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Objectives: Despite the success of cochlear implant (CI) surgery for hearing restoration, reducing CI electrode insertion forces is an ongoing challenge with the goal to further reduce post-implantation hearing loss. While research in this field shows that both friction and quasistatic pressure forces occur during CI insertion, there is a lack of studies distinguishing between these origins. The present study was conducted to analyze the contribution of both force phenomena during automated CI insertion., Methods: Five MED-EL FLEX28 CI electrode arrays were inserted into both a regular and uncoiled version of the same average scala tympani (ST). Both ST models had a pressure release hole at the apical end, which was kept open or closed to quantify pressure forces. ST models were filled with different sodium dodecyl sulfate (SDS) lubricants (1, 5, and 10% SDS, water). The viscosity of lubricants was determined using a rheometer. Insertions were conducted with velocities ranging from v= 0.125 mm/s to 2.0 mm/s., Results: Viscosity of SDS lubricants at 20°C was 1.28, 1.96, and 2.51 mPas for 1, 5, and 10% SDS, respectively, which lies within the values reported for human perilymph. In the uncoiled ST model, forces remained within the noise floor (maximum: 0.049 × 10 -3  N ± 1.5 × 10 -3  N), indicating minimal contribution from quasistatic pressure. Conversely, forces using the regular, coiled ST model were at least an order of magnitude larger (minimum: F max  = 28.95 × 10 -3  N, v = 1 mm/s, 10% SDS), confirming that friction forces are the main contributor to total insertion forces. An N-way ANOVA revealed that both lubricant viscosity and insertion speed significantly reduce insertion forces ( p  < 0.001)., Conclusion: For the first time, this study demonstrates that at realistic perilymph viscosities, quasistatic pressure forces minimally affect the total insertion force profile during insertion. Mixed friction is the main determinant, and significantly decreases with increaseing insertion speeds. This suggests that in clinical settings with similar ST geometries and surgical preparation, quasistatic pressure plays a subordinate role. Moreover, the findings indicate that managing the hydrodynamics of the cochlear environment, possibly through pre-surgical preparation or the use of specific lubricants, could effectively reduce insertion forces., Competing Interests: MF, JD, and DS were employed by MED-EL Medical Electronics GmbH. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Fröhlich, Deutz, Wangenheim, Rau, Lenarz, Kral and Schurzig.)

Objective: Preservation of residual hearing is one of the main goals in cochlear implantation. There are many factors that can influence hearing preservation after cochlear implantation. The purpose of the present study was to develop an algorithm for validated preoperative cochlear volume analysis and to elucidate the role of cochlear volume in preservation of residual hearing preservation after atraumatic cochlear implantation., Study Design: Retrospective analysis., Setting: Tertiary referral center., Patients: A total of 166 cochlear implant recipients were analyzed. All patients were implanted with either a MED-EL (Innsbruck, Austria) FLEXSOFT (n = 3), FLEX28 (n = 72), FLEX26 (n = 1), FLEX24 (n = 41), FLEX20 (n = 38), or FLEX16 (n = 11, custom made device) electrode array through a round window approach. Main outcome measures: Cochlear volume as assessed after manual segmentation of cochlear cross-sections in cone beam computed tomography, and preservation of residual hearing 6 months after implantation were analyzed. The association between residual hearing preservation and cochlear volume was then assessed statistically., Results: Rapid and valid cochlear volume analysis was possible using the individual cross-sections and a newly developed and validated algorithm. Cochlear volume had the tendency to be larger in patients with hearing preservation than in those with hearing loss. Significant correlations with hearing preservation could be observed for the basal width and length of the basal turn., Conclusions: Preservation of residual hearing after cochlear implantation may depend on cochlear volume but appears to be influenced more strongly by other cochlear dimensions., Competing Interests: The authors disclose no conflicts of interest., (Copyright © 2024, Otology & Neurotology, Inc.)

