Colon cancer screening with virtual colonoscopy: promise, polyps, politics

A scoping review of factors influencing the implementation of liquid biopsy for cancer care

BACKGROUND

Liquid biopsy (LB) offers a promising, minimally invasive alternative to traditional tissue biopsies in cancer care, enabling real-time monitoring and personalized treatment. Despite its potential, the routine implementation of LB in clinical practice faces significant challenges. This scoping review examines the barriers and facilitators influencing the implementation of liquid biopsies into standard cancer care.

METHODS

Four academic databases (PubMed, Scopus, Embase, and Web of Science) were systematically searched without language restrictions. We included peer-reviewed articles that were published between January 2019 and March 2024 that focused on the implementation of LB in cancer care or described barriers and facilitators to its implementation. Data relevant to the review objective, including key article characteristics; barriers and facilitators of implementation; and recommendations for advancement or optimisation; were extracted and analysed using thematic and visual network analyses.

RESULTS

The majority of the included articles were narrative review articles (84%), with most from China (24.2%) and the United States (20%). Thematic analysis identified four main categories and their associated barriers and facilitators to the implementation of LB in cancer care: (1) Laboratory and personnel requirements; (2) Disease specificity; (3) Biomarker-based liquid biopsy; and (4) Policy and regulation. The majority of barriers identified were concentrated in the pre-analytical phase, highlighting the lack of standardization in LB technologies and outcomes.

CONCLUSIONS

Through a thematic analysis of the barriers and facilitators to LB implementation, we present an integrated tool designed to encourage the standardization of testing methods for clinical practice guidelines in the field.

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.

Combined assessment using optical colonoscopy and computed tomographic colonography improves the determination of tumor location and invasion depth

INTRODUCTION

An accurate assessment of the depth of tumor invasion in patients with colon cancer is an important part of the preoperative evaluation. Whether computed tomographic colonography (CTC) or optical colonoscopy (OC) is better to accurately determine tumor location and invasion depth has not been definitively determined. The aim of this study was to determine the diagnostic accuracy of tumor localization and tumor invasion depth of colon cancer by preoperative OC alone or combined with CTC.

METHODS

Study participants include 143 patients who underwent both preoperative CTC using automated CO₂ insufflation and OC from July 2012 to August 2013.

RESULTS

The accuracy of tumor localization was significantly better with CTC than with OC (OC, 90%; CTC, 98%; P < 0.05). No tumor in the descending colon was localized accurately via OC alone. The accuracy of tumor invasion depth was better with CTC plus OC than with OC alone (OC, 55%; CTC, 73%; P < 0.05).

CONCLUSIONS

OC combined with CTC provides a more accurate preoperative determination of tumor localization and invasion depth than OC alone.

Attraction Propagation: A User-Friendly Interactive Approach for Polyp Segmentation in Colonoscopy Images

The article raised a user-friendly interactive approach-Attraction Propagation (AP) in segmentation of colorectal polyps. Compared with other interactive approaches, the AP relied on only one foreground seed to get different shapes of polyps, and it can be compatible with pre-processing stage of Computer-Aided Diagnosis (CAD) under the systematically procedure of Optical Colonoscopy (OC). The experimental design was based on challenging distinct datasets that totally includes 1691 OC images, and the results demonstrated that no matter in accuracy or calculating speed, the AP performed better than the state-of-the-art.

Comparison of 64-Detector CT Colonography and Conventional Colonoscopy in the Detection of Colorectal Lesions

Background:

Colon cancer is a leading cause of morbidity and mortality in developed countries. The early detection of colorectal cancer using screening programs is important for managing early-stage colorectal cancers and polyps. Modalities that allow examination of the entire colon are conventional colonoscopy, double contrast barium enema examination and multi-detector computed tomography (MDCT) colonography.

Objectives:

To compare CT colonography and conventional colonoscopy results and to evaluate the accuracy of CT colonography for detecting colorectal lesions.

Patients and Methods:

In a prospective study performed at Gastroenterology and Radiology Departments of Medical Faculty of Eskisehir Osmangazi University, CT colonography and colonoscopy results of 31 patients with family history of colorectal carcinoma, personal or family history of colorectal polyps, lower gastrointestinal tract bleeding, change in bowel habits, iron deficiency anemia and abdominal pain were compared. Regardless of the size, CT colonography and conventional colonoscopy findings for all the lesions were cross - tabulated and the sensitivity, specificity, and positive and negative predictive values were calculated. To assess the agreement between CT colonography and conventional colonoscopy examinations, the Kappa coefficient of agreementt was used. Statistical analysis was performed by SPSS ver 15.0.

Results:

Regardless of the size, MDCT colonography showed 83% sensitivity and 95% specificity, with a positive predictive value of 95% and a negative predictive value of 83% for the detection of colorectal polyps and masses. MDCT colonography displayed 92% sensitivity and 95% specificity, with a positive predictive value of 92% and a negative predictive value of 95% for polyps ≥ 10 mm. For polyps between 6mm and 9 mm, MDCT colonography displayed 75% sensitivity and 100% specificity, with a positive predictive value of 100% and a negative predictive value of 90%. For polyps ≤ 5 mm MDCT colonography displayed 88% sensitivity and 100% specificity with a positive predictive value of 100% and a negative predictive value of 95%.

Conclusions:

CT colonography is a safe and minimally invasive technique, a valuable diagnostic tool for examining the entire colon and a good alternative compared to other colorectal cancer screening tests because of its high sensitivity values in colorectal lesions over 1 cm.

Topology preserving thinning of cell complexes

A topology preserving skeleton is a synthetic representation of an object that retains its topology and many of its significant morphological properties. The process of obtaining the skeleton, referred to as skeletonization or thinning, is a very active research area. It plays a central role in reducing the amount of information to be processed during image analysis and visualization, computer-aided diagnosis, or by pattern recognition algorithms. This paper introduces a novel topology preserving thinning algorithm, which removes simple cells-a generalization of simple points-of a given cell complex. The test for simple cells is based on acyclicity tables automatically produced in advance with homology computations. Using acyclicity tables render the implementation of thinning algorithms straightforward. Moreover, the fact that tables are automatically filled for all possible configurations allows to rigorously prove the generality of the algorithm and to obtain fool-proof implementations. The novel approach enables, for the first time, according to our knowledge, to thin a general unstructured simplicial complex. Acyclicity tables for cubical and simplicial complexes and an open source implementation of the thinning algorithm are provided as an additional material to allow their immediate use in the vast number of applications arising in medical imaging and beyond.

