Andrzej Zarowski

Anatomic considerations of cochlear morphology and its implications for insertion trauma in cochlear implant surgery.

Hypothesis: The goal of this study is to analyze the 3-dimensional anatomy of the cochlear spiral and to investigate the consequences of its course to insertion trauma during cochlear implantation. Background: Insertion trauma in cochlear implant surgery is a feared surgical risk, potentially causing neural degeneration and altered performance of the implant. In literature, insertion trauma is reported to occur at specific locations. This has been ascribed to surgical technique and electrode design in relation to the size of the scala tympani. This study investigates whether there is an underlying anatomic substrate serving as a potential source for insertion trauma at these specific locations. Methods: The 3-dimensional path of the cochlear spiral of 8 human temporal bones was determined by segmentation, skeletonization, distance mapping, and wave propagation technique applied on microcomputer tomography images. Potential pressure points along this path were estimated with linear regression. Results: The cochlear lumen shows a noncontinuous spiraling path leading to potential pressure points during cochlear implantation at the basilar membrane in the region of 180 to 225 (12-14 mm) and 725 degrees (22-26 mm) and at the floor of the scala tympani around 0 to 90, 225 to 270, and 405 to 450 degrees. Conclusion: Our data favor the idea that the intrinsic 3-dimensional cochlear morphology contributes to the risk for insertion trauma during cochlear implantation at specific locations.

Auditory brainstem implantation in children and non-neurofibromatosis type 2 patients: a consensus statement.

On the 18th of September 2009, a group of health care professionals and scientists involved in implantation of the auditory system attended a meeting convened by the Hacettepe Cochlear Implant Group. The aim of the meeting was to have a detailed discussion on the pressing and pertinent issues around

Identification of the impedance model of an implanted cochlear prosthesis from intracochlear potential measurements

Those suffering from a severe to profound sensorineural hearing loss can obtain substantial benefit from a cochlear implant prosthesis. An electrode array implanted in the inner ear stimulates auditory nerve fibers by direct injection of electrical current. A major limitation of todays technology is the imprecise control of intracochlear current flow, particularly the relatively wide spread of neural excitation. A better understanding of the intracochlear electrical fields is, therefore, required. This paper analyzes the structure of intracochlear potential measurements in relation to both the subjects anatomy and to the properties of the electrode array. An electrically equivalent network is proposed, composed of small lumped circuits for the interface impedance and for the cochlear tissues. The numerical methods required to estimate the model parameters from high-quality electrical potential recordings are developed. Finally, some models are presented for subjects wearing a Clarion CII device with a HiFocus electrode and discussed in terms of model reliability.

Clinical results of AutoNRT, a completely automatic ECAP recording system for cochlear implants.

Objective: AutoNRT™ is the completely automatic electrically evoked compound action potential (ECAP) measuring algorithm in the recently released Nucleus Freedom cochlear implant system. AutoNRT allows clinicians to automatically record T-NRT profiles that in turn can be used as a guide for initial fitting. The algorithm consists of a pattern recognition part that judges if the traces contain an ECAP and an intelligent flow that optimizes the measurement parameters and finds the ECAP threshold (T-NRT). The objective of this study was to determine how accurate, reliable, and fast the automatic measurements are. Design: Data on more than 400 electrodes were collected as part of the multicenter clinical trial of the Nucleus Freedom cochlear implant system. T-NRT values determined by the algorithm were compared with T-NRT determinations on the same data by different human observers. Also, the time the measurements took was analyzed. Results: In 90% of the cases, the absolute difference between the AutoNRT and the human observer determined T-NRT was less than 9 CL; the median absolute difference was 3 CL. A second experiment, in which a group of human observers were asked to analyze NRT data, showed high variability in T-NRT; in some cases, two experienced clinicians disagreed by more than 30 current levels. Compared with the group, AutoNRT performed as well as the “average” clinician, with the advantage that the AutoNRT threshold determinations are objective. Analysis of the timing data showed an average intraoperative measurement time of less than 20 sec per electrode with a standard deviation of 5 sec, suggesting that the total array of 22 electrodes can be measured intraoperatively in about 7 minutes on average. Conclusions: AutoNRT provides comparable accuracy to an average clinician but with the added benefit of significant time savings over manual recordings. This makes it a valuable tool for clinical measurement of ECAP threshold in cochlear implant recipients.

