Neural response telemetry in cochlear implant users

Programming of multichannel cochlear implants requires subjective responses to a series of sophisticated psychophysical percepts. It is often difficult for cochlear implant patients (especially young prelinguistically deaf children) to provide adequate responses for device fitting. However, the neural response telemetry (NRT) system renders possible the measurement of the compound action potential threshold. We performed NRT examinations in 27 cochlear implant users with Nucleus 24-channel cochlear implants. Measurements were obtained from five electrodes (3, 5, 10, 15, and 20) in each patient. Our goal was to look for correlation between behavioral subjective thresholds and compound action potentials. The action potentials could be elicited in 23 patients in all measured electrodes. The NRT threshold values were highly correlated with electrical threshold levels obtained through subjective responses. Our results suggest that the electrically elicited neural responses may yield very important information for device fitting in patients with cochlear implants.     

小儿正常耳蜗与内耳畸形人工耳蜗植入术后电极阻抗及NRT值对比研究

目的：探讨小儿正常耳蜗与内耳畸形人工耳蜗植入手术后,植人体电极阻抗值及神经反应遥测（NRT）值的变化特点及规律。方法：将88例澳大利亚CochlearNucleus24型人工耳蜗植人手术患儿分为正常耳蜗组与内耳畸形耳蜗组,测试手术中及手术后1年阻抗值及NRT值,并分析对比。结果：两组患者阻抗值差异有统计学意义（P〉0．05）,其阻抗变化趋势相同。开机3个月内阻抗值变化明显,其后趋于稳定。两组患者NRT值差异有统计学意义（P〈0．05）,其NRT值变化趋势相同。总的趋势是低频值较低,高频值较高,术中至术后1年NRT值逐渐增高。结论：电极阻抗值及NRT值开机3个月内变化明显,故需多次调机,以使患者语言感知达到最佳状态。     

Objective methods in postlingually and prelingually deafened adults for programming cochlear implants: ESR and NRT

This study compared responses of prelingually and postlingually deafened adult Nucleus 24 cochlear implant users on two objective measures employed to predict programming levels: neural response telemetry (NRT) and electrically evoked stapedial reflexes (eSR). Thirty experienced postlingually and prelingually deafened adult implant users underwent standard behavioural judgements of maximum comfortable loudness levels (C levels) and thresholds (Ts) followed by eSR and NRT measurements. Two different programs were created based on both the subjective judgement and the objective estimates of C levels (eSR thresholds) and these were compared. Relationships between the subjective and the objective measures were statistically analysed. Maximum stimulation levels estimated by both eSR and NRT were highly correlated with C levels. Variability of NRT results was higher than for eSR results. Mean NRT thresholds for postlingually deafened patients were higher than for prelingually deafened patients. A number of prelingually deafened users could distinguish no difference between programs; however, the majority of postlingually deafened users were sensitive to the difference and many reported preference for the program with eSR-estimated C levels. Neural response telemetry thresholds and eSRTs obtained in Nucleus 24 patients are highly correlated with C levels and Ts. Results suggest that estimation of C levels and Ts using NRT or eSR requires different correction factors for prelingually versus postlingually deafened adult subjects.     

Correlation between NRT measurement level and behavioral levels in pediatrics cochlear implant patients

Objective

To determine the relationship between the electrically evoked nerve action potential (Neural Response Telemetry [NRT]) and behavioral levels (T- and C-level) for pediatric patients using the Nucleus 24 cochlear implant system.

Method

A hospital based study of pediatric cochlear implant patients in the period between June 2000 and December 2008. At King Abdul-Aziz University Hospital (KAUH) Saudi Arabia the Neural Response Telemetry was administered to 47 children (mean age at implantation: 4 years) with the Nucleus 24 cochlear implants. Four intra cochlear electrodes (numbers 5, 10, 15, and 20) were tested one-month post-implantation, the neural response threshold compared with the behavioral threshold and the maximum comfort level estimated at the same time.

Results

At all the electrode numbers, the mean for NRT level measurements was significantly higher than that for the T-level measurements and the mean for the C-level measurements was significantly higher than that for NRT level measurements The correlation analyses showed positive correlation between C-level and NRT level measurements and T-level and NRT level measurements.

