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

Összefoglaló. Bevezetés: Az elmúlt években a cochlearis implantátum a súlyos halláskárosodás vagy a teljes siketség rutinszerű és hatékony kezelési eszközévé vált. Korunk egyik leggyakrabban használt és leghatékonyabb újítása a cochlearis implantációban a perimodiolaris vékony elektródasorok alkalmazása. A cochlea középtengelyét, a modiolust szorosan ölelő atraumatikus elektródasor igen meggyőző eredménnyel bizonyítja népszerűségét, mind az elektrofiziológiai mérések során, mind az akusztikus hallás megőrzése terén nyújtott teljesítményével. Ugyanakkor igen kevés publikáció írja le az elektródasor nem megfelelő helyzetének előfordulási gyakoriságát, pontosabban a visszatekeredését a csúcsi szakaszon. Célkitűzés: Tanulmányunk célja olyan szoftveres technika, a transzimpedancia-mátrix (TIM) beillesztése a rutin intraoperatív elektrofiziológiai mérési metodikák közé, amely képes objektív diagnosztikai lehetőséget biztosítani ahhoz, hogy korán felismerhessük a cochlearis implantátum elektródasorán keletkezett hurkot. Módszer: Hároméves kisgyermek kétoldali cochlearis implantációját követően, posztoperatív röntgenfelvételen a bal oldalon az elektródasor megfelelő pozíciója figyelhető meg, míg a jobb oldalon az intracochlearis elektródasor végének visszatekeredése igazolódott. Képalkotó vizsgálatot követően elektrofiziológiai metódusként TIM-vizsgálatot végeztünk. Az eljárás során a mérőeszköz a kijelölt stimuláló elektródákon 1 V nagyságrendű feszültséget közöl állandó áramerősség mellett a cochlea közel eső struktúrái felé. Mérőelektródák segítségével regisztráljuk a szöveteken mérhető feszültséget, majd transzimpedancia-mátrixszá alakítjuk a mért értékeket. Eredmények: Az elektródasor visszatekeredése, amelyet korábban radiológiai vizsgálattal igazoltunk, az objektív elektrofiziológiai mérések segítségével is jól azonosítható, és a vizsgálatok szoros párhuzamot mutatnak. Következtetés: Az elektródák helyzetének megjelenítésére szolgáló standard radiológiai képalkotási technikák kiegészíthetők, illetve kiválthatók egyszerűen elvégezhető, hatékony, objektív elektrofiziológiai vizsgálatokkal. Intraoperatíven, még a sebzárás előtt kimutatható, ha az elektródasor nem megfelelő helyzetbe került, így csökkenthetjük a radiológiai vizsgálatokkal járó sugárterhelés és annak finanszírozási problémáját. Orv Hetil. 2021; 162(25): 988–996. Summary. Introduction: In recent years, the cochlear implant has become a routine and effective treatment tool for severe hearing loss and total deafness. One of the commonly used and effective innovations of our time in cochlear implantation is the perimodiolar thin electrode array. The atraumatic electrode array, which closely embraces the central axis of the cochlea (modiolus), has served its popularity with very convincing results, with its performance in both electrophysiological measurements and acoustic hearing preservation. However, very few publications describe the frequency of improper positioning of the electrode array, which is known as ‘tip fold-over’. Objective: The aim of our study is to incorporate a software technique, the transimpedance matrix (TIM), into routine intraoperative electrophysiological measurement methodologies to provide a potential objective diagnostic opportunity for early detection of tip fold-over of the electrode array. Method: Following bilateral cochlear implantation of a three-year-old child, postoperative radiography showed the correct position of the electrode array on the left side, while tip fold-over of the intracochlear electrode array was detected on the right side. Following imaging, a TIM study was performed as an electrophysiological method. During the procedure, the measuring device transmits a voltage of the order of 1 V to the nearby structures of the cochlea at a constant current at the designated stimulus electrodes. Measuring electrodes were used to register the voltage measured on the tissues, and then converted into a TIM. Results: Electrode tip fold-over was previously diagnosed by radiological examination, while it can also be diagnosed by objective electrophysiological measurements now, and these two tests correlate well. Conclusion: Standard radiological imaging techniques for electrode positioning can be supplemented or replaced by easy-to-perform, effective objective electrophysiological studies. Tip fold-over can be detected intraoperatively, even before wound closure, if the electrode array is in the wrong position, thus reducing the radiation exposure associated with radiological examinations as well as reducing relevant costs. Orv Hetil. 2021; 162(25): 988–996.

