Reader training in CT colonography: how much is enough?

CT urography for hematuria

Hematuria can signify serious disease such as bladder cancer, upper urinary tract urothelial cell carcinoma (UUT-UCC), renal cell cancer or urinary tract stones. CT urography is a rapidly evolving technique made possible by recent advances in CT technology. CT urography is defined as CT examination of the kidneys, ureters and bladder with at least one series of images acquired during the excretory phase after intravenous contrast administration. The reasoning for using CT urography to investigate hematuria is based on its high diagnostic accuracy for urothelial cell carcinoma (UCC) and favorable comparison with other imaging techniques. The optimum diagnostic imaging strategy for patients with hematuria at high-risk for UCC involves the use of CT urography as a replacement for other imaging tests (ultrasonography, intravenous urography, or retrograde ureteropyelography) and as a triage test for cystoscopy, resulting in earlier diagnosis and improved prognosis of bladder cancer, UUT-UCC, renal cell cancer and stones. Current problems with CT urography for investigating hematuria might be solved with a formative educational program simulating clinical reporting to reduce reader error, and a new technique for image-guided biopsy of UUT-UCC detected by CT urography for histopathological confirmation of diagnosis and elimination of false-positive results. CT urography is recommended as the initial imaging test for hematuria in patients at high-risk for UCC.

Evaluation of a standardized CT colonography training program for novice readers

PURPOSE

To determine how many computed tomographic (CT) colonography training studies have to be evaluated by novice readers to obtain an adequate level of competence in polyp detection.

MATERIALS AND METHODS

The study was approved by the Institutional Review Board. Informed consent was obtained from all participants. Six physicians (one radiologist, three radiology residents, two researchers) and three technicians completed a CT colonography training program. Two hundred CT colonographic examinations with colonoscopic verification were selected from a research database, with 100 CT colonographic examinations with at least one polyp 6 mm or larger. After a lecture session and short individual hands-on training, CT colonography training was done individually with immediate feedback of colonoscopy outcome. Per-polyp sensitivity was calculated for four sets of 50 CT colonographic examinations for lesions 6 mm or larger. By using logistic regression analyses, the number of CT colonographic examinations to reach 90% sensitivity for lesions 6 mm or larger was estimated. Reading times were registered.

RESULTS

The average per-polyp sensitivity for lesions 6 mm or larger was 76% (207 of 270) in the first set of 50 CT colonographic examinations, 77% (262 of 342) in the second (P = .96 vs first set), 80% (310 of 387) in the third (P = .67 vs first set), and 91% (261 of 288) in the fourth (P = .018). The estimated number of CT colonographic examinations for a sufficient sensitivity was 164. Six of nine readers reached this level of competence within 175 CT colonographic examinations. Reading times decreased significantly from the first to the second set of 50 CT colonographic examinations for six readers.

CONCLUSION

Novice CT colonography readers obtained sensitivity equal to that of experienced readers after practicing on average 164 CT colonographic studies.

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 training for radiographers--a formal evaluation

AIMS

To evaluate the efficacy of a new intensive "hands-on" course designed to train small teams of radiographers in computed tomography colonography (CTC) technique and initial interpretation for patient triage.

MATERIALS AND METHODS

The course comprised small-group lectures, active participation in the daily CTC service with practical technique and image interpretation training by experienced radiologists and radiographers. Evaluation was by assessment of knowledge using randomized sets of multiple choice questions (MCQ; pre/post-course), practical technique using checklists and expert global scores, and interpretation performance outcomes using randomized pre/post-course test datasets (five validated CTC examinations each). Paired t-tests were used to investigate change in performance for MCQ score and interpretation accuracy.

RESULTS

Thirteen courses with 49 participants were evaluated over 2 years. Practical skills were high, with mean (SD) checklist scores of 14/15 (0.85) and global scores of 26/30 (2.3). MCQ scores increased significantly from a mean of 59% pre-course to 69% post-course, p<0.001. Correct classification of CTC examination improved significantly from a mean of 55% pre-course to 71% post-course, p<0.001. Cancer and large polyp (>10mm) detection rates also improved significantly from 49% to 60%, p=0.002.

