Morphologic Analysis of the Scala Tympani Using Synchrotron: Implications for Cochlear Implantation

OBJECTIVES

To use synchrotron radiation phase-contrast imaging (SR-PCI) to visualize and measure the morphology of the entire cochlear scala tympani (ST) and assess cochlear implant (CI) electrode trajectories.

METHODS

SR-PCI images were used to obtain geometric measurements of the cochlear scalar diameter and area at 5-degree increments in 35 unimplanted and three implanted fixed human cadaveric cochleae.

RESULTS

The cross-sectional diameter and area of the cochlea were found to decrease from the base to the apex. This study represents a wide variability in cochlear morphology and suggests that even in the smallest cochlea, the ST can accommodate a 0.4 mm diameter electrode up to 720°. Additionally, all lateral wall array trajectories were within the anatomically accommodating insertion zone.

CONCLUSION

This is the first study to use SR-PCI to visualize and quantify the entire ST morphology, from the round window to the apical tip, and assess the post-operative trajectory of electrodes. These high-resolution anatomical measurements can be used to inform the angular insertion depth that can be accommodated in CI patients, accounting for anatomical variability.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 134:2889-2897, 2024.

Microanatomy of the human tunnel of Corti structures and cochlear partition-tonotopic variations and transcellular signaling

Auditory sensitivity and frequency resolution depend on the optimal transfer of sound-induced vibrations from the basilar membrane (BM) to the inner hair cells (IHCs), the principal auditory receptors. There remains a paucity of information on how this is accomplished along the frequency range in the human cochlea. Most of the current knowledge is derived either from animal experiments or human tissue processed after death, offering limited structural preservation and optical resolution. In our study, we analyzed the cytoarchitecture of the human cochlear partition at different frequency locations using high-resolution microscopy of uniquely preserved normal human tissue. The results may have clinical implications and increase our understanding of how frequency-dependent acoustic vibrations are carried to human IHCs. A 1-micron-thick plastic-embedded section (mid-modiolar) from a normal human cochlea uniquely preserved at lateral skull base surgery was analyzed using light and transmission electron microscopy (LM, TEM). Frequency locations were estimated using synchrotron radiation phase-contrast imaging (SR-PCI). Archival human tissue prepared for scanning electron microscopy (SEM) and super-resolution structured illumination microscopy (SR-SIM) were also used and compared in this study. Microscopy demonstrated great variations in the dimension and architecture of the human cochlear partition along the frequency range. Pillar cell geometry was closely regulated and depended on the reticular lamina slope and tympanic lip angle. A type II collagen-expressing lamina extended medially from the tympanic lip under the inner sulcus, here named "accessory basilar membrane." It was linked to the tympanic lip and inner pillar foot, and it may contribute to the overall compliance of the cochlear partition. Based on the findings, we speculate on the remarkable microanatomic inflections and geometric relationships which relay different sound-induced vibrations to the IHCs, including their relevance for the evolution of human speech reception and electric stimulation with auditory implants. The inner pillar transcellular microtubule/actin system's role of directly converting vibration energy to the IHC cuticular plate and ciliary bundle is highlighted.

Development and validation of a surgical planning tool for bone-conduction implants

Background

The BONEBRIDGE® (Med-El GmbH) is a bone-conduction device comprising an external audio processor and an internal Bone Conduction-Floating Mass Transducer (BC-FMT) surgically anchored to the temporal bone. Due to the implant's size, its placement may be challenging in certain anatomies, necessitating thorough surgical planning. Manual planning methods are laborious, time-intensive, and prone to errors. This study aimed to develop and validate an automated algorithm for determining skull thickness, aiding in the surgical planning of the BONEBRIDGE and other devices requiring similar bone thickness estimations.

Materials and methods

Twelve cadaveric temporal bones underwent clinical computed tomography (CT). A custom Python algorithm was developed to automatically segment bone from soft tissue, generate 3D models, and perform ray-tracing to estimate bone thickness. Two thickness colormaps were generated for each sample: the cortical thickness to the first air cell and the total thickness down to the dura. The algorithm was validated against expert manual measurements to achieve consensus interpretation.

Results

The algorithm estimated bone-to-air thicknesses (mean = 4.7 mm, 95% Confidence Interval [CI] of 4.3-5.0 mm) that closely matched the expert measurements (mean = 4.7 mm, CI of 4.4-5.0 mm), with a mean absolute difference (MAD) of 0.3 mm. Similarly, the algorithm's estimations to the dura (6.0 mm, CI of 5.4-6.5 mm) were comparable to the expert markings (5.9 mm, CI of 5.4-6.5 mm), with a MAD of 0.3 mm.

Conclusions

The first automated algorithm to calculate skull thickness to both the air cells and dura in the temporal bone was developed. Colormaps were optimized to aid with the surgical planning of BONEBRIDGE implantation, however the tool can be generalized to aid in the surgical planning of any bone thickness application. The tool was published as a freely available extension to the open-source 3D Slicer software program (www.slicer.org).

Virtual Reality Simulation for the Middle Cranial Fossa Approach: A Validation Study

BACKGROUND AND OBJECTIVES

Virtual reality (VR) surgical rehearsal is an educational tool that exists in a safe environment. Validation is necessary to establish the educational value of this platform. The middle cranial fossa (MCF) is ideal for simulation because trainees have limited exposure to this approach and it has considerable complication risk. Our objectives were to assess the face, content, and construct validities of an MCF VR simulation, as well as the change in performance across serial simulations.

METHODS

Using high-resolution volumetric data sets of human cadavers, the authors generated a high-fidelity visual and haptic rendering of the MCF approach using CardinalSim software. Trainees from Neurosurgery and Otolaryngology-Head and Neck Surgery at two Canadian academic centers performed MCF dissections on this VR platform. Randomization was used to assess the effect of enhanced VR interaction. Likert scales were used to assess the face and content validities. Performance metrics and pre- and postsimulation test scores were evaluated. Construct validity was evaluated by examining the effect of the training level on simulation performance.

RESULTS

Twenty trainees were enrolled. Face and content validities were achieved in all domains. Construct validity, however, was not demonstrated. Postsimulation test scores were significantly higher than presimulation test scores ( P < .001 ). Trainees demonstrated statistically significant improvement in the time to complete dissections ( P < .001 ), internal auditory canal skeletonization ( P < .001 ), completeness of the anterior petrosectomy ( P < .001 ), and reduced number of injuries to critical structures ( P = .001 ).

CONCLUSION

This MCF VR simulation created using CardinalSim demonstrated face and content validities. Construct validity was not established because no trainee included in the study had previous MCF approach experience, which further emphasizes the importance of simulation. When used as a formative educational adjunct in both Neurosurgery and Otolaryngology-Head and Neck Surgery, this simulation has the potential to enhance understanding of the complex anatomic relationships of critical neurovascular structures.

Influence of the Frequency-to-Place Function on Recognition with Place-Based Cochlear Implant Maps

OBJECTIVE

Comparison of acute speech recognition for cochlear implant (CI) alone and electric-acoustic stimulation (EAS) users listening with default maps or place-based maps using either a spiral ganglion (SG) or a new Synchrotron Radiation-Artificial Intelligence (SR-AI) frequency-to-place function.

METHODS

Thirteen adult CI-alone or EAS users completed a task of speech recognition at initial device activation with maps that differed in the electric filter frequency assignments. The three map conditions were: (1) maps with the default filter settings (default map), (2) place-based maps with filters aligned to cochlear SG tonotopicity using the SG function (SG place-based map), and (3) place-based maps with filters aligned to cochlear Organ of Corti (OC) tonotopicity using the SR-AI function (SR-AI place-based map). Speech recognition was evaluated using a vowel recognition task. Performance was scored as the percent correct for formant 1 recognition due to the rationale that the maps would deviate the most in the estimated cochlear place frequency for low frequencies.

