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Objectives: To assess the feasibility of flat-panel detector based volumetric CT (fpVCT) scanning of the whole human skull base and maxillofacial region, which has thus far only been demonstrated on small, excised specimens. Flat-panel detectors offer more favourable imaging properties than image intensifiers. It is therefore likely that they will replace them in cone-beam CT scanners that are currently used to scan parts of the skull base and maxillofacial region. Furthermore, the resolution of current CT imaging limits diagnosis, surgical planning and intraoperative navigation within these regions. fpVCT might overcome these limitations because it offers higher resolution of high contrast structures than current CT. Methods: Three embalmed cadaver heads were scanned in two scanners: an experimental fpVCT that offers a scan field large enough for a whole human head, and in a current multislice CT (MSCT). 28 structures were compared. Results: Both scanners produced bone images of diagnostic quality. Small high contrast structures such as parts of the ossicular chain and thin bony laminas were better delineated in fpVCT than in MSCT. fpVCT of maxillofacial region and skull base was rated superior to MSCT (P = 0.002) as found in this limited, experimental study. Conclusions: High spatial resolution fpVCT scanning of both regions in a whole human head is feasible and might be slightly superior to MSCT. fpVCT could improve diagnostic accuracy in selected cases, as well as surgical planning and intraoperative navigation accuracy. [ABSTRACT FROM AUTHOR]

Objectives: Three-dimensional computed tomography (3D-CT) of facial fractures has been reported as beneficial using surface (SR) and volume rendering (VR). There are controversial statements concerning the preferable algorithm. The purpose of this study was to evaluate and compare SR and VR for clinical 3D-CT in facial fractures on an experimental basis. Methods: Multislice CT was obtained in 22 patients with facial fractures using two data acquisition protocols. Five SR and VR post-processing protocols were applied. Five assessors independently evaluated the quality of visualization of the fracture gap and dislocated fragments as well as the overall image quality using a five-point rating scale. The potential benefit of the 3D- images for radiological diagnosis and presentation was evaluated. The influence of the data acquisition protocol was analysed. Results: SR in general achieved better evaluation scores than VR at corresponding thresholds. Variation of evaluation scores for all criteria was found for SR and VR depending on the segmentation threshold. Apart from the overall image quality no significant influence of the data acquisition technique was found for the evaluated criteria. Conclusions: SR provided sufficient and time efficient means for 3D-visualization of facial fractures in this study. No diagnostic benefit of VR over SR was found. [ABSTRACT FROM AUTHOR]

Introduction: The essential aspect of the CI surgery is the placement of the CI electrode into the cochlea. However, the main part of the conventional surgical procedure is dealing with the approach to the cochlea. Reducing the approach to a slim tunnel, drilled by high accurate surgical instruments based on temporal bone imaging would reduce the vast extent of the conventional surgical approach. We develop currently a mini-stereotactic frame to hit the cochlea by drilling a tunnel in the mastoid through the facial recess, called RoboJig. The success of the system is mainly dependent its accuracy. We investigated how accurate the target point needs to be reached and how accurate the RoboJig system may be under lab conditions. Methods: Relevant anatomical structures for the CI surgery approach were segmented in eight 3D histological data sets of human temporal bone specimens. Different straight trajectories from the surface of the mastoid passing through the facial recess and entering the cochlea were planned in this virtual environment. A circular region was defined indicating proper places for Cochleostomy To determine the technical accuracy of the system, 20 RoboJig guiding platforms with different trajectories were fabricated and the position and orientation of an inserted drill guide were measured in lab, using a portable coordinate measuring machine. Results: On average the suitable target region was 1.56mm ± 0.11 mm in diameter leading to a mean safety margin of 0.28 mm if the cochleostomy has a diameter of 1.0 mm. On the other side, positioning accuracy was 0.11 mm ± 0.04 mm. Conclusions: Based on planning the surgical root for the straight approach to the cochlea in virtual histological dataset, the RoboJig system seems to be accurate enough for minimally invasive cochlear implantation surgery. However, additional error sources are expected if the drilling is performed in the inhomogeneous bone of the mastoid. [ABSTRACT FROM AUTHOR]

