The EU Physical Agents (Electromagnetic Fields) Directive and its Impact on Magnetic Resonance Imaging Stephen Keevil Department of Medical Physics, Guy’s and St Thomas’ NHS Foundation Trust features In 2003, the magnetic resonance (MR) physics community in the UK became aware of a draft European Directive to limit occupational exposure to electromagnetic fields (EMF). The regulators who drew up the Directive were largely concerned about exposure of workers in industries such as electricity generation and distribution, telecommunications and transport: the possibility of significant impact on magnetic resonance imaging (MRI) does not seem to have occurred to them. However, we soon realised that the proposed restrictions would seriously inhibit some MRI activities – both clinical practice and research work – and that there was very little scientific evidence behind them. 1 Despite making strong representations to the Health and Safety Executive (HSE), responsible for negotiating the Directive on behalf of the UK, we were unable to influence matters significantly. The Directive was adopted by the EU in 2004, and like all other member states, the UK is now bound by treaty to incorporate it into national law by the end of April 2008. Scientists and radiologists have embarked on a campaign both in the UK and at the European level to highlight the problems that the Directive poses, and to try to improve matters before the implementation deadline. This has brought our community into contact with politics, the media and public affairs to an unusual, perhaps unprecedented, extent. The aim of this article is to summarise the impact of the Directive on MRI, the scientific evidence base underlying the proposed limits, and the action that has been and is now being taken by the MR community. Progress has been made, and although the matter is by no means concluded, it at last seems possible that there may be a positive outcome. The Physical Agents (Electromagnetic Fields) Directive (Directive 2004/40/EC) 2 claims to protect workers from ‘known short-term adverse effects in the human body’ arising from exposure to EMFs in the frequency range 0–300 GHz. It is concerned only with acute effects, excluding the possibility of long-term or cumulative effects because of the lack of scientific evidence. The Directive gives legislative force to exposure guidelines produced some years ago by the International Commission on Non-Ionising Radiation Protection (ICNIRP). 3 It contains ‘exposure limit values’ (replicating ICNIRP ‘basic restrictions’), expressed in terms of the current density induced in the body by time-varying magnetic fields, and at higher frequencies in terms of specific absorption rate (SAR) to limit tissue heating. Because current density and SAR cannot easily be assessed in vivo, there are also subsidiary ‘action values’ (ICNIRP ‘reference levels’), expressed in more easily measurable terms such as electric and magnetic field strength. These are set conservatively, so that compliance ensures that the exposure limits themselves are satisfied. If the action values are exceeded, it is necessary to assess whether the exposure limits are met, which can only be done using a computational model. The exposure limits themselves may not be exceeded under any circumstances: there is no room for leeway in implementation or exceptions for specific occupational sectors. Neither is there any allowance for risk–benefit analysis, bearing in mind the hazards associated with alternative techniques (such as X-rays, in the case of MRI). MRI uses EMFs in three frequency ranges – a static magnetic field, time-varying magnetic fields in the frequency range 100s–1000s Hz (the switched gradients), and radiofrequency (RF) fields (10s–100s