Three-dimensional virtual model of the human temporal bone: a stand-alone, downloadable teaching tool

Mammalian middle ear mechanics: A review

The middle ear is part of the ear in all terrestrial vertebrates. It provides an interface between two media, air and fluid. How does it work? In mammals, the middle ear is traditionally described as increasing gain due to Helmholtz's hydraulic analogy and the lever action of the malleus-incus complex: in effect, an impedance transformer. The conical shape of the eardrum and a frequency-dependent synovial joint function for the ossicles suggest a greater complexity of function than the traditional view. Here we review acoustico-mechanical measurements of middle ear function and the development of middle ear models based on these measurements. We observe that an impedance-matching mechanism (reducing reflection) rather than an impedance transformer (providing gain) best explains experimental findings. We conclude by considering some outstanding questions about middle ear function, recognizing that we are still learning how the middle ear works.

On the hearing effects of a cholesteatoma growing: A biomechanical study

Chronic otitis media enables the appearance of a benign middle ear tumor, known as a cholesteatoma, that may compromise hearing. To evaluate the influence of a cholesteatoma growth on the hearing function, a computational middle ear model based on the finite element method was used and three different size of cholesteatoma were modeled. The cholesteatoma solidification and the consequent degradation of the ossicles were also simulated as two condition that commonly occurs during cholesteatoma evolution. A sound pressure level of 80 dB SPL was applied in the tympanic membrane and a steady state analysis was performed for frequencies from 100 Hz to 10 kHz. The displacements of both the tympanic membrane and the stapes footplate were measured. The results were compared with a healthy case and it was shown that the cholesteatoma development leads to a decrease in the umbo and stapes displacements. The ossicles degradation simulation showed the higher difference comparing with the cholesteatoma in an initial stage, with lower displacements in the stapes footplate mainly for high frequencies. The observed displacement differences are directly connected to hearing loss, being possible to conclude that cholesteatoma evolution in the middle ear will lead to hearing problems, mainly in an advanced stage.

BPPV Viewer: A downloadable 3D BPPV model for study of otolith disease

OBJECTIVE

To develop a downloadable three-dimensional (3D) study tool of the membranous labyrinth in order to facilitate the study of benign paroxysmal positional vertigo (BPPV).

BACKGROUND

The diagnosis and treatment of BPPV depend on an understanding of the anatomy of the vestibular labyrinth and its position relative to the head. To date, many illustrations have been made to explain principles of diagnosis and treatment of BPPV, but few have been based on anatomical studies of the membranous labyrinth.

METHODS

A previously reported 3D model of a human labyrinth was transposed to a 3D development software to allow the creation of markers along the semicircular ducts and utricle. These markers represent otoliths at different positions during movement of the model within the 3D environment. User-friendly tools were created to navigate the model, to allow clear documentation and communication of studied problems, and to study the model across relevant planes. The final model can be downloaded and is available for general useat https://bppvviewer.com/download/.

RESULTS

The model allows visualization of true membranous labyrinth anatomy in both ears simultaneously. The dependent portion of each semicircular duct, the planes of the cristae, and the position of the utricle can easily be visualized in any head position. Moveable markers can mark the expected progress of otolith debris with changes in head position and images can be captured to document simulations in various draw styles.

CONCLUSION

This simple model could offer insights that lead to more accurate diagnosis and treatment of BPPV. It may also be useful as a tool to teach BPPV.

Lateral Modified Brandt-Daroff Exercises: A Novel Home Treatment Technique for Horizontal Canal BPPV

OBJECTIVES

Brandt-Daroff exercises (BDEs) are commonly used as an at-home treatment for posterior canalithiasis, but their efficacy in the treatment of benign paroxysmal positional vertigo (BPPV) of the horizontal canal (HC-BPPV) has not been previously studied. Using biomechanical model simulation, we investigated modifications that may optimize BDE use for HC-BPPV treatment.

