Ulf Tiede

Segmentation of the Visible Human for high-quality volume-based visualization

This article describes a combination of interactive classification and super-sampling visualization algorithms that greatly enhances the realism of 3-D reconstructions of the Visible Human data sets. Objects are classified on the basis of ellipsoidal regions in RGB space. The ellipsoids are used for super-sampling in the visualization process.

Symbolic modeling of human anatomy for visualization and simulation

Visualization of human anatomy in a 3D atlas requires both spatial and more abstract symbolic knowledge. Within our intelligent volume model which integrates these two levels, we developed and implemented a semantic network model for describing human anatomy. Concepts for structuring (abstraction levels, domains, views, generic and case-specific modeling, inheritance) are introduced. Model, tools for generation and exploration and applications in our 3D anatomical atlas are presented and discussed.

Visualization blackboard: visualizing the visible human

Visualization of the human body and its inner structure has challenged artists and scientists for centuries. For 500 years, since Leonardo da Vinci, drawings have been the main resource for learning anatomy because they allow the mixture of realism and abstraction suitable for didactic purposes. With the discovery of X-rays 100 years ago, it became possible to look into the living body. Only since the 1970s have computer tomography (CT) and magnetic resonance imaging (MRI) made it possible to acquire image data in three dimensions. Based on these techniques, 3D computer graphics generated the first models of the living body. These represent a tremendous advance for diagnosis and surgical planning, but the resolution is still poor when viewed from an anatomists point of view. The National Library of Medicines Visible Human Project provided much more realistic data-the Visible Human data set, created at the University of Colorado School of Medicine. This project produced transverse cross sectional photographic images of a male cadaver with a resolution of 0.33 mm and slice distance of 1 mm.

Realistic haptic interaction in volume sculpting for surgery simulation

Realistic haptic interaction in volume sculpting is a decisive prerequisite for successful simulation of bone surgery.We present a haptic rendering algorithm, based on a multi-point collision detection approach which provides realistic tool interactions. 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. With a simulated drill bony structures can be removed interactively. The characteristics of the real drilling procedure like material distribution around the drill are considered to enable a realistic sensation. All forces are calculated at an extra high update rate of 6000 Hz which enables rendering of drilling vibrations and stiff surfaces. As a main application, a simulator for petrous bone surgery was developed. With the simulated drill, access paths to the middle ear can be studied. This allows a realistic training without the need for cadaveric material.

Display Of Multiple 3D-Objects Using The Generalized Voxel-Model

3D-display of medical objects derived from cross-sectional images has demonstrated its clinical usefulness in various applications such as surgery planning and recently also in diagnostic radiology. Instead of viewing sequences of images the region of interest can be looked at in its 3D-shape or at least as a cross-sectional image within the anatomical surroundings (fig, 1,2). This new way of viewing is certainly more natural and understandable than the conventional one. If we imagine that the invention of X-rays, CT or MR had not been made yet, would we not aim at an imaging modality which would deliver images as known from anatomy? So having the new 3D-imaging facilities the physicians might act in the future Hore like anatomists (with radiological eyes), A 3D-image, however, if generated from a single parameter (such as a Hounsfield value in CT) does not nearly have the information content of the anatomical reality. In addition, the capability of performing a dissection at the computer screen requires, that the program behind the screen is able to perform the corresponding anatomic segmentation, This means that the data structure on which the anatomist program is working must contain more detailed information on the organs to be displayed,

Framework for the generation of 3-D anatomical atlases

In current practice computerized anatomical atlases are based on a collection of images that can be accessed via a hypermedia program shell. In order to overcome the drawback of a limited number of available views, we propose an approach that uses an anatomical model as data base. The model has a two layer structure. The lower level is a volume model with a set of semantic attributes belonging to each voxel. Its spatial representation is derived from data sets of magnetic resonance imaging and computer tomography. The semantic attributes are assigned by an anatomist using a volume editor. The upper level is a set of relations between these attributes which are specified by the expert as well. Interactive visualization tools such as multiple surface display, transparent rendering, and cutting are provided. As a substantial feature of the implementation the semantic and the visualization oriented descriptions are stored in a knowledge base. It is shown that the combination of this object oriented data structure with advanced volume visualization tools provides the `look and feel of a real dissection. The concept, which even allows simulations like surgery rehearsal, is claimed to be superior to all presently known atlas techniques.

Interactive 3-D segmentation

Segmentation is a prerequisite for 3-D visualization of image volumes. It has turned out to be extremely difficult to formalize for automatic computation. We describe an interactive segmentation method that circumvents this difficulty by using low level segmentation tools, which are interactively controlled by a human user via 3-D display. Segmentation tools implemented so far are simple thresholding and morphological operations. The method has been implemented on a workstation under UNIX using an X-Window interface based on the OSF/MOTIF toolkit. It is shown with examples from different applications that this simple approach delivers good results in only a short amount of time.

Simulating motion of anatomical objects with volume-based 3D visualization

Simulation and 3D visualization of object motion is a prerequisite for any surgical planning system. In order to provide feedback to show whether a realistic motion has been simulated, it is necessary to detect, quantify and visualize interpenetrating volumes. This cannot be achieved by common surface based methods. Therefore we developed a voxel-based approach, providing the full information of the tomographic volume data. We present an extended ray-casting algorithm which allows visualization of object motion using ray compositing, thus avoiding explicit manipulation of the image volume. Possible volumetric intersections may be visualized and quantified and interior properties of scenes with any displace objects may be explored using volume cuts.

Intepretation of tomographic images using automatic atlas lookup

We describe a system that automates atlas look-up when viewing cross-sectional images at a viewing station. Using simple specification of landmarks a linear transformation to a volume based anatomical atlas is performed. As a result corresponding atlas pictures containing information about structures, function, or blood supply, or classical atlas pages (like Talairach) appear next to the patient data for any chosen slice. In addition the slices are visible in the 3D context of the VOXEL-MAN 3D atlas, providing all its functionality.

Virtual endoscopy of branched objects based on cubic panoramas

Virtual endoscopy needs some precomputation of the data (segmentation, path finding) before the diagnostic process can take place. We propose a method that precomputes multinode cubic panorama movies using Quick-Time-VR. This technique allows almost the same navigation and visualization capabilities as a real endoscopic procedure, a significant reduction of interaction input is achieved and the movie represents a document of the procedure.