Personal exposure to static and time-varying magnetic fields during MRI system test procedures.
OBJECTIVE
To assess personal time-weighted average (TWA) static magnetic field and time-varying magnetic field exposure for several system testing tasks routinely conducted by engineers at an MRI manufacturing plant.


METHODS
Personal exposure was measured using a personal dosimeter that measured B and dB/dt in all three orthogonal directions with a 1 Hz frequency. TWA exposure was calculated and random effects and linear mixed effects models were used to assess exposure levels and variability.


RESULTS
Whereas full-body peak (2T) and TWA (200 mT/8 h) exposure limits for the static magnetic field originally proposed by ICNIRP were not exceeded, time-varying magnetic field peaks (dB/dt) did exceed the proposed threshold value (767.9 mT/s) suggested by IEEE on several occasions at the 3.0 Tesla (T) whole-body cylindrical system.


CONCLUSIONS
TWA exposure levels are well below the proposed limit values, but peak exposure limits are exceeded during certain procedures performed on 1.0T to 3.0T systems.
Occupational and Environmental Health Research Group, School of Translational Medicine, Faculty of Medical and Human Sciences, University of Manchester, Manchester, United Kingdom. frank.devocht@manchester.ac.uk
Frank
F
de Vocht
Floris
F
Muller
Hans
H
Engels
Hans
H
Kromhout
D002138:Calibration; D004574:Electromagnetic Fields; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D016273:Occupational Exposure; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000295:instrumentation / Q000379:methods; D011835:Radiation Protection / Q000295:instrumentation / Q000379:methods; D011874:Radiometry / Q000379:methods*; D015203:Reproducibility of Results; D018570:Risk Assessment; D013997:Time Factors