The elephant in the room: bowel preparation for CT colonography

Comparative safety of bowel cleansers: protocol for a systematic review and network meta-analysis

INTRODUCTION

The US Food and Drug Administration has withdrawn the bowel cleansing kit HalfLytely (PEG 3500) with 10 mg bisacodyl tablets due to an increased risk of ischaemic colitis compared with the same kit with only 5 mg bisacodyl. This is of interest in Canada given that the bowel cleansing kit Bi-Peglyte (PEG 3500) with 15 mg bisacodyl is currently approved for use. The objective is to assess the comparative safety of various bowel cleansers with or without bisacodyl, with a primary interest inpolyethylene glycol (PEG)-based and sodium-picosulfate-based products.

METHODS AND ANALYSIS

Given the existing volume of the literature, the review will be conducted in two stages. Stage 1 will consist of a scoping exercise by searching MEDLINE, Embase and the Cochrane Library (up to 21 November 2017) to identify randomised controlled trials, quasirandomised studies and non-randomised studies in which any bowel cleanser regimens were compared among persons undergoing colonoscopy. The outcomes will be mapped to establish a listing of the studies and their comparisons and outcomes currently available in the literature. From this, a data synthesis plan will be determined. In stage 2, a systematic review with meta-analyses will be pursued, focused on the bowel cleanser comparisons and outcomes of interest identified in stage 1. Two reviewers will screen, extract and quality assess the articles. Outcomes of interest include ischaemic colitis, electrolyte imbalances and their consequences, seizures, bowel perforation and patient tolerability. If sufficient data exist and studies are of sufficient homogeneity, network meta-analyses (NMAs) will be performed.

ETHICS AND DISSEMINATION

Ethics approval was not necessary due to study design. Updating the safety profile of bowel cleansers among the generally healthy population undergoing colonoscopy is pertinent given recent approval changes. This will be the first NMA within this population. Policy considerations may be reconsidered to minimise risk during bowel cleanser use.

PROSPERO REGISTRATION NUMBER

CRD42018084720.

Electronic cleansing in computed tomography colonography using AT layer identification with integration of gradient directional second derivative and material fraction model

Background

In computed tomography colonography images, electronic cleansing (EC) is applied to remove opacified residual materials, called fecal-tagging materials (FTM), using positive-contrast tagging agents and laxative to facilitate polyp detection.

Methods

The proposed EC, EC_prop, integrates the gradient directional second derivative into material fraction model to preserve submerged soft tissue (ST) under FTM. Three-material fraction model is used to remove FTM and artifacts at air-tagging (AT) layers and T-junctions where air, ST, and FTM material meet simultaneously. Moreover, the proposed AT layer identification is used to distinguish AT layers from air-tissue-tagging (ATT) layers in order to preserve ATT layers during cleansing. The clinical evaluation on 467 3-Dimensional band view images was conducted by the abdominal radiologist using four grading levels of cleansing quality with five causes of low quality EC. The amount of the remaining artifacts at T-junctions was approximated from the results of EC_prop. The results from EC_prop were compared with the results from syngo.via Client 3.0 Software, EC_syngo, and the fast three-material modeling, EC_prev, using the preference of the radiologist. Two-tailed paired Wilcoxon signed rank test is used to indicate statistical significance.

Results

The average grade on cleansing quality is 2.89 out of 4. The artifacts at T-junctions from 86.94% of the test images can be removed, whereas artifacts at T-junctions from only 13.06% of the test images cannot be removed. For 13.06% of the test images, the results from EC_prop are more preferable to the results from EC_syngo (p<0.008). For all the test images, the results from EC_prop are more preferable to the results from EC_prev (p<0.001). Finally, the visual assessment shows that EC_prop can preserve ATT layers, submerged polyps and folds while EC_prev can preserve only submerged folds but fails to preserve ATT layers.

Conclusion

From our implementation, EC_prop can improve the performance of the existing EC, such that it can preserve ST, especially ATT layers and remove the artifacts at T-junctions which have never been proposed by any other methods before.

Automated image-based colon cleansing for laxative-free CT colonography computer-aided polyp detection

PURPOSE

To evaluate the performance of a computer-aided detection (CAD) system for detecting colonic polyps at noncathartic computed tomography colonography (CTC) in conjunction with an automated image-based colon cleansing algorithm.

METHODS

An automated colon cleansing algorithm was designed to detect and subtract tagged-stool, accounting for heterogeneity and poor tagging, to be used in conjunction with a colon CAD system. The method is locally adaptive and combines intensity, shape, and texture analysis with probabilistic optimization. CTC data from cathartic-free bowel preparation were acquired for testing and training the parameters. Patients underwent various colonic preparations with barium or Gastroview in divided doses over 48 h before scanning. No laxatives were administered and no dietary modifications were required. Cases were selected from a polyp-enriched cohort and included scans in which at least 90% of the solid stool was visually estimated to be tagged and each colonic segment was distended in either the prone or supine view. The CAD system was run comparatively with and without the stool subtraction algorithm.

RESULTS

The dataset comprised 38 CTC scans from prone and/or supine scans of 19 patients containing 44 polyps larger than 10 mm (22 unique polyps, if matched between prone and supine scans). The results are robust on fine details around folds, thin-stool linings on the colonic wall, near polyps and in large fluid/stool pools. The sensitivity of the CAD system is 70.5% per polyp at a rate of 5.75 false positives/scan without using the stool subtraction module. This detection improved significantly (p = 0.009) after automated colon cleansing on cathartic-free data to 86.4% true positive rate at 5.75 false positives/scan.

CONCLUSIONS

An automated image-based colon cleansing algorithm designed to overcome the challenges of the noncathartic colon significantly improves the sensitivity of colon CAD by approximately 15%.