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.
Ilvonen
Sami
S
Department of Radio Science and Engineering, Helsinki University of Technology, Otakaari 5 A, 02150 Espoo, Finland. sami.ilvonen@tkk.fi
Laakso
Ilkka
I
D000328:Adult; D001698:Biomedical Engineering; D055592:Biophysical Phenomena; D007758:Ear, Inner; D004574:Electromagnetic Fields / Q000009:adverse effects*; D055590:Electromagnetic Phenomena; D005260:Female; D020342:Finite Element Analysis; D006257:Head; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000009:adverse effects; D008280:Magnetics; D008297:Male; D008953:Models, Anatomic; D019047:Phantoms, Imaging; D012160:Retina; D012399:Rotation; D055815:Young Adult