Objectives: During the insertion of cochlear implant (CI) electrode arrays, forces occur which may cause trauma and poorer hearing outcomes. Unfortunately, research groups investigating factors influencing insertion forces come to contradicting results, especially regarding insertion speed. This study was conducted to investigate the origin of these contradicting results and to determine how different testing conditions influence experimental findings., Methods: Repeated, automated insertions with three different FLEX28 CI electrode arrays (MED-EL, Innsbruck, Austria) were performed into a newly developed, anatomically correct and 3D-printed mean scala tympani phantom. The testing protocol for each electrode included variations in insertion speed (v = 0.1-2.0 mm/s) and lubrication (90%, 50%, and 10% liquid soap), resulting in 51 insertions per electrode array and a total of 153 insertions., Results: The test setup and protocol allowed for repeatable insertions with only minimal change in the morphology of the insertion force profiles per testing condition. Strong but varying dependencies of the maximal insertion forces and work were found regarding both lubrication and speed: work-speed dependency is constant for the 10% lubricant, negative for the 50% lubricant and positive for the 90% lubricant., Conclusion: Our results can explain part of the contradicting results found within previous studies by translating interrelations known from lubricated rubber friction to the field of CI electrode array insertion. We show that the main driver behind measured bulk forces are most likely the generated friction forces, which are strongly dependent on insertion speed and lubrication. The employed test setup allows for conducting repeatable and comparable insertion studies, which can be recapitulated by other centers due to the detailed explanation of the test setup as well as the developed and freely available insertion phantom. This study hence represents another important step toward standardizing CI array insertion testing., Competing Interests: MF and DS are partly or fully employed by MED-EL. MED-EL paid scientific congress charges and related traveling costs for TR and TL. This does not alter our adherence to PLOS ONE policies. There are no patents related to this study, but the study was conducted using parts of products from MED-EL (i.e., the electrode arrays used for insertion testing are part of a commercially available product)., (Copyright: © 2024 Fröhlich et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Objective: The guinea pig serves as a well-established animal model for inner ear research, offering valuable insights into the anatomy, physiology, and therapeutic interventions of the auditory system. However, the heterogeneity of results observed in both in-vivo experiments and clinical studies poses challenges in understanding and optimizing pharmacotherapy outcomes. This heterogeneity may be due to individual differences in the size of the guinea pig cochlea and thus in the volume of the scala tympani (ST), which can lead to different drug concentrations in the ST, a fact that has been largely overlooked thus far. To address this issue, we aimed to develop an approach for calculating the individual volume of perilymph within the ST before and after cochlear implant insertion., Method: In this study, high-resolution μCT images of a total of n  = 42 guinea pig temporal bones were used to determine the volume of the ST. We compared fresh, frozen, and fixed tissues from both colored and albino strains to evaluate the potential influence of tissue condition and strain on the results., Results: Our findings demonstrate a variability in mean ST volume with a relative standard deviation (RSD) of 14.7%, comparable to studies conducted with humans (range RSD: 5 to 20%). This indicates that the guinea pig cochlea exhibits similar variability to that of the human cochlea. Consequently, it is crucial to consider this variability when designing and conducting studies utilizing the guinea pig as an animal model. Furthermore, we successfully developed a tool capable of estimating ST volume without the need for manual segmentation, employing two geometric parameters, basal diameter (A) and width (B) of the cochlea, corresponding to the cochlear footprint. The tool is available for free download and use on our website., Conclusion: This novel approach provides researchers with a valuable tool to calculate individual ST volume in guinea pigs, enabling more precise dosing strategies and optimization of drug concentrations for pharmacotherapy studies. Moreover, our study underscores the importance of acknowledging and accounting for inter-individual variability in animal models to enhance the translational relevance and applicability of research outcomes in the field of inner ear investigations., Competing Interests: The CI electrodes employed for the present investigations were supplied by MED-EL. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Grzybowski, Malfeld, Lenarz, Scheper and Schurzig.)

