The Intra-Cochlear Impedance-Matrix (IIM) test for the Nucleus® cochlear implant

Abstract

Objective: To describe the principles and operation of a new telemetry-based function test for the Nucleus ® cochlear implant, known as the CS19 Intra-Cochlear Impedance Matrix (IIM) and to present results from a multicentre clinical study to establish reproducibility (test-retest reliability) and normative ranges. Method: The IIM test measures bipolar impedances between all electrode pairs and employs a normalization procedure based on common ground impedances in order to identify abnormal current paths among electrodes. Six European clinics collected IIM data from a total of 192 devices. Results: Reproducibility was high between initial and repeat measurements. The normative analysis demonstrated narrow ranges among devices after normalization of impedance data. The IIM is able to identify abnormal current paths that are not evident from standard impedance telemetry and may otherwise only be found utilising average electrode voltage measurements (AEV). Conclusions:The IIM test was found to be straightforward to perform clinically and demonstrated reproducible data with narrow ranges in normally-functioning devices. Because this test uses a very low stimulation level the IIM test is well suited for children or multiply handicapped CI users who cannot reliably report on their auditory percepts. The new algorithms show potential to improve implant integrity testing capabilities if implemented in future clinical software.

Analysis of Neural Interface When Using Modiolar Electrode Stimulation. Radiological Evaluation, Trans-Impedance Matrix Analysis and Effect on Listening Effort in Cochlear Implantation

“…The full set of electrical spread curves, when normalized by the current, is known as trans-impedance matrix (TIM). Several studies have demonstrated the utility of TIM and other voltage measurement algorithms [16,17] to identify the intra-cochlear electrode positioning. The proximity of the electrode to the modiolar wall may result in some variation in the tissue and fluid environment, and it is of interest to investigate the effect of the modiolar proximity, the measured transimpedance and the cognitive effort on pitch discrimination.…”

The usefulness integrity testing in children: A single institution experience of 86 tests over a period of 20 years

“…Ten children underwent multiple integrity tests. All integrity testing was carried out using the Crystal and the CS 19 IT system …”

“…During the test, electrodes are placed in the scalp and electrically induced Auditory Brainstem Responses (EABR) are used to measure the electric current passed between the electrodes and the auditory nerve. During an integrity test, impedances between all electrode pairs are measured and normalised to identify any abnormal current path among the electrode array . Once the testing is completed, it can take up to 2 weeks to get results analysed and reported.…”

Az elektródasor visszatekeredésének kimutatása transzimpedanciamátrix (TIM)-vizsgálattal cochlearis implantátumban

“…A rögzített feszültségértékekből feszültségmát rixot hozunk létre. A feszültségmátrixot ezután transzim pedanciamátrixszá alakítjuk, elosztva az egyes feszültség méréseket a stimuláló árammal (Ohm törvénye), így megkapjuk a transzimpedancia értékét az elektródasorra vonatkozólag (intracochlearis áram folyik az intracoch learis kontaktus és az extracochlearis referenciaelektróda között) [19,23]. A TIMet "hőtérkép" segítségével je löljük.…”

“…Míg a SOE az egyes elektró dák körüli neuralis gerjesztőmezők szelektivitását ábrá zolja, addig az EFI az intracochlearis elektródpárok egyes kombinációi közötti elektromos impedanciát és feszültségváltozást vizsgálja. Mindkét forgatókönyv sze rint az a hipotézis, hogy az elektródavisszatekeredés kapcsán az átfedő elektródák jelenléte esetén további, eltérő válasz is jelen van [19][20][21][22][23][24].…”