Fecal-tagging CT colonography (CTC) presents an opportunity to minimize colon cleansing while maintaining high diagnostic accuracy for the detection of colorectal lesions. However, the pseudo-enhancement introduced by tagging agents presents several problems for the application of computer-aided detection (CAD). We developed a correction method that minimizes pseudo-enhancement in CTC data by modeling of the pseudo-enhancement as a cumulative Gaussian energy distribution. The method was optimized by use of an anthropomorphic colon phantom, and its effect on our fully automated CAD scheme was tested by use of leave-one-patient-out evaluation on 23 clinical CTC cases with reduced colon cleansing based upon dietary fecal tagging. There were 28 colonoscopy-confirmed polyps ≥6 mm. Visual evaluation indicated that the method reduced CT attenuation of pseudo-enhanced polyps to standard soft-tissue Hounsfield unit (HU) range without affecting untagged regions. At a 90% detection sensitivity for polyps ≥6 mm, CAD yielded 8.5 false-positive (FP) detections and 3.9 FP detections per volumetric scan without and with the application of the pseudo-enhancement correction method. These results indicate that the pseudo-enhancement correction method is a potentially useful pre-processing step for automated detection of polyps in fecal-tagging CTC, and that CAD can yield a high detection sensitivity with a relatively low FP rate in CTC with patient-friendly reduced colon preparation.
The purpose of this study was to perform CT colonography (CTC) without cathartic colon cleansing. Four groups of 3 patients were prepared the day before CTC with a dedicated low residue diet, a hydration control allowing 2 liters of fluid intake and barium as tagging agent. Four different barium regimens were investigated.
Groups 1 and 3 ingested barium over 1 day at different concentrations and groups 2 and 4 over 2 days. The barium volume to drink the day before CTC was 750 ml in groups 1 and 2 and 50 ml in groups 3 and 4. The fluid, density measurements of the fecal residue and tagging efficacy were evaluated. All fecal residue with
densities ≥ 150 H.U. was electronically labeled. Per segment a visual labeling score (0, 25, 50, 75, 100%) was performed. The fluid was evaluated according to its proportion to the maximum anteroposterior diameter of the colonic segment where it was detected. No significant differences in densities of tagged residue were detected. The visual labeling scores varied between 90 and 100% in all segments. There were 6 fluid levels: 5 covering < 10% and one covering 50% of the colonic lumen. The lowest density of the fluid was 360 H.U. In this preliminary study we could conclude that CTC without cathartic cleansing and with barium produced efficient
labeling of fecal residue. The barium intake could be reduced to one day and to 50 ml.