Detection of flat colorectal polyps at screening CT colonography in comparison with conventional polypoid lesions

Background Although the screening of small, flat polyps is clinically important, the role of CT colonography (CTC) screening in their detection has not been thoroughly investigated. Purpose To evaluate the detection capability and usefulness of CTC in the screening of flat and polypoid lesions by comparing CTC with optic colonoscopy findings as the gold standard. Material and Methods We evaluated the CTC detection capability for flat colorectal polyps with a flat surface and a height not exceeding 3 mm (n = 42) by comparing to conventional polypoid lesions (n = 418) according to the polyp diameter. Four types of reconstruction images including multiplanar reconstruction, volume rendering, virtual gross pathology, and virtual endoscopic images were used for visual analysis. We compared the abilities of the four reconstructions for polyp visualization. Results Detection sensitivity for flat polyps was 31.3%, 44.4%, and 87.5% for lesions measuring 2-3 mm, 4-5 mm, and ≥6 mm, respectively; the corresponding sensitivity for polypoid lesions was 47.6%, 79.0%, and 91.7%. The overall sensitivity for flat lesions (47.6%) was significantly lower than polypoid lesions (64.1%). Virtual endoscopic imaging showed best visualization among the four reconstructions. Colon cancers were detected in eight patients by optic colonoscopy, and CTC detected colon cancers in all eight patients. Conclusion CTC using 64-row multidetector CT is useful for colon cancer screening to detect colorectal polyps while the detection of small, flat lesions is still challenging.     

Optimization of the technique of virtual colonoscopy using a multislice spiral computerized tomography

PURPOSE: To optimize scanning parameters for virtual colonoscopy utilizing a multislice Helical CT scanner in an in vitro study (using a homemade colonic phantom) and in a preliminary clinical study. MATERIAL AND METHODS: A colonic phantom was built using a plastic tube and 12 plastiline polyps were placed inside. The colonic phantom was studied with a multislice Helical CT scanner. Axial images were obtained with the phantom parallel to the long axis of the moving table (in order to simulate the evaluation of ascending and descending colon): oblique images were acquired with the phantom at 45 degrees relative to the long axis of the moving table (in order to simulate the evaluation of sigmoid colon and colonic flexures). Four different scanning protocols were tested: 1) slice collimation, 5 mm; slice width, 7 mm; table speed, 25 mm; reconstruction index, 5 mm; 2) slice collimation, 2.5 mm; slice width, 3 mm; table speed, 15 mm; reconstruction index, 3 mm; 3) slice collimation, 1 mm; slice width, 1.25 mm; table speed, 5 mm; reconstruction index, 1 mm; 4) slice collimation, 1 mm; slice width, 1.25 mm; table speed, 4 mm; reconstruction index, 1 mm. Quantitative analysis consisted in evaluation of the number of identified polyps and polyp size along the longitudinal axis. Qualitative analysis consisted in the evaluation of image artifacts and quality of 3D reconstructed images (step artifacts and polyp geometry distortion). This preliminary clinical study was performed in 12 patients (7 men and 5 women) who underwent multislice Helical CT colonography. We selected patients with clinical indications for conventional colonoscopy or after unsuccessful conventional colonoscopy. RESULTS: Multislice Helical CT colonography was 100% sensitive in the detection of all polyps and in all scanning protocols. With oblique scans, only a 3-mm polyp was missed during protocol 1 (sensitivity: 92%). Polyp geometry distortion was observed on longitudinal reconstructions, whereas no distortion was seen on axial images. Image quality was graded as optimal for protocols 2, 3, and 4; protocol 1 was graded as good on transverse scans and as poor on oblique scans. In our preliminary clinical study, two colonic carcinomas and three polyps were identified. CONCLUSIONS: At present, the introduction of multislice technology in virtual colonoscopy permits to improve spatial resolution and image definition. The actual clinical advantage, in terms of increased diagnostic accuracy, needs further investigation in larger clinical studies.     