CONCLUSION

Structured training in CTC can significantly improve knowledge and interpretation skills of radiographers, while assessing safe procedural performance. Implementation of similar programmes nationally may help reduce performance gaps between centres.

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.

Radiologists should read CT colonography

This article defines the necessary skill set and knowledge base required for accurate computed tomography colonography (CTC) interpretation. The components of the interpretative process as well as the various strategies currently employed are discussed. The role of extracolonic evaluation as an integral part of this examination is also covered. Within this context, the question of whether a radiologist or gastroenterologist is better suited to interpret this examination is explored.

Magnetic resonance (MR) colonography in the detection of colorectal lesions: a systematic review of prospective studies

Objective

To determine the diagnostic accuracy of MR-colonography for the detection of colorectal lesions.

Methods

A comprehensive literature search was performed for comparative MR-colonography studies, published between May 1997 and February 2009, using the MEDLINE, EMBASE and Cochrane databases. We included studies if MR-colonography findings were prospectively compared with conventional colonoscopy in (a)symptomatic patients. Two reviewers independently extracted study design characteristics and data for summarising sensitivity and specificity. Heterogeneity in findings between studies was tested using I² test statistics. Sensitivity and specificity estimates with 95% confidence intervals (CI) were calculated on per patient basis and summary sensitivity on per polyp basis, using bivariate and univariate statistical models.

Results

Thirty-seven studies were found to be potentially relevant and 13 fulfilled the inclusion criteria. The study population comprised 1,285 patients with a mean disease prevalence of 44% (range 22–63%). Sensitivity for the detection of CRC was 100%. Significant heterogeneity was found for overall per patient sensitivity and specificity. For polyps with a size of 10 mm or larger, per patient sensitivity and specificity estimates were 88% (95% CI 63–97%; I² = 37%) and 99% (95% CI 95–100%; I² = 60%). On a per polyp basis, polyps of 10 mm or larger were detected with a sensitivity of 84% (95% CI 66–94%; I² = 51%). The data were too heterogeneous for polyps smaller than 6 mm and 6–9 mm.

Conclusion

MR-colonography can accurately detect colorectal polyps more than 10 mm in size

Polyp characteristics correctly annotated by computer-aided detection software but ignored by reporting radiologists during CT colonography

PURPOSE

To retrospectively describe the characteristics of polyps incorrectly dismissed by radiologists despite appropriate computer-aided detection (CAD) prompting during computed tomographic (CT) colonography.

MATERIALS AND METHODS

Ethics committee approval and patient informed consent were obtained from institutions that provided the data sets used in this HIPAA-compliant study. A total of 111 polyps that had a diameter of at least 6 mm and were detected with CAD were collated from three previous studies in which researchers investigated radiologist performance with and without CAD (total, 25 readers). Two new observers graded each polyp with predefined criteria, including polyp size, morphology, and location; data set quality; ease of visualization; tagging use and polyp coating; colonic curvature; CAD mark obscuration; and number of false-positive findings. The 86 polyps that were missed before CAD (those that were unreported by one or more original readers) were divided into those that remained unreported after CAD (no CAD gain, n = 36) and those that were reported correctly by at least one additional reader (CAD gain, n = 50). Logistic-regression analysis and the Fisher exact and Mann-Whitney tests were used to compare the results of both groups with each other and with a control group of 25 polyps, all of which were detected by readers without CAD.

RESULTS

Before CAD, polyps 10 mm in diameter or larger, those that were rated easy to visualize, and those that were uncoated by tagged fluid were less likely to be missed (72%, 76%, and 80% of control polyps vs 43%, 43%, and 59% of missed polyps, respectively; P < .001, P < .01, and P < .03, respectively). After CAD, the odds of CAD gain decreased with increasing polyp size (odds ratio, 0.92; 95% confidence interval: 0.85, 1.00; P = .04) and irregular morphology (odds ratio, 0.28; 95% confidence interval: 0.08, 0.92; P = .04).

CONCLUSION

Larger irregular polyps are a common source of incorrect radiologist dismissal, despite correct CAD prompting.

Influence of computer-aided detection false-positives on reader performance and diagnostic confidence for CT colonography

OBJECTIVE

The objective of our study was to investigate whether an increasing number of computer-aided detection (CAD) false-positives decreases reader sensitivity, specificity, and confidence for nonexpert readers of CT colonography (CTC).

