Experimental Validation of a Three-Dimensional Heat Transfer Model Within the Scala Tympani With Application to Magnetic Cochlear Implant Surgery

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, which may cause thermal trauma, and removed from the scala tympani. Objectives: The objective of this work is to experimentally validate a threedimensional (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 isothermal 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% ( p = 0.84). For the most conservative case where all boundaries of the model except the insertion opening are adiabatic, the power required to release the magnet attached to the implant electrode array by 1 mm3 of paraffin is approximately half of the predicted maximum safe input power. Conclusions: A 3D heat transfer model of the scala tympani is successfully validated and enables predicting the maximum safe input power required to detach the magnet from the implant electrode array. Significance: This work will enable the design of a thermally safe magnetic cochlear implant surgery procedure.