Flat colorectal lesions in asymptomatic adults: implications for screening with CT virtual colonoscopy

OBJECTIVE: The clinical significance of flat lesions in colorectal cancer screening remains uncertain. The purpose of this study was to investigate the frequency, histology, and virtual colonoscopy detection of flat lesions in an asymptomatic screening population. SUBJECTS AND METHODS: The morphology of all detected polyps was prospectively recorded as flat or polypoid (sessile or pedunculated) in 1,233 consecutive asymptomatic adults who underwent same-day virtual colonoscopy and optical colonoscopy. A flat morphology was defined as a shallow plaquelike broad-based lesion with a height of less than one half of its width. RESULTS: Of 344 polyps of 6 mm or greater confirmed at optical colonoscopy, 17 (4.9%) were labeled as flat at both virtual colonoscopy and optical colonoscopy; 17 (4.9%), at optical colonoscopy only; and 25 (7.3%), at virtual colonoscopy only, yielding 59 total lesions in 52 (4.2%) of 1,233 patients. Twenty-nine (49.2%) of 59 flat lesions were adenomatous, of which four measured 10 mm or greater and one 6- to 9-mm lesion was histologically advanced. None of the 148 diminutive flat lesions (< or = 5 mm) detected at optical colonoscopy was histologically advanced. Virtual colonoscopy prospectively detected 24 (82.8%) of 29 flat adenomas and 47 (80.0%) of all 59 flat lesions 6 mm or greater. In comparison, the sensitivity of virtual colonoscopy for the detection of polypoid adenomas and all polypoid lesions of 6 mm or greater was 86.2% (156/181, p = 0.58) and 81.0% (231/285, p = 0.86), respectively. CONCLUSION: Flat adenomas measuring 6 mm or greater are uncommon in a typical Western screening population, and advanced flat neoplasms are rare. The sensitivity of virtual colonoscopy for detecting flat lesions was similar to that of polypoid lesions. These results indicate that flat lesions are not a significant drawback for virtual colonoscopy screening.     

Spiral CT pneumocolon: applications, status and limitations

CT pneumocolon is a promising new technique in the diagnosis and management of colon pathology. CT pneumocolon can detect (sensitivity >95%) and stage (accuracy 79%) colorectal cancer and is very accurate in the differentiation of malignant from benign colonic pathologies. It has excellent detection rates for polyps >10 mm in diameter. Several studies using 3D virtual colonoscopy have already proven its high sensitivity and specificity in polyp detection making this technique robust as a screening tool. The combined results for virtual colonoscopy, from all centres, show a sensitivity of >85% in the detection of polyps 10 mm or greater in size, 70-80% for 5-9 mm polyps and an overall specificity of 90%. CT pneumocolon is a safe, non-invasive and cost-effective method for detecting colonic carcinomas and adenomas and correctly identifying which patients need further colonoscopy. The technique is quick, well tolerated and non-operator dependent. It can also image the proximal colon when distal stenoses prevent endoscopic and barium examination. CT pneumocolon is able to identify the features and complications of inflammatory bowel disease. Further research is warranted to fully assess its impact in terms of a screening tool, acceptability, availability and cost benefit.     

Virtual colonoscopy--chances for a screening procedure?

In principle, virtual colonoscopy is capable to be used as method for early detection of colorectal cancer (CRC), even if the accuracy of the method and radiation exposure are matters discussion in the radiological community. Virtual colonoscopy is able to detect any pathology which is relevant for early detection of CRC especially when using multislice CT, but also with single slice CT. The diagnosis of small lesions, less than 7 mm in diameter (polyps and flat lesions) is still problematic as it is in conventional colonoscopy. The exposure to x-rays in asymptomatic patients, without any increased risk of developing cancer is highly problematic and should be reduced to a minimum. Using special post processing filters on the volume dataset it can be shown that a tube current of 20 mAs is sufficient without any loss in accuracy. Measurements on the Alderson-phantom showed, that an effective dose exposure of 1.2 mSv is obtained using these reduced mAs values. It has to be differentiated between virtual colonoscopy for early detection of polyps and CRC in individual patients or as a screening examination of a large population. Virtual colonoscopy as a screening examination necessitates reduction of radiation dose, a high degree of automatization in 3D reconstructions as well as the assessment of the entire mucosa. High risk patients, whom refuse fibreoptic colonoscopy should undergo virtual colonoscopy. Virtual colonoscopy has a good chance to become an accepted tool for general screening, if efficient dose reduction, complete visualization of the colon mucosa and automatization of the post processing procedures can be achieved.     