MATERIALS AND METHODS

Fifty CTC data sets (29 men; mean age, 65 years), 25 of which contained 35 polyps > or = 5 mm, were selected in which CAD had 100% polyp sensitivity at two sphericity settings (0 and 75) but differed in the number of false-positives. The data sets were read by five readers twice: once at each sphericity setting. Sensitivity, specificity, report time, and confidence before and after second-read CAD were compared using the paired exact and Student's t test, respectively. Receiver operating characteristic (ROC) curves were generated using reader confidence (1-100) in correct case classification (normal or abnormal).

RESULTS

CAD generated a mean of 42 (range, 3-118) and 15 (range, 1-36) false-positives at a sphericity of 0 and 75, respectively. CAD at both settings increased per-patient sensitivity from 82% to 87% (p = 0.03) and per-polyp sensitivity by 8% and 10% for a sphericity of 0 and 75, respectively (p < 0.001). Specificity decreased from 84% to 79% (sphericity 0 and 75, p = 0.03 and 0.07). There was no difference in sensitivity, specificity, or reader confidence between sphericity settings (p = 1.0, 1.0, 0.11, respectively). The area under the ROC curve was 0.78 (95% CI, 0.70-0.86) and 0.77 (0.68-0.85) for a sphericity of 0 and 75, respectively. CAD added a median of 4.4 minutes (interquartile range [IQR], 2.7-6.5 minutes) and 2.2 minutes (IQR, 1.2-4.0 minutes) for a sphericity of 0 and 75, respectively (p < 0.001). CONCLUSION. CAD has the potential to increase the sensitivity of readers inexperienced with CTC, although specificity may be reduced. An increased number of CAD-generated false-positives does not negate any beneficial effect but does reduce efficiency.

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.

Computer-aided detection for CT colonography: update 2007

Computed tomographic colonography (CTC) is an emerging technique for polyp detection in the colon. However, lesion detection can be challenging due to insufficient patient preparation, chosen CT technique or reader imperfection. The primary goal of computer-aided detection (CAD) for CTC is locating possible polyps, and presenting the reader with these polyp candidates. Other goals are sensitivity improvement and reduction of reading time and inter-observer variability. The multistep CAD procedure typically consists of segmentation of the colonic wall (e.g. region growing); selection of intermediate polyp candidates (curvature analysis, sphere fitting, normal analysis, slope density function ...); classification of final candidates for detection and listing suspicious polyps (location, size and volume). Remaining task for the radiologist is the validation or rejection of the polyp candidates. State-of-the-art CAD systems should require minimal or even no user interaction for the extraction of the colonic wall, offer a computation time less than 10-20 min and high sensitivity and specificity for different polyp sizes and shapes, with a low number of false positives. These systems have the potential to increase radiologist's performance and to decrease inter-reader variability. Besides CAD key techniques we also discuss new developments in CAD and describe recent applications facilitating CTC.

Computed tomographic colonography: clinical value

Computed tomographic colonography (CTC) has the potential to reliably detect polyps in the colon. Its clinical value is accepted for several indications. The main target is screening asymptomatic people for colorectal cancer (CRC). As in large multi-centre trials controversial results were obtained, acceptance of this indication on a large scale is still pending. Agreement exists that in experienced hands screening can be performed with CTC. This emphasizes the importance of adequate and intensive training. Besides this, other problems have to be solved. A low complication profile is mandatory. Perforation rate is very low. Ultra-low dose radiation should be used. When screening large patient cohorts, CTC will need a time-efficient and cost-effective management without too many false positives and additional exploration. Can therefore a cut-off size of polyp detection safely be installed? Is the flat lesion an issue? Can extra-colonic findings be treated efficiently? A positive relationship with the gastro-enterologists will improve the act of screening. Improvements of scanning technique and software with dose reduction, improved 3D visualisation methods and CAD are steps in the good direction. Finally, optimisation of laxative-free CTC could be invaluable in the development of CTC as a screening tool for CRC.

