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

Polyp Sizing Poster Improves Polyp Measurement but not Adenoma Detection Rates by Endoscopists in a Large Community Practice

BACKGROUND & AIMS

Accurate sizing of polyps and improving adenoma detection rates (ADR) are important goals for high-quality colonoscopy. Surveillance intervals are based on accurate sizing of polyps. There are no clinical tools or interventions that have demonstrated improvement in both these metrics. We investigated the efficacy of a simple, low-cost intervention, based on use of polyp sizing posters to improve measurements of polyps and increase ADRs during colonoscopy at a large gastroenterology community practice.

METHODS

We collected data on polyp measurements and ADRs by 62 gastrointestinal endoscopists at a large multi-site community practice, from January to November 2015 (baseline). In a prospective study, endoscopy units were given a polyp sizing poster to be hung above the endoscopy video monitor (intervention group, for 33 endoscopists) or for usual care (control group, for 29 endoscopists) in December 2015, and we collected data on polyp measurements and ADRs over the following 6 months (January-June 2016). We compared the endoscopists' assessment of polyp size and their ADRs before and after the intervention using a mixed effects proportional odds model, controlling for provider age and sex and patient and indication for colonoscopy. Our primary aim was to assess the effect of the snare and forcep-based polyp sizing poster on change in polyp size. The secondary aim was to study the effect of the polyp sizing poster on ADR.

RESULTS

Our final analysis included 85,657 polyps from 38,307 colonoscopies. The characteristics of patients who underwent colonoscopy were similar between the control and intervention group (median age, 61 years; 48.1% female; 53.9% undergoing screening; 31.4% undergoing surveillance; 14.7% receiving a diagnostic colonoscopy). The endoscopists' median age was 51 years (range, 33-76) years, and 15 were women (24.2%). During the baseline period, male endoscopists were more likely to size polyps larger than measurements made by female endoscopists (odds ratio [OR], 1.78; 95% CI, 1.24-2.55; P = .002). For the intervention group, 78.6% of polyps were assigned to the 1-5 mm category during the baseline period compared to 76.0% after the intervention, whereas the proportions of polyps assigned to the 6-10 mm category increased from 16.9% during the baseline period to 18.3% after the intervention. In the control group, 78.9% of polyps were assigned to the 1-5 mm category during the baseline period and 78.3% were assigned to this group in the prospective study; 16.5% of polyps were assigned to the 6-10 mm during the baseline period and 17.5% were assigned to this group in the prospective study. The interaction between intervention group and timing (baseline vs after the intervention) was statistically significant, with an increase in the odds of larger polyp sizing after the intervention (OR, 1.15; 95% CI, 1.08-1.23; P < .001). The odds of larger polyp measurement during the intervention period, compared to the baseline period, increased for male endoscopists (OR, 1.17; 95% CI, 1.09-1.27; P < .001) and female endoscopists (OR, 1.18; 95% CI, 1.01-1.36; P = .04), as well as for younger physicians (<50 years; OR, 1.32; 95% CI, 1.20-1.46; P < .001) but not for older physicians (>50 years; OR, 0.96; 95% CI, 0.88-1.06; P = .44). The average ADR for male and female endoscopists combined during the baseline period was 42%. The change in ADR from the baseline vs the post-intervention was an increase of 2.6% in the control group compared to 5.7% in the intervention group (P = .39) CONCLUSIONS: Placement of a polyp sizing poster above the endoscopy video monitor increases the odds of polyps being assigned a larger size but does not affect ADRs.

CT colonography: size reduction of submerged colorectal polyps due to electronic cleansing and CT-window settings

OBJECTIVES

To assess whether electronic cleansing (EC) of tagged residue and different computed tomography (CT) windows influence the size of colorectal polyps in CT colonography (CTC).

METHODS

A database of 894 colonoscopy-validated CTC datasets of a low-prevalence cohort was retrospectively reviewed to identify patients with polyps ≥6 mm that were entirely submerged in tagged residue. Ten radiologists independently measured the largest diameter of each polyp, two-dimensionally, before and after EC in colon, bone, and soft-tissue-windows, in randomised order. Differences in size and polyp count before and after EC were calculated for size categories ≥6 mm and ≥10 mm. Statistical testing involved 95% confidence interval, intraclass correlation and mixed-model ANOVA.