RESULTS

On average, participants had better performance with the OC SR-AI place-based map as compared to the SG place-based map and the default map. A larger performance benefit was observed for EAS users than for CI-alone users.

CONCLUSION

These pilot data suggest that EAS and CI-alone users may experience better performance with a patient-centered mapping approach that accounts for the variability in cochlear morphology (OC SR-AI frequency-to-place function) in the individualization of the electric filter frequencies (place-based mapping procedure).

LEVEL OF EVIDENCE

3 Laryngoscope, 133:3540-3547, 2023.

Finite element modelling of the human middle ear using synchrotron-radiation phase-contrast imaging

Finite element (FE) models of the middle ear often lack accurate geometry of soft tissue structures, such as the suspensory ligaments, as they can be difficult to discern using conventional imaging modalities, such as computed tomography. Synchrotron-radiation phase-contrast imaging (SR-PCI) is a non-destructive imaging modality that has been shown to produce excellent visualization of soft tissue structures without the need for extensive sample preparation. The objectives of the investigation were to firstly use SR-PCI to create and evaluate a biomechanical FE model of the human middle ear that includes all soft tissue structures, and secondly, to investigate how modelling assumptions and simplifications of ligament representations affect the simulated biomechanical response of the FE model. The FE model included the suspensory ligaments, ossicular chain, tympanic membrane, the incudostapedial and incudomalleal joints, and the ear canal. Frequency responses obtained from the SR-PCI-based FE model agreed well with published laser doppler vibrometer measurements on cadaveric samples. Revised models with exclusion of the superior malleal ligament (SML), simplification of the SML, and modification of the stapedial annular ligament were studied, as these revised models represented modelling assumptions that have been made in literature.

Machine learning approaches used to analyze auditory evoked responses from the human auditory brainstem: A systematic review

BACKGROUND

The application of machine learning algorithms for assessing the auditory brainstem response has gained interest over recent years with a considerable number of publications in the literature. In this systematic review, we explore how machine learning has been used to develop algorithms to assess auditory brainstem responses. A clear and comprehensive overview is provided to allow clinicians and researchers to explore the domain and the potential translation to clinical care.

METHODS

The systematic review was performed based on PRISMA guidelines. A search was conducted of PubMed, IEEE-Xplore, and Scopus databases focusing on human studies that have used machine learning to assess auditory brainstem responses. The duration of the search was from January 1, 1990, to April 3, 2021. The Covidence systematic review platform (www.covidence.org) was used throughout the process.

RESULTS

A total of 5812 studies were found through the database search and 451 duplicates were removed. The title and abstract screening process further reduced the article count to 89 and in the proceeding full-text screening, 34 articles met our full inclusion criteria.

CONCLUSION

Three categories of applications were found, namely neurologic diagnosis, hearing threshold estimation, and other (does not relate to neurologic or hearing threshold estimation). Neural networks and support vector machines were the most commonly used machine learning algorithms in all three categories. Only one study had conducted a clinical trial to evaluate the algorithm after development. Challenges remain in the amount of data required to train machine learning models. Suggestions for future research avenues are mentioned with recommended reporting methods for researchers.

Micro-CT of the human ossicular chain: Statistical shape modeling and implications for otologic surgery

The ossicular chain is a middle ear structure consisting of the small incus, malleus and stapes bones, which transmit tympanic membrane vibrations caused by sound to the inner ear. Despite being shown to be highly variable in shape, there are very few morphological studies of the ossicles. The objective of this study was to use a large sample of cadaveric ossicles to create a set of three-dimensional models and study their statistical variance. Thirty-three cadaveric temporal bone samples were scanned using micro-computed tomography (μCT) and segmented. Statistical shape models (SSMs) were then made for each ossicle to demonstrate the divergence of morphological features. Results revealed that ossicles were most likely to vary in overall size, but that more specific feature variability was found at the manubrium of the malleus, the long process and lenticular process of the incus, and the crura and footplate of the stapes. By analyzing samples as whole ossicular chains, it was revealed that when fixed at the malleus, changes along the chain resulted in a wide variety of final stapes positions. This is the first known study to create high-quality, three-dimensional SSMs of the human ossicles. This information can be used to guide otological surgical training and planning, inform ossicular prosthesis development, and assist with other ossicular studies and applications by improving automated segmentation algorithms. All models have been made publicly available.

Aeration of the Human Prussak's Space: A 3D Synchrotron Imaging Study

OBJECTIVES

Prussak's space (PS) is an intricate middle ear region which may play an essential role in the development of middle ear disease. The three-dimensional (3D) anatomy of the human PS and its drainage routes remain relatively unknown. Earlier studies have histologically analyzed PS, by micro-dissection and endoscopy. Here, we used synchrotron-radiation phase-contrast imaging (SR-PCI), 3D reconstructions, and modeling to study the framework of the human PS, including aeration pathways. It may lead to increased understanding of development of middle ear pathology.

DESIGN

Nine human temporal bone specimens underwent in-line SR-PCI at the Canadian Light Source in Saskatoon, Saskatchewan, Canada. Data were processed with volume-rendering software to create 3D reconstructions using scalar opacity mapping and segmentations to visualize its walls in fixed, undecalcified human temporal bones.

RESULTS

The PS was found to be an irregular, variably shaped chamber with different aeration systems. Three different drainage pathways were found: 1) via the posterior malleolar pouch of von Tröltsch in seven of nine ears; 2) directly posterior-inferior into the mesotympanum medial to the posterior malleolar pouch in one ear; and 3) anteriorly in another. The posterior-inferior communications depended on the anatomy of the posterior malleolar fold. In one bilateral case, the aeration differed between the ears. Earlier descriptions of upper ventilation routes between the PS and the epitympanic spaces could not be substantiated.

CONCLUSIONS

The 3D anatomy of the membrane folds organizing the PS in humans was demonstrated for the first time using in-line SR-PCI. The PS was always aerated into the mesotympanum, suggesting its relative independence of attic ventilation. The impact of its various drainage routes on middle ear ventilation and disease were discussed.

A Synchrotron and Micro-CT Study of the Human Endolymphatic Duct System: Is Meniere's Disease Caused by an Acute Endolymph Backflow?

Background: The etiology of Meniere's disease (MD) and endolymphatic hydrops believed to underlie its symptoms remain unknown. One reason may be the exceptional complexity of the human inner ear, its vulnerability, and surrounding hard bone. The vestibular organ contains an endolymphatic duct system (EDS) bridging the different fluid reservoirs. It may be essential for monitoring hydraulic equilibrium, and a dysregulation may result in distension of the fluid spaces or endolymphatic hydrops. Material and Methods: We studied the EDS using high-resolution synchrotron phase contrast non-invasive imaging (SR-PCI), and micro-computed tomography (micro-CT). Ten fresh human temporal bones underwent SR-PCI. One bone underwent micro-CT after fixation and staining with Lugol's iodine solution (I2KI) to increase tissue resolution. Data were processed using volume-rendering software to create 3D reconstructions allowing orthogonal sectioning, cropping, and tissue segmentation. Results: Combined imaging techniques with segmentation and tissue modeling demonstrated the 3D anatomy of the human saccule, utricle, endolymphatic duct, and sac together with connecting pathways. The utricular duct (UD) and utriculo-endolymphatic valve (UEV or Bast's valve) were demonstrated three-dimensionally for the first time. The reunion duct was displayed with micro-CT. It may serve as a safety valve to maintain cochlear endolymph homeostasis under certain conditions. Discussion: The thin reunion duct seems to play a minor role in the exchange of endolymph between the cochlea and vestibule under normal conditions. The saccule wall appears highly flexible, which may explain occult hydrops occasionally preceding symptoms in MD on magnetic resonance imaging (MRI). The design of the UEV and connecting ducts suggests that there is a reciprocal exchange of fluid among the utricle, semicircular canals, and the EDS. Based on the anatomic framework and previous experimental data, we speculate that precipitous vestibular symptoms in MD arise from a sudden increase in endolymph pressure caused by an uncontrolled endolymphatic sac secretion. A rapid rise in UD pressure, mediated along the fairly wide UEV, may underlie the acute vertigo attack, refuting the rupture/K+-intoxication theory.

