Relationship Between Electrode-to-Modiolus Distance and Current Levels for Adults With Cochlear Implants

Is the spread of excitation different between adults and children cochlear implants users?

PURPOSE

While cochlea is adult size at birth, etiologies and bone density may differ between children and adults. Differences in neural response thresholds (tNRT) and the spread of excitation (SOE) width may impact the use of artificial intelligence algorithms in speech processor fitting.

AIM

To identify whether neural response telemetry threshold and spread of excitation width are similar in adults and children.

METHODS

Retrospective cross-sectional study approved by the Ethical Board. Intraoperative tNRT and SOE recordings of consecutive cochlear implant surgeries in adults and children implanted with Cochlear devices (Cochlear™, Australia) were selected. SOE was recorded on electrode 11 (or adjacent, corresponding to the medial region of the cochlea) through the standard forward-masking technique in Custom Sound EP software, which provides SOE width in millimeters. Statistical comparison between adults and children was performed using the Mann-Whitney test (p ≤ 0.05).

RESULTS

Of 1282 recordings of intraoperative evaluations, 414 measurements were selected from children and adults. Despite the tNRT being similar between adults and children, SOE width was significantly different, with lower values in children with perimodiolar arrays. Besides, it was observed that there is a difference in the electrode where the SOE function peak occurred, more frequently shifted to electrode 12 in adults implanted. In straight arrays, there was no difference in any of the parameters analyzed on electrode 11.

CONCLUSION

Although eCAP thresholds are similar, SOE measurements differ between adults and children in perimodiolar electrodes.

Dependability of Electrode to Modiolus Distance in Patients Specific Electrode Selection: A Cadaveric Model Study

OBJECTIVE

This study aims to discern the disparities in the electrode-to-modiolus distance (EMD) between cochleostomy and round window approaches when performed sequentially in the same temporal bone. Additionally, the study seeks to identify the cochlear metrics that contribute to these differences.

METHODOLOGY

A cross-sectional study was conducted, involving the sequential insertion of a 12-electrode array through both round window and cochleostomy approaches in cadaveric temporal bones. Postimplantation high-resolution CT scans were employed to calculate various parameters.

RESULTS

A total of 12 temporal bones were included in the imaging analysis, revealing a mean cochlear duct length of 32.892 mm. The EMD demonstrated a gradual increase from electrode 1 (C1) in the apex (1.9 ± 0.07 mm; n = 24) to electrode 12 (C12) in the basal turn (4.6 ± 0.24 mm; n = 12; p < 0.01). Significantly higher EMD values were observed in the cochleostomy group. Correlation analysis indicated a strong positive correlation between EMD and cochlear perimeter (CP) (rs = 0.64; n = 12; p = 0.03) and a strong negative correlation with the depth of insertion (DOI) in both the middle and basal turns (rs = - 0.78; n = 20; p < 0.01). Additionally, EMD showed a strong negative correlation with the DOI-CP ratio (rs = -0.81; n = 12; p < 0.01).

CONCLUSION

The cochleostomy group exhibited a significantly higher EMD compared with the round window group. The strong negative correlation between EMD and DOI-CP ratio suggests that in larger cochleae with shallower insertions, EMD is greater than in smaller cochleae with deeper insertions.

LEVEL OF EVIDENCE

N/A Laryngoscope, 2024.

A Multicenter Comparison of 1-yr Functional Outcomes and Programming Differences Between the Advanced Bionics Mid-Scala and SlimJ Electrode Arrays

OBJECTIVE

To determine if there is a difference in hearing outcomes or stimulation levels between Advanced Bionics straight and precurved arrays.

STUDY DESIGN

Retrospective chart review across three implant centers.

SETTING

Tertiary centers for cochlear and auditory brainstem implantation.

PATIENTS

One hundred fifteen pediatric and 205 adult cochlear implants (CIs) were reviewed. All patients were implanted under the National Institute for Health and Care Excellence 2009 guidelines with a HiRes Ultra SlimJ or Mid-Scala electrode array.

MAIN OUTCOME MEASURES

Hearing preservation after implantation, as well as CI-only listening scores for Bamford-Kowal-Bench sentences were compared 1 year after implantation. Stimulation levels for threshold and comfort levels were also compared 1 year after implantation.

RESULTS

Hearing preservation was significantly better with the SlimJ compared with the Mid-Scala electrode array. Bamford-Kowal-Bench outcomes were not significantly different between the two arrays in any listening condition. Stimulation levels were not different between arrays but did vary across electrode contacts. At least one electrode was deactivated in 33% of implants but was more common for the SlimJ device.

CONCLUSION

Modern straight and precurved arrays from Advanced Bionics did not differ in hearing performance or current requirements. Although hearing preservation was possible with both devices, the SlimJ array would still be the preferred electrode in cases where hearing preservation was a priority. Unfortunately, the SlimJ device was also prone to poor sound perception on basal electrodes. Further investigation is needed to determine if deactivated electrodes are associated with electrode position/migration, and if programming changes are needed to optimize the use of these high-frequency channels.

Electrode-Modiolus Distance Affects Speech Perception for Lateral Wall Electrodes

OBJECTIVES

The goal of this study was to use cone-beam computed tomography to locate the electrode-modiolus distance (EMD) and correlate this with speech perception in cochlear implant (CI) recipients of the 31.5-mm lateral wall (LW) electrode arrays.

STUDY DESIGN

Retrospective review.

PATIENTS

Forty-five child CI recipients with prelingual profound sensorineural hearing loss of inserted 31.5-mm LW arrays listening with a CI-alone device.

INTERVENTIONS

Stepwise forward multiple linear regression was performed to control and reduce the variability in implant performance to determine whether EMD affects speech perception.

MAIN OUTCOME MEASURES

Electrode location (angular insertion depth [AID], EMD), together with the electrode impedance (EI), surgical approach, sex, CI age, and preimplant hearing aid usage were estimated as independent variables. The dependent variables were the Meaningful Use of Speech Scale (MUSS) and parents' evaluation of children's aural/oral performance (PEACH) assessed with the CI alone at 12 months postactivation.

RESULTS

EMD and CI age were predictive variables for PEACH/MUSS. A negative correlation was found between AID and EMD (r = -0.56, p < 0.01), whereas EMD had a moderately positive correlation with EI (r = 0.32, p < 0.01).

CONCLUSIONS

The best "location-related" predictor of postoperative speech perception was EMD with a 31.5-mm array among CI-alone users.

Effects of the Number of Channels and Channel Stimulation Rate on Speech Recognition and Sound Quality Using Precurved Electrode Arrays

PURPOSE

This study investigated the relationship between the number of active electrodes, channel stimulation rate, and their interaction on speech recognition and sound quality measures while controlling for electrode placement. Cochlear implant (CI) recipients with precurved electrode arrays placed entirely within scala tympani and closer to the modiolus were hypothesized to be able to utilize more channels and possibly higher stimulation rates to achieve better speech recognition performance and sound quality ratings than recipients in previous studies.

METHOD

Participants included seven postlingually deafened adult CI recipients with Advanced Bionics Mid-Scala electrode arrays confirmed to be entirely within scala tympani using postoperative computerized tomography. Twelve conditions were tested using four, eight, 12, and 16 electrodes and channel stimulation rates of 600 pulse per second (pps), 1,200 pps, and each participant's maximum allowable rate (1,245-4,800 pps). Measures of speech recognition and sound quality were acutely assessed.

RESULTS

For the effect of channels, results showed no significant improvements beyond eight channels for all measures. For the effect of channel stimulation rate, results showed no significant improvements with higher rates, suggesting that 600 pps was sufficient for maximum speech recognition performance and sound quality ratings. However, across all conditions, there was a significant relationship between mean electrode-to-modiolus distance and all measures, suggesting that a lower mean electrode-to-modiolus distance was correlated with higher speech recognition scores and sound quality ratings.

CONCLUSION

These findings suggest that even well-placed precurved electrode array recipients may not be able to take advantage of more than eight channels or higher channel stimulation rates (> 600 pps), but that closer electrode array placement to the modiolus correlates with better outcomes for these recipients.

Intraoperative Electrically Evoked Compound Action Potential Growth and Maximum Amplitudes in Hearing Preservation Cochlear Implant Recipients

BACKGROUND

Electrically evoked compound action potentials (eCAPs) obtained from cochlear implant (CI) recipients reflect responsiveness of the auditory nerve to electrical stimulation. The recent use of atraumatic electrode arrays and expansion of CI candidacy to listeners with greater residual hearing may lead to increased clinical utility of intraoperative eCAP recordings.