RESULTS

Thirty-seven patients with 48 polyps were included. Mean polyp size before EC was 9.8 mm in colon, 9.9 mm in bone and 8.2 mm in soft-tissue windows. After EC, the mean polyp size decreased significantly to 9.4 mm in colon, 9.1 mm in bone and 7.1 mm in soft-tissue windows. Compared to unsubtracted colon windows, EC, performed in colon, bone and soft-tissue windows, led to a shift of 6 (12,5%), 10 (20.8%) and 25 (52.1%) polyps ≥6 mm into the next smaller size category, thus affecting patient risk stratification.

CONCLUSIONS

EC and narrow CT windows significantly reduce the size of polyps submerged in tagged residue. Polyp measurements should be performed in unsubtracted colon windows.

KEY POINTS

• EC significantly reduces the size of polyps submerged in tagged residue. • Abdominal CT-window settings significantly underestimate 2D sizes of submerged polyps. • Size reduction in EC is significantly greater in narrow than wide windows. • Underestimation of polyp size due to EC may lead to inadequate treatment. • Polyp measurements should be performed in unsubtracted images using a colon window.

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.

Computed Tomography Colonography Phantom: Construction, Validation and Literature Review

Background

Several dedicated computed tomography (CT) colonography phantoms have been described previously.

Objectives

To compare their pros and cons and describe the construction of a dedicated phantom that can be easily manufactured.

Materials and Methods

We found 15 different phantom designs by literature search and compared their advantages and disadvantages based on their description and images. We tested various materials for density and mechanical properties and constructed a phantom from polypropylene pipes (30 mm and 50 mm in diameter, 52 cm in length). Haustral folds were created by heat shaping and 39 intermediate sessile polyps with a target size of 6-10 mm and two flat lesions were created from silicone. Nine polyps were attached to a fold. The model was placed in a 30-cm barrel filled with water to simulate attenuation of human body. Attenuation of polyps was compared to intermediate polyps found in patients.

Results

None of the earlier colonic phantoms found in the literature incorporated all the properties that would ensure both reproducibility and validity of the model (including a rigid wall, density of the wall and polyps similar to human colon, at least two levels of distension and durability). In the present phantom, the average size of sessile polyps was 8.6 ± 0.9 mm and their density was 53 ± 24 HU. We found no significant difference in polyp density between simulated polyps in the phantom and polyps in human subjects (P = 0.70). All polyps, with the exception of one flat lesion, were detected by computer aided detection.

Conclusion

We constructed and validated a CT colonography phantom with correct density allowing performance of reproducible experiments.

Development of the local magnification method for quantitative evaluation of endoscope geometric distortion

With improved diagnostic capabilities and complex optical designs, endoscopic technologies are advancing. As one of the several important optical performance characteristics, geometric distortion can negatively affect size estimation and feature identification related diagnosis. Therefore, a quantitative and simple distortion evaluation method is imperative for both the endoscopic industry and the medical device regulatory agent. However, no such method is available yet. While the image correction techniques are rather mature, they heavily depend on computational power to process multidimensional image data based on complex mathematical model, i.e., difficult to understand. Some commonly used distortion evaluation methods, such as the picture height distortion (DPH) or radial distortion (DRAD), are either too simple to accurately describe the distortion or subject to the error of deriving a reference image. We developed the basic local magnification (ML) method to evaluate endoscope distortion. Based on the method, we also developed ways to calculate DPH and DRAD. The method overcomes the aforementioned limitations, has clear physical meaning in the whole field of view, and can facilitate lesion size estimation during diagnosis. Most importantly, the method can facilitate endoscopic technology to market and potentially be adopted in an international endoscope standard.

Ultrasound virtual endoscopy: Polyp detection and reliability of measurement in an in vitro study with pig intestine specimens

AIM: To present our initial experience regarding the feasibility of ultrasound virtual endoscopy (USVE) and its measurement reliability for polyp detection in an in vitro study using pig intestine specimens.