Hypothesis: Assessment techniques for the cochlear spatial lateral wall are associated with inter-rater variability, but derived clinical recommendations nonetheless offer value for individualized electrode selection., Background: Anatomical variations influence the location of cochlear implant electrodes inside the cochlea. Preoperative planning allows individualization of the electrode based on characterization of the bony lateral wall., Methods: The study used publicly available digitized temporal bones based on microslicing and computed tomography. Four experienced observers assessed the lateral wall applying manual tracing, linear regression scaling and elliptic-circular approximation methods in all modalities. Radial and height differences were computed in 90-degree steps from the round window center to the apex. Total length, total angular length, and tonotopic frequencies were computed for each reconstruction., Results: Differences were found most pronounced between assessment methods in vertical direction across observers and imaging modalities. One of the five anatomies was consistently found to be of shorter cochlear duct length with estimation techniques yielding more conservative results compared with manual tracings., Conclusions: Assessment techniques for the bony lateral wall yield method, observer, and image modality related deviations. Automation of the anatomical characterization may offer potential in minimizing inaccuracies. Nonetheless, observers were consistently able to detect a smaller inner ear demonstrating the ability of current methods to contribute to an optimized choice of electrodes based on individual patient anatomy., Competing Interests: Daniel Schurzig is partly employed by medical industry. The remaining authors disclose no conflicts of interest., (Copyright © 2023, Otology & Neurotology, Inc.)

In cochlear implantation, current preoperative planning procedures allow for estimating how far a specific implant will reach into the inner ear of the patient, which is important to optimize hearing preservation and speech perception outcomes. Here we report on the development of a methodology that goes beyond current planning approaches: the proposed model does not only estimate specific outcome parameters but allows for entire, three-dimensional virtual implantations of patient-specific cochlear anatomies with different types of electrode arrays. The model was trained based on imaging datasets of 186 human cochleae, which contained 171 clinical computer tomographies (CTs) of actual cochlear implant patients as well as 15 high-resolution micro-CTs of cadaver cochleae to also reconstruct the refined intracochlear structures not visible in clinical imaging. The model was validated on an independent dataset of 141 preoperative and postoperative clinical CTs of cochlear implant recipients and outperformed all currently available planning approaches, not only in terms of accuracy but also regarding the amount of information that is available prior to the actual implantation., (Copyright © 2022. Published by Elsevier B.V.)

Cochlear variability is of key importance for the clinical use of cochlear implants, the most successful neuroprosthetic device that is surgically placed into the cochlear scala tympani. Despite extensive literature on human cochlear variability, few information is available on the variability of the modiolar wall. In the present study, we analyzed 108 corrosion casts, 95 clinical cone beam computer tomographies (CTs) and 15 µCTs of human cochleae and observed modiolar variability of similar and larger extent than the lateral wall variability. Lateral wall measures correlated with modiolar wall measures significantly. ~ 49% of the variability had a common cause. Based on these data we developed a model of the modiolar wall variations and related the model to the design of cochlear implants aimed for perimodiolar locations. The data demonstrate that both the insertion limits relevant for lateral wall damage (approximate range of 4-9 mm) as well as the dimensions required for optimal perimodiolar placement of the electrode (the point of release from the straightener; approximate range of 2-5mm) are highly interindividually variable. The data demonstrate that tip fold-overs of preformed implants likely result from the morphology of the modiolus (with radius changing from base to apex), and that optimal cochlear implantation of perimodiolar arrays cannot be guaranteed without an individualized surgical technique., (© 2022. The Author(s).)

Objectives: (1) To assess variations of the human intracochlear anatomy and quantify factors which might be relevant for cochlear implantation (CI) regarding surgical technique and electrode design. (2) Search for correlations of these factors with clinically assessable measurements., Design: Human temporal bone study with micro computed tomography (μCT) data and analysis of intracochlear geometrical variations: μCT data of 15 fresh human temporal bones was generated, and the intracochlear lumina scala tympani (ST) and scala vestibuli were manually segmented using custom software specifically designed for accurate cochlear segmentation. The corresponding datasets were processed yielding 15 detailed, three-dimensional cochlear models which were investigated in terms of the scalae height, cross-sectional size, and rotation as well as the interrelation of these factors and correlations to others., Results: The greatest anatomical variability was observed within the round window region of the cochlea (basal 45°), especially regarding the cross-sectional size of the ST and its orientation relative to the scala vestibuli, which were found to be correlated (p < 0.001). The cross-sectional height of the ST changes substantially for both increasing cochlear angles and lateral wall distances. Even small cochleae were found to contain enough space for all commercially available CI arrays. Significant correlations of individual intracochlear parameters to clinically assessable ones were found despite the small sample size., Conclusion: While there is generally enough space within the ST for CI, strong intracochlear anatomical variations could be observed highlighting the relevance of both soft surgical technique as well as a highly flexible and self-adapting cochlear implant electrode array design. Cochlear dimensions (especially at the round window) could potentially be used to indicate surgically challenging anatomies., Competing Interests: D.S. is a MED-EL employee. The other authors have no conflicts of interest to disclose., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

