Potential benefits from deeply inserted cochlear implant electrodes

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.

High-frequency Cochlear Nerve Deficit Region: Relationship With Deaf Duration and Cochlear Implantation Performance in Postlingual Deaf Adults

OBJECTIVE

To analyze the changes of cochlear nerve diameter and the presence of a cochlear nerve deficit at a high-frequency region and investigate their effects on cochlear implant (CI) performance in postlingual deaf adults.

STUDY DESIGN

Retrospective.

SETTING

Tertiary care academic center.

PATIENTS

Eighty-three postlingual deaf adults with no labyrinthine anomalies or cognitive deficits who received a CI with perimodiolar electrodes from a single manufacturer.

MAIN OUTCOMES AND MEASURES

We evaluated the changes of cochlear nerve diameter and the presence of a "tail sign," defined as identifiable nerve fibers originating from the far basal turn of the cochlea, which represents the presence of cochlear nerve at a high-frequency region in magnetic resonance imaging, on monosyllabic word recognition scores.

RESULTS

The cochlear nerve diameter showed a positive correlation with word recognition scores (maximum diameter, R2 = 0.26, p < 0.01; minimum diameter, R2 = 0.26, p < 0.01), but a negative correlation with deaf duration. Recipients with a positive tail sign performed better (73 ± 19%) than those without (45 ± 24%, p < 0.01). A positive tail sign was more commonly found in good performers (52 of 62, 84%) than in poor performers (5 of 21, 24%, p < 0.01).

CONCLUSIONS

Favorable outcomes could be anticipated in postlingual deaf adults with a large cochlear nerve diameter and positive tail sign. A presence of cochlear nerve at a high-frequency region may be an imaging marker for predicting good CI performance.

Frequency-to-Place Mismatch: Characterizing Variability and the Influence on Speech Perception Outcomes in Cochlear Implant Recipients

OBJECTIVES

The spatial position of a cochlear implant (CI) electrode array affects the spectral cues provided to the recipient. Differences in cochlear size and array length lead to substantial variability in angular insertion depth (AID) across and within array types. For CI-alone users, the variability in AID results in varying degrees of frequency-to-place mismatch between the default electric frequency filters and cochlear place of stimulation. For electric-acoustic stimulation (EAS) users, default electric frequency filters also vary as a function of residual acoustic hearing in the implanted ear. The present study aimed to (1) investigate variability in AID associated with lateral wall arrays, (2) determine the subsequent frequency-to-place mismatch for CI-alone and EAS users mapped with default frequency filters, and (3) examine the relationship between early speech perception for CI-alone users and two aspects of electrode position: frequency-to-place mismatch and angular separation between neighboring contacts, a metric associated with spectral selectivity at the periphery.

DESIGN

One hundred one adult CI recipients (111 ears) with MED-EL Flex24 (24 mm), Flex28 (28 mm), and FlexSOFT/Standard (31.5 mm) arrays underwent postoperative computed tomography to determine AID. A subsequent comparison was made between AID, predicted spiral ganglion place frequencies, and the default frequency filters for CI-alone (n = 84) and EAS users (n = 27). For CI-alone users with complete insertions who listened with maps fit with the default frequency filters (n = 48), frequency-to-place mismatch was quantified at 1500 Hz and angular separation between neighboring contacts was determined for electrodes in the 1 to 2 kHz region. Multiple linear regression was used to examine how frequency-to-place mismatch and angular separation of contacts influence consonant-nucleus-consonant (CNC) scores through 6 months postactivation.

RESULTS

For CI recipients with complete insertions (n = 106, 95.5%), the AID (mean ± standard deviation) of the most apical contact was 428° ± 34.3° for Flex24 (n = 11), 558° ± 65.4° for Flex28 (n = 48), and 636° ± 42.9° for FlexSOFT/Standard (n = 47) arrays. For CI-alone users, default frequency filters aligned closely with the spiral ganglion map for deeply inserted lateral wall arrays. For EAS users, default frequency filters produced a range of mismatches; absolute deviations of ≤ 6 semitones occurred in only 37% of cases. Participants with shallow insertions and minimal or no residual hearing experienced the greatest mismatch. For CI-alone users, both smaller frequency-to-place mismatch and greater angular separation between contacts were associated with better CNC scores during the initial 6 months of device use.

CONCLUSIONS

There is significant variability in frequency-to-place mismatch among CI-alone and EAS users with default frequency filters, even between individuals implanted with the same array. When using default frequency filters, mismatch can be minimized with longer lateral wall arrays and insertion depths that meet the edge frequency associated with residual hearing for CI-alone and EAS users, respectively. Smaller degrees of frequency-to-place mismatch and decreased peripheral masking due to more widely spaced contacts may independently support better speech perception with longer lateral wall arrays in CI-alone users.

Comparative Performance of Lateral Wall and Perimodiolar Cochlear Implant Arrays

OBJECTIVE

The physical shape of cochlear implant (CI) arrays may impact hearing outcomes. The goal of this study was to compare post-operative speech and melody perception between patients with lateral wall (LW) and perimodiolar (PM) electrode arrays across a range of lengths and manufacturers.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary Care Hospital.

PATIENTS

119 adult patients with post-lingual hearing loss who underwent cochlear implantation.

