Postoperative Impedance-Based Estimation of Cochlear Implant Electrode Insertion Depth.
Stephan Schraivogel, Philipp Aebischer, Franca Wagner and 4 others
PMID 37157125WHAT IT FOUND
An impedance-based model estimated cochlear implant electrode depth without CT, with an average error of 0.88 mm, about half the 2.1 mm electrode spacing, in 47 fully inserted cases.
With one, two, or three electrodes outside the cochlea, average errors were 2.7 mm, 4.6 mm, and 5.2 mm.
Key findings
01The model estimated linear insertion depth with an absolute error of 0.88 mm ± 0.6 mm in 47 fully inserted cases.
02For cases with one, two, or three extracochlear electrodes, mean absolute estimation error was 2.7 mm, 4.6 mm, and 5.2 mm, respectively.
03The early and late phenomenological models did not differ (p = 0.15).
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
Retrospective analysis from one center using only FLEX 28 electrode arrays, so results may not apply to other arrays or settings. The main accuracy result came from 47 cases with fully inserted arrays; cases with extracochlear electrodes had mean absolute errors of 2.7 mm, 4.6 mm, and 5.2 mm, and the model needs better detection of extracochlear electrodes. Long-term stability of the model was checked in only five cases with a second postoperative CT scan. CT resolution, voltage quantization, and electrode labeling can add error; the reported estimation error was already in the same order of magnitude as the calculated noise floor of 0.4 mm ± 0.3 mm. Four cases with pathological cochlear conditions showed different tissue resistance curves and may bias the estimate. The paper reports accuracy against CT scans, not hearing or speech outcomes.
Declared interests
The authors declared no conflicts of interest.
The easy way to misread this
Do not read this as a validated replacement for CT in all cochlear implant patients. The method was accurate mainly for 47 fully inserted FLEX 28 arrays. Cases with extracochlear electrodes had mean absolute errors of 2.7 mm, 4.6 mm, and 5.2 mm, and the study did not test hearing or speech outcomes.