In the field of cochlear implantation, artificial/physical models of the inner ear are often employed to investigate certain phenomena like the forces occurring during implant insertions. Up to now, no such models are available for the analysis of diffusion processes inside the cochlea although drug delivery is playing an increasingly important role in this field. For easy access of the cochlea along its whole profile, e.g., for sequential sampling in an experimental setting, such a model should ideally be longitudinal/uncoiled. Within this study, a set of 15 micro-CT imaging datasets of human cochleae was used to derive an average representation of the scala tympani. The spiral profile of this model was then uncoiled along different trajectories, showing that these trajectories influence both length and volume of the resulting longitudinal model. A volumetric analysis of the average spiral model was conducted to derive volume-to-length interrelations for the different trajectories, which were then used to generate two tubular, longitudinal scala tympani models with volume and length properties matching the original, spiral profile. These models can be downloaded for free and used for reproducible and comparable simulative and experimental investigations of diffusion processes within the inner ear.

The human cochlea has a highly individual microanatomy. Cochlear implantation therefore requires an evaluation of the individual cochlear anatomy to reduce surgical risk of implantation trauma. However, in-vivo cochlear imaging is limited in resolution. To overcome this issue, cochlear models based on exact anatomical data have been developed. These models can be fitted to the limited parameters available from clinical imaging to provide a prediction of the precise cochlear microanatomy. Recently, models have become available with improved precision that additionally allow predicting the 3D form of an individual cochlea. The present study has further improved the precision of modelling by incorporating microscopic details of a large set of 108 human cochleae from corrosion casts. The new model provides a more flexible geometric shape that can better predict local variations like vertical dips and jumps and provides an approximation of frequency allocation in the cochlea. The outcome of this and five other models have been quantified (validated) on an independent set of 20 µCTs of human cochleae. The new model outperformed previous models and is freely available for download and use., Competing Interests: Declaration of Competing Interest None., (Copyright © 2021. Published by Elsevier B.V.)

Virtual reality surgical simulation of temporal bone surgery requires digitized models of the full anatomical region in high quality and colour information to allow realistic texturization. Existing datasets which are usually based on microCT imaging are unable to fulfil these requirements as per the limited specimen size, and lack of colour information. The OpenEar Dataset provides a library consisting of eight three-dimensional models of the human temporal bone to enable surgical training including colour data. Each dataset is based on a combination of multimodal imaging including Cone Beam Computed Tomography (CBCT) and micro-slicing. 3D reconstruction of micro-slicing images and subsequent registration to CBCT images allowed for relatively efficient multimodal segmentation of inner ear compartments, middle ear bones, tympanic membrane, relevant nerve structures, blood vessels and the temporal bone. Raw data from the experiment as well as voxel data and triangulated models from the segmentation are provided in full for use in surgical simulators or any other application which relies on high quality models of the human temporal bone.

Objective: In the field of cochlear implantation, the current trend toward patient-specific electrode selection and the achievement of optimal audiologic outcomes has resulted in implant manufacturers developing a large portfolio of electrodes. The aim of this study was to bridge the gap between the known variability of cochlea length and this electrode portfolio., Design: Retrospective analysis on cochlear length and shape in micro-computed tomography and cone beam computed tomography data., Setting: Tertiary care medical center., Subjects and Methods: A simple 2-step approach was developed to accurately estimate the individual cochlear length as well as the projected length of an electrode array inside the cochlea. The method is capable of predicting the length of the cochlea and the inserted electrode length at any specific angle. Validation of the approach was performed with 20 scans of human temporal bones (micro-computed tomography) and 47 pre- and postoperative clinical scans (cone beam computed tomography)., Results: Mean ± SD absolute errors in cochlear length estimations were 0.12 ± 0.10 mm, 0.38 ± 0.26 mm, and 0.71 ± 0.43 mm for 1, 1.5, and 2 cochlea turns, respectively. Predicted insertion angles based on clinical cone beam computed tomography data showed absolute deviations of 27° ± 18° to the corresponding postoperative measurements., Conclusion: With accuracy improvements of 80% to 90% in comparison with previously proposed approaches, the method is well suited for the use in individualized cochlear implantation.