MATERIALS AND METHODS

The BPPV Viewer, a three-dimensional model of the human labyrinth, was used to analyze BDE for HC-BPPV treatment. While moving the model through sequential BDE positions, the expected position of otoliths was demonstrated. Treatment steps were adjusted to maximize otolith movement around the canal circumference without compromising otolith repositioning into the semicircular duct's anterior arm. All adjustments were integrated into lateral modified BDEs (LMBDEs) presented here.

RESULTS

By implementing several modifications, BDE can effectively treat HC-BPPV. Model simulation indicates tilting the head 20° upward in the lateral position, instead of 45° specified by the original technique, which significantly increases displacement of otoliths originating from the horizontal duct's anterior and intermediate segments. LMBDE can be performed as a direct two-step sequence without pausing in the upright position before switching sides. If the affected ear is known, positioning the head 45° below horizontal on the unaffected side as a third treatment step can promote actual canal evacuation. These treatment enhancements increase circumferential otolith movement around the canal and may promote horizontal canal evacuation.

CONCLUSION

LMBDEs are a modification of BDE that may increase their effectiveness for use in patients with HC-BPPV. This safe treatment adjunct between office visits may promote long-term symptom reduction.

Short CRP for Anterior Canalithiasis: A New Maneuver Based on Simulation With a Biomechanical Model

Introduction/Objective: Anterior canalithiasis is an uncommon and challenging diagnosis. This is due in part to the difficulty of defining the affected side, the extreme positioning required to carry out described therapeutic maneuvers, and the infrequent use of specific maneuvers. Our objective is to present a new treatment alternative for anterior canalithiasis which is based on the well-known canalith repositioning procedure (CRP) described by Epley and which is used routinely in the treatment of both posterior and anterior canalithiasis. Analysis of the standard CRP for anterior canalithiasis with a biomechanical model validates that this new maneuver is an enhanced treatment option for anterior canalithiasis. We call the new maneuver the “short CRP.”

Methods: A previously published 3D biomechanical model of the human labyrinths for the study of BPPV was used to analyze the conventional CRP in the treatment of anterior canalithiasis. The expected position of free otoliths near the anterior ampulla of the anterior semicircular duct was followed while recreating the sequential positions of the CRP. Although the standard CRP was possibly effective, certain enhancements were evident that could increase successful repositioning. These enhancements were incorporated into the modification of the CRP presented here as the “short CRP” for anterior canalithiasis.

Results: The traditional CRP used for posterior canalithiasis can also be used for anterior canalithiasis. Although in the traditional CRP the head hangs 30° below horizontal, our simulation shows that a 40° head-hang below horizontal is an enhancement and may ensure progression of anterior otolith debris. Elimination of Position 4 of the classic CRP, in which the face is turned 45° toward the floor, was also seen as an enhancement as this position is predicted to cause retrograde movement of otoliths back into the anterior canal if the patient tucks the chin in position 4 or when sitting up.

Conclusion: A modification of the CRP called the “short CRP” can be used to treat anterior canalithiasis. Model analysis predicts possible increased efficacy over the standard CRP. Model analysis of existing BPPV treatments is a valuable exercise for examination and can lead to realistic enhancements in patient care.

Augmented reality-based learning for the comprehension of cardiac physiology in undergraduate biomedical students

The integrated mechanisms of heart contraction are some of the most complex processes for undergraduate biomedical students to understand. Visual models have the potential to enhance learning environments by providing visual representations of complex mechanisms. Despite their benefits, the use of visual models in undergraduate classrooms is still limited. For this study, we tested the effect of a learning sequence of activities related to the cardiac cycle using an augmented reality (AR) application for smartphones and tablets. We were interested in understanding the ability of students to draw and label figures reflecting cardiac function after experiencing the learning sequence using AR. Undergraduate students of the biomedical sciences (control n = 43, experimental n = 58) were enrolled in the course, and their drawings were evaluated using multiple levels of complexity (1 = basic to 5 = complex) through a pre-/posttest structure that included a learning sequence based on AR in the experimental group and regular lecture-based activities in the control group. The complexity of students' drawings was evaluated on the anatomical, physiological, and molecular aspects of heart contraction. We used Cohen's kappa index for interrater reliability when determining the complexity of drawings. Control and experimental groups showed no differences in baseline knowledge (preexamination quiz). The students who experienced the AR activities showed an increase in the complexity of representation levels in posttest results and also showed a significant difference in scores for the final exam in the heart physiology course. Our results indicate that using AR enhances the comprehension of anatomical and physiological concepts of the cardiac cycle for undergraduate biomedical students.

