Imaging-based frequency mapping for cochlear implants - Evaluated using a daily randomized controlled trial.

Background: Due to variation in electrode design, insertion depth and cochlear morphology, patients with a cochlear implant (CI) often have to adapt to a substantial mismatch between the characteristic response frequencies of cochlear neurons and the stimulus frequencies assigned to electrode contacts. We introduce an imaging-based fitting intervention, which aimed to reduce frequency-to-place mismatch by aligning frequency mapping with the tonotopic position of electrodes. Results were evaluated in a novel trial set-up where subjects crossed over between intervention and control using a daily within-patient randomized approach, immediately from the start of CI rehabilitation. Methods: Fourteen adult participants were included in this single-blinded, daily randomized clinical trial. Based on a fusion of pre-operative imaging and a post-operative cone beam CT scan (CBCT), mapping of electrical input was aligned to natural place-pitch arrangement in the individual cochlea. That is, adjustments to the CI's frequency allocation table were made so electrical stimulation of frequencies matched as closely as possible with corresponding acoustic locations in the cochlea. For a period of three months, starting at first fit, a scheme was implemented whereby the blinded subject crossed over between the experimental and standard fitting program using a daily randomized wearing schedule, and thus effectively acted as their own control. Speech outcomes (such as speech intelligibility in quiet and noise, sound quality and listening effort) were measured with both settings throughout the study period. Results: On a group level, standard fitting obtained subject preference and showed superior results in all outcome measures. In contrast, two out of fourteen subjects preferred the imaging-based fitting and correspondingly had better speech understanding with this setting compared to standard fitting. Conclusion: On average, cochlear implant fitting based on individual tonotopy did not elicit higher speech intelligibility but variability in individual results strengthen the potential for individualized frequency fitting. The novel trial design proved to be a suitable method for evaluation of experimental interventions in a prospective trial setup with cochlear implants.

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.

Systematic Review on Late Cochlear Implantation in Early-Deafened Adults and Adolescents: Clinical Effectiveness.

OBJECTIVES: Cochlear implantation in early-deafened patients, implanted as adolescents or adults, is not always advised due to poor expected outcomes. In order to judge whether such reluctance is justified, the current systematic review aimed to gather all available evidence on postoperative outcomes obtained by early-deafened patients using a state-of-the art cochlear implant (CI). DESIGN: Five electronic databases (PubMed, Embase, the Cochrane library, CINAHL, and PsycInfo) were systematically searched for studies in English, French, German, or Dutch, published between 2000 and September 2017. Studies that reported pre- and postoperative outcomes on any measure of speech or sound perception, audiovisual or subjective benefit (quality of life) were included. Study quality was assessed with the Institute of Health Economics quality appraisal tool for case series studies. RESULTS: The systematic search and subsequent full-text evaluation identified 38 studies meeting the inclusion criteria. Only a limited number of studies were judged to be of high quality according to the Institute of Health Economics tool, with lack of (clear) presentation of relevant study information being a recurring problem. Twenty-five studies presented viable outcomes on open-set speech understanding in quiet: mean postoperative scores obtained with CI remained below 50% for the vast majority of studies; significant postoperative improvements were found in 16 studies, although this number might have been higher if appropriate statistical testing had been performed in all studies. Eight studies observed increased audiovisual performance after implantation, which was statistically significant in six studies. A validated measure of hearing-related quality of life was used in only 5 of the 16 studies assessing subjective outcomes, showing significant postoperative improvements for most questionnaire domains. The relation between auditory and subjective outcomes was assessed in two studies, with contradictory results. CONCLUSIONS: The current review showed that late cochlear implantation in early-deafened subjects resulted in significantly improved open-set speech perception, audiovisual speech perception, and (hearing-related) quality of life in the majority of the studies involved. Nonetheless, more and especially higher-quality research is needed in order to gain a more detailed understanding of the outcomes of cochlear implantation in this population.

Systematic Review on Late Cochlear Implantation in Early-Deafened Adults and Adolescents: Predictors of Performance.

OBJECTIVES: Early-deafened, late-implanted adolescents and adults constitute a unique group of cochlear implant (CI) users, showing a large variability in outcomes. The current systematic review aimed to determine which preimplantation factors are relevant in predicting postoperative outcomes in this patient group. DESIGN: A systematic search for studies published between 2000 and September 2017 was performed in five electronic databases (PubMed, Embase, the Cochrane library, CINAHL, and PsycInfo). Prognostic studies that assessed the relation between patient-related factors and CI outcomes in early-deafened but late-implanted adolescent and adult CI users were included. Study quality was assessed with the Quality In Prognosis Studies (QUIPS) tool. RESULTS: The systematic search and subsequent full-text evaluation identified 13 studies that had a clear prognostic study goal. Eight out of these 13 studies had a high risk of bias for at least one of the five QUIPS domains. Analysis of the outcomes identified that communication mode (in childhood), preoperative speech intelligibility, and preoperative speech recognition scores were significantly related to speech perception outcomes for this group of CI users. A number of additional factors considered worth for further investigation were also identified. CONCLUSIONS: The analysis of the studies assessing the effect of a number of patient-related factors on outcome with CI in early-deafened adolescents and adults identified three potential prognostic factors and a number of additional factors to be incorporated in future research. More high-quality prognosis studies in the investigated patient population are still needed.

Fitting prelingually deafened adult cochlear implant users based on electrode discrimination performance.