MAIN OUTCOME MEASURES

A total of seven different electrodes were evaluated including 5 different LW electrodes (CI422 [Cochlear American], 1J [Advanced Bionics], Medium [Med El], Standard [Med El], Flex28 [Med El]) and 2 PM electrodes (Contour [Cochlear American], MidScala [Advanced Bionics]). Speech perception outcomes (n = 119 patients) were measured by Consonant-Nucleus-Consonant (CNC) scores collected 3, 6, 12 and 24 months after implantation. Melody perception outcomes (n = 35 CI patients and n = 6 normal hearing patients) were measured by Melodic Contour Identification (MCI).

RESULTS

CNC scores increased over time after implantation across all array designs. PM designs exhibited higher CNC scores compared to LW electrodes, particularly 6-months after implantation. Pre-operative pure tone averages did not correlate with post-operative CNC scores. PM arrays outperformed LW electrodes in terms of MCI scores.

CONCLUSIONS

The physical shape of cochlear implant electrode arrays may impact hearing performance. Compared to LW designs, PM arrays appear to offer superior speech perception during the first 6 months after implantation, with performance equalizing between groups by 24 months. Compared to LW designs, PM arrays also appear to afford superior melody perception.

Incidence of Complete Insertion in Cochlear Implant Recipients of Long Lateral Wall Arrays

OBJECTIVE

High rates of partial insertion have been reported for cochlear implant (CI) recipients of long lateral wall electrode arrays, presumably caused by resistance encountered during insertion due to cochlear morphology. With recent advances in long-electrode array design, we sought to investigate (1) the incidence of complete insertions among patients implanted with 31.5-mm flexible arrays and (2) whether complete insertion is limited by cochlear duct length (CDL).

STUDY DESIGN

Retrospective review.

SETTING

Tertiary referral center.

METHODS

Fifty-one adult CI recipients implanted with 31.5-mm flexible lateral wall arrays underwent postoperative computed tomography to determine the rate of complete insertion, defined as all contacts being intracochlear. CDL and angular insertion depth (AID) were compared between complete and partial insertion cohorts.

RESULTS

Most cases had a complete insertion (96.1%, n = 49). Among the complete insertion cohort, the median CDL was 33.6 mm (range, 30.3-37.9 mm), and median AID was 641° (range, 533-751°). Two cases of partial insertion had relatively short CDL (31.8 mm and 32.3 mm) and shallow AID (542° and 575°). Relatively shallow AID for the 2 cases of partial insertion fails to support the idea that CDL alone prevents a complete insertion.

CONCLUSION

Complete insertion of a 31.5-mm flexible array is feasible in most cases and does not appear to be limited by the range of CDL observed in this cohort. Future studies are needed to estimate other variations in cochlear morphology that could predict resistance and failure to achieve complete insertion with long arrays.

Comparison of Speech Recognition and Localization Ability in Single-sided Deaf Patients Implanted With Different Cochlear Implant Electrode Array Designs

OBJECTIVE

Choice of electrode array (EA) design and differences in outcome are major concerns both to patients with single-sided deafness (SSD) and to surgeons before cochlear implant (CI) surgery. The present work investigates the effects of EA design on 1) insertion depths, and 2) audiological outcomes of SSD CI recipients.

STUDY DESIGN

Retrospective study.

SETTING

Tertiary academic center.

PATIENTS

Forty patients with acquired SSD matched according to duration of deafness MAIN OUTCOME MEASURES:: Fourteen CI recipients were implanted with a perimodiolar electrode (cochlear perimodiolar [CPM]), 12 with a shorter lateral wall electrode (cochlear lateral wall [CLW]), and 14 with a longer lateral wall electrode array (medEl lateral wall [MLW]). Postoperative rotational tomography was evaluated to determine cochlear size and EA angle of insertion depth (AID). Binaural speech comprehension in noise (in three configuration presentations) and localization ability were assessed 12 months postoperatively with CI.

RESULTS

AID was significantly deeper in MLW (mean 527.94 degrees) compared with the CPM (mean 366.35 degrees) and CLW groups (mean 367.01 degrees). No significant difference in AID was seen between the CPM and CLW groups (difference 0.66 degrees). Cochlear sizes revealed no significant differences between any groups. All three groups showed significant improvement in head shadow effect (difference on average CPM: 6.3 dB SPL, CLW 5 dB SPL, and MLW 4.05 dB SPL) and localization ability at 12 months postoperatively (difference on average CPM: 19.72 degrees, CLW: 24 degrees, and MLW: 12.9 degrees). No significant difference in the extent of audiological benefit was observed between any groups.

CONCLUSION

No effect on binaural benefit was apparent from the selection of the three EA designs in SSD CI recipients. Further studies focusing on subjective results, sound quality, and music perception depending on EA design in SSD CI recipients are needed.