Conclusion

There was a positive correlation between NRT value measurements and both T and C value measurements. Therefore, it is useful to use the NRT values to predict the behavioral T and C values in prelingual children.     

客观听觉监测技术在人工耳蜗植入中的临床应用

目的：比较电诱发镫骨肌反射技术（ESR）及神经反应遥测技术（NRT）的临床特点及应用价值。方法：对21例行Cochlear Nucleus 24R（CA）型人工耳蜗植入者分别选取1、7、11、17、22号电极,应用Cochlear公司提供的NRT3.0软件分别进行术中ESR和NRT检测、术后主观心理物理测试,测定电诱发镫骨肌反射阈值（ESRT）、电诱发听神经复合动作电位阈值（ECAP）和听阈阈值（T-levels）,并对其ESRT、ECAP和T-levels进行相关性研究。结果：ESRT、NRT、T-levels检出率分别为96.19%、93.33%、100%。ESRT平均阈值为206.61±10.74、208.48±13.64、205.52±14.63、203.76±12.97、199.5±11.19;NRT平均阈值分别为184.11±6.35、188.55±11.70、187.00±12.29、181.85±13.22、179.00±10.50;T-levels平均阈值分别为145.48±18.66、148.62±8.22、146.62±18.08、142.52±13.11、140.33±13.68。各电极ESRT阈值均远远大于心理物理测试得到的T-levels阈值。ESRT、NRT、T-levels三者的均值趋势有较强的一致性。术中测试时间、测试方式、单方检出率、ESR均优于NRT。以所有电极作为观察对象,ESRT与NRT的相关性为0.69,NRT与T值的相关性为0.62,ESRT与T值之间的相关性为0.39。结论：术中应用ESR和NRT技术,可以第一时间反映植入体及听觉传导通路的情况,相对于NRT而言,ESR更为灵活、方便、精确和直观,在低龄患儿术后调试方面前者显示出更加客观的优越性。     

儿童人工耳蜗植入术后神经反应遥测阈值的变化

目的:通过对儿童患者术后神经反应遥测 (NRT) 阈值的分析,总结其变化规律,为儿童人工耳蜗植入术后调试提供帮助.方法:测试40例接受Nucleus CI24R 型多导人工耳蜗单侧植入术的患儿.测试使用澳大利亚Cochlear公司提供的便携式调试系统及NRT3.1版本软件.采用削减算法提取NRT反应波形,分别测试每位患者的第1、5、10、15、20号电极,NRT阈值使用NRT软件计算.分别在开机时、开机3、6和12个月时进行测试.结果:在术后同一测试时间,位于耳蜗不同部位电极的NRT阈值存在差异.耳蜗底部和顶部电极的NRT阈值较低,而位于耳蜗中部的电极NRT阈值较高.经单因素方差分析,不同部位NRT阈值均差异有统计学意义.同一测试电极,随术后开机时间的增长,NRT阈值呈逐渐增加的趋势.经单因素方差分析,术后不同测试时间NRT阈值均差异有统计学意义.结论:术后开机1年内,NRT阈值呈逐渐增加的趋势.若人工耳蜗植入术后调试需要NRT进行辅助,每次均应测试NRT阈值,以便更准确估算患者的行为反应T、C级,尤其对植入术后1年内的儿童患者更为重要.     

Accuracy of intraoperative electrophysiological testing in confirming correct cochlear implant electrode positions

Objective: To investigate the accuracy of intraoperative electrophysiological studies in detecting incorrectly positioned electrodes in cochlear implant surgery.

Study design: A retrospective chart review.

Setting: Tertiary referral centre.

Patients: In total, 104 consecutive patients with a mean age of 5 years underwent cochlear implant surgery at our centre between January 2012 and December 2013. All patients were implanted with Cochlear Nucleus Freedom implants.

Method: A retrospective study to compare intraoperative neural response telemetry (NRT), impedance and electrode position using Stenver’s transorbital plain X-ray view.

Results: Intraoperative electrophysiological tests for patients with Cochlear Nucleus Freedom implants showed 97% sensitivity and 100% specificity compared with postoperative X-ray imaging.