Objective: Within the field of cochlear implantation (CIs), the role of utilizing patient-specific cochlear anatomy for choosing the optimal implant electrode is becoming increasingly important. Unfortunately, performing detailed anatomical measurements of a cochlea using clinical imaging data is rather time consuming and hence difficult to implement into the clinical routine. In order to accelerate clinical cochlear anatomy evaluations, previously developed mathematical models can be adjusted to the patient-specific anatomy by measuring just a few overall cochlear dimensions. However, the accuracy of model-based cochlear anatomy estimations is unclear, and incorrect evaluations may lead to false conclusions regarding the suitability of specific implant electrodes., Methods: Based on 10 cochleae, an error evaluation of various commonly used curve fitting approaches for cochlear shape and duct length approximation was conducted. Spline tracings of the cochlear contours were used as reference values for the various approximations., Results: Parameterized average cochlear helix models and two of five analytical approaches were found to be suitable for reconstructing the cochlear helical shape and estimating its length., Discussion: Spline curve reconstructions are the most accurate and reliable method for assessing patient-specific cochlear geometry, especially in the case of anatomical irregularities. The most accurate results within the group of model-based evaluations still resulted in mean overall cochlear length deviations of approximately 5%., Conclusion: Spline curve reconstructions appear to be the best option for anatomical diagnostics in clinical practice. Retrospective studies can be performed to further evaluate model-based evaluations.

Hypothesis: Methods for cochlear coverage determination vary in their accuracy and are hence not equally reliable., Background: The audiological outcome after cochlear implantation is known to depend on several factors. One factor shown to positively correlate with speech perception is the insertion angle. This parameter is one of the ways to describe the fraction of the cochlea spiral exposed to electric stimulation after implantation, also known as cochlear coverage, which itself is dependent on the length and type of electrode array as well as the size and shape of the implanted cochlea. While the assessment of cochlear coverage as the insertion angle is quick and uncomplicated, the accuracy of representing the relative fraction of the cochlea exposed to electric stimulation by this single measurement value remains unknown., Methods: Both the cochlea spiral and implanted electrode array of N = 10 cochlear implant patients were traced within clinical imaging data and processed to derive the respective cochlear coverage values. These values were compared to ones derived with alternative measures like the insertion angle as well as other methods to yield the accuracy and reliability of these approaches., Results: The insertion angle as well as two novel approaches were found to be superior to all other analyzed assessment options and well suited for clinical cochlear coverage evaluations., Conclusion: Insertion angle measurements are well suited for cochlear coverage determination, especially regarding retrospective analyses. Prospective studies independent of anatomical irregularities should be performed with the newly proposed approaches.

Cochlear implantation can restore a certain degree of auditory impression of patients suffering from profound hearing loss or deafness. Furthermore, studies have shown that in case of residual hearing, patients benefit from the use of a hearing aid in addition to the cochlear implant. The presented studies aim at the improvement of this electromechanical stimulation (EMS) approach by substituting the external hearing aid by an internal stimulus provided by miniaturized piezoelectric actuators. Finite element analyses are performed in order to derive fundamental guidelines for the actuator layout aiming at maximal mechanical stimuli. Further analyses aim at investigating how the actuator position inside the cochlea influences the basilar membrane oscillation profile. While actuator layout guidelines leading to maximized acoustic stimuli could be derived, some of these guidelines are of complementary nature suggesting that further studies under realistic boundary conditions must be performed. Actuator positioning inside the cochlea is shown to have a significant influence on the resulting auditory impression of the patient. Based on the results, the main differences of external and internal stimulation of the cochlea mechanism are identified. It is shown that if the cochlea tonotopy is considered, the frequency selectivity resulting from the mechanical cochlea stimulus may be improved.

