gms | German Medical Science

To increase the potential benefits of cochlear implants, it is necessary to develop more effective ways to stimulate the surviving auditory neurons of the patient. To this purpose, this study was designed to derive a realistic numerical model in order to understand the relationship between the electrode array position and insertion depth with the spatial spread of neural excitation. For each patient (10 subjects) involved in this study, a 3D geometrical model of the implanted cochlea, the Rosenthal's canal, and the inner ear canal was developed by the 3D volumetric reconstruction of CT scan obtained after implantation. The 3D cochlear model of the patient was used to compute the potential distribution within the cochlea due to the stimulating current sources of the implant array. A finite element method (FEM) was employed to solve the volume conduction problem. The different structures inside the cochlea and its surroundings were characterized by conductivities derived from physiological measures. A realistic model of the Nucleus^®24 electrode array was developed. It was put inside the 3D cochlear model by matching its position with that derived from CT scans of the patient. For each patient, spatial spread of neural excitation (SOE) were extracted from ECAP responses measured by the Cochlear NRT software. For each, the results of the comparison between functional SOE and the potential distribution inside the 3D model were used to fit the model parameters on the specific electrical characteristics of the patient cochlea and nerve. Simulations were done to derive the spread of excitation using different montages and by varying the duration of the current stimulus.