CT colonography: current status and future promise

CT colonography (CTC) is an innovative technology that entails CT examination of the entire colon and computerized processing of the raw data after colon cleansing and colonic distention. CTC could potentially increase the screening rate for colon cancer because of its relative safety, relatively low expense, and greater patient acceptance, but its role in mass colon cancer screening is controversial because of its highly variable sensitivity, the inability to sample polyps for histologic analysis, and lack of therapeutic capabilities. This article reviews the CTC literature, including imaging and adjunctive techniques, radiologic interpretation, procedure indications, contraindications, risks, sensitivity, interpretation pitfalls, and controversies.

Virtual colonoscopy: effect of computer-assisted detection (CAD) on radiographer performance

AIM

To investigate the effect of a virtual colonoscopy (VC) computed-assisted detection (CAD) system on polyp detection by trained radiographers.

MATERIALS AND METHODS

Four radiographers trained in VC interpretation and utilization of CAD systems read a total of 62 endoscopically validated VC examinations containing 150 polyps (size range 5-50mm) in four sessions, recording any polyps found and the examination interpretation time, first without and then with the addition of CAD as a "second reader". After a temporal separation of 6 weeks to reduce recall bias, VC examinations were re-read using "concurrent reader" CAD. Interpretation times, polyp detection, and number of false-positives were compared between the different reader paradigms using paired t and paired exact tests.

RESULTS

Overall, use of "second reader" CAD significantly improved polyp detection by 12% (p<0.001, CI 6%,17%)) from 48 to 60%. There was no significant improvement using CAD as a concurrent reader (p=0.20; difference of 7%, CI -3%, 16%) and no significant overall difference in recorded false-positives with second reader or concurrent CAD paradigms compared with unassisted reading (p=0.25 and 0.65, respectively). The mean interpretation time was 21.7 min for unassisted reading, 29.6 (p<0.001) min for second reader and 19.1 min (p=0.12) for concurrent reading paradigms.

CONCLUSION

CAD, when used as a second reader, can significantly improve radiographer reading performance with only a moderate increase in interpretation times.

Computer-aided detection for CT colonography: incremental benefit of observer training

The purpose of this study was to investigate the incremental effect of focused training on observer performance when using computer-assisted detection (CAD) software to interpret CT colonography (CTC). Six radiologists who were relatively inexperienced with CTC interpretation underwent 1 day of focused training before reading 20 patient datasets with the assistance of CAD software (ColonCAR 1.3, Medicsight PLC). Sensitivity, specificity and interpretation times were determined and compared with previous performance when reading the same datasets but without the benefit of focused training, using the binomial exact test and Wilcoxon's signed rank test. Per-polyp sensitivity improved after training by 18% overall (95% confidence interval (CI): 14-24%, p<0.001) and was greatest for polyps of 6-9 mm (26%, 95% CI: 18-34%, p<0.001). Absolute sensitivity was 23% (9-36%), 51% (33-71%) and 74% (44-100%) for polyps of <or=5 mm, 6-9 mm and >or=10 mm, respectively. Specificity fell significantly after focused training (median of 5.5 false positives per 20 datasets (interquartile range (IQR): 4-6) post-training vs median of 2.5 (IQR: 1-5) pre-training, p = 0.03). Interpretation time also increased significantly after training (from a median of 9.3 min (IQR: 9.3-14.5 min) to a median of 17.1 min (IQR: 15.4-19.4 min), p = 0.03). In conclusion, one day of training increases observer polyp sensitivity when using CAD for CTC at the expense of increased reporting time and reduction in specificity.

What is the value of computered tomography colonography in patients screening positive for fecal occult blood? A systematic review and economic evaluation

BACKGROUND & AIMS

Computerized tomography colonography (CTC) is a highly accurate test for the detection of colorectal polyps and cancers and has been proposed as a potential alternative to colonoscopy. Bowel cancer screening using fecal occult blood testing (FOBT) and follow-up diagnostic colonoscopy is an effective intervention that currently is being implemented in screening programs internationally. Because of high false-positive rates for FOBT, concerns have been raised about patient uptake and access to colonoscopy services. This study assessed the value of CTC as an alternative to colonoscopy in FOBT-positive individuals.