Current status on performance of CT colonography and clinical indications

CT colonography (CTC) is a robust and reliable imaging test of the colon. Accuracy for the detection of colorectal cancer (CRC) is as high as conventional colonoscopy (CC). Identification of polyp is size dependent, with large lesions (≥10 mm) accurately detected and small lesions (6–9 mm) identified with moderate to good sensitivity. Recent studies show good sensitivity for the identification of nonpolypoid (flat) lesions as well.     

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.     

螺旋CT仿真内窥镜诊断大肠息肉初探

目的 探讨螺旋ＣＴ仿真内窥镜对大肠息肉的诊断价值和临床意义。方法 １８例有反复便血、慢性腹泻、腹痛的病人行１次屏气全结肠容积扫描,重叠重建图像并输至工作站进行四维容积重建（４Ｄ ａｎｇｉｏ）,选择导航者（Ｖｏｙａｇｅｒ）软件和合适阈值及透明度,航进观察大肠黏膜。全部资料经纤维结肠镜和（或）手术证实。结果 １８例中发现大肠息肉９例,均为多发,共检出息肉７１枚,直径２～２０ｍｍ,其中升结肠１枚,结肠肝     

CT colonography: multiobserver diagnostic performance

PURPOSE: To prospectively evaluate multiobserver diagnostic performance and reader agreement for colorectal polyp detection in a well-characterized cohort of patients with increased number of polyps, compared with an average-risk patient, with colonoscopy as the reference standard. MATERIALS AND METHODS: A cohort of 70 patients suspected of having polyps was examined with spiral computed tomographic (CT) colonography, with colonoscopy performed the same day. After air insufflation per rectum, supine and prone images were obtained with single-detector row CT (5-mm collimation, 8-mm table increment, 2-mm reconstruction interval). Images were analyzed independently by four experienced abdominal radiologists using two-dimensional multiplanar reformation followed by selective use of three-dimensional endoscopic volume-rendered images. Data were analyzed both per polyp and per patient. RESULTS: Analysis per polyp demonstrated a pooled sensitivity of 0.68 for lesions 10 mm or larger (n = 40), with 75% agreement among the four readers. Analysis per patient demonstrated improved detection and agreement, with a pooled sensitivity of 0.88 for patients with polyps or cancers 10 mm or larger (n = 28), with 94% agreement. When sensitivity and receiver operating characteristic analyses were analyzed per polyp size threshold, results among readers converged and peaked at polyp diameters of approximately 10 mm. CONCLUSION: In this patient cohort, diagnostic performance and interobserver agreement with single-detector row CT colonography was sufficient for detection of patients with lesions 10 mm or larger, with more variable results for smaller polyps.     

Magnetic resonance colonography and virtual magnetic resonance colonoscopy with the 1.0-T system: a feasibility study

RATIONALE AND OBJECTIVES: An ex vivo study and a clinical, prospective, patient study were undertaken to evaluate the feasibility of magnetic resonance (MR) colonography with a 1.0-T system. METHODS: An ex vivo colon model was scanned. A cleaned pig colon was prepared with six simulated sessile polyps (diameters of 4-12 mm) and one simulated pedunculated polyp (diameter of 5 mm). Subsequently, five patients (aged 39-81 years; four women, one man) were examined with MR colonography, immediately followed by endoscopic colonoscopy. After preparation for colonoscopy, the colon was filled with a Gd-DTPA/water solution (1:100). A breath-hold 3D gradient-echo sequence was acquired in both the prone and supine positions and after intravenous Gd-DTPA administration. Images were analyzed interactively by using multiplanar projections, maximum-intensity projection, and a virtual endoscopic view. The MR results were compared with the findings of the fiberoptic endoscopy. RESULTS: All seven simulated lesions of the colon model could be detected by MR imaging. In one patient, an advanced colon cancer as well as an additional small polyp was depicted. In the other four patients, single polyps with a diameter of 1 to 2.5 cm and a large adenoma were visualized by MR colonography. Contrast enhancement of the polyps was noted only after subtraction. CONCLUSIONS: The 1.0-T system is feasible for MR colonography. Reduced requirements for hardware could contribute to establish the novel technique as a screening method for colorectal polyps.     

