The value of trans-impedance matrix (TIM) measurements for detecting new bone formation (NBF) and influence on electrophysiology, residual hearing and performance

Rationale:
Cochlear implantation (CI) can result in post-operative intracochlear changes such as the formation of connective tissue and even new bone formation. This has been observed to lead to higher impedances, subsequent higher energy consumption and out-of-compliance issues. It may also influence long term residual hearing, lead to channel interaction and impact performance directly. Trans-impedance matrix (TIM) measurement is a promising non-invasive and simple technique which could possibly be used as a clinical diagnostic tool for NBF in the future.

Objective:
Determine the value of prospective TIM-measurement for the detection of NBF in patients after cochlear implantation by comparing to ultra-high resolution (UHR) CT imaging and determine the clinical relevance of NBF by studying the relationship between NBF and electrophysiological parameters, residual hearing and speech perception development.

Study design:
Prospective pilot study

Study population:
30 patients selected for cochlear implantation at the Radboudumc with Cochlear Ltd. electrodes (Nucleus Slim Straight, Nucleus Contour Advance and Nucleus Slim Modiolar electrode) without contraindications for CT-scan or an anatomical situation that may influence normal insertion of the CI.

Intervention:
Intra- and post-operative TIM measurement and pre- and postoperative UHR CT-scan of the petrosal bone

Follow-up:
1 year including (standard) scheduled follow-up visits at 1, 2, 4, 6, 8 weeks and at 3, 6 and 12 months.

Primary outcome measure:
Predictive value of TIM-measurement for detection of NBF

Secondary outcomes measures:
Influence of NBF on residual hearing, C-T level changes in relation to NBF growth, timing of NBF formation

Data analysis:
An initial analysis at patient level will be performed in which we will evaluate the relationship between the fraction of electrode contacts with NBF per patient per timepoint with the average TIM measurement for that patient and timepoint, as well as with the increase in TIM level up to that timepoint. If possible, a ROC curve will be estimated, although the amount of data will presumably be too small for this analysis to be confirmative.
Additional analysis will also be performed to evaluated the new bone formation at electrode level, using a complex logistic regression model with NBF at individual contact level as dependent variable per timepoint and with a random effect for patient and TIM parameters as independent variables.

Previous, unpublished research performed in our center showed promising results for the ability of TIM measurements to predict the presence of new bone in CI patients; higher TIM values were measured in contacts with NBF compared to those without. Therefore, we expect to find an association between an increase in TIM level over time and presence of NBF in CI patients.

1. <6 months prior to surgery
2. Baseline (Implantation date)
3. 1 week
4. 2 weeks
5. 4 weeks
6. 6 weeks
7. 8 weeks
8. 3 months
9. 6 months
10. 12 months

Trans-impedance matrix (TIM) measurement, ultra-high resolution CT-scan