Development of a system for frequency-specific stimulation of the basal electrode contact in cochlear implantation

Determining the individual frequency of each electrode contact is the basis for the so-called “anatomy-based” fitting. This might be a problem for the basal electrode contact, which is usually in the range of more than 10 kHz, but current audio processors only allow fitting up to 8.5 kHz. This discrepancy could be the reason for the higher perception of sounds or speech that CI patients sometimes report. The aim of this work was to place the basal electrode contact of a specially developed CI electrode array with marker rings below 8.5 kHz by means of preoperative frequency determination.

Flat-panel volume CT (fpVCT) images were obtained from 3 human temporal bone specimens. Secondary reconstructions were composed with a slice thickness of 100 µm. Cochlear length was determined using 3D-curved multiplanar reconstruction. The distance from the round window to the site where the basal electrode contact should be located (approximately 8.25 kHz) was calculated and the electrode array was inserted accordingly. A postoperative fpVCT image was taken to verify the electrode positioning.

The electrode array was inserted into the cochlea without any problems. Positioning with the help of the marker rings of the basal electrode contact was successful with only a small deviation of max. 200 Hz from the desired frequency location.

Using the method described, it was possible to position the basal electrode contact in an area of the cochlea that could be correctly stimulated by the existing speech processors in the context of anatomy-based fitting. Whether this will improve the patients' pitch perception has to be evaluated in clinical trials.

Publication History

Article published online:
24 May 2022