An Approach for Individualized Cochlear Frequency Mapping Determined from 3D Synchrotron Radiation Phase-Contrast Imaging

OBJECTIVE

Cochlear implants are traditionally programmed to stimulate according to a generalized frequency map, where individual anatomic variability is not considered when selecting the centre frequency of stimulation of each implant electrode. However, high variability in cochlear size and spatial frequency distributions exist among individuals. Generalized cochlear implant frequency maps can result in large pitch perception errors and reduced hearing outcomes for cochlear implant recipients. The objective of this work was to develop an individualized frequency mapping technique for the human cochlea to allow for patient-specific cochlear implant stimulation.

METHODS

Ten cadaveric human cochleae were scanned using synchrotron radiation phase-contrast imaging (SR-PCI) combined with computed tomography (CT). For each cochlea, ground truth angle-frequency measurements were obtained in three-dimensions using the SR-PCI CT data. Using an approach designed to minimize perceptual error in frequency estimation, an individualized frequency function was determined to relate angular depth to frequency within the cochlea.

RESULTS

The individualized frequency mapping function significantly reduced pitch errors in comparison to the current gold standard generalized approach.

CONCLUSION AND SIGNIFICANCE

This paper presents for the first time a cochlear frequency map which can be individualized using only the angular length of cochleae. This approach can be applied in the clinical setting and has the potential to revolutionize cochlear implant programming for patients worldwide.

Vestibular Organ and Cochlear Implantation-A Synchrotron and Micro-CT Study

Background: Reports vary on the incidence of vestibular dysfunction and dizziness in patients following cochlear implantation (CI). Disequilibrium may be caused by surgery at the cochlear base, leading to functional disturbances of the vestibular receptors and endolymphatic duct system (EDS) which are located nearby. Here, we analyzed the three-dimensional (3D) anatomy of this region, aiming to optimize surgical approaches to limit damage to the vestibular organ. Material and Methods: A total of 22 fresh-frozen human temporal bones underwent synchrotron radiation phase-contrast imaging (SR-PCI). One temporal bone underwent micro-computed tomography (micro-CT) after fixation and staining with Lugol's iodine solution (I2KI) to increase tissue contrast. We used volume-rendering software to create 3D reconstructions and tissue segmentation that allowed precise assessment of anatomical relationships and topography. Macerated human ears belonging to the Uppsala collection were also used. Drilling and insertion of CI electrodes was performed with metric analyses of different trajectories. Results and Conclusions: SR-PCI and micro-CT imaging demonstrated the complex 3D anatomy of the basal region of the human cochlea, vestibular apparatus, and EDS. Drilling of a cochleostomy may disturb vestibular organ function by injuring the endolymphatic space and disrupting fluid barriers. The saccule is at particular risk due to its proximity to the surgical area and may explain immediate and long-term post-operative vertigo. Round window insertion may be less traumatic to the inner ear, however it may affect the vestibular receptors.

Comparison of machine learning models to classify Auditory Brainstem Responses recorded from children with Auditory Processing Disorder

INTRODUCTION

Auditory brainstem responses (ABRs) offer a unique opportunity to assess the neural integrity of the peripheral auditory nervous system in individuals presenting with listening difficulties. ABRs are typically recorded and analyzed by an audiologist who manually measures the timing and quality of the waveforms. The interpretation of ABRs requires considerable experience and training, and inappropriate interpretation can lead to incorrect judgments about the integrity of the system. Machine learning (ML) techniques may be a suitable approach to automate ABR interpretation and reduce human error.

OBJECTIVES

The main objective of this paper was to identify a suitable ML technique to automate the analysis of ABR responses recorded as a part of the electrophysiological testing in the Auditory Processing Disorder clinical test battery.

METHODS

ABR responses recorded during routine clinical assessment from 136 children being evaluated for auditory processing difficulties were analyzed using several common ML algorithms: Support Vector Machines (SVM), Random Forests (RF), Decision Trees (DT), Gradient Boosting (GB), Extreme Gradient Boosting (Xgboost), and Neural Networks (NN). A variety of signal feature extraction techniques were used to extract features from the ABR waveforms as inputs to the ML algorithms. Statistical significance testing and confusion matrices were used to identify the most robust model capable of accurately identifying neurological abnormalities present in ABRs.

RESULTS

Clinically significant features in the time-frequency representation of the signal were identified. The ML model trained using the Xgboost algorithm was identified as the most robust model with an accuracy of 92% compared to other models.

CONCLUSION

The findings of the present study demonstrate that it is possible to develop accurate ML models to automate the process of analyzing ABR waveforms recorded at suprathreshold levels. There is currently no ML-based application to screen children with listening difficulties. Therefore, it is expected that this work will be translated into an evaluation tool that can be used by audiologists in the clinic. Furthermore, this work may aid future researchers in exploring ML paradigms to improve clinical test batteries used by audiologists in achieving accurate diagnoses.

Three-dimensional tonotopic mapping of the human cochlea based on synchrotron radiation phase-contrast imaging

The human cochlea transforms sound waves into electrical signals in the acoustic nerve fibers with high acuity. This transformation occurs via vibrating anisotropic membranes (basilar and tectorial membranes) and frequency-specific hair cell receptors. Frequency-positions can be mapped within the cochlea to create a tonotopic chart which fits an almost-exponential function with lowest frequencies positioned apically and highest frequencies positioned at the cochlear base (Bekesy 1960, Greenwood 1961). To date, models of frequency positions have been based on a two-dimensional analysis with inaccurate representations of the cochlear hook region. In the present study, the first three-dimensional frequency analysis of the cochlea using dendritic mapping to obtain accurate tonotopic maps of the human basilar membrane/organ of Corti and the spiral ganglion was performed. A novel imaging technique, synchrotron radiation phase-contrast imaging, was used and a spiral ganglion frequency function was estimated by nonlinear least squares fitting a Greenwood-like function (F = A (10^ax − K)) to the data. The three-dimensional tonotopic data presented herein has large implications for validating electrode position and creating customized frequency maps for cochlear implant recipients.

PWD-3DNet: A Deep Learning-Based Fully-Automated Segmentation of Multiple Structures on Temporal Bone CT Scans

The temporal bone is a part of the lateral skull surface that contains organs responsible for hearing and balance. Mastering surgery of the temporal bone is challenging because of this complex and microscopic three-dimensional anatomy. Segmentation of intra-temporal anatomy based on computed tomography (CT) images is necessary for applications such as surgical training and rehearsal, amongst others. However, temporal bone segmentation is challenging due to the similar intensities and complicated anatomical relationships among critical structures, undetectable small structures on standard clinical CT, and the amount of time required for manual segmentation. This paper describes a single multi-class deep learning-based pipeline as the first fully automated algorithm for segmenting multiple temporal bone structures from CT volumes, including the sigmoid sinus, facial nerve, inner ear, malleus, incus, stapes, internal carotid artery and internal auditory canal. The proposed fully convolutional network, PWD-3DNet, is a patch-wise densely connected (PWD) three-dimensional (3D) network. The accuracy and speed of the proposed algorithm was shown to surpass current manual and semi-automated segmentation techniques. The experimental results yielded significantly high Dice similarity scores and low Hausdorff distances for all temporal bone structures with an average of 86% and 0.755 millimeter (mm), respectively. We illustrated that overlapping in the inference sub-volumes improves the segmentation performance. Moreover, we proposed augmentation layers by using samples with various transformations and image artefacts to increase the robustness of PWD-3DNet against image acquisition protocols, such as smoothing caused by soft tissue scanner settings and larger voxel sizes used for radiation reduction. The proposed algorithm was tested on low-resolution CTs acquired by another center with different scanner parameters than the ones used to create the algorithm and shows potential for application beyond the particular training data used in the study.