OBJECTIVES

To examine the effect of electrode array (slim modiolar versus slim straight) on suprathreshold intraoperative eCAP recordings in hearing preservation CI recipients. A secondary goal was to examine potential clinical applications of intraoperative eCAPs for predicting immediate hearing preservation and speech perception outcomes.

METHODS

Retrospective study of 113 adult hearing preservation CI candidates implanted from 2015 to 2019 with either a slim modiolar or slim straight electrode array. Intraoperative eCAP growth functions and maximum amplitudes were obtained at several intracochlear electrodes and examined as a function of implanted array and hearing preservation status, while controlling for electrode impedance.

RESULTS

From basal to apical electrodes, progressively larger eCAP amplitudes and steeper slopes were recorded. Steeper eCAP slopes at apical electrodes were also seen for recipients of the slim modiolar array (versus slim straight). Suprathreshold eCAP responses did not differ as a function of hearing preservation and were not associated with speech recognition.

CONCLUSIONS

More robust eCAP responses were obtained from apical electrodes, which is consistent with better low-frequency thresholds in hearing preservation recipients. This effect was compounded by type of electrode array. Results also suggest that intraoperative, suprathreshold eCAPs cannot be used to predict the success of hearing preservation surgery or performance with the CI.

Dynamic Behavior and Insertional Forces of a Precurved Electrode Using the Pull-Back Technique in a Fresh Microdissected Cochlea

HYPOTHESIS

This study evaluated the utility of the pull-back technique in improving perimodiolar positioning of a precurved cochlear implant (CI) electrode array (EA) with simultaneous insertion force profile measurement and direct observation of dynamic EA behavior.

BACKGROUND

Precurved EAs with perimodiolar positioning have improved outcomes compared with straight EAs because of lowered charge requirements for stimulation and decreased spread of excitation. The safety and efficacy of the pull-back technique in further improving perimodiolar positioning and its associated force profile have not been adequately demonstrated.

METHODS

The bone overlying the scala vestibuli was removed in 15 fresh cadaveric temporal bones, leaving the scala tympani unviolated. Robotic insertions of EAs were performed with simultaneous force measurement and video recording. Force profiles were obtained during standard insertion, overinsertion, and pull-back. Postinsertion CT scans were obtained during each of the three conditions, enabling automatic segmentation and calculation of angular insertion depth, mean perimodiolar distance ( Mavg ), and cochlear duct length.

RESULTS

Overinsertion did not result in significantly higher peak forces than standard insertion (mean [SD], 0.18 [0.06] and 0.14 [0.08] N; p = 0.18). Six temporal bones (40%) demonstrated visibly improved perimodiolar positioning after the protocol, whereas none worsened. Mavg significantly improved after the pull-back technique compared with standard insertion (mean [SD], 0.34 [0.07] and 0.41 [0.10] mm; p < 0.01).

CONCLUSIONS

The pull-back technique was not associated with significantly higher insertional forces compared with standard insertion. This technique was associated with significant improvement in perimodiolar positioning, both visually and quantitatively, independent of cochlear size.

Toward neural health measurements for cochlear implantation: The relationship among electrode positioning, the electrically evoked action potential, impedances and behavioral stimulation levels

Introduction

Estimating differences in neural health across different sites within the individual cochlea potentially enables clinical applications for subjects with a cochlear implant. The electrically evoked compound action potential (ECAP) is a measure of neural excitability that possibly provides an indication of a neural condition. There are many factors, however, that affect this measure and increase the uncertainty of its interpretation. To better characterize the ECAP response, its relationship with electrode positioning, impedances, and behavioral stimulation levels was explored.

Methods

A total of 14 adult subjects implanted with an Advanced Bionics cochlear electrode array were prospectively followed up from surgery to 6 months postoperative. Insertion depth, distance to the modiolus, and distance to the medial wall were assessed for each electrode by postoperative CT analysis. ECAPs were measured intraoperatively and at three visits postoperatively on all 16 electrodes using the NRI feature of clinical programming software and characterized using multiple parameters. Impedances and behavioral stimulation levels were measured at every fitting session.

Results

Patterns in ECAPs and impedances were consistent over time, but high variability existed among subjects and between different positions in the cochlea. Electrodes located closer to the apex of the cochlea and closer to the modiolus generally showed higher neural excitation and higher impedances. Maximum loudness comfort levels were correlated strongly with the level of current needed to elicit a response of 100 μV ECAP.

Conclusion

Multiple factors contribute to the ECAP response in subjects with a cochlear implant. Further research might address whether the ECAP parameters used in this study will benefit clinical electrode fitting or the assessment of auditory neuron integrity.

Slim Modiolar Electrode Placement in Candidates for Electroacoustic Stimulation

OBJECTIVES

To determine rates of hearing preservation and performance in patients who met candidacy for electroacoustic stimulation (EAS) and were implanted with a slim modiolar electrode (CI532 or CI632).

DESIGN

Adult patients meeting Food and Drug Administration criteria for electroacoustic stimulation (preoperative low-frequency pure-tone average [LFPTA] less than 60 dB at 125, 250, and 500 Hz and monosyllabic word scores between 10% and 60% in the ear to be implanted), who received a slim modiolar electrode were included. Main outcome measures included rates of hearing preservation, defined as a LFPTA ≤80 dB at 125, 250, and 500 Hz, as well as postoperative low-frequency pure-tone threshold shifts, consonant-Nucleus-Consonant (CNC) word scores and AzBio sentences in noise scores.

RESULTS

Forty-six patients met inclusion criteria during a 4-year period. Mean (standard deviation) preoperative LFPTA was 34.5 (13.0) dB, and 71.7% had preserved hearing at initial activation. The mean LFPTA shift in patients who preserved hearing at initial activation was 19.7 (14.6) dB, compared with 62.6 (17.7) dB in patients who did not preserve hearing as per our definition. Perioperative steroid use was not different in patients with and without preserved hearing (X 2 (1, N = 46) = 0.19, p = .67, V = 0.06). One year after surgery, 57% of patients had a decline in LFPTA >80 dB and were no longer considered candidates for EAS, with 34.7% still retaining low-frequency thresholds ≤80 dB. CNC word scores at 1 year were 69.9% and 61.4% among individuals with and without preserved low-frequency hearing respectively, measured in their CI ear alone, in their regular listening condition of EAS or electric only ( t (32) = 1.13, p = 0.27, d = 0.39, 95% CI = -6.51, 22.86). Device use time did not differ between groups. Among adults with preserved residual hearing at 1 year (n = 16), 44% used EAS, although there was no significant difference in performance between EAS users and nonusers with preserved hearing. Loss of residual hearing over time did not result in a decline in speech perception performance.

CONCLUSION

The present study demonstrated favorable early rates of hearing preservation with a slim modiolar array. Performance was not significantly different in individuals with and without preserved low-frequency acoustic hearing, independent of EAS use. Compared with reports of short electrode use, the loss of residual hearing in patients implanted with this array did not impact speech perception performance.

Speech Recognition Performance Differences Between Precurved and Straight Electrode Arrays From a Single Manufacturer

OBJECTIVE

Precurved cochlear implant (CI) electrode arrays have demonstrated superior audiometric outcomes compared with straight electrodes in a handful of studies. However, previous comparisons have often failed to account for preoperative hearing and age. This study compares hearing outcomes for precurved and straight electrodes by a single manufacturer while controlling for these and other factors in a large cohort.

STUDY DESIGN

Retrospective cohort study.

SETTING

Tertiary academic medical center.

PATIENTS

Two hundred thirty-one adult CI recipients between 2015 and 2021 with cochlear (Sydney, Australia) 522/622 (straight) or 532/632 (precurved) electrode arrays.

INTERVENTIONS

Postactivation speech recognition and audiometric testing.

MAIN OUTCOME MEASURES

Speech recognition testing (consonant-nucleus-consonant word [CNCw] and AzBio) was collected at 6 and 12 months postactivation. Hearing preservation was characterized by a low-frequency pure-tone average shift, or the change between preoperative and postoperative low-frequency pure-tone average.