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

Virtual colonoscopy (CT colonography) promises to become a primary method for colorectal cancer screening and return radiologists to a major role in colon cancer prevention. Results from major centers in the United States show accuracy to be comparable to conventional colonoscopy for detection of polyps of significant size--that is, greater than 10 mm--with few false-positives. The advent of virtual colonoscopy has also heightened awareness of the natural history of colonic polyps, particularly in terms of identifying an appropriate target size for detection in colorectal screening programs. Small polyps (<10 mm) are often either hyperplastic on histology or are unlikely to progress to frank cancer in the patient's lifetime and are therefore of little clinical significance for the average adult. Thus, the rationale for detecting and removing each and every colonic polyp regardless of size has come under increasing scrutiny in the context of cost-benefit analysis of various test strategies for colorectal cancer screening. Virtual colonoscopy may allow patients to obtain reliable information about the status of their colonic mucosa noninvasively and thus make a more informed decision as to whether to proceed to conventional colonoscopy for polypectomy.     

Die virtuelle Realität der MR-Kolonographie

Early detection and subsequent removal of colorectal polyps have been shown to constitute an effective approach for decreasing the incidence of colorectal cancer. The lack of an ideal modality for colorectal polyp screening stimulated interest in the development of CT-colonography and MR-colonography. Both techniques allow the colon to be analyzed in a cross-sectional as well as a virtual endoscopic format. Causing no side-effects and not concerning for radiation exposure MR-colonography warrants further consideration. Additional to detecting polyps down to 6 mm in size the inner wall contour and the morphology of the colonic wall itself can be assessed. New developments like fecal tagging will increase patients acceptance comparing to other diagnostic techniques. In search of an ideal modality for polyp screening MR-colonography will become a potent option in the diagnostic arsenal.     

Colon dissection: a new three-dimensional reconstruction tool for computed tomography colonography

PURPOSE: To improve the sensitivity of computed tomography (CT) colonography in the detection of polyps by comparing the 3D reconstruction tool "colon dissection" and endoluminal view (virtual colonoscopy) with axial 2D reconstructions. MATERIAL AND METHODS: Forty-eight patients (22 M, 26 F, mean age 57 +/- 21) were studied after intra-anal air insufflation in the supine and prone positions using a 16-slice helical CT (16 x 0.625 mm, pitch 1.7; detector rotation time 0.5 s; 160 mAs und 120 kV) and conventional colonoscopy. Two radiologists blinded to the results of the conventional colonoscopy analyzed the 3D reconstruction in virtual-endoscopy mode, in colon-dissection mode, and axial 2D slices. RESULTS: Conventional colonoscopy revealed a total of 35 polyps in 15 patients; 33 polyps were disclosed by CT methods. Sensitivity and specificity for detecting colon polyps were 94% and 94%, respectively, when using the "colon dissection", 89% and 94% when using "virtual endoscopy", and 62% and 100% when using axial 2D reconstruction. Sensitivity in relation to the diameter of colon polyps with "colon dissection", "virtual colonoscopy", and axial 2D-slices was: polyps with a diameter >5.0 mm, 100%, 100%, and 71%, respectively; polyps with a diameter of between 3 and 4.9 mm, 92%, 85%, and 46%; and polyps with a diameter < 3 mm, 89%, 78%, and 56%. The difference between "virtual endoscopy" and "colon dissection" in diagnosing polyps up to 4.9 mm in diameter was statistically significant. CONCLUSION: 3D reconstruction software "colon dissection" improves sensitivity of CT colonography compared with the endoluminal view.     

