Step 9 Texture Maps and Special Effects

Texture maps can be applied to polygon models in order to make them look like a real tissue structure. A texture map is synonymous to a two-dimensional sticker that is

FIGURE3 ■ Volumetric model types.

FIGURE3 ■ Volumetric model types.

Developers can provide data derived from in vivo or in vitro experiments that can be used to create algorithms in the virtual environment.

wrapped around the three-dimensional surface. A texture map might be a picture of the real anatomy or a set of pictures stitched together to form a visually appealing skin. It is also possible to use video clips to form a "live" texture map so that the look of the surface changes over time (30).

Developers can provide data derived from in vivo or in vitro experiments that can be used to create algorithms in the virtual environment.

The University of Washington did this when calibrating blood flow, irrigant, and prostate tissue resection algorithms, for their transurethral resection of the prostate simulator, as well as when obtaining information on the material properties of organs/tissues (30-32). Another possible use of texture mapping is for tissue blanching.

Special effects make models look more realistic. A technique known as bump mapping is commonly employed. This is a technique by which individual pixels on the two-dimensional texture map are illuminated to different degrees to give the impression that the surface is textured rather than flat (Fig. 5). Lighting sources can also be simulated in order to add ambient light, specular and diffuse light to a scene. Without lighting, it is very difficult to perceive an object as three-dimensional. Shadowing can also help to improve visual realism.

Other special effects such as bleeding across solid tissue surfaces, irrigation, smoke, electrocautery, fragmentation, and debris are frequently modeled using particle-flow methods (Fig. 6).

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