Auteurs
Sibella F, Parazzini M, Paglialonga A, Ravazzani P. (2009). Assessment of SAR in the tissues near a cochlear implant exposed to radiofrequency electromagnetic fields. Phys Med Biol. 54(8):N135-141.

Background

A few studies focused on the possible effects of RF EMF exposure on people wearing metallic implants (in particular cochlear implants CI). Cochlear implants are implanted auditory prosthesis used to partially restore hearing in profound deaf people. Both adults and children (even babies) can get a CI. This could lead to stronger energy absorption near the implant with a consequent rise in the temperature and possible damages in the tissue.

Methodology
The human head model was obtained by image segmentation of the magnetic resonance imaging (MRI) scans of the head of a young male subject (image resolution 0.93 × 0.93 × 1 mm), while the model of the inner ear was obtained from computer tomography (CT) images of the petrous bone of an implanted patient (image resolution 0.35 × 0.35 × 0.63 mm). The electrode array of the cochlear implant was modelled as a geometric structure according to the size, shape and materials of a true cochlear implant array. The RF exposure source was modelled as a uniform plane wave at the centre frequencies of GSM and UMTS uplink (respectively 900 MHz, 1750 MHz and 1950 MHz), striking the side of the head where the array was inserted, while the CI acted as a passive object inside the cochlea. 

Results
The results showed higher maximum point SAR values in the presence of the CI. SAR in the cochlea with CI reaches its maximum for occupational exposure at 900 MHz with vertical polarization (approximately 0.24W/kg): this can be considered a small value, although no other specific reference values are available in regulatory issues. The results also showed that exceeding the power reference levels does not necessary imply that SAR local basic restrictions are exceeded.

Conclusions
The results of this study show that the presence of an electrode array in a head, exposed to an external RF EMF source, produces negligible variations in the averaged SAR values, both considering the SAR in the cochlea. It can be concluded from the current study that harmful effects in the cochlear tissues will be unlikely. However, since the factors influencing the electromagnetic interaction between implanted medical devices and exposure to external EMF are wide ranging and complex, conclusions of this paper can be considered valid for exposure conditions similar to those here presented.


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