Fast three-material modeling with triple arch projection for electronic cleansing in CTC

In this paper, we propose a fast three-material modeling for electronic cleansing (EC) in computed tomographic colonography. Using a triple arch projection, our three-material modeling provides a very quick estimate of the three-material fractions to remove ridge-shaped artifacts at the T-junctions where air, soft-tissue (ST), and tagged residues (TRs) meet simultaneously. In our approach, colonic components including air, TR, the layer between air and TR, the layer between ST and TR (L(ST/TR)), and the T-junction are first segmented. Subsequently, the material fraction of ST for each voxel in L(ST/TR) and the T-junction is determined. Two-material fractions of the voxels in L(ST/TR) are derived based on a two-material transition model. On the other hand, three-material fractions of the voxels in the T-junction are estimated based on our fast three-material modeling with triple arch projection. Finally, the CT density value of each voxel is updated based on our fold-preserving reconstruction model. Experimental results using ten clinical datasets demonstrate that the proposed three-material modeling successfully removed the T-junction artifacts and clearly reconstructed the whole colon surface while preserving the submerged folds well. Furthermore, compared with the previous three-material transition model, the proposed three-material modeling resulted in about a five-fold increase in speed with the better preservation of submerged folds and the similar level of cleansing quality in T-junction regions.

Fold-preserving electronic cleansing using a reconstruction model integrating material fractions and structural responses

In this paper, we propose an electronic cleansing method using a novel reconstruction model for removing tagged materials (TMs) in computed tomography (CT) images. To address the partial volume (PV) and pseudoenhancement (PEH) effects concurrently, material fractions and structural responses are integrated into a single reconstruction model. In our approach, colonic components including air, TM, an interface layer between air and TM, and an interface layer between soft-tissue (ST) and TM (IL ST/TM ) are first segmented. For each voxel in IL ST/TM, the material fractions of ST and TM are derived using a two-material transition model, and the structural response to identify the folds submerged in the TM is calculated by the rut-enhancement function based on the eigenvalue signatures of the Hessian matrix. Then, the CT density value of each voxel in IL ST/TM is reconstructed based on both the material fractions and structural responses. The material fractions remove the aliasing artifacts caused by a PV effect in IL ST/TM effectively while the structural responses avoid the erroneous cleansing of the submerged folds caused by the PEH effect. Experimental results using ten clinical datasets demonstrated that the proposed method showed higher cleansing quality and better preservation of submerged folds than the previous method, which was validated by the higher mean density values and fold preservation rates for manually segmented fold regions.

Ultrasound detection of colonic polyps: perspective

Colorectal cancer is often preventable if the precursor adenoma is detected and removed. Although ultrasound is clearly not one of the widely accepted screening techniques, this non-invasive and radiation-free modality is also capable of detecting colonic polyps, both benign and malignant. Such colon lesions may be encountered when not expected, usually during general abdominal sonography. The discovery of large colonic polyps is important and can potentially help reduce the incidence of a common cancer, whereas detection of a malignant polyp at an early stage may result in a curative intervention. This pictorial review highlights our experience of sonographic detection of colonic polyps in 43 adult patients encountered at our institutions over a 2-year period. 4 out of 50 discovered polyps were found to be malignant lesions, 3 polyps were hyperplastic, 1 polyp was a hamartomatous polyp and the rest were benign adenomas. The smallest of the detected polyps was 1.3 cm in diameter, the largest one was 4.0 cm (mean 1.7 cm; median 1.6 cm). In each case, polyps were discovered during a routine abdominal or pelvic examination, particularly when scanning was supplemented by a brief focused sonographic inspection of the colon with a 6-10 MHz linear transducer. In this paper, we illustrate the key sonographic features of different types of commonly encountered colonic polyps in the hope of encouraging more observers to detect these lesions, which may be subtle.

Role of CT colonography in symptomatic assessment, surveillance and screening

INTRODUCTION

When 'whole colonic imaging' is indicated, clinicians must decide between optical colonoscopy, barium enema and CT colonography (CTC). CTC is a relatively new technique which has become increasingly accessible in the UK over the past 5 years. As radiologists have gained experience and scanning parameters have standardised, there have been substantial improvements in both the accuracy and safety of CTC.

METHODS

We review evidence from observational studies and randomised trials, and draw on expert opinion, to provide a comprehensive discussion of the current role of CTC in both symptomatic and asymptomatic individuals.

CONCLUSIONS

The emergence of CTC could soon entirely obviate the need for barium enema. CTC now has a complementary role alongside colonoscopy in symptomatic patients and a possible future role in colorectal cancer screening in the UK.

Colorectal cancer screening in women: an underutilized lifesaver

OBJECTIVE

Colorectal cancer (CRC) represents the third most common cancer diagnosed and a major cause of cancer-related deaths in women. Despite strong evidence that early screening decreases colorectal cancer incidence and mortality rates, colorectal cancer screening rates in women still lag significantly behind screening rates for breast and cervical cancers. Additionally, women have been found to be less likely than men to undergo CRC screening. This is despite the fact that the overall lifetime risk for the development of colorectal carcinoma is similar in both sexes. Barriers to screening have been found to be different for women compared with men. Screening adherence in women also appears to be associated with various social and demographic factors.

CONCLUSION

CT colonography (CTC) is an accurate, minimally invasive, and well-tolerated examination that is newly endorsed by the American Cancer Society, U.S. Multisociety Task Force, and the American College of Radiology. Improved screening compliance may occur in women with further dissemination of CTC.

Current techniques in the performance, interpretation, and reporting of CT colonography

The technical objective of computed tomographic colonography (CTC) is to acquire high-quality computed tomography images of the cleansed, well-distended colon for polyp detection. In this article the authors provide an overview of the technical components of CTC, from preparation of the patient to acquisition of the imaging data and basic methods of interpretation. In each section, the best evidence for current practices and recommendations is reviewed. Each of the technical components must be optimized to achieve high sensitivity in polyp detection.

