Pearls and Pitfalls of Interpretation in CT Colonography.

The accuracy of computed tomography (CT) colonography (CTC) requires that the radiologist be well trained in the recognition of pitfalls of interpretation. In order to achieve a high sensitivity and specificity, the interpreting radiologist must be well versed in the causes of both false-positive and false-negative results. In this article, we review the common and uncommon pitfalls of interpretation in CTC.

Abnormal Pouchogram Predicts Pouch Failure Even in Asymptomatic Patients.

BACKGROUND: Anastomotic complications after restorative total proctocolectomy with IPAA for ulcerative colitis alter functional outcomes and quality of life and may lead to pouch failure. Routine contrast enema of the pouch assesses anastomotic integrity before ileostomy reversal, but its clinical use is challenged. OBJECTIVE: The purpose of this research was to assess the relationship among preoperative clinical characteristics, abnormal pouchography, and long-term pouch complications. DESIGN: This was a retrospective chart review. SETTINGS: The study was conducted at a tertiary care center between 2000 and 2010. PATIENTS: Ulcerative colitis patients with IPAA undergoing pouchography before ileostomy closure were included. MAIN OUTCOME MEASURES: Patient demographics, incidence of pouch-related complications, and findings on pouchogram were recorded. Primary outcome was pouch failure, defined as excision or permanent diversion of the ileoanal pouch. Independent predictors of pouch failure were determined by multivariate regression. RESULTS: A total of 262 patients with ulcerative colitis were included. Contrast extravasation was seen in 27 patients (10.3%): 14 (51.9%) were clinically asymptomatic at the time of pouchogram. Six (22.2%) of 27 patients with extravasation developed pouch failure despite normalization of the pouchogram before ileostomy closure. Forty patients (15.3%) were found to have pouch-anal anastomotic stenosis; only 1 developed pouch failure. Pre-IPAA serum albumin and hemoglobin levels were inversely associated with contrast extravasation (serum albumin: OR = 0.42; hemoglobin: OR = 0.77; p < 0.05). Contrast extravasation was associated with delayed takedown operation (average = 67 d), increased risk (OR = 5.25; p < 0.01), and shorter time (median = 32.0 vs 72.5 mo; HR = 5.88; p < 0.05) to pouch failure, as well as increased risk of pouch-related complications (p < 0.05). LIMITATIONS: The study was limited by its retrospective nature and small number of patients who developed pouch failure. CONCLUSIONS: Pouchography before ileostomy takedown is useful in identifying patients with ulcerative colitis at risk for postoperative complications. Radiologic resolution of IPAA-related leak does not reliably predict healing; caution is warranted in this subgroup. See Video Abstract at http://links.lww.com/DCR/A818.

Errors in CT colonography.

CT colonography (CTC) is a colorectal cancer screening modality which is becoming more widely implemented and has shown polyp detection rates comparable to those of optical colonoscopy. CTC has the potential to improve population screening rates due to its minimal invasiveness, no sedation requirement, potential for reduced cathartic examination, faster patient throughput, and cost-effectiveness. Proper implementation of a CTC screening program requires careful attention to numerous factors, including patient preparation prior to the examination, the technical aspects of image acquisition, and post-processing of the acquired data. A CTC workstation with dedicated software is required with integrated CTC-specific display features. Many workstations include computer-aided detection software which is designed to decrease errors of detection by detecting and displaying polyp-candidates to the reader for evaluation. There are several pitfalls which may result in false-negative and false-positive reader interpretation. We present an overview of the potential errors in CTC and a systematic approach to avoid them.

CT colonography with computer-aided detection: recognizing the causes of false-positive reader results.

