gms | German Medical Science

Fourth International Symposium and Workshops: Objective Measures in Cochlear Implants

Medical University of Hannover

01.06. bis 04.06.2005, Hannover

The longitudinal spread of the effective stimulation field (ESF) in the implanted human cochlea, from ECAP and finite element analysis

Meeting Abstract

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  • corresponding author L. Cohen - Co-operative Research Centre for Cochlear Implant and Hearing Aid Innovation, Melbourne
  • L. Richardson - Co-operative Research Centre for Cochlear Implant and Hearing Aid Innovation, Melbourne
  • R. Cowan - Co-operative Research Centre for Cochlear Implant and Hearing Aid Innovation, Melbourne

Medical University of Hannover, Department of Otolaryngology. Fourth International Symposium and Workshops: Objective Measures in Cochlear Implants. Hannover, 01.-04.06.2005. Düsseldorf, Köln: German Medical Science; 2005. Doc05omci020

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Veröffentlicht: 31. Mai 2005

© 2005 Cohen et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielf&aauml;ltigt, verbreitet und &oauml;ffentlich zug&aauml;nglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Introduction

Modern telemetry systems for recording the ECAP have made possible the measurement of longitudinal spread of neural excitation (SOE) in the electrically-stimulated cochlea. A major determinant of SOE is the spread of the stimulation field. Determination of field spread would enable quantification of residual factors, which are more indicative of neural characteristics.

Materials and Methods

Measurement of the field spread was made at three separate probe locations in five Nucleus 24 cochlear implant system recipients (three subjects with straight and two subjects with Contour electrode arrays). Using Neural Response Telemetry (NRT) in the Nucleus 24 system, and with the probe location and current fixed, the masker current required to fully mask the probe was determined for maskers at numerous locations along the array. This provided a measure of attenuation of the effective stimulation field (ESF) as a function of the separation of masker and probe. To aid interpretation of the results, finite element analysis (FEA) was used to model voltage at the inner wall of scala tympani, for a straight array positioned at the outer wall and a mid-scalar Contour array.

Results

The NRT results indicated a broader spread of ESF than predicted by the FEA model. Nevertheless, the modelled spread functions provided a reasonable fit to the NRT data, provided they were scaled along the longitudinal position axis (percentage length along the organ of Corti). The ratio of the widths of spread functions for Contour and straight arrays was similar for the experimental data and the model: spread of ESF was less for the Contour.

Conclusions

The FEA model described both the general shape of the ESF spread and the relative spread for the Contour compared to the straight electrode array. However, the experimental spread was broader, consistent with the site of neural excitation being more remote from the stimulated electrode than the inner wall of scala tympani (the modelled site). Measurement of the ESF represents an important step towards quantification of the neural excitation produced by electrical stimulation in the individual patient and, thence, the development of improved speech processing algorithms tailored to the individual.