EU regulators examine safety of very high field strengths

Restrictions could limit staff exposure above 2T

Concerns about x-ray dose surfaced in Europe years before they did in the U.S. Now similar concerns have risen about MR.

Following discussion by a European Commission working group in July, which examined the safety of electromagnetic fields, the EU Parliament is considering a measure that would prohibit direct exposure of workers' heads and trunks to field strengths above 2T. Exposure of limbs would not be allowed above 5T. If approved, the regulations would make it illegal to enter the bore of any MR system over 2T.

MR quality control and siting could be affected, as radiologic technicians and engineers often enter the scanners to adjust and maintain equipment. Regulators are also considering requirements for the installation of increased shielding and the establishment of buffer zones to limit public exposure.

To ensure safety, medical personnel may be required to wear static field dosimetry badges that would record exposure to electromagnetic fields. The badges, which have yet to be developed, would measure "teslas-per-hour."

Such restrictive regulations would be years away, at the earliest. The European imaging community is concerned, however, about the effect they would have on European physicians' ability to provide state-of-the-art care and to conduct cutting-edge research. There would be an economic effect as well.

Compliance with the proposed regulations could involve engineering changes that make equipment more expensive to produce, buy, install, and operate, said Dr. Roger Ordidge, a professor of physics applied to medicine at University College London. Ordidge, who conducts research on a 4.7T MR, fears that adding cost to the practice of high-field imaging could make it more difficult for Europe to compete against research centers in the U.S., where no such restrictions are currently in force or being considered.

"Clearly, this matter is of grave concern for people who want to do high-field MR," Ordidge said.

It could be a problem for vendors as well. The proposed regulations could require the manufacture of specialized 3T systems for European sites. The added cost could dissuade some potential buyers against the purchase of these systems. Even the hint that these regulations might be enacted raises problems, as potential customers considering 3T systems might delay their purchases until the situation is resolved.

About 25 new 3T systems are currently on order for European sites, according to Alistair Howseman, senior clinical scientist at Philips Medical Systems' U.K. office. About 35 are already operating in Europe, including 10 in Germany, four in the Netherlands, and five in the U.K. At least another 15 research systems with field strengths above 2T were installed in the early 1990s and are still operating. The proposed regulations could render these systems useless, say their opponents.

Arwel Barrett, principal specialist inspector at the U.K.'s Health and Safety Executive scoffs at such suggestions. Because they relate only to workers, and not patients, vendors could develop equipment that would allow them to perform tasks remotely to avoid entering prohibited field strengths of installed systems, he said. New systems could be designed to allow compliance with the regulations.

"Manufacturers (would) need to think about how they design these machines, and users (would) need to think how to maintain and operate them," Barrett said. "They are all incredibly clever people, and to say you need to put your head in to adjust a system is a very simplistic approach. That argument is specious."

Opponents counter with disdain for the proposed regulations. The main health concern, they say, is that exposure to high field strength magnets sometimes causes dizziness. While evidence shows this can occur, the condition is not common. Also dizziness, when it occurs, does not persist nor is there evidence that it poses a long-term health risk, Ordidge said.

The proposed regulations are based on guidelines set by the International Commission on Non-Ionizing Radiation Protection. They are similar to guidelines established by the U.K. National Radiological Protection Board. These guidelines starkly contrast with those in the U.S., where authorities are relaxing restrictions related to field strength. The FDA adjusted in July from 4T to 8T the tesla threshold that requires authorization for most MR studies.

"The safety issue will be a thorn in the side of Europe," Ordidge said. "We don't want to be at a disadvantage, particularly as the Americans have extended their limits."