RESULTS

Two hundred thirty-one patients (253 ears) with 6-month and/or 12-month CNCw or AzBio testing were included. One hundred forty-nine (59%) and 104 (41%) ears were implanted with straight and precurved electrode arrays, respectively. Average age at implantation was 70 years (interquartile range [IQR], 58-77 y). There was no significant difference in mean age between groups. CNCw scores were significantly different ( p = 0.001) between straight (51%; IQR, 36-67%) and precurved arrays (64%; IQR, 48-72%). AzBio scores were not significantly different ( p = 0.081) between straight (72%; IQR, 51-87%) and precurved arrays (81%; IQR, 57-90%). Controlling for age, race, sex, preoperative hearing, and follow-up time, precurved electrode arrays performed significantly better on CNCw (b = 10.0; 95% confidence interval, 4.2-16.0; p < 0.001) and AzBio (b = 8.9; 95% confidence interval, 1.8-16.0;, p = 0.014) testing. Hearing preservation was not different between electrodes on adjusted models.

CONCLUSION

During the study period, patients undergoing placement of precurved electrode arrays had significantly higher CNC and AzBio scores than patients receiving straight electrodes, even after controlling for age, preoperative hearing, and follow-up time.

PROFESSIONAL PRACTICE GAP AND EDUCATIONAL NEED

Understanding the difference in audiometric outcomes between precurved and straight electrode arrays will help to guide electrode selection.

LEARNING OBJECTIVE

To understand differences in speech recognition scores postoperatively by electrode array type (precurved versus straight).

DESIRED RESULT

To demonstrate a difference in hearing performance postoperatively by electrode type.

LEVEL OF EVIDENCE

III.

INDICATE IRB OR IACUC

Approved by the Institutional IRB (090155).

Activation region overlap visualization for image-guided cochlear implant programming

Objective. The cochlear implant is a neural prosthesis designed to directly stimulate auditory nerve fibers to induce the sensation of hearing in those experiencing severe-to-profound hearing loss. After surgical implantation, audiologists program the implant's external processor with settings intended to produce optimal hearing outcomes. The likelihood of achieving optimal outcomes increases when audiologists have access to tools that objectively present information related to the patient's own anatomy and surgical outcomes. This includes visualizations like the one presented here, termed the activation region overlap image, which is designed to decrease subjectivity when determining amounts of overlapping stimulation between implant electrodes.Approach. This visualization uses estimates of electric field strength to indicate spread of neural excitation due to each electrode. Unlike prior visualizations, this method explicitly defines regions of nerves receiving substantial stimulation from each electrode to help clinicians assess the presence of significant overlapping stimulation. A multi-reviewer study compared this and an existing technique on the consistency, efficiency, and optimality of plans generated from each method. Statistical significance was evaluated using the two-sided Wilcoxon rank sum test.Main results. The study showed statistically significant improvements in consistency (p < 10-12), efficiency (p < 10-15), and optimality (p < 10-5) when generating plans using the proposed method versus the existing method.Significance. This visualization addresses subjectivity in assessing overlapping stimulation between implant electrodes, which currently relies on reviewer estimates. The results of the evaluation indicate the provision of such objective information during programming sessions would likely benefit clinicians in making programming decisions.

The Relationship Between Interaural Insertion-Depth Differences, Scalar Location, and Interaural Time-Difference Processing in Adult Bilateral Cochlear-Implant Listeners

Sensitivity to interaural time differences (ITDs) in acoustic hearing involves comparison of interaurally frequency-matched inputs. Bilateral cochlear-implant arrays are, however, only approximately aligned in angular insertion depth and scalar location across the cochleae. Interaural place-of-stimulation mismatch therefore has the potential to impact binaural perception. ITD left-right discrimination thresholds were examined in 23 postlingually-deafened adult bilateral cochlear-implant listeners, using low-rate constant-amplitude pulse trains presented via direct stimulation to single electrodes in each ear. Angular insertion depth and scalar location measured from computed-tomography (CT) scans were used to quantify interaural mismatch, and their association with binaural performance was assessed. Number-matched electrodes displayed a median interaural insertion-depth mismatch of 18° and generally yielded best or near-best ITD discrimination thresholds. Two listeners whose discrimination thresholds did not show this pattern were confirmed via CT to have atypical array placement. Listeners with more number-matched electrode pairs located in the scala tympani displayed better thresholds than listeners with fewer such pairs. ITD tuning curves as a function of interaural electrode separation were broad; bandwidths at twice the threshold minimum averaged 10.5 electrodes (equivalent to 5.9 mm for a Cochlear-brand pre-curved array). Larger angular insertion-depth differences were associated with wider bandwidths. Wide ITD tuning curve bandwidths appear to be a product of both monopolar stimulation and angular insertion-depth mismatch. Cases of good ITD sensitivity with very wide bandwidths suggest that precise matching of insertion depth is not critical for discrimination thresholds. Further prioritizing scala tympani location at implantation should, however, benefit ITD sensitivity.

Speech recognition as a function of the number of channels for pediatric cochlear implant recipients

This study investigated the number of channels required for asymptotic speech recognition for ten pediatric cochlear implant (CI) recipients with precurved electrode arrays. Programs with 4-22 active electrodes were used to assess word and sentence recognition in noise. Children demonstrated significant performance gains up to 12 electrodes for continuous interleaved sampling (CIS) and up to 22 channels with 16 maxima. These data are consistent with the latest adult CI studies demonstrating that modern CI recipients have access to more than 8 independent channels and that both adults and children exhibit performance gains up to 22 channels.

Speech recognition as a function of the number of channels for Mid-Scala electrode array recipients

This study investigated the number of channels needed for maximum speech understanding and sound quality in 15 adult cochlear implant (CI) recipients with Advanced Bionics (AB) Mid-Scala electrode arrays completely within scala tympani. In experiment I, CI programs used a continuous interleaved sampling (CIS)-based strategy and 4-16 active electrodes. In experiment II, CI programs used an n-of-m strategy featuring 16 active electrodes with either 8- or 12-maxima. Speech understanding and sound quality measures were assessed. For CIS programs, participants demonstrated performance gains using up to 4-10 electrodes on speech measures and sound quality ratings. For n-of-m programs, there was no significant effect of maxima, suggesting 8-maxima is sufficient for this sample's maximum performance and sound quality. These results are largely consistent with previous studies using straight electrode arrays [e.g., Fishman, Shannon, and Slattery (1997). J. Speech Lang. Hear. Res. 40, 1201-1215; Friesen, Shannon, Baskent, and Wang (2001). J. Acoust. Soc. Am. 110, 1150-1163; Shannon, Cruz, and Galvin (2011). Audiol. Neurotol. 16, 113-123; Berg, Noble, Dawant, Dwyer, Labadie, and Gifford (2020). J. Acoust. Soc. Am. 147, 3646-3656] and in contrast with recent studies looking at cochlear precurved electrode arrays [e.g., Croghan, Duran, and Smith (2017). J. Acoust. Soc. Am. 142, EL537-EL543; Berg, Noble, Dawant, Dwuer, Labadie, and Gifford (2019b). J. Acoust. Soc. Am. 145, 1556-1564], which found continuous improvements up to 16 independent channels. These findings suggest that Mid-Scala electrode array recipients demonstrate similar channel independence to straight electrode arrays rather than other manufacturer's precurved electrode arrays.

Quality-assured training in the evaluation of cochlear implant electrode position: a prospective experimental study

BACKGROUND

The objective of this study was to demonstrate the utility of an approach in training predoctoral medical students, to enable them to measure electrode-to-modiolus distances (EMDs) and insertion-depth angles (aDOIs) in cochlear implant (CI) imaging at the performance level of a single senior rater.

METHODS

This prospective experimental study was conducted on a clinical training dataset comprising patients undergoing cochlear implantation with a Nucleus® CI532 Slim Modiolar electrode (N = 20) or a CI512 Contour Advance electrode (N = 10). To assess the learning curves of a single medical student in measuring EMD and aDOI, interrater differences (senior-student) were compared with the intrarater differences of a single senior rater (test-retest). The interrater and intrarater range were both calculated as the distance between the 0.1th and 99.9th percentiles. A "deliberate practice" training approach was used to teach knowledge and skills, while correctives were applied to minimize faulty data-gathering and data synthesis.

RESULTS

Intrarater differences of the senior rater ranged from - 0.5 to 0.5 mm for EMD and - 14° to 16° for aDOI (respective medians: 0 mm and 0°). Use of the training approach led to interrater differences that matched this after the 4th (EMD) and 3rd (aDOI) feedback/measurement series had been provided to the student.

CONCLUSIONS

The training approach enabled the student to evaluate the CI electrode position at the performance level of a senior rater. This finding may offer a basis for ongoing clinical quality assurance for the assessment of CI electrode position.

