A downloadable three-dimensional virtual model of the visible ear

Cochlear implant surgery: Learning curve in virtual reality simulation training and transfer of skills to a 3D-printed temporal bone - A prospective trial

OBJECTIVE

Mastering Cochlear Implant (CI) surgery requires repeated practice, preferably initiated in a safe - i.e. simulated - environment. Mastoidectomy Virtual Reality (VR) simulation-based training (SBT) is effective, but SBT of CI surgery largely uninvestigated. The learning curve is imperative for understanding surgical skills acquisition and developing competency-based training. Here, we explore learning curves in VR SBT of CI surgery and transfer of skills to a 3D-printed model.

METHODS

Prospective, single-arm trial. Twenty-four novice medical students completed a pre-training CI inserting test on a commercially available pre-drilled 3D-printed temporal bone. A training program of 18 VR simulation CI procedures was completed in the Visual Ear Simulator over four sessions. Finally, a post-training test similar to the pre-training test was completed. Two blinded experts rated performances using the validated Cochlear Implant Surgery Assessment Tool (CISAT). Performance scores were analyzed using linear mixed models.

RESULTS

Learning curves were highly individual with primary performance improvement initially, and small but steady improvements throughout the 18 procedures. CI VR simulation performance improved 33% (p < 0.001). Insertion performance on a 3D-printed temporal bone improved 21% (p < 0.001), demonstrating skills transfer.

DISCUSSION

VR SBT of CI surgery improves novices' performance. It is useful for introducing the procedure and acquiring basic skills. CI surgery training should pivot on objective performance assessment for reaching pre-defined competency before cadaver - or real-life surgery. Simulation-based training provides a structured and safe learning environment for initial training.

CONCLUSION

CI surgery skills improve from VR SBT, which can be used to learn the fundamentals of CI surgery.

Embedding interactive, three-dimensional content in portable document format to deliver gross anatomy information and knowledge

The Portable Document Format (PDF) is likely the most widely used digital file format for scholarly and scientific electronic publishing. Since format specification version 1.6, three-dimensional (3D) models in Universal 3D (U3D) format can be embedded into PDF files. The present study demonstrates a repertoire of graphic strategies and modes of presentation that exploit the potentials of 3D models embedded in PDF to deliver anatomical information and knowledge. Three-dimensional models and scenes representing anatomical structures generated by 3D surface scanning or by segmentation from either clinical imaging data or cadaver sectional images were converted into U3D format and then embedded into PDF files using both freely and commercially available software. The relevant steps and required software tools are described. Built-in tools in Adobe Acrobat and JavaScript scripting both were used to pre-configure user interaction with 3D contents. Eight successive proof-of-concept examples of increasing complexity are presented and provided as supplementary material, including both unannotated and annotated 3D specimens, use of bitmap-textures, guided navigation through predetermined 3D scenes, 3D animation, and interactive navigation through tri-planar sectional human cadaver images. Three-dimensional contents embedded in PDF files are generally comparable to multimedia and dedicated 3D software in terms of quality, flexibility, and convenience, and offer new unprecedented opportunities to deliver anatomical information and knowledge.

Micro-anatomy of the ear of the southern white rhinoceros (Ceratotherium simum simum)

The white rhinoceros is the largest of the five extant rhinoceros species. The population is declining rapidly because of intense poaching. However, normal anatomical descriptions in this species are lacking. The purpose of this study is to describe the osseous anatomy of the middle and inner ear of the southern white rhinoceros using micro-focus X-ray computed tomography imaging. Four temporal bones obtained from two 1-day old southern white rhinoceros preserved in 10% formalin were scanned. Tri-dimensional reconstructions were obtained and volumes of the middle ear ossicles and inner ear structures were calculated. Excellent high spatial resolution 3D images were obtained for all samples and virtual models of the auditory ossicles and bony labyrinth were generated. Visualization of the tympanic membrane, middle ear and inner ear structures was possible in all samples. Whereas the stapes and incus had a shape similar to their human or equine counterparts, the malleus showed a unique appearance with a long rostral branch projecting latero-distally to the manubrium. The cochlea described 2 turns rostro-laterally around its axis, with a medial direction of rotation. However, identification of the soft tissue structures of the middle ear was sometimes difficult and visualization of the small structures of the membranous labyrinth was not possible using this formalin fixation and alternative techniques should be investigated. Further investigations are needed in order to provide a complete virtual model including both soft and bone tissues of this difficultly accessible region.

