MRI - EC Physical Agents Directive

This note provides information on the European Commission (EC) Directive 2004/40/EC, its relevance to the exposure of workers using magnetic resonance imaging (MRI), international guidelines on limiting occupational exposure to electromagnetic fields (EMFs) and initiatives undertaken by the HPA, the World Health Organization (WHO) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) in further understanding possible adverse health effects associated with the use of MRI.

Introduction

Concern has been expressed within the medical community and elsewhere that the implementation of the EC Physical Agents Directive 2004/40/EC could have severe implications for medical and research use and for maintenance and testing of MRI equipment. Indeed, it has been claimed that it could restrict and in some cases prevent the use of MRI. The principal concern being expressed is about possible over-exposure of operators and appears to relate mainly to static magnetic fields and low frequency time-varying magnetic fields.

The Directive sets out minimum health and safety requirements regarding the exposure of workers to the risks arising from EMFs. The concern derives from the belief that workers, including medical staff attending patients, using MRI machines could exceed the limits of exposure set out in the Directive. The Directive does not apply to patients or volunteers undergoing MRI examination.

Responsibility for matters relating to the protection of workers and practical implementation of the Directive in the UK lies principally with the Health and Safety Executive (HSE).

The HPA Radiation Protection Division (RPD) provides advice to Government and other agencies on radiation protection including protection from EMFs. The Medicines and Healthcare products Regulatory Agency (MHRA), which is an executive agency of the Department of Health (DH), has a remit that includes ensuring that medical equipment (including MRI machines) meet appropriate standards of safety, quality, performance and effectiveness, and are used safely.

In its former existence as the National Radiological Protection Board (NRPB), the RPD has both carried out and commissioned comprehensive reviews of the effects of electromagnetic fields on human health by its own scientific staff, by the independent Advisory Group on Non-ionising Radiation (AGNIR) and by other external experts. It has also contributed extensively to the work of WHO on EMFs and health and to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [outside link]. ICNIRP sets international guidelines for limiting exposure to EMFs that have been adopted by many countries including the UK.

EC Directive 2004/40/EC

The Directive was published in its final form, on 24 May 2004 (EC, 2004). It addresses minimum health and safety requirements regarding the exposure of workers to the risks arising from EMFs. The Directive defines the risks as those due to short-term adverse health effects in the human body caused by induced currents, energy absorption and contact currents. It does not address possible long-term effects.

Exposure limit values and action values

The Directive sets out 'exposure limit values' and 'action values' for EMFs in the frequency range 0-300 GHz. These have been derived from EMF exposure guidelines published by ICNIRP (ICNIRP, 1998). The exposure limit values in the Directive are for time-varying fields only and are expressed in terms of induced current density for frequencies less than 10 MHz and specific energy absorption rate (SAR) for frequencies greater than 100 kHz. No exposure limit value is provided for static magnetic fields, which are a major component of exposure from MRI.

Action values are expressed in terms of measurable field quantities, which are - for frequencies less than 10 MHz, electric field strength, magnetic field strength and magnetic flux density - and for frequencies greater than 10 MHz additionally, power density. Action values are not exposure limit values and may be exceeded. However, doing so triggers a requirement to undertake one or more specified measures set out in the Directive, including the need to carry out an assessment of compliance with the exposure limit value.

The emissions from MRI equipment, and therefore the requirements for assessment include static magnetic fields, low frequency time-varying magnetic fields and radiofrequency fields.

MRI exposures and the Directive

With respect to static magnetic fields and low frequency time-varying magnetic fields, the important parameters to consider are the static magnetic flux density action value of 200 mT and a range of time-varying magnetic flux densities set out in the Directive. Exceeding these values, among other requirements of the Directive, triggers the need to demonstrate compliance with the relevant exposure limit values. As noted above, no exposure limit value for static magnetic fields is provided in the Directive. The exposure limit values for low frequency fields are expressed in the Directive in terms of induced current densities. Compliance assessment involves an analysis of the coupling of the worker with the field using computational assessment techniques such as described in an HPA information note (HPA, 2005).

International Commission on Non-Ionizing Radiation Protection (ICNIRP)

ICNIRP carries out reviews of the science of EMFs and health and has published advice and exposure guidelines on EMF for all frequencies relevant to MRI.

Recent reviews include one of static and low frequency electromagnetic fields, biological effects and health consequences published by ICNIRP in its 'Blue Book' series (ICNIRP, 2003).

Guidelines for limiting exposure of workers to EMFs relevant to MRI are set out in two publications, viz, 'Guidelines on limits of exposure to static magnetic fields' (ICNIRP, 1994) and 'Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz)' (ICNIRP, 1998). These guidelines form the basis for the exposure limit and action values in the EC Directive.

ICNIRP is currently reviewing its guidance on limiting exposure to both static and low frequency magnetic fields and this is expected to be completed by 2006 Information is available on this area of work [outside link].