Effects of noise on integration of acoustic and electric hearing within and across ears

In bimodal listening, cochlear implant (CI) users combine electric hearing (EH) in one ear and acoustic hearing (AH) in the other ear. In electric-acoustic stimulation (EAS), CI users combine EH and AH in the same ear. In quiet, integration of EH and AH has been shown to be better with EAS, but with greater sensitivity to tonotopic mismatch in EH. The goal of the present study was to evaluate how external noise might affect integration of AH and EH within or across ears. Recognition of monosyllabic words was measured for normal-hearing subjects listening to simulations of unimodal (AH or EH alone), EAS, and bimodal listening in quiet and in speech-shaped steady noise (10 dB, 0 dB signal-to-noise ratio). The input/output frequency range for AH was 0.1–0.6 kHz. EH was simulated using an 8-channel noise vocoder. The output frequency range was 1.2–8.0 kHz to simulate a shallow insertion depth. The input frequency range was either matched (1.2–8.0 kHz) or mismatched (0.6–8.0 kHz) to the output frequency range; the mismatched input range maximized the amount of speech information, while the matched input resulted in some speech information loss. In quiet, tonotopic mismatch differently affected EAS and bimodal performance. In noise, EAS and bimodal performance was similarly affected by tonotopic mismatch. The data suggest that tonotopic mismatch may differently affect integration of EH and AH in quiet and in noise.

Assessment of Angular Insertion-Depth of Bilateral Cochlear Implants Using Plain X-ray Scans

OBJECTIVE

To evaluate in cochlear implant patients, the feasibility and reliability of angular depth of insertion (aDOI) measurements using plain x-ray scans.

STUDY DESIGN

Retrospective study where three observers independently evaluated and compared intraoperative anterior-posterior and oblique x-ray scans.

SETTING

A tertiary pediatric medical center.

PATIENTS

Included were 50 children (100 ears) who underwent bilateral simultaneous cochlear implantation during 2008 to 2015.

MAIN OUTCOME MEASURES

Inter-rater agreement of aDOI measured in plain x-ray scans; effect of head position on measured aDOI; and symmetry of aDOI between patients' ears in bilateral simultaneous cochlear implantations.

RESULTS

Differences in the average aDOI measurements among the three observers ranged between 2 and 7 degrees. There was high inter-rater agreement (R = 0.99, p < 0.01) among all observers, and strong correlations between each pair of observers (0.92-0.99). Head rotation of 45 degrees (between the two views) resulted in a median difference in aDOI of 14 degrees, with excellent correlation among the observers. The rate of asymmetry was high, with a median difference of 39 degrees and up to 220 degrees between ears.

CONCLUSIONS

Assessment of aDOI using intraoperative plain x-rays is efficient and reliable. The effect of head positioning on measurement is small. Further studies are needed to evaluate the effect of aDOI and insertion symmetry on functional outcomes.

The Effect of Cochlear Coverage on Auditory and Speech Performance in Cochlear Implant Patients

OBJECTIVE

To determine the effect of cochlear coverage on audiological and speech parameters in patients with cochlear implants. Previous work has investigated the effect of tailoring electrode size to a cochlear implant recipient's individual cochlear duct length (CDL). However, no clear relationship has been found between speech development and the extent of electrode insertion, and the benefits of apical stimulation are not yet clear.

METHODOLOGY

In this retrospective study, we assessed the effect of cochlear coverage on audiological and speech performance. Participants were prelingually deaf children who received cochlear implants between June 2013 and December 2014 under the care of a single cochlear implant surgeon. Cochlear coverage was estimated for each ear according to electrode type, depth of insertion, and the number of active electrodes. Electrode type and length were determined by the individual's CDL, measured by computed tomography (CT), and full insertion was documented intraoperatively. The number of active electrodes was recorded using intraoperative audiological response telemetry. Audiological assessments were obtained 6 months and 1 year postoperatively. Results of the categories of auditory performance-II and speech intelligibility rating scales were obtained after 3 years. Patients were divided into two groups based on their cochlear coverage and their audiological and speech outcomes were compared.

RESULTS

Of the 97 children recruited, 47 were girls. Temporal bone CT scans showed the right and left mean CDLs among girls were 27.7 and 27.9 mm, respectively, and 29.2 mm for both ears in boys. For each sex, the right and left CDLs did not differ significantly (p = 0.07). Twenty patients were lost to follow-up, leaving 77 patients (120 ears), which were divided into groups according to cochlear coverage (complete vs. incomplete). Significant between-group differences were not found in assessments of audiology, categories of auditory performances, or speech intelligibility ratings after 3 years.

CONCLUSION

Audiological parameters do not differ according to the degree of cochlear coverage, specifically for low-frequency tones. Speech parameters are also comparable. Therefore, complete cochlear coverage does not appear to provide significant benefit over incomplete coverage for prelingually deaf cochlear implant recipients.

Low-Frequency Pitch Perception in Cochlear Implant Recipients With Normal Hearing in the Contralateral Ear