METHODS

A systematic review of studies comparing the accuracy of CTC and colonoscopy for the detection of lesions 10 mm or greater and cancers in nonscreening populations was conducted. A modeled economic analysis was undertaken to assess cost per life-year saved.

RESULTS

Five eligible studies were identified. Pooled sensitivity and specificity for the detection of lesions 10 mm or greater were 63% (95% confidence interval [CI], 55%-71%) and 95% (95% CI, 94%-97%) for CTC, and 95% (95% CI, 90%-98%) and 99.8% (95% CI, 99.5%-100%) for colonoscopy, respectively (3 studies). Pooled sensitivity and specificity for the detection of cancer were 89% (95% CI, 70%-98%) and 97% (95% CI, 95%-98%) for CTC, and 96% (95% CI, 80%-100%) and 99.7% (95% CI, 99%-100%) for colonoscopy, respectively (3 studies). The base case economic analysis showed that CTC is less effective and more costly than colonoscopy. At a low prevalence of polyps, sensitivity analysis found CTC was less effective and less costly than colonoscopy; if CTC was more sensitive than colonoscopy, CTC was more effective, at higher cost.

CONCLUSIONS

Overall, CTC appears less accurate, less effective, and potentially more costly than colonoscopy in individuals with a positive FOBT.

Fundamental elements for successful performance of CT colonography (virtual colonoscopy)

There are many factors affecting the successful performance of CT colonography (CTC). Adequate colonic cleansing and distention, the optimal CT technique and interpretation with using the newest CTC software by a trained reader will help ensure high accuracy for lesion detection. Fecal and fluid tagging may improve the diagnostic accuracy and allow for reduced bowel preparation. Automated carbon dioxide insufflation is more efficient and may be safer for colonic distention as compared to manual room air insufflation. CT scanning should use thin collimation of < or =3 mm with a reconstruction interval of < or =1.5 mm and a low radiation dose. There is not any one correct method for the interpretation of CTC; therefore, readers should be well-versed with both the primary 3D and 2D reviews. Polyps detected at CTC should be measured accurately and reported following the "polyp size-based" patient management system. The time-intensive nature of CTC and the limited resources for training radiologists appear to be the major barriers for implementing CTC in Korea.

Computer-aided detection of colorectal polyps: can it improve sensitivity of less-experienced readers? Preliminary findings

PURPOSE

To determine whether computer-aided detection (CAD) applied to computed tomographic (CT) colonography can help improve sensitivity of polyp detection by less-experienced radiologist readers, with colonoscopy or consensus used as the reference standard.

MATERIALS AND METHODS

The release of the CT colonographic studies was approved by the individual institutional review boards of each institution. Institutions from the United States were HIPAA compliant. Written informed consent was waived at all institutions. The CT colonographic studies in 30 patients from six institutions were collected; 24 images depicted at least one confirmed polyp 6 mm or larger (39 total polyps) and six depicted no polyps. By using an investigational software package, seven less-experienced readers from two institutions evaluated the CT colonographic images and marked or scored polyps by using a five-point scale before and after CAD. The time needed to interpret the CT colonographic findings without CAD and then to re-evaluate them with CAD was recorded. For each reader, the McNemar test, adjusted for clustered data, was used to compare sensitivities for readers without and with CAD; a Wilcoxon signed-rank test was used to analyze the number of false-positive results per patient.

RESULTS

The average sensitivity of the seven readers for polyp detection was significantly improved with CAD-from 0.810 to 0.908 (P=.0152). The number of false-positive results per patient without and with CAD increased from 0.70 to 0.96 (95% confidence interval for the increase: -0.39, 0.91). The mean total time for the readings was 17 minutes 54 seconds; for interpretation of CT colonographic findings alone, the mean time was 14 minutes 16 seconds; and for review of CAD findings, the mean time was 3 minutes 38 seconds.

CONCLUSION

Results of this feasibility study suggest that CAD for CT colonography significantly improves per-polyp detection for less-experienced readers.

