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

EFI-Model Analysis of Current Spread with the Hifocus Electrode with and without Positioner

Meeting Abstract

  • corresponding author F.B. van der Beek - ENT department, Leiden University Medical Centre, Leiden, The Netherlands
  • B.M. Verbist - Department of Neuroradiology, Leiden University Medical Centre, Leiden, The Netherlands
  • F.J. Vanpoucke - Advanced Bionics Advanced Research Europe, Antwerp, Belgium
  • J.J. Briaire - ENT department, Leiden University Medical Centre, Leiden, The Netherlands
  • J.H.M. Frijns - ENT department, Leiden University Medical Centre, Leiden, The Netherlands

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. Doc05omci009

Die elektronische Version dieses Artikels ist vollständig und ist verfügbar unter: http://www.egms.de/de/meetings/omci2005/05omci009.shtml

Veröffentlicht: 31. Mai 2005

© 2005 van der Beek 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

The objectives of this study were to clarify the effects of intrascalar position and insulating properties of electrode arrays on intracochlear electrical fields.

Materials and Methods

A recently developed impedance model, which uses Electrical Field Imaging (EFI) recordings as input, was applied to study the spatial distribution of injected current in two patient groups implanted with the CII implant. The first group was implanted with a HiFocus 1 electrode with a partially inserted silastic positioner (19), whereas the other without (20). These data were compared with the insertion depths of all their electrode contacts, which were obtained with high quality MSCT-imaging.

Results

In all patients the transversal resistances, which modelled the current straying out of the cochlea, were a factor 100 higher than the longitudinal resistors, representing the current flow along the scala tympani. These longitudinal resistors were shown to be significantly higher for the basal contacts in the presence of a positioner (p<0.05). Additionally, the basal resistor, modelling the current drain from the basal end of the cochlea, was twice as high for the positioner group. A significant correlation (r<0.8; p<0.001) existed between insertion depth and this basal resistor in non-positioner patients.

Conclusions

Longitudinal conductivity paths along the array dominate, but are reduced with a positioner, facilitating confinement of the spread of excitation to a more restricted area. Basal current drains can explain the basal increase in T-levels, seen with shallowly inserted non-positioner electrodes. We propose EFI-measurements of basal resistors as an intraoperative measure of insertion depth.