Surface visualization at 3D endoluminal CT colonography: degree of coverage and implications for polyp detection

The Natural History of Colorectal Polyps: Overview of Predictive Static and Dynamic Features

For decades, colorectal screening strategies have been largely driven by static features, particularly polyp size. Although cross-sectional features of polyp size, morphology, and location are important determinants of clinical relevance before histology, they lack any dynamic information on polyp growth rates. Computed tomography colonography allows for in vivo surveillance of colorectal polyps, providing volumetric growth rates that are providing new insights into tumorigenesis. In this article, existing cross-sectional and longitudinal data on colorectal polyps are reviewed, with an emphasis on how these features may affect clinical relevance and patient management.

CT colonography interpretation: how to maximize polyp detection and minimize overcalling

This article outlines how to achieve maximum accuracy in interpreting CT colonography (CTC) regarding colonic findings. Interpreting extracolonic findings seen on CTC is a separate diagnostic task and will not be addressed in this article. While many interpretive pitfalls are in fact related to CTC techniques, this article focuses on issues that are related to interpretive knowledge and skills, avoiding in-depth discussions on CTC techniques. Principal methods and further tips for detecting possible polyp candidates and for confirming true soft-tissue polyps will be discussed. Specific points about optimizing interpretation strategies for difficult flat polyps including sessile serrated polyp will be raised. There are numerous interpretive pitfalls regarding the colonic interpretation of CTC. Knowledge of these pitfalls will shorten the learning curve and help achieve accurate reads.

Full-spectrum (FUSE) versus standard forward-viewing colonoscopy in an organised colorectal cancer screening programme

OBJECTIVE

Miss rate of polyps has been shown to be substantially lower with full-spectrum endoscopy (FUSE) compared with standard forward-viewing (SFV) colonoscopy in a tandem study at per polyp analysis. However, there is uncertainty on whether FUSE is also associated with a higher detection rate of colorectal neoplasia, especially advanced lesions, in per patient analysis.

METHODS

Consecutive subjects undergoing colonoscopy following a positive faecal immunochemical test (FIT) by experienced endoscopists and performed in the context of a regional colorectal cancer population-screening programme were randomised between colonoscopy with either FUSE or SFV colonoscopy in seven Italian centres. Randomisation was stratified by gender, age group and screening history. Primary outcomes included detection rates of advanced adenomas (A-ADR), adenomas (ADR) and sessile-serrated polyps (SSPDR).

RESULTS

Of 741 eligible subjects, 658 were randomised to either FUSE (n=328) or SFV (n=330) colonoscopy and included in the analysis. Overall, 293/658 and 143/658 subjects had at least one adenoma (ADR 44.5%) and advanced adenoma (A-ADR 21.7%), respectively, while SSP was the most advanced lesion in 18 cases (SSPDR 2.7%). ADR and A-ADR were 43.6% and 19.5% in the FUSE arm, and 45.5% and 23.9% in the SFV arm, with no difference for both ADR (OR for FUSE: 0.96, 95% CI 0.81 to 1.14) and A-ADR (OR for FUSE: 0.82, 95% CI 0.61 to 1.09). No difference in SSPDR or multiplicity was detected between the two arms. In the per polyp analysis, the mean number of adenomas and proximal adenomas per patient was 0.81±1.25 and 0.47±0.93 in the FUSE arm, and 0.85±1.33 and 0.48±0.96 in the SFV colonoscopy arm (p=NS for both comparisons).

CONCLUSIONS

No statistically significant difference in ADR and A-ADR between FUSE and SFV colonoscopy was detected in a per patient analysis in FIT-positive patients.

TRIAL REGISTRATION NUMBER

ISRCTN10357435.

Recent Advances in Diagnostic Colonoscopy for Colorectal Cancer Screening: An Update for Radiologists

OBJECTIVE

Colonoscopy accuracy in detecting colorectal neoplasia is critical for colorectal cancer prevention but has been shown to be operator- and technology-dependent. This article will discuss several recent improvements in the technique and technology of colonoscopy.