In the process of cochlear implant electrode array development and characterization the measurement of insertion forces in a cochlea bench model is a standard procedure for estimating trauma. Bench models made of various materials, like PTFE, glass, acrylic, epoxy, etc. in combination with various lubricants, are commonly used for these measurements. The question is if these materials are a valid model in respect to the frictional properties in comparison to a live patient. The measurement of insertion forces in a live patient is not possible at the moment and therefore we decided to use fresh never frozen temporal bones. As fresh never frozen human temporal bones are not easy to obtain, we decided to work with fresh never frozen animal temporal bones in this initial study. The cochlea of a pig was chosen because of its similar proportion to the human. Furthermore it provides straightforward surgical access and is readily available. For the insertion force measurement an automated insertion tool was used and a single axis load cell was equipped with the cut down fresh never frozen porcine temporal bone specimens. Dummy electrodes based on the Cochlear Slim Straight electrode were inserted in the porcine cochlea to a depth of approximately 15 mm or one turn. The measurements could be repeated in each bone. Based on the corresponding DVT scans of the porcine specimen a Teflon bench model was built matching the dimensions of the porcine cochlea. This bench model was also used for insertion measurements in the same automated setup with using the similar dummy electrodes based on the Slim Straight electrode. The obtained insertion forces of both sets of measurements were compared to check the accuracy of the bench model. [ABSTRACT FROM AUTHOR]

Background: Minimally invasive cochlear implant surgery by using a microstereotactic frame demands solid connection to the bone. We aimed to determine the stability of commercially available orthodontic miniscrews to evaluate their feasibility for frame's fixation. In addition, which substitute material most closely resembles the mechanical properties of the human temporal bone was evaluated., Methods: Pull-out tests were carried out with five different types of orthodontic miniscrews in human temporal bone specimens. Furthermore, short fiber filled epoxy (SFFE), solid rigid polyurethane (SRPU50), bovine femur, and porcine iliac bone were evaluated as substitute materials. In total, 57 tests in human specimens and 180 tests in the substitute materials were performed., Results: In human temporal bone, average pull-out forces ranged from 220 N to 285 N between screws. Joint stiffness in human temporal bone ranged between 14 N/mm and 358 N/mm. Statistically significant differences between the tested screws were measured in terms of stiffness and elastic energy. One screw type failed insertion due to tip breakage. No significant differences occurred between screws in maximum pull-out force. The average pull-out values of SFFE were 14.1 N higher compared to human specimen., Conclusion: Orthodontic miniscrews provided rigid fixation when partially inserted in human temporal bone, as evidenced by pull-out forces and joint stiffness. Average values exceeded requirements despite variations between screws. Differences in stiffness and elastic energy indicate screw-specific interface mechanics. With proper insertion, orthodontic miniscrews appear suitable for microstereotactic frame anchoring during minimally invasive cochlear implant surgery. However, testing under more complex loading is needed to better predict clinical performance. For further pull-out tests, the most suitable substitute material is SFFE., Competing Interests: Declaration of Conflicting InterestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Purpose: Minimally invasive cochlear implant surgery using a micro-stereotactic surgical targeting system with on-site moulding of the template aims for a reliable, less experience-dependent access to the inner ear under maximal reduction of trauma to anatomic structures. We present an accuracy evaluation of our system in ex-vivo testing., Methods: Eleven drilling experiments were performed on four cadaveric temporal bone specimens. The process involved preoperative imaging after affixing the reference frame to the skull, planning of a safe trajectory preserving relevant anatomical structures, customization of the surgical template, execution of the guided drilling and postoperative imaging for determination of the drilling accuracy. Deviation between the drilled and desired trajectories was measured at different depths., Results: All drilling experiments were successfully performed. Other than purposely sacrificing the chorda tympani in one experiment, no other relevant anatomy, such as facial nerve, chorda tympani, ossicles or external auditory canal were harmed. Deviation between the desired and achieved path was found to be 0.25 ± 0.16 mm at skulls' surface and 0.51 ± 0.35 mm at the target level. The closest distance of the drilled trajectories' outer circumference to the facial nerve was 0.44 mm., Conclusions: We demonstrated the usability for drilling to the middle ear on human cadaveric specimen in a pre-clinical setting. Accuracy proved to be suitable for many applications such as procedures within the field of image-guided neurosurgery. Promising approaches to reach sufficient submillimetre accuracy for CI surgery have been outlined., (© 2023. The Author(s).)