Purpose Three experiments were carried out to evaluate the low-frequency pitch perception of adults with unilateral hearing loss who received a cochlear implant (CI). Method Participants were recruited from a cohort of CI users with unilateral hearing loss and normal hearing in the contralateral ear. First, low-frequency pitch perception was assessed for the 5 most apical electrodes at 1, 3, 6, and 12 months after CI activation using an adaptive pitch-matching task. Participants listened with a coding strategy that presents low-frequency temporal fine structure (TFS) and compared the pitch to that of an acoustic target presented to the normal hearing ear. Next, participants listened with an envelope-only, continuous interleaved sampling strategy. Pitch perception was compared between coding strategies to assess the influence of TFS cues on low-frequency pitch perception. Finally, participants completed a vocal pitch-matching task to corroborate the results obtained with the adaptive pitch-matching task. Results Pitch matches roughly corresponded to electrode center frequencies (CFs) in the CI map. Adaptive pitch matches exceeded the CF for the most apical electrode, an effect that was larger for continuous interleaved sampling than TFS. Vocal pitch matches were variable but correlated with the CF of the 3 most apical electrodes. There was no evidence that pitch matches changed between the 1- and 12-month intervals. Conclusions Relatively accurate and asymptotic pitch perception was observed at the 1-month interval, indicating either very rapid acclimatization or the provision of familiar place and rate cues. Early availability of appropriate pitch cues could have played a role in the early improvements in localization and masked speech recognition previously observed in this cohort. Supplemental Material https://doi.org/10.23641/asha.8862389.

The Effect of Cochlear Size on Cochlear Implantation Outcomes

Objectives

To determine if cochlear duct length and cochlear basal diameter, measured using routinely available radiology software, affect hearing outcomes after cochlear implantation with two different length electrodes.

Methods

55 patients who received a Med-El Flex electrode were retrospectively reviewed. 34 patients received the Flex 31 electrode (31mm) and 21 patients received the Flex 28 electrode (28mm). Preoperative high-resolution CT scans of the temporal bone were reformatted in the axial and coronal plane. The basal diameter of the cochlear (A-value) and the outer-wall lengths of the cochlear duct were measured using readily available imaging software. Postoperative plane X-rays were used to determine the degree of electrode insertion and the number of electrodes within the cochlea and speech discrimination scores at 6 months were evaluated.

Results

The cochlear metrics obtained were comparable with those previously published in the literature. There was no significant difference in the degree of insertion or speech outcomes between the two electrode lengths. However, when the group who had received the shorter electrode were analysed, there was an association seen between both cochlear duct length and cochlear diameter and speech outcomes.

Conclusions

Cochlear size may be a factor in determining speech outcomes that cannot be explained solely by insertion depth or degrees of insertion. Further studies are required to determine if cochlear duct length is an independent predictor of speech outcomes.

CT-scan contouring technique allows for direct and reliable measurements of the cochlear duct length: implication in cochlear implantation with straight electrode-arrays

OBJECTIVES

The advent of hybrid electro-acoustic implants requires precise positioning of the electrode-array (EA) within the cochlea. The cochlea size, that is, the length of the cochlear scala tympani, is often indirectly estimated from distance A by Escudé's method. This technique has been confirmed by anatomical studies, in a bunch of cadaveric specimens, but it is not yet widely established in the field of computed tomography (CT). We compared cochlear duct length obtained by Escudé's method to those directly acquired on CT images.

MATERIALS AND METHODS

The lengths of cochlear scala tympani were directly measured on CT scans by contouring the external cochlear wall (contouring technique-CoT). In fifteen patients implanted with a straight EA, the length of the EA and the measured length of the cochlea by the CoT were compared, to check the reliability of the CoT. Then, in 200 CT-scans, the length of the cochlear duct was measured by the CoT then compared to Escudé's method.

RESULTS

In the 200 CT-scans which served for cochlear length measurements, a significant variability between the cochleae were observed, as expected. At 360°, the correlation between the measurements of the length of the cochlear scala tympani between the two techniques differed, with a difference of 0.2 ± 0.7 mm at 360° (extreme: 2 mm; p < 0.001) and 2.2 ± 1.2 mm at 540° (extreme: 5.6 mm; p < 0.001).

CONCLUSION

The CoT can predict with accuracy the length of EA-insertion depth, more precisely than estimation methods such as Escudé's.

Measurement of pitch perception as a function of cochlear implant electrode and its effect on speech perception with different frequency allocations

OBJECTIVE

An experiment was conducted to investigate the possibility that speech perception could be improved for some cochlear implant (CI) users by adjustment of the frequency allocation to the electrodes, following assessment of pitch perception along the electrode array.

STUDY SAMPLE

Thirteen adult CI users with MED-EL devices participated in the study.

DESIGN

Pitch perception was assessed for individual CI electrode pairs using the Pitch Contour Test (PCT), giving information on pitch discrimination and pitch ranking for adjacent electrodes. Sentence perception in noise was also assessed with ten different frequency allocations, including the default.

RESULTS

Pitch perception was found to be poorer for both discrimination and ranking scores at either end of the electrode array. A significant effect of frequency allocation was found for sentence scores [F(4.24,38.2) = 7.14, p < 0.001] and a significant interaction between sentence score and PCT ranking score for basal electrodes was found [F(4.24,38.2) = 2.95, p = 0.03]. Participants with poorer pitch perception at the basal end had poorer scores for some allocations with greater basal shift.

CONCLUSIONS

The results suggest that speech perception could be improved for CI users by assessment of pitch perception using the PCT and subsequent adjustment of pitch-related stimulation parameters.

Mechanical Effects of Cochlear Implant on Acoustic Hearing

Residual hearing loss in cochlear implant users is investigated using the mechanical-human-cochlear model. Hearing loss due to stiffening of the round window increases significantly as input frequencies decrease from 3 kHz to 1 kHz but remains constant at lower frequencies, whereas loss due to the presence of an electrode insert becomes significantly higher at lower frequencies ([Formula: see text] kHz). The latter also shifts the characteristic frequency map toward the basal end of the cochlea. In the region away from the end of the electrode insert, cochlear function recovers, but the user still suffers from hearing loss caused by round window stiffening.