CONCLUSION

More rigorous training and retraining programs, active monitoring of endoscopist technique and outcomes, and exclusion of poorly performing endoscopists are urgently needed to improve the ultimate efficacy of colorectal cancer screening programs.

CT colonography after incomplete optical colonoscopy: bowel preparation quality at same-day vs. deferred examination

PURPOSE

To objectively compare the volume, density, and distribution of luminal fluid for same-day oral-contrast-enhanced CTC following incomplete optical colonoscopy (OC) vs. deferred CTC on a separate day utilizing a dedicated CTC bowel preparation.

METHODS

HIPAA-compliant, IRB-approved retrospective study compared 103 same-day CTC studies after incomplete OC (utilizing 30 mL oral diatrizoate) against 151 CTC examinations performed on a separate day after failed OC using a dedicated CTC bowel preparation (oral magnesium citrate/dilute barium/diatrizoate the evening before). A subgroup of 15 patients who had both same-day CTC and separate-day routine CTC was also identified and underwent separate analysis. CTC exams were analyzed for opacified fluid distribution within the GI tract, as well as density and volume. Data were analyzed utilizing Kruskal-Wallis and Wilcoxon Signed Rank tests.

RESULTS

Opacified luminal fluid extended to the rectum in 56% (58/103) of same-day CTC vs. 100% (151/151) of deferred separate-day CTC (p < 0.0001). For same-day CTC, contrast failed to reach the colon in 11% (11/103) and failed to reach the left colon in 26% (27/103). Volumetric colonic fluid segmentation for fluid analysis (successful in 80 same-day and 147 separate-day cases) showed significantly more fluid in the same-day cohort (mean, 227 vs. 166 mL; p < 0.0001); the actual difference is underestimated due to excluded cases. Mean colonic fluid attenuation was significantly lower in the same-day cohort (545 vs. 735 HU; p < 0.0001). Similar findings were identified in the smaller cohort with direct intra-patient CTC comparison.

CONCLUSIONS

Dedicated CTC bowel preparation on a separate day following incomplete OC results in a much higher quality examination compared with same-day CTC.

Mechanisms of hyoscine butylbromide to improve adenoma detection: A case-control study of surface visualization at simulated colonoscope withdrawal

BACKGROUND AND STUDY AIMS

Antispasmodics may improve mucosal visualization during colonoscope withdrawal, potentially improving polyp and adenoma detection. Meta-analysis and case-control studies suggest a 9 % to 13 % relative increase in adenoma and polyp detection. We aimed to assess the impact of hyoscine butylbromide on the expected visualization during colonoscope withdrawal using a CT colonography (CTC) simulation.

PATIENTS AND METHODS

Datasets from a previous CTC study examining the effect of antispasmodic were re-analyzed with customised CTC software, adjusted to simulate a standard colonoscopic view. Eighty-six patients received intravenous (IV) hyoscine butylbromide 20 mg, 40 mg or no antispasmodic. Main outcome measurements at unidirectional flythrough, simulating colonoscope withdrawal, were percentage colonic surface visualization, numbers and sizes of unseen areas, and colonic length.

RESULTS

Use of antispasmodic was associated with a significant relative increase in percentage surface visualization of 2.6 % to 3.9 %, compared with no antispasmodic, P < 0.006. Total numbers of missed areas and intermediate sized (300 - 1000 mm(2)) missed areas were significantly decreased, by approximately 20 %. There were no differences between the 20-mg and 40-mg doses. Mean colonic length (161 - 169 cm) was unchanged by antispasmodic.

CONCLUSIONS

IV hyoscine butylbromide at simulated colonoscope withdrawal was associated with significant increases in surface visualization, which might explain up to half the improvement in adenoma detection seen in clinical studies.