The facial nerve canal: an important cochlear conduction path revealed by Clarion electrical field imaging.

Hypothesis: Electrical properties of the implanted scala tympani could be accurately modeled by means of a simple resistive ladder network model. The subject-specific model parameters can be obtained from electrical field imaging (EFI) recordings. It is a powerful tool for analysis of the cochlear current spread. Background: In EFI mode, the telemetry systems of contemporary cochlear implants can measure the intracochlear potential distribution. At present, the clinical use of EFI is typically limited to checking the implant’s proper functioning. Methods: Accurate EFI measurements and estimation algorithms have been developed to fit a small, yet physically relevant electrical model of the conductivity of the intracochlear structures. Results: The model can attain up to 95% agreement with in vivo EFI data. A first discovery is that in a majority of the tested subjects, a substantial fraction of the monopolar current leaves the scala along the facial nerve canal. The role of the facial nerve canal has been confirmed by a temporal bone study and a high-resolution computed tomography (HRCT) scan in two of the implanted subjects. Conclusions: The clinical use of EFI is not limited to checking the implant’s status. For the Clarion II implant, a purely resistive model is able to match in vivo EFI recordings. The model indicates that the facial nerve canal is an important conduction path to the reference electrode. EFI can provide clinically relevant information, especially in problematic cases of cochlear malformations, postoperative fibrosis/ossification, implanted otosclerotic cochleae, postoperative facial nerve stimulation, increased stimulation thresholds, and so on.

Skin reactions following BAHA surgery using the skin flap dermatome technique

The objectives of the study were to determine the incidence of skin reactions and complications associated with bone-anchored hearing aid (BAHA) implantation. The study is a retrospective case review done in a tertiary referral center. One hundred thirty-eight consecutive patients between 1998 and 2008 underwent implantation of a BAHA and were regularly seen for follow-up. Indications included conductive or mixed hearing loss where a hearing aid cannot be used and since 2000 also had contralateral single-sided perceptive hearing loss. BAHA implantation was done by creating a pedicled flap using the skin flap dermatome technique. Postoperative incidence of skin reactions and complications were measured. Significant postoperative complications requiring revision surgery occurred 37 times in 30 patients. Normal skin healing was seen in 52 patients (63.4%), while abnormal skin healing occurred in 30 patients (36.6%). This study showed that skin problems occur more often than expected. Because of the skin problems with the skin flap technique, the authors have switched to the linear incision technique, hoping to decrease the incidence of skin problems.

Stapedotomy with Microdrill or Carbon Dioxide Laser: Influence on Inner Ear Function

Objectives: A prospective randomized audiological analysis of 336 otosclerosis operations was conducted to compare the evolution of bone conduction thresholds after primary stapedotomy with Two different techniques to open the footplate: microdrill and carbon dioxide laser stapedotomy. Methods: To monitor the inner ear function, we compared the preoperative bone conduction thresholds with the postoperative levels at day 2, week 2, week 6, and month 6. Evolution of the bone conduction was compared for the Two studied groups (laser versus microdrill). Results: An average bone conduction loss of 1.8 dB was measured at day 2 for the middle frequencies (0.5, 1, and 2 kHz). At 4 kHz, a bone conduction loss of 7 dB was found. The bone conduction thresholds measured in the first and second months after surgery showed a gradual recovery with overclosure as the end result. Conclusions: Our results confirm the transient depression of inner ear function in the immediate postoperative period, with recovery within the first weeks after surgery. In the studied population, no statistically significant difference was found between the Two techniques that were used to make the calibrated hole (laser versus microdrill). These results demonstrate that both techniques possess the same early effect regarding inner ear function. The authors hypothesize that an early inflammatory reaction could be the cause of the transient bone conduction shift.

Clinical evaluation of cochlear implant sound coding taking into account conjectural masking functions, MP3000™

Abstract Efficacy of the SPEAK and ACE coding strategies was compared with that of a new strategy, MP3000™, by 37 European implant centers including 221 subjects. The SPEAK and ACE strategies are based on selection of 8–10 spectral components with the highest levels, while MP3000 is based on the selection of only 4–6 components, with the highest levels relative to an estimate of the spread of masking. The pulse rate per component was fixed. No significant difference was found for the speech scores and for coding preference between the SPEAK/ACE and MP3000 strategies. Battery life was 24% longer for the MP3000 strategy. With MP3000 the best results were found for a selection of six components. In addition, the best results were found for a masking function with a low-frequency slope of 50 dB/Bark and a high-frequency slope of 37 dB/Bark (50/37) as compared to the other combinations examined of 40/30 and 20/15 dB/Bark. The best results found for the steepest slopes do not seem to agree with current estimates of the spread of masking in electrical stimulation. Future research might reveal if performance with respect to SPEAK/ACE can be enhanced by increasing the number of channels in MP3000 beyond 4–6 and it should shed more light on the optimum steepness of the slopes of the masking functions applied in MP3000.