Selection of the appropriate cochlear electrode array using a specifically developed research software application

Objective

To evaluate the usefulness and reliability of a research software application for the estimation of an individual's cochlear duct length as a basis for electrode selection.

Methods

In this prospective cohort study, 21 consecutive patients (23 ears) implanted with a cochlear electrode were investigated. The study comprised 19 children (2 bilateral) and 2 adults.

Results

The measured ‘A’ distances (the largest distance from the round window to the contralateral wall) corresponded to cochlear duct lengths of 28.5–36.4 mm. The mean cochlear duct length was 34.05 ± 1.72 mm (33.60 ± 2.27 mm in females and 34.35 ± 1.27 mm in males). Full insertion was achieved in all but two cases. No misplaced electrode array or electrode fold-over was detected. In all but three ears, the electrode was chosen based on the research software application's indication.

Conclusion

The results show a good correlation between the pre-operatively predicted insertion depths using the software application and those post-operatively measured using X-ray. The insertion length predicted by the software was always longer than that measured via X-ray.

Contemporary imaging of auditory implants

There have been significant advances in the diversity and effectiveness of hearing technologies in recent years. Implanted auditory devices may be divided into those that stimulate the cochlear hair cells (bone conduction devices and middle ear implants), and those that stimulate the neural structures (cochlear implants and central auditory implants). Contemporary preoperative and postoperative imaging may be used to help individualise implant selection, optimise surgical technique and predict auditory outcome. This review will introduce the concepts behind auditory implants, and explains how imaging is increasingly used to aid insertion and evaluation of these devices.

Modeling Electrode Place Discrimination in Cochlear Implant Stimulation

OBJECTIVE

By modeling the cochlear implant (CI) electrode-to-nerve interface and quantifying electrode discriminability in the model, we address the questions of how many individual channels can be distinguished by CI recipients and the extent to which performance might be improved by inserting electrodes deeper into the cochlea.

METHOD

We adapt an artificial neural network to model electrode discrimination as well as a commonly used psychophysical measure (four-interval forced-choice) in CI stimulation and predict how well the locations of the stimulating electrodes can be inferred from simulated auditory nerve spiking patterns.

RESULTS

We show that a longer electrode leads to better electrode place discrimination in our model. For a simulated four-interval forced-choice procedure, correct classification rates significantly reduce with decreasing distance between the test electrodes and the reference electrodes, and higher correct classification rates may be achieved by the basal electrodes than apical electrodes.

CONCLUSION

Our results suggest that enhanced electrode discriminability results from a longer CI electrode array, and the locations where the errors occur along the electrode array are not only affected by the distance between electrodes but also the twirling angle between electrodes.

SIGNIFICANCE

Our models and simulations provide theoretical insights into several important clinically relevant problems that will inform future designs of CI electrode arrays and stimulation strategies.

Use of the Phantom Electrode strategy to improve bass frequency perception for music listening in cochlear implant users

OBJECTIVES

The Phantom Electrode strategy makes use of partial bipolar stimulation on the two most apical electrodes in an effort to extend the frequency range available to cochlear implant (CI) users. This study aimed to quantify the effect of the Phantom Electrode strategy on bass frequency perception in music listening in CI users.

METHODS

Eleven adult Advanced Bionics users with the Fidelity 120 processing strategy and 16 adult normal hearing (NH) individuals participated in the study. All subjects completed the CI-multiple stimulus with hidden reference and anchor (MUSHRA), a test of an individual's ability to make discriminations in sound quality following the removal of bass frequency information. NH participants completed the CI-MUSHRA once, whereas CI users completed the task twice - once with their baseline clinical program and once with the Phantom Electrode strategy, in random order. CI users' performance was assessed in comparison with NH performance.

RESULTS

The Phantom Electrode strategy improved CI users performance on the CI-MUSHRA compared with Fidelity 120.

DISCUSSION

Creation of a Phantom Electrode percept through partial bipolar stimulation of the two most apical electrodes appears to improve CI users' perception of bass frequency information in music, contributing to greater accuracy in the ability to detect alterations in musical sound quality.

CONCLUSION

The Phantom Electrode processing strategy may enhance the experience of listening to music and thus acoustic stimuli more broadly by improving perception of bass frequencies, through direction of current towards the apical portion of the cochlea beyond the termination of the electrode.

Depth of Cochlear Implant Array Within the Cochlea and Performance Outcome

OBJECTIVE

To evaluate whether the depth of cochlear implant array within the cochlea affects performance outcomes 1 year following cochlear implantation.

METHODS

A retrospective case review of 120 patients who were implanted with the Advanced Bionics HiFocus 1J. Post-implantation plain-radiographs were retrospectively reviewed, and the depth of insertion was measured in degrees from the round window to the electrode tip. Correlation between the depth of insertion and 1-year post-activation Hearing in Noise Test (HINT) scores was analyzed. Intrascala position was not assessed.

