MRI helium leak triggers alert in U.K. hospitals

May 28, 2003

Design flaws show up in vent pipesRadiology departments in the U.K. are checking their MR scanners to ensure proper installation after two Scottish hospitals reported flaws with built-in safety systems. The cases highlight two

Design flaws show up in vent pipes

Radiology departments in the U.K. are checking their MR scanners to ensure proper installation after two Scottish hospitals reported flaws with built-in safety systems. The cases highlight two separate problems with MRI venting pipes, which keep ultracold helium gas from harming patients and hospital staff if the magnet quenches.

The U.K. Medicines and Healthcare products Regulatory Agency (MHRA) issued May 9 a nationwide alert to hospitals and primary-care facilities, urging radiology service managers, radiology directors, MR safety advisors, MRI superintendent radiographers, and facilities managers to check that their external quench pipes meet vendor specifications.

"Under U.K. health and safety legislation, the manufacturer, installer, and owner of the equipment all have responsibilities for the safety of equipment in use," said a spokesperson for the MHRA, who refused to name the hospitals and equipment vendors involved.

Modern MR scanners based on superconducting magnets are cooled by liquid helium. If the magnets lose superconductivity, the stored energy turns to heat, causing the helium to rapidly boil off. Venting pipes are supposed to channel the freezing gas from the scanner environment, preventing potential injuries from asphyxiation, frostbite, or simply panic. But that didn't happen at one Scottish hospital, where water blown into the pipe during a rainstorm collected in a bend and froze, causing a blockage. When the magnet quenched, trapped helium gas spewed into the exam room. Fortunately, staff were not present at the time of the accident.

A second Scottish hospital found that its vent pipe had a smaller internal diameter than the vendor had specified. Analysis of the pipe determined that a quench would have raised internal pressure to 250% of its design value, which may have been enough to rupture the pipe. Emission of the ultracold helium, combined with a significant increase in room pressure and displacement of oxygen, could have proved fatal to anyone in the exam room, the MHRA said.

Because quenching rarely occurs, some hospitals may overlook the importance of maintaining their quench vent pipe, according to Lindsay Beaton, communications executive for Siemens Medical Solutions. The company is preparing to contact its U.K. MRI customers, offering advice on vent pipe installation and maintenance.

"The quench pipe is, strictly speaking, the hospital's responsibility, because it is routed through the building to the outside," she said.

MR scanners fitted by Siemens employees meet or exceed recommendations in company guidelines, according to Beaton. Hospitals that install the hardware themselves are given full planning guidelines, but the company cannot control whether these are followed.

Similarly, Philips Medical Systems offers comprehensive scanner installation advice to local engineers and contractors. The company provides full instruction on suitable construction materials and the location of MRI quench vent pipes, said Guido Stomp, global director of MR field marketing for Philips Medical Systems.

"We undertake continual risk analysis of safety issues and are constantly updating our siting brochures and manuals," he said. "When our guidelines are updated, they are implemented worldwide."