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

Electronic cleansing for 24-h limited bowel preparation CT colonography using principal curvature flow

CT colonography (CTC) is one of the recommended methods for colorectal cancer screening. The subject's preparation is one of the most burdensome aspects of CTC with a cathartic bowel preparation. Tagging of the bowel content with an oral contrast medium facilitates CTC with limited bowel preparation. Unfortunately, such preparations adversely affect the 3-D image quality. Thus far, data acquired after very limited bowel preparation were evaluated with a 2-D reading strategy only. Existing cleansing algorithms do not work sufficiently well to allow a primary 3-D reading strategy. We developed an electronic cleansing algorithm, aimed to realize optimal 3-D image quality for low-dose CTC with 24-h limited bowel preparation. The method employs a principal curvature flow algorithm to remove heterogeneities within poorly tagged fecal residue. In addition, a pattern recognition-based approach is used to prevent polyp-like protrusions on the colon surface from being removed by the method. Two experts independently evaluated 40 CTC cases by means of a primary 2-D approach without involvement of electronic cleansing as well as by a primary 3-D method after electronic cleansing. The data contained four variations of 24-h limited bowel preparation and was based on a low radiation dose scanning protocol. The sensitivity for lesions ≥ 6 mm was significantly higher for the primary 3-D reading strategy (84%) than for the primary 2-D reading strategy (68%) (p = 0.031). The reading time was increased from 5:39 min (2-D) to 7:09 min (3-D) (p = 0.005); the readers' confidence was reduced from 2.3 (2-D) to 2.1 (3-D) ( p = 0.013) on a three-point Likert scale. Polyp conspicuity for cleansed submerged lesions was similar to not submerged lesions (p = 0.06). To our knowledge, this study is the first to describe and clinically validate an electronic cleansing algorithm that facilitates low-dose CTC with 24-h limited bowel preparation.

Comparison of accuracy and time-efficiency of CT colonography between conventional and panoramic 3D interpretation methods: an anthropomorphic phantom study

PURPOSE

To retrospectively compare the conventional three-dimensional (3D) interpretation method with the panoramic 3D method with regard to accuracy and time-efficiency in the detection of colonic polyps, using pig colonic phantoms as the standard of reference.

MATERIALS AND METHODS

One-hundred and sixty-two polyps were created in 18 pig colonic phantoms. CT colonography was performed with a 64-row detector CT scanner. Two-week interval reviews for the CTC image dataset with both the conventional and the panoramic 3D interpretation method were independently performed by three radiologists. The sensitivities of both methods were compared with the McNemar test. The mean interpretation time for each interpretation method was also assessed and compared with the Wilcoxon signed-rank test.

RESULTS

Compared with the conventional 3D method (0.96 for reader 1, 0.89 for reader 2, and 0.97 for reader 3), the panoramic method revealed comparable sensitivities (0.91 for reader 1, 0.86 for reader 2, and 0.93 for reader 3) (p>0.05). Interpretation time was significantly shorter with the panoramic method (115.1±32.7 s for reader 1, 229.7±72.2 s for reader 2, and 282.6±113.7 s for reader 3) than with the conventional method (218.9±59.9 s for reader 1, 379.4±117.0 s for reader 2, and 458.7±149.4 s for reader 3) for all readers (p<0.05).

CONCLUSION

Compared with the conventional 3D interpretation method, the panoramic 3D interpretation method shows improved time-efficiency and comparable sensitivity in the detection of colonic polyps.

Improving the accuracy of CTC interpretation: computer-aided detection

Computer-aided polyp detection aims to improve the accuracy of the colonography interpretation. The computer searches the colonic wall to look for polyplike protrusions and presents a list of suspicious areas to a physician for further analysis. Computer-aided polyp detection has developed rapidly in the past decade in the laboratory setting and has sensitivities comparable with those of experts. Computer-aided polyp detection tends to help inexperienced readers more than experienced ones and may also lead to small reductions in specificity. In its currently proposed use as an adjunct to standard image interpretation, computer-aided polyp detection serves as a spellchecker rather than an efficiency enhancer.

Current techniques in the performance, interpretation, and reporting of CT colonography

The technical objective of computed tomographic colonography (CTC) is to acquire high-quality computed tomography images of the cleansed, well-distended colon for polyp detection. In this article the authors provide an overview of the technical components of CTC, from preparation of the patient to acquisition of the imaging data and basic methods of interpretation. In each section, the best evidence for current practices and recommendations is reviewed. Each of the technical components must be optimized to achieve high sensitivity in polyp detection.

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 2-8mm size, was distended with air and scanned in a water phantom using multidetector-row CT with 4mm x 1mm 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.

Primary 2D versus primary 3D polyp detection at screening CT colonography

OBJECTIVE

Disparate results from the existing large CT colonography (CTC) trials suggest that 2D polyp detection is less sensitive than 3D detection, but no direct evidence exists to support this claim. Our goal was to assess the sensitivity of primary 2D polyp detection with cases from the Department of Defense CTC screening trial and compare results with the primary 3D evaluation and previous 2D CTC trials.

MATERIALS AND METHODS

Ten radiologists, blinded to polyp findings, retrospectively interpreted 730 consecutive colonoscopy-proven CTC cases in asymptomatic adults using a primary 2D approach, with 3D reserved for problem solving. Primary 2D CTC performance was compared with the primary 3D CTC results from the original trial of 1,233 asymptomatic adults. The 10 2D reviewers were significantly more experienced in CTC interpretation (> 100 cases interpreted) than the six reviewers from the original 3D trial.

