Surface visualization at CT colonography simulated colonoscopy: effect of varying field of view and retrograde view.

OBJECTIVES

Colonoscopy is the gold standard for diagnosis of mucosal disease, but has a recognized "miss rate" for polyps probably because some lesions lie in areas of the colonic surface that do not enter the field of view. Using CT colonography (CTC) simulation this pilot study aimed to determine how much colonic surface is visualized with a standard, modern optical colonoscope (field of view 140 degrees ) with or without the addition of a retrograde viewing auxiliary imaging device (RVAID; 135 degrees ) and of a wide-angle (170 degrees ) colonoscope.

METHODS

Supine CTC datasets for 20 patients were reviewed with customized CTC software that calculated the percentage of colonic surface seen and number and area of nonvisualized "missed" areas at a unidirectional three-dimensional (3D) endoluminal flythrough, approximating the view obtained at optical colonoscopy. The field of view could be varied from 0-180 degrees . The combination of a colonoscope with RVAID was simulated by an additional flythrough facing the rectum.

RESULTS

Mean colonic surface area was 2,743 +/- 759 cm2. Percentage colonic surface visualized at simulated optical colonoscopy with a 90 degrees , 140 degrees , and 170 degrees field of view was 68.0 +/- 5.2%, 86.6 +/- 3.3%, and 92.2 +/- 3.3%, respectively, P < 0.001. Simulation of a 140 degrees colonoscope with an RVAID resulted in almost complete surface visualization, 98.7 +/- 0.5%, with total missed area reduced 10-fold compared with a 170 degrees colonoscope, P < 0.001.

CONCLUSION

CTC simulated 140 degrees optical colonoscopy visualizes over 85% of the colonic surface. 170 degrees colonoscopy provides a modest reduction in missed surface and the simulated addition of RVAIDs appears beneficial.