Modeling Intracochlear Magnetic Stimulation: A Finite-Element Analysis

Abstract

This study models induced electric fields, and their gradient, produced by pulsatile current stimulation of submillimeter inductors for cochlear implantation. Using finite-element analysis, the lower chamber of the cochlea, scala tympani, is modeled as a cylindrical structure filled with perilymph bounded by tissue, bone, and cochlear neural elements. Single inductors as well as an array of inductors are modeled. The coil strength (~100 nH) and excitation parameters (Peak current of 1 – 5 A, Voltages of 16 – 20 V) are based on a formative feasibility study conducted by our group. In that study, intracochlear micro-magnetic stimulation achieved auditory activation as measured through the auditory brainstem response in a feline model. With respect to the finite element simulations, axial symmetry of the inductor geometry is exploited to improve computation time. It is verified that the inductor coil orientation greatly affects strength of the induced electric field and thereby the ability to affect the transmembrane potential of nearby neural elements. Furthermore, upon comparing an array of micro-inductors with a typical multi-site electrode array, magnetically excited arrays retain greater focus in terms of the gradient of induced electric fields. Once combined with further in-vivo analysis, this modeling study may enable further exploration of the mechanism of magnetically induced, and focused neural stimulation.

Characterization and Miniaturization of Silver-Nanoparticle Microcoil via Aerosol Jet Printing Techniques for Micromagnetic Cochlear Stimulation

“…Our group has previously explored cochlear stimulation through finite element modeling (FEM) where the lower chamber of the cochlea was modelled to surround a model of a commercially available cylindrical, coil inductor. It was demonstrated that the coil was capable of micromagnetic stimulation of the cochlea in a feline model [3]. Moving forward from these findings, a new coil structure has been designed and tested for the cochlear application to potentially improve spatial resolution and move towards system that may reduce implantation trauma.…”

“…One possible challenge is the spread of cochlear activation thereby diminishing the fidelity of sound. Fortunately, recent studies have shown that utilizing eddy currents generated from electromagnetic fields to stimulate nearby tissue [2], rather than direct current injection, can improve spatial resolution of the tissue in the cochlea [3] and improve CI functionality [4], and ultimately hearing perception.…”

ASA Algorithm Combined with Current Simulation Method (CSM) for the Magnetic Induction under HV Power Lines in 3D Analysis Model

“…This illustrates that taking into account the effect of conductor sag in the magnetic induction analysis is a very practical factor to model the real curvature of the power line; it plays an important role in determining the exact values of the magnetic induction. As a result, it can be seen that the maximum values obtained of the magnetic induction are below the limits set by the ICNIRP recommendations and therefore they do not present any appreciable hazard to human health [43,44].…”

Magnetic Stimulation Allows Focal Activation of the Mouse Cochlea

“…Further, the spread of magnetic fields in the scala tympani is less sensitive to the high conductivity of perilymph, further helping to confine activation. While the strength of the fields induced by micro-coils is small, computational studies suggest that the spatial gradient of the resulting fields is suprathreshold (17)(18)(19)(20)(21)(22), and simulations specific to the cochlea suggest a multi-turn spiral coil should produce fields strong enough to activate SGNs (23). It is not clear however whether spiral coil designs are best for use in a high-count, multi-coil array designed for the cochlea, as they might reduce the flexibility of the implant and thus could increase the risk for iatrogenic trauma during insertion.…”