Effect of Proximity to the Modiolus for the Cochlear CI532 Slim Modiolar Electrode Array on Evoked Compound Action Potentials and Programming Levels

BACKGROUND

The first surgeries with CI532 showed an effect of the proximity of the electrode to the modiolus on the Evoked Compound Action Potentials (ECAPs).

OBJECTIVES

Objectives of the study were to investigate the effect of the "pullback" procedure on intraoperative ECAP responses in three different electrode array positions and additionally to compare behavioral thresholds with the thresholds obtained in a group of patients using the standard insertion. The hypothesis of this study is that pullback will cause lower ECAPs and behavioral thresholds.

PATIENTS

The study included 40 patients, 20 in the pullback insertion group and 20 in the standard insertion group (without pullback).

METHOD

During insertion of the CI532 electrode array, ECAP was performed in three different positions for the pullback group: at initial insertion, at over-insertion, and after pullback. Insertion was monitored by fluoroscopy. In the standard group, ECAP was performed at the initial position, which is also the final position. ECAP thresholds (T-ECAPs) were compared within subjects at the initial and the final position in the pullback group and between groups in the final positions of the pullback and standard groups. Programming levels (C- and T-levels) were compared between the two groups 1 year after switch-on.

RESULTS

Intraoperative measurements pullback shows lower average T-ECAPs after pullback compared to thresholds in initial position. Comparison of intraoperative T-ECAPs at the final positions showed no statistically significant difference between the pullback group and the standard insertion group. Furthermore, 1 year after switch-on there was no statistically significant difference in C- and T-levels between the two groups.

CONCLUSION

The pullback maneuver of the CI532 electrode array after an over-insertion gave significantly lower T-ECAPs compared to the thresholds at the initial position. However, the between-groups analysis of pullback and standard insertion showed neither significantly different T-ECAPs nor different programming levels. Because T-ECAPs and programming levels vary considerably between subjects, large groups are required to detect differences between groups. Additionally, the effect pullback technique to preserving the residual hearing is not known yet.

Predicting Cochlear Implant Electrode Placement Using Monopolar, Three-Point and Four-Point Impedance Measurements

OBJECTIVE

This study aimed to investigate the relationship between cochlear implant (CI) electrode distances to the cochleas inner wall (the modiolus) and electrical impedance measurements made at the CIs electrode contacts. We introduced a protocol for three-point impedances in which we recorded bipolar impedances in response to monopolar stimulation at a neighboring electrode. We aimed to assess the usability of three-point impedances and two existing CI impedance measurement methods (monopolar and four-point impedances) for predicting electrode positioning during CI insertion.

METHODS

Impedances were recorded during stepwise CI electrode array insertions in cadaveric human temporal bones. The positioning of the electrodes with respect to the modiolus was assessed at each step using cone beam computed tomography. Linear mixed regression analysis was performed to assess the relationship between the impedances and electrode-modiolar distances. The experimental results were compared to clinical impedance data and to an existing lumped-element model of an implanted CI.

RESULTS

Three-point and four-point impedances strongly correlated with electrode-modiolar distance. In contrast, monopolar impedances were only minimally affected by changes in electrode positioning with respect to the modiolus. An overall model specificity of 62% was achieved when incorporating all impedance parameters. This specificity could be increased beyond 73% when prior expectations of electrode positioning were incorporated in the model.

CONCLUSION

Three-point and four-point impedances are promising measures to predict electrode-modiolar distance in real-time during CI insertion.

SIGNIFICANCE

This work shows how electrical impedance measurements can be used to predict the CIs electrode positioning in a biologically realistic model.

3D printed biomimetic cochleae and machine learning co-modelling provides clinical informatics for cochlear implant patients

Cochlear implants restore hearing in patients with severe to profound deafness by delivering electrical stimuli inside the cochlea. Understanding stimulus current spread, and how it correlates to patient-dependent factors, is hampered by the poor accessibility of the inner ear and by the lack of clinically-relevant in vitro, in vivo or in silico models. Here, we present 3D printing-neural network co-modelling for interpreting electric field imaging profiles of cochlear implant patients. With tuneable electro-anatomy, the 3D printed cochleae can replicate clinical scenarios of electric field imaging profiles at the off-stimuli positions. The co-modelling framework demonstrated autonomous and robust predictions of patient profiles or cochlear geometry, unfolded the electro-anatomical factors causing current spread, assisted on-demand printing for implant testing, and inferred patients' in vivo cochlear tissue resistivity (estimated mean = 6.6 kΩcm). We anticipate our framework will facilitate physical modelling and digital twin innovations for neuromodulation implants.

Effects of in vivo repositioning of slim modiolar electrodes on electrical thresholds and speech perception

The slim modiolar electrode has been reported to ensure better modiolar proximity than previous conventional perimodiolar electrodes and consistently high scala tympani localization. Nonetheless, variability in modiolar proximity exists even among slim modiolar electrodes, still leaving room for further improvement of modiolar proximity, which may positively affect functional outcomes. Given this, the pull-back maneuver was reported to increase the modiolar proximity of slim modiolar electrodes in a cadaveric study, but in vivo repositioning effects remain to be established. Here we identified that the pull-back maneuver led to better modiolar proximity than conventional insertion while maintaining a similar angular insertion depth. Notably, the reduced electrode-modiolus distance from the pull-back maneuver was associated with significantly lower impedances across electrodes postoperatively as well as reduced intraoperative electrophysiological thresholds than conventional insertion. Among adult cochlear implant recipients, this maneuver resulted in significantly better sentence recognition scores at three months postoperatively when compared to those with a conventional insertion; however, this benefit was not observed at later intervals. Collectively, slim modiolar electrodes with the pull-back maneuver further enhance the modiolar proximity, possibly leading to better open-set sentence recognition, at least in the early postoperative stage.

Using the electrically-evoked compound action potential (ECAP) interphase gap effect to select electrode stimulation sites in cochlear implant users

Studies in cochlear implanted animals show that the IPG Effect for ECAP growth functions (i.e., the magnitude of the change in ECAP amplitude growth function (AGF) slope or peak amplitude when the interphase gap (IPG) is increased) can be used to estimate the densities of spiral ganglion neurons (SGNs) near the electrode stimulation and recording sites. In humans, the same ECAP IPG Effect measures correlate with speech recognition performance. The present study examined the efficacy of selecting electrode sites for stimulation based on the IPG Effect, in order to improve performance of CI users on speech recognition tasks. We measured the ECAP IPG Effect for peak amplitude in adult (>18 years old) CI users (N= 18 ears), and created experimental programs to stimulate electrodes with either the highest or lowest ECAP IPG Effect for peak amplitude. Subjects also listened to a program without any electrodes deactivated. In a subset of subject ears (11/18), we compared performance differences between the experimental programs to post-operative computerized tomography (CT) scans to examine underlying factors that might contribute to the efficacy of an electrode site-selection approach. For sentences-in-noise, average performance was better when subjects listened to the experimental program that stimulated electrodes with the highest rather than the lowest IPG Effect for ECAP peak amplitude. A similar pattern was noted for transmission and perception of consonant place cues in a consonant recognition task. However, on average, performance when listening to a program with higher IPG Effect values was equal to that when listening with all electrodes activated. Results also suggest that scalar location (scala tympani or vestibuli) should be considered when using an ECAP-based electrode site-selection procedure to optimize CI performance.

Evaluation of hearing preservation in adults with a slim perimodiolar electrode

PURPOSE

Numerous endeavors have been undertaken to preserve hearing in cochlear implant (CI) patients. Particularly, optimization of electrode array design aims at preservation of residual hearing (RH). This study examines whether a slim perimodiolar (PM) electrode array could bear the capability to preserve hearing.

METHODS

A total of 47 patients underwent cochlear implantation receiving the PM electrode. (i) Patients with pure tone audiogram (PTA) thresholds better than 85 dB and/or hearing loss for Freiburg speech test numbers less than 60 dB and more than 50% maximum monosyllabic understanding were assigned to the RH group (n = 17), while all others belonged to the noRH group (n = 30). (ii) Another group implanted with a slim straight, lateral wall (LW) electrode was recruited for comparison.

RESULTS

We compared 17 RH-30 noRH patients all receiving the PM electrode. RH in PM recipients decreased faster than in LW recipients. No significant differences were observed between both (RH v/s noRH) groups in NRT thresholds, Freiburg speech test and A§E^® phonemes. Analogous satisfaction levels were indicated through the questionnaires in terms of sound quality, hearing in silence, noise and directional hearing in both groups.