Contrast-enhanced CT colonography with 64-slice MDCT compared to endoscopic colonoscopy in the follow-up of patients after colorectal cancer resection

BACKGROUND

Seventy percent of newly diagnosed colorectal cancer cases are potential candidates for curative surgery, but after resection, in 30%, the tumor will recur. Postoperative follow-up includes endoscopic colonoscopy (EC) and computed tomography (CT). There have been only a few publications on the use of contrast-enhanced CT colonography (CECTC) in the follow-up of these patients.

METHODS

Twenty-nine consecutive patients after resection of colorectal cancer underwent CECTC and EC on the same day. CECTC studies were reviewed for identification of strictures, recurrence, polyps and metastases.

RESULTS

The anastomosis was identified in 96% of patients on CECTC and in 82% on endoscopic colonoscopy. One stricture was identified by both techniques. One extraluminal recurrence was depicted only on CECTC. Sensitivity in detecting polyps was per polyp 93% and per patient 100%.

CONCLUSION

CECTC performed on a 64-slice multidetector CT is reliable in imaging the postoperative colon for the follow-up of patients after resection of colorectal cancer.

Computer-aided detection of polyps in CT colonography using logistic regression

We present a computer-aided detection (CAD) system for computed tomography colonography that orders the polyps according to clinical relevance. The CAD system consists of two steps: candidate detection and supervised classification. The characteristics of the detection step lead to specific choices for the classification system. The candidates are ordered by a linear logistic classifier (logistic regression) based on only three features: the protrusion of the colon wall, the mean internal intensity, and a feature to discard detections on the rectal enema tube. This classifier can cope with a small number of polyps available for training, a large imbalance between polyps and non-polyp candidates, a truncated feature space, unbalanced and unknown misclassification costs, and an exponential distribution with respect to candidate size in feature space. Our CAD system was evaluated with data sets from four different medical centers. For polyps larger than or equal to 6 mm we achieved sensitivities of respectively 95%, 85%, 85%, and 100% with 5, 4, 5, and 6 false positives per scan over 86, 48, 141, and 32 patients. A cross-center evaluation in which the system is trained and tested with data from different sources showed that the trained CAD system generalizes to data from different medical centers and with different patient preparations. This is essential to application in large-scale screening for colorectal polyps.

CT colonography: techniques and applications

CT colonography (CTC), also termed virtual colonoscopy, is increasingly accepted at sites throughout the world as a new effective tool for the diagnosis and screening of colorectal carcinoma. This article presents information of related issues of bowel cleansing, stool and fluid tagging, bowel distention and multidetector CT scanning parameters. The author presents discussion of interpretation of CTC, appropriate applications of CTC and potential complications.

Virtual colonoscopy in paediatric patients Usefulness of a colon dissection technique

OBJECTIVE

To determine the usefulness of perspective-filet view for polypoid lesions in paediatric patients in comparison with conventional virtual colonoscopy (VC) analysis and optical colonoscopy.

METHODS

Sixty-one patients (mean age 5 years old) with a previous episode of rectal bleeding were studied using a 16 slices CT scanner. All patients underwent a colonic preparation. Two acquisitions were done in supine and prone positions with slices of 2mm thickness; increment 1mm, 30-50mA; 90-120kV. In a workstation an experienced radiologist reviewed images twice. The first read was done using the conventional virtual colonoscopy technique with the evaluation of two-dimensional (2D), three-dimensional (3D) and endoscopical images. Later, in a second session, perspective-filet view was used. It shows a 360 degrees unrolled visualization of the inner colon. The presence, size and location of the lesions were determined. A record of the reading time was made.

RESULTS

At per patient evaluation the conventional virtual colonoscopy analysis obtained a sensitivity of 86% and a specificity of 98%. The perspective-filet view obtained a sensitivity of 91% and a specificity of 99%. In the evaluation on a per lesion basis the conventional analysis had a sensitivity of 81% and a specificity of 88%. Perspective-filet view, had a sensitivity of 82% and specificity of 90%. The average total reading time using conventional colonoscopy technique was 18+/-3min, versus 4+/-1min using the perspective-filet view.

CONCLUSION

Virtual colon dissection with perspective-filet view is more time-efficient than conventional virtual colonoscopy evaluation with correct correlation in results.

Virtual colonoscopy vs conventional colonoscopy in patients at high risk of colorectal cancer--a prospective trial of 150 patients

OBJECTIVE

Virtual colonoscopy (VC)/CT colonography has advantages over the well-documented limitations of colonoscopy/barium enema. This prospective blinded investigative comparison trial aimed to evaluate the ability of VC to assess the large bowel, compared to conventional colonoscopy (CC), in patients at high risk of colorectal cancer (CRC).

METHOD

We studied 150 patients (73 males, mean age 60.9 years) at high risk of CRC. Following bowel preparation, VC was undertaken using colonic insufflation and 2D-spiral CT acquisition. Two radiologists reported the images and a consensual agreement reached. Direct comparison was made with CC (performed later the same day). Interobserver agreement was calculated using the Kappa method. Postal questionnaires sought patient preference.

RESULTS

Virtual colonoscopy visualized the caecum in all cases. Five (3.33%) VCs were classified as inadequate owing to poor distension/faecal residue. CC completion rate was 86%. Ultimately, 44 patients had normal findings, 44 had diverticular disease, 11 had inflammatory bowel disease, 18 had cancers, and 33 patients had 42 polyps. VC identified 19 cancers--a sensitivity and specificity of 100% and 99.2% respectively. For detecting polyps > 10 mm, VC had a sensitivity and specificity (per patient) of 91% and 99.2% respectively. VC identified four polyps proximal to stenosing carcinomas and extracolonic malignancies in nine patients (6%). No procedural complications occurred with either investigation. A Kappa score achieved for interobserver agreement was 0.777.

CONCLUSION

Virtual colonoscopy is an effective and safe method for evaluating the bowel and was the investigation of choice amongst patients surveyed. VC provided information additional to CC on both proximal and extracolonic pathology. VC may become the diagnostic procedure of choice for symptomatic patients at high risk of CRC, with CC being reserved for therapeutic intervention, or where a tissue diagnosis is required.