Vestibular Aqueduct Morphology Correlates With Endolymphatic Sac Pathologies in Menière's Disease-A Correlative Histology and Computed Tomography Study

Hypothesis:

The vestibular aqueduct (VA) in Menière's disease (MD) exhibits different angular trajectories depending on the presenting endolymphatic sac (ES) pathology, i.e., 1) ES hypoplasia or 2) ES degeneration.

Background:

Hypoplasia or degeneration of the ES was consistently found in inner ears affected by MD. The two etiologically distinct ES pathologies presumably represent two disease “endotypes,” which may be associated with different clinical traits (“phenotypes”) of MD. Recognizing these endotypes in the clinical setting requires a diagnostic tool.

Methods:

1) Defining the angular trajectory of the VA (ATVA) in the axial plane. 2) Measuring age-dependent normative data for the ATVA in postmortem temporal bone histology material from normal adults and fetuses. 3) Validating ATVA measurements from normative CT imaging data. 4) Correlating the ATVA with different ES pathologies in histological materials and CT imaging data from MD patients.

Results:

1) The ATVA differed significantly between normal adults and MD cases with ES degeneration, as well as between fetuses and MD cases with ES hypoplasia; 2) a strong correlation between ATVA measurements in histological sections and CT imaging data was found; 3) a correlation between the ATVA, in particular its axial trajectory in the opercular region (angle α_exit), with degenerative (α_exit < 120°) and hypoplastic ES pathology (α_exit > 140°) was demonstrated.

Conclusion:

We established the ATVA as a radiographic surrogate marker for ES pathologies. CT-imaging-based determination of the ATVA enables endotyping of MD patients according to ES pathology. Future studies will apply this method to investigate whether ES endotypes distinguish clinically meaningful subgroups of MD patients.

Three-Dimensional Reconstruction of the Semicircular Canals with a Two-Hands Model

Objective

To help understand the anatomy and the diseases of the semicircular canals (SCCs) by defining the three-dimensional reconstruction of the SCCs in a model reconstructed using the two hands (two-hands model) and to determine the three-dimensional configuration of the two hands by measuring the angle between the SCCs and the sagittal plane.

Methods

Patients older than 18 years of age with computed tomography (CT) scans of the temporal bones taken between 2017 and 2018 at the Yeditepe University Hospital were included in the study. CT images were evaluated by a radiologist. The angles between every SCC and the sagittal plane were measured with the MIMICS 12.1 program. Mean angles between the SCCs and the sagittal plane were measured. These angles were demonstrated on the two-hands model of the SCCs by means of a goniometer and photographed.

Results

Thirty patients and 60 temporal bones were included in the study. Mean angles between the superior, the posterior, and the horizontal SCCs and the sagittal plane were found as 37.1±3.3°, 50.4±4.1°, and 89.5±4.7°, respectively.

Conclusion

This is the first study to define the three-dimensional representation of the SCCs with a two-hands model. This may allow for a better understanding and the better teaching of the anatomy and diseases of SCCs.

Morphological validation of a novel bi-material 3D-printed model of temporal bone for middle ear surgery education

Background

A new model of 3D-printed temporal bone with an innovative distinction between soft and hard tissues is described and presented in the present study. An original method is reported to quantify the model's ability to reproduce the complex anatomy of this region.

Methods

A CT-scan of temporal bone was segmented and prepared to obtain 3D files adapted to multi-material printing technique. A final product was obtained with two different resins differentiating hard from soft tissues. The reliability of the anatomy was evaluated by comparing the original CT-scan and the pre-processed files sent to the printer in a first step, and by quantifying the printing technique in a second step. Firstly, we evaluated the segmentation and mesh correction steps by segmenting each anatomical region in the CT-scan by two different other operators without mesh corrections, and by computing distances between the obtained geometries and the pre-processed ones. Secondly, we evaluated the printing technique by comparing the printed geometry imaged using µCT with the pre-processed one.