The BONEBRIDGE active transcutaneous bone conduction implant: effects of location, lifts and screws on sound transmission

BACKGROUND

The BONEBRIDGE (MED-EL, Innsbruck, Austria) is a bone-conduction implant used in the treatment of conductive and mixed hearing loss. The BONEBRIDGE consists of an external audio processor and a bone-conduction floating mass transducer that is surgically implanted into the skull in either the transmastoid, retrosigmoid or middle fossa regions. The manufacturer includes self-tapping screws to secure the transducer; however, self-drilling screws have also been used with success. In cases where the skull is not thick enough to house the transducer, lifts are available in a variety of sizes to elevate the transducer away from the skull. The objective of the present study was to investigate the effects of screw type, lift thickness, and implant location on the sound transmission of the BONEBRIDGE.

METHOD

Six cadaveric temporal bones were embalmed and dried for use in this study. In each sample, a hole was drilled in each of the three implant locations to house the implant transducer. At the middle fossa, six pairs of screw holes were pre-drilled; four pairs to be used with self-tapping screws and lifts (1, 2, 3, and 4 mm thick lifts, respectively), one pair with self-tapping screws and no lifts, and one pair with self-drilling screws and no lifts. At the transmastoid and retrosigmoid locations, one pair of screw holes were pre-drilled in each for the use of the self-tapping screws. The vibration of transmitted sound to the cochlea was measured using a laser Doppler vibrometry technique. The measurements were performed on the cochlear promontory at eight discrete frequencies (0.5, 0.75, 1, 1.5, 2, 3, 4 and 6 kHz). Vibration velocity of the cochlear wall was measured in all samples. Measurements were analyzed using a single-factor ANOVA to investigate the effect of each modification.

RESULTS

No significant differences were found related to either screw type, lift thickness, or implant location.

CONCLUSIONS

This is the first known study to evaluate the effect of screw type, lift thickness, and implant location on the sound transmission produced by the BONEBRIDGE bone-conduction implant. Further studies may benefit from analysis using fresh cadaveric samples or in-vivo measurements.

Assessment of a virtual reality temporal bone surgical simulator: a national face and content validity study

BACKGROUND

Trainees in Otolaryngology-Head and Neck Surgery must gain proficiency in a variety of challenging temporal bone surgical techniques. Traditional teaching has relied on the use of cadavers; however, this method is resource-intensive and does not allow for repeated practice. Virtual reality surgical training is a growing field that is increasingly being adopted in Otolaryngology. CardinalSim is a virtual reality temporal bone surgical simulator that offers a high-quality, inexpensive adjunct to traditional teaching methods. The objective of this study was to establish the face and content validity of CardinalSim through a national study.

METHODS

Otolaryngologists and resident trainees from across Canada were recruited to evaluate CardinalSim. Ethics approval and informed consent was obtained. A face and content validity questionnaire with questions categorized into 13 domains was distributed to participants following simulator use. Descriptive statistics were used to describe questionnaire results, and either Chi-square or Fishers exact tests were used to compare responses between junior residents, senior residents, and practising surgeons.

RESULTS

Sixty-two participants from thirteen different Otolaryngology-Head and Neck Surgery programs were included in the study (32 practicing surgeons; 30 resident trainees). Face validity was achieved for 5 out of 7 domains, while content validity was achieved for 5 out of 6 domains. Significant differences between groups (p-value of < 0.05) were found for one face validity domain (realistic ergonomics, p = 0.002) and two content validity domains (teaching drilling technique, p = 0.011 and overall teaching utility, p = 0.006). The assessment scores, global rating scores, and overall attitudes towards CardinalSim, were universally positive. Open-ended questions identified limitations of the simulator.

CONCLUSION

CardinalSim met acceptable criteria for face and content validity. This temporal bone virtual reality surgical simulation platform may enhance surgical training and be suitable for patient-specific surgical rehearsal for practicing Otolaryngologists.

Vascular Supply of the Human Spiral Ganglion: Novel Three-Dimensional Analysis Using Synchrotron Phase-Contrast Imaging and Histology

Human spiral ganglion (HSG) cell bodies located in the bony cochlea depend on a rich vascular supply to maintain excitability. These neurons are targeted by cochlear implantation (CI) to treat deafness, and their viability is critical to ensure successful clinical outcomes. The blood supply of the HSG is difficult to study due to its helical structure and encasement in hard bone. The objective of this study was to present the first three-dimensional (3D) reconstruction and analysis of the HSG blood supply using synchrotron radiation phase-contrast imaging (SR-PCI) in combination with histological analyses of archival human cochlear sections. Twenty-six human temporal bones underwent SR-PCI. Data were processed using volume-rendering software, and a representative three-dimensional (3D) model was created to allow visualization of the vascular anatomy. Histologic analysis was used to verify the segmentations. Results revealed that the HSG is supplied by radial vascular twigs which are separate from the rest of the inner ear and encased in bone. Unlike with most organs, the arteries and veins in the human cochlea do not follow the same conduits. There is a dual venous outflow and a modiolar arterial supply. This organization may explain why the HSG may endure even in cases of advanced cochlear pathology.

Characterization of the human helicotrema: implications for cochlear duct length and frequency mapping

Background

Despite significant anatomical variation amongst patients, cochlear implant frequency-mapping has traditionally followed a patient-independent approach. Basilar membrane (BM) length is required for patient-specific frequency-mapping, however cochlear duct length (CDL) measurements generally extend to the apical tip of the entire cochlea or have no clearly defined end-point. By characterizing the length between the end of the BM and the apical tip of the entire cochlea (helicotrema length), current CDL models can be corrected to obtain the appropriate BM length. Synchrotron radiation phase-contrast imaging has made this analysis possible due to the soft-tissue contrast through the entire cochlear apex.

Methods

Helicotrema linear length and helicotrema angular length measurements were performed on synchrotron radiation phase-contrast imaging data of 14 cadaveric human cochleae. On a sub-set of six samples, the CDL to the apical tip of the entire cochlea (CDL_TIP) and the BM length (CDL_BM) were determined. Regression analysis was performed to assess the relationship between CDL_TIP and CDL_BM.

Results

The mean helicotrema linear length and helicotrema angular length values were 1.6 ± 0.9 mm and 67.8 ± 37.9 degrees, respectively. Regression analysis revealed the following relationship between CDL_TIP and CDL_BM: CDL_BM = 0.88(CDL_TIP) + 3.71 (R² = 0.995).

Conclusion

This is the first known study to characterize the length of the helicotrema in the context of CDL measurements. It was determined that the distance between the end of the BM and the tip of the entire cochlea is clinically consequential. A relationship was determined that can predict the BM length of an individual patient based on their respective CDL measured to the apical tip of the cochlea.

The middle fossa approach with self-drilling screws: a novel technique for BONEBRIDGE implantation

Background

Bone conduction implants can be used in the treatment of conductive or mixed hearing loss. The BONEBRIDGE bone conduction implant (BB-BCI) is an active, transcutaneous device. BB-BCI implantation can be performed through either the transmastoid or retrosigmoid approach with their respective limitations. Here, we present a third, novel approach for BB-BCI implantation.