Volume-based Feature Analysis of Mucosa for Automatic Initial Polyp Detection in Virtual Colonoscopy

In this paper, we present a volume-based mucosa-based polyp candidate determination scheme for automatic polyp detection in computed colonography. Different from most of the existing computer-aided detection (CAD) methods where mucosa layer is a one-layer surface, a thick mucosa of 3-5 voxels wide fully reflecting partial volume effect is intentionally extracted, which excludes the direct applications of the traditional geometrical features. In order to address this dilemma, fast marching-based adaptive gradient/curvature and weighted integral curvature along normal directions (WICND) are developed for volume-based mucosa. In doing so, polyp candidates are optimally determined by computing and clustering these fast marching-based adaptive geometrical features. By testing on 52 patients datasets in which 26 patients were found with polyps of size 4-22 mm, both the locations and number of polyp candidates detected by WICND and previously developed linear integral curvature (LIC) were compared. The results were promising that WICND outperformed LIC mainly in two aspects: (1) the number of detected false positives was reduced from 706 to 132 on average, which significantly released our burden of machine learning in the feature space, and (2) both the sensitivity and accuracy of polyp detection have been slightly improved, especially for those polyps smaller than 5mm.

Multidetector CT colonoscopy: evaluation of the perspective-filet view virtual colon dissection technique for the detection of elevated lesions

BACKGROUND

The purpose of our study was to determine the usefulness of a virtual computed tomography colon dissection visualization technique for the detection of polypoid lesions in comparison with conventional virtual colonoscopy analysis and optical colonoscopy.

METHODS

Twenty-three patients were evaluated with optical colonoscopy and computed tomography colonoscopy using 16-row MDCT on the same day. CT images were analyzed by the colon dissection workup with unfolded haustra visualization and also using the conventional virtual colonoscopy technique (axial images and endoluminal views). The CT analysis was performed by an experienced radiologist using both viewing methods in a randomized order and blinded to optical colonoscopy results.

RESULTS

Optical colonoscopy revealed 35 colonic lesions; 15 < 5 mm, 18 between 5-9 mm and 2 > 9 mm. For conventional virtual colonoscopy analysis the overall sensitivity was 86.67%; for the colon dissection visualization technique, the overall sensitivity was 82.86%. The average reading time for conventional virtual colonoscopy was 15 +/- 3 vs. 8 +/- 2 min for the colon dissection visualization technique.

CONCLUSIONS

Our results showed that there is a significant reduction in the reading time using the colon dissection visualization technique without detriment to the detection rate, that is, competitive to conventional virtual colonoscopy interpretation results.

Colorectal cancer screening tests: pros and cons, and for whom?

The past decade has seen major advances internationally in the implementation of colorectal cancer screening, influenced in differing ways by the profession, the public and by government. Relatively unique to colorectal cancer screening is the availability of so many test alternatives, which have substantial variation in methodology. While perhaps spoilt for choice, discerning the key advantages and disadvantages of each test is often difficult, depending on the perspective from which screening is viewed. Accordingly, this article provides an evaluation of screening tests as might be perceived by governments, the patient and the profession. Aligned issues such as choosing a screening test and provision of informed consent are discussed. Finally, the article identifies current problems with various screening tests that, if attended to, might change the perception of a test's value to a particular interest group.

Computed tomography colonography compared with conventional colonoscopy for the detection of colorectal polyps

OBJECTIVE

To determine the diagnostic accuracy of computed tomography colonography (CTC) compared with conventional colonoscopy (CC).

METHODS

Patients with an indication of CC were included. Fifty patients underwent CTC using multidetector CT before diagnostic colonoscopy was performed by an expert colonoscopist. Diagnostic accuracy was assessed individually both for each polyp and for each patient.

RESULTS

Fifty patients were included and 40 polyps were analyzed. The by-polyp sensitivity of CTC was 15% for polyps 5 mm or less, 75% for polyps 5- 10 mm and 75% for polyps 10 mm or larger. By-patient specificity was 6% for polyps 5 mm or less, 75% for polyps 5-10 mm and 80% for polyps 10 mm or larger. The specificity of CTC was 94%. CTC was preferred over CC by 90% of the patients. The mean colonoscopy examination time was 30 minutes for CC and 35 minutes for CTC (p < 0.05).

CONCLUSIONS

The sensitivity of CTC is moderate in detecting polyps larger than 10 mm, low in detecting 5-10 mm polyps and very low in detecting those less than 5 mm. The overall specificity of the procedure was 94%. Procedure time was lower with CC than with CTC but the latter was better tolerated by most patients.

A probabilistic model for haustral curvatures with applications to colon CAD

Among the many features used for classification in computer-aided detection (CAD) systems targeting colonic polyps, those based on differences between the shapes of polyps and folds are most common. We introduce here an explicit parametric model for the haustra or colon wall. The proposed model captures the overall shape of the haustra and we use it to derive the probability distribution of features relevant to polyp detection. The usefulness of the model is demonstrated through its application to a colon CAD algorithm.

Sigmoid colon perforation at CT colonography secondary to a possible obstructive mechanism: report of a case

We report a case of colonic perforation in CT colonography, which was observed in a sigmoid colon segment contained within an inguinal hernia. At surgery, apart from the perforation, a normal large-bowel wall was found. Although rare, perforation may occur in patients with normal bowel wall, possibly resulting from a mechanical strain caused by gaseous overdistention. Radiologists performing the procedure must be aware of this possibility.

CT colonoscopy in inflammatory bowel disease

Virtual colonoscopy is used worldwide for the detection of colon polyps, but this technique has not been used much for the evaluation of inflammatory bowel diseases. The advent of multidetector-computed tomography and the use of high quality 3D and virtual images opened up the opportunity to assess these patients with this non-invasive technique. Early and late colonic changes are illustrated.

Polyp measurement reliability, accuracy, and discrepancy: optical colonoscopy versus CT colonography with pig colonic specimens

PURPOSE

To prospectively evaluate the reliability and accuracy of optical colonoscopy and computed tomographic (CT) colonography in polyp measurement, by using direct measurement as the reference standard, and to understand the basis for measurement discrepancy between both modalities.