CT colonography in the diagnosis and management of colorectal cancer: Emphasis on pre- and post-surgical evaluation

This article addresses the use of computed tomographic colonography (CTC) for the diagnosis and management of colorectal cancer, focusing on presurgical evaluation of the colon proximal to an occlusive cancer and surveillance after cancer resection surgery. The key evidences accumulated in the literature and future work needed are summarized. CTC is a technically robust and the most practical method to evaluate the colon proximal to an occlusive cancer, which prevents colonoscopic examination past the occlusion, either before or after metallic stent placement. The high sensitivity of CTC for detecting cancers and advanced adenomas in the proximal colon can help prevent additional surgical procedures in patients showing negative results. However, the accuracy of CTC for distinguishing intramural cancers from adenomas is low, and the technique is limited in guiding management when a medium-sized lesion that do not show invasive features such as pericolic extension or nodal metastasis is found in the proximal colon. A maximal diameter ≥ 15 mm has been proposed as a criterion for surgical removal of proximal lesions. However, this needs to be verified in a larger cohort. In addition, the influence of presurgical CTC results on the current post-cancer resection colonic surveillance timeline remains to be determined. CTC can be readily added to the routine abdominopelvic CT in the form of contrast-enhanced CTC, which can serve as an effective stand-alone tool for post-cancer resection surveillance of both the colorectum and extracolonic organs. Although the accuracy of CTC has been demonstrated, its role in the current colonoscopy-based postoperative colonic surveillance protocols remains to be determined. Readers of CTC also need to be knowledgeable on the colonic lesions that are unique to the postoperative colon.

Retroview colonoscopy

A retroview in the colon permits an 11-25% increase in the adenoma detection rate when compared with a standard straight forward view during colonoscopy. This can often be accomplished in the rectum or the proximal colon by using dial controls and shaft manipulation to turn the tip of a standard colonoscope 180°. A special slim caliber instrument, the "Third Eye Retroscope" (a backward viewing device) has been developed which is inserted through the working channel of a colonoscope. New colonoscopes are being developed that have the capability of side vision with accompanying light illumination which, with wide angle lenses, provide an almost complete retroview of the colon.

Virtual colonoscopy: Utility, impact and overview

Computed tomography (CT) colonoscopy is a well-established technique for evaluation of colorectal cancer. Significant advances have been made in the technique of CT colonoscopy since its inception. Excellent results can be achieved in detecting both colorectal cancer and significant sized polyps as long as a meticulous technique is adopted while performing CT colonoscopy. Furthermore, it is important to realize that there is a learning curve involved in interpreting these studies and adequate experience is essential to achieve high sensitivity and specificity with this technique. Indications, contraindications, technique and interpretation, including potential pitfalls in CT colonoscopy imaging, are reviewed in this article. Recent advances and the current role of CT colonoscopy in colorectal cancer screening are also discussed.

CT colonography: pitfalls in interpretation

As with any radiologic imaging test, there are several potential interpretive pitfalls at CT colonography that need to be recognized and handled appropriately. Perhaps the single most important step in learning to avoid most of these diagnostic traps is simply to be aware of their existence. With a little experience, most of these potential pitfalls are easily recognized. This article systematically covers the key pitfalls confronting the radiologist at CT colonography interpretation, primarily dividing them into those related to technique and those related to underlying anatomy. Tips and pointers for how to effectively handle these potential pitfalls are included.

Haustral fold segmentation with curvature-guided level set evolution

Human colon has complex structures mostly because of the haustral folds. The folds are thin flat protrusions on the colon wall, which complicate the shape analysis for computer-aided detection (CAD) of colonic polyps. Fold segmentation may help reduce the structural complexity, and the folds can serve as an anatomic reference for computed tomographic colonography (CTC). Therefore, in this study, based on a model of the haustral fold boundaries, we developed a level-set approach to automatically segment the fold surfaces. To evaluate the developed fold segmentation algorithm, we first established the ground truth of haustral fold boundaries by experts' drawing on 15 patient CTC datasets without severe under/over colon distention from two medical centers. The segmentation algorithm successfully detected 92.7% of the folds in the ground truth. In addition to the sensitivity measure, we further developed a merit of segmented-area ratio (SAR), i.e., the ratio between the area of the intersection and union of the expert-drawn folds and the area of the automatically segmented folds, to measure the segmentation accuracy. The segmentation algorithm reached an average value of SAR = 86.2%, showing a good match with the ground truth on the fold surfaces. We believe the automatically segmented fold surfaces have the potential to benefit many postprocedures in CTC, such as CAD, taenia coli extraction, supine-prone registration, etc.