Results

The evaluation of the segmentation and mesh correction steps revealed that the distance between both geometries was globally less that one millimeter for each anatomical region and close to zero for regions such as temporal bone, semicircular canals or facial nerve. The evaluation of the printing technique revealed mismatches of 0.045±0.424 mm for soft and -0.093±0.240 mm for hard tissues between the initial prepared geometry and the actual printed model.

Conclusions

While other reported models for temporal bone are simpler and have only been validated subjectively, we objectively demonstrated in the present study that our novel artificial bi-material temporal bone is consistent with the anatomy and thus could be considered into ENT surgical education programs. The methodology used in this study is quantitative, inspired by engineer sciences, making it the first of its kind. The validity of the manufacturing process has also been verified and could, therefore, be extended to other specialties, emphasizing the importance of cross-disciplinary collaborations concerning new technologies.

Morphological Immaturity of the Neonatal Organ of Corti and Associated Structures in Humans

Although anatomical development of the cochlear duct is thought to be complete by term birth, human newborns continue to show postnatal immaturities in functional measures such as otoacoustic emissions (OAEs). Some of these OAE immaturities are no doubt influenced by incomplete maturation of the external and middle ears in infants; however, the observed prolongation of distortion-product OAE phase-gradient delays in newborns cannot readily be explained by conductive factors. This functional immaturity suggests that the human cochlea at birth may lack fully adult-like traveling-wave motion. In this study, we analyzed temporal-bone sections at the light microscopic level in newborns and adults to quantify dimensions and geometry of cochlear structures thought to influence the mechanical response of the cochlea. Contrary to common belief, results show multiple morphological immaturities along the length of the newborn spiral, suggesting that important refinements in the size and shape of the sensory epithelium and associated structures continue after birth. Specifically, immaturities of the newborn basilar membrane and organ of Corti are consistent with a more compliant and less massive cochlear partition, which could produce longer DPOAE delays and a shifted frequency-place map in the neonatal ear.

Clinical Imaging Findings of Vestibular Aqueduct Trauma in a Patient With Posttraumatic Meniere's Syndrome

Posttraumatic Meniere's syndrome is a rare clinical entity. The pathomechanism by which temporal bone trauma leads to fluctuating audiovestibular symptoms, in some cases with a delay of onset many years after trauma, remains elusive. Here, a clinical case and the respective temporal bone imaging data were reviewed to investigate the underlying inner ear pathology. A 44-year-old patient presented with left-sided Meniere's syndrome 34 years after he suffered an ipsilateral temporal bone fracture caused by a car accident. Clinical imaging showed left cochleovestibular hydrops (gadolinium-enhanced MRI) and bony obliteration of the left VA (CT imaging), resulting in discontinuity of the ES. Our findings suggest that a temporal bone fracture with a “retrolabyrinthine” course, traversing the VA, caused intraaqueductal callus bone formation and progressive blockage of the VA. As a result, the extraosseous (distal) endolymphatic sac (eES) became separated from the cochleovestibular labyrinth, an event that presumably underlies endolymphatic hydrops formation and that precipitates the onset of clinical Meniere's symptoms in this case.

Qualitative analysis of the Dix-Hallpike maneuver in multi-canal BPPV using a biomechanical model: Introduction of an expanded Dix-Hallpike maneuver for enhanced diagnosis of multi-canal BPPV

INTRODUCTION/OBJECTIVE

Multiple canal BPPV can be a diagnostic challenge to the clinician. This is due in part to the complex anatomy of the labyrinth but also to complex and often simultaneous ocular responses that result from stimulation of multiple canals during traditional diagnostic testing. Our objective was to analyze the Dix-Hallpike maneuver used in the diagnosis of BPPV to look for patterns of simultaneous canal response and to develop a diagnostic maneuver that will allow separation of canal responses in multiple canal BPPV.