Objectives: Drilling a minimally invasive access to the inner ear is a demanding task in which a computer-assisted surgical system can support the surgeon. Herein, we describe the design of a new micro-stereotactic targeting system dedicated to cochlear implant (CI) surgery and its experimental evaluation in an ex vivo study., Methods: The proposed system consists of a reusable, bone-anchored reference frame, and a patient-specific drilling jig on top of it. Individualization of the jig is simplified to a single counterbored hole drilled out of a blank. For accurate counterboring, the setup includes a manufacturing device for individual positioning of the blank. The system was tested in a preclinical setting using twelve human cadaver donors. Cone beam computed tomograph (CBCT) scans were obtained and a drilling trajectory was planned pointing towards the basal part of the cochlea. The surgical drill was moved forward manually and slowly while the jig constrained the drill along the predetermined path., Results: Drilling could be performed with preservation of facial nerve in all specimens. The mean error caused by the system at the target point in front of the cochlea was 0.30 mm ± 0.11 mm including an inaccuracy of 0.09 mm ± 0.03 mm for counterboring the guiding aperture into the jig., Conclusion: Feasibility of the proposed system to perform a minimally invasive posterior tympanotomy approach was shown successfully in all specimens., Significance: First evaluation of the new system in a comprehensive ex vivo study demonstrating sufficient accuracy and the feasibility of the whole concept.

For cochlear implants (CI) a final position of the electrode array (EA) along the inner wall of the spirally shaped cochlea is considered to be beneficial because it results in a closer proximity to the auditory nerve fibers. A shape memory effect (SME) could facilitate such shift of the EA toward the cochlear inner wall, but its implementation remains to be solved. The current study presents an EA prototype featuring the SME with minute adjustments of the material properties of Nitinol, a shape memory alloy, in combination with a suitable cooling strategy to prevent premature curling. Ten samples were successfully inserted by a CI surgeon into an artificial cochlear model submerged into a temperature-controllable water bath to simulate temporary hypothermia of the inner ear (31°C). Gentle insertions were possible, with an average insertion speed of 0.81 ± 0.14 mm/s. After recovery of body temperature, the desired position shift toward the modiolus was observed in all trials. Angular insertion depth increased by approximately 81.8° ± 23.4°. We demonstrate for the first time that using the body temperature responsive SME for perimodiolar EA positioning is feasible and does not impede a gentle surgical insertion., (© 2022 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals LLC.)

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.)

Purpose: We explain our concept for customization of a guidance instrument, present a prototype, and describe a set of experiments to evaluate its positioning and drilling accuracy. Methods: Our concept is characterized by the use of bone cement, which enables fixation of a specific configuration for each individual surgical template. This well-established medical product was selected to ensure future intraoperative fabrication of the template under sterile conditions. For customization, a manually operated alignment device is proposed that temporary defines the planned trajectory until the bone cement is hardened. Experiments ( n = 10 ) with half-skull phantoms were performed. Analysis of accuracy comprises targeting validations and experiments including drilling in bone substitutes. Results: The resulting mean positioning error was found to be 0.41 ± 0.30    mm at the level of the target point whereas drilling was possible with a mean accuracy of 0.35 ± 0.30    mm . Conclusion: We proposed a cost-effective, easy-to-use approach for accurate instrument guidance that enables template fabrication under sterile conditions. The utilization of bone cement was proven to fulfill the demands of an easy, quick, and prospectively intraoperatively doable customization. We could demonstrate sufficient accuracy for many surgical applications, e.g., in neurosurgery. The system in this early development stage already outperforms conventional stereotactic frames and image-guided surgery systems in terms of targeting accuracy., (© 2021 The Authors.)