The effect of diagnostic confidence on the probability of optical colonoscopic confirmation of potential polyps detected on CT colonography: prospective assessment in 1,339 asymptomatic adults

OBJECTIVE: We sought to evaluate the effect of interpreter confidence on the likelihood that a lesion detected on CT colonography (CTC) will correspond to a matched polyp seen on optical colonoscopy. SUBJECTS AND METHODS: Same-day CTC and optical colonoscopy were performed on 1,339 asymptomatic adults. A standard matching algorithm for polyp size and location was used. For each potential polyp detected on CTC, the level of diagnostic confidence was prospectively rated on a 3-point scale (1, least certain; 2, intermediate; and 3, most certain). RESULTS: For CTC-detected lesions 6 mm or larger, diagnostic confidence levels of 1, 2, and 3 corresponded to matched polyps on optical colonoscopy in 33.3% (45/135), 50.0% (103/206), and 66.8% (157/235) of cases, respectively (p < 0.01). Similar trends were present for categories of lesions that measured 6-7 mm, 8-9 mm, and 10 mm or larger, rising to a match rate of 82.1% (55/67) for lesions 10 mm or larger that were diagnosed with a level-3 confidence rating. The likelihood that a matched polyp was adenomatous increased with greater levels of diagnostic confidence. Of note, level-3 confidence for lesions measuring 8-9 mm on CTC more often yielded a matching neoplasm on optical colonoscopy than level-1 or level-2 confidence for lesions measuring 10 mm or larger (60.3% [35/58] vs 20.8% [10/48]; p < 0.0001). CONCLUSION: Greater diagnostic confidence for an individual lesion detected on CTC correlates with a significantly increased likelihood that a matching polyp will be found on optical colonoscopy and that this matched polyp will be neoplastic. Although polyp size represents the primary criterion for CTC screening algorithms, this data could help guide the decision to opt for noninvasive CTC surveillance versus optical colonoscopy for polypectomy.     

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

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

Diagnostic performance of CT colonography for the detection of colorectal polyps.

OBJECTIVE: To investigate the diagnostic value of CT colonography for the detection of colorectal polyps. MATERIALS AND METHODS: From December 2004 to December 2005, 399 patients underwent CT colonography and follow-up conventional colonoscopy. We excluded cases of advanced colorectal cancer. We retrospectively analyzed the CT colonography findings and follow-up conventional colonoscopy findings of 113 patients who had polyps more than 6 mm in diameter. Radiologists using 3D and 2D computer generated displays interpreted the CT colonography images. The colonoscopists were aware of the CT colonography findings before the procedure. RESULTS: CT colonography detected 132 polyps in 107 of the 113 patients and conventional colonoscopy detected 114 colorectal polyps more than 6 mm in diameter in 87 of the 113 patients. The sensitivity of CT colonography analyzed per polyp was 91% (41/45) for polyps more than 10 mm in diameter and 89% (101/114) for polyps more than 6 mm in diameter. Thirteen polyps were missed by CT colonography and were detected on follow-up conventional colonoscopy. CONCLUSION: CT colonography is a sensitive diagnostic tool for the detection of colorectal polyps and adequate bowel preparation, optimal bowel distention and clinical experience are needed to reduce the rate of missing appropriate lesions.     

Virtual colon dissection with CT colonography compared with axial interpretation and conventional colonoscopy: preliminary results

OBJECTIVE: The aim of this study was to determine whether a new virtual colon dissection 3D visualization technique for CT colonography has a shorter analysis time and better sensitivity for detection of colonic polyps than interpretation of axial CT images. SUBJECTS AND METHODS. CT colonography was performed in 22 patients using 4-MDCT followed by conventional colonoscopy on the same day. The CT colonography data sets were analyzed by virtual colon dissection, which virtually bisects and unfolds the colon along its longitudinal axis to inspect the inner colonic surface for polyps. The same CT data sets were independently evaluated using axial interpretation. All data sets were independently interpreted by two radiologists in a blinded manner. RESULTS: Conventional colonoscopy revealed 31 colonic lesions in 20 patients. Twenty two of the lesions were smaller than 10 mm; nine were 10 mm or larger. Two of the original 22 patients were excluded, one because of residual stool and fluid and the other because of an impassable stenosing rectal wall cancer. For virtual colon dissection, the per-lesion sensitivity was 42% for observer 1 and 68% for observer 2; for axial interpretation, the respective sensitivities were 48% and 61%. For polyps 10 mm or larger, the respective sensitivities were 67% and 89% for virtual colon dissection and 89% and 100% for axial interpretation. The average time for reconstruction and analysis of virtual colon dissection was 36.8 min versus 29.2 min for axial images. Virtual colon dissection was feasible in both the supine and the prone positions in 45.5% of colonic segments, in either the supine or the prone position in 24.5%, and in neither position in 30% of segments. CONCLUSION: Although virtual colon dissection may facilitate detection of colonic polyps in isolated cases, its detection rate is not superior to axial interpretation, which is mainly attributable to failed rendering of insufficiently distended colonic segments or regions with residual feces. Virtual colon dissection is also the more time-consuming of the two procedures. With further improvement of path-finding and image segmentation, however, virtual colon dissection has the potential to be a useful interpretation tool for CT colonography.     