Characterization of lesions missed on interpretation of CT colonography using a 2D search method

OBJECTIVE: We examined potential factors that may cause false-negative results on CT colonography examinations. MATERIALS AND METHODS: In this prospective and retrospective study, 500 asymptomatic patients at high risk for colorectal cancer underwent CT colonography and colonoscopy. Each CT data set was interpreted by two independent observers, who were unaware of endoscopic findings, using a method of searching through enlarged axial images to detect intraluminal lesions. Another observer identified and characterized lesions missed at prospective interpretation. Polyps were assessed for size, method of visualization, intrinsic and extrinsic features, and examination quality. RESULTS: We found 116 polyps at least 5 mm in diameter, 54 (47%) of which were missed by at least one of the prospective observers. Polyps seen in only one position were missed more often than polyps seen in both supine and prone positions (84% vs 50%, p < 0.01). Polyps located in suboptimally prepared colonic segments or along a thickened colonic wall were more frequently missed (p = 0.02 and p = 0.05, respectively). Endoscopic morphology and irregular surface contour were associated with missed lesions of all sizes (p = 0.03 and p = 0.04, respectively). Rounded intraluminal lesions were detected more often than other morphologies on CT (p = 0.04). CONCLUSION: Factors that influence the likelihood that a polyp may be missed at interpretation of CT colonography include being seen only in one position, having flat endoscopic or CT morphology, having surface irregularity, and being located in a poorly prepared segment or along a thickened colonic wall. Understanding these features should lead to improved polyp detection on CT colonography.     

Comparison of time-efficient CT colonography with two- and three-dimensional colonic evaluation for detecting colorectal polyps

OBJECTIVE: We compared the findings of time-efficient CT colonography with complete two-dimensional (2D) and three-dimensional (3D) CT colonography and conventional colonoscopy in detecting colorectal polyps. SUBJECTS AND METHODS: Forty-two patients undergoing colonoscopy screening were examined with CT colonography before endoscopy. Data were examined following one of two methods. In method 1, axial 2D data sets were examined in a cine mode. If findings were suggestive of abnormality, focal areas were examined with 3D CT colonography. In method 2, data sets were examined exactly as in method 1, and subsequent to that review, data sets were examined with simultaneous 3D "fly-through" CT colonography (surface-rendered images) and multiplanar reformatted images. The time required to examine CT colonography using each technique was recorded and abnormal findings were documented. Results of methods 1 and 2 were compared with findings on colonoscopy. RESULTS: Colonoscopy detected 16 polyps in 13 patients (polyp size, 2-10 mm). Ten polyps measured 5 mm or less, five measured between 6 and 9 mm, and one measured 10 mm or more. Using method 1, two of 10 polyps measuring less than 5 mm, three of five polyps measuring between 6 and 9 mm, and one polyp measuring 10 mm were detected. We noted no false-positive polyps. Average evaluation time was 16 min. With method 2, the same polyps were seen as with method 1. No additional polyps were detected, and the average evaluation time was 40 min. CONCLUSION: Axial 2D CT colonography can be performed quickly and is comparable with complete 2D and 3D CT colonography in detecting colorectal polyps.     

CT colonography: Protocol optimization with multi-detector row CT--study in an anthropomorphic colon phantom

PURPOSE: To determine optimal detector collimation, section thickness, and tube current for multi-detector row computed tomography (CT) colonography. MATERIALS AND METHODS: An anthropomorphic colon phantom with simulated polyps of varying size (2, 6, 8, 10, and 12 mm) was examined by using multi-detector row CT with varying combinations of detector collimation (4 x 1.0 mm and 4 x 2.5 mm), dose per section (10, 20, 40, 60, 80, 100, and 140 mAs), and section thickness/reconstruction interval (1.25/0.6, 2.0/1.0, 3.0/1.0, and 5.0/2.0 mm). Polyp depiction, longitudinal polyp distortion, and presence of rippling artifacts were assessed on reformatted three-dimensional endoluminal images by three reviewers. RESULTS: Longitudinal distortion and rippling artifacts increased with increasing section thickness and use of broader detector collimation. Polyps 8 mm or larger were depicted with any combination of section thickness, detector collimation, and tube current. Depiction of polyps 6 mm or smaller depended on the detector collimation/reconstructed section thickness and was rated optimal for the 4 x 1.0-mm detector collimation with a section thickness of 1.25 mm. This was also observed for low-dose protocols. Polyps 6 mm or smaller that were not detected with 3-mm section thickness and 4 x 2.5-mm detector collimation were detected with 1.25-mm section thickness and 10 mAs. CONCLUSION: A narrow detector collimation with thin-section imaging (4 x 1.0-mm detector collimation, 1.25-mm section thickness) is a prerequisite for low-dose (10-mAs) multi-detector row CT colonography.     