RESULTS

Primary 2D CTC sensitivity for adenomas > or = 6 mm was 44.1% (56/127), compared with 85.7% (180/210) at 3D (p < 0.001). Sensitivity of 2D CTC for adenomas > or = 10 mm was 75.0% (27/36) compared with 92.2% (47/51) at 3D (p = 0.027). Similar sensitivity trends were seen for the by-patient analysis and for all polyps at the 6-mm and 10-mm thresholds. By-patient specificity for 2D evaluation at the 10-mm threshold was 98.1% (676/689), compared with 97.4% (1,131/1,161) at 3D evaluation (p = 0.336).

CONCLUSION

Primary 2D CTC is less sensitive than primary 3D CTC for polyp detection in low-prevalence screening cohorts. The disappointing 2D sensitivity in this study was very similar to results obtained with primary 2D evaluation in previous CTC trials.

Transparent rendering of intraluminal contrast for 3D polyp visualization at CT colonography

We developed a classifier that permits transparent rendering of both tagging material and air to facilitate interpretation of tagged computed tomographic (CT) colonography. With this technique, a reader can simultaneously appreciate polyps on endoluminal views both covered with tagging material and against air, along with unmodified 2-dimensional CT images. Evaluated with 49 polyps from 26 patients (data from public National Library of Medicine, Health Insurance Portability and Accountability Act compliant), 3 readers were able to determine the presence/absence of polyps in tagged locations with equivalent accuracy compared with polyps in air. This method offers an alternative way to visualize tagged CT colonography.

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.

Two- versus Three-dimensional Colon Evaluation with Recently Developed Virtual Dissection Software for CT Colonography

This retrospective study was institutional review board approved; the requirement for informed patient consent was waived. The purpose of this study was to retrospectively compare a two-dimensional (2D) data interpretation technique with a three-dimensional (3D) colon dissection technique in terms of interpretation time and sensitivity for colonic polyp detection, with colonoscopy as the reference standard. Ninety-six patients (56 men, 40 women; mean age, 54.8 years) underwent colonoscopy and multidetector computed tomographic (CT) colonography on the same day. Two radiologists independently analyzed the data on a per-polyp and per-patient basis. The sensitivity of both approaches was compared by using the McNemar test. The time required to interpret CT colonographic data with each technique was also assessed. Compared with the conventional 2D colonic polyp detection method, primary 3D interpretation with use of virtual dissection software for CT colonography revealed comparable per-polyp (77% and 69% for two readers) and per-patient (77% and 73% for two readers) sensitivities and comparable per-patient specificity (99% and 89% for two readers) for the detection of polyps 6 mm in diameter or larger and involved a shorter interpretation time.

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.

Three-dimensional virtual dissection at CT colonography: unraveling the colon to search for lesions

Computed tomographic (CT) colonography is a promising noninvasive examination for colorectal cancer screening; however, the optimal interpretation strategy remains undecided. Virtual dissection is an innovative technique whereby the three-dimensional (3D) model of the colon is virtually unrolled, sliced open, and displayed as a flat 3D rendering of the mucosal surface, similar to a gross pathologic specimen. This technique has the potential to reduce evaluation time by providing a more rapid 3D image assessment than is possible with an antegrade and retrograde 3D endoluminal fly-through. It may also ultimately improve accuracy by reducing blind spots present with 3D endoluminal displays and by reducing reader fatigue. A disadvantage of virtual dissection is the potential for distortion of colonic lesions and normal anatomy. To avoid potential pitfalls in image interpretation, the radiologist must be familiar with the unique appearance of the normal colon anatomy and of various pathologic findings when using virtual dissection with two-dimensional axial and 3D endoluminal CT colonographic image data sets.

A comparison of primary two- and three-dimensional methods to review CT colonography

The aim of our study was to compare primary three-dimensional (3D) and primary two-dimensional (2D) review methods for CT colonography with regard to polyp detection and perceptive errors. CT colonography studies of 77 patients were read twice by three reviewers, first with a primary 3D method and then with a primary 2D method. Mean numbers of true and false positives, patient sensitivity and specificity and perceptive errors were calculated with colonoscopy as a reference standard. A perceptive error was made if a polyp was not detected by all reviewers. Mean sensitivity for large (> or = 10 mm) polyps for primary 3D and 2D review was 81% (14.7/18) and 70%(12.7/18), respectively (p-values > or = 0.25). Mean numbers of large false positives for primary 3D and 2D were 8.3 and 5.3, respectively. With primary 3D and 2D review 1 and 6 perceptive errors, respectively, were made in 18 large polyps (p = 0.06). For medium-sized (6-9 mm) polyps these values were for primary 3D and 2D, respectively: mean sensitivity: 67%(11.3/17) and 61%(10.3/17; p-values > or = 0.45), number of false positives: 33.3 and 15.6, and perceptive errors : 4 and 6 (p = 0.53). No significant differences were found in the detection of large and medium-sized polyps between primary 3D and 2D review.