Purpose: A cochlea modeling approach is presented allowing for a user defined degree of geometry simplification which automatically adjusts to the patient specific anatomy. Model generation can be performed in a straightforward manner due to error estimation prior to the actual generation, thus minimizing modeling time. Therefore, the presented technique is well suited for a wide range of applications including finite element analyses where geometrical simplifications are often inevitable., Methods: The method is presented for n=5 cochleae which were segmented using a custom software for increased accuracy. The linear basilar membrane cross sections are expanded to areas while the scalae contours are reconstructed by a predefined number of arc segments. Prior to model generation, geometrical errors are evaluated locally for each cross section as well as globally for the resulting models and their basal turn profiles. The final combination of all reconditioned features to a 3D volume is performed in Autodesk Inventor using the loft feature., Results: Due to the volume generation based on cubic splines, low errors could be achieved even for low numbers of arc segments and provided cross sections, both of which correspond to a strong degree of model simplification. Model generation could be performed in a time efficient manner., Conclusion: The proposed simplification method was proven to be well suited for the helical cochlea geometry. The generated output data can be imported into commercial software tools for various analyses representing a time efficient way to create cochlea models optimally suited for the desired task.

Cochlear Implants (CIs) are medical implantable devices that can restore the sense of hearing in people with profound hearing loss. Clinical trials assessing speech intelligibility in CI users have found large intersubject variability. One possibility to explain the variability is the individual differences in the interface created between electrodes of the CI and the auditory nerve. In order to understand the variability, models of the voltage distribution of the electrically stimulated cochlea may be useful. With this purpose in mind, we developed a parametric model that can be adapted to each CI user based on landmarks from individual cone beam computed tomography (CBCT) scans of the cochlea before and after implantation. The conductivity values of each cochlea compartment as well as the weighting factors of different grounding modes have also been parameterized. Simulations were performed modeling the cochlea and electrode positions of 12 CI users. Three models were compared with different levels of detail: a homogeneous model (HM), a non-patient-specific model (NPSM), and a patient-specific model (PSM). The model simulations were compared with voltage distribution measurements obtained from the backward telemetry of the 12 CI users. Results show that the PSM produces the lowest error when predicting individual voltage distributions. Given a patient-specific geometry and electrode positions, we show an example on how to optimize the parameters of the model and how to couple it to an auditory nerve model. The model here presented may help to understand speech performance variability and support the development of new sound coding strategies for CIs.

Purpose: Cross-sectional visualization of anatomical structures in DICOM viewers is usually presented in parallel slices. For visualizing the inner ear, this concept is unfavourable due to the spiral shape of the cochlea. Radial slicing through its central axis (known as midmodiolar view) is advantageous. Therefore, a custom DICOM viewer was developed, which allows the visualization of the cochlea in a midmodiolar slice plane that rotates around the central axis of the cochlea, always cutting the latter radially., Methods: The program was written in C++ using the open-source libraries ITK, VTK, GDCM and Qt. The rotation axis is defined by placing two points in the modiolus within a conventional slice visualization of the dataset. A midmodiolar visualization is calculated based on this axis. Scrolling the mouse wheel rotates slice plane around the axis, displaying midmodiolar slices at variable angles. Measurement options are provided as well as interactive placement of marker points whose coordinates can be exported for post-processing in other programs., Results: The program can be used in multiple applications including the determination of cochlear dimensions, especially its length, and post-operative positions of cochlear implant (CI) electrode carriers. Computer-aided design models of the cochlea can be generated from exported marker points., Conclusion: The proposed DICOM viewer directly focuses on the needs of cochlear visualization, thus making it a valuable tool in CI related research. The ease of use facilitates future clinical use, e.g. for pre-operative selection of optimal CI electrode carrier length based on the patient's cochlear length.