CT attenuation of colorectal polypoid lesions: evaluation of contrast enhancement in CT colonography

The aim of this study was to calculate pre- and postcontrast CT attenuation values of benign colorectal polyp and carcinoma lesions detected by virtual colonoscopy, and to investigate whether contrast enhancement of these lesions can be potentially used for differentiation from residual fluid in the colon. Fifteen benign polyps and 21 colorectal carcinoma lesions detected by virtual colonoscopy in 18 patients were included in our study. All of the polyps and carcinoma lesions were confirmed by colonoscopic biopsy. Measurement of CT attenuation values was performed in precontrast (supine) and postcontrast (prone) scans for each polyp and carcinoma. The CT attenuation values of residual fluid in the colon was also measured from the same location before and after intravenous contrast administration. On unenhanced CT scan mean attenuation values of benign polyps and colorectal carcinomas were 32.4 and 42.6 HU, respectively. Following contrast enhancement, mean attenuation value increased to 78.9 HU for polyps and 90.7 HU for carcinomas. Increase in the CT attenuation values of these lesions was significant ( p <0.0001). Mean CT attenuation value of residual fluid before and after administration of IV contrast were 14.6 and 13.8 HU, respectively. The difference between CT attenuation value of residual fluid in the colon before and after contrast material was not significant ( p =0.29). Colorectal benign polyps and carcinomas demonstrate significant enhancement following contrast administration and use of intravenous contrast material during virtual colonoscopy may help in some cases in differentiating these solid lesions from residual colonic fluid that does not enhance. This paper was presented at RSNA 2001 meeting.     

CT colonography: comparison of a colon dissection display versus 3D endoluminal view for the detection of polyps

The purpose of this study was to compare sensitivity, specificity, and postprocessing time of a colon dissection approach to regular 3D-endoluminal workup of computed tomography (CT) colonography for the detection of polypoid lesions. Twenty-one patients who had received conventional colonoscopy after CT colonography were selected; 18 patients had either colon polyps or colon cancer and three had no findings. CT colonography was performed using a 4-channel multi-detector-row (MDR) CT in ten cases and a 16-channel MDR-CT in 11 cases. A blinded reader retrospectively evaluated all colonographies using both viewing methods in a randomized order. Thirty-seven polyps were identified by optical colonoscopy. An overall per-lesion sensitivity of 47.1% for lesions smaller than 5 mm, 56.3% for lesions between 5 mm and 10 mm, and 75.0% for lesion larger than 10 mm was calculated using the colon dissection approach. This compared to an overall per-lesion sensitivity of 35.3% (<5 mm), 81.5% (5–10 mm), and 100.0% (>10 mm) using the endoluminal view. The average time consumption for CT colonography evaluation with the colon dissection software was 10 min versus 38 min using the endoluminal view. A colon dissection approach may provide a significant time advantage for evaluation of CT colonography while obtaining a high sensitivity. It is especially superior in the detection of lesions smaller than 5 mm.     

CT colonography: techniques, indications, findings

Computed tomographic colonography (CTC) is a minimally invasive technique for imaging the entire colon. Based on a helical thin-section CT of the cleansed and air-distended colon, two-dimensional and three-dimensional projections are used for image interpretation. Several clinical improvements in patient preparation, technical advances in CT, and new developments in evaluation software have allowed CTC to develop into a powerful diagnostic tool. It is already well established as a reliable diagnostic tool in symptomatic patients. Many experts currently consider CTC a comparable alternative to conventional colonoscopy, although there is still debate about its sensitivity for the detection of colonic polyps in a screening population. This article summarizes the main indications, the current techniques in patient preparation, data acquisition and data analysis as well as imaging features for common benign and malignant colorectal lesions.     