CT colonography: influence of 3D viewing and polyp candidate features on interpretation with computer-aided detection

PURPOSE

To retrospectively determine if three-dimensional (3D) viewing improves radiologists' accuracy in classifying true-positive (TP) and false-positive (FP) polyp candidates identified with computer-aided detection (CAD) and to determine candidate polyp features that are associated with classification accuracy, with known polyps serving as the reference standard.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained; this study was HIPAA compliant. Forty-seven computed tomographic (CT) colonography data sets were obtained in 26 men and 10 women (age range, 42-76 years). Four radiologists classified 705 polyp candidates (53 TP candidates, 652 FP candidates) identified with CAD; initially, only two-dimensional images were used, but these were later supplemented with 3D rendering. Another radiologist unblinded to colonoscopy findings characterized the features of each candidate, assessed colon distention and preparation, and defined the true nature of FP candidates. Receiver operating characteristic curves were used to compare readers' performance, and repeated-measures analysis of variance was used to test features that affect interpretation.

RESULTS

Use of 3D viewing improved classification accuracy for three readers and increased the area under the receiver operating characteristic curve to 0.96-0.97 (P<.001). For TP candidates, maximum polyp width (P=.038), polyp height (P=.019), and preparation (P=.004) significantly affected accuracy. For FP candidates, colonic segment (P=.007), attenuation (P<.001), surface smoothness (P<.001), distention (P=.034), preparation (P<.001), and true nature of candidate lesions (P<.001) significantly affected accuracy.

CONCLUSION

Use of 3D viewing increases reader accuracy in the classification of polyp candidates identified with CAD. Polyp size and examination quality are significantly associated with accuracy.

Time efficiency of CT colonography: 2D vs 3D visualization

We aimed to compare the time efficiency of three visualization methods in CT colonography and to identify the colonic factors influencing the time for interpretation. Twenty CT colonographic examinations were prospectively analysed. Three reading methods were adopted: method 1, primary 2D analysis with the use of virtual endoscopy as problem solver, method 2, primary standard virtual endoscopy with semiautomatic navigation through the colon and use of 2D images as problem solver; method 3, primary virtual endoscopy with automatic navigation and the use of 2D images as problem solver. In method 1, time for 2D analysis ranged between 6 and 18min (mean 12) for evaluation of both supine and prone decubitus with a synchronization method. In method 2, time for 3D manual navigation in supine plus prone ranged between 9 and 24min (mean 17). In method 3, time for automated navigation ranged between 6 and 20min (mean 12) for evaluation of both supine and prone decubitus. A statistically significant difference was found between time efficiency of methods 1 and 2 (p=0.009, t-test, unequal variances). Methods 2 and 3 showed a tendency to significant differences (p=0.054, t-test, unequal variances). Faecal or fluid residuals were reported as major drawbacks in 3D navigations, requiring constant correlation with 2D images; tortuous folds influenced mostly the 2D analysis; diverticula were reported as influencing factor in all three methods. No differences in sensitivity and specificity were observed between the three viewing methods. The 3D semiautomatic navigation method* tended to increase the time for interpretation in almost all cases. There is, in particular, greatest time efficiency for 2D analysis as compared with 3D manual analysis. Two-dimensional and automated 3D navigation reading have comparable time efficiencies in a routine clinical setting.

Tagging-based, electronically cleansed CT colonography: evaluation of patient comfort and image readability

PURPOSE

To prospectively compare the homogeneity, adequacy, and patient acceptance of nonionic iodine-based regimens with those of a barium-based regimen for computed tomographic (CT) colonography with electronic subtraction cleansing.

MATERIALS AND METHODS

After institutional review board approval and informed consent were obtained, 68 subjects (41 men (60%) men, 27 (40%) women; mean age, 60 years +/- 6 [standard deviation]) with average or moderate risk factors for development of colorectal carcinoma were recruited and placed into three study groups. Group 1 (n = 25) ingested 150-mL aliquots of 2% barium sulfate suspension with meals and snacks for 48 hours prior to imaging, without other diet modification or a cathartic. Group 2 (n = 21) ingested 10-mL aliquots of nonionic iodinated contrast material (iopromide) with a concentration of 300 mg per milliliter with meals and snacks for 2 days before imaging, without diet modification or a cathartic. Group 3 (n = 22) ingested nonionic iodinated contrast material (iohexol) with a concentration of 300 mg per milliliter with meals and snacks for 2 days before imaging and ingested 34 g of magnesium citrate the evening prior to imaging. CT colonography was also performed on 10 control subjects who ingested polyethylene glycol electrolyte solution prior to imaging. Subjective and numerical measures of bowel preparation quality, homogeneity, and patient comfort among the noncathartic and cathartic cohorts were compared with nonparametric analysis of variance, the Fisher exact test, and the F test, as appropriate. The study was HIPAA compliant.

RESULTS

Study subjects who received tagging preparations reported significantly improved discomfort scores when compared with those of the control subjects (P < .05, each comparison). There was no significant difference in discomfort scores among groups 1, 2, and 3. For each reader, scores of subtracted image readability were highest for group 3. Dichotomized rates of preparation "success" were also greatest for group 3.

CONCLUSION

In this series, the patient discomfort scores were significantly improved with tagging preparations for CT colonography. Nonionic iodinated contrast material in conjunction with a hyperosmotic laxative (magnesium citrate) was associated with the best subjective and numerical indices of readability.