Objective: Statistical knowledge about many patients could be exploited using machine learning to provide supporting information to otolaryngologists and other hearing health care professionals, but needs to be made accessible. The Common Audiological Functional Parameters (CAFPAs) were recently introduced for the purpose of integrating data from different databases by providing an abstract representation of audiological measurements. This paper aims at collecting expert labels for a sample database and to determine statistical models from the labelled data set. Design: By an expert survey, CAFPAs as well as labels for audiological findings and treatment recommendations were collected for patients from the database of Hörzentrum Oldenburg. Study sample: A total of 287 single patient cases were assessed by twelve highly experienced audiological experts. Results: The labelled data set was used to derive probability density functions for categories given by the expert labels. The collected data set is suitable for estimating training distributions due to realistic variability contained in data for different, distinct categories. Suitable distribution functions were determined. The derived training distributions were compared regarding different audiological questions. Conclusions: The method-expert survey, sorting data into categories, and determining training distributions - could be extended to other data sets, which could then be integrated via the CAFPAs and used in a classification task.

Background: The aim of the study was to investigate the extent of MRI artefacts due to the magnet of selected auditory implants. Study design: Artefacts of the Synchrony cochlear implant at 1.5 T as well as at 3 T MRI devices were examined in cadavers and compared to the artefacts in MRI scans at 1.5 T of 17 patients implanted with CI ( n  = 12) and auditory brainstem implants (ABI) ( n  = 5). Results: None of the scanned implants showed any failure after MRI. After removal of the magnet, only a portion of the images in the direct neighbourhood of the implant, especially in the temporal and parietal lobe, contained artefacts. More anatomical substructures were visible without artefacts using the MedEl Synchrony device. Conclusion: Artefacts can be markedly reduced by rotating, self-aligning magnet. Removal of the magnet also results in reduction of artefacts.

Objective: The intracochlear position of an electrode array may influence the outcome after cochlear implantation. The design of the electrode array can increase the risk of trauma causing penetration of the basilar membrane or shift of the electrode array into the scala vestibuli. The aim of the present study was to identify a scalar shift after implantation of two different electrode arrays developed by one manufacturer., Study Design: Retrospective analysis., Setting: Tertiary referral center., Patients and Intervention: Cochlear implant recipients implanted between 2010 and 2014 and receiving either a mid-scala (n = 30) or a perimodiolar (n = 30) electrode array., Main Outcome Measure: Occurrence of scalar shift in association with the electrode type., Results: Scalar shift occurred in 26.7% (8 of 30) of the patients implanted with a perimodiolar electrode array and in 6.7% (2 of 30) of the patients implanted with the mid-scala electrode array. The mean insertion depth in the patients experiencing scalar shift after implantation of the mid-scala electrode was much deeper (21.59 ± 0.34 mm) when compared with the mean insertion depth of the patients with scalar shift after implantation with a perimodiolar electrode array (17.85 ± 2.19 mm). There tends to be a correlation between the cochlear length and the occurrence of a scalar shift. However, the number of patients with scalar shift in the mid-scala group is rather small., Conclusion: Based on the presented data, more patients implanted with a perimodiolar electrode array have a scalar shift when compared with the midscalar electrode array.

