Towards unblinding the surgeons: Complex electrical impedance for electrode array insertion guidance in cochlear implantation
The complications during electrode array insertion in scala tympani for cochlear implantation may cause trauma, residual hearing loss and affect speech outcomes. The inner ear is like a black box for surgeons during the insertion process with no real-time feedback and must rely on radiation- based extraoperative imaging. Impedance measurement of electrodes during insertion is a simple yet effective method to assess array position. For this, an impedance meter has been designed which can measure magnitude (|Z|), phase (θ), real (R) and imaginary (Xc) parts of impedance. A switching circuit can sequentially scan all electrode pairs at regular intervals during insertion. An Evo straight electrode array is inserted in a transparent 2:1 scaled up 2D cochlear model (11 trials) filled with 0.9% saline using a 3-degrees-of- freedom actuation system. Bipolar impedance measurements of 8 pairs (40 samples each) are taken at regular intervals during 25 mm insertion at speed of 0.05mm/sec. A notable increase in |Z| and R is observed in the apical 3 electrode pairs when they first get in to contact with the lateral wall. At the same time, the phase gets less negative (more resistive impedance) and Xc increases (less capacitance). These results show that impedance can be used for electrode array localization in cochlea and impedance change due to electrode proximity to different materials can have application in other electrode implants.
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