METHODS: Six porcine intestine specimens containing 30 synthetic polyps underwent USVE, computed tomography colonography (CTC) and optical colonoscopy (OC) for polyp detection. The polyp measurement defined as the maximum polyp diameter on two-dimensional (2D) multiplanar reformatted (MPR) planes was obtained by USVE, and the absolute measurement error was analyzed using the direct measurement as the reference standard.

RESULTS: USVE detected 29 (96.7%) of 30 polyps, remaining a 7-mm one missed. There was one false-positive finding. Twenty-six (89.7%) of 29 reconstructed images were clearly depicted, while 29 (96.7%) of 30 polyps were displayed on CTC with one false-negative finding. In OC, all the polyps were detected. The intraclass correlation coefficient was 0.876 (95%CI: 0.745-0.940) for measurements obtained with USVE. The pooled absolute measurement errors ± the standard deviations of the depicted polyps with actual sizes ≤ 5 mm, 6-9 mm, and ≥ 10 mm were 1.9 ± 0.8 mm, 0.9 ± 1.2 mm, and 1.0 ± 1.4 mm, respectively.

CONCLUSION: USVE is reliable for polyp detection and measurement in in vitro study.

Noncathartic CT colonography: Image quality assessment and performance and in a screening cohort

OBJECTIVE

Cathartic bowel preparation is a major barrier for colorectal cancer screening. We examined noncathartic CT colonography (CTC) quality and performance using four similar bowel-tagging regimens in an asymptomatic screening cohort.

SUBJECTS AND METHODS

This prospective study included 564 asymptomatic subjects who underwent noncathartic CTC without dietary modification but with 21 g of barium with or without iodinated oral contrast material (four regimens). The quality of tagging with oral agents was evaluated. A gastrointestinal radiologist evaluated examinations using primary 2D search supplemented by electronic cleansing (EC) and 3D problem solving. Results were compared with complete colonoscopy findings after bowel purgation and with retrospective unblinded evaluation in 556 of the 564 (99%) subjects.

RESULTS

Of the 556 subjects, 7% (37/556) and 3% (16/556) of patients had 52 and 20 adenomatous polyps ≥ 6 and ≥ 10 mm, respectively. The addition of iodine significantly improved the percentage of labeled stool (p ≤ 0.0002) and specificity (80% vs 89-93%, respectively; p = 0.046). The overall sensitivity of noncathartic CTC for adenomatous polyps ≥ 6 mm was 76% (28/37; 95% CI, 59-88%), which is similar to the sensitivity of the iodinated regimens with most patients (sensitivity: 231 patients, 74% [14/19; 95% CI, 49-91%]; 229 patients, 80% [12/15; 95% CI, 52-96%]). The negative predictive value was 98% (481/490), and the lone cancer was detected (0.2%, 1/556). EC was thought to improve conspicuity of 10 of 21 visible polyps ≥ 10 mm.

CONCLUSION

In this prospective study of asymptomatic subjects, the per-patient sensitivity of noncathartic CTC for detecting adenomas ≥ 6 mm was approximately 76%. Inclusion of oral iodine contrast material improves examination specificity and the percentage of labeled stool. EC may improve polyp conspicuity.

Teleradiology based CT colonography to screen a population group of a remote island; at average risk for colorectal cancer

PURPOSE

To prospectively assess the performance of teleradiology-based CT colonography to screen a population group of an island, at average risk for colorectal cancer.

MATERIALS AND METHODS

A cohort of 514 patients living in Madeira, Portugal, was enrolled in the study. Institutional review board approval was obtained and all patients signed an informed consent. All patients underwent both CT colonography and optical colonoscopy. CT colonography was interpreted by an experienced radiologist at a remote centre using tele-radiology. Per-patient sensitivity, specificity, positive (PPV) and negative (NPV) predictive values with 95% confidence intervals (95%CI) were calculated for colorectal adenomas and advanced neoplasia ≥6 mm.

RESULTS

510 patients were included in the study. CT colonography obtained a per-patient sensitivity, specificity, PPV and, NPV for adenomas ≥6 mm of 98.11% (88.6-99.9% 95% CI), 90.97% (87.8-93.4% 95% CI), 56.52% (45.8-66.7% 95% CI), 99.75% (98.4-99.9% 95% CI). For advanced neoplasia ≥6 mm per-patient sensitivity, specificity, PPV and, NPV were 100% (86.7-100% 95% CI), 87.07% (83.6-89.9% 95% CI), 34.78% (25.3-45.5% 95% CI) and 100% (98.8-100% 95% CI), respectively.