OBJECTIVE: This study investigated the hypotheses that (1) prelingually deafened CI users do not have perfect electrode discrimination ability and (2) the deactivation of non-discriminable electrodes can improve auditory performance. DESIGN: Electrode discrimination difference limens were determined for all electrodes of the array. The subjects' basic map was subsequently compared to an experimental map, which contained only discriminable electrodes, with respect to speech understanding in quiet and in noise, listening effort, spectral ripple discrimination and subjective appreciation. STUDY SAMPLE: Subjects were six prelingually deafened, late implanted adults using the Nucleus cochlear implant. RESULTS: Electrode discrimination difference limens across all subjects and electrodes ranged from 0.5 to 7.125, with significantly larger limens for basal electrodes. No significant differences were found between the basic map and the experimental map on auditory tests. Subjective appreciation was found to be significantly poorer for the experimental map. CONCLUSIONS: Prelingually deafened CI users were unable to discriminate between all adjacent electrodes. There was no difference in auditory performance between the basic and experimental map. Potential factors contributing to the absence of improvement with the experimental map include the reduced number of maxima, incomplete adaptation to the new frequency allocation, and the mainly basal location of deactivated electrodes.

Late Cochlear Implantation in Early-Deafened Adults: A Detailed Analysis of Auditory and Self-Perceived Benefits.

OBJECTIVES: It is known that early-deafened cochlear implant (CI) users are a very heterogeneously performing group. To gain more insight into this population, this study investigated (1) postoperative changes in auditory performance over time based on various outcome measures, focusing on poor performers, (2) self-perceived outcomes, (3) relations between auditory and self-perceived outcomes, and (4) preimplantation factors predicting postoperative outcomes. METHODS: Outcomes were assessed prospectively in a group of 27 early-deafened, late-implanted CI users, up to 3 years after implantation. Outcome measures included open-set word and sentence recognition, closed-set word recognition, speech tracking and a questionnaire on self-perceived outcomes. Additionally, the relative influence of 8 preimplantation factors on CI outcome was assessed with linear regression analyses. RESULTS: Significant improvements were found for auditory performance measures and most of the questionnaire domains. Significant changes of the closed-set word test, speech tracking and questionnaire were also found for a subgroup of poor performers. Correlations between auditory and self-perceived outcomes were weak and nonsignificant. Preoperative word recognition and preoperative hearing thresholds, both for the implanted ear, were significant predictors of postoperative outcome in the multivariable regression model, explaining 63.5% of the variation. CONCLUSIONS: Outcome measurement in this population should be adjusted to the patients' individual performance level and include self-perceived benefit. There is still a need for more knowledge regarding predictors of CI outcomes in this group, but the current study suggests the importance of the preoperative performance of the ear to be implanted.

Amplitude Modulation Detection and Speech Recognition in Late-Implanted Prelingually and Postlingually Deafened Cochlear Implant Users.

OBJECTIVES: Many late-implanted prelingually deafened cochlear implant (CI) patients struggle to obtain open-set speech understanding. Because it is known that low-frequency temporal-envelope information contains important cues for speech understanding, the goal of this study was to compare the temporal-envelope processing abilities of late-implanted prelingually and postlingually deafened CI users. Furthermore, the possible relation between temporal processing abilities and speech recognition performances was investigated. DESIGN: Amplitude modulation detection thresholds were obtained in eight prelingually and 18 postlingually deafened CI users, by means of a sinusoidally modulated broadband noise carrier, presented through a loudspeaker to the CI user's clinical device. Thresholds were determined with a two-down-one-up three-interval oddity adaptive procedure, at seven modulation frequencies. Phoneme recognition (consonant-nucleus-consonant [CNC]) scores (percentage correct at 65 dB SPL) were gathered for all CI users. For the prelingually deafened group, scores on two additional speech tests were obtained: (1) a closed-set monosyllable-trochee-spondee test (percentage correct scores at 65 dB SPL on word recognition and categorization of the suprasegmental word patterns), and (2) a speech tracking test (number of correctly repeated words per minute) with texts specifically designed for this population. RESULTS: The prelingually deafened CI users had a significantly lower sensitivity to amplitude modulations than the postlingually deafened CI users, and the attenuation rate of their temporal modulation transfer function (TMTF) was greater. None of the prelingually deafened CI users were able to detect modulations at 150 and 200 Hz. High and significant correlations were found between the results on the amplitude modulation detection test and CNC phoneme scores, for the entire group of CI users. In the prelingually deafened group, CNC phoneme scores, word scores on the monosyllable-trochee-spondee test, and speech tracking scores correlated significantly with the mean amplitude modulation detection threshold of the modulation frequencies between 5 and 100 Hz and with almost all separate amplitude modulation thresholds. High correlations with these speech measures were also found for the attenuation rate of and the surface area below the TMTF. In postlingually deafened CI users, CNC phoneme scores only correlated significantly with the 100-Hz and 150-Hz amplitude modulation thresholds, as well as with the attenuation rate of and surface area below the TMTF. CONCLUSIONS: Prelingually deafened CI users were less sensitive to temporal modulations than postlingually deafened CI users, and the attenuation rate of their TMTF was steeper. For all CI users, subjects with better amplitude modulation detection skills tended to score better on measures of speech understanding. Significant correlations with low modulation frequencies were found only for the prelingually deafened CI users and not for the postlingually deafened CI users.