Computed tomography (CT) colonography is a screening modality used to detect colonic polyps before they progress to colorectal cancer. Computer-aided detection (CAD) is designed to decrease errors of detection by finding and displaying polyp candidates for evaluation by the reader. CT colonography CAD false-positive results are common and have numerous causes. The relative frequency of CAD false-positive results and their effect on reader performance on the basis of a 19-reader, 100-case trial shows that the vast majority of CAD false-positive results were dismissed by readers. Many CAD false-positive results are easily disregarded, including those that result from coarse mucosa, reconstruction, peristalsis, motion, streak artifacts, diverticulum, rectal tubes, and lipomas. CAD false-positive results caused by haustral folds, extracolonic candidates, diminutive lesions (<6 mm), anal papillae, internal hemorrhoids, varices, extrinsic compression, and flexural pseudotumors are almost always recognized and disregarded. The ileocecal valve and tagged stool are common sources of CAD false-positive results associated with reader false-positive results. Nondismissable CAD soft-tissue polyp candidates larger than 6 mm are another common cause of reader false-positive results that may lead to further evaluation with follow-up CT colonography or optical colonoscopy. Strategies for correctly evaluating CAD polyp candidates are important to avoid pitfalls from common sources of CAD false-positive results.

The National CT Colonography Trial: assessment of accuracy in participants 65 years of age and older.

PURPOSE: To conduct post-hoc analysis of National CT Colonography Trial data and compare the sensitivity and specificity of computed tomographic (CT) colonography in participants younger than 65 years with those in participants aged 65 years and older. MATERIALS AND METHODS: Of 2600 asymptomatic participants recruited at 15 centers for the trial, 497 were 65 years of age or older. Approval of this HIPAA-compliant study was obtained from the institutional review board of each site, and informed consent was obtained from each subject. Radiologists certified in CT colonography reported lesions 5 mm in diameter or larger. Screening detection of large (≥10-mm) histologically confirmed colorectal neoplasia was the primary end point; screening detection of smaller (6-9-mm) colorectal neoplasia was a secondary end point. The differences in sensitivity and specificity of CT colonography in the two age cohorts (age < 65 years and age ≥ 65 years) were estimated with bootstrap confidence intervals (CIs). RESULTS: Complete data were available for 477 participants 65 years of age or older (among 2531 evaluable participants). Prevalence of adenomas 1 cm or larger for the older participants versus the younger participants was 6.9% (33 of 477) versus 3.7% (76 of 2054) (P < .004). For large neoplasms, mean estimates for CT colonography sensitivity and specificity among the older cohort were 0.82 (95% CI: 0.644, 0.944) and 0.83 (95% CI: 0.779, 0.883), respectively. For large neoplasms in the younger group, CT colonography sensitivity and specificity were 0.92 (95% CI: 0.837, 0.967) and 0.86 (95% CI: 0.816, 0.899), respectively. Per-polyp sensitivity for large neoplasms for the older and younger populations was 0.75 (95% CI: 0.578, 0.869) and 0.84 (95% CI: 0.717, 0.924), respectively. For the older and younger groups, per-participant sensitivity was 0.72 (95% CI: 0.565, 0.854) and 0.81 (95% CI: 0.745, 0.882) for detecting adenomas 6 mm in diameter or larger. CONCLUSION: For most measures of diagnostic performance and in most subsets, the difference between senior-aged participants and those younger than 65 years was not statistically significant.

ACRIN CT colonography trial: does reader's preference for primary two-dimensional versus primary three-dimensional interpretation affect performance?

PURPOSE: To determine whether the reader's preference for a primary two-dimensional (2D) or three-dimensional (3D) computed tomographic (CT) colonographic interpretation method affects performance when using each technique. MATERIALS AND METHODS: In this institutional review board-approved, HIPAA-compliant study, images from 2531 CT colonographic examinations were interpreted by 15 trained radiologists by using colonoscopy as a reference standard. Through a survey at study start, study end, and 6-month intervals, readers were asked whether their interpretive preference in clinical practice was to perform a primary 2D, primary 3D, or both 2D and 3D interpretation. Readers were randomly assigned a primary interpretation method (2D or 3D) for each CT colonographic examination. Sensitivity and specificity of each method (primary 2D or 3D), for detecting polyps of 10 mm or larger and 6 mm or larger, based on interpretive preference were estimated by using resampling methods. RESULTS: Little change was observed in readers' preferences when comparing them at study start and study end, respectively, as follows: primary 2D (eight and seven readers), primary 3D (one and two readers), and both 2D and 3D (six and six readers). Sensitivity and specificity, respectively, for identifying examinations with polyps of 10 mm or larger for readers with a primary 2D preference (n = 1128 examinations) were 0.84 and 0.86, which was not significantly different from 0.84 and 0.83 for readers who preferred 2D and 3D (n = 1025 examinations) or from 0.76 and 0.82 for readers with a primary 3D preference (n = 378 examinations). When performance by using the assigned 2D or 3D method was evaluated on the basis of 2D or 3D preference, there was no difference among those readers by using their preferred versus not preferred method of interpretation. Similarly, no significant difference among readers or preferences was seen when performance was evaluated for detection of polyps of 6 mm or larger. CONCLUSION: The reader's preference for interpretive method had no effect on CT colonographic performance.