Objective

Describe the detailed surgical technique of BB-BCI implantation through a middle fossa approach with self-drilling screws and present preliminary audiometric outcome data following this approach.

Methods

A single institution, retrospective chart review was completed for patients implanted with the BB-BCI via the middle fossa approach. Preoperative planning and modelling were performed using 3D Slicer. Audiological testing was performed pre- and post-operatively following standard audiometric techniques.

Results

Forty patients underwent BB-BCI implantation using the middle fossa approach. Modelling techniques allowed for implantation through the use of external landmarks, obviating the need for intraoperative image guidance. The surgical technique was refined over time through experience and adaptation. Mean follow-up was 29 months (range 3–71 months) with no surgical complications, favourable cosmesis, and expected audiometric outcomes. An average functional gain of 39.6 dB (± 14.7 SD) was found.

Conclusion

The middle fossa technique with self-drilling screws is a safe and effective option for BONEBRIDGE implantation. As a reference for other groups considering this approach, an annotated video has been included as a supplement to the study.

Electronic supplementary material

The online version of this article (10.1186/s40463-019-0354-7) contains supplementary material, which is available to authorized users.

Skill Transference of a Probe-Tube Placement Training Simulator

BACKGROUND

Probe-tube placement is a necessary step in hearing aid verification which needs ample hands-on experience and confidence before performing in clinic. To improve the methods of training in probe-tube placement, a manikin-based training simulator was developed consisting of a 3D-printed head, a flexible silicone ear, and a mounted optical tracking system. The system is designed to provide feedback to the user on the depth and orientation of the probe tube, and the time required to finish the task. Although a previous validation study was performed to determine its realism and teachability with experts, further validation is required before implementation into educational settings.

PURPOSE

This study aimed to examine the skill transference of a newly updated probe-tube placement training simulator to determine if skills learned on this simulator successfully translate to clinical scenarios.

RESEARCH DESIGN

All participants underwent a pretest in which they were evaluated while performing a probe-tube placement and real-ear-to-coupler difference (RECD) measurement on a volunteer. Participants were randomized into one of two groups: the simulator group or the control group. During a two-week training period, all participants practiced their probe-tube placement according to their randomly assigned group. After two weeks, each participant completed a probe-tube placement on the same volunteer as a posttest scenario.

STUDY SAMPLE

Twenty-five novice graduate-level student clinicians.

DATA COLLECTION AND ANALYSIS

Participants completed a self-efficacy questionnaire and an expert observer completed a questionnaire evaluating each participant's performance during the pre- and posttest sessions. RECD measurements were taken after placing the probe tube and foam tip in the volunteer's ear. Questionnaire results were analyzed through nonparametric t-tests and analysis of variance, whereas RECD results were analyzed using a nonlinear mixed model method.

RESULTS

Results suggested students in the simulator group were less likely to contact the tympanic membrane when placing a probe tube, appeared more confident, and had better use of the occluding foam tip, resulting in more improved RECD measurements.

CONCLUSIONS

The improved outcomes for trainees in the simulator group suggest that supplementing traditional training with the simulator provides useful benefits for the trainees, thereby encouraging its usage and implementation in educational settings.

Three-dimensional imaging of the human internal acoustic canal and arachnoid cistern: a synchrotron study with clinical implications

A thorough knowledge of the gross and micro‐anatomy of the human internal acoustic canal (IAC) is essential in vestibular schwannoma removal, cochlear implantation (CI) surgery, vestibular nerve section, and decompression procedures. Here, we analyzed the acoustic‐facial cistern of the human IAC, including nerves and anastomoses using synchrotron phase contrast imaging (SR‐PCI). A total of 26 fresh human temporal bones underwent SR‐PCI. Data were processed using volume‐rendering software to create three‐dimensional (3D) reconstructions allowing soft tissue analyses, orthogonal sectioning, and cropping. A scalar opacity mapping tool was used to enhance tissue surface borders, and anatomical structures were color‐labeled for improved 3D comprehension of the soft tissues. SR‐PCI reproduced, for the first time, the variable 3D anatomy of the human IAC, including cranial nerve complexes, anastomoses, and arachnoid membrane invagination (acoustic‐facial cistern; an extension of the cerebellopontine cistern) in unprocessed, un‐decalcified specimens. An unrecognized system of arachnoid pillars and trabeculae was found to extend between the arachnoid and cranial nerves. We confirmed earlier findings that intra‐meatal vestibular schwannoma may grow unseparated from adjacent nerves without duplication of the arachnoid layers. The arachnoid pillars may support and stabilize cranial nerves in the IAC and could also play a role in local fluid hydrodynamics.

Face and Content Validity of a Probe Tube Placement Training Simulator

BACKGROUND

Probe tube placement is an important skill audiologists must learn to make real-ear measurements in an audiology clinic. With current evidence-based guidelines recommending insertion of the probe tube within 5 mm of the tympanic membrane (TM) for proper acoustical measurements, students must be well trained to ensure they are capable to perform this placement in clinical practice. This is not always the case as it has been found that real-ear measurements are not performed in a clinic as often as required. To address this, a simulator consisting of a 3D-printed ear model and an optical tracking system was developed to provide a training system for students to practice probe tube placement and to provide a method to evaluate competency before starting clinical practicum placements. Two simulators were developed, an adult model and a pediatric model.

PURPOSE

To assess the face and content validity of the two probe tube placement simulators (adult and pediatric) and define barriers and facilitators to implementing this system into an educational setting.

RESEARCH DESIGN

Participants followed the setup and operating instructions designed to guide them through each functionality of the simulator. A questionnaire was used to assess face and content validity, applicability to an educational setting, and to determine perceived barriers and facilitators to using the probe tube simulators for training purposes. Five additional probe tube placements with each simulator were performed in which distance-to-TM was recorded.

STUDY SAMPLE

Twelve participants with significant probe tube placement experience.

DATA COLLECTION AND ANALYSIS

Participants rated each question in the questionnaire from 0% to 100% depending on their level of agreement. Averages and standard deviations (SDs) were compiled and presented for each section (face validity, content validity, and applicability to an educational setting). Final facilitators and barriers for the simulator were compiled and the top answers of each are presented. The five quantitative probe tube placement measurements for each participant were averaged, SDs were calculated, and contacts with the TM while placing the probe tube were recorded.

RESULTS

The average face validity score over all questions for the adult model was 65% (SD = 18.2) whereas the pediatric model received a score of 64% (16.4). The overall content validity average score was 78.7% (17) and applicability to an educational setting had an average score of 80% (5.33). The average distance-to-TM across all trials and participants was 3.74 mm (1.82) for the adult model and 2.77 mm (0.94) for the pediatric model with only one participant exceeding the recommended maximum of 5 mm. Listed shortcomings of the current simulator included realism of the 3D-printed ear, ease of insertion of an otoscope tip into the ear, ability to visualize the ear canal "landmarks" and the TM, and foam tip insertion experience.

CONCLUSIONS

Results were generally very positive for the simulator, and future iterations will look to improve the flexibility and texture of the ear, as well as the otoscopic view of the ear canal and TM.

Human inner ear blood supply revisited: the Uppsala collection of temporal bone-an international resource of education and collaboration

BACKGROUND

The Uppsala collection of human temporal bones and molds is a unique resource for education and international research collaboration. Micro-computerized tomography (micro-CT) and synchrotron imaging are used to investigate the complex anatomy of the inner ear. Impaired microcirculation is etiologically linked to various inner ear disorders, and recent developments in inner ear surgery promote examination of the vascular system. Here, for the first time, we present three-dimensional (3D) data from investigations of the major vascular pathways and corresponding bone channels.

