The Virtual Temporal Bone / Abstract

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The Virtual Temporal Bone

THEODORE P. MASON M.D. ¹, Edward L. Applebaum M.D. ¹, Mary Rasmussen ², Alan Millman ², Ray Evenhouse ², Walter Panko Ph.D. ²

1 - Department of Otolaryngology - Head and Neck Surgery, University of Illinois at Chicago Hospital
2 - School of Biomedical and Health Information Sciences, University of Illinois at Chicago

INTRODUCTION
BACKGROUND
PURPOSE OF WORK
METHODS
RESULTS
CONCLUSIONS

INTRODUCTION

Mastery of the complex anatomic interrelationships of the human temporal bone is an essential part of otolaryngologic residency training, requiring untold hours of study not only from anatomic and pathologic texts, but also from within the practical realm of the temporal bone lab and operating room. For the occasional ear surgeon, maintenance of this knowledge through home studies and courses remains essential to keep the skills of temporal bone drilling honed. Unfortunately, the time and costs required in both of these endeavors are enormous. In this relatively new era of powerful yet easily accessible computers, there emerges a new potential tool for both the learning and maintenance of temporal bone anatomy knowledge.

In a joint project between the University of Illinois Department of Otolaryngology - Head and Neck Surgery and the School of Biomedical and Health Information Sciences, we have created the first generation of a fully interactive and anatomically precise human temporal bone computer model, designed to make use of the cutting-edge 3-dimensional virtual environment known as the CAVE^TM.

BACKGROUND

In many of the disease processes that affect the human ear, surgical intervention is often required. Otologists carry this out by drilling into the temporal bone, the portion of the skull that houses the very delicate organs of hearing and balance, vital nerves and blood vessels, as well as the tiny bones that conduct sound captured by the tympanic membrane. The very fact that these structures are encased in bone makes surgical landmarks few and far between, the surgeon having to rely on a precise knowledge of their complex interrelationships to provide clues as to where drilling will be safe and where it would lead to disaster.

PURPOSE OF WORK

Current teaching tools used for temporal bone anatomy are a combination of 2-dimensional anatomic illustrations and photographs, histologic sections, CT and MRI scans, as well as 3-dimensional sculpted models and cadaver dissections. Unfortunately, none of these tools provides the student of temporal bone anatomy with all of the important 3-dimensional structural spatial relationships simultaneously and interactively. Our model was designed to provide that crucial information in a way that will make the learning process of the aspiring otologic surgeon much faster and easier.

METHODS

For this initial project, we used 300 serial histologic sections of a human temporal bone as a basis for its 3-dimensional re-creation. The principle behind our method of reconstruction is simple: if one were able to restack all of these 2-dimensional slices atop one another in order and in perfect alignment, a complete 3-dimensional temporal bone would be re-created. Using a high resolution transparency scanner, the histologic slides were directly scanned and saved as image files. These serial images were then painstakingly aligned with respect to one another by hand and re-saved in a consistent format. Unfortunately, the raw histologic data contained too much artifactual data to be able to isolate the important anatomic structures for modeling purposes. Therefore, these important structures were traced by hand in each image and recombined into a simplified histologic data set. These images were then sent to a Silicon Graphics workstation, where a marching cubes algorithm was used to reconstruct 3-dimensional structures. Subtle irregularities of the resulting objects were the smoothed using a box filtering algorithm.

Because of poor representation within the histologic data set, the ossicle bones required reconstruction by a different method. Large sized ossicles were sculpted using real ossicles as a template. The surface data for the models was then captured by CT scan, reconstructed into 3-D models, and imported into the final model.

RESULTS

The final model is an anatomically precise human temporal bone that contains many of the important structures encountered during otologic surgery such as the labyrinth, cochlea, facial nerve and ossicles, among others. The primary display engine for the model uses a Silicon Graphics Maximum Impact workstation and an Immersadesk^TM viewer. This setup allows for the use of CAVE technology, giving the user the sensation of total immersion within a virtual environment. With the aid of special liquid crystal goggles, the user is able to view the model within this fully stereoscopic 3-dimensional virtual environment, allowing the user not only to manipulate the model in real time, but to actually travel within the model itself. The degree of anatomic accuracy provides the user with real information that will be directly transferable to work in the cadaver lab as well as in the operating room. Various features such as transparency control, specific object selection, animation, and a variety of manipulation modes make visualization of the anatomic relationships of the normally hidden structures a refreshingly simple prospect.

CONCLUSIONS

This new anatomically accurate model provides a new and much needed tool in the teaching and learning of temporal bone anatomy. We feel confident that this model and planned future generations will soon be a vital part of the training program of residents of Otolaryngology, allowing for faster acquisition and better long term maintenance of anatomic knowledge.

Contact: Theodore Mason MD
University of Illinois at Chicago Hospital
Eye and Ear Infirmary (M/C 648)
1855 West Taylor Street
Chicago, IL 60612
Phone: (312 )996-6582
fax: (312) 996-1282
e-mail: tpmason@uic.edu

University of Illinois at Chicago - School of Biomedical and Health Information Sciences
1919 West Taylor Street - Chicago, Illinois  60612-7249. Direct questions and comments to mary@uic.edu .