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