MR safety: simultaneous B0, dض/dt, and dB/dt measurements on MR-workers up to 7T
- نوع فایل : کتاب
- زبان : انگلیسی
- مؤلف : Jens Groebner · Reiner Umathum · Michael Bock · Axel J. Krafft · Wolfhard Semmler · Jaane Rauschenberg
- چاپ و سال / کشور: 2011
Description
Object The EU directive on safety requirements (2004/40/ EC) limits the exposure to time varying magnetic fields to dB/dt = 200 mT/s. This action value is not clearly defined as it considers only the temporal change of the magnitude of B . Thus, only the translational motion in the magnet’s fringe field is considered and rotations are neglected. Materials and methods A magnetic field probe was constructed to simultaneously record the magnetic flux density B (x, y, z) with a 3-axis Hall sensor and the induced voltage due to movements with a set of three orthogonal coils. Voltages were converted into time-varying magnetic flux dض(x, y, z)/dt serving as an exposition parameter for both translations and rotations. To separate the two types of motion, dB/dt was additionally calculated on the basis of the Hall sensor’s data. The calibrated probe was attached to the forehead of 8 healthcare workers and 17 MR physicists, and B and dض/dt were recorded during standard operating procedures at three different MR systems up to 7T. Results The maximum percentage of the translational motion referring the data including both translations and rotations amounts to 32%. During volunteer measurements, maximum exposure values of dض/dt=21 mWb/s, dB/dt = 1.40 T/s and B = 2.75 T were found. Conclusion The findings in this work indicate that both translations and rotations in the vicinity of an MR system should be taken into account, and that a single regulatory action level might not be sufficient
Magn Reson Mater Phy DOI 10.1007/s10334-011-0270-y Received: 24 March 2011 / Revised: 21 June 2011 / Accepted: 22 June 2011