CT colonography: an update

Computed tomographic (CT) colonography (CTC)--also known as "virtual colonoscopy"--was first described more than a decade ago. As advancements in scanner technology and three-dimensional (3D) postprocessing helped develop this method to mature into a potential option in screening for colorectal cancer, the fundamentals of the examination remained the same. It is a minimally invasive, CT-based procedure that simulates conventional colonoscopy using 2D and 3D computerized reconstructions. The primary aim of CTC is the detection of colorectal polyps and carcinomas. However, studies reveal a wide performance variety in regard to polyp detection, especially for smaller polyps. This article reviews the available literature, discusses established indications as well as open issues and highlights potential future developments of CTC.

Optimization of CT colonography technique: a practical guide

In this article we provide practical advice for optimizing computed tomography colonography (CTC) technique to help ensure that reproducible, high-quality examinations are achieved. Relevant literature is reviewed and specific attention is paid to patient information, bowel cleansing, insufflation, anti-spasmodics, patient positioning, CT technique, post-procedure care and complications, as well as practical problem-solving advice. There are many different approaches to performing CTC; our aim is to not to provide a comprehensive review of the literature, but rather to present a practical and robust protocol, providing guidance, particularly to those clinicians with little prior experience of the technique.

European Society of Gastrointestinal and Abdominal Radiology (ESGAR): consensus statement on CT colonography

Rapid clinical dissemination of CT colonography (CTC) is occurring in parallel with continued research into technique optimisation and diagnostic performance. A need exists therefore for current guidance as to basic prerequisites for effective clinical implementation. A questionnaire detailing CTC technique, analysis, training and clinical implementation was developed by the European Society of Gastrointestinal and Abdominal Radiology (ESGAR) CTC committee and circulated to all faculty members of previous ESGAR "hands-on" CTC training courses. Responses were collated and a consensus statement produced. Of 27 invited to participate, 24 responded. Reasonable consensus was reached on bowel preparation, colonic distension, patient positioning, use of IV contrast and optimal scan parameters. Both primary 2D and primary 3D analysis were advocated equally, with some evidence that more experienced readers prefer primary 2D. Training was universally recommended, although there was no consensus regarding minimum requirements. CTC was thought superior to barium enema, although recommended for screening only in the presence of validated local experience. There was consensus that polyps 4 mm or less could be ignored assuming agreement from local gastroenterological colleagues. There is increasing consensus amongst European experts as to the current best practice in CTC.

Colorectal polyps on portal phase contrast-enhanced CT colonography: lesion attenuation and distinction from tagged feces

OBJECTIVE

The purpose of our study was to determine the attenuation of colorectal polyps on portal phase contrast-enhanced CT colonography (CTC) and evaluate whether enhanced polyps can be clearly distinguished from tagged feces during CTC review.

MATERIALS AND METHODS

Our institutional review board approved this study and waived patient informed consent. Forty-eight colonoscopy-proven polyps (6-20 mm) and 41 polypoid tagged feces (6-19 mm) were selected from contrast-enhanced CTC performed without (n = 37 examinations) and with (n = 10 examinations) fecal tagging, respectively. Scanning was performed 72 seconds after i.v. injection of 150 mL of contrast material at a rate of 2.5 mL/s. Fecal tagging consisted of three doses of 200 mL of 5% weight/volume (w/v) barium sulfate suspension taken at each meal the day before CTC. Attenuation of the polyps and tagged feces was measured. Four independent blinded radiologists reviewed the polyps and tagged feces at both wide (width, 1,500 H; level -400 H) and soft-tissue (width, 400 H; level, 20 H) window settings to distinguish them by using subjective visual assessment.

RESULTS

Polyp attenuation on the portal phase was not correlated with size (R = -0.003; p = 0.99) and was not different between histologic types (p = 0.884). Enhanced polyps (mean +/- SD, 119.9 +/- 25.3 H; range, 50-173 H) showed significantly lower attenuation than did tagged feces (1,521.4 +/- 683.6 H; range, 495-2,683 H) without any overlap (p < 0.0005). An 8-mm sessile adenomatous polyp was misinterpreted as tagged feces by one reviewer. The rest of the lesions were correctly interpreted by all reviewers, resulting in high interobserver agreement (kappa value, 0.988).

CONCLUSION

Polyp attenuation on portal phase contrast-enhanced CTC ranges from 50 to 173 H. Contrast-enhanced polyps are clearly and consistently distinguished from barium-tagged polypoid feces.