Surgical treatment with a cochlear implant (CI) for hearing rehabilitation requires a highly accurate and personalized opening of the inner ear (cochlea) to protect the delicate intra-cochlear fine structures, whose functional integrity needs to be maintained to preserve residual hearing. Spatial orientation within the complex anatomy of the lateral skull base during the procedure is a highly demanding task for the surgeon. In order to reduce risk of facial nerve palsy and loss of residual hearing as well as to establish minimally invasive CI surgery (minCIS), image-guided procedures incorporating surgical assistance systems are under development. However, there is a lack of an accuracy threshold value or range that such a system needs to fulfill to be considered sufficiently accurate for atraumatic opening of the inner ear. In this study, high resolution three-dimensional (3D) morphological images of eight human temporal bone specimens were manually segmented to build anatomical models of the human inner ear including all surgically relevant intra-cochlear structures as well as the facial recess. These 3D models were used to plan the surgical access path to the basal turn of the cochlea using the mastoidectomy posterior tympanotomy approach (MPTA). Therefore, custom-made image-processing software was developed to perform both path planning and identification of the valid target region- i.e., the largest possible region for atraumatic opening of the scala tympani. The developed 3D models provide visualization of the complex and variable anatomy of the basal portion of the human cochlear duct (also known as cochlear "hook region") as well as its spatial relationship to the facial recess. Their spatial arrangement directly impacts the accessibility of the hook region and limits the entry direction into scala tympani. The average diameter of the target region was found to be 1.56 mm ± 0.10 mm (range: 1.43 to 1.72 mm). The anatomic variability and the need for a high safety level of at least 95% for hearing preservation CI surgery lead to a remaining safety margin of approximately 0.3 mm. In the future, this accuracy threshold value can serve as benchmark during the pre-clinical evaluation of image-guidance technologies to allow for highly accurate CI surgery., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Purpose: Minimally invasive cochlear implant surgery is a challenging procedure due to high demands on accuracy. For clinical success, an according assistance system has to compete against the traditional approach in terms of risk, operating time and cost. It has not yet been determined what kind of system is the most suited. The purpose of this study is a proof of concept of surgical process modeling as a preclinical development tool and the comparison of workflow concepts for this new approach., Methods: Three preclinical systems (two stereotactic and one robotic) for minimally invasive cochlear implant surgery are compared using the method of surgical process modeling. All three systems were successfully tested with ex vivo human specimen to create minimally invasive surgical access to the cochlea. Those systems where chosen for comparison, because they represent three diverse approaches with different corresponding workflows for the same intervention. The experiments were used to create a process model for each system by recording the interventions., Results: All three conceptual systems developed by our group have shown their eligibility. The recorded process models provide a convenient method for direct comparison. Reduction in the surgical time has a higher impact on the process, than time that is needed for setting up a system beforehand. The stereotactic approaches have little preparation effort and are low cost in terms of hardware compared to the robotic approach, which in return is beneficial in terms of workload reduction for the surgeon., Conclusion: Surgical process modeling is suitable for comparison of different assistant systems for minimally invasive cochlear implantation. The benefit of reduced trauma, compared to the traditional mastoidectomy, can now be assessed with consideration of the workflow of each technique. The process models enable an assessment in the regard of surgical time and workload.

Objective: As a step towards objectifying audiological rehabilitation and providing comparability between different test batteries and clinics, the Common Audiological Functional Parameters (CAFPAs) were introduced as a common and abstract representation of audiological knowledge obtained from diagnostic tests., Design: Relationships between CAFPAs as an intermediate representation between diagnostic tests and audiological findings, diagnoses and treatment recommendations (summarised as "diagnostic cases") were established by means of an expert survey. Expert knowledge was collected for 14 given categories covering different diagnostic cases. For each case, the experts were asked to indicate expected ranges of diagnostic test outcomes, as well as traffic light-encoded CAFPAs., Study Sample: Eleven German experts in the field of audiological rehabilitation from Hanover and Oldenburg participated in the survey., Results: Audiological findings or treatment recommendations could be distinguished by a statistical model derived from the experts' answers for CAFPAs as well as audiological tests., Conclusions: The CAFPAs serve as an abstract, comprehensive representation of audiological knowledge. If more detailed information on certain functional aspects of the auditory system is required, the CAFPAs indicate which information is missing. The statistical graphical representations for CAFPAs and audiological tests are suitable for audiological teaching material; they are universally applicable for real clinical databases.

