Metal detector guards the door to screen ferromagnetic objects

FerroGuard fits in entryway to MR suites

Injuries and damage due to accidents involving MR scanners might be avoided with a device that sounds an alarm before metal objects turn into projectiles. The device, developed by ETS-Lindgren, works much like any other metal detector, except its quarry is very specific. Aluminum oxygen tanks pass without triggering the alarm, but not ferrous objects that can become high-powered projectiles in an MR magnetic field.

The metal detector, called FerroGuard, can be mounted in the doorway leading to an MR suite, for example, allowing staff and patients to be scanned automatically. An alarm sounds when the device detects ferromagnetic metal.

Sensitivity can be adjusted to suit the staff. The greater the sensitivity, the smaller the object that triggers the alarm. FerroGuard can detect objects as small as a car key. But staff might not want too much sensitivity, as it may predispose the device to false alarms, picking up spurious indicators of metal or detecting objects that pose little or no danger to patients and staff.

A device tuned just to ferrous metals was deemed necessary to avoid the ambivalence that would result from the use of conventional metal detectors, which are triggered by virtually any metal.

"After awhile, you tend to get tired of those false alarms," said Benjamin D. Turner, vice president of sales and marketing at ETS-Lindgren. "You turn the volume down or unplug the thing."

ETS-Lindgren is best known for building MR enclosures and shields that block radio and other electromagnetic energy. The company began developing the ferrous metal detector after a six-year-old child was killed in July 2001 by a metal oxygen tank erroneously brought into the MR suite of Westchester Medical Centre in Valhalla, NY (SCAN 8/08/2001).

Accidents involving personal injury are rare, but those that damage the scanner are less so. Even minor accidents involving relatively small objects can cause thousands of dollars in repairs and lost time. Nonferromagnetic products, including oxygen tanks, are available, but safety protocols requiring their use are prone to human error. This is especially true with nonradiological staff, who may think nothing of bringing a metal mop bucket into the MR suite.

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

The potential for accidents will increase as more MR scanners are installed outside radiology departments, where staff may not be as well schooled in the dangers of high-power magnetic fields. The introduction of 3T systems raises the stakes, as the increased field strength will accelerate metal objects faster, causing them to have a greater impact than if they were drawn by a 1.5T magnet.

ETS-Lindgren is hoping to attract the attention of staff new to MR, as well as those at the 15,000 MR units installed worldwide, with a list price that should be well within the reach of most budgets-$15,000. The system is scheduled for commercial launch later this year. Turner will target end users directly and through architects, because end users-not OEMs-will receive an ongoing benefit from purchase of the device.

"Just saving one accident from happening more than pays for this product," Turner said.

Before going to market, however, ETS-Lindgren will be looking for feedback from staff using the device at some 10 clinical sites in the U.S. The company will be looking for ways to fine-tune the design.

"We want to make sure the appearance and size of the device and the alarm appeal to the customer," he said. "After that, it should be just plug and go."