An Investigation into Occupational Exposure to Electromagnetic Fields for Personnel Working With and Around Medical Magnetic Resonance Imaging Equipment

Myles Capstick(1), Donald McRobbie(2,3), Jeff Hand(2,3), Andreas Christ(1), Sven Kühn(1), Kjell Hansson Mild(4), Eugenia Cabot(1), Yan Li(2), Amir Melzer(1), Annie Papadak(3), Klaas Prüssmann(5), Rebecca Quest(3), Marc Rea(3), Salome Ryf(5), Michael Oberle(1), and Niels Kuster(1)

(1) IT'IS Foundation, Zurich, Switzerland, (2) Imperial College, London, United Kingdom, (3) Imperial College Health Care NHS Trust (Radiological Sciences Unit), London, United Kingdom, (4) Umeå University, Department of Radiation Physics, Umeå, Sweden, (5) MR Center, University Hospital Zurich, Zurich, Switzerland

EU COMMISSION Study on MRI (Project VT/2007/017), 287pp., April 4, 2008

Magnetic Resonance Imaging (MRI) is a rapidly developing diagnostic technology that provides an unmatched view inside the human body without applying ionizing radiation. Improved image quality and novel applications, however, generally require higher electromagnetic field (EMF) strengths and faster image acquisitions, both of which may result in an increase in the EMF exposure of patients and workers. Over the past 30 years, safety standards limiting human exposure to EMFs were developed by agencies such as the FDA and NRPB along with product standard organizations to specifically address the safety of patients undergoing MRI scans as well as by standard bodies like ICNIRP and ICES to establish safety limits. The MRI exposure guidelines are mainly based on specific research results on nerve stimulation by induced low frequency currents, whereas the latter standards are based on biological experiments conducted at different frequencies and conditions and that were extrapolated to the entire spectrum including the MR relevant frequencies. Inconsistencies inevitably resulted, although no attempt was ever made to resolve them with targeted research projects.

The overall project objectives addressed were:

• Gaining a comprehensive understanding of existing and future medical procedures and technologies.
• Identifying possible worst-case scenarios with respect to pulse sequences, phase coding, field gradients, etc.
• Developing appropriate instrumentations and systematically measuring the strength of the fields during pre-selected procedures.
• Applying experimentally validated numerical models to assess if the measured incident fields exceed the physical limits set out in Directive 2004/40/EC.
• Extrapolation of the findings to any scanner and all procedures by uncertainty evaluations.
• Examining protocols and medical practices used in and assessing possible changes to eliminate or reduce exposure.

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