Purpose: Latest research on cochlear implantations focuses on hearing preservation during insertion of the implant's electrode array by reducing insertion trauma. One parameter which may influence trauma is insertion speed. The objective of this study was to extend the range of examined insertion speeds to include ultra-low velocities, being lower than manually feasible, and investigate whether these reduce insertion forces., Methods: 24 custom-made cochlear implant test samples were fabricated and inserted into an artificial scala tympani model using 12 different insertion speeds while measuring the resulting insertion forces. Three commercially available slim straight electrode carriers were inserted using the same setup to analyze whether the results are comparable., Results: Insertions of the test samples using high insertion speeds (2.0/2.8 mm/s) showed significantly higher insertion forces than insertions done with low insertion speeds (0.2 mm/s) or ultra-low insertion speeds (< 0.1 mm/s). The insertions with commercial slim straight electrode arrays showed significantly reduced insertion forces when using a low insertion speed as well., Conclusions: Slow insertions showed significantly reduced insertion forces. Insertion speeds which are lower than manually feasible showed even lower insertion forces.

Introduction: Different approaches have been developed to find the position of the internal auditory canal (IAC) in middle cranial fossa approach. A feasibility study was performed to investigate the combination of cone beam computed tomography (CBCT), optical coherence tomography (OCT), and laser ablation to assist a surgeon in a middle cranial fossa approach by outlining the internal auditory canal (IAC)., Materials and Methods: A combined OCT laser setup was used to outline the position of IAC on the surface of the petrous bone in cadaveric semi-heads. The position of the hidden structures, such as IAC, was determined in MATLAB software using an intraoperative CBCT scan. Four titanium spheres attached to the edge of the craniotomy served as reference markers visible in both CBCT and OCT images in order to transfer the plan to the patient. The integrated erbium-doped yttrium aluminum garnet laser was used to mark the surface of the bone by shallow ablation under OCT-based navigation before the surgeon continued the operation., Result: The technical setup was feasible, and the laser marking of the border of the IAC was performed with an overall accuracy of 300 μm. The depth of each ablation phase was 300 μm. The marks indicating a safe path supported the surgeon in the surgery., Conclusion: The technique investigated in the present study could decrease the surgical risks for the mentioned structures and improve the pace and precision of operation.

Objectives: The aim of this study was to identify anatomical indication ranges for different lateral wall cochlear implant electrodes to support surgeons in the preoperative preparation., Methods: 272 patients who were implanted with a FLEX20, FLEX24, FLEX28, or a custom-made device (CMD) were included in this study. The cochlear duct length (CDL) and basal cochlear diameter (length A) were measured within preoperative imaging data. The parameter A was then employed to additionally compute CDL estimates using literature approaches. Moreover, the inserted electrode length (IEL) and insertion angle (IA) were measured in postoperative CT data. By combining the preoperative measurements with the IA data, the covered cochlea length (CCL) and relative cochlear coverage (CC) were determined for each cochlea., Results: The measurements of the CDL show comparable results to previous studies. While CDL measurements and estimations cover similar ranges overall, severe deviations occur in individual cases. The electrode specific IEL and CCL are fairly consistent and increase with longer electrodes, but relatively wide ranges of electrode specific CC values were found due to the additional dependence on the respective CDL. Using the correlation of IEL and CCL across electrode arrays, CDL ranges for selected arrays were developed (FLEX24: 31.3-34.4, FLEX28: 36.2-40.1, FLEXSoft: 40.6-44.9)., Conclusions: Our analysis shows that electrode specific CC varies due to the CDL variation. Preoperative measurement of the CDL allows for an individualized implant length selection yielding optimized stimulation and a reduced risk of intraoperative trauma. The CDL, as derived from preoperative CT imaging studies, can help the implant surgeon select the appropriate electrode array to maximize the patient's outcomes., Competing Interests: Company MedEl paid for one scientific congress charge, traveling and hotel costs for Max Eike Timm and Thomas Lenarz in the past (2017,2018). This does not alter our adherence to PLOS ONE policies on sharing data and materials.

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.