RESULTS

Depth of electrode insertion ranged from 180° to 720°, and HINT scores ranged from 0% to 100%. A Mann-Whitney U test demonstrated significantly improved 1-year post-activation HINT scores in patients with an insertion depth of 360° or more in comparison with patients with insertion depth of less than 360° (81% vs 61%, P = .048). Patients with 13 to 15 contacts within cochlear turns performed as well as patients with full insertion of all 16 contacts, while patients with only 12 contacts performed poorly.

CONCLUSIONS

Insertion depth of the AB HiFocus 1J electrode of less than 360° is associated with reduced 1-year post-activation HINT scores when compared with deeper insertions. Partial insertion of 13 active contacts or more led to similar results as full insertion.

The Relationship Between Insertion Angles, Default Frequency Allocations, and Spiral Ganglion Place Pitch in Cochlear Implants

OBJECTIVES

Commercially available cochlear implant systems attempt to deliver frequency information going down to a few hundred Hertz, but the electrode arrays are not designed to reach the most apical regions of the cochlea, which correspond to these low frequencies. This may cause a mismatch between the frequencies presented by a cochlear implant electrode array and the frequencies represented at the corresponding location in a normal-hearing cochlea. In the following study, the mismatch between the frequency presented at a given cochlear angle and the frequency expected by an acoustic hearing ear at the corresponding angle is examined for the cochlear implant systems that are most commonly used in the United States.

DESIGN

The angular insertion of each of the electrodes on four different electrode arrays (MED-EL Standard, MED-EL Flex28, Advanced Bionics HiFocus 1J, and Cochlear Contour Advance) was estimated from X-ray. For the angular location of each electrode on each electrode array, the predicted spiral ganglion frequency was estimated. The predicted spiral ganglion frequency was compared with the center frequency provided by the corresponding electrode using the manufacturer's default frequency-to-electrode allocation.

RESULTS

Differences across devices were observed for the place of stimulation for frequencies below 650 Hz. Longer electrode arrays (i.e., the MED-EL Standard and Flex28) demonstrated smaller deviations from the spiral ganglion map than the other electrode arrays. For insertion angles up to approximately 270°, the frequencies presented at a given location were typically approximately an octave below what would be expected by a spiral ganglion frequency map, while the deviations were larger for angles deeper than 270°. For frequencies above 650 Hz, the frequency to angle relationship was consistent across all four electrode models.

CONCLUSIONS

A mismatch was observed between the predicted frequency and the default frequency provided by every electrode on all electrode arrays. The mismatch can be reduced by changing the default frequency allocations, inserting electrodes deeper into the cochlea, or allowing cochlear implant users to adapt to the mismatch. Further studies are required to fully assess the clinical significance of the frequency mismatch.

Random walks with shape prior for cochlea segmentation in ex vivo μCT

PURPOSE

Cochlear implantation is a safe and effective surgical procedure to restore hearing in deaf patients. However, the level of restoration achieved may vary due to differences in anatomy, implant type and surgical access. In order to reduce the variability of the surgical outcomes, we previously proposed the use of a high-resolution model built from [Formula: see text] images and then adapted to patient-specific clinical CT scans. As the accuracy of the model is dependent on the precision of the original segmentation, it is extremely important to have accurate [Formula: see text] segmentation algorithms.

METHODS

We propose a new framework for cochlea segmentation in ex vivo [Formula: see text] images using random walks where a distance-based shape prior is combined with a region term estimated by a Gaussian mixture model. The prior is also weighted by a confidence map to adjust its influence according to the strength of the image contour. Random walks is performed iteratively, and the prior mask is aligned in every iteration.

RESULTS

We tested the proposed approach in ten [Formula: see text] data sets and compared it with other random walks-based segmentation techniques such as guided random walks (Eslami et al. in Med Image Anal 17(2):236-253, 2013) and constrained random walks (Li et al. in Advances in image and video technology. Springer, Berlin, pp 215-226, 2012). Our approach demonstrated higher accuracy results due to the probability density model constituted by the region term and shape prior information weighed by a confidence map.

CONCLUSION

The weighted combination of the distance-based shape prior with a region term into random walks provides accurate segmentations of the cochlea. The experiments suggest that the proposed approach is robust for cochlea segmentation.

Computational Models for Predicting Outcomes of Neuroprosthesis Implantation: the Case of Cochlear Implants

Electrical stimulation of the brain has resulted in the most successful neuroprosthetic techniques to date: deep brain stimulation (DBS) and cochlear implants (CI). In both cases, there is a lack of pre-operative measures to predict the outcomes after implantation. We argue that highly detailed computational models that are specifically tailored for a patient can provide useful information to improve the precision of the nervous system electrode interface. We apply our framework to the case of CI, showing how we can predict nerve response for patients with both intact and degenerated nerve fibers. Then, using the predicted response, we calculate a metric for the usefulness of the stimulation protocol and use this information to rerun the simulations with better parameters.