Reprint of Corrosion casting of the temporal bone: Review of the technique

The temporal bone has the most sophisticated anatomy of the whole skeleton. Its study is a challenge for students and surgeons. An inverse model of the visually obscured cavities and canals can facilitate better three-dimensional orientation and investigation. This can be made by means of corrosion casting, which is an established technique first documented on the temporal bone at the beginning of the nineteenth century. The prepared specimens are suitable not only for teaching purposes but also for research on the fascinating topography of the osseous labyrinth and the whole temporal bone. Many important studies on temporal bone anatomy are based on this technique. An extensive review of the pertinent literature is provided in relation to each method available.

Corrosion casting of the temporal bone: Review of the technique

The temporal bone has the most sophisticated anatomy of the whole skeleton. Its study is a challenge for students and surgeons. An inverse model of the visually obscured cavities and canals can facilitate better three-dimensional orientation and investigation. This can be made by means of corrosion casting, which is an established technique first documented on the temporal bone at the beginning of the nineteenth century. The prepared specimens are suitable not only for teaching purposes but also for research on the fascinating topography of the osseous labyrinth and the whole temporal bone. Many important studies on temporal bone anatomy are based on this technique. An extensive review of the pertinent literature is provided in relation to each method available.

Human Otopathology of Cochlear Implant Drill-out Procedures

OBJECTIVE

Human otopathology following drill-out procedures for cochlear implantation (CI) in cases with labyrinthitis ossificans (LO) has not been previously described. This study uses the high sensitivity of histopathology to (1) evaluate surgical drill-out technique with associated intracochlear findings and (2) quantify spiral ganglion neuron populations in a series of patients with LO who underwent CI.

STUDY DESIGN

Retrospective otopathology study.

SETTING

Otopathology laboratory.

SUBJECTS AND METHODS

Temporal bone (TB) specimens from cases with evidence of preoperative intracochlear fibroossification that required a drill-out procedure for CI electrode array insertion were included. All cases were histopathologically evaluated and 3-dimensional reconstructions of the cochleae were performed to interpret drilling paths and electrode trajectories.

RESULTS

Five TB specimens were identified, of which 4 underwent drill-out of the basal turn of the cochlea and 1 underwent a radical cochlear drill-out. In multiple TBs, drilling was imprecise with resultant damage to essential structures. Two TBs showed injury to the modiolus, which was associated with substantially decreased or even absent neuronal populations within these areas. In addition, 2 cases with inadequate drill-out or extensive LO of the basal turn resulted in extracochlear placement of electrode arrays into the vestibule due to persistent obstruction within the basal turn.

CONCLUSION

Otopathology highlights the challenges of drill-out procedures in cases of LO. Imprecise drilling paths, due to distortion of normal cochlear anatomy, risk injury to the modiolus and adjacent neurons as well as extracochlear placement of electrode arrays, both of which may contribute to poorer hearing outcomes.

The human otitis media with effusion: a numerical-based study

Otitis media is a group of inflammatory diseases of the middle ear. Acute otitis media and otitis media with effusion (OME) are its two main types of manifestation. Otitis media is common in children and can result in structural alterations in the middle ear which will lead to hearing losses. This work studies the effects of an OME on the sound transmission from the external auditory meatus to the inner ear. The finite element method was applied on the present biomechanical study. The numerical model used in this work was built based on the geometrical information obtained from The visible ear project. The present work explains the mechanisms by which the presence of fluid in the middle ear affects hearing by calculating the magnitude, phase and reduction of the normalized umbo velocity and also the magnitude and phase of the normalized stapes velocity. A sound pressure level of 90 dB SPL was applied at the tympanic membrane. The harmonic analysis was performed with the auditory frequency varying from 100 Hz to 10 kHz. A decrease in the response of the normalized umbo and stapes velocity as the tympanic cavity was filled with fluid was obtained. The decrease was more accentuated at the umbo.