Surface visualization at 3D endoluminal CT colonography: degree of coverage and implications for polyp detection

BACKGROUND & AIMS

Effective colonoscopic screening for polyps, whether by optical or virtual means, requires adequate visualization of the entire colonic surface. The purpose of this study was to assess prospectively the degree of surface coverage at 3-dimensional (3D) endoluminal computed tomography colonography (CTC) after retrograde fly-through, combined retrograde-antegrade fly-through, and review of remaining missed regions.

METHODS

The study group consisted of 223 asymptomatic adults (mean age, 57.8 +/- 7.2 y; 111 men, 112 women) undergoing primary CTC screening. CTC studies were interpreted by experienced readers using a primary 3D approach. The CTC software system that was used continually tracks the percentage of endoluminal surface visualized. The degree of coverage was assessed prospectively after retrograde and combined retrograde-antegrade navigation. The added effect of reviewing missed regions was also assessed prospectively.

RESULTS

The mean surface coverage after only retrograde 3D endoluminal fly-through from rectum to cecum was 76.6% +/- 4.8% (range, 63%-92%); coverage was 80% or less in 181 (81.2%) patients. Antegrade navigation back to the rectum increased the overall coverage to 94.1% +/- 2.3% (range, 84%-99%; P < .0001). A review of missed regions 300 mm(2) or larger increased coverage to 97.9% +/- 1.1% (range, 93%-99%; P < .0001) and added 21.4 +/- 11.4 seconds to the interpretation time (range, 3-67 s).

CONCLUSIONS

Combined bidirectional retrograde and antegrade 3D navigation, supplemented by rapid review of missed regions, effectively covers the entire evaluable surface at CTC. Unidirectional retrograde 3D fly-through typically excludes 20% or more of the endoluminal surface, which may provide insight into potential limitations at optical colonoscopy.

Computed tomography colonography: current issues

OBJECTIVE

Direct and indirect evidence supports the concept of screening for adenomas and early stage colorectal cancer in reducing the incidence and disease-specific mortality. Controversy remains as to the appropriateness of and preferred methods for screening an asymptomatic population.

METHODS

Review of computed tomography (CT) colonography based on the literature and personal experience.

RESULTS AND CONCLUSIONS

Current discrepancies in the data on accuracy and patient acceptance of CT colonography reflect differences in the performance and evaluation of this examination. Before CT colonography can be implemented in colorectal cancer screening, factors that cause this variability must be elucidated. Studies in which high-resolution scanning, three-dimensional review methods and an enhanced colonoscopic reference are used achieve an accuracy that is similar to colonoscopy. At the same time the evidence that ultra-low radiation dose CT colonography is feasible is mounting, a development that dramatically reduces one of the largest obstacles for large-scale application of this technique.

CT colonography: where have we been and where are we going?

Over the past decade, computed tomographic (CT) colonography (also known as virtual colonoscopy) has been used to investigate the colon for colorectal neoplasia. Numerous clinical and technical advances have allowed CT colonography to advance slowly from a research tool to a viable option for colorectal cancer screening. However, substantial controversy remains among radiologists, gastroenterologists, and other clinicians with regard to the current role of CT colonography in clinical practice. On the one hand, all agree there is much excitement about a noninvasive imaging examination that can reliably depict clinically important colorectal lesions. However, this is tempered by results from several recent studies that show the sensitivity of CT colonography may not be as great when performed and the images interpreted by radiologists without expertise and training. The potential to miss important lesions exists; moreover, if polyps cannot be differentiated from folds and residual fecal matter, unnecessary colonoscopy will be performed. In this review, current issues will be discussed regarding colon cancer and the established and reimbursed strategies to screen for it and the past, current, and potential future role of CT colonography.

Assessment of real-time 3D visualization for cardiothoracic diagnostic evaluation and surgery planning

RATIONALE AND OBJECTIVES

Three-dimensional (3D) real-time volume rendering has demonstrated improvements in clinical care for several areas of radiological imaging. We test whether advanced real-time rendering techniques combined with an effective user interface will allow radiologists and surgeons to improve their performance for cardiothoracic surgery planning and diagnostic evaluation.

MATERIAL AND METHODS

An interactive combination 3D and 2D visualization system developed at the University of North Carolina at Chapel Hill was compared against standard tiled 2D slice presentation on a viewbox. The system was evaluated for 23 complex cardiothoracic computed tomographic (CT) cases including heart-lung and lung transplantation, tumor resection, airway stent placement, repair of congenital heart defects, aortic aneurysm repair, and resection of pulmonary arteriovenous malformation. Radiologists and surgeons recorded their impressions with and without the use of the interactive visualization system.

RESULTS

The cardiothoracic surgeons reported positive benefits to using the 3D visualizations. The addition of the 3D visualization changed the surgical plan (65% of cases), increased the surgeon's confidence (on average 40% per case), and correlated well with the anatomy found at surgery (95% of cases). The radiologists reported fewer and less major changes than the surgeons in their understanding of the case due to the 3D visualization. They found new findings or additional information about existing findings in 66% of the cases; however, they changed their radiology report in only 14% of the cases.

CONCLUSION

With the appropriate choice of 3D real-time volume rendering and a well-designed user interface, both surgeons and radiologists benefit from viewing an interactive 3D visualization in addition to 2D images for surgery planning and diagnostic evaluation of complex cardiothoracic cases. This study finds that 3D visualization is especially helpful to the surgeon in understanding the case, and in communicating and planning the surgery. These results suggest that including real-time 3D visualization would be of clinical benefit for complex cardiothoracic CT cases.

