Detection of Extracochlear Electrodes Using Electrical Field Imaging (EFI)

Objective: To analyze the use of electrical field imaging (EFI) in the detection of extracochlear electrodes in cochlear implants (CI).

Study design: Retrospective cohort study.

Setting: Tertiary academic medical center.

Methods: EFI patterns from 6 recipients with extracochlear electrodes were compared with 10 recipients with all intracochlear electrodes to identify differences in EFI patterns between these two groups. For the extracochlear group, EFI patterns were analyzed using two methods: visual inspection and calculation of the average impedance difference (AID) between specific EFI curves. These results were then compared with information from CT and plain film imaging, surgical notes, and audiology tests to confirm the placement of the electrodes in each recipient.

Results: An average AID of 0.06 kΩ was calculated from the EFI patterns for recipients with complete electrode insertion, whereas an average AID of 0.15 kΩ was calculated from the EFI curves measured for the extracochlear electrodes. Visual analysis of the EFI impedance curves for extracochlear electrodes showed a distinct separation from those measured for intracochlear electrodes. Based on AID analysis and visual inspection the EFI, patterns were in close agreement with the number of extracochlear electrodes detected based on either imaging, intraoperative surgical note, or audiological findings.

Conclusion: EFI is a noninvasive, inexpensive, and time-efficient measurement that can be used to detect extracochlear electrodes and monitor electrode migration from the cochlea.