Feasibility study of computed tomography colonography using limited bowel preparation at normal and low-dose levels study

Abstract

The purpose was to evaluate low-dose CT colonography without cathartic cleansing in terms of image quality, polyp visualization and patient acceptance. Sixty-one patients scheduled for colonoscopy started a low-fiber diet, lactulose and amidotrizoic-acid for fecal tagging 2 days prior to the CT scan (standard dose, 5.8-8.2 mSv). The original raw data of 51 patients were modified and reconstructed at simulated 2.3 and 0.7 mSv levels. Two observers evaluated the standard dose scan regarding image quality and polyps. A third evaluated the presence of polyps at all three mSv levels in a blinded prospective way. All observers were blinded to the reference standard: colonoscopy. At three times patients were given questionnaires relating to their experiences and preference. Image quality was sufficient in all patients, but significantly lower in the cecum, sigmoid and rectum. The two observers correctly identified respectively 10/15 (67%) and 9/15 (60%) polyps > or =10 mm, with 5 and 8 false-positive lesions (standard dose scan). Dose reduction down to 0.7 mSv was not associated with significant changes in diagnostic value (polyps > or =10 mm). Eighty percent of patients preferred CT colonography and 13% preferred colonoscopy (P<0.001). CT colonography without cleansing is preferred to colonoscopy and shows sufficient image quality and moderate sensitivity, without impaired diagnostic value at dose-levels as low as 0.7 mSv.

Fig. 1

Figure showing RDOR with confidence intervals of all six segments of the colorectum in both prone and supine position regarding overall image quality, distension, presence of stool and homogeneity. All segments are compared to the best segment (DOR by definition 1). Confidence intervals not reaching 1 indicate significantly inferior results

Fig. 2

A 76-year-old woman with a 7-mm stalked polyp (arrow) submerged in a layer of tagged stool at CTC (original dose; a: supine position, b prone position) and at colonoscopy (c)

Fig. 3

Figure showing a large 12-mm false-positive lesion (arrow) in the transverse colon at three different dose levels in a 65-year-old male patient (a: 0.7 mSv, b: 2.3 mSv, c: original). At lower dose levels it is more difficult to differentiate this lesion from a true-positive lesion (polyp) when fecal material is insufficiently tagged, this especially applied to smaller lesions. Well-tagged material is clearly differentiated from colon wall, even at 0.7 mSv (arrowhead)

Fig. 4

Figure showing a large 10-mm stalked polyp (arrowhead) in the sigmoid at three different dose levels in a 57-year-old male patient (a: 0.7 mSv, b: 2.3 mSv, c: original)

Fig. 5

Graph showing how patients rated the three different components of CTC with limited bowel preparation. How burdensome were the diet, lactulose and the contrast agent?

Fig. 6

Graphs show patients’ experience of the bowel preparation (upper left) and the CTC examination (upper right) and patient preference for one of the two modalities (CTC with limited bowel preparation versus CTC with standard bowel preparation, lower). How burdensome was the limited bowel preparation prior to CTC (grey) as compared to cleansing prior to CC (black)? How burdensome were the CTC (grey) and CC (black) examinations (upper right graphs)? What did participants prefer for their next examination (lower graph) directly after both examinations and in the questionnaire sent at home 5 weeks later?