A feasibility study of unidirectional 240°-angle 3D CT colonography

In three-dimensional (3D) CT colonography (CTC), a wider viewing angle provides a larger field of view. The purpose of this study was to investigate the polyp detection rate and time efficiency of unidirectional 240°-angle 3D CTC compared with bidirectional 120°-angle CTC. CTC data sets of 40 patients were reviewed by two readers using the two methods. The unidirectional 240°-angle CTC showed a performance in polyp detection similar to the bidirectional 120°-angle CTC with improved time efficiency.

Wide view and retroview during colonoscopy

Colonoscopy is the best imaging device currently available for the detection of lesions in the large bowel, but may be an imperfect tool against colon cancer. Because recent guidelines for colorectal cancer screening and surveillance depend on whether polyps are found on colonoscopy and on their size, the need to identify all the neoplasia in the colon has assumed greater importance. This article reviews and assesses the latest developments in colonoscopy including wide-angle optics, endoscope caps and hoods, retroflexion and the use of the third eye retroscope.

Comparison of diagnostic accuracy and interpretation times for a standard and an advanced 3D visualisation technique in CT colonography

OBJECTIVE

To compare the diagnostic accuracy of a standard bi-directional, three-dimensional (3D) CT colonography (CTC) fly-through (standard view, SV) with a unidirectional, 3D unfolding technique (panoramic view, PV).

METHODS

150 consecutive endoscopically-validated CTC patient datasets were retrospectively reviewed twice by two expert radiologists: first, with bidirectional SV, second, after 6-15 months, with unidirectional PV. Per-polyp sensitivities, percentage of visualised colonic mucosa, and reading times were calculated for both 3D visualisations. Results were tested for statistical significance by equivalence analysis for paired proportions and Student's paired t-test.

RESULTS

In 81 patients, 236 polyps (101 adenomas, 135 non-adenomas) were detected. Sensitivities for polyps ≤5 mm, 6-9 mm and ≥10 mm were 60.1% (113/188), 92.9% (26/28) and 95.0% (19/20) with bidirectional SV, and 60.6% (114/188), 96.4% (27/28) and 95.0% (19/20) with unidirectional PV. Overall sensitivity for adenomas was 86.1% and 84.2% for SV and PV. Both methods provided equivalent polyp detection, with an equivalence limit set at 5%. PV and SV visualised 98.9 ± 1.1% (97.0-99.9%) and 96.2 ± 2.3% (91.4-98.8%) of the colonic mucosa (p > 0.05). Mean interpretation time decreased from 14.6 ± 2.5 (9.2-22.8) minutes with SV to 7.5 ± 3.2 (5.0-14.4) using PV (p < 0.0001).

CONCLUSION

3D CTC interpretation using unidirectional PV is equally as accurate, but significantly faster than an interpretation based on bidirectional SV.

CT colonography for combined colonic and extracolonic surveillance after curative resection of colorectal cancer

PURPOSE

To determine the accuracy of contrast material-enhanced computed tomographic (CT) colonography for postoperative surveillance in colorectal cancer patients without clinical or laboratory evidence of disease recurrence.

MATERIALS AND METHODS

The Institutional Review Board approved this HIPAA-compliant study and waived informed consent. Between January 2006 and December 2007, 742 consecutive patients without clinical or laboratory evidence of recurrence following curative-intent colorectal cancer surgery underwent contrast-enhanced CT colonography. Of these, 548 patients who had subsequent colonoscopy and pathologic confirmation of colonic lesions (reference standard) were included in the colonic analysis. All 742 patients were included in the extracolonic analysis. Sensitivity and specificity of CT colonography for nonanastomotic colonic lesions at least 6 mm in size and anastomotic lesions of any size, including performance according to lesion histologic type, were determined. Diagnostic yields of contrast-enhanced CT colonography for colonic cancers and for extracolonic recurrences were obtained.