CONCLUSIONS

The results suggest that hearing preservation is influenced not only by electrode shape but various factors. This study opens an avenue for further investigations to elucidate and enumerate the causes for progressive hearing loss.

Speech recognition as a function of the number of channels for an array with large inter-electrode distances

This study investigated the number of channels available to cochlear implant (CI) recipients for maximum speech understanding and sound quality for lateral wall electrode arrays-which result in large electrode-to-modiolus distances-featuring the greatest inter-electrode distances (2.1-2.4 mm), the longest active lengths (23.1-26.4 mm), and the fewest number of electrodes commercially available. Participants included ten post-lingually deafened adult CI recipients with MED-EL electrode arrays (FLEX28 and STANDARD) entirely within scala tympani. Electrode placement and scalar location were determined using computerized tomography. The number of channels was varied from 4 to 12 with equal spatial distribution across the array. A continuous interleaved sampling-based strategy was used. Speech recognition, sound quality ratings, and a closed-set vowel recognition task were measured acutely for each electrode condition. Participants did not demonstrate statistically significant differences beyond eight channels at the group level for almost all measures. However, several listeners showed considerable improvements from 8 to 12 channels for speech and sound quality measures. These results suggest that channel interaction caused by the greater electrode-to-modiolus distances of straight electrode arrays could be partially compensated for by a large inter-electrode distance or spacing.

Scalar Translocation Comparison Between Lateral Wall and Perimodiolar Cochlear Implant Arrays - A Meta-Analysis

Objectives/Hypothesis

Two types of electrode arrays for cochlear implants (CIs) are distinguished: lateral wall and perimodiolar. Scalar translocation of the array can lead to intracochlear trauma by penetrating from the scala tympani into the scala vestibuli or scala media, potentially negatively affecting hearing performance of CI users. This systematic review compares the lateral wall and perimodiolar arrays with respect to scalar translocation.

Study Design

Systematic review.

Methods

PubMed, Embase, and Cochrane databases were reviewed for studies published within the last 11 years. No other limitations were set. All studies with original data that evaluated the occurrence of scalar translocation or tip fold‐over (TF) with postoperative computed tomography (CT) following primary cochlear implantation in bilateral sensorineuronal hearing loss patients were considered to be eligible. Data were extracted independently by two reviewers.

Results

We included 33 studies, of which none were randomized controlled trials. Meta‐analysis of five cohort studies comparing scalar translocation between lateral wall and perimodiolar arrays showed that lateral wall arrays have significantly lower translocation rates (7% vs. 43%; pooled odds ratio = 0.12). Translocation was negatively associated with speech perception scores (weighted mean 41% vs. 55%). Tip fold‐over of the array was more frequent with perimodiolar arrays (X² = 6.8, P < .01).

Conclusions

Scalar translocation and tip fold‐overs occurred more frequently with perimodiolar arrays than with lateral wall arrays. In addition, translocation of the array negatively affects hearing with the cochlear implant. Therefore, if one aims to minimize clinically relevant intracochlear trauma, lateral wall arrays would be the preferred option for cochlear implantation. Laryngoscope, 131:1358–1368, 2021

Intraoperative Impedance-Based Estimation of Cochlear Implant Electrode Array Insertion Depth

OBJECTIVE

Cochlear implant impedances are influenced by the intracochlear position of the electrodes. Herein, we present an intuitive approach to calculate tissue resistances from transimpedance recordings, ultimately enabling to estimate the insertion depth of cochlear implant electrodes.

METHODS

Electrode positions were measured in computed-tomography images of 20 subjects implanted with the same lateral wall cochlear implant model. The tissue resistances were estimated from intraoperative telemetry data using bivariate spline extrapolation from the transimpedance recordings. Using a phenomenological model, the electrode insertion depths were estimated.

RESULTS

The proposed method enabled the linear insertion depth of all electrodes to be estimated with an average error of 0.76 ± 0.53 mm.

CONCLUSION

Intraoperative telemetry recordings correlate with the linear and angular depth of electrode insertion, enabling estimations with an accuracy that can be useful for clinical applications.

SIGNIFICANCE

The proposed method can be used to objectively assess surgical outcomes during and after cochlear implantation based on non-invasive and readily available telemetry recordings.

Evaluation of artifacts of cochlear implant electrodes in cone beam computed tomography

Purpose

Cone Beam Computed Tomography (CBCT) offers a valid alternative to conventional Computed Tomography (CT). A possible radiation dose reduction with the use of CBCT in postoperative imaging of CIs is of great importance. Whether the visualization of Cochlear Implant (CI) electrodes in CBCT correlates with the radiation dose applied was investigated in this study.

Methods

We compared the visualization quality of Contour Advance CIs to Straight CIs from Cochlear using CBCT with varying tube parameters on whole-head specimen.

Results

The internal diameter of the cochlea decreases from base to apex, resulting in a significantly different intracochlear positioning of the two tested CI models. While electrodes of the Contour Advance series are located close to the modiolus, thus closer to the spiral ganglion neurons, those of the Straight series are located further away. The artifact portion of the electrode amounts to 50–70% of the radiological diameter of the electrode. An increase in artifact portion from the base (electrode #1 approx. 50%) to the apex (electrode #20 approx. 70%) of the cochlea was observed. The visualization of electrodes in the medial and apical part of the cochlea is limited due to artifact overlapping. There was no correlation between the artifact size and the applied radiation dose.

Conclusion

The results indicate that a reduction of the radiation dose by up to 45% of the currently applied radiation dose of standard protocols would be possible. Investigations of the effects on subjective image quality still need to be performed.

Comparison of Perimodiolar Electrodes: Imaging and Electrophysiological Outcomes

BACKGROUND

The perimodiolar CI532 Slim Modiolar electrode has been designed to bring the electrode contacts close to auditory nerve while reducing cochlear trauma during its insertion. It is currently unknown to what extent the electrode position and electrophysiological outcomes of the Slim Modiolar electrode differ from other perimodiolar electrodes.

OBJECTIVES

The objective was to compare the electrode position and electrophysiological outcomes between the CI532 Slim Modiolar and CI512 Contour Advance electrode.

METHOD

Forty-six adult patients received a Slim Modiolar or Contour Advance electrode. Electrode types were compared using intraoperative electrode impedances, evoked compound action potential (ECAP) and stapedius reflex thresholds, as well as position parameters from postoperative computed tomography or digital volume tomography images (medial-lateral position, electrode-to-modiolus distance, insertion angle).

RESULTS

The medial-lateral position indicates a closer modiolar placement of the Slim Modiolar compared with the Contour Advance. Individual electrode contact measurements, however, showed significantly larger electrode-to-modiolus distances and higher ECAP thresholds for the Slim Modiolar in the basal region. On contacts E20-22 the Slim Modiolar is slightly closer to the modiolus compared with the Contour Advance, but this did not result in lower ECAP thresholds.

CONCLUSIONS

Perimodiolar electrodes can vary in their intracochlear position, leading to divergent electrophysiological outcomes. To detect these differences, investigations must be done for each electrode contact rather than using a global factor for the whole electrode array. While the electrode dislocation rate is lower with the Slim Modiolar than with the Contour Advance, electrode-to-modiolus proximity is smaller and ECAP thresholds are lower with the Contour Advance in the basal cochlear region.

Effect of age, electrode array, and time on cochlear implant impedances

Objectives: To determine the impact of age, electrode array, and time on impedance patterns in cochlear implant (CI) patients. Methods: A retrospective case review was performed on 98 patients implanted with the CI24RE perimodiolar (PM) and CI422 lateral wall (LW) arrays between 2010 and 2014 to assess impedances at the 1 week and 3-6 month visit after initial stimulation (IS). Results: With respect to age, impedances were higher in young patients compared to older patients in the middle and apical turns. With time, there were significant reductions in impedances across most electrodes. Electrode array type also had a significant impact on impedance measurements with PM and LW arrays having higher impedances in the basal turn and apical turns, respectively. Furthermore, PM arrays demonstrated significantly lower impedances in the middle and apical turn with time, when compared to LW arrays. Conclusions: Age, electrode array, and time can independently affect CI impedances. Moreover, we show that PM arrays may be advantageous to LW arrays, due to demonstrated lower impedances in the middle and apical turns long term. Understanding the impact of impedance on speech discrimination and determining the intracochlear processes that contribute to differences in impedance are future research directions.

