263. MRI operator exposure to static magnetic fields

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Purpose This work aims at assessing compliance of MRI operators work conditions with European Directive’s [1] new limits, expressed in terms of ELVs (Exposure Limit Values) and ALs (Action Levels), addressing the prevention of direct and indirect scientifically well-established short term effects of exposure to electro-magnetic fields in humans. Methods and materials The static magnetic field B0 around two scanners (Magnetom Espree 1.5 T, Siemens and Discovery 750 3 T, General Electric) was spatially mapped along four straight lines – roughly representative of the operator paths in the magnet room – starting from the patient bed edge until the 0.5 mT isomagnetic border, at steps ΔS of 5 cm (see Fig. 1). The temporal variation of the magnetic field ΔB0/Δt experienced by the operator moving across the spatial gradient GS of static magnetic field was estimated as Δ B 0 / Δ t = Δ B 0 / Δ S ∗ Δ S / Δ t = G S ∗ v . G S (i.e. Δ B 0 / Δ S ) was calculated from measured data, whereas for the operator speed v, the value of 1.0 m/s was assumed. The maximum values estimated for Δ B 0 / Δ t for the two scanners were then converted to internal electric fields using the coefficients deduced from Glover [2] . Results The maximum values estimated for Δ B 0 / Δ t occurred in proximity to the edge of the patient’s bed and were 3.2 and 5.9 T/s for the 1.5 T and 3 T respectively. The correspondent electric fields induced in the body of the operator are shown in Table 1 . Conclusion The highest values for Δ B 0 / Δ t were found for the 3 T magnet. The estimated electric fields induced in the operator’s body respected the European Directive’s limit for sanitary effects.