In addition, ICNIRP has published guidance on MRI procedures in the form of statements on protection of patients (ICNIRP, 1991 and 2004).

Health Protection Agency (HPA)

Formal advice to Government on limiting exposure to EMFs has been published by the NRPB prior to its merging with the HPA (NRPB, 2004a). This advice was based upon an extensive review of the scientific literature carried out by NRPB scientists (NRPB, 2004b) and updated previously published advice (NRPB, 1993). In developing the review, the NRPB took advice from individuals in the UK, international scientific experts, and from published comprehensive reviews by expert groups. It also took advice from an ad hoc expert group on weak electric field effects in the body and the proceedings of an international workshop organised by the NRPB on weak electric field effects (NRPB, 2003). Also considered were the views expressed in response to a consultation document issued in May 2003, as well as listening to the concerns raised at a public open meeting on power lines in December 2002. The NRPB advice recommended the adoption of the ICNIRP exposure guidelines for limiting exposure to EMFs in the UK.

With respect to protection of workers to static magnetic fields, the NRPB noted that vertigo, nausea, a metallic taste and phosphenes can be induced during movement in static magnetic fields larger than about 2 T. In addition, flow potentials induced in a magnetic field of this value have been calculated to generate electric fields of about 200 mV  m ^-1 near the sino-atrial (pacemaker) node of the heart during the relative refractory period of the cardiac cycle, when cardiac excitability is relatively low. The NRPB concluded that acute adverse responses would not occur for exposure to static magnetic fields of less than 2 T. It considered that there was insufficient evidence from animal and cellular studies to determine long-term health effects due to chronic exposure to static magnetic fields. On the basis of the evidence on acute effects, and the uncertainty concerning long-term effects, the NRPB considered that a cautious approach to restricting exposure to static magnetic fields was merited. The NRPB concluded that restricting whole-body time-weighted average exposure to a magnetic flux density of 200 mT was appropriate for occupational exposure to static magnetic fields with an instantaneous ceiling of 2 T. For exposure of the limbs, a ceiling of 5 T is appropriate. The paucity of data on health effects of static magnetic fields was noted and prompted the organisation of an international workshop on 'Effects of static magnetic fields relevant to human health'.

Additionally, the NRPB had reviewed and published guidance on the principles for the protection of patients and volunteers during clinical magnetic resonance diagnostic procedures (NRPB, 1991a). In the report it noted the need for further research on the effects of static magnetic fields. It also set out limits on patient and volunteer exposure together with recommendations for their practical application (NRPB, 1991b).

Static Magnetic Field Workshop

The workshop was organised by the NRPB in collaboration with WHO and ICNIRP and was supported by the DH and the HSE. It brought together experts in relevant scientific and medical fields to review the subject and the proceedings were published in February 2005 (NRPB, 2005). In respect of exposure guidelines the conclusions of the workshop were as follows.

• There is a paucity of information regarding the long-term health effects associated with exposure to static magnetic fields.
• Perceptual and other acute effects have been demonstrated above a threshold of about 2 T, and these form the basis for human exposure standards at present.
• Exposures well above this threshold are increasingly becoming more common as the technology associated with magnetic resonance imaging advances. Therefore priority should be given to assessing the health risks associated with exposures to such fields.
• Studies should include a prospective cohort study investigating cancer risks of workers and patients exposed to fields in excess of 2 T; a study investigating effects on human cognitive performance from repeated exposures, and a molecular biology study investigating acute changes in genomic responses in volunteers exposed to fields of up to 8 T.
• Studies investigating the effects of long-term exposure on cancer, and on neurobehavioral development are also recommended using animals, where the use of transgenic models is encouraged.
• In addition, dosimetric studies should be conducted using high resolution male, female and pregnant voxel phantoms, as should theoretical studies investigating the local currents induced in the eye and in the heart by movement during exposure.
• Studies are recommended to investigate further the ability of static magnetic fields to significantly affect radical pair reactions in biological systems.

Independent Advisory Group on Non-ionising Radiation (AGNIR)

The AGNIR is an independent expert group set up by the Director of the NRPB in 1990, the terms of reference of which are to review work on the biological effects of non-ionising radiation relevant to human health and to advise on research priorities. The Group was reconstituted in 1999 as an independent advisory group and reported directly to the Board of NRPB; since April 2005 it reports to the sub-committee of the Board of the HPA that deals with radiation, chemical and environmental hazards. In addition to the work of the Advisory Group, subgroups address specific issues.

The AGNIR had been asked by the Board of the NRPB to carry out a review of any hazards from exposures of patients and staff to static magnetic fields in particular during MRI procedures. The programme of work has been defined and it is expected that a report will be prepared over the next two to three years.