Comparison of axial, coronal, and primary 3D review in MDCT colonography for the detection of small polyps: a phantom study

Purpose

The purpose of this phantom study is to compare the influence of the reading technique (axial images alone in comparison to 3D endoluminal, coronal, and combined 2D/3D review methods) on the sensitivity and inter-reader variability with MDCT colonography for the detection of small colonic polyps.

Methods

An anthropomorphic pig colon phantom with 75 randomly distributed simulated small polyps of 2–8 mm size, was distended with air and scanned in a water phantom using multidetector-row CT with 4 mm × 1 mm collimation. Three radiologists rated the presence of polyps on a five-point scale. Performance with axial sections alone was compared to the performance with coronal sections, virtual endoscopy (VE), and a combined 2D/3D approach. We calculated sensitivities for polyp detection and used ROC analysis for data evaluation.

Results

There was no significant difference between the mean area under the curve (A_z) for axial images and VE (A_z = 0.934 versus 0.932), whereas coronal images were significantly inferior (A_z = 0.876) to both. The combined 2D/3D approach yielded the best results, with an A_z of 0.99. Differences in sensitivity between individual readers were significant in axial images (sensitivity, 75–93%, p = 0.001) and coronal images (sensitivity, 69–80%, p = 0.028), but became non-significant with VE (83–88%, p = 0.144) and the combined 2D/3D approach (95–97%, p = 0.288).

Conclusion

Evaluation of axial sections alone leads to significant differences in detection rates between individual observers. A combined 2D/3D evaluation improves sensitivities for polyp detection and reduces inter-individual differences to an insignificant level.     

Feasibility of planar virtual pathology: a new paradigm in volume-rendered CT colonography.

Planar virtual pathology (PVP) is an isometric rendering method for examining the CT colonography dataset, which renders the colon in discrete colonic segments. Ten patients with 36 polyps were evaluated using traditional 2D axial, 2D multiplanar reformatted, and 3D endoluminal images as well as PVP. PVP displayed 13 of 17 (76%) polyps of >1 cm, whereas 11 of 17 (65%) were detected using traditional rendering methods. PVP may be a useful adjunct in detecting additional polyps at CT colonography.     

Protocol optimization of multidetector computed tomography colonography using pig colonic phantoms

OBJECTIVE: The introduction of multidetector computed tomography (CT) increases the possibility of enhanced polyp detection using CT colonography. The effects of collimation and tube currents on polyp detection were investigated in pig colonic phantoms to determine the optimal scanning parameters. MATERIALS AND METHODS: Twenty pig colons were prepared, and polyps with diameters ranging from 3 mm to 15 mm were created and randomly distributed. There was a total of 60 polyps; 20 polyps were 3 to 5 mm in size, 21 polyps 6 to 9 mm, and 19 polyps 10 to 15 mm. The pig colons were sealed, distended with air, submerged in water, and were arranged to mimic the in vivo arrangement. CT was performed using a 4-row multidetector CT scanner with collimations of 1, 2.5, and 5 mm, a pitch of 1.75, and mA of 100. A low-dose protocol (mA of 50) was added with a collimation of 1 mm. Two blinded observers independently analyzed the datasets. RESULTS:: The overall sensitivities of CT colonography were 94.2% with 1-mm collimation, 80% with 2.5-mm collimation, and 75% with 5-mm collimation. Considering the sensitivity of each protocol for the size of the polyps, the 1-mm collimation protocol had a sensitivity of 87.5% for 3- to 5-mm polyps, 95.2% sensitivity for 6- to 9-mm polyps, and 100% sensitivity for 10- to 15-mm polyps; the 2.5-mm protocol had 50%, 92.9%, and 97.4% sensitivities, respectively; and the 5-mm protocol had 47.5%, 88.1%, and 89.5% sensitivities, respectively, for the respective polyp size group. A significant difference in sensitivity among the protocols was present in the 3- to 5-mm polyps. No significant difference was seen between the standard- and the low-dose protocols. CONCLUSIONS: The sensitivity of multidetector CT colonography for detecting polyps larger than 5 mm is robust over a range of collimation in pig colonic phantoms. However, reliable detection of polyps 5 mm or smaller requires a 1-mm collimation. Sensitivity is not influenced by lowering the mA from 100 to 50.     