Virtual colonoscopy training and accreditation: a national survey of radiologist experience and attitudes in the UK

AIM

Expert consensus recommends directed training and possibly in the future, formal accreditation before independent virtual colonoscopy (VC) reporting. We surveyed radiologists' experience of VC training, compared with barium enema, and assessed attitudes towards accreditation.

MATERIALS AND METHODS

A questionnaire was sent to 78 consultant radiologists from 72 centres (65 National Health Service hospitals; seven independent primary screening centres) offering a VC service.

RESULTS

Fifty-four (69%) eligible radiologists responded. They had interpreted 18,152 examinations (range 3-1500) in total versus 232,350 (13 times more) barium enemas. Twenty-two (41%) deemed their VC training as inadequate [including five (45%) of screening centre radiologists], and only 14 (26%) had attended a training workshop due to lack of availability (54%) or financial/study leave constraints (24%). Eleven (20%) radiologists routinely double-reported VC examinations versus 37 (69%) barium enemas, yet 21 (39%) considered requirements for VC training were greater than barium enema. Thirty-eight (70%) favoured accreditation beyond internal audit for VC versus 15(28%) for barium enema. Of these 38, seven (18%) favoured "one-off," and 18 (47%) periodic testing, with 16 (42%) favouring external audit alone or in combination with testing. Overall, 42 (78%) considered specific accreditation for reporting screening examinations appropriate and 45 (83%) respondents preferred a national radiological organization to regulate such a scheme.

CONCLUSION

There is wide variability in reporting experience and recommendations for VC training have not been widely adopted, in part due to limited access to dedicated workshops. UK radiologists are generally in favour of VC accreditation, governed by a national radiology organization.

Effect of computer-aided detection as a second reader in multidetector-row CT colonography

Our purpose was to assess the effect of computer-aided detection (CAD) on lesion detection as a second reader in computed tomographic colonography, and to compare the influence of CAD on the performance of readers with different levels of expertise. Fifty-two CT colonography patient data-sets (37 patients: 55 endoscopically confirmed polyps > or =0.5 cm, seven cancers; 15 patients: no abnormalities) were retrospectively reviewed by four radiologists (two expert, two nonexpert). After primary data evaluation, a second reading augmented with findings of CAD (polyp-enhanced view, Siemens) was performed. Sensitivities and reading time were calculated for each reader without CAD and supported by CAD findings. The sensitivity of expert readers was 91% each, and of nonexpert readers, 76% and 75%, respectively, for polyp detection. CAD increased the sensitivity of expert readers to 96% (P = 0.25) and 93% (P = 1), and that of nonexpert readers to 91% (P = 0.008) and 95% (P = 0.001), respectively. All four readers diagnosed 100% of cancers, but CAD alone only 43%. CAD increased reading time by 2.1 min (mean). CAD as a second reader significantly improves sensitivity for polyp detection in a high disease prevalence population for nonexpert readers. CAD causes a modest increase in reading time. CAD is of limited value in the detection of cancer.

Reader error during CT colonography: causes and implications for training

This study investigated the variability in baseline computed tomography colonography (CTC) performance using untrained readers by documenting sources of error to guide future training requirements. Twenty CTC endoscopically validated data sets containing 32 polyps were consensus read by three unblinded radiologists experienced in CTC, creating a reference standard. Six readers without prior CTC training [four residents and two board-certified subspecialty gastrointestinal (GI) radiologists] read the 20 cases. Readers drew a region of interest (ROI) around every area they considered a potential colonic lesion, even if subsequently dismissed, before creating a final report. Using this final report, reader ROIs were classified as true positive detections, true negatives correctly dismissed, true detections incorrectly dismissed (i.e., classification error), or perceptual errors. Detection of polyps 1-5 mm, 6-9 mm, and > or =10 mm ranged from 7.1% to 28.6%, 16.7% to 41.7%, and 16.7% to 83.3%, respectively. There was no significant difference between polyp detection or false positives for the GI radiologists compared with residents (p=0.67, p=0.4 respectively). Most missed polyps were due to failure of detection rather than characterization (range 82-95%). Untrained reader performance is variable but generally poor. Most missed polyps are due perceptual error rather than characterization, suggesting basic training should focus heavily on lesion detection.