METHODS

A previously created and published 3D biomechanical model of the human labyrinths for the study of BPPV was used to analyze and compare the position and movement of otoliths in the Dix-Hallpike maneuver as well as in a proposed expanded version of the traditional Dix-Hallpike maneuver.

RESULTS

The traditional Dix-Hallpike maneuver with the head hanging may promote movement of otoliths in 5 of the six semicircular canals. The Dix-Hallpike maneuver with the head lowered only to the horizontal position allows for otoconia in only the lowermost posterior canal to fall to the most gravity dependent position. This position allows for minimal or no movement of otoconia in the contralateral posterior canal, or in either superior canal. Turning the head ninety degrees to the opposite side while still in the horizontal position will provoke otolith movement in only the contralateral posterior canal. The superior canals can then be examined for free otolith debris by extending the neck to a head-hanging position. These positions may be assumed directly from one to the next in the lying position. There seems to be no advantage to sitting up between positions.

CONCLUSION

The Dix-Hallpike maneuver may cause simultaneous movement of otoliths present in multiple canals and create an obstacle to accurate diagnosis in multi-canal BPPV. An expanded Dix-Hallpike maneuver is described which adds intermediate steps with the head positioned to the right and left in the horizontal position before head-hanging. This expanded maneuver has helped to isolate affected semi-circular canals for individual assessment in multiple canal BPPV.

Dynamic property changes in stapedial annular ligament associated with acute otitis media in the chinchilla

Located at the end of the ossicular chain, the stapedial annular ligament (SAL) serves as a closed yet mobile boundary between the cochlear fluid and stapes footplate. It is unclear how SAL properties change with acute otitis media (AOM). This paper reports the measurements of SAL dynamic properties in chinchilla AOM model using dynamic mechanical analyzer (DMA) and frequency-temperature superposition (FTS) principle. AOM was analyzed in two infection groups: 4 days (4D) and 8 days (8D) post induction. SAL specimens were measured using DMA at three temperatures: 5, 25, and 37°C. To extend the testing frequencies to higher levels, FTS principle was employed. Then generalized Maxwell model was utilized to define the constitutive equations of the SAL. The complex shear moduli were obtained from seven samples of control, 4D, and 8D groups. Results show that the storage and loss shear moduli of SALs decreased due to AOM. The storage moduli for 4D and 8D ears were similar below 100Hz, and the loss modulus for 4D was significantly larger than 8D across the entire frequency range. This study reports data that contributes to ear biomechanics and improves understanding on the effects of AOM in middle ear tissues.

Establishing a Temporal Bone Laboratory in Teaching Institutes to Train Future Otorhinolaryngologists and Fundamentals of Temporal Bone Laboratory: Considerations and Requirements

Temporal bone dissection has important role in educating, and training the surgeons. Temporal bone has complicated three dimensional anatomy and it is challenging for young surgeons to understand and operate. Not knowing the anatomy may cause serious consequences to patient due to injury to vital structures. It is important to learn temporal bone harvesting techniques, preservation of specimens, fixation and to reduce the health hazards posed by these specimens by taking safety measures. Spending more time in temporal bone laboratory and repeated dissection of temporal bones provides the skills necessary in the operating room for future generation. All training institutes should establish temporal bone laboratory in their department to provide the necessary expertise to future generation while maintaining safe and secure environment.

A 3D benign paroxysmal positional vertigo model for study of otolith disease

Objective

To develop a three-dimensional study tool of the membranous labyrinth in order to study the pathophysiology, diagnostic workup and treatment of benign paroxysmal positional vertigo (BPPV). BPPV is the most common cause of peripheral vertigo. Its diagnosis and treatment depend on an understanding of the anatomy of the vestibular labyrinth and its position relative to the head. To date, many illustrations have been made to explain principals of diagnosis and treatment of BPPV, but few have been based on anatomical studies of the membranous labyrinth.

Methods

A cadaveric human membranous labyrinth was axially sectioned at 20 μm resolution, stained and segmented to create a high-resolution digital model. The model was cloned to create an enantiomeric pair of labyrinths. These were associated a 3D model of a human skull, segmented from MRI data, and were oriented according to established anatomic norms. Canal markers representing otoliths were created to mark canalith position during movement of the model within the 3D environment.