The Panoramic ECAP Method: Estimating Patient-Specific Patterns of Current Spread and Neural Health in Cochlear Implant Users

The knowledge of patient-specific neural excitation patterns from cochlear implants (CIs) can provide important information for optimizing efficacy and improving speech perception outcomes. The Panoramic ECAP (‘PECAP’) method (Cosentino et al. 2015) uses forward-masked electrically evoked compound action-potentials (ECAPs) to estimate neural activation patterns of CI stimulation. The algorithm requires ECAPs be measured for all combinations of probe and masker electrodes, exploiting the fact that ECAP amplitudes reflect the overlapping excitatory areas of both probes and maskers. Here we present an improved version of the PECAP algorithm that imposes biologically realistic constraints on the solution, that, unlike the previous version, produces detailed estimates of neural activation patterns by modelling current spread and neural health along the intracochlear electrode array and is capable of identifying multiple regions of poor neural health. The algorithm was evaluated for reliability and accuracy in three ways: (1) computer-simulated current-spread and neural-health scenarios, (2) comparisons to psychophysical correlates of neural health and electrode-modiolus distances in human CI users, and (3) detection of simulated neural ‘dead’ regions (using forward masking) in human CI users. The PECAP algorithm reliably estimated the computer-simulated scenarios. A moderate but significant negative correlation between focused thresholds and the algorithm’s neural-health estimates was found, consistent with previous literature. It also correctly identified simulated ‘dead’ regions in all seven CI users evaluated. The revised PECAP algorithm provides an estimate of neural excitation patterns in CIs that could be used to inform and optimize CI stimulation strategies for individual patients in clinical settings.

Radiological and NRT-Ratio–Based Estimation of Slim Straight Cochlear Implant Electrode Positions

Objectives: An intraoperative neural response telemetry-ratio (NRT-ratio) was established, which can provide information about the intraoperative intracochlear electrode array position for perimodiolar electrodes. Methods: In a retrospective controlled study in 2 tertiary referral centers, the electrophysiological data sets of 50 patients with measured intraoperative auto-NRTs and postoperative radiological examinations were evaluated. All patients were implanted with Nucleus slim straight electrodes. The NRT-ratio was calculated by dividing the average auto-NRT data from electrodes 16 to 18 with the average from electrodes 5 to 7. Using a flat panel tomography system or a computed tomography, the position of the electrode array was certified radiological. Results: Radiologically, 2 out of 50 patients were identified with an electrode translocated from the scala tympani into the scala vestibuli. The radiologically estimated electrodes indicating a scalar change showed a regular NRT-ratio but nonspecific NRT-level changes at the localization of translocation.

Electrophysiological Detection of Scalar-Changing Perimodiolar Cochlear Electrode Arrays: A Six-Month Follow-Up Study

The position of the cochlear electrode array within the scala tympani is essential for optimal hearing benefit. An intraoperative neural response telemetry ratio (NRT ratio; a threshold ratio of pairs of apical and basal electrodes) has been established, which can provide information about the intracochlear electrode array position. Out of a previous collective of 85 patients, the 6-month follow-up electrophysiological NRT data of 37 patients have been included in this study. Comparing the intraoperatively estimated NRT ratio with the 6-month follow-up NRT ratio, it remained unchanged intraindividually in 92% of cases. Within this group the NRT ratio and the intracochlear position of the electrode array matched in all cases. There were two newly occurring mismatches and one new match was observed. After a period of 6 months the NRT ratio remained unchanged in most cases and showed a good correlation with the intracochlear position of the electrode array.

Modiolus-Hugging Intracochlear Electrode Array with Shape Memory Alloy

In the cochlear implant system, the distance between spiral ganglia and the electrodes within the volume of the scala tympani cavity significantly affects the efficiency of the electrical stimulation in terms of the threshold current level and spatial selectivity. Because the spiral ganglia are situated inside the modiolus, the central axis of the cochlea, it is desirable that the electrode array hugs the modiolus to minimize the distance between the electrodes and the ganglia. In the present study, we propose a shape-memory-alloy-(SMA-) embedded intracochlear electrode which gives a straight electrode a curved modiolus-hugging shape using the restoration force of the SMA as triggered by resistive heating after insertion into the cochlea. An eight-channel ball-type electrode array is fabricated with an embedded titanium-nickel SMA backbone wire. It is demonstrated that the electrode array changes its shape in a transparent plastic human cochlear model. To verify the safe insertion of the electrode array into the human cochlea, the contact pressures during insertion at the electrode tip and the contact pressures over the electrode length after insertion were calculated using a 3D finite element analysis. The results indicate that the SMA-embedded electrode is functionally and mechanically feasible for clinical applications.

Effects of Clarion Electrode Design on Mapping Levels in Children

The design of the placement of the Clarion cochlear implant's intracochlear electrode array has undergone 2 revisions since its introduction, each to improve modiolar proximity. Stimulation with modiolar proximity may reduce current requirements for threshold levels and most comfortable levels of stimulation. This study analyzed the effects of electrode design on programming levels for deaf children implanted with the 3 cochlear implant designs and followed at The Children's Hospital of Philadelphia. Psychophysical data were reported if measurements were taken approximately 3 months after initial activation, and programming parameters included nonsequential monopolar stimulation of 75-μs-per-phase biphasic pulses presented at 813 Hz per electrode. The threshold level and most comfortable programming level were measured by standard clinical techniques appropriate for children. The results indicate that the 2 electrode placement revisions have each significantly reduced threshold levels and most comfortable stimulation levels. These results are discussed in the context of device aesthetics, safety, and function.