Use of Screening CT Colonography by Age and Race: A Study of Potential Access Barriers Related to Medicare Noncoverage Based on Data From the ACR's National CT Colonography Registry.

OBJECTIVE: The primary objectives of this investigation were to evaluate the use of screening CT colonography (CTC) examinations by age comparing individuals of Medicare-eligible age to younger cohorts and to determine if the association between use of CTC and Medicare-eligible age varies by race. Although the Affordable Care Act requires commercial insurance coverage of screening CTC, Medicare does not cover screening CTC. MATERIALS AND METHODS: Using the ACR's CTC registry, the distribution of procedures by age was evaluated using a negative binomial model with patient age (to capture overall trend), indicator of Medicare-eligible age (to capture immediate changes in trend at age 65), and their interaction (to capture gradual changes after age 65) as independent variables. The association between the number of screening CTCs and age was compared by racial identity. RESULTS: The CTC registry contained data on 12,648 screening examinations. Between ages 52 and 64, the number of screening examinations increased; each additional age year was associated with a 5.3% (P < .001) increase in the number of screenings. However, after age 65, the number of screening examinations decreased by -6.9% per additional year of age above 65 compared with the trend between ages 52 and 64 (P < .001). The modal age group for CTC use was 65 to 69 years in white and 55 to 59 in black individuals. CONCLUSION: After age 65, the number of screening CTC examinations decreased, likely due, at least in part, to lack of Medicare coverage. Medicare noncoverage may have a disproportionate impact on black patients and other racial minorities.

CT colonography's role in the COVID-19 pandemic: a safe(r), socially distanced total colon examination.

PURPOSE: To describe the favorable procedural profile of CT colonography (CTC) during the COVID-19 pandemic. CONCLUSION: Postponement of cancer screening due to COVID-19 has resulted in a backlog of individuals needing to undergo structural examination of the colon. The experience during the initial COVID-19 surge with urgent evaluation of the colon for transplant patients prior to transplant suggests that CTC can be done in a lower risk manner as compared to other structural examinations. The procedural profile of CTC is advantageous during this pandemic as maintaining social distancing and preserving healthcare supplies including PPE are of paramount importance. CTC is an important option to utilize in the screening armamentarium to allow effective screening of average risk asymptomatic individuals in the COVID-19 era.

Effect of computer-aided detection for CT colonography in a multireader, multicase trial.