METHODS

We used the archival Uppsala collection of temporal bones and molds consisting of 324 inner ear casts and 113 macerated temporal bones. Micro-CT was used to investigate vascular bone channels, and 26 fresh human temporal bones underwent synchrotron radiation phase contrast imaging (SR-PCI). Data were processed by volume-rendering software to create 3D reconstructions allowing orthogonal sectioning, cropping, and soft tissue analyses.

RESULTS

Micro-CT with 3D rendering was superior in reproducing the anatomy of the vascular bone channels, while SR-PCI replicated soft tissues. Arterial bone channels were traced from scala vestibuli (SV) arterioles to the fundus, cochlea, and vestibular apparatus. Drainage routes along the aqueducts were examined.

CONCLUSION

Human inner ear vessels are difficult to study due to the adjoining hard bone. Micro-CT and SR-PCI with 3D reconstructions revealed large portions of the micro-vascular system in un-decalcified specimens. The results increase our understanding of the organization of the vascular system in humans and how altered microcirculation may relate to inner ear disorders. The findings may also have surgical implications.

Visualizing the 3D cytoarchitecture of the human cochlea in an intact temporal bone using synchrotron radiation phase contrast imaging

The gold standard method for visualizing the pathologies underlying human sensorineural hearing loss has remained post-mortem histology for over 125 years, despite awareness that histological preparation induces severe artifacts in biological tissue. Historically, the transition from post-mortem assessment to non-invasive clinical biomedical imaging in living humans has revolutionized diagnosis and treatment of disease; however, innovation in non-invasive techniques for cellular-level intracochlear imaging in humans has been difficult due to the cochlea's small size, complex 3D configuration, fragility, and deep encasement within bone. Here we investigate the ability of synchrotron radiation-facilitated X-ray absorption and phase contrast imaging to enable visualization of sensory cells and nerve fibers in the cochlea's sensory epithelium in situ in 3D intact, non-decalcified, unstained human temporal bones. Our findings show that this imaging technique resolves the bone-encased sensory epithelium's cytoarchitecture with unprecedented levels of cellular detail for an intact, unstained specimen, and is capable of distinguishing between healthy and damaged epithelium. All analyses were performed using commercially available software that quickly reconstructs and facilitates 3D manipulation of massive data sets. Results suggest that synchrotron radiation phase contrast imaging has the future potential to replace histology as a gold standard for evaluating intracochlear structural integrity in human specimens, and motivate further optimization for translation to the clinic.

Visualizing the 3D cytoarchitecture of the human cochlea in an intact temporal bone using synchrotron radiation phase contrast imaging

The gold standard method for visualizing the pathologies underlying human sensorineural hearing loss has remained post-mortem histology for over 125 years, despite awareness that histological preparation induces severe artifacts in biological tissue. Historically, the transition from post-mortem assessment to non-invasive clinical biomedical imaging in living humans has revolutionized diagnosis and treatment of disease; however, innovation in non-invasive techniques for cellular-level intracochlear imaging in humans has been difficult due to the cochlea's small size, complex 3D configuration, fragility, and deep encasement within bone. Here we investigate the ability of synchrotron radiation-facilitated X-ray absorption and phase contrast imaging to enable visualization of sensory cells and nerve fibers in the cochlea's sensory epithelium in situ in 3D intact, non-decalcified, unstained human temporal bones. Our findings show that this imaging technique resolves the bone-encased sensory epithelium's cytoarchitecture with unprecedented levels of cellular detail for an intact, unstained specimen, and is capable of distinguishing between healthy and damaged epithelium. All analyses were performed using commercially available software that quickly reconstructs and facilitates 3D manipulation of massive data sets. Results suggest that synchrotron radiation phase contrast imaging has the future potential to replace histology as a gold standard for evaluating intracochlear structural integrity in human specimens, and motivate further optimization for translation to the clinic.

Estimation of the Young's moduli of fresh human oropharyngeal soft tissues using indentation testing

Finite element (FE)-based biomechanical simulations of the upper airway are promising computational tools to study abnormal upper airway deformations under obstructive sleep apnea (OSA) conditions and to help guide minimally invasive surgical interventions in case of upper airway collapse. To this end, passive biomechanical properties of the upper airway tissues, especially oropharyngeal soft tissues, are indispensable. This research aimed at characterizing the linear elastic mechanical properties of the oropharyngeal soft tissues including palatine tonsil, soft palate, uvula, and tongue base. For this purpose, precise indentation experiments were conducted on freshly harvested human tissue samples accompanied by FE-based inversion schemes. To minimize the impact of the probable nonlinearities of the tested tissue samples, only the first quarter of the measured force-displacement data corresponding to the linear elastic regime was utilized in the FE-based inversion scheme to improve the accuracy of the tissue samples' Young's modulus calculations. Measured Young's moduli of the oropharyngeal soft tissues obtained in this study are presented. They include first estimates for palatine tonsil tissue samples while measured Young's moduli of other upper airway tissues were obtained for the first time using fresh human tissue samples.

The secondary spiral lamina and its relevance in cochlear implant surgery

OBJECTIVE

We used synchrotron radiation phase contrast imaging (SR-PCI) to study the 3D microanatomy of the basilar membrane (BM) and its attachment to the spiral ligament (SL) (with a conceivable secondary spiral lamina [SSL] or secondary spiral plate) at the round window membrane (RWM) in the human cochlea. The conception of this complex anatomy may be essential for accomplishing structural preservation at cochlear implant surgery.

MATERIAL AND METHODS

Sixteen freshly fixed human temporal bones were used to reproduce the BM, SL, primary and secondary osseous spiral laminae (OSL), and RWM using volume-rendering software. Confocal microscopy immunohistochemistry (IHC) was performed to analyze the molecular constituents.

RESULTS

SR-PCI reproduced the soft tissues including the RWM, Reissner's membrane (RM), and the BM attachment to the lateral wall (LW) in three dimensions. A variable SR-PCI contrast enhancement was recognized in the caudal part of the SL facing the scala tympani (ST). It seemed to represent a SSL allied to the basilar crest (BC). The SSL extended along the postero-superior margin of the round window (RW) and immunohistochemically expressed type II collagen.

CONCLUSIONS

Unlike in several mammalian species, the human SSL is restricted to the most basal portion of the cochlea around the RW. It anchors the BM and may influence its hydro-mechanical properties. It could also help to shield the BM from the RW. The microanatomy should be considered at cochlear implant surgery.

An automated A-value measurement tool for accurate cochlear duct length estimation

BACKGROUND

There has been renewed interest in the cochlear duct length (CDL) for preoperative cochlear implant electrode selection and postoperative generation of patient-specific frequency maps. The CDL can be estimated by measuring the A-value, which is defined as the length between the round window and the furthest point on the basal turn. Unfortunately, there is significant intra- and inter-observer variability when these measurements are made clinically. The objective of this study was to develop an automated A-value measurement algorithm to improve accuracy and eliminate observer variability.

METHOD

Clinical and micro-CT images of 20 cadaveric cochleae specimens were acquired. The micro-CT of one sample was chosen as the atlas, and A-value fiducials were placed onto that image. Image registration (rigid affine and non-rigid B-spline) was applied between the atlas and the 19 remaining clinical CT images. The registration transform was applied to the A-value fiducials, and the A-value was then automatically calculated for each specimen. High resolution micro-CT images of the same 19 specimens were used to measure the gold standard A-values for comparison against the manual and automated methods.

RESULTS

The registration algorithm had excellent qualitative overlap between the atlas and target images. The automated method eliminated the observer variability and the systematic underestimation by experts. Manual measurement of the A-value on clinical CT had a mean error of 9.5 ± 4.3% compared to micro-CT, and this improved to an error of 2.7 ± 2.1% using the automated algorithm. Both the automated and manual methods correlated significantly with the gold standard micro-CT A-values (r = 0.70, p < 0.01 and r = 0.69, p < 0.01, respectively).