Finite element modelling of sound transmission from outer to inner ear

The ear is one of the most complex organs in the human body. Sound is a sequence of pressure waves, which propagates through a compressible media such as air. The pinna concentrates the sound waves into the external auditory meatus. In this canal, the sound is conducted to the tympanic membrane. The tympanic membrane transforms the pressure variations into mechanical displacements, which are then transmitted to the ossicles. The vibration of the stapes footplate creates pressure waves in the fluid inside the cochlea; these pressure waves stimulate the hair cells, generating electrical signals which are sent to the brain through the cochlear nerve, where they are decoded. In this work, a three-dimensional finite element model of the human ear is developed. The model incorporates the tympanic membrane, ossicular bones, part of temporal bone (external auditory meatus and tympanic cavity), middle ear ligaments and tendons, cochlear fluid, skin, ear cartilage, jaw and the air in external auditory meatus and tympanic cavity. Using the finite element method, the magnitude and the phase angle of the umbo and stapes footplate displacement are calculated. Two slightly different models are used: one model takes into consideration the presence of air in the external auditory meatus while the other does not. The middle ear sound transfer function is determined for a stimulus of 60 dB SPL, applied to the outer surface of the air in the external auditory meatus. The obtained results are compared with previously published data in the literature. This study highlights the importance of external auditory meatus in the sound transmission. The pressure gain is calculated for the external auditory meatus.

Using 3D Modeling Techniques to Enhance Teaching of Difficult Anatomical Concepts

RATIONALE AND OBJECTIVES

Anatomy is an essential component of medical education as it is critical for the accurate diagnosis in organs and human systems. The mental representation of the shape and organization of different anatomical structures is a crucial step in the learning process. The purpose of this pilot study is to demonstrate the feasibility and benefits of developing innovative teaching modules for anatomy education of first-year medical students based on three-dimensional (3D) reconstructions from actual patient data.

MATERIALS AND METHODS

A total of 196 models of anatomical structures from 16 anonymized computed tomography datasets were generated using the 3D Slicer open-source software platform. The models focused on three anatomical areas: the mediastinum, the upper abdomen, and the pelvis. Online optional quizzes were offered to first-year medical students to assess their comprehension in the areas of interest. Specific tasks were designed for students to complete using the 3D models.

RESULTS

Scores of the quizzes confirmed a lack of understanding of 3D spatial relationships of anatomical structures despite standard instruction including dissection. Written task material and qualitative review by students suggested that interaction with 3D models led to a better understanding of the shape and spatial relationships among structures, and helped illustrate anatomical variations from one body to another.

CONCLUSIONS

The study demonstrates the feasibility of one possible approach to the generation of 3D models of the anatomy from actual patient data. The educational materials developed have the potential to supplement the teaching of complex anatomical regions and help demonstrate the anatomical variation among patients.

Three-Dimensional Histological Structures of the Human Dermis

Spatial information has been shown to be critical for cell differentiation and function. Therefore, a better understanding of skin microstructures is very important for biomimetic and bioengineered scaffolds of engineering skin. The purpose of the study was to generate collagen/elastin-based three-dimensional (3D) images of human dermis to further understand the microstructures of the skin, which is believed to be helpful in the fabrication of bionic engineered skin. Skin samples were fixed, embedded, serially sectioned, stained with aldehyde-fuchsin, and photographed as serial panoramas. Dermal subregions were divided according to dermal depth and distance to hair follicle. The porosity, pore diameters, and wall thickness of human acellular dermal matrix (ADM) were measured by microcomputed tomography (micro-CT). Three-dimensional reconstructed images of collagen and elastic fibers were generated. Our results showed that there were fewer elastic fibers in the subregions close to hair follicles than in the subregions far away from hair follicles (p<0.001), but the collagen fibers were evenly distributed. Both collagen and elastic fibers were found in fewer numbers in the layers either close to the epidermis or close to the hypodermis. The mean proportions of collagen fibers and elastic fibers in the whole dermis were 28.96%±14.63% and 8.06%±3.75%, respectively. The porosity of ADM calculated by micro-CT was 68.3%±5.8%. The mean pore diameter of ADM was 131.2±96.8 μm, and the wall thickness of pores was 207.2±251.7 μm. This study represents for the first time that 3D histological cutaneous structures have been presented, which may be helpful for the next generation of skin engineering.