CONCLUSION

In this prospective trial, teleradiology-based CT colonography was accurate to screen a patient cohort of a remote island, at average risk for colorectal cancer.

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.

The second ESGAR consensus statement on CT colonography

Objective

To update quality standards for CT colonography based on consensus among opinion leaders within the European Society of Gastrointestinal and Abdominal Radiology (ESGAR).

Material and methods

A multinational European panel of nine members of the ESGAR CT colonography Working Group (representing six EU countries) used a modified Delphi process to rate their level of agreement on a variety of statements pertaining to the acquisition, interpretation and implementation of CT colonography. Four Delphi rounds were conducted, each at 2 months interval.

Results

The panel elaborated 86 statements.

In the final round the panelists achieved complete consensus in 71 of 86 statements (82 %). Categories including the highest proportion of statements with excellent Cronbach's internal reliability were colon distension, scan parameters, use of intravenous contrast agents, general guidelines on patient preparation, role of CAD and lesion measurement.

Lower internal reliability was achieved for the use of a rectal tube, spasmolytics, decubitus positioning and number of CT data acquisitions, faecal tagging, 2D vs. 3D reading, and reporting.

Conclusion

The recommendations of the consensus should be useful for both the radiologist who is starting a CTC service and for those who have already implemented the technique but whose practice may need updating.

Key Points

• Computed tomographic colonography is the optimal radiological method of assessing the colon

• This article reviews ESGAR quality standards for CT colonography

• This article is aimed to provide CT-colonography guidelines for practising radiologists

• The recommendations should help radiologists who are starting/updating their CTC services

Reduced cathartic bowel preparation for CT colonography: prospective comparison of 2-L polyethylene glycol and magnesium citrate

PURPOSE

To prospectively compare adequacy of colonic cleansing, adequacy of solid stool and fluid tagging, and patient acceptance by using reduced-volume, 2-L polyethylene glycol (PEG) versus magnesium citrate bowel preparations for CT colonography.

MATERIALS AND METHODS

This study was approved by the institutional Committee on Human Research and was compliant with HIPAA; all patients provided written consent. In this randomized, investigator-blinded study, 50 patients underwent oral preparation with either a 2-L PEG or a magnesium citrate solution, tagging with oral contrast agents, and subsequent CT colonography and segmentally unblinded colonoscopy. The residual stool (score 0 [best] to 3 [worst]) and fluid (score 0 [best] to 4 [worst]) burden and tagging adequacy were qualitatively assessed. Residual fluid attenuation was recorded as a quantitative measure of tagging adequacy. Patients completed a tolerance questionnaire within 2 weeks of scanning. Preparations were compared for residual stool and fluid by using generalized estimating equations; the Mann-Whitney test was used to compare the qualitative tagging score, mean residual fluid attenuation, and adverse effects assessed on the patient experience questionnaire.

RESULTS

The mean residual stool (0.90 of three) and fluid burden (1.05 of four) scores for PEG were similar to those for magnesium citrate (0.96 [P = .58] and 0.98 [P = .48], respectively). However, the mean fecal and fluid tagging scores were significantly better for PEG (0.48 and 0.28, respectively) than for magnesium citrate (1.52 [P < .01] and 1.28 [P < .01], respectively). Mean residual fluid attenuation was higher for PEG (765 HU) than for magnesium citrate (443 HU, P = .01), and mean interpretation time was shorter for PEG (14.8 minutes) than for magnesium citrate (18.0 minutes, P = .04). Tolerance ratings were not significantly different between preparations.

CONCLUSION

Reduced-volume PEG and magnesium citrate bowel preparations demonstrated adequate cleansing effectiveness for CT colonography, with better tagging and shorter interpretation time observed in the PEG group. Adequate polyp detection was maintained but requires further validation because of the small number of clinically important polyps.

