To investigate the efficacy of CT virtual colonoscopy with carbon dioxide (CO₂) versus room air and the effects of bowel cleanliness on polyp detection rate.

A total of 186 patients who underwent CT virtual colonoscopy in the Affiliated Hospital of Hangzhou Normal University (Hangzhou Second People's Hospital), China between October 2015 and November 2020 were included in this study. They were randomly divided into CO₂ and control groups (n = 93/group). In the CO₂ and control groups, CO₂ and room air were respectively injected through the anus to fill the intestinal cavity. The Boston Bowel Preparation Scale (BBPS) score, abdominal distension score, Visual Analogue Scale (VAS) score, Bruggrmann comfort scale (BCS) score and polyp detection rate were compared between the two groups.

According to BBPS score, there were 62 and 60 patients with good bowel cleanliness (BBPS score ≥ 7 points), and 31 and 33 patients with poor bowel cleanliness (BBPS score < 7 points) in the CO ₂ and control groups, respectively. There were no significant differences in abdominal distension score, VAS score and BCS score measured during the examination between the two groups (all P > 0.05). At 30 minutes after examination, abdominal distension score and VAS score in the CO ₂ group were (2.21 ± 0.40) points and (1.43 ± 0.34) points, respectively, which were significantly lower than those in the control group [(3.50 ± 0.49) points, (3.03 ± 0.55) points, t = 2.59, 2.38, both P < 0.05)]. At 60 minutes after examination, abdominal distension score, VAS score and BCS score in the CO ₂ group were (1.15 ± 0.39) points, (1.22 ± 0.28) points, (1.27 ± 0.35) points, which were significantly lower than those in the control group [(2.16 ± 0.43) points, (1.91 ± 0.32) points, (1.85 ± 0.37) points, t = 2.45, 2.27, 2.40, allP < 0.05). The detection rate of small (< 6 mm) - and large (≥ 6 mm) -sized polyps in the CO ₂ group was 32.7% (34/104) and 88.1% (37/42), respectively and they were 29.0% (29/100) and 85.1% (40/47) respectively in the control group. There were no significant differences in the detection rate of small- and large-sized polyps between CO₂ and control groups (both P > 0.05). The detection rate of large-sized polyps in patients with good bowel cleanliness in the CO ₂ group was 92.3% (24/26) and 89.7% (26/29), respectively, which were significantly higher than those in patients with poor bowel cleanliness in the control group [81.3% (13/16), 77.8% (14/18), χ² = 6.03, 6.44, both P < 0.05]. The detection rate of small-sized polyps in patients with poor bowel cleanliness in the CO ₂ group was 41.9% (26/62) and 42.9% (21/49), respectively, which were significantly higher than those in patients with poor bowel cleanliness in the control group [19.0% (8/42), 15.7% (8/51), χ² = 15.32, 13.78, both P < 0.01].

CT virtual colonoscopy with CO₂ injection is less uncomfortable than CT virtual colonoscopy with room air and it does not affect polyp detection rate. Bowel cleanliness has a remarkable effect on polyp detection rate in virtual colonoscopy.

Colonoscopy; Tomography,X-ray computed; Carbon dioxide; Air; Flatulence; Visual analog scale; Intestinal polyps; Case-control studies