Bernhard Pflesser

Creating a high-resolution spatial/symbolic model of the inner organs based on the Visible Human.

Computerized three-dimensional models of the human body, based on the Visible Human Project of the National Library of Medicine, so far do not reflect the rich anatomical detail of the original cross-sectional images. In this paper, a spatial/symbolic model of the inner organs is developed, which is based on more than 1000 cryosections and congruent fresh and frozen CT images of the male Visible Human. The spatial description is created using color-space segmentation, graphic modeling, and a matched volume visualization with subvoxel resolution. It is linked to a symbolic knowledge base, providing an ontology of anatomical terms. With over 650 three-dimensional anatomical constituents, this model offers an unsurpassed photorealistic presentation and level of detail. A three-dimensional atlas of anatomy and radiology based on this model is available as a PC-based program.

A 'virtual body' model for surgical education and rehearsal

A general digital model of human anatomy is very helpful both in supporting the process of anatomical segmentation and as a reference system for simulating surgical situations or even rehearsal of interventions. This article describes the data structure and implementation of such a model. Neither superhero nor crash-test dummy, Voxel-Man is an attempt to combine in a single framework a detailed spatial model enabling realistic visualization with a symbolic model of the human body. We show that although a general model does not correspond in detail to an individual patient, it does provide a variety of novel features for surgical education and training.

Haptic volume interaction with anatomic models at sub-voxel resolution

An approach for haptic volume interaction with high resolution voxel-based anatomic models is presented. The haptic rendering is based on a multi-point collision detection approach which provides realistic tool interaction with the models. Both haptics and graphics are rendered at sub-voxel resolution, which leads to a high level of detail and enables the exploration of the models at any scale. Forces are calculated at an update rate of 6000 Hz and sent to a 3-degree-of-freedom (3-DOF) force-feedback device. Compared to point-based haptic rendering, the unique approach of the multi-point collision detection in combination with sub-voxel rendering provides more realistic and very detailed haptic sensations. As a main application, a simulator for petrous bone surgery was developed. With a simulated drill, bony structure can be removed and the access path to the middle ear can be studied.

Virtual reality: A new paranasal sinus surgery simulator

Virtual surgical training systems are of growing value. Current prototypes for endonasal sinus surgery simulation are very expensive or lack running stability. No reliable system is available to a notable number of users yet. The purpose of this work was to develop a dependable simulator running on standard PC hardware including a detailed anatomic model, realistic tools and handling, stereoscopic view, and force feedback.

Exploring the Visible Human using the VOXEL-MAN framework

In principle the Visible Human data sets are an ideal basis for building electronic atlases. While it is easy to construct such atlases by just offering the possibility of browsing through the 2D slices, constructing realistic 3D models is a huge project. As one rather easy way to establish 3D use, we have registered the Visible Human data to the already existing 3D atlas VOXEL-MAN/brain. This procedure enables one to lookup anatomical detail in an atlas based on radiological images. Concerning the segmentation problem, which is the prerequisite for a real 3D atlas, we have developed an interactive classification method that delivers realistic perspective views of the Visible Human. As these volume based methods require high-end workstations, we finally have developed a multimedia program that runs on standard PCs and uses Quicktime VR movies.

Virtual dental surgery as a new educational tool in dental school

PURPOSE The virtual environment of the Voxel-Man simulator that was originally designed for virtual surgical procedures of the middle ear has been adapted to intraoral procedures. To assess application of the simulator to dentistry, virtual apicectomies were chosen as the pilot-test model. METHODS A group of 53 dental students provided their impressions after virtual simulation of apicectomies in the Voxel-Man simulator. RESULTS Fifty-one of the 53 students recommended the virtual simulation as an additional modality in dental education. The students indicated that the force feedback (e.g. simulation of haptic pressure), spatial 3D perception, and image resolution of the simulator were sufficient for virtual training of dental surgical procedures. CONCLUSION The feedback from dental students involved in this pilot-test has encouraged our interdisciplinary group to continue further development of the simulator with the goal of creating new training strategies in dental and medical education.

Towards Realistic Visualization for Surgery Rehearsal

A method for free-form cutting in tomographic volume data is presented. As a basic data structure, the generalized voxel model is chosen. Removed regions are indicated using attributes. Tools like a “rasp” or a “knife” are presented. Methods for detection and visualization of cut surfaces, both for mapping of original gray values and of color labels for the segmented objects, are discussed. It is claimed that the possibilities of the described method are exceeding those of any surface-based approach.

A Realistic Model of the Inner Organs from the Visible Human Data

The computer-based 3D models of the human body reported to date suffer from poor spatial resolution. The Visible Human project has delivered high resolution cross-sectional images that are suited for generation of high-quality models. Yet none of the 3D models described to date reflect the quality of the original images. We present a method of segmentation and visualization which provides a new quality of realism and detail. Using the example of a 3D model of the inner organs, we demonstrate that such models, especially when combined with a knowledge base, open new possibilities for scientific, educational, and clinical work

Specification, Modeling and Visualization of Arbitrarily Shaped Cut Surfaces in the Volume Model

So far, exploration of volume models is limited to cut planes or addition/removal of segmented objects. More capable exploration techniques are needed in order to allow a ‘look and feel’ close to a real dissection. This is especially important for applications like the simulation of osteotomy surgery. Therefore, we have developed methods for free-form volume-sculpting operations which allow the interactive specification, representation and high-quality rendering of free form regions. The novelty of this approach is that these regions are represented within the generalized-voxel-model, together with a simulation of the partial-volume-effect, which allows a sub-voxel localization of cut surfaces. These techniques are implemented in our VOXEL-MAN visualization system, thus enhancing the exploration techniques for volume data. Furthermore, we developed an extended ray-casting algorithm for 3D-visualization of object motion with detection and visualization of interpenetrating volumes. These methods together provide a powerful tool for volume exploration and applications like the rehearsal of surgical interventions.

Realistic haptic volume interaction for petrous bone surgery simulation

In this paper, a new approach for haptic volume interaction with high resolution voxel-based anatomic models is presented. The haptic rendering is based on a multi-point collision detection approach which provides realistic tool interaction with the models. Both haptics and graphics are rendered at sub-voxel resolution, which leads to a high level of detail and enables the exploration of the models at any scale. Forces are calculated at an update rate of 6000 Hz and sent to a 3-Degree-of-Freedom (3-DOF) force-feedback device. Compared to single-point based haptic rendering, the unique approach of the multi-point collision detection in combination with sub-voxel rendering provides more realistic and very detailed haptic sensations. As a main application, a simulator for petrous bone surgery was developed. With a simulated drill, bony structure can be removed and the access path to the middle ear can be studied in a realistic manner.