Sources of false positives in computer-assisted CT colonography

The application of computer-aided detection (CAD) is expected to improve reader sensitivity and to reduce inter-observer variance in computed tomographic (CT) colonography. However, current CAD systems display a large number of false-positive (FP) detections. The reviewing of a large number of FP CAD detections increases interpretation time, and it may also reduce the specificity and/or sensitivity of a computer-assisted reader. Therefore, it is important to be aware of the patterns and pitfalls of FP CAD detections. This pictorial essay reviews common sources of FP CAD detections that have been observed in the literature and in our experiments in computer-assisted CT colonography. Also the recommended computer-assisted reading technique is described.

Prospective blinded comparison of polyp size on computed tomography colonography and endoscopic colonoscopy

BACKGROUND & AIMS

The size of polyps found on computed tomography colonography (CTC) has been suggested as the major determinant of patient management. We compared polyp size as seen on CTC with endoscopic visualization, in vivo probe measurement, and ex vivo size before and after fixation.

METHODS

Polyps measured on CTC sent for endoscopic removal were evaluated for polyp size in a blinded fashion by endoscopic estimation, in vivo probe measurement, and after removal.

RESULTS

Fifty-six polyps were included in the study. There was no significant difference between CTC polyp size, real-time colonoscopy size estimation, or probe measurement. The size of polyp measured immediately ex vivo and after pathology fixation was significantly smaller. Management would be altered in 6 of 56 polyps (10.7%) on the basis of differences between size of the polyp on endoscopy and CTC.

CONCLUSIONS

(1) CTC polyp size measurement is not significantly different from colonoscopy in vivo visual estimation and linear probe measurement. (2) Differences in size of polyps as measured on CTC and endoscopy will affect patient management in 10% of cases.

Incremental benefit of computer-aided detection when used as a second and concurrent reader of CT colonographic data: multiobserver study

PURPOSE

To quantify the changes in reader performance levels, if any, during interpretation of computed tomographic (CT) colonographic data when a computer-aided detection (CAD) system is used as a second or concurrent reader.

MATERIALS AND METHODS

After institutional review board approval was obtained, 16 experienced radiologists searched for polyps in 112 patients, 56 of whom had 132 polyps. Each case was interpreted on three separate occasions by using an unassisted (without CAD), second-read CAD, or concurrent CAD reading paradigm. The reading paradigm and case order were randomized, with a minimal interval of 1 month between consecutive interpretations. The readers' findings were compared with the reference-truth interpretation. The mean per-patient sensitivity and mean per-patient specificity with CAD were compared with those achieved with unassisted reading. An increase in per-patient sensitivity was considered to be clinically more important than an equivalent decrease in specificity.

RESULTS

The mean per-patient sensitivity for identification of patients with polyps of any size increased significantly with use of second-read CAD (mean increase, 7.0%; 95% confidence interval [CI]: 4.0%, 9.8%) and concurrent CAD (mean increase, 4.5%; 95% CI: 0.8%, 8.2%). The mean per-patient specificity did not decrease significantly with use of second-read CAD (mean decrease, -2.5%; 95% CI: -5.2%, 0.1%) or concurrent CAD (mean decrease, -2.2%; 95% CI: -4.6%, 0.2%). With analysis restricted to patients with polyps 6 mm or larger, the benefit in sensitivity with second-read CAD remained (mean increase, 7.1%; 95% CI: 3.0%, 11.1%), whereas the increase with concurrent CAD was not significant (mean increase, 4.2%; 95% CI: -0.5%, 8.9%). Use of second-read CAD significantly increased the per-polyp sensitivity for polyps 6 mm or larger (mean increase, 9.0%; 98.3% CI: 4.9%, 12.8%) and polyps 5 mm or smaller (mean increase, 5.9%; 98.3% CI: 3.2%, 9.1%), but use of concurrent CAD increased the per-polyp sensitivity for only those polyps 5 mm or smaller (mean increase, 4.8%; 98.3% CI: 2.2%, 7.9%).

CONCLUSION

Use of second-read CAD significantly improves readers' per-patient and per-polyp detection. Concurrent CAD is less effective.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100354/-/DC1.