CONCLUSION

An automated A-value measurement tool using atlas-based registration methods was successfully developed and validated. The automated method eliminated the observer variability and improved accuracy as compared to manual measurements by experts. This open-source tool has the potential to benefit cochlear implant recipients in the future.

Measuring Cochlear Duct Length - a historical analysis of methods and results

Background

Cochlear Duct Length (CDL) has been an important measure for the development and advancement of cochlear implants. Emerging literature has shown CDL can be used in preoperative settings to select the proper sized electrode and develop customized frequency maps. In order to improve post-operative outcomes, and develop new electrode technologies, methods of measuring CDL must be validated to allow usage in the clinic.

Purpose

The purpose of this review is to assess the various techniques used to calculate CDL and provide the reader with enough information to make an informed decision on how to conduct future studies measuring the CDL.

Results

The methods to measure CDL, the modality used to capture images, and the location of the measurement have all changed as technology evolved. With recent popularity and advancement in computed tomography (CT) imaging in place of histologic sections, measurements of CDL have been focused at the lateral wall (LW) instead of the organ of Corti (OC), due to the inability of CT to view intracochlear structures. After analyzing results from methods such as directly measuring CDL from histology, indirectly reconstructing the shape of the cochlea, and determining CDL based on spiral coefficients, it was determined the three dimensional (3D) reconstruction method is the most reliable method to measure CDL. 3D reconstruction provides excellent visualization of the cochlea and avoids errors evident in other methods. Due to the number of varying methods with varying accuracies, certain guidelines must be followed in the future to allow direct comparison of CDL values between studies.

Conclusion

After summarizing and analyzing the interesting history of CDL measurements, the use of standardized guidelines and the importance of CDL for future cochlear implant developments is emphasized for future studies.

Micro-CT versus synchrotron radiation phase contrast imaging of human cochlea

High-resolution images of the cochlea are used to develop atlases to extract anatomical features from low-resolution clinical computed tomography (CT) images. We compare visualization and contrast of conventional absorption-based micro-CT to synchrotron radiation phase contrast imaging (SR-PCI) images of whole unstained, nondecalcified human cochleae. Three cadaveric cochleae were imaged using SR-PCI and micro-CT. Images were visually compared and contrast-to-noise ratios (CNRs) were computed from n = 27 regions-of-interest (enclosing soft tissue) for quantitative comparisons. Three-dimensional (3D) models of cochlear internal structures were constructed from SR-PCI images using a semiautomatic segmentation method. SR-PCI images provided superior visualization of soft tissue microstructures over conventional micro-CT images. CNR improved from 7.5 ± 2.5 in micro-CT images to 18.0 ± 4.3 in SR-PCI images (p < 0.0001). The semiautomatic segmentations yielded accurate reconstructions of 3D models of the intracochlear anatomy. The improved visualization, contrast and modelling achieved using SR-PCI images are very promising for developing atlas-based segmentation methods for postoperative evaluation of cochlear implant surgery.

Fiber Arrangement in the Rat Tympanic Membrane

The fiber arrangement in the pars tensa of the rat tympanic membrane (TM) was observed using a high resolution scanning electron microscope. The entire pars tensa is composed of fibrils with diameter of approximately 25 nm. These fibrils can be grouped into radial, circular, parabolic, and oblique fibers as reported in other mammals. The radial fibrils interweave into a planar form rather than into discrete cylindrical fibers. Before attaching to the manubrium and tympanic ring, the radial fibrils bend and cross neighboring fibrils to form a random fibril network, and change their direction from perpendicular to somewhat parallel to the manubrium and tympanic ring. The circular fibrils form cylindrical fibers near the peripheral part of the TM while closer to the manubrium, they form planar bundles. The observed fiber morphology and arrangement may provide helpful information in improving numerical models for the TM's acoustical response and designing a fibrous graft for the repair of TM perforations. Anat Rec, 299:1531-1539, 2016. © 2016 Wiley Periodicals, Inc.

Iodine potassium iodide improves the contrast-to-noise ratio of micro-computed tomography images of the human middle ear

High-resolution imaging of middle-ear geometry is necessary for finite-element modeling. Although micro-computed tomography (microCT) is widely used because of its ability to image bony structures of the middle ear, it is difficult to visualize soft tissues - including the tympanic membrane and the suspensory ligaments/tendons - because of lack of contrast. The objective of this research is to quantitatively evaluate the efficacy of iodine potassium iodide (IKI) solution as a contrast agent. Six human temporal bones were used in this experiment, which were obtained in right-left pairs, from three cadaveric heads. All bones were fixed using formaldehyde. Three bones (one from each pair) were stained in IKI solution for 2 days, whereas the other three were not stained. Samples were scanned using a microCT system at a resolution of 20 μm. Eight soft tissues in the middle ear were segmented: anterior mallear ligament, incudomallear joint, lateral mallear ligament, posterior incudal ligament, stapedial annular ligament, stapedius muscle, tympanic membrane and tensor tympani muscle. Contrast-to-noise ratios (CNRs) of each soft tissue were calculated for each temporal bone. Combined CNRs of the soft tissues in unstained samples were 6.1 ± 3.0, whereas they were 8.1 ± 2.7 in stained samples. Results from Welch's t-test indicate significant difference between the two groups at a 95% confidence interval. Results for paired t-tests for each of the individual soft tissues also indicated significant improvement of contrast in all tissues after staining. Relatively large soft tissues in the middle ear such as the tympanic membrane and the tensor tympani muscle were impacted by staining more than smaller tissues such as the stapedial annular ligament. The increase in contrast with IKI solution confirms its potential application in automatic segmentation of the middle-ear soft tissues.

Face and content validity of a virtual-reality simulator for myringotomy with tube placement

BACKGROUND

Myringotomy with tube insertion can be challenging for junior Otolaryngology residents as it is one of the first microscopic procedures they encounter. The Western myringotomy simulator was developed to allow trainees to practice microscope positioning, myringotomy, and tube placement. This virtual-reality simulator is viewed in stereoscopic 3D, and a haptic device is used to manipulate the digital ear model and surgical tools.

OBJECTIVE

To assess the face and content validity of the Western myringotomy simulator.

METHODS

The myringotomy simulator was integrated with new modules to allow speculum placement, manipulation of an operative microscope, and insertion of the ventilation tube through a deformable tympanic membrane. A questionnaire was developed in consultation with instructing surgeons. Fourteen face validity questions focused on the anatomy of the ear, simulation of the operative microscope, appearance and movement of the surgical instruments, deformation and cutting of the eardrum, and myringotomy tube insertion. Six content validity questions focused on training potential on surgical tasks such as speculum placement, microscope positioning, tool navigation, ear anatomy, myringotomy creation and tube insertion. A total of 12 participants from the Department of Otolaryngology-Head and Neck Surgery were recruited for the study. Prior to completing the questionnaire, participants were oriented to the simulator and given unlimited time to practice until they were comfortable with all of its aspects.

RESULTS

Responses to 12 of the 14 questions on face validity were predominantly positive. One issue of concern was with contact modeling related to tube insertion into the eardrum, and the second was with the movement of the blade and forceps. The former could be resolved by using a higher resolution digital model for the eardrum to improve contact localization. The latter could be resolved by using a higher fidelity haptic device. With regard to content validity, 64% of the responses were positive, 21% were neutral, and 15% were negative.

CONCLUSIONS

The Western myringotomy simulator appears to have sufficient face and content validity. Further development with automated metrics and skills transference testing is planned.

Face and content validity of a novel, web-based otoscopy simulator for medical education

Background

Despite the fact that otoscopy is a widely used and taught diagnostic tool during medical training, errors in diagnosis are common. Physical otoscopy simulators have high fidelity, but they can be expensive and only a limited number of students can use them at a given time.