The Influence of Cochlear Implant Electrode Position on Performance

Objectives: To study the relation between variables related to cochlear implant electrode position and speech perception performance scores in a large patient population. Design: The study sample consisted of 203 patients implanted with a CII or HiRes90K implant with a HiFocus 1 or 1J electrode of Advanced Bionics. Phoneme and word score averages for the 1- and 2-year follow-up were calculated for 41 prelingually deaf and 162 postlingually deaf patients. Analyses to reveal correlations between these performance outcomes and 6 position-related variables (angle of most basal electrode contact, surgical insertion angle, surgical insertion, wrapping factor, angular insertion depth, linear insertion depth) were executed. The scalar location, as an indication for the presence of intracochlear trauma, and modiolus proximity beyond the basal turn were not evaluated in this study. In addition, different patient-specific variables (age at implantation, age at onset of hearing loss, duration of deafness, preoperative phoneme and word scores) were tested for correlation with performance. Results: The performance scores of prelingual patients were correlated with age at onset of hearing loss, duration of deafness and preoperative scores. For the postlingual patients, performance showed correlations with all 5 patient-specific variables. None of the 6 position-related variables influenced speech perception in cochlear implant patients. Conclusions: Although several patient-specific variables showed correlations with speech perception outcomes, not one of the studied angular and linear position-related variables turned out to have a demonstrable influence on performance.

Effects of Electrode Array Length on Frequency-Place Mismatch and Speech Perception with Cochlear Implants

Frequency-place mismatch often occurs after cochlear implantation, yet its effect on speech perception outcome remains unclear. In this article, we propose a method, based on cochlea imaging, to determine the cochlear place-frequency map. We evaluated the effect of frequency-place mismatch on speech perception outcome in subjects implanted with 3 different lengths of electrode arrays. A deeper insertion was responsible for a larger frequency-place mismatch and a decreased and delayed speech perception improvement by comparison with a shallower insertion, for which a similar but slighter effect was noticed. Our results support the notion that selecting an electrode array length adapted to each individual's cochlear anatomy may reduce frequency-place mismatch and thus improve speech perception outcome.

Optimizing frequency-to-electrode allocation for individual cochlear implant users

Individual adjustment of frequency-to-electrode assignment in cochlear implants (CIs) may potentially improve speech perception outcomes. Twelve adult CI users were recruited for an experiment, in which frequency maps were adjusted using insertion angles estimated from post-operative x rays; results were analyzed for ten participants with good quality x rays. The allocations were a mapping to the Greenwood function, a compressed map limited to the area containing spiral ganglion (SG) cells, a reduced frequency range map (RFR), and participants' clinical maps. A trial period of at least six weeks was given for the clinical, Greenwood, and SG maps although participants could return to their clinical map if they wished. Performance with the Greenwood map was poor for both sentence and vowel perception and correlated with insertion angle; performance with the SG map was poorer than for the clinical map. The RFR map was significantly better than the clinical map for three participants, for sentence perception, but worse for three others. Those with improved performance had relatively deep insertions and poor electrode discrimination ability for apical electrodes. The results suggest that CI performance could be improved by adjustment of the frequency allocation, based on a measure of insertion angle and/or electrode discrimination ability.

Electroacoustic stimulation: now and into the future

Cochlear implants have provided hearing to hundreds of thousands of profoundly deaf people around the world. Recently, the eligibility criteria for cochlear implantation have been relaxed to include individuals who have some useful residual hearing. These recipients receive inputs from both electric and acoustic stimulation (EAS). Implant recipients who can combine these hearing modalities demonstrate pronounced benefit in speech perception, listening in background noise, and music appreciation over implant recipients that rely on electrical stimulation alone. The mechanisms bestowing this benefit are unknown, but it is likely that interaction of the electric and acoustic signals in the auditory pathway plays a role. Protection of residual hearing both during and following cochlear implantation is critical for EAS. A number of surgical refinements have been implemented to protect residual hearing, and the development of hearing-protective drug and gene therapies is promising for EAS recipients. This review outlines the current field of EAS, with a focus on interactions that are observed between these modalities in animal models. It also outlines current trends in EAS surgery and gives an overview of the drug and gene therapies that are clinically translatable and may one day provide protection of residual hearing for cochlear implant recipients.

Scala-Tympani Phantom With Cochleostomy and Round-Window Openings for Cochlear-Implant Insertion Experiments

Experiments with scala-tympani (ST) phantoms are used to evaluate new electrode arrays and cochlear-implant insertion techniques. To date, phantoms have not accounted for clinical orientations and geometric differences between round-window (RW) insertions and anteroinferior cochleostomy insertions. For improved assessments of insertion experiments, we present a scala-tympani phantom that offers three distinct benefits over previous phantoms: it mimics the standard otologic position, it accommodates for both round-window and anteroinferior cochleostomy insertions, and it incorporates a visual coordinate system based on industry consensus making standardized angular measurements possible.

