Medical Community: Abstracts




RSNA, Radiological Society of North America:
Mark. Wax, Kevin. Kreeger and Joe. Anderson

Purpose: To compare the amount of lumen surface visualized by virtual colonoscopy to optical, and to use a novel technique to provide complete coverage of all clinically significant areas of the colon.

Methods and Materials:
Breath-hold, supine and prone spiral CT scans were performed on 103 patients after bowel preparation and colon distention with 2L of CO2. After automatic segmentation and electronic cleansing of the colon lumen, the medial axis (centerline) was extracted. To simulate optical colonoscopy a virtual camera was passed along this centerline in one direction. The camera was modeled after the Olympus (Melville, NY) CF-1T 140L/I video Colonoscope (120° FOV, 5-100mm focal range). The percentage of lumen surface visualized in this flight was measured by counting the visible surface voxels and comparing to the total count of all surface voxels. For virtual colonoscopy the camera was passed both antegrade and retrograde, and the combined visible surface voxel count was recorded. After both fly-throughs, all "patches" of connected surface area not yet seen were identified, measured, sorted by size, and counted. Clinically significant patches ¾ defined as smallest diameter being ³5; mm ¾ were sequentially visualized by stepping through the sorted list, followed by all patches. The total visualized surface was recorded for each.

Results: Simulated optical colonoscopy viewed an average of 80% (range 61-91) of the colon surface, primarily missing the backsides of haustral folds and around sharp bends. Combined antegrade and retrograde virtual colonoscopy flythrough, without interactive navigation, viewed an average of 94% (range 84-99) of the surface. A t-test showed an extremely significant difference between the two populations (p = 4.3*10-54). Even with 94% average coverage, there was an average of 40 (range 13-91) clinically significant patches not yet visualized. After identifying and viewing these areas, 98-100% of the lumen surface was seen. When all patches, regardless of size, were viewed, 100% of the surface was covered.

Conclusion: By enabling endoscopic navigation along the colon centerline, in both antegrade and retrograde directions, virtual colonoscopy allows evaluation behind haustral folds and around sharp bends, thereby visualizing significantly more surface area than optical colonoscopy. However, this still leaves a considerable number of clinically significant areas unseen. By marking the visualized surface area and automatically identifying and viewing unseen patches, up to 100% of the surface can be examined.

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