The benefit of transimpedance matrix for intraoperative estimation of electrode position and postoperative monitoring of positional changes

For cochlear implantation, the transimpedance matrix (TIM) has been shown to be very efficient in detecting electrode array misplacements (Klabbers et al. 2021, Hoppe et al. 2022). Furthermore, it has been shown that in principle the insertion depth of the electrode array can be derived from the TIM (Aebischer et al. 2021). Based on this, Schraivogel et al. (2022) recently assumed postoperative position shifts by evaluating TIMs using a multiparametric mixed model. In the following study, the methodological approach of Hoppe et al. (2022) is followed, in which the phases of the gradients are investigated rather than the transimpedances directly. The purpose was to test how accurately insertion depth can be estimated by this approach and whether postoperative positional shifts can be observed from the comparison of intra- and postoperative TIM measurements. TIMs were measured for 27 patients and additionally postoperative TIMs (at least 3 months after intial activation of the sound processor) for 19 patients. All of these patients were implanted with a CI622 from Cochlear ltd. Postoperatively, a Stenvers projection was taken to determine the insertion depth of the electrode array. The results of this study show that the insertion depth can be very well estimated by using the mean value of the gradient phases (26°±35°). It also show that postoperatively the estimated insertion depth of the electrode array significantly decrease by a mean of -24°±10°. This suggests that the electrode position undergoes postoperative changes. One explanation for this negative drift can be an expansion of the electrode array towards the lateral wall.

Publication History

Article published online:
12 May 2023