RESULTS

CT colonography depicted all six metachronous cancers and one anastomotic recurrence within the colon in six patients (0.8%; 95% confidence interval [CI]: 0.3%, 1.8%]), for per-patient and per-lesion sensitivities of 100% (95% CIs: 64.3%, 100% and 67.8%, 100%, respectively). All cancer lesions within the colon were amenable to additional curative treatment. CT colonography per-patient and per-lesion sensitivity was 81.8% (95% CI: 60.9%, 93.3%) and 80.8% (95% CI: 64.3%, 97.2%), respectively, for advanced neoplasia and 80.0% (95% CI: 68.6%, 88.1%) and 78.5% (95% CI: 68.3%, 88.7%), respectively, for all adenomatous lesions. Negative predictive values for adenocarcinoma, advanced neoplasia, and all adenomatous lesions were 100%, 99.1%, and 97.0%, respectively. CT colonography specificity was 93.1% (95% CI: 90.4%, 95.2%). Contrast-enhanced CT colonography enabled detection of extracolonic recurrences in an additional 11 patients (1.5%; 95% CI: 0.8%, 2.7%).

CONCLUSION

Contrast-enhanced CT colonography is an accurate and practical surveillance tool following colorectal cancer surgery in patients without clinical or laboratory evidence of recurrence, allowing for simultaneous less-invasive evaluation of both colon and extracolonic organs.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100385/-/DC1.

Polyp detection at 3-dimensional endoluminal computed tomography colonography: sensitivity of one-way fly-through at 120 degrees field-of-view angle

PURPOSE

To investigate whether increasing the visual field-of-view (FOV) angle at 3-dimensional (3D) endoluminal computed tomography colonography (CTC) from 90 degrees to 120 degrees allows for single pass fly-through examination of the supine and prone views without sacrificing polyp detection.

METHODS

Primary 3D endoluminal CTC evaluation using a 120 degree FOV was performed by 2 experienced radiologists on 73 patients harboring 104 colonoscopy-proven polyps measuring 6 mm or larger. Unidirectional fly-through evaluation consisted of rectal-to-cecal (retrograde) navigation on the supine display and cecal-to-rectal (antegrade) navigation on the prone display. Electronic fluid subtraction was not used.

RESULTS

All 104 (100%) polyps were detectable with the single-pass 3D evaluation on either the retrograde supine or antegrade prone fly-through, with 86 (82.7%) of 104 polyps seen on both fly-through views. Of the 18 polyps detected on only one of the two 3D endoluminal passes (10 prone, 8 supine), 13 were either submerged under fluid (n = 12) or within a collapsed segment (n = 1); therefore, these were also undetectable on the corresponding 90 degrees bidirectional fly-through. The remaining 5 (4.8%) polyps were located behind a fold, but these polyps were all detectable on the other fly-through in the reverse direction.

CONCLUSIONS

Increasing the visual FOV angle to 120 degrees allows for a decrease in the total number of supine and prone 3D endoluminal fly-through passes from 4 to 2 without negatively impacting overall polyp detection.

Computed tomographic colonography

Computed tomographic colonography is a modern technique to evaluate the colon, which may be more appealing to patients than invasive methods. The potential of this test, including current and future developments are presented in this review. The essential steps required to perform a diagnostic quality computed tomographic colonography are discussed as well as different methods of study interpretation. The current status and promising areas of future investigation are also discussed.

[CT colonography: techniques of visualization and findings]

Evaluation and interpretation of CT colonography is based on both 2D and 3D techniques. The 2D techniques are popular mainly because the time needed for evaluation is short. The 3D techniques allow better definition than the 2D techniques, especially of polyps close to folds or at the base of a fold. The evaluation strategies generally accepted so far (primarily 2D, with 3D for problem cases, or vice versa) demand knowledge of both 2D and 3D techniques. Newer 3D visualization techniques help make it possible to acquire more complete and faster recording particularly of areas that are not easily accessible to endoscopic examination. These user-friendly developments are thus well suited to improving the detection and the security of detection of polyps. It must be remembered that experience and the knowledge of associated artifacts and the limitations they can impose on diagnosis are prime requirements for the implementation of such visualization techniques.