Matched Cohort Comparison Indicates Superiority of Precurved Electrode Arrays

OBJECTIVE

Characterize differences in adult cochlear implant outcomes and programming parameters for a straight (CI422/522) and a precurved (CI532) electrode array.

SETTING

Cochlear implant (CI) program at a tertiary otologic center.

PATIENTS

Fifty-eight adults were included in the study; 29 were implanted with CI422 or CI522 and 29 were implanted with CI532. Each CI532 recipient was matched to a CI422/522 recipient in terms of age and preoperative hearing thresholds for comparison purposes.

MAIN OUTCOME MEASURES

Consonant-Nucleus-Consonant (CNC) words, AzBio sentences, residual audiometric thresholds, and Speech Spatial Qualities (SSQ) questionnaire collected 6 months postoperatively were used to characterize outcomes. Pulse duration, maxima, impedances, and overall charge measurements were used to characterize programming parameters.

RESULTS

Postoperative unaided low frequency pure-tone average (LFPTA) was significantly better for the CI532 group. CNC scores were significantly better for the CI532 group. Impedances and pulse duration were significantly lower for the CI532 group, but there was no difference in overall charge between the groups.

CONCLUSION

The CI532 group showed either similar or statistically superior results on all measures when compared with the CI422/522 suggesting that the CI532 electrode may be an advantageous substitute for the CI522.

Speech recognition with cochlear implants as a function of the number of channels: Effects of electrode placement

This study investigated the effects of cochlear implant (CI) electrode array type and scalar location on the number of channels available to CI recipients for maximum speech understanding and sound quality. Eighteen post-lingually deafened adult CI recipients participated, including 11 recipients with straight electrode arrays entirely in scala tympani and 7 recipients with translocated precurved electrode arrays. Computerized tomography was used to determine electrode placement and scalar location. In each condition, the number of channels varied from 4 to 22 with equal spatial distribution across the array. Speech recognition (monosyllables, sentences in quiet and in noise), subjective speech sound quality, and closed-set auditory tasks (vowels, consonants, and spectral modulation detection) were measured acutely. Recipients with well-placed straight electrode arrays and translocated precurved electrode arrays performed similarly, demonstrating asymptotic speech recognition scores with 8-10 channels, consistent with the classic literature. This finding contrasts with recent work [Berg, Noble, Dawant, Dwyer, Labadie, and Gifford. (2019). J. Acoust. Soc. Am. 145, 1556-1564] that found precurved electrode arrays well-placed in scala tympani demonstrate continuous performance gains beyond 8-10 channels. Given these results, straight and translocated precurved electrode arrays are theorized to have less channel independence secondary to their placement farther away from neural targets.

Shape of the Cochlear Basal Turn: An Indicator for an Optimal Electrode-to-Modiolus Proximity With Precurved Electrode Type

OBJECTIVE

The objective of this study was to determine the shape of cochlear basal turn through basic cochlear parameters measurement. The secondary aim was to overlay an image of the precurved electrode array on top of the three-dimensional (3D) image of the cochlea to determine which shape of the cochlear basal turn gives optimal electrode-to-modiolus proximity.

MATERIALS AND METHODS

Computed tomography (CT) preoperative image-data sets of 117 ears were made available for the measurements of cochlear parameters retrospectively. Three-dimensional slicer was used in the visualization and measurement of cochlear parameters from both 3D and 2D (2-dimensional) images of the inner ear. Cochlear parameters including basal turn diameter (A), width of the basal turn (B), and cochlear height (H) were measured from the appropriate planes. B/A ratio was made to investigate which ratios correspond to round and elliptical shape of the cochlear basal turn.

RESULTS

The cochlear size as measured by A value ranged between 7.4 mm and 10 mm. The B value and the cochlear height (H) showed a weak positive linear relation with A value. The ratio between the B and A values anything above or below 0.75 could be an indicator for a more round- or elliptical shaped cochlear basal turn, respectively. One sized/shaped commercially available precurved electrode array would not offer a tight electrode-to-modiolus in the cochlea that has an elliptical shaped basal turn as identified by the B/A ratio of <0.75.

CONCLUSION

Accurate measurement of cochlear parameters adds value to the overall understanding of the cochlear geometry before a cochlear implantation procedure. The shape of cochlear basal turn could have clinical implications when comes to electrode-to-modiolus proximity.

Cochlear Implantation with the CI512 and CI532 Precurved Electrode Arrays: One-Year Speech Recognition and Intraoperative Thresholds of Electrically Evoked Compound Action Potentials

INTRODUCTION

Precurved cochlear implant (CI) electrode arrays were developed in an attempt to improve the auditory outcome of cochlear implantation, which varies greatly. The recent CI532 (Cochlear Corp., Sydney, Australia) may offer further advantages as its electrode array is thinner than previous precurved CI electrode arrays. The aims here were to investigate 1-year postoperative speech recognition, intraoperative electrically evoked compound action potentials (ECAPs), and their possible relation in patients implanted with a CI532 or its predecessor CI512.

METHODS

A retrospective analysis of data from 63 patients subjected to cochlear implantation at the Karolinska University Hospital, Sweden, was performed. Speech recognition of the implanted ear was evaluated using phonemically balanced monosyllabic Swedish words at 65 dB SPL. ECAPs were evaluated using the intraoperative ECAP threshold across ≥8 electrodes generated by the automated neural response telemetry of the CI.

RESULTS

The median aided speech recognition score (SRS) 1 year after implantation was 52% (quartile 1 = 40%, quartile 3 = 60%, n = 63) and did not differ statistically significantly between patients with CI512 (n = 38) and CI532 (n = 25). The mean ECAP threshold was 188 CL (current level; SD = 15 CL, n = 54) intraoperatively and did not differ statistically significantly between patients with CI512 (n = 32) and CI532 (n = 22), but the threshold for each electrode varied more between patients with a CI512 (p < 0.0001). A higher mean ECAP threshold was associated with a worse SRS (Spearman's ρ = -0.46, p = 0.0004, n = 54). The association remained among those with a CI512 (Spearman's ρ = -0.62, p = 0.0001, n = 32) when stratified by CI electrode array.

CONCLUSION

No statistically significant difference in speech recognition 1 year after cochlear implantation or in mean threshold of ECAP intraoperatively was found between patients with a CI512 and the more recent, slim CI532, but the ECAP thresholds varied more between those with a CI512. A statistically significant association between SRS and mean ECAP threshold was found, but stratified analysis suggests that the association may be true only for patients with a CI512.

The Insertion Results of a Mid-scala Electrode Assessed by MRI and CBCT Image Fusion

OBJECTIVES

To investigate the results of clinical surgical insertions with a Mid-scala array (HIFocus Mid-Scala Electrode, HFms).

STUDY DESIGN

Consecutive retrospective case study.

SETTINGS

Tertiary referral center.

PATIENTS

Analyses of imaging data of 26 consecutive patients (31 insertions) implanted with the HFms.

INTERVENTION (S)

The evaluation of insertion trauma evoked by a previously validated image fusion technique. Electrode reconstructions from postoperative cone-beam computed tomography (CBCT) were overlaid onto preoperative magnetic resonance imaging (MRI) scans to create artifact-free images.

MAIN OUTCOME MEASURES

The electrode position was quantified in relation to the basilar membrane. Trauma scaling adopted from Eshraghi was used for evaluating insertion trauma. The results of the visual assessment of the postoperative CBCT were compared to those obtained with the fusion technique.

RESULTS

Three insertions had to be excluded due to incompatibility of the imaging data with the fusion software. We found consistent peri- to mid-modiolar placement of the HFms with a mean insertion depth angle of 376°. According to the medical records, a visual examination of the postoperative CBCT indicated that there had been no scala dislocations but when assessed by the image fusion technique, five scala dislocations (17.8%) were found. Additionally, one tip fold-over was detected in the postoperative CBCT even though this was not evident in any intraoperative measurements.

CONCLUSION

HFms showed atraumatic surgical insertion results with consistent mid-modiolar placement. Image fusion enhances the accuracy of the insertion trauma assessment. Routine postoperative imaging is recommended for identifying tip fold-over as well as for quality control and documentation.

Musical Sound Quality as a Function of the Number of Channels in Modern Cochlear Implant Recipients

Objectives

This study examined musical sound quality (SQ) in adult cochlear implant (CI) recipients. The study goals were to determine: the number of channels needed for high levels of musical SQ overall and by musical genre; the impact of device and patient factors on musical SQ ratings; and the relationship between musical SQ, speech recognition, and speech SQ to relate these findings to measures frequently used in clinical protocols.