The presence of large serrated polyps increases risk for colorectal cancer

BACKGROUND & AIMS

There is evidence that serrated polyps (serrated adenomas and hyperplastic polyps) have different malignant potential than traditional adenomas. We used a colonoscopy database to determine the association between the presence of serrated colorectal polyps and colorectal neoplasia.

METHODS

We performed a multicenter observational study of 10,199 subjects who underwent first-time colonoscopies. Data collected on study subjects included age and sex and the location, size, and histology of polyps or tumors found at colonoscopy. Serrated polyps were defined as those diagnosed by the pathologists in the participating hospitals as a serrated lesion (a lesion given the term of "classical hyperplastic polyp," "traditional serrated adenoma," "sessile serrated adenoma," or "mixed serrated polyp"). Large serrated polyps (LSPs) were defined as those ≥ 10 mm.

RESULTS

There were 1573 patients (15.4%) with advanced neoplasia, 708 patients (6.9%) with colorectal cancer (CRC), and 140 patients (1.4%) with LSPs in our cohort. Multivariate analysis associated the presence of LSPs with advanced neoplasia (odds ratio [OR], 4.01; 95% confidence interval [CI], 2.83-5.69) and CRC (OR, 3.34; 95% CI, 2.16-5.03). The presence of LSPs was the greatest risk factor for CRC, particularly for proximal CRC (OR, 4.79; 95% CI, 2.54-8.42). Proximal and protruded LSPs were the highest risk factors for proximal CRC (OR, 5.36; 95% CI, 2.40-10.8 and OR, 9.00; 95% CI, 2.75-19.2, respectively).

CONCLUSIONS

The presence of LSPs is a risk factor for CRC, particularly CRC of the proximal colon.

Polyp size measurement at CT colonography: what do we know and what do we need to know?

Polyp size is a critical biomarker for clinical management. Larger polyps have a greater likelihood of being or of becoming an adenocarcinoma. To balance the referral rate for polypectomy against the risk of leaving potential cancers in situ, sizes of 6 and 10 mm are increasingly being discussed as critical thresholds for clinical decision making (immediate polypectomy versus polyp surveillance) and have been incorporated into the consensus CT Colonography Reporting and Data System (C-RADS). Polyp size measurement at optical colonoscopy, pathologic examination, and computed tomographic (CT) colonography has been studied extensively but the reported precision, accuracy, and relative sizes have been highly variable. Sizes measured at CT colonography tend to lie between those measured at optical colonoscopy and pathologic evaluation. The size measurements are subject to a variety of sources of error associated with image acquisition, display, and interpretation, such as partial volume averaging, two- versus three-dimensional displays, and observer variability. This review summarizes current best practices for polyp size measurement, describes the role of automated size measurement software, discusses how to manage the measurement uncertainties, and identifies areas requiring further research.

Performance of CT colonography for detecting small, diminutive, and flat polyps

The primary goal of colorectal cancer screening and prevention is the detection and removal of advanced neoplasia. Computerized tomography (CT) colonography is now well established as an effective screening test. Areas of greater uncertainty include the performance characteristics of CT colonography for detecting small (6-9 mm), diminutive (< or =5 mm), and flat (nonpolypoid) lesions. However, the actual clinical relevance of small, diminutive, and flat polyps has also been the source of debate. This article addresses these controversial and often misunderstood issues.

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.

Polyp measurement based on CT colonography and colonoscopy: variability and systematic differences

Objective

To assess the variability and systematic differences in polyp measurements on optical colonoscopy and CT colonography.

Materials

Gastroenterologists measured 51 polyps by visual estimation, forceps comparison and linear probe. CT colonography observers randomly assessed polyp size two-dimensionally (abdominal and intermediate window) and three-dimensionally (manually and semi-automatically). Linear mixed models were used to assess the variability and systematic differences between CT colonography and optical colonoscopy techniques.

Results

The variability of forceps and linear probe measurements was comparable and both showed less variability than measurement by visual assessment. Measurements by linear probe were 0.7 mm smaller than measurements by visual assessment or by forceps. The variability of all CT colonography techniques was lower than for measurements by forceps or visual assessment and sometimes lower (only 2D intermediate window and manual 3D) compared with measurements by linear probe. All CT colonography measurements judged polyps to be larger than optical colonoscopy, with differences ranging from 0.7 to 2.3 mm.