Polyp size at CT colonography after electronic subtraction cleansing in an anthropomorphic colon phantom

PURPOSE

To evaluate the effect of various bowel contrast material concentrations and subtraction software on size measurements of well-defined polyp lesions in a colon phantom at CT colonography.

MATERIALS AND METHODS

Repeated scanning and a precise reference standard required the use of a colon phantom in which 21 polyps were randomly distributed. Two readers who had each reviewed computed tomographic (CT) colonographic images from more than 100 cases evaluated polyp size on images obtained when the phantom was partially filled with varying concentrations of contrast material, scanned by using CT colonography, and subjected to electronic subtraction cleansing. The single largest dimension was recorded for each reader for a randomized series of polyps. These measurements were compared with a reference standard that was based on a combination of the manufacturer's polyp size specifications and the subsequent verification of these sizes by an independent consensus panel. Six weeks after initial observations, readers evaluated images of the phantom scanned without the presence of contrast material. Polyp size estimations for the two readers for each series were compared with the reference standard to obtain a mean absolute measurement error for each reader for each series. Data for each reader were compared by using a nonparametric Kruskal-Wallis analysis of variance test. A pair-wise comparison of the experimental and control series was then performed by using the Dunn post hoc test.

RESULTS

Contrast material dilutions resulting in an average attenuation of less than 500 HU resulted in complete subtraction and the absence of streak artifacts. There was no statistically significant difference between the average measurement error for contrast attenuations between 300 and 500 HU when compared with that of control. Streak artifact was noticeable for the highest dilution (mean, 840 HU). No statistically significant differences were observed for series in which cleansing software was used in the absence of bowel contrast material.

CONCLUSION

The combination of electronic cleansing and bowel contrast enhancement in the range of 300-500 HU results in no substantial change in readers' estimations of polyp size at CT colonography.

Colonography by computed tomography

Computed tomographic colonography ('virtual colonoscopy') has shown promising results in the detection of large (> or = 10 mm) polyps in populations with a high prevalence of polyps. Recent studies in low prevalence populations, however, show variable results in sensitivity, ranging from 55% to 94% for the detection of patients with polyps measuring 10 mm or longer. Therefore questions have been raised about computed tomographic colonography as a screening method, probably the most valuable use of this technique. This article describes possible causes of these remarkable differences as well as advances in computed tomographic colonography.

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.

Consensus on current clinical practice of virtual colonoscopy

OBJECTIVE

The purpose of our study was to determine the current opinions regarding the performance, interpretation, reporting, and clinical role of virtual colonoscopy among a group of selected experts to develop a consensus statement.

MATERIALS AND METHODS

A questionnaire was sent to 33 selected experts in virtual colonoscopy. Responses were tabulated and results were used to develop a consensus statement. The results of the questionnaire and consensus statement were sent to respondents for comment and approval.

RESULTS

Thirty-one (93.9%) of 33 surveys were returned. Eighty-seven percent (27/31) of respondents believe virtual colonoscopy is a credible screening method. Oral sodium phosphate solution is the laxative preferred by more than 66% (18/27), whereas 62% (13/21) do not believe fecal tagging is necessary. All respondents (25/25) think that both prone and supine imaging is required, with most (81%, 21/26) believing IV contrast material is not necessary. The routine use of spasmolytics is suggested by only 15% (4/26). The largest acceptable slice thickness of 3 mm is agreed on by 88% (22/25). All respondents believe screening virtual colonoscopy should be performed at a lower dose per slice than conventional CT. Most (80%, 20/25) believe the optimum method of interpreting virtual colonoscopy should be primary axial review, with 3D used for problem solving. All but one respondent (96%, 26/27) agree there is a threshold size below which polyps are not clinically important. When reporting virtual colonoscopy results, 59% (16/27) believe polyps less than 4 mm need not be reported.

CONCLUSION

A consensus is developing among experts as to the appropriate manner in which virtual colonoscopy should be performed, interpreted, and reported.

Colorectal cancer screening and surveillance with CT colonography: current controversies and obstacles

Computed tomographic (CT) colonography has been advocated as an alternative colorectal screening method because studies in populations with a high prevalence of polyps have demonstrated that sensitivity for patients with large (> or =10 mm) polyps is generally high (approximately 90%). In three recent studies in low-prevalence populations, however, these values vary from 55% to 94%. Many questions have been raised as to the cause of this remarkable variability, which hampers the implementation of CT colonography in colorectal cancer screening and surveillance. We provide an overview of some potential causes and discuss the available, often indirect, evidence. In addition, several other obstacles that may influence implementation are discussed. Many differences between the study with high sensitivity (94%) and the two studies with low sensitivity (55% and 64%) exist: the primary method to review the data (two or three dimensional), bowel preparation (with or without oral contrast agents), study design (verification method and analysis of adenomas only), reader's experience, and scanning technique (single vs. multislice, thin vs. thick sections). Additional obstacles for implementation in prevention of colorectal cancer may be controversial results concerning patient acceptance, the large-scale use of ionizing radiation, difficulties in detecting flat adenomas, and extracolonic findings. Use of primary three-dimensional review methods, addition of oral contrast agents to bowel preparation, and endoscopic verification of false-positive results on CT colonography are speculated to have a positive influence on sensitivity. Future investigations should demonstrate the influence of these potential factors on sensitivity of CT colonography. Despite a growing body of evidence, it remains uncertain to what extent patient acceptance, radiation issues, flat lesions, and extracolonic findings will be a stumbling block to using CT colonography for colorectal cancer screening.