Place pitch versus electrode location in a realistic computational model of the implanted human cochlea

Place pitch was investigated in a computational model of the implanted human cochlea containing nerve fibres with realistic trajectories that take the variable distance between the organ of Corti and spiral ganglion into account. The model was further updated from previous studies by including fluid compartments in the modiolus and updating the electrical conductivity values of (temporal) bone and the modiolus, based on clinical data. Four different cochlear geometries are used, modelled with both lateral and perimodiolar implants, and their neural excitation patterns were examined for nerve fibres modelled with and without peripheral processes. Additionally, equations were derived from the model geometries that describe Greenwood's frequency map as a function of cochlear angle at the basilar membrane as well as at the spiral ganglion. The main findings are: (I) in the first (basal) turn of the cochlea, cochlear implant induced pitch can be predicted fairly well using the Greenwood function. (II) Beyond the first turn this pitch becomes increasingly unpredictable, greatly dependent on stimulus level, state of the cochlear neurons and the electrode's distance from the modiolus. (III) After the first turn cochlear implant induced pitch decreases as stimulus level increases, but the pitch does not reach values expected from direct spiral ganglion stimulation unless the peripheral processes are missing. (IV) Electrode contacts near the end of the spiral ganglion or deeper elicit very unpredictable pitch, with broad frequency ranges that strongly overlap with those of neighbouring contacts. (V) The characteristic place pitch for stimulation at either the organ of Corti or the spiral ganglion can be described as a function of cochlear angle by the equations presented in this paper.

A novel perfusion-based method for cochlear implant electrode insertion

A cochlear implant (CI) restores partial hearing to profoundly deaf individuals. CI electrodes are inserted manually in the cochlea and surgeons rely on tactile feedback from the implant to determine when to stop the insertion. This manual insertion method results in a large degree of variability in surgical outcomes and intra-cochlear trauma. Additionally, implants often span only the basal turn. In the present study we report on the development of a new method to assist CI electrode insertion. The design objectives are (1) an automated and standardized insertion technique across patients with (2) more apical insertion than is possible by the contemporary methods, while (3) minimizing insertion trauma. The method relies on a viscous fluid flow through the cochlea to carry the electrode array with it. A small cochleostomy (∼100-150 um in diameter) is made in scala vestibuli (SV) and the round window (RW) membrane is opened. A flow of diluted Sodium Hyaluronate (also known as Hyaluronic Acid, (HA)) is set up from the RW to the SV opening using a perfusion pump that sets up a unidirectional flow. Once the flow is established an implant is dropped into the ongoing flow. Here we present a proof-of-concept study where we used this technique to insert silicone implants all the way to the cochlear apex in rats and gerbils. In light-microscopic histology, the implantation occurred without cochlear trauma. To further assess the ototoxicity of the HA perfusion, we measured compound action potential (CAP) thresholds following the perfusion of HA, and found that the CAP thresholds were substantially elevated. Thus, at this point the method is promising, and requires further development to become clinically viable.

The role of post-operative imaging in cochlear implant surgery: a review of 220 adult cases

OBJECTIVES

To determine the incidence of abnormal radiological findings after cochlear implantation and their effect on clinical outcomes.

METHODS

Retrospective review of 220 adult cochlear implants. Clinical records and post-operative plain X-rays were reviewed and compared with pre-operative and 6-month post-operative City University of New York (CUNY) speech scores.

RESULTS

There were no cases of extra-cochlear array misplacement. Imaging showed 20 cases of incomplete array insertion (9.2%), 3 cases of kinking of the array (1.4%), 2 cases of tip rollover (0.9%), and 1 case of apparent array fracture (0.5%). Patient management was not altered by abnormal imaging. Patients with abnormal radiological findings had slightly minor improvements (median 39 vs. 56%) in City University of New York (CUNY) speech discrimination scores at 6 months (Mann-Whitney U test, P = 0.043).

CONCLUSION

All abnormalities on post-operative imaging were minor and did not alter patient management. The future role of post-operative imaging is discussed.

Perceptual changes in place of stimulation with long cochlear implant electrode arrays

Long (31.5 mm) electrode arrays are inserted deeper into the cochlea than the typical 1.25 turn insertion. With these electrode arrays, the apical electrodes are closer to (and possibly extend past) the end of the spiral ganglion. Using multi-dimensional scaling with patients implanted with a 31.5 mm electrode array, the perceptual space between electrodes was measured. The results suggest that deeper insertion increases the range of place pitches, but the perceptual differences between adjacent electrodes become smaller in the apex.

Effects of various electrode configurations on music perception, intonation and speaker gender identification

Advances in speech coding strategies and electrode array designs for cochlear implants (CIs) predominantly aim at improving speech perception. Current efforts are also directed at transmitting appropriate cues of the fundamental frequency (F0) to the auditory nerve with respect to speech quality, prosody, and music perception. The aim of this study was to examine the effects of various electrode configurations and coding strategies on speech intonation identification, speaker gender identification, and music quality rating. In six MED-EL CI users electrodes were selectively deactivated in order to simulate different insertion depths and inter-electrode distances when using the high definition continuous interleaved sampling (HDCIS) and fine structure processing (FSP) speech coding strategies. Identification of intonation and speaker gender was determined and music quality rating was assessed. For intonation identification HDCIS was robust against the different electrode configurations, whereas fine structure processing showed significantly worse results when a short electrode depth was simulated. In contrast, speaker gender recognition was not affected by electrode configuration or speech coding strategy. Music quality rating was sensitive to electrode configuration. In conclusion, the three experiments revealed different outcomes, even though they all addressed the reception of F0 cues. Rapid changes in F0, as seen with intonation, were the most sensitive to electrode configurations and coding strategies. In contrast, electrode configurations and coding strategies did not show large effects when F0 information was available over a longer time period, as seen with speaker gender. Music quality relies on additional spectral cues other than F0, and was poorest when a shallow insertion was simulated.