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.     

Parallel imaging enhanced MR colonography using a phantom model

PURPOSE: To compare various Array Spatial and Sensitivity Encoding Technique (ASSET)-enhanced T2W SSFSE (single shot fast spin echo) and T1-weighted (T1W) 3D SPGR (spoiled gradient recalled echo) sequences for polyp detection and image quality at MR colonography (MRC) in a phantom model. Limitations of MRC using standard 3D SPGR T1W imaging include the long breath-hold required to cover the entire colon within one acquisition and the relatively low spatial resolution due to the long acquisition time. Parallel imaging using ASSET-enhanced T2W SSFSE and 3D T1W SPGR imaging results in much shorter imaging times, which allows for increased spatial resolution. MATERIALS AND METHODS: Using two porcine colon phantoms each with eight simulated 3-10-mm "polyps," baseline reference sequences acquired without ASSET (6-mm slices and readout bandwidth [BW] 62 kHz) were compared with 11 SSFSE and 8 SPGR sequences acquired with 2-fold ASSET acceleration. ASSET-enhanced SSFSE and SPGR sequences comprised BW/matrix combinations ranging from 20-62 kHz/256-352x256, respectively, with slice thicknesses adjusted from 3.0 to 4.5 mm to maintain a 23-26-second acquisition time and 30 cm slab thickness. Two experienced radiologists viewed the datasets in a randomized, blinded fashion. RESULTS: Compared to reference sequences, ASSET-enhanced SSFSE and SPGR sequences facilitated better polyp detection and had similar overall image quality and per-phantom specificity. The two best ASSET-enhanced SSFSE (3 and 4.5 mm slices, each with BW of 62.5 kHz and 352x256 matrices) and three best ASSET-enhanced SPGR BW/slice thickness/matrix combinations of 31 kHz/4.4 msec/192x256; 62/3.4/192x256; and 62/4.0/192x256, respectively, permitted detection of all polyps>or=5 mm. CONCLUSION: Parallel imaging using ASSET-enhanced T2W SSFSE and T1W 3D SPGR improves the ability to detect significant colon polyps in an MRC phantom model.     

Colorectal neoplasms: prospective comparison of thin-section low-dose multi-detector row CT colonography and conventional colonoscopy for detection

PURPOSE: To prospectively compare thin-section low-dose multi-detector row computed tomographic (CT) colonography with conventional colonoscopy for the detection of colorectal neoplasms. MATERIALS AND METHODS: One hundred five patients underwent CT colonography immediately before colonoscopy. Supine and prone CT colonographic acquisitions to image the region during a 30-second breath hold were performed. CT colonographic images were prospectively interpreted for the presence, location, size, and morphologic features of polyps. The time of image interpretation was noted. Sensitivity, specificity, and positive and negative predictive values of CT colonography were calculated, with 95% CIs, by using colonoscopic findings as the reference standard. The weighted CT dose index was calculated on the basis of measurements in a standard body phantom. Effective dose was calculated by using commercially available software. RESULTS: Median CT data interpretation time was 12 minutes. One hundred thirty-two polyps in 59 patients were identified at colonoscopy; no polyps were detected in 46 patients. Sensitivities for detection of polyps smaller than 5 mm, 6-9 mm, and larger than 10 mm in diameter were 12% (11 of 91 polyps), 70% (19 of 27 polyps), and 93% (13 of 14 polyps), respectively. Estimated overall specificity was 97.7% (515 of 527 imaging results). The total weighted CT dose index for combined supine and prone CT colonography was 11.4 mGy. The effective doses for combined CT colonography were 5.0 mSv and 7.8 mSv for men and women, respectively. CONCLUSION: Low-dose multi-detector row CT colonography has excellent sensitivity and specificity for detection of colorectal neoplasms 10 mm and larger.     

