed in surgical suites attached to MR rooms. Patients leaving the surgical theater would be scanned for ferrous instruments before transferring to the scanner.

Both devices are a year or more away from market