MATERIALS AND METHODS

Eighty-six simulated polyps that ranged from 3 to 15 mm were constructed by using pig colons obtained from an abattoir. Approval of the animal care and use committee for the study was not required. CT colonographic measurement was performed by two independent radiologists by using two-dimensional (2D) optimized multiplanar reformatted planes and three-dimensional (3D) endoluminal views. Optical colonoscopic measurement was performed by two independent gastroenterologists by using open biopsy forceps. Interobserver agreement, measurement error, measurement discrepancy defined as the result of subtracting the optical colonoscopic measurement from the CT colonographic measurement, and false-mismatch (ie, designation of matched polyps as mismatched between both modalities) rates according to different matching criteria were analyzed.

RESULTS

Intraclass correlation coefficients were 0.879 (95% confidence interval: 0.780, 0.930) for optical colonoscopy, 0.979 (95% confidence interval: 0.956, 0.989) for 2D CT colonography, and 0.985 (95% confidence interval: 0.976, 0.990) for 3D CT colonography. The mean standardized polyp size +/- standard deviation for each observer was 76.3% +/- 14.7 and 85.3% +/- 18.8 for optical colonoscopy, 104.6% +/- 11.6 and 101.6% +/- 10.1 for 2D CT colonography, and 114% +/- 12.4 and 113.4% +/- 13.2 for 3D CT colonography. These values indicated that there was a statistically significant difference among the methods (P<.001). Measurement discrepancy was not proportional to polyp size. A percentage-of-error criterion showed increasing false-mismatch rates with decreasing polyp size, whereas a fixed margin-of-error criterion resulted in more uniform false-mismatch rates across polyp size.

CONCLUSION

CT colonography is more reliable and accurate than optical colonoscopy for polyp measurement. A fixed margin-of-error criterion is better than a percentage-of-error criterion for polyp matching between CT colonography and optical colonoscopy with open biopsy forceps.

CT colonography: automated measurement of colonic polyps compared with manual techniques--human in vitro study

PURPOSE

To prospectively investigate the relative accuracy and reproducibility of manual and automated computer software measurements by using polyps of known size in a human colectomy specimen.

MATERIALS AND METHODS

Institutional review board approval was obtained for the study; written consent for use of the surgical specimen was obtained. A colectomy specimen containing 27 polyps from a 16-year-old male patient with familial adenomatous polyposis was insufflated, submerged in a container with solution, and scanned at four-section multi-detector row computed tomography (CT). A histopathologist measured the maximum dimension of all polyps in the opened specimen. Digital photographs and line drawings were produced to aid CT-histologic measurement correlation. A novice (radiographic technician) and an experienced (radiologist) observer independently estimated polyp diameter with three methods: manual two-dimensional (2D) and manual three-dimensional (3D) measurement with software calipers and automated measurement with software (automatic). Data were analyzed with paired t tests and Bland-Altman limits of agreement.

RESULTS

Seven polyps (<or=6-mm diameter) could not be extracted by using the software; 20 polyps (5-15-mm diameter) remained for analysis. Automated measurement was not significantly different from histologic size for the experienced reader (mean difference, 0.63 mm; P=.06) or novice reader (mean difference, 0.58 mm; P=.12). With manual 2D measurement and manual 3D measurement, the experienced reader (1.21-mm mean difference, P<.001, and 0.68-mm mean difference, P=.03, respectively) and novice reader (1.54-mm mean difference, P<.001, and 0.84-mm mean difference, P=.002, respectively) significantly underestimated polyp size. Interobserver agreement was good and similar for all three methods (95% limits of agreement span, approximately 2.5 mm). Intraobserver agreement was related to reader experience, with differences of up to 2.5 mm within expected limits of agreement.

CONCLUSION

For polyps smaller than 1 cm, measurement differences of up to 2.5 mm are within the expected limits of inter- and intraobserver agreement for all measurement techniques. Automated and manual 3D polyp measurements are more accurate than manual 2D measurements.

An improved electronic colon cleansing method for detection of colonic polyps by virtual colonoscopy

Electronic colon cleansing (ECC) aims to segment the colon lumen from a patient abdominal image acquired using an oral contrast agent for colonic material tagging, so that a virtual colon model can be constructed. Virtual colonoscopy (VC) provides fly-through navigation within the colon model, looking for polyps on the inner surface in a manner analogous to that of fiber optic colonoscopy. We have built an ECC pipeline for a commercial VC navigation system. In this paper, we present an improved ECC method. It is based on a partial-volume (PV) image-segmentation framework, which is derived using the well-established statistical expectation-maximization algorithm. The presented ECC method was evaluated by both visual inspection and computer-aided detection of polyps (CADpolyp) within the cleansed colon lumens obtained using 20 patient datasets. Compared to our previous ECC pipeline, which does not sufficiently consider the PV effect, the method presented in this paper demonstrates improved polyp detection by both visual judgment and CADpolyp measure.

Reduction of false positives by internal features for polyp detection in CT-based virtual colonoscopy

In this paper, we present a computer-aided detection (CAD) method to extract and use internal features to reduce false positive (FP) rate generated by surface-based measures on the inner colon wall in computed tomographic (CT) colonography. Firstly, a new shape description global curvature, which can provide an overall shape description of the colon wall, is introduced to improve the detection of suspicious patches on the colon wall whose geometrical features are similar to that of the colonic polyps. By a ray-driven edge finder, the volume of each detected patch is extracted as a fitted ellipsoid model. Within the ellipsoid model, CT image density distribution is analyzed. Three types of (geometrical, morphological, and textural) internal features are extracted and applied to eliminate the FPs from the detected patches. The presented CAD method was tested by a total of 153 patient datasets in which 45 patients were found with 61 polyps of sizes 4-30 mm by optical colonoscopy. For a 100% detection sensitivity (on polyps), the presented CAD method had an average FPs of 2.68 per patient dataset and eliminated 93.1% of FPs generated by the surface-based measures. The presented CAD method was also evaluated by different polyp sizes. For polyp sizes of 10-30 mm, the method achieved mean number of FPs per dataset of 2.0 with 100% sensitivity. For polyp sizes of 4-10 mm, the method achieved 3.44 FP per dataset with 100% sensitivity.

