  In traditional cochlear implant surgery, physical trauma may occur during
electrode array insertion. Magnetic guidance of the electrode array has been
proposed to mitigate this medical complication. After insertion, the guiding
magnet attached to the tip of the electrode array must be detached via a
heating process and removed. This heating process may, however, cause thermal
trauma within the cochlea. In this study, a validated three-dimensional finite
element heat transfer model of the human cochlea is applied to perform an
intracochlear thermal analysis necessary to ensure the safety of the magnet
removal phase. Specifically, the maximum safe input power density to detach the
magnet is determined as a function of the boundary conditions, heating
duration, cochlea size, implant electrode array radius and insertion depth,
magnet size, and cochlear fluid. A dimensional analysis and numerical
simulations reveal that the maximum safe input power density increases with
increasing cochlea size and the radius of the electrode array, whereas it
decreases with increasing electrode array insertion depth and magnet size. The
best cochlear fluids from the thermal perspective are perilymph and a soap
solution. Even for the worst case scenario in which the cochlear walls are
assumed to be adiabatic except at the round window, the maximum safe input
power density is larger than that required to melt 1 $\rm{mm^3}$ of paraffin
bonding the magnet to the implant electrode array. By combining the outcome of
this work with other aspects of the design of the magnetic insertion process,
namely the magnetic guidance procedure and medical requirements, it will be
possible to implement a thermally safe patient-specific surgical procedure.