Colorectal cancer: screening double-contrast barium enema examination in average-risk adults older than 50 years

PURPOSE: To retrospectively determine the diagnostic yield of double-contrast barium enema examinations performed for colorectal cancer screening of neoplasms 1 cm or larger or advanced neoplastic lesions of any size in average-risk adults older than 50 years. MATERIALS AND METHODS: The Institutional Review Board at the affiliated Veterans Affairs Medical Center approved this HIPAA-compliant study protocol and did not require informed consent from patients. Computerized databases revealed 276 double-contrast barium enema examinations performed for colorectal cancer screening in average-risk adults older than 50 years. Radiographic and pathologic reports were reviewed to determine the number of patients who had polypoid lesions 1 cm or larger, polyps smaller than 1 cm, or advanced neoplastic lesions of any size. Forty-five (16.3%) of the 276 patients underwent follow-up sigmoidoscopy or colonoscopy. Medical, endoscopic, and pathologic records were reviewed and compared with radiographic findings. RESULTS: The results of double-contrast barium enema examination revealed 74 (26.8%) of 276 patients with 104 polypoid lesions in the colon, including 32 patients (11.6%) with 41 polypoid lesions 1 cm or larger, 15 patients (5.4%) with 19 polyps 6-9 mm, and 27 patients (9.8%) with 44 polyps 5 mm or smaller. Endoscopy was performed in 24 (75%) of 32 patients, the results of which confirmed 23 (72%) of 32 radiographically diagnosed lesions 1 cm or larger in 16 (67%) of 24 patients. In two of these individuals, the polyps were hyperplastic. The remaining 14 patients had a total of 21 neoplastic lesions 1 cm or larger, including 11 tubular adenomas, seven tubulovillous adenomas, one villous adenoma with marked dysplasia, and two cancers. The diagnostic yield of screening double-contrast barium enema examination was 5.1% (14 of 276 patients) for neoplastic lesions 1 cm or larger and 6.2% (17 of 276 patients) for advanced neoplastic lesions of any size. CONCLUSION: Double-contrast barium enema examinations performed in average-risk adults older than 50 years have a diagnostic yield of 5.1% for neoplastic lesions 1 cm or larger and 6.2% for advanced neoplastic lesions, regardless of size.     

Display modes for CT colonography. Part II. Blinded comparison of axial CT and virtual endoscopic and panoramic endoscopic volume-rendered studies.

PURPOSE: To determine the sensitivity of radiologist observers for detecting colonic polyps by using three different data review (display) modes for computed tomographic (CT) colonography, or "virtual colonoscopy." MATERIALS AND METHODS: CT colonographic data in a patient with a normal colon were used as base data for insertion of digitally synthesized polyps. Forty such polyps (3.5, 5, 7, and 10 mm in diameter) were randomly inserted in four copies of the base data. Axial CT studies, volume-rendered virtual endoscopic movies, and studies from a three-dimensional mode termed "panoramic endoscopy" were reviewed blindly and independently by two radiologists. RESULTS: Detection improved with increasing polyp size. Trends in sensitivity were dependent on whether all inserted lesions or only visible lesions were considered, because modes differed in how completely the colonic surface was depicted. For both reviewers and all polyps 7 mm or larger, panoramic endoscopy resulted in significantly greater sensitivity (90%) than did virtual endoscopy (68%, P = .014). For visible lesions only, the sensitivities were 85%, 81%, and 60% for one reader and 65%, 62%, and 28% for the other for virtual endoscopy, panoramic endoscopy, and axial CT, respectively. Three-dimensional displays were more sensitive than two-dimensional displays (P < .05). CONCLUSION: The sensitivity of panoramic endoscopy is higher than that of virtual endoscopy, because the former displays more of the colonic surface. Higher sensitivities for three-dimensional displays may justify the additional computation and review time.