Emerging technologies in colorectal cancer screening

CRC is a preventable disease through early detection, yet screening rates remain low and mortality rates remain high. The discomfort associated with the preparation and performance of some of the currently available screening modalities and the lack of public awareness about CRC and screening procedures likely account for low rates of screening. CT colonography and stool DNA testing are new promising screening technologies that are less invasive, accurate, and suitable for the public more than the current screening procedures. Before both tests can be promoted for population-based screening programs, several issues that have been detailed in this article must be addressed further, including technical improvements for improving accuracy, development of virtual preparation, test availability, patient and provider acceptability and cost-effectiveness for CTC, and identifying the optimal combination of molecular targets for stool DNA testing. The year 2005 will tell us if the ideal technology from the public health point of view was achieved. A skill-independent, anesthesia-free, self-propelling, self-navigating miniaturized endoscopic device that may move along the entire length of the colon may change the natural history of CRC. We should aim to achieve a new definition of CRC--a rare disease occurring in a subset of the population who has not been screened for the disease.

Colorectal polyps: detection with low-dose multi-detector row helical CT colonography versus two sequential colonoscopies

PURPOSE

To prospectively evaluate the diagnostic accuracy of low-radiation-dose computed tomographic (CT) colonography for detection of colorectal polyps by using two sequential colonoscopies, with the second colonoscopy as the reference standard.

MATERIALS AND METHODS

The study was local ethics committee approved, and all patients gave written informed consent. Colonographic images were acquired by using a low-dose multi-detector row CT protocol (effective milliampere-second setting, 10 mAs). Three observers interpreted the CT colonographic data separately and independently by using a two-dimensional technique. Initial conventional colonoscopy was performed by an endoscopist unaware of the CT colonographic findings. Second colonoscopy performed within 2 weeks by a colonoscopist aware of both the CT colonographic and the initial colonoscopic findings served as the reference standard. The sensitivities of CT colonography and initial colonoscopy were calculated on a per-polyp and a per-patient basis. Specificities and positive and negative predictive values also were calculated on a per-patient basis.

RESULTS

Eighty-eight patients underwent CT colonography and initial conventional colonoscopy on the same day. Per-polyp sensitivities were 62% and 83% for CT colonography and initial colonoscopy, respectively. Sensitivities for detection of polyps 6 mm in diameter or larger were 86% and 84% for CT colonography and initial colonoscopy, respectively. Initial colonoscopy failed to depict 16 polyps, six of which were correctly detected with CT colonography. For identification of patients with polyps 6 mm in diameter or larger, CT colonography and initial colonoscopy, respectively, had sensitivities of 84% and 90%, specificities of 82% and 100%, positive predictive values of 70% and 100%, and negative predictive values of 91% and 95%.

CONCLUSION

Low-dose CT colonography compares favorably with colonoscopy for detection of colorectal polyps 6 mm in diameter or larger, with markedly decreased performance for detection of polyps 5 mm in diameter or smaller.

Virtual colonoscopy for colorectal cancer screening: current status

Computed tomography colonography (CTC) (also known as ‘virtual colonoscopy’) is a noninvasive method of imaging the colon using helical CT. Although CTC has been shown to be useful for certain clinical indications, it has not yet been endorsed as a colorectal cancer screening test. The purpose of this article is to review the current status of CTC for colorectal cancer screening. CTC is an accurate method to detect colonic polyps and to select patients who would benefit from colonoscopy. The major advantages of CTC over conventional colonography include its relatively low risk and greater tolerance by patients. In this article, the CTC procedure and results of clinical trials are reviewed, as well as potential pitfalls related to CTC performance and interpretation. Finally, radiation dose, the discovery of incidental extracolonic findings with CTC, bowel preparation methods, and computer-aided diagnosis are addressed.

Centerline-based colon segmentation for CT colonography

We have developed a fully automated algorithm for colon segmentation, centerline-based segmentation (CBS), which is faster than any of the previously presented segmentation algorithms, but also has high sensitivity as well as high specificity. The algorithm first thresholds a set of unprocessed CT slices. Outer air is removed, after which a bounding box is computed. A centerline is computed for all remaining regions in the thresholded volume, disregarding segments related to extracolonic structures. Centerline segments are connected, after which the anatomy-based removal of segments representing extracolonic structures occurs. Segments related to the remaining centerline are locally region grown, and the colonic wall is found by dilation. Shape-based interpolation provides an isotropic mask. For 38 CT datasets, CBS was compared with the knowledge-guided segmentation (KGS) algorithm for sensitivity and specificity. With use of a 1.5 GHz AMD Athlon-based PC, the average computation time for the segmentation was 14.8 s. The sensitivity was, on average, 96%, and the specificity was 99%. A total of 21% of the voxels segmented by KGS, of which 96% represented extracolonic structures and 4% represented the colon, were removed.

The role of CT colonography in colorectal cancer screening

Computed tomographic colonography (CTC) is a relatively noninvasive technique for large bowel imaging that has the ability to detect colorectal neoplasia. Already well established as a reliable diagnostic tool in symptomatic patients who are unable to undergo complete colonoscopy, it is now being considered as a viable method for population screening. Advances in technique over the past 10 yr make this an attractive alternative, including reduced bowel preparation and stool tagging, three-dimensional (3D) image reconstruction, computer-aided detection software, and low-radiation dose protocols. CTC may be favored by patients compared to other available screening tests due to the ease of performance and comfort. Although published studies vary in relation to the sensitivity of this test for the detection of polyps, in the best hands a sensitivity of greater than 90% for detection of polyps at least 10 mm in diameter may be obtained. Although not yet endorsed for widespread use by major gastroenterological societies, CTC shows promise as a screening tool.

Spasmolysis at CT colonography: butyl scopolamine versus glucagon

PURPOSE

To retrospectively determine if the use of butyl scopolamine or glucagon in the supine patient improves colonic distention and reduces the number of collapsed intestinal segments at computed tomographic (CT) colonography.