Colorectal neoplasia: performance characteristics of CT colonography for detection in 300 patients

PURPOSE: To determine the sensitivity and specificity of computed tomographic (CT) colonography for colorectal polyp and cancer detection by using colonoscopy as the reference standard. MATERIALS AND METHODS: Three hundred patients underwent CT colonography followed by standard colonoscopy. Bowel preparation consisted of magnesium citrate and polyethylene glycol. After colonic air insufflation, patients underwent scanning in the supine and prone positions with 3-mm collimation during a single breath hold. The transverse CT images, sagittal and coronal reformations, and three-dimensional endoluminal images were interpreted by two radiologists independently, and then a consensus reading was performed. CT colonographic findings were correlated with standard colonoscopic and histologic findings. RESULTS: The overall sensitivity and specificity of CT colonography for polyp detection were 90.1% (164 of 182) and 72.0% (85 of 118), respectively. By using direct polyp matching, the overall sensitivity was 69.7% (365 of 524). The sensitivity was 90% (74 of 82) for the detection of polyps 10 mm or larger, 80.1% (113 of 141) for polyps 5.0-9.9 mm, and 59.1% (178 of 301) for polyps smaller than 5 mm. The sensitivity was 94% (64 of 68) for the detection of adenomas 10 mm or larger, 82% (72 of 88) for adenomas 5.0-9.9 mm, and 66.9% (95 of 142) for adenomas smaller than 5 mm. CT colonography was used to identify all eight carcinomas. CONCLUSION: CT colonography has excellent sensitivity for the detection of clinically important colorectal polyps and cancer.     

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.     

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.     

False-negative results at multi-detector row CT colonography: multivariate analysis of causes for missed lesions

PURPOSE: To determine causes of false-negative results at multi-detector row computed tomographic (CT) colonography and determine presumptive causes with logistic regression analysis. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. The study included 394 colonic segments in 31 men and 25 women at high risk for colorectal cancer (mean age +/- standard deviation, 60.2 years +/- 9.3 for men and 56.8 years +/- 13.3 for women). Multi-detector row CT colonography and colonoscopy (reference standard) were performed in a blinded manner, and the results were compared. CT colonographic findings were interpreted in consensus by two readers using a primary two-dimensional with three-dimensional problem-solving approach. Adequacy of colonic preparation and distention was recorded. Sensitivity and specificity were obtained with 95% confidence intervals (CIs). Lesions missed at CT colonography were retrospectively reassessed to identify why they were missed, and, if the causes were not apparent, logistic regression analysis was performed to determine the presumptive causes. RESULTS: Colonic preparation and distention were optimal in 17 patients (30%) but suboptimal in 37 (66%) and poor enough to make the results nondiagnostic in two (4%). Twenty-nine of 63 lesions were missed at CT colonography. When all flat, sessile, and pedunculated lesions (n = 63) were included, sensitivities were 75% (nine of 12; 95% CI: 48%, 100%) for lesions 10 mm or larger and 79% (19 of 24; 95% CI: 65%, 93%) for those 6 mm or larger. When only sessile and pedunculated lesions (n = 60) were included, corresponding sensitivities were 100% (nine of nine; 73%, 100%) and 90% (19 of 21; 78%, 100%), respectively. All three missed lesions larger than 10 mm were flat, and all three flat lesions were missed. Two 3-mm high lesions, including one invasive adenocarcinoma, were misinterpreted as feces at blinded image review; one 1-mm high tubular adenoma with adenocarcinoma foci could not be visualized even in retrospect. Sessile or pedunculated polyps 5 mm or smaller were significantly more likely to be missed than those 6 mm or larger (adjusted odds ratio, 11.6; P = .027). CONCLUSION: Aside from inadequate bowel preparation and/or distention, flat lesions and small polyps are the two main causes for missed lesions at multi-detector row CT colonography.     