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.

Reconstruction of cochlea based on micro-CT and histological images of the human inner ear

The study of the normal function and pathology of the inner ear has unique difficulties as it is inaccessible during life and, so, conventional techniques of pathologic studies such as biopsy and surgical excision are not feasible, without further impairing function. Mathematical modelling is therefore particularly attractive as a tool in researching the cochlea and its pathology. The first step towards efficient mathematical modelling is the reconstruction of an accurate three dimensional (3D) model of the cochlea that will be presented in this paper. The high quality of the histological images is being exploited in order to extract several sections of the cochlea that are not visible on the micro-CT (mCT) images (i.e., scala media, spiral ligament, and organ of Corti) as well as other important sections (i.e., basilar membrane, Reissner membrane, scala vestibule, and scala tympani). The reconstructed model is being projected in the centerline of the coiled cochlea, extracted from mCT images, and represented in the 3D space. The reconstruction activities are part of the SIFEM project, which will result in the delivery of an infrastructure, semantically interlinking various tools and libraries (i.e., segmentation, reconstruction, and visualization tools) with the clinical knowledge, which is represented by existing data, towards the delivery of a robust multiscale model of the inner ear.

Evaluation of a temporal bone prototype by experts in otology

BACKGROUND

Inexperienced otologists require training on the temporal bone drilling process, prior to any surgical activity. The shortage of cadaveric temporal bones exerts pressure to create realistic physical prototypes. This paper describes the evaluation by otology experts of a specially developed temporal bone resin model.

METHODS

Computed tomography images were transformed into digital files, and anatomically identical right temporal bone models were created using stereolithography. These hand-painted resin prototypes were sent to 25 otologists, accompanied by a 20-item questionnaire.

RESULTS

Satisfaction rate was 92 per cent. The overall prototype score was 48.87 out of 60. Average scores were: 12.63 out of 15 for anatomy-morphology, 6.98 out of 9 for quality of drilling, 16.74 out of 21 for identification of anatomical elements and 7.41 out of 9 for stages of drilling. Limitations of the model included an excessively vivid facial nerve colour and difficulty in identifying the posterior semicircular canal. Disadvantages related to the thickness of the resin and its residues were identified.

CONCLUSION

The prototype appears to provide an attractive solution to the shortage of cadaveric temporal bones. However, interest in the model for drilling technique training for inexperienced otologists has not yet been assessed.

Freely-available, true-color volume rendering software and cryohistology data sets for virtual exploration of the temporal bone anatomy

BACKGROUND

Cadaveric dissection of temporal bone anatomy is not always possible or feasible in certain educational environments. Volume rendering using CT and/or MRI helps understanding spatial relationships, but they suffer in nonrealistic depictions especially regarding color of anatomical structures. Freely available, nonstained histological data sets and software which are able to render such data sets in realistic color could overcome this limitation and be a very effective teaching tool.

METHODS

With recent availability of specialized public-domain software, volume rendering of true-color, histological data sets is now possible. We present both feasibility as well as step-by-step instructions to allow processing of publicly available data sets (Visible Female Human and Visible Ear) into easily navigable 3-dimensional models using free software.

RESULTS

Example renderings are shown to demonstrate the utility of these free methods in virtual exploration of the complex anatomy of the temporal bone. After exploring the data sets, the Visible Ear appears more natural than the Visible Human.

CONCLUSION

We provide directions for an easy-to-use, open-source software in conjunction with freely available histological data sets. This work facilitates self-education of spatial relationships of anatomical structures inside the human temporal bone as well as it allows exploration of surgical approaches prior to cadaveric testing and/or clinical implementation.