Digital subtraction bowel cleansing for CT colonography using morphological and linear filtration methods

We describe a method to perform postacquisition processing of computed tomography colonography (virtual colonoscopy) datasets that results in electronic removal of opacified, ingested bowel contents while reconstructing natural appearing boundaries of colon lumen and thereby permitting three-dimensional visual analyses of the resulting colon models.

Prospective comparison of contrast enhanced CT colonography and conventional colonoscopy for detection of colorectal neoplasms in a single institutional study using second-look colonoscopy with discrepant results

BACKGROUND

Colorectal cancer is the second leading cause of death from cancer in Western countries. Early detection by colorectal cancer screening can effectively cut its mortality rate. CT colonography represents a promising, minimally invasive alternative to conventional methods of colorectal carcinoma screening.

AIMS

The purpose of this prospective single institutional study was to compare the abilities of routine clinical CT colonography and conventional colonoscopy to detect colorectal neoplasms using second-look colonoscopy to clarify discrepant results.

PATIENTS AND METHODS

CT colonography was performed in 100 symptomatic patients using contrast enhanced multidetector CT followed by conventional colonoscopy on the same day. If results were discrepant, a second-look colonoscopy was performed after unblinding. CT colonographic findings were compared with those of conventional colonoscopy.

RESULTS

Conventional colonoscopy found 122 colorectal neoplasms in 49 patients. The overall sensitivity of CT colonography at detecting patients with at least one polyp 6 mm or larger was 76% and its specificity was 88%. Its by-patient sensitivity for polyps 10 mm or larger was 95% and its specificity was 98%. By-polyp sensitivities were 71% for polyps 10 mm or larger, and 61% for polyps 6 mm or larger. A second-look colonoscopy was performed in 19 patients and two initial false-positive findings of CT colonography were reclassified as true-positive. For conventional colonoscopy, this produced a by-polyp sensitivity of 94% for detection of lesions 6 mm and larger.

CONCLUSIONS

CT colonography had both a high by-patient sensitivity and specificity for detection of clinically important colorectal neoplasms 10 mm or larger. This suggests that CT colonography has the potential to become a valuable clinical screening method for colorectal neoplasms.

Endoluminal perspective volume rendering of coronary arteries using electron-beam computed tomography

Remarkable progress has been made in the treatment of coronary heart diseases because of a variety of new interventional devices, but as each new device or procedure has suitability for a particular type of patient or purpose, patient selection is increasingly important. Endoluminal perspective volume renderings of the coronary arteries of a 70-year-old male with old myocardial infarction and recurrent chest pain were carried out using electron-beam computed tomography. Conventional coronary angiography had revealed significant stenosis of the distal portion of the left anterior descending branch, and subsequent conventional balloon angioplasty had failed to expand the stenotic site. Perspective volume rendering images can distinguish differences in objects and evaluate the cross sectional area of the lumen and the morphology of calcification. In the present patient, a huge mass of calcified plaque occupied most of the lumen at a site corresponding to the angiographic site of stenosis. According to this finding, rotational atherectomy was indicated and had a good outcome. The qualitative information for characterizing and determining the morphology of atherosclerotic plaque provided by perspective volume rendering may be useful in selecting the appropriate intervention.

CT colonography: feasibility of substantial dose reduction--comparison of medium to very low doses in identical patients

In a feasibility study, the authors compared polyp detection and interobserver variability at computed tomographic (CT) colonography in 15 patients with doses ranging from medium to very low (12.00-0.05 mSv). At levels down to 2% of the medium dose, the mean detection of polyps 5 mm or larger remained at least 74%, while the number of false-positive results decreased and the interobserver agreement remained constant. Initial observations indicate that it is feasible to reduce the radiation dose required for CT colonography. Further studies are needed, however, to investigate the clinical value of very low-dose CT colonography.

Computed Tomography Colonography

OBJECTIVE

: To determine the feasibility of a computer-aided detection (CAD) algorithm as the "first reader" in computed tomography colonography (CTC).

METHODS

: In phase 1 of a 2-part blind trial, we measured the performance of 3 radiologists reading 41 CTC studies without CAD. In phase 2, readers interpreted the same cases using a CAD list of 30 potential polyps.

RESULTS

: Unassisted readers detected, on average, 63% of polyps > or =10 mm in diameter. Using CAD, the sensitivity was 74% (not statistically different). Per-patient analysis showed a trend toward increased sensitivity for polyps > or =10 mm in diameter, from 73% to 90% with CAD (not significant) without decreasing specificity. Computer-aided detection significantly decreased interobserver variability (P = 0.017). Average time to detection of the first polyp decreased significantly with CAD, whereas total reading case reading time was unchanged.

CONCLUSION

: Computer-aided detection as a first reader in CTC was associated with similar per-polyp and per-patient detection sensitivity to unassisted reading. Computer-aided detection decreased interobserver variability and reduced the time required to detect the first polyp.