The effect of reconstruction algorithm on conspicuity of polyps in CT colonography

OBJECTIVE: CT colonography studies to date have used a standard CT algorithm. To determine whether nonstandard algorithms may result in better performance of CT colonography, we conducted a prospective, blinded-observer study of the effect of the reconstruction algorithm on the conspicuity of colonic polyps and folds. SUBJECTS AND METHODS: CT colonography of patients with proven polyps, masses, or polypoid folds was performed on an MDCT scanner, and the images were reconstructed using the standard, soft, lung, and detail algorithms. Two experiments were performed. The first used four patient data sets of a short segment of colon (30-60 images), each reconstructed using all four algorithms and then viewed on a workstation in a four-on-one format that allowed all four reconstructions to be viewed simultaneously. The second used six sets of cut-film images (four or eight images each); images within each set differed only in the reconstruction algorithm used to generate them (eight-image sets were prepared with two different level settings). Twenty-one reviewers with varying levels of experience who were unaware of the purpose of the study were asked to rank the images within each set according to their value in the detection of either polyps or masses. RESULTS: Reviewers showed statistically significant differences in preference for the four algorithms (p = 0.037 in the computer-based experiment; for the cut-film experiment, p = 0.029 for the four-image sets and p = 0.041 for the eight-image sets). In the computer-based experiment, reviewers preferred the detail algorithm to the standard algorithm with an estimated probability of 0.67 (95% confidence interval [CI], 0.57-0.75) and the soft algorithm over the standard algorithm with an estimated probability of 0.59 (95% CI, 0.51-0.66). However, reviewers with the most experience (having interpreted at least 250 cases) preferred the soft algorithm over the standard algorithm by the same two-to-one margin as observed for the detail algorithm. In contrast, the standard and detail algorithms were ranked similarly in the cut-film experiment, with the soft and lung algorithms ranked worst. CONCLUSION: To our knowledge, ours is the first observer study on the effect of the reconstruction algorithm on conspicuity of folds and polyps in CT colonography. Our results indicate significant differences in the reconstruction algorithms, with the soft and detail algorithms being preferred over the standard algorithm by experienced reviewers when interpreting images on a workstation. These results indicate the need for further research into the effect of reconstruction algorithms on CT colonography.     

Diagnostic accuracy of translucency rendering to differentiate polyps from pseudopolyps at 3D endoluminal CT colonography: a feasibility study

Purpose

The aim of this study was to assess the accuracy of translucency rendering (TR) in computed tomographic (CT) colonography without cathartic preparation using primary 3D reading.

Materials and methods

From 350 patients with 482 endoscopically verified polyps, 50 pathologically proven polyps and 50 pseudopolyps were retrospectively examined. For faecal tagging, all patients ingested 140 ml of orally administered iodinated contrast agent (diatrizoate meglumine and diatrizoate sodium) at meals 48 h prior to CT colonography examination and two h prior to scanning. CT colonography was performed using a 64-section CT scanner. Colonoscopy with segmental unblinding was performed within 2 weeks after CT. Three independent radiologists retrospectively evaluated TRCT clonographic images using a dedicated software package (V3D-Colon System). To enable size-dependent statistical analysis, lesions were stratified into the following size categories: small (≤5 mm), intermediate (6–9 mm), and large (≥10 mm).

Results

Overall average TR sensitivity for polyp characterisation was 96.6%, and overall average specificity for pseudopolyp characterisation was 91.3%. Overall average diagnostic accuracy (area under the curve) of TR for characterising colonic lesions was 0.97.

Conclusions

TR is an accurate tool that facilitates interpretation of images obtained with a primary 3D analysis, thus enabling easy differentiation of polyps from pseudopolyps.     

