ALBERT

Description: Object   The EU directive on safety requirements (2004/40/EC) limits the exposure to time varying magnetic fields to d B /d t = 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 d Φ ( x , y , z )/d t serving as an exposition parameter for both translations and rotations. To separate the two types of motion, d B /d t 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 d Φ /d t were recorded during standard operating procedures at three different MR systems up to 7 T. 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 d Φ /dt = 21 mWb/s, d B /d t = 1.40 T/s and ê ê ® B   ê ê = 2.75 Twere 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. Content Type Journal Article Category Research Article Pages 315-322 DOI 10.1007/s10334-011-0270-y Authors Jens Groebner, Department of Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany Reiner Umathum, Department of Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany Michael Bock, Department of Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany Axel J. Krafft, Department of Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany Wolfhard Semmler, Department of Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany Jaane Rauschenberg, Department of Medical Physics in Radiology (E020), German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany Journal Magnetic Resonance Materials in Physics, Biology and Medicine Online ISSN 1352-8661 Print ISSN 0968-5243 Journal Volume Volume 24 Journal Issue Volume 24, Number 6