  Magnetic guidance of cochlear implants is a promising technique to reduce the
risk of physical trauma during surgery. In this approach, a magnet attached to
the tip of the implant electrode array is guided within the scala tympani using
a magnetic field. After surgery, the magnet must be detached from the implant
electrode array via localized heating and removed from the scala tympani which
may cause thermal trauma. Objectives: The objective of this work is to
experimentally validate a three-dimensional (3D) heat transfer model of the
scala tympani which will enable accurate predictions of the maximum safe input
power to avoid localized hyperthermia when detaching the magnet from the
implant electrode array. Methods: Experiments are designed using a rigorous
scale analysis and performed by measuring transient temperatures in a
3D-printed scala tympani phantom subjected to a sudden change in its thermal
environment and localized heating via a small heat source. Results: The
measured and predicted temperatures are in good agreement with an error less
than 6$\%$. Conclusions: The validated 3D heat transfer model of the scala
tympani is finally applied to evaluate the maximum safe input power to avoid
localized hyperthermia when detaching the magnet. For the most conservative
case where all boundaries except the insertion opening are adiabatic, the power
required to release the magnet attached to the implant electrode array by 1
mm$^3$ of paraffin is approximately half of the predicted maximum safe input
power. Significance: This work will enable the design of a thermally safe
magnetic cochlear implant surgery procedure.
