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Methodology: |
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The pelvic region of a female cadaver transected below the level of the iliac crests and at the upper thighs, approximately 20cm., was prepared by removing the small intestine, and filling the pelvic cavity and bladder with gelatinous fluid. The specimen was fixed in the vertical position to optimize organ relationships, and the specimen and the surrounding fluid were then frozen. Registration (fiducial) rods were pushed into holes drilled into the surrounding ice, and the ends stopped before re-freezing.
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The frozen specimen was initially sectioned in halves with a band saw. Successive cryo-sectioning was achieved by planing approximately 2 mm sections off the specimen with a jointer adjusted to minimum thickness. (See Figure 1) The specimen was placed on an adjustable stand beneath a tripod-mounted 35 mm camera such that the sectioned surface was always the same distance from the lens. Two angled strobe lights with polarized gels lit the specimen surface. The gels combined with a polarized lens filter on the camera, eliminated most of the glare on the specimen. After each pass with the jointer that removed a 2mm slice, the specimen was wiped with 80% ethanol to eliminate frost buildup and to remove debris. (See Figure 2)Three photographic exposures of each section were taken with Kodak Ektachrome 100 Plus Professional Film. |
Figure 1 |
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Figure 2: Matt Lewis slicing the specimen |
Three photographic exposures of each section were taken with Kodak Ektachrome 100 Plus Professional Film. After three to five sectionings, the specimen was placed face down in a mixture of 80% ethanol and dry ice for several minutes to re-freeze the surface. The best photographic exposure was chosen for the entire series of 95 sections and the series was then converted to photo-CD commercially. Registration:The images were oriented and aligned manually, using the fiducials, and confirmed with anatomic structures using Adobe's Photoshop 4.0 software operating on a Macintosh computer. The color balance of each photo was rigorously standardized. Each slice represented about eight megabytes of data. Segmentation and Extraction:Thirty-two structures were identified in the first segmentation procedure (Lucy 2.0). Later, in Lucy 2.1, additional segmentation of the musculo-skeletal system, and lumena of the colon and rectum, and the bladder and ureters was added. Each structure was selected and it's 'mask' defined manually. These were copied and accumulated in files for further processing. |
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The masks for each structure were made into wire-frame and surface-textured models using the Visualization Toolkit's (vtk) marching cubes algorithm and the Tcl interpretive language operating on a SGI Indigo 2 workstation. Slice data were connected into a stack of planar polygons and then into a 3D triangulated surface model. Further refinement, smoothing and decimation, was accomplished by converting the models (written to STL format) into Inventor format and applying VisModel CAD modeling software; colors were assigned from a palate. These 3D images can be visualized stereoscopically with 'shutter' glasses.
Algorithms based on a mass-spring model permit a limited number of surgical manipulations of these surface models. Deformability is adjustible for individual structures. Exploration (probing) and excision have been developed with appropriate virtual surgical tools. These allow for portions of a tubal ligation and an ovariectomy to be selected and practiced in a Web-based environment enabled with a haptics device. The deformable model labeled Lucy 2.5 has been developed during 2000 with Kevin Montgomery and colleagues at the Stanford-NASA Biocomputation Center. |
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