| Description |
Cochlear implants consist of an external sound processor and an electrode array that is inserted within one of the cochlear canals called scala tympani. In 30% of surgeries, the electrode array insertion causes intracochlear physical trauma, which damages the patient's remaining hearing ability and decreases the functionality of the cochlear implants. Magnetic guidance of the cochlear implant's electrode array decreases the insertion force by 50%, and consequently reduces the risk of intracochlear physical trauma. In this paradigm, an external magnetic field steers a magnet attached to the tip of the electrode array through the scala tympani. The magnet should be removed from the scala tympani after the surgery to avoid medical complications. Magnetic guidance of cochlear implants faces two main thermal challenges: (1) resistive heating within the device generating the external magnetic field (Omnimagnet) may result in melting the wire insulation, which may yield device failure due to a short circuit, and (2) the detachment of the magnet may release heat that may cause thermal trauma to delicate tissues. Therefore, the research objectives to address these two challenges are: Objective 1 is to develop a thermal transient model of the Omnimagnet to control the temperature of the Omnimagnet. Objective 2 is to determine the maximum safe input power density to detach the magnet. Objective 3 is to validate the simulation results of Objective 2 with an experimental heat transfer study in a scala tympani phantom. A validated transient thermal model of an Omnimagnet (error < 12%) shows that active cooling of frames is the most effective method to remove the excessive heat (Objective 1). A study of heat transfer within coiled and uncoiled models of the cochlea shows that natural convection is negligible during the magnet detachment process (Objective 2). Then, the numerical results are validated (error < 6%) with experimental data using the measured temperature within a scale tympani phantom (Objective 3). Finally, a parametric study conducted with a three-dimensional (3D) heat transfer model within the cochlear canals shows that the safe input power density to avoid thermal damage to the tissues is at least one order of magnitude larger than the required input power density to detach the magnet. The magnet detachment process will be thermally safe if paraffin is applied to attach the magnet to the electrode array. |
