Experimental and Modeling Analyses of Human Motion Across the Static Magnetic Field of an MRI Scanner

Abstract

It is established that human movements in the vicinity of a permanent static magnetic field, such as those in magnetic resonance imaging (MRI) scanners induce electric fields in the human body; this raises potential severe risks of health to radiographers and cleaners exposed routinely to these fields in MRI rooms. The relevant directives and parameters, however, are based on theoretical models, and accurate studies on the simulation of the effects based on human movement data obtained in real conditions are still lacking. Two radiographers and one cleaner, familiar with MRI room activities and these directives, were gait analyzed during the execution of routine job motor tasks at different velocities. Full body motion was recorded in a gait laboratory arranged to reproduce the workspace of a room with an MRI full-body scanner. Body segments were tracked with clusters of at least three markers, from which position and velocity of the centroids were calculated. These were used as input in an established computer physical model able to map the stray field in an MRI room. The spatial peak values of the calculated electric field induced by motion of the head and of the entire body during these tasks, for both the health and sensory effects, were found smaller than the thresholds recommended by the European directives, for both 1.5 T and 3.0 T MRI. These tasks therefore seem to guarantee the safety of MRI room operators according to current professional good practice for exposure risks. Physical modeling and experimental measures of human motion can also support occupational medicine.

Assessment of Exposure to Spatially Varying Magnetic Fields in MRI Environments: Modeling Analysis for Simulation Tools

“…The results presented here in terms of induced electric field, are valid under the chosen specific exposure conditions and for the chosen modelling parameters. For this reason, a comparison with results reported in similar works [29]- [31] are difficult, also since the lack of a standard procedure to estimate the electric fields induced by exposure to timevarying magnetic fields. Moreover, a rigorous procedure to verify the compliance of the exposure metrics with the imposed limits should include a frequency analysis [28] and the implementation of the weighted peak method (WPM), according to ICNIRP guidelines [15], [17].…”

“…In the most simply model, the MRI workers can be supposed to move translationally and with constant speed [27], [28], [30]. To obtain a more rigorous model, it would be necessary to have a full body kinematic characterization of real MRI operators at work, obtaining by human movement analysis (HMA) using stereophotogrammetry, an established technique which allows for accurate 3D tracking in the space of body segments during the execution of locomotion tasks [31]. This gait analysis requires a specific laboratory and instrumentation which are not generally available in MRI facilities.…”

“…On the back of these studies, Gurrera et al [30] presented an analytical model to verify the compliance of the exposure with the Directive: the model was based on the 3D map of the stray field of a magnetic dipole. Later, they added to the model an accurate human movements analysis: full body motion was recorded in a gait laboratory arranged to reproduce the workspace of a room with an MRI full-body scanner, by using a stereophotogrammetric system to obtain speed trend during the movements [31]. Commercial personal dosimeter were instead used from Acri et al [32] to measure the magnetic flux density related to the operator movement inside the MRI room and then calculate the corresponding dB/dt curves.…”

Occupational Exposure Assessment of the Static Magnetic Field Generated by Nuclear Magnetic Resonance Spectroscopy: A Case Study

“…The walking speed was chosen considering some studies in the literature [25,28,35] that are based on both theoretical consideration and observation of movements of workers in real scenarios. We set some models of walking speed and some values of maximum walking speed, for a linear path along the x-axis from the console to the NMR spectrometer and vice versa.…”

“…Various studies assessing the health risk for MRI workers have been published [19][20][21][22][23]. Workers' exposure to static magnetic fields and their movements in fringe fields have been evaluated and discussed in sites that used MRI scanners ranging from 0.25 T up to 3.0 T [24][25][26].…”