Improving the sensitivity of cochlear implant integrity testing: recording electrode voltages with surface electrodes to diagnose partial short circuits in Advanced Bionics Ultra V1 devices

Grasmeder, Mary, Rogers, Katrine, Aydin, Ziya, Hough, Kate, Verschuur, Carl and Newman, Tracey (2023) Improving the sensitivity of cochlear implant integrity testing: recording electrode voltages with surface electrodes to diagnose partial short circuits in Advanced Bionics Ultra V1 devices. 11th International Symposium on Objective Measures in auditory implants, Flanders Meeting & Convention Centre, Antwerp, Belgium. 25 - 28 Sep 2023.

Abstract

Background: advanced Bionics (AB) Ultra V1 devices are vulnerable to partial short circuits, resulting from moisture ingress. The manufacturer provides clinicians with a diagnostic test to identify this fault, “Electric Field Imaging” (EFI), using trans-impedance measurements. AB estimate the sensitivity of the algorithm incorporated in the test to be between 70 and 90%. We Recorded Electrode Voltages (REVs) using surface electrodes and compared these with the EFI test.

Method: 65 AB Ultra V1 devices supported by the University of Southampton Auditory Implant Service were assessed by REVs and EFI during routine clinic appointments. 32 devices had been tested at least twice, 16 in children and 16 in adults by March 2023. REVs was performed with surface electrodes placed on the earlobes and forehead, whilst the implant was simulated in live mode, taking approximately five minutes per ear.

Results: 10 of the 32 devices which had been tested at least twice presented as normal at the earlier test, based on the EFI test and two criteria previously suggested in the published literature for REVs. Relative Electrode Voltages (EVs) across the electrode array were calculated for measurements made with the
recording electrodes on the ipsilateral and contralateral earlobes. These were fitted to a polynomial (cubic) function, showing excellent agreement, mean R-squared=0.97 (range 0.89-0.997). For individual electrodes, the mean absolute difference between the predicted and measured values was 1.1%, st dev 1.3%. All REVs differed by Devices which presented as abnormal on the EFI test gave a poorer fit to a cubic function, mean Rsquared=0.79 (range 0.40-0.96), based on the later tests (N=33). The mean absolute difference between the predicted and measured EVs was 8.2%, st dev 9.3%. All devices had at least one electrode with an EV ≥9% different from the predicted value. 32 devices were returned as normal on the later EFI tests. Of these, 15 devices had REVs with a REV ≥9% different from the predicted value.

Conclusions: REVs was found to be highly sensitive to partial short circuits caused by moisture ingress in AB Ultra V1 devices. EVs were well fitted to a cubic function in normal devices. Results suggest that 77% of devices tested were affected by the fault at the later test.

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Contributors

Author: Kate Hough

Author: Tracey Newman

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