Results

The model allows visualization of true membranous labyrinth anatomy in both ears simultaneously. The dependent portion of each semicircular duct and of the utricle can easily be visualized in any head position. Moveable markers can mark the expected progress of otolith debris with changes in head position and images can be captured to document simulations. The model can be used to simulate pathology as well as diagnostic maneuvers and treatment procedures used for BPPV. The model has great potential as a teaching tool.

Conclusion

A simple model based on human anatomy has been created to allow careful study of BPPV pathophysiology and treatment. Going forward, this tool could offer insights that may lead to more accurate diagnosis and treatment of BPPV.

Dynamic properties of human stapedial annular ligament measured with frequency-temperature superposition

Stapedial annular ligament (SAL) is located at the end of human ear ossicular chain and provides a sealed but mobile boundary between the stapes footplate and cochlear fluid. Mechanical properties of the SAL directly affect the acoustic-mechanical transmission of the middle ear and the changes of SAL mechanical properties in diseases (e.g., otosclerosis) may cause severe conductive hearing loss. However, the mechanical properties of SAL have only been reported once in the literature, which were obtained under quasi-static condition (Gan, R. Z., Yang, F., Zhang, X., and Nakmali, D., 2011, "Mechanical Properties of Stapedial Annular Ligament," Med. Eng. Phys., 33, pp. 330-339). Recently, the dynamic properties of human SAL were measured in our lab using dynamic-mechanical analyzer (DMA). The test was conducted at the frequency range from 1 to 40 Hz at three different temperatures: 5 °C, 25 °C, and 37 °C. The frequency-temperature superposition (FTS) principle was applied to extend the testing frequency range to a much higher level. The generalized Maxwell model was employed to describe the constitutive relation of the SAL. The storage shear modulus G' and the loss shear modulus G" were obtained from seven specimens. The mean storage shear modulus was 31.7 kPa at 1 Hz and 61.9 kPa at 3760 Hz. The mean loss shear modulus was 1.1 kPa at 1 Hz and 6.5 kPa at 3760 Hz. The dynamic properties of human SAL obtained in this study provide a better description of the damping behavior of soft tissues than the classic Rayleigh type damping, which was widely used in the published ear models. The data reported in this study contribute to ear biomechanics and will improve the accuracy of finite element (FE) model of the human ear.

Differences in the diameter of facial nerve and facial canal in bell's palsy--a 3-dimensional temporal bone study

Bell's palsy is hypothesized to result from virally mediated neural edema. Ischemia occurs as the nerve swells in its bony canal, blocking neural blood supply. Because viral infection is relatively common and Bell's palsy relatively uncommon, it is reasonable to hypothesize that there are anatomic differences in facial canal (FC) that predispose the development of paralysis. Measurements of facial nerve (FN) and FC as it follows its tortuous course through the temporal bone are difficult without a 3D view. In this study, 3D reconstruction was used to compare temporal bones of patients with and without history of Bell's palsy.

METHODS

Twenty-two temporal bones (HTBs) were included in the study, 12 HTBs from patients with history of Bell's palsy and 10 healthy controls. Three-dimensional models were generated from HTB histopathologic slides with reconstruction software (Amira), diameters of the FC and FN were measured at the midpoint of each segment.

RESULTS

The mean diameter of the FC and FN was significantly smaller in the tympanic and mastoid segments (p = 0.01) in the BP group than in the controls. The FN to FC diameter ratio (FN/FC) was significantly bigger in the mastoid segment of BP group, when compared with the controls. When comparing the BP and control groups, the narrowest part of FC was the labyrinthine segment in control group and the tympanic segment in the BP.

CONCLUSION

This study suggests an anatomic difference in the diameter of FC in the tympanic and mastoid segments but not in the labyrinthine segment in patients with Bell's palsy.