Conclusion: NRT results for the position of cochlear implants were very accurate when checked by X-ray imaging showing that this technique is sufficient in most cases. Stenver’s plain X-ray view is needed in complicated cases with abnormal NRT testing or difficult electrode insertion.     

Use of neural response telemetry measures to objectively set the comfort levels in the Nucleus 24 cochlear implant

Cochlear implant programming necessitates accurate setting of programming levels, including maximum stimulation levels, of all active electrodes. Frequently, clinical techniques are adequate for setting these levels; however, they are sometimes insufficient (e.g., very young children). In the Nucleus 24, several methods have been suggested for estimation of comfort levels (C levels) from neural response telemetry (NRT); however, many require co-application of clinical measurements. Data was obtained from 21 adult Nucleus 24 recipients to develop reliable predictions of C levels. Multiple regression analysis was performed on NRT threshold, slope of the NRT growth function, age, length of deafness, length of cochlear implant use and electrode impedance to examine predictive ability. Only the NRT threshold and slope of the growth function measures were significant predictors yielding R2 values from 0.391 to 0.769. Results demonstrated that these measures may provide an alternative means of estimating C levels when other clinical measures are unavailable.     

Nucleus24型人工耳蜗使用者电诱发听神经复合动作电位的测定

目的 :探讨电诱发听神经复合动作电位 (ECAP)的特点及在人工耳蜗临床中的应用价值和意义。方法 :应用NRT(neuralresponsetelemetry)软件 ,通过体外言语处理器和耳蜗内的植入电极系统 ,采用单极模式电极刺激和近场记录方法 ,对 37例NucleusCI2 4M装置使用者进行ECAP的记录。对其中 12例使用者做了行为测试。结果 :87.6 %的使用者记录到ECAP波形。分析了有行为阈值的 12例测试者的ECAP阈值和行为阈值的关系 ,二者之间存在显著的相关性。结论 :ECAP的检出率高且波形稳定可靠 ,在临床人工耳蜗装置的调试中可作为对行为测试的补充 ;对于年幼儿童和首次开机的患者的调试尤其重要     

Nucleus 24人工耳蜗系统直电极与弯电极神经反应遥测值的比较

目的:测试和比较Nucleus 24人工耳蜗系统中直电极与弯电极神经反应遥测(NRT)值的差别,分析内耳螺旋神经节细胞对不同电极电刺激反应特性的差异。方法:对46例进行耳蜗植入和编程的Nucleus 24人工耳蜗系统直电极与弯电极患者进行配对分析,计算患者vNRT值的均值,并进行统计学比较。结果:直电极的NRT值为160～170μV,弯电极为150～160μV,总的趋势是低频值较低而高频值较高。结论:Nucleus 24人工耳蜗系统弯电极较直电极所需电刺激量略低。     

Evaluation of NRT and behavioral measures for MAPping elderly cochlear implant users

We investigated the acceptability of electrophysiologically derived MAPs and the effect of these MAPs on speech perception in elderly adults using Nucleus 24 cochlear implants. Eight implant recipients aged 75 years or older trialed an electrophysiologically derived MAP and a behavioral MAP. The electrophysiologically derived MAP was based on the threshold and maximum comfort level for electrode 10 and evoked compound action potential thresholds measured on six electrodes using neural response telemetry (NRT). Word perception at 55 dB SPL and sentence perception in noise at 70 dB SPL were assessed after six weeks take-home experience and again after an additional two weeks of experience. During the final two weeks of take-home experience participants indicated their preferred MAP for different listening situations. The NRT derived MAP estimated behavioral T levels well, but underestimated behavioral C levels for apical electrodes in some subjects. Speech perception with NRT derived MAPs was comparable to speech perception with behaviorally measured MAPs. MAPs estimated from NRT data provided good speech perception outcomes for elderly implant recipients and were well tolerated.     

