Protection of MRI workers against magnetic fields according to EU Directive and ICNIRP Guidelines

Directive 2013/35/EU lays down minimum health and safety requirements regarding the exposure of workers to electromagnetic fields, including those present in Magnetic Resonance Imaging (MRI) facilities. For what concerns the Static Magnetic Field (SMF), the Directive follows a "flexible approach" introduced by the 2009 ICNIRP guidelines, which is based on the distinction between sensory and health effects, thus allowing in some circumstances exposed workers to possibly experience unpleasant sensory effects. In addition, the Directive provides for the possibility of derogating from the health exposure limits, explicitly referring to the case of MRI. However, protection issues related to effects associated with movements of workers in the SMF are not completely addressed by EU limits. ICNIRP has published a guideline on this matter in 2014, but it has not yet been transposed into the Directive. Measurements were performed of low frequency switched gradient magnetic fields and of the magnetic flux density experienced as variable by workers moving in the SMF of 1.5 T, 3 T and 7 T MRI scanners. In the latter case, three different metrics were applied to process the collected data and compare them with the EU Directive Exposure Limit Values (ELVs) for SMF, the ICNIRP basic restrictions (BRs) aimed at preventing vertigo effects and the ICNIRP reference levels (RLs) intended to prevent stimulation effects. Regarding movement in the SMF, reported values of the peak magnetic flux density, of its variation in 3 s and of the weighted-peak indices for stimulation effects show several cases of non-compliance with the corresponding ICNIRP BRs and RLs even when EU Directive ELVs are complied with. Results of exposure to low frequency magnetic fields are being processed.