PURPOSE: To assess the effect of using computer-aided detection (CAD) in second-read mode on readers' accuracy in interpreting computed tomographic (CT) colonographic images. MATERIALS AND METHODS: The contributing institutions performed the examinations under approval of their local institutional review board, with waiver of informed consent, for this HIPAA-compliant study. A cohort of 100 colonoscopy-proved cases was used: In 52 patients with findings positive for polyps, 74 polyps of 6 mm or larger were observed in 65 colonic segments; in 48 patients with findings negative for polyps, no polyps were found. Nineteen blinded readers interpreted each case at two different times, with and without the assistance of a commercial CAD system. The effect of CAD was assessed in segment-level and patient-level receiver operating characteristic (ROC) curve analyses. RESULTS: Thirteen (68%) of 19 readers demonstrated higher accuracy with CAD, as measured with the segment-level area under the ROC curve (AUC). The readers' average segment-level AUC with CAD (0.758) was significantly greater (P = .015) than the average AUC in the unassisted read (0.737). Readers' per-segment, per-patient, and per-polyp sensitivity for all polyps of 6 mm or larger was higher (P < .011, .007, .005, respectively) for readings with CAD compared with unassisted readings (0.517 versus 0.465, 0.521 versus 0.466, and 0.477 versus 0.422, respectively). Sensitivity for patients with at least one large polyp of 10 mm or larger was also higher (P < .047) with CAD than without (0.777 versus 0.743). Average reader sensitivity also improved with CAD by more than 0.08 for small adenomas. Use of CAD reduced specificity of readers by 0.025 (P = .05). CONCLUSION: Use of CAD resulted in a significant improvement in overall reader performance. CAD improves reader sensitivity when measured per segment, per patient, and per polyp for small polyps and adenomas and also reduces specificity by a small amount.

Bias, underestimation of risk, and loss of statistical power in patient-level analyses of lesion detection.

PURPOSE: Sensitivity and the false positive rate are usually defined with the patient as the unit of observation, i.e., the diagnostic test detects or does not detect disease in a patient. For tests designed to find and diagnose lesions, e.g., lung nodules, the usual definitions of sensitivity and specificity may be misleading. In this paper we describe and compare five measures of accuracy of lesion detection. METHODS: The five levels of evaluation considered were patient level without localization, patient level with localization, region of interest (ROI) level without localization, ROI level with localization, and lesion level. RESULTS: We found that estimators of sensitivity that do not require the reader to correctly locate the lesion overstate sensitivity. Patient-level estimators of sensitivity can be misleading when there is more than one lesion per patient and they reduce study power. Patient-level estimators of the false positive rate can conceal important differences between techniques. Referring clinicians rely on a test's reported accuracy to both choose the appropriate test and plan management for their patients. If reported sensitivity is overstated, the clinician could choose the test for disease screening, and have false confidence that a negative test represents the true absence of lesions. Similarly, the lower false positive rate associated with patient-level estimators can mislead clinicians about the diagnostic value of the test and consequently that a positive finding is real. CONCLUSION: We present clear recommendations for studies assessing and comparing the accuracy of tests tasked with the detection and interpretation of lesions...

CT colonography: advanced computer-aided detection scheme utilizing MTANNs for detection of "missed" polyps in a multicenter clinical trial.

PURPOSE: The purpose of this study was to develop an advanced computer-aided detection (CAD) scheme utilizing massive-training artificial neural networks (MTANNs) to allow detection of "difficult" polyps in CT colonography (CTC) and to evaluate its performance on false-negative (FN) CTC cases that radiologists "missed" in a multicenter clinical trial. METHODS: The authors developed an advanced CAD scheme consisting of an initial polyp-detection scheme for identification of polyp candidates and a mixture of expert MTANNs for substantial reduction in false positives (FPs) while maintaining sensitivity. The initial polyp-detection scheme consisted of (1) colon segmentation based on anatomy-based extraction and colon-based analysis and (2) detection of polyp candidates based on a morphologic analysis on the segmented colon. The mixture of expert MTANNs consisted of (1) supervised enhancement of polyps and suppression of various types of nonpolyps, (2) a scoring scheme for converting output voxels into a score for each polyp candidate, and (3) combining scores from multiple MTANNs by the use of a mixing artificial neural network. For testing the advanced CAD scheme, they created a database containing 24 FN cases with 23 polyps (range of 6-15 mm; average of 8 mm) and a mass (35 mm), which were "missed" by radiologists in CTC in the original trial in which 15 institutions participated. RESULTS: The initial polyp-detection scheme detected 63% (15/24) of the missed polyps with 21.0 (505/24) FPs per patient. The MTANNs removed 76% of the FPs with loss of one true positive; thus, the performance of the advanced CAD scheme was improved to a sensitivity of 58% (14/24) with 8.6 (207/24) FPs per patient, whereas a conventional CAD scheme yielded a sensitivity of 25% at the same FP rate (the difference was statistically significant). CONCLUSIONS: With the advanced MTANN CAD scheme, 58% of the polyps missed by radiologists in the original trial were detected and with a reasonable number of FPs. The results suggest that the use of an advanced MTANN CAD scheme may potentially enhance the detection of "difficult" polyps.