Evaluation of NRT and behavioral measures for MAPping elderly cochlear implant users

We investigated the acceptability of electrophysiologically derived MAPs and the effect of these MAPs on speech perception in elderly adults using Nucleus 24 cochlear implants. Eight implant recipients aged 75 years or older trialed an electrophysiologically derived MAP and a behavioral MAP. The electrophysiologically derived MAP was based on the threshold and maximum comfort level for electrode 10 and evoked compound action potential thresholds measured on six electrodes using neural response telemetry (NRT). Word perception at 55 dB SPL and sentence perception in noise at 70 dB SPL were assessed after six weeks take-home experience and again after an additional two weeks of experience. During the final two weeks of take-home experience participants indicated their preferred MAP for different listening situations. The NRT derived MAP estimated behavioral T levels well, but underestimated behavioral C levels for apical electrodes in some subjects. Speech perception with NRT derived MAPs was comparable to speech perception with behaviorally measured MAPs. MAPs estimated from NRT data provided good speech perception outcomes for elderly implant recipients and were well tolerated.     

A clinical study of electrophysiological correlates of behavioural comfort levels in cochlear implantees

Abstract

Objectives

Indications for cochlear implantation have expanded today to include very young children and those with syndromes/multiple handicaps. Programming the implant based on behavioural responses may be tedious for audiologists in such cases, wherein matching an effective Measurable Auditory Percept (MAP) and appropriate MAP becomes the key issue in the habilitation program. In ‘Difficult to MAP’ scenarios, objective measures become paramount to predict optimal current levels to be set in the MAP. We aimed to (a) study the trends in multi-modal electrophysiological tests and behavioural responses sequentially over the first year of implant use; (b) generate normative data from the above; (c) correlate the multi-modal electrophysiological thresholds levels with behavioural comfort levels; and (d) create predictive formulae for deriving optimal comfort levels (if unknown), using linear and multiple regression analysis.

Methods

This prospective study included 10 profoundly hearing impaired children aged between 2 and 7 years with normal inner ear anatomy and no additional handicaps. They received the Advanced Bionics HiRes 90 K Implant with Harmony Speech processor and used HiRes-P with Fidelity 120 strategy. They underwent, impedance telemetry, neural response imaging, electrically evoked stapedial response telemetry (ESRT), and electrically evoked auditory brainstem response (EABR) tests at 1, 4, 8, and 12 months of implant use, in conjunction with behavioural mapping. Trends in electrophysiological and behavioural responses were analyzed using paired t-test. By Karl Pearson's correlation method, electrode-wise correlations were derived for neural response imaging (NRI) thresholds versus most comfortable level (M-levels) and offset based (apical, mid-array, and basal array) correlations for EABR and ESRT thresholds versus M-levels were calculated over time. These were used to derive predictive formulae by linear and multiple regression analysis. Such statistically predicted M-levels were compared with the behaviourally recorded M-levels among the cohort, using Cronbach's alpha reliability test method for confirming the efficacy of this method.

Results

NRI, ESRT, and EABR thresholds showed statistically significant positive correlations with behavioural M-levels, which improved with implant use over time. These correlations were used to derive predicted M-levels using regression analysis. On an average, predicted M-levels were found to be statistically reliable and they were a fair match to the actual behavioural M-levels. When applied in clinical practice, the predicted values were found to be useful for programming members of the study group. However, individuals showed considerable deviations in behavioural M-levels, above and below the electrophysiologically predicted values, due to various factors. While the current method appears helpful as a reference to predict initial maps in ‘difficult to Map’ subjects, it is recommended that behavioural measures are mandatory to further optimize the maps for these individuals.

Conclusion

The study explores the trends, correlations and individual variabilities that occur between electrophysiological tests and behavioural responses, recorded over time among a cohort of cochlear implantees. The statistical method shown may be used as a guideline to predict optimal behavioural levels in difficult situations among future implantees, bearing in mind that optimal M-levels for individuals can vary from predicted values. In ‘Difficult to MAP’ scenarios, following a protocol of sequential behavioural programming, in conjunction with electrophysiological correlates will provide the best outcomes.     