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.

Transcanal approach for implantation of a cochlear nerve electrode array

OBJECTIVES/HYPOTHESIS

To evaluate a transcanal approach for placement of a stimulating electrode array in the cochlear nerve.

STUDY DESIGN

Prospective cadaveric temporal bone study.

METHODS

Ten human cadaveric temporal bones were dissected. Both a facial recess approach with mastoidectomy and a transcanal approach using the novel technique were performed in each bone. A middle fossa dissection of the internal auditory canal was performed to confirm the position of the electrode in the cochlear nerve.

RESULTS

The transcanal approach offered a direct approach to the cochlear nerve in all 10 bones. The procedure was quicker than the facial recess approach and did not endanger the facial or chorda tympani nerves. Inspection of the medial end of the internal auditory canal confirmed correct placement of the electrode in the cochlear nerve. In contrast, anatomical constraints, specifically the position of the facial nerve, blocked access to the cochlear nerve by the facial recess approach in three of the specimens to achieve the exposure to place the electrode at a perpendicular angle to the cochlear nerve. Sacrifice of the chorda tympani was necessary in five of the seven bones in which the cochlear nerve could be accessed.

CONCLUSIONS

The transcanal approach offers a simpler, safer approach for cochlear nerve implantation compared to the facial recess approach. This approach can be accomplished in less time and avoids the hazards of dissection around the facial nerve. Use of the proposed approach will facilitate development of intraneural stimulation for an improved auditory prosthesis.

Virtual exploration and comparison of linear mastoid drilling trajectories with true-color volume rendering and the visible ear dataset

This paper provides instructions for a virtual exploration and self-study of surgical approaches within the temporal bone. Linear drilling trajectories in the sense of "keyhole" accesses are compared with true-color rendering techniques using freeware to introduce and evaluate new otologic approaches. On the basis of public-domain cyro-histology image data from a temporal bone six different drill trajectories are presented. This virtual method has the potential to be a first step in investigation of new surgical approaches before moving to cadaver testing.

Three-dimensional representation of the human cochlea using micro-computed tomography data: presenting an anatomical model for further numerical calculations

CONCLUSION

We present a complete geometric model of the human cochlea, including the segmentation and reconstruction of the fluid-filled chambers scala tympani and scala vestibuli, the lamina spiralis ossea and the vibrating structure (cochlear partition).

OBJECTIVE

Future fluid-structure coupled simulations require a reliable geometric model of the cochlea. The aim of this study was to present an anatomical model of the human cochlea, which can be used for further numerical calculations.

METHODS

Using high resolution micro-computed tomography (µCT), we obtained images of a cut human temporal bone with a spatial resolution of 5.9 µm. Images were manually segmented to obtain the three-dimensional reconstruction of the cochlea.

RESULTS

Due to the high resolution of the µCT data, a detailed examination of the geometry of the twisted cochlear partition near the oval and the round window as well as the precise illustration of the helicotrema was possible. After reconstruction of the lamina spiralis ossea, the cochlear partition and the curved geometry of the scala vestibuli and the scala tympani were presented. The obtained data sets were exported as standard lithography (stl) files. These files represented a complete framework for future numerical simulations of mechanical (acoustic) wave propagation on the cochlear partition in the form of mathematical mechanical cochlea models. Additional quantitative information concerning heights, lengths and volumes of the scalae was found and compared with previous results.

The Usefulness of Reconstructed 3D Images in Surgical Planning for Cochlear Implantation in a Malformed Ear with an Abnormal Course of the Facial Nerve

Objectives

It is not unusual for a cochlear implantation (CI) candidate to have some type of ear malformation, in particular an abnormal course of the facial nerve (FN). In this study, we attempted to reconstruct a three-dimensional (3D) image of temporal bone structures with malformation using computed tomography (CT) imaging and examined its usefulness in the surgical planning of CI in a malformed ear.

