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Three-dimensional visualization of human organs employing currently available medical imaging modalities, such as CT (computed tomography) and MRI (magnetic resonance imaging), has been widely used for patient diagnosis, therapy, and surgery [8]. New advances in this technology, such as visualizing the inner surface of the colon employing 3D reconstructed CT data, are still under development [9,4]. Currently, colonoscopy and barium enema are the only means available for the detection of polyps or carcinoma of the colon. Unfortunately, each of these procedures has its drawbacks. Colonoscopy, an invasive procedure, is associated with a small risk of perforation. In addition, it also requires intravenous sedation and approximately 40 to 60 minutes of time to perform. Frequently, due to either technical difficulties or patient discomfort, the proximal colon cannot be fully evaluated. Furthermore, the cost of colonoscopy is high, approximately $1,300 to $1,900. Barium enema, although less expensive (at the cost of approximately $350), requires a good deal of patient positioning and thus physical cooperation from the patient. Results vary according to the technical quality of the procedure and the experience of the interpreter. While some investigators state that barium enema can be as sensitive as colonoscopy, others have reported that the sensitivity achieved with barium enema can be as low as 78% in detection of polyps in the range of 0.5cm to 2cm in diameter [5].
The motivation for this work was to develop an alternative technique to visualize the inner mucosal surface of the colonic wall, and therefore assist the physicians in detecting the presence and characteristics of mucosal lesions. In this study, after the colon of a patient has been cleansed and distended with air, a spiral CT scanner is employed to obtain a sequence of thin axial slices from the top of the splenic flexure of the colon to the rectum based upon landmarks obtained from the scout image. Then, this set of CT images is reconstructed into a 3D volume and visualized with the VolVis volume visualization system [1]. Images of the inner structures of the colon, as well as interactive flythroughs and off-line automatically-produced animations along the colon, are generated as if the viewer's eyes were freely mobile inside the colonic lumen. This provides the capability to precisely explore the inner surface of the colon for irregularities such as polyps and tumors.
In Sections 2 through 5, we describe in detail the procedure of obtaining the CT slices of the colon and the visualization techniques employed in generating the colon images, interactive flythroughs, and animations. In Section 6, we present our testing results on two plastic pipe simulations and on the Visible Human data set. Finally, we summarize and conclude in Section 7.