Heat transfer analysis in an uncoiled model of the cochlea during magnetic cochlear implant surgery

TL;DR

This study models heat transfer during magnetic cochlear implant magnet removal, identifying safe power levels to prevent thermal damage, and finds conduction dominates heat dissipation with negligible convection effects.

Contribution

The paper presents a validated finite element model of the cochlea to determine safe power densities for magnet removal, highlighting conduction as the primary heat transfer mechanism.

Findings

Heat dissipation is mainly through conduction in the cochlea.

Natural convection can be neglected during the procedure.

Safe power density range prevents thermal trauma with minimal temperature increase.

Abstract

Magnetic cochlear implant surgery requires removal of a magnet via a heating process after implant insertion, which may cause thermal trauma within the ear. Intra-cochlear heat transfer analysis is required to ensure that the magnet removal phase is thermally safe. The objective of this work is to determine the safe range of input power density to detach the magnet without causing thermal trauma in the ear, and to analyze the effectiveness of natural convection with respect to conduction for removing the excess heat. A finite element model of an uncoiled cochlea, which is verified and validated, is applied to determine the range of maximum safe input power density to detach a 1-mm-long, 0.5-mm-diameter cylindrical magnet from the cochlear implant electrode array tip. It is shown that heat dissipation in the cochlea is primarily mediated by conduction through the electrode array. The electrode array simultaneously reduces natural convection due to the no-slip boundary condition on its surface and increases axial conduction in the cochlea. It is concluded that natural convection heat transfer in a cochlea during robotic cochlear implant surgery can be neglected. It is found that thermal trauma is avoided by applying a power density from $2.265 \times 10^7$ W/m$^3$ for 114 s to $6.6\times10^7$ W/m$^3$ for 9 s resulting in a maximum temperature increase of 6$^\circ$C on the magnet boundary.