Magnetic vestibular stimulation in subjects with unilateral labyrinthine disorders

We recently discovered that static magnetic fields from high-strength MRI machines induce nystagmus in all normal humans, and that a magneto-hydrodynamic Lorentz force, derived from ionic currents in the endolymph and pushing on the cupula, best explains this effect. Individuals with no labyrinthine function have no nystagmus. The influence of magnetic vestibular stimulation (MVS) in individuals with unilateral deficits in labyrinthine function is unknown and may provide insight into the mechanism of MVS. These individuals should experience MVS, but with a different pattern of nystagmus consistent with their unilateral deficit in labyrinthine function. We recorded eye movements in the static magnetic field of a 7 T MRI machine in nine individuals with unilateral labyrinthine hypofunction, as determined by head impulse testing and vestibular-evoked myogenic potentials (VEMP). Eye movements were recorded using infrared video-oculography. Static head positions were varied in pitch with the body supine, and slow-phase eye velocity (SPV) was assessed. All subjects exhibited predominantly horizontal nystagmus after entering the magnet head-first, lying supine. The SPV direction reversed when entering feet-first. Pitching chin-to-chest caused subjects to reach a null point for horizontal SPV. Right unilateral vestibular hypofunction (UVH) subjects developed slow-phase-up nystagmus and left UVH subjects, slow-phase-down nystagmus. Vertical and torsional components were consistent with superior semicircular canal excitation or inhibition, respectively, of the intact ear. These findings provide compelling support for the hypothesis that MVS is a result of a Lorentz force and suggest that the function of individual structures within the labyrinth can be assessed with MVS. As a novel method of comfortable and sustained labyrinthine stimulation, MVS can provide new insights into vestibular physiology and pathophysiology.

Three-dimensional histological specimen preparation for accurate imaging and spatial reconstruction of the middle and inner ear

PURPOSE

This paper presents a highly accurate cross-sectional preparation technique. The research aim was to develop an adequate imaging modality for both soft and bony tissue structures featuring high contrast and high resolution. Therefore, the advancement of an already existing micro-grinding procedure was pursued. The central objectives were to preserve spatial relations and to ensure the accurate three-dimensional reconstruction of histological sections.

METHODS

Twelve human temporal bone specimens including middle and inner ear structures were utilized. They were embedded in epoxy resin, then dissected by serial grinding and finally digitalized. The actual abrasion of each grinding slice was measured using a tactile length gauge with an accuracy of one micrometre. The cross-sectional images were aligned with the aid of artificial markers and by applying a feature-based, custom-made auto-registration algorithm. To determine the accuracy of the overall reconstruction procedure, a well-known reference object was used for comparison. To ensure the compatibility of the histological data with conventional clinical image data, the image stacks were finally converted into the DICOM standard.

RESULTS

The image fusion of data from temporal bone specimens' and from non-destructive flat-panel-based volume computed tomography confirmed the spatial accuracy achieved by the procedure, as did the evaluation using the reference object.

CONCLUSION

This systematic and easy-to-follow preparation technique enables the three-dimensional (3D) histological reconstruction of complex soft and bony tissue structures. It facilitates the creation of detailed and spatially correct 3D anatomical models. Such models are of great benefit for image-based segmentation and planning in the field of computer-assisted surgery as well as in finite element analysis. In the context of human inner ear surgery, three-dimensional histology will improve the experimental evaluation and determination of intra-cochlear trauma after the insertion of an electrode array of a cochlear implant system.

Experimental measurement and modeling analysis on mechanical properties of incudostapedial joint

The incudostapedial (IS) joint between the incus and stapes is a synovial joint consisting of joint capsule, cartilage, and synovial fluid. The mechanical properties of the IS joint directly affect the middle ear transfer function for sound transmission. However, due to the complexity and small size of the joint, the mechanical properties of the IS joint have not been reported in the literature. In this paper, we report our current study on mechanical properties of human IS joint using both experimental measurement and finite element (FE) modeling analysis. Eight IS joint samples with the incus and stapes attached were harvested from human cadaver temporal bones. Tension, compression, stress relaxation and failure tests were performed on those samples in a micro-material testing system. An analytical approach with the hyperelastic Ogden model and a 3D FE model of the IS joint including the cartilage, joint capsule, and synovial fluid were employed to derive mechanical parameters of the IS joint. The comparison of measurements and modeling results reveals the relationship between the mechanical properties and structure of the IS joint.