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.

Three-dimensional endoluminal CT colonography (virtual colonoscopy): comparison of three commercially available systems

OBJECTIVE

The purposes of this study were to directly compare 3D endoluminal volume rendering and navigational capabilities of three different CT colonography systems and to assess feasibility of 3D evaluation for primary polyp detection.

MATERIALS AND METHODS

Closely matched endoluminal images from three CT colonography software systems (Navigator, Vitrea 2, and V3D-Colon) and optical colonoscopy were obtained of eight pathologically proven colorectal polyps. All images were then reviewed by 25 physicians (12 radiologists and 13 gastroenterologists) who were not familiar with the three systems. For each polyp, the images yielded by the three systems were rated according to polyp conspicuity, 3D effect (depth), subjective quality, and likeness to optical colonoscopy. For comparison of endoluminal navigation capability, automated or semiautomated flight from rectum to cecum and cecum to rectum was attempted in 10 cases (20 flights) in which a continuous colonic air column could be identified on the 2D images. Additional 3D features were also compared.

RESULTS

For polyp conspicuity, 3D effect, and likeness to optical colonoscopy, the V3D-Colon system was favored in 92.0% (184/200), 92.5% (185/200), and 92.5% (185/200) of responses, respectively (p < 0.001). For the same categories, the Navigator system ranked second in 73.0%, 74.0%, and 75.0% of cases, and the Vitrea 2 system ranked last in 79.0%, 77.5%, and 76.0% of cases, respectively. Automated or semiautomated navigation was successful in eight (40%) of 20 flights with Vitrea 2, in nine (45%) of 20 flights with Navigator, and in 20 (100%) of 20 flights with V3D-Colon (p < 0.001). The V3D-Colon system also had more navigational features than the other two systems.

CONCLUSION

Pronounced subjective and objective differences in 3D endoluminal rendering and navigational capabilities exist among the systems evaluated. Of the three, effective time-efficient primary 3D evaluation appears to be feasible only with the V3D-Colon system.

A method for detecting undisplayed regions in virtual colonoscopy and its application to quantitative evaluation of fly-through methods1

RATIONALE AND OBJECTIVES

When virtual endoscopy is used as a diagnostic tool, especially as a tool for detecting colon polyps, the user often performs automated fly-through based on automatically generated paths. In the case of automated fly-through in the colon, there are some blind areas at the backs of folds. The aim of this study is to detect undisplayed regions during fly-through and to perform quantitative evaluation.

MATERIALS AND METHODS

Undisplayed regions are detected by marking displayed triangles for surface rendering or displayed voxels for volume rendering. The voxels or triangles not having displayed marks are considered to be undisplayed triangles or voxels. Various kinds of automated fly-through paths generated from medial axes of the colon and flattened views of the colon from the viewpoint of the rate of undisplayed regions are evaluated.

RESULTS

The experiment results show that about 30% of colon regions are classified as undisplayed regions by the conventional automated fly-through along the medial axis and that the flattened view results in very few undisplayed regions.

CONCLUSION

There is a possibility that the automated fly-through methods may cause many undisplayed regions.

Three-dimensional display modes for CT colonography: conventional 3D virtual colonoscopy versus unfolded cube projection

The authors compared a conventional two-directional three-dimensional (3D) display for computed tomography (CT) colonography with an alternative method they developed on the basis of time efficiency and surface visibility. With the conventional technique, 3D ante- and retrograde cine loops were obtained (hereafter, conventional 3D). With the alternative method, six projections were obtained at 90 degrees viewing angles (unfolded cube display). Mean evaluation time per patient with the conventional 3D display was significantly longer than that with the unfolded cube display. With the conventional 3D method, 93.8% of the colon surface came into view; with the unfolded cube method, 99.5% of the colon surface came into view. Sensitivity and specificity were not significantly different between the two methods. Agreements between observers were kappa = 0.605 for conventional 3D display and kappa = 0.692 for unfolded cube display. Consequently, the latter method enhances the 3D endoluminal display with improved time efficiency and higher surface visibility.

Comparison of supine and prone scanning separately and in combination at CT colonography

PURPOSE

To compare colonic distention, adequacy of colonic preparation, and colorectal polyp detection as assessed with supine and prone scanning separately and in combination at computed tomographic (CT) colonography.

MATERIALS AND METHODS

CT colonography and colonoscopy were performed in 182 patients. Distention and preparation of eight colonic segments were rated separately on a scale of 1-4 (1, segment completely distended or no residual material; 4, segment collapsed or large amounts of residual material). The distention, preparation, and polyp detection data were compared with regard to each position alone and then in combination. CT findings were correlated with colonoscopic findings.

RESULTS

The percentage of colonic segments with grade 1 distention and preparation was 93.7% (1,364 of 1,456) and 66.6% (969 of 1,456), respectively, with combined scanning; 86.4% (1,258 of 1,456) and 52.1% (759 of 1,456), respectively, with supine scanning alone; and 85.6% (1,246 of 1,456) and 57.1% (831 of 1,456), respectively, with prone scanning alone. The sensitivity for detection of colorectal polyps 10 mm or larger, 5.0-9.9 mm, and smaller than 5 mm and polyps of all sizes was 92.7%, 79.8%, 60.3%, and 69.9%, respectively, with combined scanning. Sensitivity was 58.5%, 47.2%, 36.3%, and 42.1%, respectively, with supine scanning and 51.2%, 41.6%, 30.2%, and 36.3%, respectively, with prone scanning. The improved sensitivities for use of combined versus individual scanning positions were highly significant (P <.001) for polyps in all size categories.

