Biomagnetic Imaging of Cochlear Stimulus Currents

Spelman, Francis

Abstract

The long-term goal of this proposal is to develop a noninvasive monitor of the stimulus currents produced by a cochlear implant. We propose to show the feasibility of sampling the external magnetic field produced during electrical stimulation, and to compute the underlying electric fields that produce the magnetic field. The problem is made easier in this case since the magnitudes and locations of the stimulating cur-rent sources are known. However, the computation of the fields distributed in the tissue will not be trivial. We propose to model current sources in inhomogeneous media and to compute their magnetic fields. Using those magnetic fields, and knowledge of the locations and magnitudes of the current sources, we will compute the volume currents. We will compare the currents computed in the forward problem with those computed in the inverse problem. When we have tested our computational techniques successfully, we will use a saline tank model to produce electromagnetic fields. We will measure the volume electric fields produced with current sources buried in a conducting cylinder located near the surface of the tank, and the magnetic fields produced at the surface of the tank. We will use the algorithms developed in the computational phase of the work to reconstruct the volume currents. If this project is successful, it will provide the preliminary data for a more extensive investigation designed to develop a means to measure the distribution of stimulus currents in human patients and experimental animals who have received cochlear implants. While the project focuses on cochlear stimulation, the principle that will be proven can be extended to other kinds of electrical stimulation like cardiac pacemaking, functional neural stimulation or defibrillation.