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Effectiveness of Safe Working Procedure on SMF Exposure Levels and Work Performances in 3 T MRI System Operations

Occupational exposure to static magnetic fields (SMF) is a concern in relation to magnetic resonance imaging (MRI) system operators. Bodily movements inside the stray field around an MRI system induce an electric current inside the body, and this magnetically induced current can cause temporary sensational changes. Although self-motivated motion control near MRI equipment is recommended in order to prevent these effects, a feasible and safe working procedure is required from a health and safety management viewpoint. In this paper, a procedure involving a restricted access area set at a distance of 30 cm from the end of a 3 T MRI system is compared with a protocol in which self-motivated motion control was used (as recommended by the International Commission on Non-Ionizing Protection guidelines). The effects of this safe working procedure on occupational SMF exposure levels and worker performance were evaluated using Hall sensors and a motion capture system. Subjects performed the protocol for head MRI examination both with and without the proposed safe working procedure. The values for maximum field exposure (peak B) were reduced for all subjects using the safe working procedure. The average peak B also decreased by approximately 26%, compared with the results obtained without any restrictions (conventional protocol) (p<;0.01, t-test). Motion analysis of the subjects indicated that the minimum approach distance to the MRI equipment increased due to the adoption of the restricted access area (p<;0.05, t-test), while slight changes were also observed in sojourn time and the differences of the position along the z-axis (Δz, p<;0.05, t-test). However, there were no significant differences in the parameters more closely related to worker performance (e.g., distance moved and velocity) when using the protocols with or without the safe working procedure. These results suggest that this simple safe working procedure may be applied to MRI system operation in order to reduce occupational SMF exposure, without noticeable changes in worker performance.