Nonadenomatous polyps at CT colonography: prevalence, size distribution, and detection rates

PURPOSE: To prospectively investigate with computed tomographic (CT) colonography the prevalence and size distribution of nonadenomatous polyps in asymptomatic adults and to compare the detection rates of adenomatous and nonadenomatous polyps. MATERIALS AND METHODS: A total of 1233 asymptomatic adults (mean age, 57.8 years; 505 women, 728 men) underwent same-day CT colonography and optical colonoscopy procedures. CT colonoscopy studies were interpreted prospectively with a primary three-dimensional approach immediately before optical colonoscopy. Statistical analysis was performed with the chi(2) test. Size, prevalence, and by-polyp detection differences were compared between adenomatous and nonadenomatous polyps. RESULTS: Seven hundred fifty-six (57.7%) colorectal polyps identified at optical colonoscopy in 410 (33.3%) patients were nonadenomatous; of these lesions, 622 (82.3%) were diminutive (相似文献   

Diagnostic potential of three-dimensional ultrasound-based virtual cystoscopy: an experimental study using pig bladders

OBJECTIVE: We sought to investigate the feasibility of 3-dimensional ultrasound (3D US)-based virtual cystoscopy in experimentally designed bladder phantoms using pig bladders. MATERIALS AND METHODS: Ten bladder phantoms with simulated polypoid tumors of different sizes were constructed to provide 3D US-based virtual cystoscopic images. The simulated polypoid tumors were divided by their location into 2 groups: group 1 included the polyps on the anterior and posterior walls, and group 2 included those on the remaining 4 walls. Two genitourinary radiologists independently interpreted the virtual cystoscopic images, with a consensus reached for cases with discrepant results. RESULTS: In a consensus reading, 3D US-based virtual cystoscopy detected 44 (91.7%) of 48 polypoid lesions. All lesions (n = 4) with false-negative results were 5 mm or smaller in diameter, and so the detection rate was 81.8% (18/22) for lesions 5 mm or smaller whereas it was 100% (26/26) for lesions larger than 5 mm. The detection rate for group 1 (93.8%) was not significantly different from that for group 2 (90.6%; P = 1.000). There were 7 false-positive lesions. Of these, 5 lesions were seen in group 1, and reverberation artifacts were the most common source of these errors (n = 4). Blind areas were present in 19 (31.7%) of 60 virtual cystoscopic images and were seen only in group 2. The differences in the false-positive rate and the incidence of blind area were statistically significant between both groups (P = 0.036, P = 0.00008, respectively). CONCLUSION: 3D US-based virtual cystoscopy may have diagnostic potential in the detection of polypoid bladder tumors.     

MR colonoscopy at 3.0 T: comparison with 1.5 T in vivo and a colon model

PURPOSE: Retrospectively, magnetic resonance (MR) colonography images obtained from a colon model and in routine examinations of patients screened for polyps were compared in terms of whether, and to what degree, image quality improved at a higher field strength of 3.0 T compared to 1.5 T. MATERIALS AND METHODS: One hundred twenty-eight MR colonography images from 40 patients, of whom 20 had each been scanned at 1.5 and 3.0 T, respectively, using a four-element phased-array torso coil, were compared. At both field strengths, imaging included T1-weighted fat-suppressed spoiled gradient-echo (T1-fs-GE), T2/T1-weighted fast imaging employing steady-state acquisition (FIESTA), and T2-weighted single-shot fast spin-echo (T2-SSFSE), with breath-hold technique. Using receiver operating characteristic analysis performed by seven readers, the three types of images from the colon model and from 20 patients each at 1.5 and 3.0 T were compared. While a time window of 20 s was allowed for picture assessment in a chance-generated succession of images on a monitor, image quality was rated with a score of 1-5 (1=very good; 5=very bad). Statistical significance was calculated with Mann-Whitney U test. RESULTS: At both field strengths, T2-SSFSE images received the best ratings, followed by FIESTA images (P=.001). Although, overall, the 3.0-T images obtained scores worse than those of the 1.5-T images, a better detection of phantom polyps was noted in the colon model (P=.001). CONCLUSION: Although MR colonography with the breath-hold technique using the same four-element phased-array coil at 3.0 and 1.5 T does not perform better at a higher field strength in general, an improved detection of small polyps may be obtained.