Methods

Twenty-one post-lingually deafened adult CI recipients participated in this study. Electrode placement, including scalar location, average electrode-to-modiolus distance (M¯), and angular insertion depth were determined by CT imaging using validated CI position analysis algorithms (e.g., Noble et al., 2013; Zhao et al., 2018, 2019). CI programs were created using 4–22 electrodes with equal spatial distribution of active electrodes across the array. Speech recognition, speech SQ, music perception via a frequency discrimination task, and musical SQ were acutely assessed for all electrode conditions. Musical SQ was assessed using pre-selected musical excerpts from a variety of musical genres.

Results

CI recipients demonstrated continuous improvement in qualitative judgments of musical SQ with up to 10 active electrodes. Participants with straight electrodes placed in scala tympani (ST) and pre-curved electrodes with higher M¯ variance reported higher levels of musical SQ; however, this relationship is believed to be driven by levels of musical experience as well as the potential for preoperative bias in device selection. Participants reported significant increases in musical SQ beyond four channels for all musical genres examined in the current study except for Hip Hop/Rap. After musical experience outliers were removed, there was no relationship between musical experience or frequency discrimination ability and musical SQ ratings. There was a weak, but significant correlation between qualitative ratings for speech stimuli presented in quiet and in noise and musical SQ.

Conclusion

Modern CI recipients may need more channels for musical SQ than even required for asymptotic speech recognition or speech SQ. These findings may be used to provide clinical guidance for personalized expectations management of music appreciation depending on individual device and patient factors.

Intraoperative Electrically Evoked Compound Action Potential (ECAP) Measurements in Traditional and Hearing Preservation Cochlear Implantation

BACKGROUND

In current practice, the status of residual low-frequency acoustic hearing in hearing preservation cochlear implantation (CI) is unknown until activation two to three weeks postoperatively. The intraoperatively measured electrically evoked compound action potential (ECAP), a synchronous response from electrically stimulated auditory nerve fibers, is one of the first markers of auditory nerve function after cochlear implant surgery and such may provide information regarding the status of residual low-frequency acoustic hearing.

PURPOSE

This study aimed to evaluate the relationship between intraoperative ECAP at the time of CI and presence of preoperative and postoperative low-frequency acoustic hearing.

RESEARCH DESIGN

A retrospective case review.

STUDY SAMPLE

Two hundred seventeen adult ears receiving CI (42 Advanced Bionics, 82 Cochlear, and 93 MED-EL implants).

INTERVENTIONS

Intraoperative ECAP and CI.

DATA COLLECTION AND ANALYSIS

ECAP measurements were obtained intraoperatively, whereas residual hearing data were obtained from postoperative CI activation audiogram. A linear mixed model test revealed no interaction effects for the following variables: manufacturer, electrode location (basal, middle, and apical), preoperative low-frequency pure-tone average (LFPTA), and postoperative LFPTA. The postoperative residual low-frequency hearing status was defined as preservation of unaided air conduction thresholds ≤90 dB at 250 Hz. Electrode location and hearing preservation data were analyzed individually for both the ECAP threshold and ECAP maximum amplitude using multiple t-tests, without assuming a consistent standard deviation between the groups, and with alpha correction.

RESULTS

The maximum amplitude, in microvolts, was significantly higher throughout apical and middle regions of the cochlea in patients who had preserved low-frequency acoustic hearing as compared with those who did not have preserved hearing (p = 0.0001 and p = 0.0088, respectively). ECAP threshold, in microamperes, was significantly lower throughout the apical region of the cochlea in patients with preserved low-frequency acoustic hearing as compared with those without preserved hearing (p = 0.0099). Basal electrode maximum amplitudes and middle and basal electrode thresholds were not significantly correlated with postoperative low-frequency hearing.

CONCLUSIONS

Apical and middle electrode maximum amplitudes and apical electrode thresholds detected through intraoperative ECAP measurements are significantly correlated with preservation of low-frequency acoustic hearing. This association may represent a potential immediate feedback mechanism for postoperative outcomes that can be applied to all CIs.

Further Evidence of the Relationship Between Cochlear Implant Electrode Positioning and Hearing Outcomes

BACKGROUND

Postoperative imaging studies by numerous groups have revealed that final cochlear implant (CI) electrode position impacts audiological outcomes with scalar location consistently shown to be a significant factor. Modiolar proximity has been less extensively studied, and findings regarding the effect of insertion depth have been inconsistent.

METHODS

Using previously developed automated algorithms, we determined CI electrode position in an Institutional Review Board-approved database of 220 CI ears. Generalized linear models (GLM) were used to analyze the relationship between audiological outcomes and factors including age, duration of CI use, device type, and electrode position.

RESULTS

For precurved arrays, GLM revealed that scalar position, modiolar proximity, base insertion depth, and sex were significant factors for Consonant-Nucleus-Consonant (CNC) words (R = 0.43, p < 0.001, n = 92 arrays), while scalar position, modiolar proximity, age, and postlingual onset of deafness were significant for Bamford-Kawal-Bench Sentences in Noise (BKB-SIN) (R = 0.51, p < 0.001, n = 85) scores. Other factors were not significant in the final model after controlling for these variables. For straight arrays, we found the insertion depth, postlingual deafness, and length of CI use to be highly significant (R = 0.47, p < 0.001) factors for CNC words (91 arrays), while for BKB-SIN scores the most significant (R = 0.47, p < 0.001) factors were insertion depth, younger age, and postlingual deafness (89 arrays).

CONCLUSION

Our results confirm the significance of electrode positioning in audiological outcomes. The most significant positional predictors of outcome for precurved arrays were full scala tympani (ST) insertion and the modiolar distance, while for the lateral wall arrays the depth of insertion was the most significant factor.

Initial surgical and clinical experience with the Nucleus CI532 slim modiolar electrode in the UK

OBJECTIVE

The goal of this work is to describe the first experience in the UK with the slim pre-curved perimodiolar electrode Nucleus CI532 in a continuous series of patients in terms of surgical and clinical reliability and early performance outcomes.

METHOD

In this retrospective review we describe the complication rate (including electrode array tip fold-over), NRT thresholds, hearing preservation, power efficiency and CI performance outcomes in a continuous series of 40 cochlear implants CI532 performed between October 2016 and November 2017 in 17 adults and 13 children with severe to profound hearing loss.

RESULTS

Preliminary data from these groups reveals some low-frequency hearing preservation in the CI532 group although none of the patients were conventional hearing preservation candidates. NRT thresholds, power efficiency, and BKB sentences in quiet were measured at 3 and 6 months post activation. There were no significant differences in these results. The average BKB score in quiet increases from 22% pre-operatively to 58% at 3 months and 70% at 6 months. In addition, although hearing preservation was not an objective, low-frequency thresholds were preserved in 20% of cases at 3 and 6 months post-operatively. Complications were observed in 5 cases, one case with non-device related aerocoele and four related to the device array: two cases of tip roll over, one case of the electrode array being placed extra-cochlea, and one case with the electrode buckling into the middle ear. The last 2 cases were dealt with per-operatively.

DISCUSSION

Our preliminary results with the CI532 implant indicate that it may be reliably placed with standard surgical techniques but care is needed during the deployment of the electrode. Further initial data suggest that switch on and early electrophysiological measures are comparable to the existing CI 512 device. However whilst preliminary, our data suggest that it may be possible to use this electrode for hearing preservation. However, further studies are required to determine its definitive advantage over other electrode designs.

CONCLUSION

CI532 is a reliable device offering good initial results and could be an option for hearing preservation although further studies are required.

Speech recognition as a function of the number of channels in perimodiolar electrode recipients

This study investigated the number of channels needed for maximum speech understanding and sound quality in 30 adult cochlear implant (CI) recipients with perimodiolar electrode arrays verified via imaging to be completely within scala tympani (ST). Performance was assessed using a continuous interleaved sampling (CIS) strategy with 4, 8, 10, and 16 channels and n-of-m with 16 maxima. Listeners were administered auditory tasks of speech understanding [monosyllables, sentences (quiet and +5 dB signal-to-noise ratio, SNR), vowels, consonants], spectral modulation detection, as well as subjective estimates of sound quality. Results were as follows: (1) significant performance gains were observed for speech in quiet (monosyllables and sentences) with 16- as compared to 8-channel CIS, (2) 16 channels in a 16-of-m strategy yielded significantly higher outcomes than 16-channel CIS for sentences in noise (percent correct and subjective sound quality) and spectral modulation detection, (3) 16 channels in a 16-of-m strategy yielded significantly higher outcomes as compared to 8- and 10-channel CIS for monosyllables, sentences (quiet and noise), consonants, spectral modulation detection, and subjective sound quality, (4) 16 versus 8 maxima yielded significantly higher speech recognition for monosyllables and sentences in noise using an n-of-m strategy, and (5) the degree of benefit afforded by 16 versus 8 maxima was inversely correlated with mean electrode-to-modiolus distance. These data demonstrate greater channel independence with perimodiolar electrode arrays as compared to previous studies with straight electrodes and warrant further investigation of the minimum number of maxima and number of channels needed for maximum auditory outcomes.