Conclusion

A linear probe does not reduce the measurement variability of endoscopists compared with the forceps. Measurement differences between observers on CT colonography were usually smaller than at optical colonoscopy. Polyps appeared larger when using various CT colonography techniques than when measured during optical colonoscopy.

Colorectal cancer screening with CT colonography: key concepts regarding polyp prevalence, size, histology, morphology, and natural history

OBJECTIVE

The purpose of this article is to provide a timely update on a variety of key polyp topics to construct a proper framework for physicians who are interested in providing CT colonography screening as a clinical service.

CONCLUSION

As the medical community considers the expansion of CT colonography for screening, we believe it is prudent to update and review several key concepts regarding colorectal polyps. In particular, it is important to replace the older literature derived from high-risk and symptomatic cohorts with the wealth of newer and more applicable data from average-risk and asymptomatic screening cohorts. Familiarity with current concepts regarding flat (nonpolypoid) lesions and the natural history of small colorectal polyps is also vital to the effective application of this technique.

Endoscopic imaging and size estimation of colorectal adenomas in the multiple intestinal neoplasia mouse

BACKGROUND

The scientific potential of animal models of carcinogenesis has not been fully realized because of our limited ability to monitor tumor growth in vivo.

OBJECTIVE

To develop an endoscopy-based protocol for the accurate estimation of adenoma size in vivo from images obtained during colonoscopy.

DESIGN

To compare estimates of lesion size acquired during endoscopy with those obtained from magnetic resonance imaging (MRI) and at necropsy.

SETTING

A small-animal imaging facility.

SUBJECTS

Adenomatous polyposis coli multiple intestinal metaplasia Fox Chase Cancer Center mice that develop multiple colorectal adenomas.

METHODS

The mice received colonoscopic examination by using a rigid endoscope, and high-resolution images of colon adenomas were captured by using a charge-coupled-device camera. Lesion size was estimated by comparing the dimensions of the adenoma relative to a reference rod by using a novel geometric construction. The resulting areas were compared with estimates from MRIs and validated at necropsy.

MAIN OUTCOME MEASUREMENTS

Cross-sectional area of colon adenomas.

RESULTS

The cross-sectional area of 20 adenomas was measured in vivo during colonoscopy and compared with the size as measured at necropsy, which yielded a Pearson correlation coefficient of 0.94 (P = 6.52 x 10(-9)). Assessment of interoperator variability, when using measurements from 11 adenomas, yielded a Pearson correlation coefficient of 0.85 (P = 4.35 x 10(-3)) and demonstrated excellent reproducibility.

LIMITATIONS

Only the distal colon could be viewed, and endoscopic measurements were 2-dimensional.

CONCLUSIONS

An endoscopic method for the reliable measurement of colorectal adenomas in vivo was established. The application of this technique to mouse models of colon carcinogenesis will provide unique insight into the dynamics of adenoma growth.

CT colonography polyp matching: differences between experienced readers

The purpose of this study was to investigate if experienced readers differ when matching polyps shown by both CT colonography (CTC) and optical colonoscopy (OC) and to explore the reasons for discrepancy. Twenty-eight CTC cases with corresponding OC were presented to eight experienced CTC readers. Cases represented a broad spectrum of findings, not completely fulfilling typical matching criteria. In 21 cases there was a single polyp on CTC and OC; in seven there were multiple polyps. Agreement between readers for matching was analyzed. For the 21 single-polyp cases, the number of correct matches per reader varied from 13 to 19. Almost complete agreement between readers was observed in 15 cases (71%), but substantial discrepancy was found for the remaining six (29%) probably due to large perceived differences in polyp size between CT and OC. Readers were able to match between 27 (71%) and 35 (92%) of the 38 CTC detected polyps in the seven cases with multiple polyps. Experienced CTC readers agree to a considerable extent when matching polyps between CTC and subsequent OC, but non-negligible disagreement exists.

Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: a joint guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology

In the United States, colorectal cancer (CRC) is the third most common cancer diagnosed among men and women and the second leading cause of death from cancer. CRC largely can be prevented by the detection and removal of adenomatous polyps, and survival is significantly better when CRC is diagnosed while still localized. In 2006 to 2007, the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology came together to develop consensus guidelines for the detection of adenomatous polyps and CRC in asymptomatic average-risk adults. In this update of each organization's guidelines, screening tests are grouped into those that primarily detect cancer early and those that can detect cancer early and also can detect adenomatous polyps, thus providing a greater potential for prevention through polypectomy. When possible, clinicians should make patients aware of the full range of screening options, but at a minimum they should be prepared to offer patients a choice between a screening test that primarily is effective at early cancer detection and a screening test that is effective at both early cancer detection and cancer prevention through the detection and removal of polyps. It is the strong opinion of these 3 organizations that colon cancer prevention should be the primary goal of screening.

Measurement of colonic polyps by radiologists and endoscopists: who is most accurate?

The purpose was to determine the accuracy of polyp measurement by endoscopy and CT. A colonic phantom was constructed containing 12 simulated polyps of known diameter. Polyp diameter was estimated during endoscopy by two observers independently. The phantom was then scanned using a 64-detector-row machine and diameter estimated by a further two observers independently, using 2D and 3D visualisation methods. All measurements were obtained twice. Bland-Altman statistics were used to assess agreement between observers' estimates and the reference diameter. The mean difference between observers' measurements and the reference diameter was smallest for estimates made using 3D CT (-0.09 mm and -0.03 mm) and greatest for endoscopy (-1.10 mm and -1.19 mm), with 2D CT intermediate. However, 95% limits of agreement were largest for 3D CT estimates (-4.38 mm to 4.20 mm). Estimates by 2D CT consistently overestimated polyp diameter, whereas endoscopy consistently underestimated diameter. In contrast, measurements by 3D CT were a combination of over- and under-estimates, with a tendency for disagreement to increase with the size of the polyp. The effect of observer experience was small and repeatability was best for 2D CT. Measurement error was encountered with all three modalities tested. Estimates made by 2D CT were believed to offer the best compromise overall.

Linear polyp measurement at CT colonography: 3D endoluminal measurement with optimized surface-rendering threshold value and automated measurement

PURPOSE

To determine the optimal surface-rendering threshold value for three-dimensional (3D) endoluminal computed tomographic (CT) colonographic images for accurate manual polyp measurement, with direct measurement of simulated polyps as the reference standard, and to assess the agreement between manual 3D measurements and automated measurements.

MATERIALS AND METHODS

Institutional review board approval was not required for the experimental study with pig colons obtained at an abattoir but was obtained for the use of patient data, with waiver of informed consent. Eighty-six simulated polyps (reference size, 3-15 mm) and 14 human polyps (approximate size, 5-20 mm) were included. Automated polyp measurements and manual measurements with endoluminal views that were surface rendered at threshold values of -800, -700, -600, and -500 HU were performed by one observer. Agreement between CT colonographic measurements and reference sizes and between manual and automated measurements were assessed by using the Bland-Altman method.

RESULTS

For simulated polyps, mean measurement difference between the observed size and reference size was 0.86 mm (95% limits of agreement: -0.52 mm, 2.24 mm), 0.55 mm (95% limits of agreement: -0.75 mm, 1.85 mm), 0.20 mm (95% limits of agreement: -1.11 mm, 1.50 mm), and -0.08 mm (95% limits of agreement: -1.43 mm, 1.27 mm) for -800, -700, -600, and -500 HU, respectively. Mean measurement difference was 0.09 mm (95% limits of agreement: -1.49 mm, 1.67 mm) for automated measurement. Manual polyp size at -500 HU (P = .277) and automated polyp size (P = .288) were not significantly different from reference size. For human polyps, 10 polyps, excluding four lesions that were large, lobulated, or located adjacent to an edge of the haustral fold, showed accurate automated demarcation of lesion boundaries. Automated measurements of the 10 polyps showed the closest agreement with manual measurements at -500 HU.

CONCLUSION

The optimal surface-rendering threshold value for accurate polyp measurement is approximately -500 HU. Automated measurements agree closely with manual measurements at the optimal threshold value for well-circumscribed smooth rounded polyps.