神经反应遥测技术应用于婴幼儿人工耳蜗植入的作用和体会

目的探讨应用神经反应遥测技术（NRT）在人工耳蜗植入术中监测,术后调机中的作用和经验体会。方法回顾性分析38例经历人工耳蜗植入的婴幼儿的临床资料,收集每例患者在术中、术后开机、调机应用NRT测试电诱发听神经复合动作电位（ECAP）的阈值数据,应用听觉整合量表（IT MAIS）评估行为听觉言语功能。结果38例婴幼儿在术中植电极进入耳蜗后均实施NRT测试,每例测试5个电极,分别为1、6、11、16、22号电极,共测试了190个电极,其中163个电极（85.8%）引出了ECAP,其平均阈值为（163.8±21.2）CL。近端1号电极ECAP阈值显著高于远端22号电极（P<0.05）。从开机到开机后12个月,各电极ECAP阈值无显著变化。3岁以下患儿中,25例患儿在各次NRT测试时所有电极都能引出ECAP,而8例患儿存在1~5个电极不能引出ECAP,在开机12个月后,后者的IT MAIS积分与前者比较差异无统计学意义（P>0.05）。结论人工耳蜗植入后NRT测试的ECAP阈值在近端电极显著高于远端电极,耳蜗内数个电极引不出ECAP不影响术后的听觉言语康复。     

Neural response telemetry with the nucleus CI24M cochlear implant

OBJECTIVES: To review our intraoperative and postoperative testing protocol for cochlear implant patients. This study describes the methodologies and applications of a new technique called neural response telemetry (NRT) for the Nucleus CI24M cochlear implant system. NRT uses radiofrequency telemetry technology to measure the action potentials of the auditory nerve. STUDY DESIGN: We have developed a specific protocol for intraoperative testing of the implant device before, during, and after implantation. This includes device integrity tests, visual detection of electrical stapedius muscle reflexes (VESR), and NRT. METHODS: Our methodologies use the commercial software (Windows-based Diagnostic and Programming System [WIN-DPS] and NRT) for the Nucleus CI24M. We describe the details of our protocol used on all of the patients (14 adults and 14 children) who received CI24M implants at Mayo Clinic (Rochester, MN). Our protocol correlates the NRT threshold with the behavioral responses for each patient on at least four electrodes. RESULTS: From August 1, 1998, to December 31,1998, we completed electrode integrity tests, NRT, and VESR testing intraoperatively on 12 patients with the Nucleus CI24M. We have measured normal implant function on all 28 of our CI24M patients with one exception. One of our children had a device failure after approximately 4 months as a result of head trauma. We have also obtained NRT results from an additional 10 patients postoperatively. CONCLUSIONS: The measurement of device and electrode array function is quite simple with the CI24M software. These measurements can be obtained intraoperatively as well as postoperatively. We conclude that VESR and NRT measurements can be very helpful in programming for patients with cochlear implants, especially children, because they provides us with target settings for the speech processor.     

Effect of stylet removal on neural response telemetry and stapedial reflex thresholds during cochlear implantation

Objective

The purpose of this study was to analyze changes in neural response telemetry (NRT) and electrically evoked stapedial reflex thresholds (ESRT) before and after stylet withdrawal during cochlear implant surgery.

Methods

Thirty children (21–92 months old) who were candidates for cochlear implantation took part in this study. In all of them Nucleus Contour Advance was implanted. NRT and ESRT responses were recorded initially with the stylet in and then when the stylet was taken out during the implant procedure. The recordings were performed in the basal, middle, and apical areas of the electrode array.

Results

The threshold levels required to obtain NRT and ESRT responses after stylet removal were lower. This decrease was observed in all parts of the cochlea. It was statistically significant in all areas with the exception of the basal ESRT measurements.

Conclusion

Withdrawing the stylet results in better NRT and ESRT responses, most probably due to a favorable position change of the electrode array within the scala tympani.     

