Creating a high-resolution spatial/symbolic model of the inner organs based on the Visible Human☆
Introduction
While in classical medicine, knowledge about the human body is represented in books and atlases, present-day computer science allows for new, more powerful and versatile computer-based representations of knowledge. Their most simple manifestations are multimedia CD-ROMs containing collections of classical pictures and text, which may be browsed arbitrarily or according to various criteria. Although computerized, such media still follow the old paradigm of text printed on pages accompanied by pictures. This genre includes impressive atlases of cross-sectional anatomy, notably from the photographic cross-sections of the Visible Human Project (Ackerman, 1991, Spitzer et al., 1996).
In the past years, however, it has been shown that spatial knowledge, especially about the structure of the human body, may be much more efficiently represented by computerized three-dimensional models (Höhne et al., 1995). These can be constructed from cross-sectional images generated by computer tomography (CT), magnetic resonance imaging (MRI), or histological cryosectioning, as in the case of the Visible Human Project. Such models may be used interactively on a computer screen or in virtual reality environments. If such models are connected to a knowledge base of descriptive information, they can even be interrogated or disassembled by addressing names of organs (Höhne et al., 1995, Brinkley et al., 1999, Golland et al., 1999). They can thus be regarded as a ‘self-explaining body’.
Until now, the Visible Human Project has not reported three-dimensional models that reflect the rich anatomical detail of the original cross-sectional images. This is largely due to the fact that, for the majority of anatomical objects contained in the data, the cross-sectional images could not be converted into a set of coherent realistic surfaces. If we succeed in converting all the detail into a 3D model, we gain an unsurpassed representation of human structure that opens new possibilities for learning anatomy and simulating interventions or radiological examinations.
Section snippets
Earlier work
Building a comprehensive model of the inner organs of the Visible Human requires both a spatial description consisting of three-dimensional objects, which are displayed using methods of volume visualization, as well as a linked symbolic description of relevant anatomical terms and their relations.
In general, volume visualization may or may not include a segmentation step. In volume rendering, transparency values are assigned to the individual voxels according to the intensity values and changes
Methods and materials
We therefore aimed at a method that yields surfaces for the segmentable organs that are as exact as possible and textured with their original color. In order to arrive at a complete model, we decided to model non-segmentable objects like nerves and small blood vessels artificially on the basis of landmarks present in the image volume. Even though none of the methods presented here is entirely new, building a complex model required a number of substantial improvements.
Results
Using the methods described above, we built a model of the inner organs of the male Visible Human. It contains more then 650 three-dimensional anatomical constituents and more than 2000 relations between them. The size of segmented anatomical constituents varies between 3.8 million voxels (or mm3, equivalent to 3.8 l) for visceral fat and 124 voxels for the cystic duct. Preparation of the model using the described methods involved up to 10 people and required about 5 man years. Fig. 3 gives an
Conclusions
In this paper, we presented an approach for creating a high-resolution model of the inner organs, based on the Visible Human data. The following features of this model represent innovations:
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Because of the exact, color-space segmentation and the matched visualization method, the visual impression is one of unsurpassed realism.
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There is, to date, no computer model of the inner organs that contains and describes so many three-dimensional anatomical constituents.
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The model is space-filling, i.e. any
Supplementary Material
Acknowledgements
We thank Victor Spitzer and David Whitlock, University of Colorado, and Michael Ackerman, National Library of Medicine (US), for providing the Visible Human dataset. We are also grateful to Jochen Dormeier, Jan Freudenberg, Sebastian Gehrmann, Stefan Noster and Norman von Sternberg-Gospos, who substantially contributed to the segmentation and modeling work. The tube editor was implemented by Klaus Rheinwald. The movie in the electronic annex was produced by Andreas Petersik. The knowledge
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