MATERIALS AND METHODS

This study had institutional review board approval; subject informed consent was not required. CT colonography was performed without the administration of an intravenous spasmolytic in 80 asymptomatic subjects (group 1; 45 women, 35 men; age range, 48-77 years; mean, 61.9 years). These subjects were matched with two groups of 80 subjects who were similar in age but were premedicated with glucagon (group 2; 41 women, 39 men; age range, 43-76 years; mean, 63.1 years) or butyl scopolamine (group 3; 43 women, 37 men; age range, 34-77 years; mean, 63.4 years). All 240 subjects were examined in the supine position with multisection CT and a section thickness of 1 mm after intravenous contrast agent administration and rectal carbon dioxide insufflation. The colon was divided into seven segments, and the colon length, total volume, radial distensibility, and number of non-distended segments were calculated for each subject and compared among the three groups. Statistical analysis was performed with analysis of variance and chi2 testing.

RESULTS

Mean bowel length was not significantly different among the groups. Mean colon volumes and radial distensibilities, respectively, were 1.84 L and 3.69 cm in group 1, 2.14 L and 3.98 cm in group 2, and 2.35 L and 4.23 cm in group 3; differences in colon volume and radial distensibility were significant only between group 1 and group 3 (P < .001). At CT colonography, 29 segments in 20 group 1 subjects were collapsed, 23 segments in 12 group 2 subjects were collapsed, and 11 segments in six group 3 subjects were collapsed (P = .016).

CONCLUSION

Premedication with butyl scopolamine or, less effectively, glucagon improves colonic distention in the supine subject.

A new path planning algorithm for maximizing visibility in computed tomography colonography

In virtual colonoscopy, minimizing the blind areas is important for accurate diagnosis of colonic polyps. Although useful for describing the shape of an object, the centerline is not always the optimal camera path for observing the object. Hence, conventional methods in which the centerline is directly used as a path produce considerable blind areas, especially in areas of high curvature. Our proposed algorithm first approximates the surface of the object by estimating the overall shape and cross-sectional thicknesses. View positions and their corresponding view directions are then jointly determined to enable us to maximally observe the approximated surface. Moreover, by adopting bidirectional navigations, we may reduce the blind area blocked by haustral folds. For comfortable navigation, we carefully smoothen the obtained path and minimize the amount of rotation between consecutive rendered images. For the evaluation, we quantified the overall observable area on the basis of the temporal visibility that reflects the minimum interpretation time of a human observer. The experimental results show that our algorithm improves visibility coverage and also significantly reduces the number of blind areas that have a clinically meaningful size. A sequence of rendered images shows that our algorithm can provide a sequence of centered and comfortable views of colonography.

CT colonography after fecal tagging with a reduced cathartic cleansing and a reduced volume of barium

OBJECTIVE

The objective of our study was to assess the efficacy of fecal tagging with a small volume of barium in combination with a reduced cathartic cleansing before CT colonography.

MATERIALS AND METHODS

The study consists of a review of 200 patients examined in a clinical setting. Conventional colonoscopy and CT colonography or follow-up were used as the gold standard. All patients prepared for CT colonography the day before the examination with a dedicated low-residue diet. Fecal tagging was performed with 50 mL of barium. The residual feces and fluid were evaluated on a segmental basis. The residual feces was divided in two categories (< 6 mm and > or = 6 mm). The amount of fluid was assessed on the axial slices. The efficacy of tagging was evaluated visually.

RESULTS

For the study, 1,200 segments were evaluated. Residual feces was present in 413 segments (34.41%), with feces less than 6 mm in 210 segments (17.5%) and feces 6 mm or greater in 203 segments (16.92%). There was residual fluid in 527 segments (43.91%). Nontagged feces 6 mm or greater was present in 49 segments (4.08%) and nontagged fluid in 178 segments (14.83%). All nontagged feces 6 mm or greater was easy to assess. All fluid redistributed with dual positioning. A total of 65 lesions 6 mm or greater were correctly diagnosed on primary CT colonography. In two patients, two lesions adjacent to each other were misinterpreted as being only one. Another 8-mm lesion was missed.

CONCLUSION

In the present study, CT colonography after fecal tagging with 50 mL of barium combined with a reduced cathartic cleansing was feasible.

State-of-the-art computed tomographic and magnetic resonance imaging of the gastrointestinal system

Among the major innovations in radiology of the gastrointestinal (GI) system are the replacement of classic invasive diagnostic methods with noninvasive ones and the improvement in lesion characterization and staging of pancreatobiliary malignancies. Developments in imaging technology have led to many improvements in the field of diagnostic GI radiology. With its fast and thin-section scanning abilities, multidetector-row CT (MDCT) strengthens the place of CT as the most efficient tool to diagnose, characterize, and preoperatively stage pancreatic neoplasms. MR cholangiopancreatography has widely replaced endoscopic retrograde cholangiopancreatography in the diagnosis and staging of pancreatobiliary malignancies. MR imaging, using phased-array or endorectal coils, demonstrates local tumor invasion accurately in rectal cancers and thus allows an improved surgical planning. Virtual colonoscopy with MDCTs is an efficient screening method for colon cancer, and MDCT enterography is becoming the standard imaging technique for many small bowel disorders. The continuing developments in CT and MR technology will most probably further improve the accuracy of these and other imaging applications in the near future.

Importance of extracolonic findings at IV contrast medium-enhanced CT colonography versus those at non-enhanced CT colonography

To compare the clinical importance of extracolonic findings at intravenous (IV) contrast-enhanced CT colonography versus those at non-enhanced CT colonography. IV contrast medium-enhanced (n=72) and non-enhanced (n=30) multidetector CT colonography was performed in 102 symptomatic patients followed by conventional colonoscopy on the same day. The impact of extracolonic findings on further work up and treatment was assessed by a review of patient records. Extracolonic findings were divided into two groups: either leading to further work up respectively having an impact on therapy or not. A total of 303 extracolonic findings were detected. Of those, 71% (215/303) were found on IV contrast-enhanced CT, and 29% (88/303) were found on non-enhanced CT colonography. The extracolonic findings in 25% (26/102) of all patients led to further work up or had an impact on therapy. Twenty-two of these patients underwent CT colonography with IV contrast enhancement, and four without. The percentage of extracolonic findings leading to further work up or having an impact on therapy was higher for IV contrast-enhanced (31%; 22/72) than for non-enhanced (13%; 4/30) CT scans (P=0.12). IV contrast-enhanced CT colonography produced more extracolonic findings than non-enhanced CT colonography. A substantially greater proportion of findings on IV contrast-enhanced CT colonography led to further work up and treatment than did non-enhanced CT colonography.