Purpose: Patient specific selection of cochlear implants would benefit from pre-operative knowledge of cochlear length. Several methods for its measurement or estimation have been described in literature. This study focused on the achievable accuracy in clinically available imaging., Methods: Five simplified cochlea models milled into porcine bone were scanned in water using clinical cone beam computed tomography. Due to their well-known dimensions these phantoms served as gold standard for the length measurements. Each phantom was measured ten times using the custom software Comet. In addition, cochleae in ten image datasets taken indiscriminately from clinical routine were measured ten times each to test the precision under realistic conditions. The results were also compared to estimations based on the diameter of the basal turn (A value) as described in literature., Results: Measurement accuracy of the phantoms' lengths was high (average error: - 0.2 mm; standard deviation: 0.3 mm). The pooled standard deviation for the measurements in clinical datasets was 0.6 mm. Errors resulted mainly from problems locating the helicotrema. The estimations differed on average - 1.7 to + 0.4 mm from the manual measurements and had standard deviations between 0.5 and 0.6 mm depending on the algorithm., Conclusions: The program Comet was successfully used to accurately measure the length of the cochlea models in clinically available imaging. The lower image quality of patient scans reduced the precision of the measurement. Estimations using the A value are a quicker alternative for averagely sized cochleae in cases where the lack of accuracy is tolerable.

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.

The present study focuses on the application of scanning laser optical tomography (SLOT) for visualization of anatomical structures inside the human cochlea ex vivo. SLOT is a laser-based highly efficient microscopy technique which allows for tomographic imaging of the internal structure of transparent specimens. Thus, in the field of otology this technique is best convenient for an ex vivo study of the inner ear anatomy. For this purpose, the preparation before imaging comprises decalcification, dehydration as well as optical clearing of the cochlea samples in toto. Here, we demonstrate results of SLOT imaging visualizing hard and soft tissue structures with an optical resolution of down to 15 μm using extinction and autofluorescence as contrast mechanisms. Furthermore, the internal structure can be analyzed nondestructively and quantitatively in detail by sectioning of the three-dimensional datasets. The method of X-ray Micro Computed Tomography (μCT) has been previously applied to explanted cochlea and is solely based on absorption contrast. An advantage of SLOT is that it uses visible light for image formation and thus provides a variety of contrast mechanisms known from other light microscopy techniques, such as fluorescence or scattering. We show that SLOT data is consistent with μCT anatomical data and provides additional information by using fluorescence. We demonstrate that SLOT is applicable for cochlea with metallic cochlear implants (CI) that would lead to significant artifacts in μCT imaging. In conclusion, the present study demonstrates the capability of SLOT for resolution visualization of cleared human cochleae ex vivo using multiple contrast mechanisms and lays the foundation for a broad variety of additional studies.

This study was conducted to evaluate the effect of the round window membrane accessibility on the residual hearing after cochlear implantation surgery in adults. Moreover, the effects of the other demographics and intra-operative factors on the residual hearing loss have been evaluated. The hearing preservation cochlear implantation surgery was performed on 64 adults with residual hearing thresholds ≤80 dB at 250 and 500 Hz, who had referred to our tertiary academic center. All the patients underwent a standardized surgical approach with the same straight electrode inserted through the round window membrane. The hearing thresholds at 250, 500, and 1000 Hz were compared in pre-operative and 1 month postoperative pure-tone audiograms. The average hearing threshold shifts at these frequencies was used to evaluate the hearing preservation. The effects of the round window accessibility and other factors (including gender, age, side of the surgery, necessity of anterior-inferior drilling of the round window margin and average insertion speed) on hearing threshold shifts were analyzed. The mean low-frequency hearing threshold shift was found to be 17.5 dB for all the patients. The hearing preservation goal (threshold shifts ≤30 dB) was achieved in 58 patients. Among the evaluated parameters, only accessibility of the round window membrane could change the hearing threshold shifts significantly (p = 0.026), and was a predictor for the hearing loss (B coefficient = 7.5, p = 0.006). Incomplete accessibility of the round window membrane may be a predictor for increased hearing threshold shifts in short-term evaluations after cochlear implantation.