Impedance Measures During in vitro Cochlear Implantation Predict Array Positioning

OBJECTIVE

Improper electrode placement during cochlear implant (CI) insertion can adversely affect speech perception outcomes. However, the intraoperative methods to determine positioning are limited. Because measures of electrode impedance can be made quickly, the goal of this study was to assess the relationship between CI impedance and proximity to adjacent structures.

METHODS

An Advanced Bionics CI array was inserted into a clear, plastic cochlea one electrode contact at a time in a saline bath (nine trials). At each insertion depth, response to biphasic current pulses was used to calculate access resistance (Ra), polarization resistance (Rp), and polarization capacitance (Cp). These measures were correlated to actual proximity as assessed by microscopy using linear regression models.

RESULTS

Impedance increased with insertion depth and proximity to the inner wall. Specifically, Ra increased, Cp decreased, and Rp slightly increased. Incorporating all impedance measures afforded a prediction model (r = 0.88) while optimizing for sub-mm positioning afforded a model with 78.3% specificity.

CONCLUSION

Impedance in vitro greatly changes with electrode insertion depth and proximity to adjacent structures in a predicable manner.

SIGNIFICANCE

Assessing proximity of the CI to adjacent structures is a significant first step in qualifying the electrode-neural interface. This information should aid in CI fitting, which should help maximize hearing and speech outcomes with a CI. Additionally, knowledge of the relationship between impedance and positioning could have utility in other tissue implants in the brain, retina, or spinal cord.

Challenging aspects of contemporary cochlear implant electrode array design

Objective

A design comparison of current perimodiolar and lateral wall electrode arrays of the cochlear implant (CI) is provided. The focus is on functional features such as acoustic frequency coverage and tonotopic mapping, battery consumption and dynamic range. A traumacity of their insertion is also evaluated.

Methods

Review of up-to-date literature.

Results

Perimodiolar electrode arrays are positioned in the basal turn of the cochlea near the modiolus. They are designed to initiate the action potential in the proximity to the neural soma located in spiral ganglion. On the other hand, lateral wall electrode arrays can be inserted deeper inside the cochlea, as they are located along the lateral wall and such insertion trajectory is less traumatic. This class of arrays targets primarily surviving neural peripheral processes. Due to their larger insertion depth, lateral wall arrays can deliver lower acoustic frequencies in manner better corresponding to cochlear tonotopicity. In fact, spiral ganglion sections containing auditory nerve fibres tuned to low acoustic frequencies are located deeper than 1 and half turn inside the cochlea. For this reason, a significant frequency mismatch might be occurring for apical electrodes in perimodiolar arrays, detrimental to speech perception. Tonal languages such as Mandarin might be therefore better treated with lateral wall arrays. On the other hand, closer proximity to target tissue results in lower psychophysical threshold levels for perimodiolar arrays. However, the maximal comfort level is also lower, paradoxically resulting in narrower dynamic range than that of lateral wall arrays. Battery consumption is comparable for both types of arrays.

Conclusions

Lateral wall arrays are less likely to cause trauma to cochlear structures. As the current trend in cochlear implantation is the maximal protection of residual acoustic hearing, the lateral wall arrays seem more suitable for hearing preservation CI surgeries. Future development could focus on combining the advantages of both types: perimodiolar location in the basal turn extended to lateral wall location for higher turn locations.

Towards a Complete In Silico Assessment of the Outcome of Cochlear Implantation Surgery

Cochlear implantation (CI) surgery is a very successful technique, performed on more than 300,000 people worldwide. However, since the challenge resides in obtaining an accurate surgical planning, computational models are considered to provide such accurate tools. They allow us to plan and simulate beforehand surgical procedures in order to maximally optimize surgery outcomes, and consequently provide valuable information to guide pre-operative decisions. The aim of this work is to develop and validate computational tools to completely assess the patient-specific functional outcome of the CI surgery. A complete automatic framework was developed to create and assess computationally CI models, focusing on the neural response of the auditory nerve fibers (ANF) induced by the electrical stimulation of the implant. The framework was applied to evaluate the effects of ANF degeneration and electrode intra-cochlear position on nerve activation. Results indicate that the intra-cochlear positioning of the electrode has a strong effect on the global performance of the CI. Lateral insertion provides better neural responses in case of peripheral process degeneration, and it is recommended, together with optimized intensity levels, in order to preserve the internal structures. Overall, the developed automatic framework provides an insight into the global performance of the implant in a patient-specific way. This enables to further optimize the functional performance and helps to select the best CI configuration and treatment strategy for a given patient.

Encapsulated cell device approach for combined electrical stimulation and neurotrophic treatment of the deaf cochlea

Profound hearing impairment can be overcome by electrical stimulation (ES) of spiral ganglion neurons (SGNs) via a cochlear implant (CI). Thus, SGN survival is critical for CI efficacy. Application of glial cell line-derived neurotrophic factor (GDNF) has been shown to reduce SGN degeneration following deafness. We tested a novel method for local, continuous GDNF-delivery in combination with ES via a CI. The encapsulated cell (EC) device contained a human ARPE-19 cell-line, genetically engineered for secretion of GDNF. In vitro, GDNF delivery was stable during ES delivered via a CI. In the chronic in vivo part, cats were systemically deafened and unilaterally implanted into the scala tympani with a CI and an EC device, which they wore for six months. The implantation of control devices (same cell-line not producing GDNF) had no negative effect on SGN survival. GDNF application without ES led to an unexpected reduction in SGN survival, however, the combination of GDNF with initial, short-term ES resulted in a significant protection of SGNs. A tight fibrous tissue formation in the scala tympani of the GDNF-only group is thought to be responsible for the increased SGN degeneration, due to mechanisms related to an aggravated foreign body response. Furthermore, the fibrotic encapsulation of the EC device led to cell death or cessation of GDNF release within the EC device during the six months in vivo. In both in vitro and in vivo, fibrosis was reduced by CI stimulation, enabling the neuroprotective effect of the combined treatment. Thus, fibrous tissue growth limits treatment possibilities with an EC device. For a stable and successful long-term neurotrophic treatment of the SGN via EC devices in human CI users, it would be necessary to make changes in the treatment approach (provision of anti-inflammatories), the EC device surface (reduced cell adhesion) and the ES (initiation prior to fibrosis formation).

Radiological and NRT-Ratio-Based Estimation of Slim Straight Cochlear Implant Electrode Positions: A Multicenter Study

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.

Stimulation parameters differ between current anti-modiolar and peri-modiolar electrode arrays implanted within the same child

OBJECTIVE

To compare stimulation parameters of peri-modiolar and anti-modiolar electrode arrays using two surgical approaches.

METHODS

Impedance, stimulation thresholds, comfortably loud current levels, electrically evoked compound action potential thresholds and electrically evoked stapedial reflex thresholds were compared between 2 arrays implanted in the same child at 5 time points: surgery, activation/day 1, week 1, and months 1 and 3. The peri-modiolar array was implanted via cochleostomy in all children (n = 64), while the anti-modiolar array was inserted via a cochleostomy in 43 children and via the round window in 21 children.

RESULTS

The anti-modiolar array had significantly lower impedance, but required higher current levels to elicit thresholds, comfort, electrically evoked compound action potential thresholds and electrically evoked stapedial reflex thresholds than the peri-modiolar array across all time points, particularly in basal electrodes (p < 0.05). The prevalence of open electrodes was similar in anti-modiolar (n = 5) and peri-modiolar (n = 3) arrays.

CONCLUSION

Significant but clinically acceptable differences in stimulation parameters between peri-modiolar and anti-modiolar arrays persisted four months after surgery in children using bilateral cochlear implants. The surgical approach used to insert the anti-modiolar array had no overall effect on outcomes.