The EU Physical Agents (EMF) Directive and its Impact on MRI:Prudent Precaution or Straight Bananas?I8Stephen KEEVIL<strong>Department</strong> <strong>of</strong> Medical <strong>Physics</strong>, Guy’s and St Thomas’ NHS Foundation Trust, Guy’s Hospital, London, SE1 9RTIntroductionThe Physical Agents (Electromagnetic Fields) Directive (1) wasadopted by <strong>the</strong> European Union in 2004. Member states are obliged toincorporate it into law by April 2008, and in <strong>the</strong> UK this will take <strong>the</strong>form <strong>of</strong> <strong>the</strong> Control <strong>of</strong> EMF at Work Regulations 2008. The Directiverestricts occupational exposure to electromagnetic fields (EMF) withfrequencies up to 300 GHz. It contains ‘exposure limit values’,expressed in terms <strong>of</strong> induced current density in <strong>the</strong> head and trunk atlower frequencies and <strong>of</strong> specific absorption rate (SAR) at higherfrequencies. There are also supplementary ‘action values’ expressed inmore easily measurable terms to ensure compliance with <strong>the</strong> limits.These values are taken from guidelines issued some years ago by <strong>the</strong>International Commission on Non-Ionising Radiation Protection (2).This lecture will describe <strong>the</strong> potential impact <strong>of</strong> <strong>the</strong> Directive onMRI, <strong>the</strong> scientific basis for <strong>the</strong> limits, and <strong>the</strong> current state <strong>of</strong> playwith efforts by <strong>the</strong> MR community to have <strong>the</strong> Directive amended.Impact on MRIAll three <strong>of</strong> <strong>the</strong> EMF frequency ranges used in MRI are in principlewithin <strong>the</strong> scope <strong>of</strong> <strong>the</strong> Directive. The table summarises relevantaction values and exposure limits in each frequency range, toge<strong>the</strong>rwith estimated maximum occupational exposures for MRI workers.Static magnetic field. The draft Directive contained a static magneticfield limit <strong>of</strong> 2 T, but this was removed during negotiation; <strong>the</strong> actionvalue <strong>of</strong> 200 mT is <strong>of</strong> little practical consequence. However,movement through <strong>the</strong> temorally static but spatially varying fieldexposes staff to a slowly time-varying field, and it seems likely that<strong>the</strong> induced current density limit will be exceeded by a considerablemargin (3, 4). These limits are absolute, with no scope for timeaveraging or exemption for brief exposure.Switched Gradients. The exposure limit in <strong>the</strong> 100s – 1000s Hz rangewill create an ‘exclusion zone’ around <strong>the</strong> bore opening while imagingis taking place. The extent <strong>of</strong> this zone will depend on magnet andgradient coil design and on <strong>the</strong> pulse sequences being used. Again<strong>the</strong>re is no scope for time averaging in this frequency range, so staffwill not be permitted to enter <strong>the</strong> zone during imaging.Radi<strong>of</strong>requency. Whilst <strong>the</strong> exposure limits are low, <strong>the</strong>re is allowancefor spatial and temporal averaging, and it seems unlikely that MRworkers will exceed <strong>the</strong>m. However, <strong>the</strong> localised SAR limits for <strong>the</strong>limbs may be problematic in some cases, such as interventional MRI.Taken toge<strong>the</strong>r, <strong>the</strong>se limits threaten current clinical use and futuredevelopment <strong>of</strong> MRI. It may be impossible to work close a scannerduring imaging to provide patient care or monitoring or to performresearch procedures. Interventional MRI may be prohibited essentiallyin its entirety. Issues with <strong>the</strong> static field may impact on installation,cleaning, maintenance and patient set-up, as well as situations inwhich staff need to work close to patients or experimental apparatus.Basis <strong>of</strong> Exposure LimitationThe Directive aims to protect workers from ‘known short-termadverse effects’ arising from exposure to EMF. In <strong>the</strong> frequency rangeup to 100 kHz, <strong>the</strong>re is little scientific evidence for such effects. In <strong>the</strong>ICNIRP paper (2), occurrence <strong>of</strong> harmless physiological effects suchas magnetophosphenes at tens <strong>of</strong> hertz has been taken as indicative <strong>of</strong>possible adverse health effects over <strong>the</strong> whole frequency range. It isassumed, with no evidence at all, that <strong>the</strong>se hypo<strong>the</strong>tical effects follow<strong>the</strong> same frequency response as peripheral nerve stimulation, but withan onset threshold about two orders <strong>of</strong> magnitude lower. ICNIRP hasmore recently described <strong>the</strong> guidelines as having been ‘written manyyears ago, and... now under review’ (5), while in <strong>the</strong> UK, NRPBdescribed <strong>the</strong> limits as ‘a cautious approach… to indicate thresholdsfor adverse health effects that are scientifically plausible’ (6). There isno basis for curtailing MRI on <strong>the</strong> strength <strong>of</strong> this evidence.Prospects for AmendmentPr<strong>of</strong>essional bodies involved with MRI have been campaigning forseveral years for amendment <strong>of</strong> <strong>the</strong> Directive prior to implementation.Little progress was made until September 2005, when a press briefingwas held with <strong>the</strong> assistance <strong>of</strong> <strong>the</strong> charity Sense About Science. Thisattracted significant media coverage and led to questions being askedin <strong>the</strong> House <strong>of</strong> Lords. The relevant government minister becamepersonally involved, and a working party has been established with<strong>the</strong> Health and Safety Executive to examine impact on MRI and howit might be mitigated. The European pr<strong>of</strong>essional bodies andmanufacturers have also been active, and in March 2006representatives met with <strong>the</strong> EU Social Affairs Commissioner. Afur<strong>the</strong>r working party has subsequently been established by <strong>the</strong>European Commission, with a very similar remit. Lobbying isbeginning in o<strong>the</strong>r EU members states, and this is very important if weare to prevent implementation without amendment in 2008.In late 2005 <strong>the</strong> House <strong>of</strong> Commons Science and Technology SelectCommittee announced an inquiry into <strong>the</strong> issue as a case study ingovernment handling <strong>of</strong> scientific advice. The committee’s recentreport (7) is extremely critical <strong>of</strong> <strong>the</strong> Directive and <strong>of</strong> various nationaland international agencies for <strong>the</strong>ir handling <strong>of</strong> scientific evidence and<strong>of</strong> representations made by <strong>the</strong> MR community.References(1) Directive 2004/40/EC. Official Journal <strong>of</strong> <strong>the</strong> European Union L159 <strong>of</strong> 30 April 2004, and corrigenda L 184 <strong>of</strong> 24 May 2004.(2) ICNIRP Health <strong>Physics</strong> 74, 494-522 (1998).(3) Liu F et al J Magn Reson 161 99-107 (2003).(4) Crozier S and Liu F Prog Biophys Molec Biol 87 267-278 (2005).(5) ICNIRP Health <strong>Physics</strong> 87 197-216 (2004).(6) NRPB Doc <strong>of</strong> <strong>the</strong> NRPB 15 (3) (2004).(7) House <strong>of</strong> Commons Science and Technology Committee Watching<strong>the</strong> Directives: Scientific Advice on <strong>the</strong> EU Physical Agents(Electromagnetic Fields) Directive (2006).Static magnetic fieldFrequency Exposure limit Action value formagnetic fluxdensity0 Hz None 0.2 T 3 T (clinical)7 T (research)
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