Methods

We prepared 3D images for 6 separate CI cases before surgery. First, we manually colored preoperative CT images using Photoshop CS Extended. We then converted the colored CT images to 3D images using Delta Viewer, free-ware for Macintosh. Before surgery, we discussed any problems anticipated based on the 3D images and plans for surgery with those who would be performing the CI.

Results

Case 1: The subject was a 3-year-old boy with malformed ossicles, semicircular canal (SC) hypoplasia, internal auditory canal stenosis, and an abnormal course of the FN. 3D image indicated that the stapes were absent, and the FN was more anteriorly displaced, so that it was difficult to perform cochleostomy. The surgical findings were similar to those depicted on the 3D image, so we could insert an electrode based on the preoperative image simulation without complications. Case 2: The subject was a 7-year-old boy with malformed stapes, atresia of the round window, cochlear and SC aplasia, and an abnormal course of the FN with bifurcation. CI was performed with no problems, in the same manner as in Case 1.

Conclusion

We were able to successfully depict the structures of the inner ear, ossicles, and FN as 3D images, which are very easy to understand visually and intuitively. These 3D images of the malformed ear are useful in preoperative image simulation and in surgical planning for those performing a CI procedure.

Reconstruction and exploration of virtual middle-ear models derived from micro-CT datasets

BACKGROUND

Middle-ear anatomy is integrally linked to both its normal function and its response to disease processes. Micro-CT imaging provides an opportunity to capture high-resolution anatomical data in a relatively quick and non-destructive manner. However, to optimally extract functionally relevant details, an intuitive means of reconstructing and interacting with these data is needed.

MATERIALS AND METHODS

A micro-CT scanner was used to obtain high-resolution scans of freshly explanted human temporal bones. An advanced volume renderer was adapted to enable real-time reconstruction, display, and manipulation of these volumetric datasets. A custom-designed user interface provided for semi-automated threshold segmentation. A 6-degrees-of-freedom navigation device was designed and fabricated to enable exploration of the 3D space in a manner intuitive to those comfortable with the use of a surgical microscope. Standard haptic devices were also incorporated to assist in navigation and exploration.

RESULTS

Our visualization workstation could be adapted to allow for the effective exploration of middle-ear micro-CT datasets. Functionally significant anatomical details could be recognized and objective data could be extracted.

CONCLUSIONS

We have developed an intuitive, rapid, and effective means of exploring otological micro-CT datasets. This system may provide a foundation for additional work based on middle-ear anatomical data.

Automatic identification and 3D rendering of temporal bone anatomy

HYPOTHESIS

Using automated methods, vital anatomy of the middle ear can be identified in computed tomographic (CT) scans and used to create 3-dimensional (3D) renderings.

BACKGROUND

Although difficult to master, clinicians compile 2D data from CT scans to envision 3D anatomy. Computer programs exist that can render 3D surfaces but are limited in that ear structures, for example, the facial nerve, can only be visualized after time-intensive manual identification for each scan. Here, we present results from novel computer algorithms that automatically identify temporal bone anatomy (external auditory canal, ossicles, labyrinth, facial nerve, and chorda tympani).

METHODS

An atlas of the labyrinth, ossicles, and auditory canal was created by manually identifying the structures in a "normal" temporal bone CT scan. Using well-accepted techniques, these structures were automatically identified in (n = 14) unknown CT images by deforming the atlas to match the unknown volumes. Another automatic localization algorithm was implemented to identify the position of the facial nerve and chorda tympani. Results were compared with manual identification by measuring false-positive and false-negative error.

RESULTS

The labyrinth, ossicles, and auditory canal were identified with mean errors less than 0.5 mm. The mean errors in facial nerve and chorda tympani identification were less than 0.3 mm.

CONCLUSION

Automated identification of temporal bone anatomy is achievable. The presented combination of techniques was successful in accurately identifying temporal bone anatomy. These results were obtained in less than 10 minutes per patient scan using standard computing equipment.

VIRTUAL TEMPORAL BONE: AN INTERACTIVE 3‐DIMENSIONAL LEARNING AID FOR CRANIAL BASE SURGERY

OBJECTIVE

We have developed an interactive virtual model of the temporal bone for the training and teaching of cranial base surgery.