CT colonography using 16-MDCT in the evaluation of colorectal cancer

OBJECTIVE

This study evaluated CT colonography as a method to stage colorectal cancer and detect polyps and cancers in patients with the disease.

SUBJECTS AND METHODS

Fifty-one consecutive patients thought to have colorectal cancer underwent CT colonography, following a colonoscopy, in both the prone and supine positions. The transverse CT images, multiplanar reconstruction, volume rendered, and virtual colonoscopy images, were independently interpreted by two radiologists. Disagreements were resolved by consensus. The diagnostic accuracy of TNM staging was calculated, and the sensitivity of CT colonography for the detection of cancers and polyps, compared with that of colonoscopy, was calculated using repeated colonoscopic and surgical findings as reference standards. The technical result for distention was also graded.

RESULTS

In the 51 patients, surgery and follow-up colonoscopy revealed 21 colorectal cancers (one synchronous cancer) and 41 polyps. The diagnostic accuracies of CT colonography for TNM staging were 95%, 85%, and 100% for tumor, node, and metastasis, respectively. The sensitivity of both CT colonography and initial colonoscopy for cancer detection was 100%. The overall sensitivities of CT colonography and initial colonoscopy for polyp detection were 90% and 78%, respectively (p = 0.001). The sensitivities of CT colonography for detecting polyps of 5 mm or smaller, of 6-9 mm, and of 10 mm or larger were 84%, 94%, and 100%, respectively. The mean overall technical results for the supine and prone positions were ranked as 2.80 (SD, +/- 0.4) and 2.78 (+/- 0.4), respectively, but were without statistical significance (p = 0.781).

CONCLUSION

Our preliminary data suggest that for patients with clinical suspicion of colorectal cancer, CT colonoscopy is valuable in staging the tumor and in detecting additional polyps or cancers in areas not evaluated by conventional colonoscopy.

Recent developments in CT colonography

CT colonography allows reliable, non-invasive, rapid, high resolution imaging of the whole large bowel. Recent advances in technology such as computer-aided detection (CAD), scanning with or without bowel preparation, and low radiation are continually developing to improve the efficacy of this technique. This review will update the reader as to ongoing developments while presenting current thinking from the gastroenterological perspective.

The emerging role of virtual colonoscopy

A review of the current status of virtual colonoscopy is germane and topical. Clinicians need to be knowledgeable about this rapidly evolving and clinically relevant technology to understand the test benefits and limitations and to refer patients for this test appropriately. A critical review of the exponentially expanding literature on this subject is important. This article describes the imaging meth-ods, adjunctive techniques, and radiologic interpretation of CT colonography, and comprehensively and critically reviews the clinical data to help the clinician evaluate the current and potential applications of this technology.

Feasibility of MDCT Colonography in ultra-low-dose technique in the detection of colorectal lesions: comparison with high-resolution video colonoscopy

OBJECTIVE

The purpose of this study was to assess the feasibility of MDCT colonography in an ultra-low-dose technique in the detection of endoluminal colonic lesions compared with high-resolution video colonoscopy.

SUBJECTS AND METHODS

After standard bowel cleansing, 137 patients (77 men, 60 women; mean [+/- SD] age, 57.1 +/- 11.3 years) underwent high-resolution video colonoscopy within 2 hr after ultra-low-dose MDCT colonography had been performed. Ultra-low-dose MDCT colonography was performed with patients in the supine position only using 10 mAs (effective weighted CT dose index, 0.94 mGy). After mathematic noise reduction by nonlinear gaussian filter chains, using dedicated software (ECCET), images were analyzed by two blinded observers in simultaneously displayed interactive 2D and 3D modes. Findings of ultra-low-dose MDCT colonography were compared with the results obtained with high-resolution video colonoscopy.

RESULTS

Calculated effective doses were 0.7 and 1.2 mSv for men and women, respectively. Ultra-low-dose MDCT colonography detected 84 (62%) of 135 lesions: 11 (78.6%) of 14 large polyps (> 10 mm), 12 (85.7%) of 14 medium polyps (9.9-5 mm), and 61 (57%) of 107 small polyps (< 5 mm). On a patient-by-patient basis, an overall sensitivity of 70.3% with a specificity of 80.8% was calculated. False-positive findings were seen mostly for small lesions (eight medium and 29 small lesions). Two of the three false-negative lesions were retrospectively detected in contrast-enhanced cleansing fluid; one was a flat lipoma not detectable on ultra-low-dose MDCT colonography.

CONCLUSION

Despite an effective dose of approximately 1 mSv, MDCT colonography using an ultra-low-dose technique performs as well as MDCT colonography with a standard dose, according to published data. After mathematic noise reduction, 82% of polyps larger than 5 mm can be detected.

Randomized single blind trial of two low-volume bowel preparations for screening computed tomographic colonography

BACKGROUND

Bowel preparation is an important part of computed tomographic colonography (CTC); we evaluated two small-volume preparations for screening CTC with regard to quality of preparation and patient acceptability.

METHODS

Asymptomatic subjects at average risk for colorectal cancer from a community-based CTC screening program were randomized to bowel preparation comprising magnesium/bisacodyl/picolax or polyethylene glycol (PEG)/picolax. CTC images were evaluated by a blinded investigator for residual feces and fluid; subjects completed a questionnaire regarding acceptability of the preparation.

RESULTS

In 176 subjects randomized to magnesium/bisacodyl/picolax (n = 82) or PEG/picolax (n = 94), the former preparation was discontinued because of syncope or presyncope in four (5%) subjects. Another 137 subjects received PEG/picolax without a significant adverse event. There were no other major differences in acceptability of the preparations as reported by subjects. The quality of bowel preparations for reporting CTC was similar.

CONCLUSION

For subjects having screening CTC, both small-volume bowel preparations are generally well tolerated and result in minimal fluid and fecal residue; however, the magnesium/bisacodyl/picolax preparation was accompanied by an unacceptable incidence of syncope and is no longer used by us.