Abstract
Purpose
In an attempt to evaluate the exposure level of magnetic resonance imaging (MRI) workers to static magnetic fields, the isotropic magnetic flux density values were integrated over time to produce the cumulative exposure. To protect occupational staff a further precautionary step is proposed by introducing a weighting function incorporating the limits imposed by the Italian legislation. The results obtained should be reported, at the end of each working day, on a special dose card, in order to record each worker’s exposure to the static magnetic field. Moreover, this dose card could be an important tool if long-term effects occur because it provides a complete history of the occupational exposure in an MRI site.
Materials and methods
To conduct measurements, three Hall-sensor probes were used. The consistency of experimental data, tools and methodologies used was evaluated by performing the Kruskal–Wallis test. Finally, the weighted magnitude of the magnetic flux density was integrated over time to obtain global exposure.
Results
Measurements were performed on different MRI scanners ranging from 0.25 up to 3.0 T. The results obtained were compared with the 200 mT·h, which represents the upper limit of the Italian regulation. In no case was the 200 mT·h per day exposure exceeded: however, when the strength of the magnetic field was >200 mT the weighted function overestimated the exposure, so that it represents a highly precautionary measure taking into account possible acute and long-term effects. In addition, from the data recorded during patient positioning operations by MRI staff the dB/dt curve was obtained.
Conclusions
The areas obtained from the integral of the weighted static magnetic field strength over time can be indicative of the global exposure of the occupational staff. These values should be reported on a special dose card that could be considered as an important tool if long-term effects occur because it provides a complete history of the occupational exposure in an MRI site.
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Notes
D.M. 02/08/1991.
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).
Directive 2008/46/EC of the European Parliament and of the Council of 23 April 2008 amending Directive 2004/40/EC on 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).
Directive 2012/11/EU.
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Acknowledgments
The authors wish to thank F. Campanella (INAIL), M. Mattozzi (INAIL), Milani and Ferrari for the passionate and critical exchange of opinions. The authors also thank Tecnorad for providing the dosimeter and for assistance during data managing.
Conflict of interest
Giuseppe Acri, Testagrossa Barbara, Causa Federica, Tripepi Maria Giulia, Vermiglio Giuseppe, Novario Raffaele, Pozzi Liviana, Quadrelli Gloria declare no conflict of interest.
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Acri, G., Testagrossa, B., Causa, F. et al. Evaluation of occupational exposure in magnetic resonance sites. Radiol med 119, 208–213 (2014). https://doi.org/10.1007/s11547-013-0324-5
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DOI: https://doi.org/10.1007/s11547-013-0324-5