METHODS

The virtual model was based on the tomographic data of the Visible Human Project. The male Visible Human's computed tomographic data were volumetrically reconstructed as virtual bone tissue, and the individual photographic slices provided the basis for segmentation of the middle and inner ear structures, cranial nerves, vessels, and brainstem. These structures were created by using outlining and tube editing tools, allowing structural modeling either directly on the basis of the photographic data or according to information from textbooks and cadaver dissections. For training and teaching, the virtual model was accessed in the previously described 3-dimensional workspaces of the Dextroscope or Dextrobeam (Volume Interactions Pte, Ltd., Singapore), whose interfaces enable volumetric exploration from any perspective and provide virtual tools for drilling and measuring.

RESULTS

We have simulated several cranial base procedures including approaches via the floor of the middle fossa and the lateral petrous bone. The virtual model suitably illustrated the core facts of anatomic spatial relationships while simulating different stages of bone drilling along a variety of surgical corridors. The system was used for teaching during training courses to plan and discuss operative anatomy and strategies.

CONCLUSION

The Virtual Temporal Bone and its surrounding 3-dimensional workspace provide an effective way to study the essential surgical anatomy of this complex region and to teach and train operative strategies, especially when used as an adjunct to cadaver dissections.

3D computerized model of endolymphatic hydrops from specimens of temporal bone

CONCLUSION

The 3D models of endolymphatic and perilymphatic spaces enabled us to obtain normal and pathological volumes of each space and helped us to understand the 3D structure of various parts of the inner ear and of endolymphatic hydrops.

OBJECTIVE

To make a 3D model of the inner ear using sections of temporal bone with and without hydrops.

MATERIALS AND METHODS

Every 10th 20 microm thick section of temporal bone was collected from two ears with endolymphatic hydrops and five ears without hydrops. Using ZedView, 3D Doctor, FreeForm as analytical software, a 3D model of the inner ear was obtained by reconstruction of these sections. The volumes of the endolymphatic (EV) and perilymphatic spaces (PV) were calculated in each part of the cochlea and vestibular apparatus including the semicircular canals, but the endolymphatic duct and sac were not included.

RESULTS

In normal ears (controls), the average cochlear EV was 5.1 microl and the PV was 41.9 microl, and the average vestibular EV was 24.0 microl and the PV 75.7 microl. In one hydropic ear, the cochlear EV was 17.5 microl, cochlear PV 30.7 microl, vestibular EV 42.5 microl, and vestibular PV 33.4 microl. In the other hydropic ear, cochlear EV was 31.2 microl, cochlear PV 30.1 microl, vestibular EV 25.6 microl, and vestibular PV 71.8 microl.

A multichannel semicircular canal neural prosthesis using electrical stimulation to restore 3-d vestibular sensation

Bilateral loss of vestibular sensation can be disabling. Those afflicted suffer illusory visual field movement during head movements, chronic disequilibrium and postural instability due to failure of vestibulo-ocular and vestibulo-spinal reflexes. A neural prosthesis that emulates the normal transduction of head rotation by semicircular canals could significantly improve quality of life for these patients. Like the three semicircular canals in a normal ear, such a device should at least transduce three orthogonal (or linearly separable) components of head rotation into activity on corresponding ampullary branches of the vestibular nerve. We describe the design, circuit performance and in vivo application of a head-mounted, semi-implantable multichannel vestibular prosthesis that encodes head movement in three dimensions as pulse-frequency-modulated electrical stimulation of three or more ampullary nerves. In chinchillas treated with intratympanic gentamicin to ablate vestibular sensation bilaterally, prosthetic stimuli elicited a partly compensatory angular vestibulo-ocular reflex in multiple planes. Minimizing misalignment between the axis of eye and head rotation, apparently caused by current spread beyond each electrode's targeted nerve branch, emerged as a key challenge. Increasing stimulation selectivity via improvements in electrode design, surgical technique and stimulus protocol will likely be required to restore AVOR function over the full range of normal behavior.