Abstract
Cochlear Implants (CIs) are medical implantable devices that can restore the sense of hearing in people with profound hearing loss. Clinical trials assessing speech intelligibility in CI users have found large intersubject variability. One possibility to explain the variability is the individual differences in the interface created between electrodes of the CI and the auditory nerve. In order to understand the variability, models of the voltage distribution of the electrically stimulated cochlea may be useful. With this purpose in mind, we developed a parametric model that can be adapted to each CI user based on landmarks from individual cone beam computed tomography (CBCT) scans of the cochlea before and after implantation. The conductivity values of each cochlea compartment as well as the weighting factors of different grounding modes have also been parameterized. Simulations were performed modeling the cochlea and electrode positions of 12 CI users. Three models were compared with different levels of detail: a homogeneous model (HM), a non-patient-specific model (NPSM), and a patient-specific model (PSM). The model simulations were compared with voltage distribution measurements obtained from the backward telemetry of the 12 CI users. Results show that the PSM produces the lowest error when predicting individual voltage distributions. Given a patient-specific geometry and electrode positions, we show an example on how to optimize the parameters of the model and how to couple it to an auditory nerve model. The model here presented may help to understand speech performance variability and support the development of new sound coding strategies for CIs.
Highlights
Cochlear implants (CIs) are implantable medical devices that are used to restore the sense of hearing for people with profound hearing loss or deafness given that the auditory anatomy is fully developed (Wilson et al, 1991)
A methodology to construct a patientspecific 3D volume conduction model of the cochlea based on clinical cone beam computed tomography (CBCT) imaging data is presented
The simpler and less accurate geometry used in this study can be adapted to clinical CT scans using the electrode positions and just six parameters to characterize the cochlea
Summary
Cochlear implants (CIs) are implantable medical devices that are used to restore the sense of hearing for people with profound hearing loss or deafness given that the auditory anatomy is fully developed (Wilson et al, 1991). In CIs a broad excitation is produced, mainly because the fluids in the cochlea are highly conductive causing the charge to spread along the inner ear. This phenomenon is commonly referred to as spread of excitation. The spread of excitation is influenced by the anatomy and the conductivity of the tissues in the cochlea (Finley et al, 1990; Frijns et al, 1995; Briaire, 2008; Saba, 2012) This was confirmed using in vivo measurements of the cochlea with an implanted electrode, using resistive models and solving analytical equations of the three-dimensional (3D) volume conduction problem (Suesserman and Spelman, 1993). It is known that the anatomy (Würfel et al, 2014) and electrode positions (Landsberger et al, 2015) differ substantially from CI user to CI user
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