Realistic 3D computer model of the gerbil middle ear, featuring accurate morphology of bone and soft tissue structures

In order to improve realism in middle ear (ME) finite-element modeling (FEM), comprehensive and precise morphological data are needed. To date, micro-scale X-ray computed tomography (μCT) recordings have been used as geometric input data for FEM models of the ME ossicles. Previously, attempts were made to obtain these data on ME soft tissue structures as well. However, due to low X-ray absorption of soft tissue, quality of these images is limited. Another popular approach is using histological sections as data for 3D models, delivering high in-plane resolution for the sections, but the technique is destructive in nature and registration of the sections is difficult. We combine data from high-resolution μCT recordings with data from high-resolution orthogonal-plane fluorescence optical-sectioning microscopy (OPFOS), both obtained on the same gerbil specimen. State-of-the-art μCT delivers high-resolution data on the 3D shape of ossicles and other ME bony structures, while the OPFOS setup generates data of unprecedented quality both on bone and soft tissue ME structures. Each of these techniques is tomographic and non-destructive and delivers sets of automatically aligned virtual sections. The datasets coming from different techniques need to be registered with respect to each other. By combining both datasets, we obtain a complete high-resolution morphological model of all functional components in the gerbil ME. The resulting 3D model can be readily imported in FEM software and is made freely available to the research community. In this paper, we discuss the methods used, present the resulting merged model, and discuss the morphological properties of the soft tissue structures, such as muscles and ligaments.

Anatomy of the round window and hook region of the cochlea with implications for cochlear implantation and other endocochlear surgical procedures

HYPOTHESIS

The goal of this study was to create a three-dimensional model of the anatomy of the hook region to identify the optimal site for cochleostomy in cochlear implant surgery.

BACKGROUND

The anatomy of the hook region is complex, and spatial relationships can be difficult to evaluate using two-dimensional histological slides or cadaveric temporal bones.

METHODS

The right temporal bone of a 14-year-old adolescent boy was used to create a three-dimensional model. Sections containing the round window membrane (RWM) and surrounding cochlear structures were stained, digitized, and imported into a general purpose three-dimensional rendering and analysis software program (Amira, version 4.1). Three-dimensional models of the RWM, basilar membrane, osseous spiral lamina, spiral ligament, cochlear aqueduct, inferior cochlea vein, scala media, ductus reuniens, scala vestibuli, scala tympani, and surrounding bone were generated. The relationship between these structures and the RWM and adjacent otic capsule was evaluated. Histological sections from a different temporal bone were also analyzed. This temporal bone was sectioned in a plane perpendicular to the axis corresponding to the surgical view of the RWM, seen through the facial recess.

RESULTS

The anteroinferior margin of the RWM or adjacent otic capsule was identified as the site for a cochleostomy that will avoid damage to critical cochlear structures and allow implantation directly into the scala tympani. The model can be downloaded from: https://research.meei.harvard.edu/otopathology/3dmodels.

CONCLUSION

This three-dimensional model has implications for surgical procedures to the inner ear that aim to minimize insertional trauma.

A downloadable three-dimensional virtual model of the visible ear

PURPOSE

To develop a three-dimensional (3-D) virtual model of a human temporal bone and surrounding structures.

METHODS

A fresh-frozen human temporal bone was serially sectioned and digital images of the surface of the tissue block were recorded (the 'Visible Ear'). The image stack was resampled at a final resolution of 50 x 50 x 50/100 micro m/voxel, registered in custom software and segmented in PhotoShop 7.0. The segmented image layers were imported into Amira 3.1 to generate smooth polygonal surface models.

RESULTS

The 3-D virtual model presents the structures of the middle, inner and outer ears in their surgically relevant surroundings. It is packaged within a cross-platform freeware, which allows for full rotation, visibility and transparency control, as well as the ability to slice the 3-D model open at any section. The appropriate raw image can be superimposed on the cleavage plane. The model can be downloaded at: (https://research.meei.harvard.edu/Otopathology/3dmodels/).