Computational estimation of magnetically induced electric fields in a rotating head

Change in a magnetic field, or similarly, movement in a strong static magnetic field induces electric fields in human tissues, which could potentially cause harmful effects. In this paper, the fields induced by different rotational movements of a head in a strong homogeneous magnetic field are computed numerically. Average field magnitudes near the retinas and inner ears are studied in order to gain insight into the causes of phosphenes and vertigo-like effects, which are associated with extremely low-frequency (ELF) magnetic fields. The induced electric fields are calculated in four different anatomically realistic head models using an efficient finite-element method (FEM) solver. The results are compared with basic restriction limits by IEEE and ICNIRP. Under rotational movement of the head, with a magnetic flux rate of change of 1 T s(-1), the maximum IEEE-averaged electric field and maximum ICNIRP-averaged current density were 337 mV m(-1) and 8.84 mA m(-2), respectively. The limits by IEEE seem significantly stricter than those by ICNIRP. The results show that a magnetic flux rate of change of 1 T s(-1) may induce electric field in the range of 50 mV m(-1) near retinas, and possibly even larger values near the inner ears. These results provide information for approximating the threshold electric field values of phosphenes and vertigo-like effects.

[1]  Feng Liu,et al.  On the induced electric field gradients in the human body for magnetic stimulation by gradient coils in MRI , 2003, IEEE Transactions on Biomedical Engineering.

[2]  P. Dimbylow,et al.  Induced current densities from low-frequency magnetic fields in a 2 mm resolution, anatomically realistic model of the body. , 1998, Physics in medicine and biology.

[3]  Stuart Crozier,et al.  Exposure of workers to pulsed gradients in MRI , 2007, Journal of magnetic resonance imaging : JMRI.

[4]  K. Caputa,et al.  High-resolution organ dosimetry for human exposure to low-frequency electric fields , 1998 .

[5]  Stuart Crozier,et al.  Numerical evaluation of the fields induced by body motion in or near high-field MRI scanners. , 2005, Progress in biophysics and molecular biology.

[6]  Christopher M Collins,et al.  Consideration of magnetically‐induced and conservative electric fields within a loaded gradient coil , 2006, Magnetic resonance in medicine.

[7]  R. W. Lau,et al.  The dielectric properties of biological tissues: II. Measurements in the frequency range 10 Hz to 20 GHz. , 1996, Physics in medicine and biology.

[8]  P. Å. Öberg,et al.  Magnetophosphenes: a quantitative analysis of thresholds , 1980, Medical and Biological Engineering and Computing.

[9]  M. Stuchly,et al.  Modelling fields induced in humans by 50/60 Hz magnetic fields: reliability of the results and effects of model variations. , 2002, Physics in medicine and biology.

[10]  O. Gandhi,et al.  A 3-D impedance method to calculate power deposition in biological bodies subjected to time varying magnetic fields , 1988, IEEE Transactions on Biomedical Engineering.

[11]  J. Herbertz.  Comment on the ICNIRP guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz) , 1998, Health physics.

[12]  P. Å. Öberg,et al.  Magneto- and electrophosphenes: A comparative study , 1980, Medical and Biological Engineering and Computing.

[13]  Maria A. Stuchly,et al.  Comparison of magnetically induced elf fields in humans computed by FDTD and scalar potential FD codes , 1996, 1996 Symposium on Antenna Technology and Applied Electromagnetics.

[14]  C Gabriel,et al.  The dielectric properties of biological tissues: I. Literature survey. , 1996, Physics in medicine and biology.

[15]  Om Gandhi,et al.  An Impedance Method to Calculate Currents Induced in Biological Bodies Exposed to Quasi-Static Electromagnetic Fields , 1985, IEEE Transactions on Electromagnetic Compatibility.

[16]  R. Bowtell,et al.  Magnetic‐field‐induced vertigo: A theoretical and experimental investigation , 2007, Bioelectromagnetics.

[17]  A. Wood.  Extremely low frequency (ELF) electric and magnetic field exposure limits: Rationale for basic restrictions used in the development of an Australian standard , 2008, Bioelectromagnetics.

[18]  Martin Bencsik,et al.  Electric fields induced in the human body by time-varying magnetic field gradients in MRI: numerical calculations and correlation analysis , 2007, Physics in medicine and biology.

[19]  T. Nagaoka,et al.  Development of realistic high-resolution whole-body voxel models of Japanese adult males and females of average height and weight, and application of models to radio-frequency electromagnetic-field dosimetry. , 2004, Physics in medicine and biology.

[20]  Tamara G. Kolda,et al.  An overview of the Trilinos project , 2005, TOMS.

[21]  Stuart Crozier,et al.  Calculation of electric fields induced by body and head motion in high-field MRI. , 2003, Journal of magnetic resonance.

[22]  Michal Okoniewski,et al.  Low Frequency Finite Difference Time Domain (FDTD) for Modeling of Induced Fields in Humans Close to Line Sources , 2000 .

[23]  Reilly Jp.  Comments concerning "Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz)". , 1999 .

[24]  R. W. Lau,et al.  The dielectric properties of biological tissues: III. Parametric models for the dielectric spectrum of tissues. , 1996, Physics in medicine and biology.

[25]  Guidance on determining compliance of exposure to pulsed and complex non-sinusoidal waveforms below 100 kHz with ICNIRP guidelines. , 2003, Health physics.

[26]  P. Dimbylow.  Quandaries in the application of the ICNIRP low frequency basic restriction on current density , 2008, Physics in medicine and biology.

[27]  R Bowtell,et al.  Measurement of electric fields induced in a human subject due to natural movements in static magnetic fields or exposure to alternating magnetic field gradients , 2008, Physics in medicine and biology.

[28]  J. Sarvas,et al.  Magnetic-Field-Induced ELF Currents in a Human Body by the Use of a GSM Phone , 2007, IEEE Transactions on Electromagnetic Compatibility.