Within the field of hearing prosthetics it is known that patients with sufficient residual hearing benefit from the simultaneous employment of hearing aid and cochlear implant. Several attempts have been proposed to combine the sources of the corresponding acoustic and electric stimuli in a single, implantable device. However, since only little is known about the effect of also applying the acoustic stimulus locally from within the inner ear, the current state of research lacks detailed knowledge on the optimal stimulation at the corresponding bionic interface. Within this manuscript, a simple but yet physiologically-based inner ear model is presented which was designed specifically for the analysis of local acoustic or mechanical inner ear stimulation. A detailed model analysis is performed showing that it is capable of mirroring the known mechanical phenomena of this particular stimulation approach. Using the model, it is demonstrated how amplitude and phase shift values of stimuli applied from within the inner ear should be chosen for optimal inner ear stimulation.

The quality of hearing restored to a deaf patient by a cochlear implant in hearing preservation cochlear implant surgery (and possibly also in routine cochlear implant surgery) is believed to depend on preserving delicate cochlear membranes while accurately inserting an electrode array deep into the spiral cochlea. Membrane rupture forces, and possibly, other indicators of suboptimal placement, are below the threshold detectable by human hands, motivating a force sensing insertion tool. Furthermore, recent studies have shown significant variability in manual insertion forces and velocities that may explain some instances of imperfect placement. Toward addressing this, an automated insertion tool was recently developed by Hussong et al. By following the same insertion tool concept, in this paper, we present mechanical enhancements that improve the surgeon's interface with the device and make it smaller and lighter. We also present electomechanical design of new components enabling integrated force sensing. The tool is designed to be sufficiently compact and light that it can be mounted to a microstereotactic frame for accurate image-guided preinsertion positioning. The new integrated force sensing system is capable of resolving forces as small as 0.005 N, and we provide experimental illustration of using forces to detect errors in electrode insertion.

Purpose: Portable CT scanners are beneficial for diagnosis in the intensive care unit, emergency room, and operating room. Portable fixed-base versus translating-base CT systems were evaluated for otologic image-guided surgical (IGS) applications based on geometric accuracy and utility for percutaneous cochlear implantation., Methods: Five cadaveric skulls were fitted with fiducial markers and scanned using both a translating-base, 8-slice CT scanner (CereTom(®)) and a fixed-base, flat-panel, volume CT (fpVCT) scanner (Xoran xCAT(®)). Images were analyzed for: (a) subjective quality (i.e., noise), (b) consistency of attenuation measurements (Hounsfield units) across similar tissue, and (c) geometric accuracy of fiducial marker positions. The utility of these scanners in clinical IGS cases was tested., Results: Five cadaveric specimens were scanned using each of the scanners. The translating-base, 8-slice CT scanner had spatially consistent Hounsfield units, and the image quality was subjectively good. However, because of movement variations during scanning, the geometric accuracy of fiducial marker positions was low. The fixed-base, fpVCT system had high spatial resolution, but the images were noisy and had spatially inconsistent attenuation measurements, while the geometric representation of the fiducial markers was highly accurate., Conclusion: Two types of portable CT scanners were evaluated for otologic IGS. The translating-base, 8-slice CT scanner provided better image quality than a fixed-base, fpVCT scanner. However, the inherent error in three-dimensional spatial relationships by the translating-based system makes it suboptimal for otologic IGS use.

Conclusions: We have demonstrated that an automated insertion tool (i.e. a robot) can be used to duplicate a complex surgical motion in inserting cochlear implant (CI) electrode arrays via the 'advance-off-stylet' (AOS) technique. As compared with human operators, the forces generated by the robot were slightly larger but the robot was more reliable (i.e. less force maxima)., Objectives: We present force data collected during CI electrode insertion by human operators and by an automated insertion tool., Materials and Methods: Using a three-dimensional, anatomically correct, translucent model of the scala tympani chamber of the cochlea, CI electrodes were inserted either by one of three surgeons (26 insertions) or by the robotic insertion tool (8 insertions). Force was recorded using a load beam cell calibrated for expected forces of <0.1 Newtons (N). The insertions were also videotaped to allow correlation of force with depth of penetration into the cochlea and speed of insertion., Results: Average insertion force used by the surgeons was 0.004+/-0.001 N and for the insertion tool it was 0.005+/-0.014 N (p<0.00001, Student's t test). While the average insertion force of the automated tool was larger than that of the surgeons, the surgeons did have intermittent peaks during the AOS component of the insertion (between 120 degrees and 200 degrees ).