Heat transfer analysis in an uncoiled model of the cochlea during magnetic cochlear implant surgery. (June 2020) - Esmailie, Fateme
Highlights: Heat transfer within cochlear canals is studied for the first time. Heat transfer analysis in cochlear canals is motivated by the necessity of investigating the safety of the magnet detachment after magnetic guidance of a cochlear implant. The impact of natural convection heat transfer within cochlear canals is reported. Natural convection in an uncoiled model of a cochlea with an inserted implant electrode array is negligible. The impact of the implant electrode array on the heat removal process from the cochlea is analyzed. The electrode array acts as a heat sink transferring excessive heat to the ambient, due to the high thermal conductivity of the platinum electrodes and wires within the electrode array. The range of safe maximum input power density to detach the magnet after magnetic guidance of the cochlear implant is determined. The safe input power density is 23 MW/m 3 for 114 s to 66 MW/m 3 for 9 s of constant heating. 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 × 10 7 W/m 3 for 114 s to 6.6 × 10 7 W/m 3 for 9 s resulting in a maximum temperature increase of 6 ∘ C on the magnet boundary.