Effect of peri-modiolar cochlear implant positioning on auditory nerve responses: A neural response telemetry study

Conclusions. There was no evidence that a reduction in current was needed for nerve stimulation as a result of modiolar placement of a cochlear implant. However, modiolus hugging did reduce the spread of excitation for the basal and apical electrodes. This improved stimulation selectivity may result in improved speech discrimination by implant users. Objective. To test the effect of modiolar placement of a cochlear implant on stimulation thresholds, and to confirm whether peri-modiolar electrode placement resulted in the hypothesized reduced spread of excitation. Material and methods. Auditory nerve responses were measured by means of neural response telemetry (NRT) in 14 subjects. All subjects received a Nucleus CI24R(CS) Contour implant. For each subject, the stimulation threshold and response growth rate were determined on all the odd-numbered electrodes, using a masker-and-probe paradigm. In addition, the spatial spread of excitation was measured on electrodes 1, 6, 11, 16 and 20, using a variable-masker paradigm. All NRT measurements were performed intra-operatively, both before and after peri-modular placement of the electrode by removal of surgical stylet. Results. Removal of the stylet had no significant effect on the threshold and growth rate of NRT responses. It caused a reduction in the spread of excitation for electrodes 1, 6 and 20, but not for electrodes 11 and 16.     

小儿耳蜗植入后电诱发复合动作电位的阈值及其临床应用

目的：研究应用神经反应遥测（neural response telemetry,NRT)技术，测试电诱发复合动作电位（electrically-evoked compound action potential,ECAP)阈值以指导小儿人工耳蜗映射调图的策略与时机。方法：应用NRT3．0软件对辐值增长函数进行线性拟合，确定ECAP阈值。比较6例儿童植入者在术后1、2、3个月ECAP阈值的变化，同时比较了7例儿童术中、术后ECAP阈值的差异。结果：ECAP幅值增长函数在接近阈值或进入饱和时不再呈线性。术后ECAP阈值保持稳定。各导电极的术中ECAP阈值比术后阈值平均高约15CL，二者有显著性相关（R2＝0．9154）。结论：应选取幅值增长函数的直线段部分进行拟合以确定ECAP阈值。术后应用ECAP阈值指导小儿映射调图时，测试一次ECAP阈值即可。术中ECAP阈值可用作开机时映射图的C值。     

Intra-operative recordings of electrically evoked auditory nerve action potentials in young children by use of neural response telemetry with the nucleus C124M cochlear implant.

The electrically evoked action potential (EAP) was recorded intra-operatively by use of neural response telemetry (NRT) on the Nucleus C124M cochlear implant. The aim of the present study was to investigate the EAP in young children immediately following implant surgery and whilst the children were still anaesthetized. The effect of data collection parameters on the reliability of the EAP was assessed and the relationships of the EAP findings to the intra-operative electrical auditory brainstem response (EABR) and early behavioural threshold levels (T-levels) were also investigated. The study data comprised intra-operative recordings in 60 children. Age at implantation was less than five years in 42 (70%) of the children. Aetiology of deafness was congenital in the majority of children (55, 92%), meningitic in four children and of unknown origin in one child. Optimum test parameters for the intra-operative EAP were an amplifier gain of 40 dB and a delay of 50 micros in order to minimize the effects of amplifier saturation due to stimulus artefact and to maximize the identification of the N1 component. An intra-operative protocol was established which involved recording four stimulus levels on each of the 22 electrodes of the electrode array, the range of stimulus levels being tailored towards the expected EAP thresholds and T-levels so as to identify response threshold. There was significant correlation between the intraoperative EAP thresholds and the early T-levels (Pearson's r = 0.93 ;p<0.01) when a correction factor was introduced based on a reliable behavioural measure of the threshold of electrical stimulation on electrode 10. The intra-operative EAP threshold, when combined with a limited amount of behavioural data, may therefore be used to predict the T-level with a useful degree of accuracy. This result is also supported by the significant correlation observed between the intra-operative thresholds of the EAP and EABR.     

Neural response telemetry in patients with the double-array cochlear implant

This study aimed to evaluate the neural response in double-array cochlear implant as well as to describe the refractory recovery and the spread of excitation functions. In a prospective study 11 patients were implanted with the double-array cochlear implant. Neural response telemetry (NRT) was performed intra-operatively. NRT threshold could be registered in 6 of the 11 patients, at least in one electrode. The remaining five patients did not show measurable neural response intra-operatively. It was noted that although recovery and spread of excitation functions could be recorded in all the tested electrodes with measurable neural responses, the responses were shown to be different from the usual register in patients with other etiologies.