Objectives

1) To develop a purely web-based otoscopy simulator that can easily be distributed to students over the internet. 2) To assess face and content validity of the simulator by surveying experts in otoscopy.

Methods

An otoscopy simulator, OtoTrain™, was developed at Western University using web-based programming and Unity 3D. Eleven experts from academic institutions in North America were recruited to test the simulator and respond to an online questionnaire. A 7-point Likert scale was used to answer questions related to face validity (realism of the simulator), content validity (expert evaluation of subject matter and test items), and applicability to medical training.

Results

The mean responses for the face validity, content validity, and applicability to medical training portions of the questionnaire were all ≤3, falling between the “Agree”, “Mostly Agree”, and “Strongly Agree” categories. The responses suggest good face and content validity of the simulator. Open-ended questions revealed that the primary drawbacks of the simulator were the lack of a haptic arm for force feedback, a need for increased focus on pneumatic otoscopy, and few rare disorders shown on otoscopy.

Conclusion

OtoTrain™ is a novel, web-based otoscopy simulator that can be easily distributed and used by students on a variety of platforms. Initial face and content validity was encouraging, and a skills transference study is planned following further modifications and improvements to the simulator.

Estimation of the quasi-static Young's modulus of the eardrum using a pressurization technique

The quasi-static Young's modulus of the eardrum's pars tensa is an important modeling parameter in computer simulations. Recent developments in indentation testing and inverse modeling allow estimation of this parameter with the eardrum in situ. These approaches are challenging because of the curved shape of the pars tensa which requires special care during experimentation to keep the indenter perpendicular to the local surface at the point of contact. Moreover, they involve complicated contact modeling. An alternative computer-based method is presented here in which pressurization is used instead of indentation. The Young's modulus of a thin-shell model of the eardrum with subject-specific geometry is numerically optimized such that simulated pressurized shapes match measured counterparts. The technique was evaluated on six healthy rat eardrums, resulting in a Young's modulus estimate of 22.8±1.5MPa. This is comparable to values estimated using indentation testing. The new pressurization-based approach is simpler to use than the indentation-based method for the two reasons noted above.

Interactive computer-based simulator for training in blade navigation and targeting in myringotomy

A virtual-reality simulator was developed for the training of Otolaryngology (Ear-Nose-Throat) surgical residents to perform myringotomy, a relatively common surgical procedure in which an incision is made in the eardrum mainly to treat middle-ear infections. The simulator presents the trainee with a three-dimensional (3D) virtual model of the ear that can be viewed through a mock surgical microscope consisting of a stereo visor mounted on a custom-designed stand. The trainee interacts with the virtual ear using a real myringotomy blade, the movements of which are tracked in real time using a stereo optical tracker. Interactions of the blade with virtual tissues are calculated and rendered on the visor using freely available physics and graphics software engines. Six experienced surgical residents and surgeons assessed the effectiveness of the simulator as a viable training tool by completing a questionnaire designed specifically for this study after using the simulator. Surgeons and residents were positively impressed by the simulator as a training tool and would recommend its use as part of training.

Development and face validity testing of a three-dimensional myringotomy simulator with haptic feedback

INTRODUCTION

Considerable progress has been made in the development of three-dimensional temporal bone virtual reality simulators. However, very little attention has been paid to interactive simulation of middle ear surgery, including myringotomy. As the development of technical skills for middle ear surgery has a steep learning curve, this poses inherent risks to patients during the skills acquisition phase. The benefit of simulation training in the acquisition of surgical skills has been demonstrated with previous low-fidelity models. Tactile sensation is an important feedback mechanism in middle ear surgery, so a three-dimensional virtual reality myringotomy simulator with haptic feedback was developed at The University of Western Ontario.

OBJECTIVE

To examine the face validity of a three-dimensional myringotomy simulator with haptic feedback.

METHODS

The three-dimensional myringotomy simulator was calibrated with input from two otolaryngologists and one intermediate-level resident. The face validity of the resulting simulator was tested by four staff otolaryngologists and seven intermediate- or senior-level residents using a previously validated questionnaire.

RESULTS

The results demonstrate good to excellent face validity for the myringotomy simulator with high consistency between participants with a Cronbach alpha of .919. Favourable responses predominated for all questions with the exception of force feedback, where the average response was neutral.

CONCLUSIONS

The initial results from the development and testing of a three-dimensional virtual myringotomy simulator with haptic feedback are very encouraging. This simulator is the first of its kind and, with further refinement, has excellent potential to be of benefit in the training of proficient middle ear surgeons.

Measuring the quasi-static Young's modulus of the eardrum using an indentation technique

Accurate estimation of the quasi-static Young's modulus of the eardrum is important for finite-element modeling. In this study, we adapted a tissue indentation technique and inverse finite-element analysis to estimate the Young's modulus of the eardrum. A custom-built indentation apparatus was used to perform indentation testing on seven rat eardrums in situ after immobilizing the malleus. Testing was done in most cases on the posterior pars tensa. The unloaded shape of each eardrum was measured and used to construct finite-element models with subject-specific geometries to simulate the indentation experiment. The Young's modulus of each specimen was then estimated by numerically optimizing the Young's modulus of each model so that simulation results matched corresponding experimental data. Using an estimated value of 12 microm for the thickness of each model eardrum, the estimated average Young's modulus for the pars tensa was found to be 21.7+/-1.2 MPa. The estimated average Young's modulus is within the range reported in some of the literature. The estimation technique is sensitive to the thickness of the pars tensa used in the model but is not sensitive to relatively large variations in the stiffness of the pars flaccida and manubrium or to the pars tensa/pars flaccida separation conditions.

Prostate boundary segmentation from ultrasound images using 2D active shape models: optimisation and extension to 3D

Boundary outlining, or segmentation, of the prostate is an important task in diagnosis and treatment planning for prostate cancer. This paper describes an algorithm based on two-dimensional (2D) active shape models (ASM) for semi-automatic segmentation of the prostate boundary from ultrasound images. Optimisation of the 2D ASM for prostatic ultrasound was done first by examining ASM construction and image search parameters. Extension of the algorithm to three-dimensional (3D) segmentation was then done using rotational-based slicing. Evaluation of the 3D segmentation algorithm used distance- and volume-based error metrics to compare algorithm generated boundary outlines to gold standard (manually generated) boundary outlines. Minimum description length landmark placement for ASM construction, and specific values for constraints and image search were found to be optimal. Evaluation of the algorithm versus gold standard boundaries found an average mean absolute distance of 1.09+/-0.49 mm, an average percent absolute volume difference of 3.28+/-3.16%, and a 5x speed increase versus manual segmentation.

A geometrically nonlinear finite-element model of the cat eardrum

Current finite-element (FE) models of the eardrum are limited to low pressures because of the assumption of linearity. Our objective is to investigate the effects of geometric nonlinearity in FE models of the cat eardrum with an approximately immobile malleus for pressures up to +/-2.2 kPa, which are within the range of pressures used in clinical tympanometry. Displacements computed with nonlinear models increased less than in proportion to applied pressure, similar to what is seen in measured data. In both simulations and experiments, there is a shift inferiorly in the location of maximum displacement in response to increasingly negative middle-ear pressures. Displacement patterns computed for small pressures and for large positive pressures differed from measured patterns in the position of the maximum pars-tensa displacement. Increasing the thickness of the postero-superior pars tensa in the models shifted the location of the computed maximum toward the measured location. The largest computed pars-tensa strains were mostly less than 2%, implying that a linearized material model is a reasonable approximation. Geometric nonlinearity must be considered when simulating eardrum response to high pressures because purely linear models cannot take into account the effects of changing geometry. At higher pressures, material nonlinearity may become more important.