Effect of changing pulse rate on profile parameters of perceptual thresholds and loudness comfort levels and relation to ECAP thresholds in recipients of the Nucleus CI24RE device.

Abstract The Nucleus CI24RE ‘Freedom’ device offers higher stimulation rates and lower noise levels in action potential measurements (ECAPs) than previous devices. A study including ten European implant teams showed that the effect of changes in rate from 250 to 3500 pulses per second on tilt and curvature of the T and C profiles is insignificant. When changing rate one may change the levels at all electrodes by the same amount. Using an automated procedure ECAPs could be measured quickly and reliably at a noise level of only 1 μV. However, this did not result in improved correlations between the tilt and curvature parameters of the ECAP profiles and those of the T and C profiles. Average C levels appear to differ markedly among implant centers; a better assessment protocol is required. When increasing stimulus rate one should take into account that this requires higher pulse charges per second and more power consumption. Sumario El dispositivo Nucleus CI24RE “Freedom” ofrece tasas de estimulación mayores, y menores niveles de ruido en las mediciones del potencial de acción (ECAPs) que los dispositivos anteriores. Un estudio que incluyó diez grupos europeos de implantes, mostró que el efecto de los cambios en la tasa de 250 a 3500 pulsos por segundo en la inclinación y la curvatura de los perfiles T y C es insignificante. Cuando se cambian las tasas, uno puede cambiar los niveles de todos los electrodos en la misma medida. Utilizando un procedimiento automatizado, los ECAPs pueden medirse en forma rápida y confiable a un nivel de ruido de solo 1mV. Sin embargo, esto no conlleva (a) una mejoría en las correlaciones entre los parámetros de inclinación y de curvatura de los perfiles ECAP y aquellos de los perfiles de T y C. Los niveles C promedio parecen diferir marcadamente entre los centros de implante; se requiere un mejor protocolo de evaluación. Cuando se incrementa la tasa de estimulación uno debe tomar en cuenta que eso requiere una mayor carga de pulsos por segundo y mayor poder de consumo.

Speech enhancement based on neural networks improves speech intelligibility in noise for cochlear implant users

&NA; Speech understanding in noisy environments is still one of the major challenges for cochlear implant (CI) users in everyday life. We evaluated a speech enhancement algorithm based on neural networks (NNSE) for improving speech intelligibility in noise for CI users. The algorithm decomposes the noisy speech signal into time‐frequency units, extracts a set of auditory‐inspired features and feeds them to the neural network to produce an estimation of which frequency channels contain more perceptually important information (higher signal‐to‐noise ratio, SNR). This estimate is used to attenuate noise‐dominated and retain speech‐dominated CI channels for electrical stimulation, as in traditional n‐of‐m CI coding strategies. The proposed algorithm was evaluated by measuring the speech‐in‐noise performance of 14 CI users using three types of background noise. Two NNSE algorithms were compared: a speaker‐dependent algorithm, that was trained on the target speaker used for testing, and a speaker‐independent algorithm, that was trained on different speakers. Significant improvements in the intelligibility of speech in stationary and fluctuating noises were found relative to the unprocessed condition for the speaker‐dependent algorithm in all noise types and for the speaker‐independent algorithm in 2 out of 3 noise types. The NNSE algorithms used noise‐specific neural networks that generalized to novel segments of the same noise type and worked over a range of SNRs. The proposed algorithm has the potential to improve the intelligibility of speech in noise for CI users while meeting the requirements of low computational complexity and processing delay for application in CI devices. HighlightsAn algorithm for improving speech understanding in noise for cochlear implant users is evaluated.Significant improvements were found for stationary and non‐stationary noise types.It generalizes to a novel speaker and works over a range of signal‐to‐noise ratios.The small algorithmic delay makes it suitable for real‐time application.