2020/03/24 by Neumayer, Hannah-Lina, Adel, Youssef, Baumann, Uwe
#610 Medical sciences #Cochlea-Implantat-Elektroden #Cochlea-Implantate #Frequenz-Zuordnung #Insertionswinkel #Medicine #Tonotopie #cochlear implant electrodes #cochlear implants #frequency assignment #insertion angle #tonotopy
paper · doi:10.3205/zaud000006
Cochlear implants (CIs) are currently the therapy of choice to regain hearing sensation in patients with severe or complete hearing loss. The electrode carrier inserted into the cochlea can electrically stimulate auditory nerve fibers at different locations. The stimulated population depends on the length and design of the electrode, as well as the individual anatomical variations of the cochlea. The frequency mismatch between the bandpass filter frequency assigned to each electrode and the normal tonotopic distribution of characteristic frequencies along the basilar membrane depends mainly on the insertion depth of the electrode array. In this study, cone-beam CT was collected from 32 ears after cochlear implantation (MED-EL FLEX28, Innsbruck, Austria) to assess electrode placement. CT images were analyzed to determine electrode positions and to calculate individual frequency mismatch. An overlay of selected slices was used to estimate individual cochlear duct length (CDL). CDL was calculated after setting reference points according to Escudé et al (2006). CDL results were generally comparable with the data presented by Escudé et al. Furthermore, insertion angles of all electrodes were measured. Using the insertion angles, the tonotopic assignment according to Greenwood (position to frequency mapelectrode , Ep-Fm) of the individual electrode contacts was determined using the models of Escudé et al. as well as Stakhovskaya et al (2007). The comparison of these results with the frequency band assignment of the individual CI processor fitting (MED-EL SONNET) showed a frequency mismatch between 175.8 Hz and 5.48 kHz, which was higher in the apical than in the basal region. The results of this study showed that the calculation proposed by Stakhovskaya et al. with the organ of Corti as the reference point yielded the minimal interquartile range of the Ep-Fm difference from the individualized model according to Escudé. Thus it can be concluded that for electrode locations close to the lateral wall this method allows more accurate determination of characteristic frequency allocations.