Surface visualization at CT colonography simulated colonoscopy: effect of varying field of view and retrograde view

OBJECTIVES

Colonoscopy is the gold standard for diagnosis of mucosal disease, but has a recognized "miss rate" for polyps probably because some lesions lie in areas of the colonic surface that do not enter the field of view. Using CT colonography (CTC) simulation this pilot study aimed to determine how much colonic surface is visualized with a standard, modern optical colonoscope (field of view 140 degrees ) with or without the addition of a retrograde viewing auxiliary imaging device (RVAID; 135 degrees ) and of a wide-angle (170 degrees ) colonoscope.

METHODS

Supine CTC datasets for 20 patients were reviewed with customized CTC software that calculated the percentage of colonic surface seen and number and area of nonvisualized "missed" areas at a unidirectional three-dimensional (3D) endoluminal flythrough, approximating the view obtained at optical colonoscopy. The field of view could be varied from 0-180 degrees . The combination of a colonoscope with RVAID was simulated by an additional flythrough facing the rectum.

RESULTS

Mean colonic surface area was 2,743 +/- 759 cm2. Percentage colonic surface visualized at simulated optical colonoscopy with a 90 degrees , 140 degrees , and 170 degrees field of view was 68.0 +/- 5.2%, 86.6 +/- 3.3%, and 92.2 +/- 3.3%, respectively, P < 0.001. Simulation of a 140 degrees colonoscope with an RVAID resulted in almost complete surface visualization, 98.7 +/- 0.5%, with total missed area reduced 10-fold compared with a 170 degrees colonoscope, P < 0.001.

CONCLUSION

CTC simulated 140 degrees optical colonoscopy visualizes over 85% of the colonic surface. 170 degrees colonoscopy provides a modest reduction in missed surface and the simulated addition of RVAIDs appears beneficial.

Screening CT colonography: how I do it

OBJECTIVE

The purpose of this article is to detail an approach to CT colonographic screening that has evolved at one institution.

CONCLUSION

CT colonography is a rapidly advancing technology that has great potential for addressing a deadly but preventable disease-colorectal carcinoma. CT colonography is ideally suited for widespread screening of asymptomatic adults and has become an integral component of the screening efforts at my institution since local third-party coverage was initiated.

Effect of Slice Thickness and Primary 2D Versus 3D Virtual Dissection on Colorectal Lesion Detection at CT Colonography in 452 Asymptomatic Adults

OBJECTIVE

The objective of our study was to compare the performance of primary 3D search using 360 degree virtual dissection with primary 2D search using a 2.5- versus a 1.25-mm slice thickness.

SUBJECTS AND METHODS

Four hundred fifty-two asymptomatic patients underwent CT colonography (CTC) and colonoscopy. Examinations were reconstructed to 1.25- and 2.5-mm slice thicknesses and interpreted using primary 3D search (360 degree virtual dissection) and primary 2D search. Two of three experienced reviewers were randomly assigned to each case; 1,808 interpretations were performed.

RESULTS

There were 64 adenomas > or = 6 mm, 26 of which were large adenomas > or = 1 cm. For adenomas 6-9 mm in diameter, the area under the receiver operating characteristic curve (AUC) using 2.5-mm data sets was 0.66, 0.62, 0.90 and 0.78, 0.69, 0.67 for reviewers 1, 2, and 3, respectively, using primary 3D versus 2D search (p = not significant [NS]). For neoplasms > or = 10 mm, the AUC using 2.5-mm data sets was 0.74, 0.85, 0.89 and 0.66, 0.86, 0.92 for reviewers 1, 2, and 3 using primary 3D versus 2D search (p = NS). There was no significant difference using 1.25-mm collimation. Double review using both primary 3D and 2D search yielded sensitivities of 84% (16/19) and 95% (18/19) for large neoplasms (> or = 1 cm) using 2.5- and 1.25-mm data sets, respectively. Five of five (100%) adenocarcinomas were identified. The sensitivity of colonoscopy for large neoplasms was 77% (20/26) (20% [1/5] for adenocarcinoma).

CONCLUSION

No advantage exists for 1.25- or 2.5-mm slice thickness or for primary 3D versus 2D search at CTC. Double review using primary 3D (virtual dissection) and 2D search reduces interobserver variability and competes with colonoscopy for the detection of large lesions.