Can radiologist training and testing ensure high performance in CT colonography? Lessons From the National CT Colonography Trial.

OBJECTIVE: The objective of this article is to describe the experience of the National CT Colonography Trial with radiologist training and qualification testing at CT colonography (CTC) and to correlate this experience with subsequent performance in a prospective screening study. SUBJECTS AND METHODS: Ten inexperienced radiologists participated in a 1-day educational course, during which partial CTC examinations of 27 cases with neoplasia and full CTC examinations of 15 cases were reviewed using primary 2D and 3D search. Subsequently 15 radiologists took a qualification examination composed of 20 CTC cases. Radiologists who did not pass the first qualification examination attended a second day of focused retraining of 30 cases, which was followed by a second qualification examination. The results of the initial and subsequent qualification tests were compared with reader performance in a large prospective screening trial. RESULTS: All radiologists took and passed the qualification examinations. Seven radiologists passed the qualification examination the first time it was offered, and eight radiologists passed after focused retraining. Significantly better sensitivities were obtained on the second versus the first examination for the retrained radiologists (difference = 16%, p < 0.001). There was no significant difference in sensitivities between the groups who passed the qualification examination the first time versus those who passed the second time in the prospective study (88% vs 92%, respectively; p = 0.612). In the prospective study, the odds of correctly identifying diseased cases increased by 1.5 fold for every 50-case increase in reader experience or formal training (p < 0.025). CONCLUSION: A significant difference in performance was observed among radiologists before formalized training, but testing and focused retraining improved radiologist performance, resulting in an overall high sensitivity across radiologists in a subsequent, prospective screening study.

Flat lesions in CT colonography.

Flat lesions have been a source of controversy because of concerns that CT colonography (CTC) is insensitive in detecting these lesions, yet they may harbor a high incidence of advanced neoplasia. The wide variation in the reported incidence of flat lesions may in part be due to the lack of a uniform definition of "flat", and in fact in many prior reports the inclusion criteria for flat are not even clearly specified. Emphasis on the more recent CTC literature suggests that when limited the target lesion to neoplasia (adenomas or adenocarcinoma), the incidence of flat lesions is low and most can be detected by CTC. Using fecal tagging and careful attention to the proper methods of searching for flat lesions with both 3D and 2D techniques can maximize the detection of flat lesions at CTC. Computer-aided detection may be helpful.

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.

Comparison of polyp size and volume at CT colonography: implications for follow-up CT colonography.

OBJECTIVE: The purpose of this study was to evaluate the reliability of polyp measurements at CT colonography and the factors that affect the measurements. MATERIALS AND METHODS: Fifty colonoscopically proven cases of polyps 6 mm in diameter or larger were analyzed by two observers who measured each polyp in supine and prone views. Manual measurements of 2D volume by summation of areas, 2D maximum diameter, and 3D maximum diameter and automated measurements of 3D maximum diameter and volume were recorded for each observer and were repeated for one of the observers. Intraobserver and interobserver agreement was calculated. Analysis was performed to determine the measurement parameter that correlated most with summation-of-areas volume. Supine and prone measurements as a surrogate for tracking change in polyp size over time were analyzed to determine the measurement parameter with the least variation. RESULTS: Maximum diameter measured manually on 3D images had the highest correlation with summation-of-areas volume. Manual summation-of-areas volume was found to have the least variation between supine and prone measurements. CONCLUSION: Linear polyp measurement in the 3D endoluminal view appears to be the most reliable parameter for use in the decision to excise a polyp according to current guidelines. In our study, manual calculation of volume with summation of areas was found to be the most reliable measurement parameter for observing polyp growth over serial examinations. High reliability of polyp measurements is essential for adequate assessment of change in polyp size over serial examinations because many patients with intermediate-size polyps are expected to choose surveillance.

