Can a cochlear implant be used as an electrical impedance tomography device?

Abstract

The imaging of the live cochlea is a challenging task. Regardless of the quality of images obtained from modern clinical imaging techniques, the internal structures of the cochlea mainly remain obscured. Electrical impedance tomography (EIT) is a safe, low-cost alternative medical imaging technique with applications in various clinical scenarios. In this article, EIT is investigated as an alternative method to image and extract the centre of gravity of the modiolus in vivo. This information can be used to augment present postoperative medical imaging techniques to investigate the cochlea. The cochlear implant EIT system was simulated by modelling user-specific electrode array trajectories within a simple conductive medium containing an inhomogeneity representing the modiolus. The method included an adapted adjacent stimulation protocol for data collection. For the image reconstruction, NOSER and Tikhonov priors were considered. A parameter analysis was conducted to find the most robust combination of image priors and hyperparameters for this application. The cochlear implant EIT methodology was validated at different noise levels for four electrode array trajectories. Comparing the NOSER and Tikhonov priors, it was observed that the NOSER prior exhibits superior centre of gravity localisation performance in cochlear implant EIT image reconstruction for different noise levels and user-dependent variability in electrode array trajectories. Image reconstruction, using a NOSER prior at a hyperparameter value of approximately 0.001, resulted in an average centre of gravity localisation error of less than 4% for all electrode array trajectories using difference imaging and less than 5.5% using absolute imaging.