Medicines and Healthcare products Regulatory Agency (MHRA)

The MHRA is an executive agency of the DH and has a remit that includes ensuring that medical equipment (including MRI machines) meet appropriate standards of safety, quality, performance and effectiveness, and are used safely. In 2002 the Medical Devices Agency (MDA), which is now part of the MHRA, published updated guidelines for magnetic resonance equipment for clinical use with particular reference to safety (MDA, 2002; MHRA, 2003). The guidelines set out detailed advice and requirements to ensure the safety of patients, volunteers, patient escorts and staff. With respect to occupational exposure, the guidelines recommended that the NRPB basic restrictions for EMFs should be complied with (NRPB, 1993). For the use of MRI equipment using static magnetic flux densities greater than 2 T, the guidelines recommended that the MR unit carry out a risk assessment 'in order to understand staff and patient escort exposure to electromagnetic fields and noise'. For static fields, it was noted that 'it is the responsibility of the employer to assess staff exposure levels' and that 'staff monitoring may be required to ensure that exposure limits ??.. are not exceeded'.

World Health Organization (WHO)

The International Agency for Research on Cancer (IARC) is an agency of WHO the mission of which is to co-ordinate and conduct research on the causes of human cancer, the mechanisms of carcinogenesis, and to develop scientific strategies for cancer control. IARC has carried out an assessment of the carcinogenicity of static and extremely low frequency electric and magnetic fields (IARC, 2002) and, with respect to static magnetic fields, concluded that 'static electric and magnetic fields and extremely low frequency electric fields are not classifiable as to their carcinogenicity to humans (Group 3)'.

WHO, through the activities of its International EMF Project [outside link], advises member states on the health impact of EMFs. As part of this project, WHO is currently undertaking a health risk assessment of static electric and magnetic fields. The risk assessment process was completed by an expert panel in December 2004 and the final assessment report will be published by WHO in its 'Environmental Health Criteria (EHC)' series of publications.

References

EC (2004). Corrigendum to Directive 2004/40/EC of the European Parliament and of the Council of 29 April 2004 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields) (18th individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC). Official Journal of the European Union L184/1. 24 May 2004.

HPA (2005). Application of ICNIRP exposure guidelines for 50 Hz power frequency fields. HPA information note of 11 April 2005 www.hpa.org.uk/radiation/understand/information_sheets/icnirp_exp_guidelines.htm.

IARC (2002). Non-ionizing Radiation, part 1: Static and Extremely Low Frequency Electric and Magnetic Fields. IARC Monographs Vol. 80. Lyon, International Agency for Research on Cancer.

ICNIRP (1991). Protection of the patient undergoing a magnetic resonance examination. Health Physics, 61(6), 923-8.

ICNIRP (1994). Guidelines on limits of exposure to static magnetic fields . Health Physics, 66(1), 100-106.

ICNIRP (1998). Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz). Health Physics, 74(4), 494-522.

ICNIRP (2003). Exposure to static and low frequency electromagnetic fields, biological effects and health consequences (0-100 kHz) - review of the scientific evidence and health consequences. (JH Bernhardt, R Matthes, A McKinlay, P.Vecchia, and B Veyret, Eds.).

ICNIRP (2004). Statement on medical magnetic resonance (MR) procedures: protection of patients. Health Physics, 87(2), 197-216.

MDA (2002). Guidelines for magnetic equipment in clinical use with particular reference to safety. London, Medical Devices Agency.

MHRA (2003). Guidelines for magnetic equipment in clinical use with particular reference to safety - Issued by the MDA, December 2002 - corrections to page 29. London, Medicines and Healthcare products Regulatory Agency.

NRPB (1991a). Board statement on clinical magnetic resonance diagnostic procedures. Principles for the protection of patients and volunteers during clinical magnetic resonance diagnostic procedures. Documents of the NRPB, 2(1).

NRPB (1991b). Board statement on clinical magnetic resonance diagnostic procedures - limits on patient and volunteer exposure during clinical magnetic resonance diagnostic procedures: Recommendations for the practical application of the Board's Statement. Documents of the NRPB, 2(1).

NRPB (1993). Restrictions on human exposure to static and time-varying electromagnetic fields and radiation. Documents of the NRPB, 4(5).

NRPB (2003). Weak electric field effects in the body. Proceedings of an international workshop, NRPB, Chilton, UK, March 24-25, 2003. Radiation Protection Dosimetry, 106, 4.

NRPB (2004a). Review of the scientific evidence for limiting exposure to electromagnetic fields (0-300 GHz). Documents of the NRPB, 15(3).

NRPB (2004b). Advice on limiting exposure to electromagnetic fields (0-300 GHz). Documents of the NRPB, 15(2).

NRPB (2005). Proceedings of an international workshop 'Effects of Static Magnetic Fields Relevant to Human Health'. Progress in Biophysics and Molecular Biology, 87(2 and 3).

First issue - September 2005

Last reviewed: 4 September 2008