MR colonography

Combining the advantages of unsurpassed soft tissue contrast and lack of ionizing radiation, MR imaging of the gastrointestinal tract has become increasingly used clinically. Both bowel inflammation and tumor disease of the large bowel can be well visualized by means of MR colonography (MRC). This article describes current techniques of MRC and gives an overview of its clinical outcome. Special focus is directed toward the evaluation of patients' acceptance of MRC.

CT colonography: visualization methods, interpretation, and pitfalls

Virtual colonoscopy interpretation is improving rapidly with the development of efficient software using two-dimensional, three-dimensional (3D) endoluminal, and 3D novel views such as those that seem to cut the colon open and lay it flat for interpretation. Comparison of these various views, comparisons of supine and prone positioning, and comparisons of lung and soft tissue windows aid in the recognition of various pitfalls of interpretation.

Dépistage de masse du cancer colorectal: présent et avenir

Hemoccult II is the only method of screening for colorectal cancer whose effectiveness in reducing specific mortality has been proved by randomized controlled trials. The first experience of French districts based on this strategy reproduced on a population scale the results of the experimental studies. Expanding screening in France to the general public is a public health priority. Large-scale media campaigns, which currently do not exist, could then be launched, and prevention opportunities seized. Immunological tests identifying the presence of blood in the stool have better sensitivity than the guaiac smear tests, especially for the diagnosis of adenomas and to a lesser extent, for that of cancers as a whole. These tests may constitute an alternative to guaiac tests, but are more expensive. Total colonoscopy, proposed every 10 years from the age of 50 years or once in a lifetime around the age of 60 years, is not a realistic method because of its cost and its risks. Sigmoidoscopies are under evaluation in several countries in randomized controlled trials but do not seem appropriate to either the epidemiologic trends of colorectal cancer or to the practice of endoscopy in France. Virtual colonoscopy is an attractive alternative to searching for blood in stool. The evaluation now underway should not interfere with the broad expansion of methods of proven efficacy. Virtual colonoscopy may face competition from numerous emerging techniques of endoscopic exploration of the colon, including the video-capsule. To obtain widespread participation in colorectal cancer screening, policy-makers must take the opinions of healthcare professionals and of the public into account. The medicoeconomic data will be a decisive factor in the choice between these new strategies.

CAD in CT colonography without and with oral contrast agents: progress and challenges

Computed tomographic colonography (CTC), also known as virtual colonoscopy, is an emerging alternative technique for screening of colon cancers. CTC uses CT to provide a series of cross-sectional images of the colon for detection of polyps and masses. Fecal tagging is a means of labeling of residual feces by an oral contrast agent for improving the accuracy in the detection of polyps. Computer-aided diagnosis (CAD) for CTC automatically determines the locations of suspicious polyps and masses in CTC and presents them to radiologists, typically as a second opinion. Despite its relatively short history, CAD has become one of the mainstream techniques that could make CTC prime time for screening of colorectal cancer. Rapid technical developments have advanced CAD substantially during the last several years, and a fundamental scheme for the detection of polyps has been established, in which sophisticated 3D image processing, analysis, and display techniques play a pivotal role. The latest CAD systems indicate a clinically acceptable high sensitivity and a low false-positive rate, and observer studies have demonstrated the benefits of these systems in improving radiologists' detection performance. Some technical and clinical challenges, however, remain unresolved before CAD can become a truly useful tool for clinical practice. Also, new challenges are facing CAD as the methods for bowel preparation and image acquisition, such as tagging of fecal residue with oral contrast agents, and interpretation of CTC images evolve. This article reviews the current status and future challenges in CAD for CTC without and with fecal tagging.

CT Colonography (Virtual Colonoscopy): A Practical Approach for Population Screening

CT colonography (CTC), also known as virtual colonoscopy, is a minimally invasive test for the detection of colorectal polyps and masses. At the authors' institution, asymptomatic screening has been the overwhelming indication for CTC referral since local third-party coverage was initiated in April 2004. This practical review details the authors' current approach to CTC screening, which has evolved and matured over time. It discusses the entire spectrum from program set-up through patient disposition following CTC examination. The authors hope this article will provide a roadmap for radiologists who wish to institute a CTC screening program.