Formative evaluation of standardized training for CT colonographic image interpretation by novice readers.

PURPOSE: To introduce an educational intervention-specifically, a specialized training course-and perform a formative evaluation of the effect of the intervention on novice reader interpretation of computed tomography (CT) colonographic data. MATERIALS AND METHODS: The study was institutional review board approved. Ten normal and 50 abnormal cases, those of 60 patients with 93 polyps-61 polyps 6-9 mm in diameter and 32 polyps 10 mm or larger-were selected from a previously published trial. Seven novice readers underwent initial training that consisted of a 1-day course, reading assignments, a self-study computer module (with 61 limited data sets), observation of an expert interpreting three cases, and full interpretation of 10 cases with unblinding after each case. After training, the observers independently interpreted 60 cases by means of primary two-dimensional reading with unblinding after each case. For each case, the reading time and the location and maximal diameter of the polyp(s) were recorded. A t test was used to evaluate the observers' improvements, and empirical receiver operating characteristic (ROC) curves were constructed. RESULTS: By-patient sensitivities and specificities were determined for each observer. The lowest by-patient sensitivity at the 6 mm or larger polyp threshold was 86%, with 90% specificity. Four observers had 100% by-patient sensitivity at the 10 mm or larger polyp threshold, with 82%-97% specificity. For polyps 10 mm or larger, mean sensitivity and specificity were 98% and 92%, respectively. For the last 20 cases, the average interpretation time per case was 25 minutes. The range of areas under the ROC curve across observers was low: 0.86-0.95. CONCLUSION: In the described polyp-enriched cohort, novice CT colonographic data readers achieved high sensitivity and good specificity at formative evaluation of a comprehensive training program. Use of a similar comprehensive training method might reduce interreader variability in interpretation accuracy and be useful for reader certification.

Mixture of expert 3D massive-training ANNs for reduction of multiple types of false positives in CAD for detection of polyps in CT colonography.

One of the major challenges in computer-aided detection (CAD) of polyps in CT colonography (CTC) is the reduction of false-positive detections (FPs) without a concomitant reduction in sensitivity. A large number of FPs is likely to confound the radiologist's task of image interpretation, lower the radiologist's efficiency, and cause radiologists to lose their confidence in CAD as a useful tool. Major sources of FPs generated by CAD schemes include haustral folds, residual stool, rectal tubes, the ileocecal valve, and extra-colonic structures such as the small bowel and stomach. Our purpose in this study was to develop a method for the removal of various types of FPs in CAD of polyps while maintaining a high sensitivity. To achieve this, we developed a "mixture of expert" three-dimensional (3D) massive-training artificial neural networks (MTANNs) consisting of four 3D MTANNs that were designed to differentiate between polyps and four categories of FPs: (1) rectal tubes, (2) stool with bubbles, (3) colonic walls with haustral folds, and (4) solid stool. Each expert 3D MTANN was trained with examples from a specific non-polyp category along with typical polyps. The four expert 3D MTANNs were combined with a mixing artificial neural network (ANN) such that different types of FPs could be removed. Our database consisted of 146 CTC datasets obtained from 73 patients whose colons were prepared by standard pre-colonoscopy cleansing. Each patient was scanned in both supine and prone positions. Radiologists established the locations of polyps through the use of optical-colonoscopy reports. Fifteen patients had 28 polyps, 15 of which were 5-9 mm and 13 were 10-25 mm in size. The CTC cases were subjected to our previously reported CAD method consisting of centerline-based extraction of the colon, shape-based detection of polyp candidates, and a Bayesian-ANN-based classification of polyps. The original CAD method yielded 96.4% (27/28) by-polyp sensitivity with an average of 3.1 (224/73) FPs per patient. The mixture of expert 3D MTANNs removed 63% (142/224) of the FPs without the loss of any true positive; thus, the FP rate of our CAD scheme was improved to 1.1 (82/73) FPs per patient while the original sensitivity was maintained. By use of the mixture of expert 3D MTANNs, the specificity of a CAD scheme for detection of polyps in CTC was substantially improved while a high sensitivity was maintained.