CONCLUSION

Colonic distention and preparation at CT colonography were significantly improved by using supine and prone scanning in combination, and results correlated directly with improved sensitivity of polyp detection.

Virtual endoscopy: current perspectives

Virtual endoscopy is a new method for evaluating the gastrointestinal tract using either thin-section computed tomography (CT) or magnetic resonance imaging (MRI). The acquired data are then subjected to computer manipulation to render images simulating the conventional endoscopic view. CT and MR imaging data can provide information that is not accessible endoscopically. These important features include information on tissue extending through and beyond organ walls and the anatomic context of the entire gastrointestinal tract, which permits correct anatomic localization of the lesion. Many clinical studies have shown that it is a safe, noninvasive, well-tolerated alternative to conventional endoscopy. Virtual endoscopy may have potential as a method of screening for colorectal cancer. This review describes the technique, reviews reported results, and discusses the present and future applications of this technique, focusing on CT colography (CTC).

Edge displacement field-based classification for improved detection of polyps in CT colonography

Colorectal cancer can easily be prevented provided that the precursors to tumors, small colonic polyps, are detected and removed. Currently, the only definitive examination of the colon is fiber-optic colonoscopy, which is invasive and expensive. Computed tomographic colonography (CTC) is potentially a less costly and less invasive alternative to FOC. It would be desirable to have computer-aided detection (CAD) algorithms to examine the large amount of data CTC provides. Most current CAD algorithms have high false positive rates at the required sensitivity levels. We developed and evaluated a postprocessing algorithm to decrease the false positive rate of such a CAD method without sacrificing sensitivity. Our method attempts to model the way a radiologist recognizes a polyp while scrolling a cross-sectional plane through three-dimensional computed tomography data by classification of the changes in the location of the edges in the two-dimensional plane. We performed a tenfold cross-validation study to assess its performance using sensitivity/specificity analysis on data from 48 patients. The mean specificity over all experiments increased from 0.19 (0.35) to 0.47 (0.56) for a sensitivity of 1.00 (0.95).

CT colonography (virtual colonoscopy) for the detection of colorectal polyps and neoplasms. current status and future developments

Computed tomography colonography (CTC) is a new, rapidly developing non-invasive CT technique used to detect colonic polyps and cancers. It employs two- (2D) and three-dimensional (3D) images of the colon in order to display neoplastic lesions. Clinical trials demonstrate promising results for the detection of polyps and cancers greater than or equal to 10 mm in size. Our purpose is to describe the technique of CT colonography, review recent published trials of CT colonography, and elucidate current clinical applications. Continuing technical innovations such as multidetector CT, computer-aided diagnosis, new image display techniques and faecal tagging promise to improve the performance and patient acceptance of CT colonography in the future.

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.

Virtual colonoscopy

Computerized tomographic colonography (CT colonography) is a new, non-invasive technique that has been developed over the last few years; it looks at the large bowel in detail. In this chapter we look at how the examination is performed and we consider how the images are displayed. We describe the normal features of the colon, as seen using this technique, as well as the features of common pathological conditions. We will discuss screening for colorectal cancer and the performance of CT colonography; we compare the latter with other procedures currently employed in the screening and diagnosis of colorectal pathology. We consider the difficulties in interpreting these CT colonographic images and look at ways to overcome such difficulties. Finally we discuss future developments of this exciting, new technique.

Computed tomography colonography (virtual colonoscopy): review

Computed tomography examination of the colon performed after bowel cleansing and distension of the lumen with gas goes by several different names--CT colonography (CTC) and CT colography perhaps being the most common. Strictly, the term 'virtual colonoscopy' (VC), should be reserved for the process of examining 3-D, simulated endoluminal images with a capability to navigate through the bowel using appropriate software. Computed tomography colonography appears to be the name that has gained favour among radiologists, although it is suspected that 'virtual colonoscopy' will persist as a generic term due to its attractive 'high-tech' connotations for non-radiological medical and lay persons. Whatever the name, the technique has been made possible through the advent of fast helical CT scanners which allow acquisition of a volume of data, and of proprietary software which enables multiplanar reformatting and 3-D endoluminal reconstructions. It is evident that if CTC/VC can be shown to be acceptable to patients, safe, affordable and accurate, it has enormous potential as a diagnostic and screening tool for colorectal neoplasia.

Quantification of distention in CT colonography: development and validation of three computer algorithms

Three bowel distention-measuring algorithms for use at computed tomographic (CT) colonography were developed, validated in phantoms, and applied to a human CT colonographic data set. The three algorithms are the cross-sectional area method, the moving spheres method, and the segmental volume method. Each algorithm effectively quantified distention, but accuracy varied between methods. Clinical feasibility was demonstrated. Depending on the desired spatial resolution and accuracy, each algorithm can quantitatively depict colonic diameter in CT colonography.

A statistical 3-D pattern processing method for computer-aided detection of polyps in CT colonography

Adenomatous polyps in the colon are believed to be the precursor to colorectal carcinoma, the second leading cause of cancer deaths in United States. In this paper, we propose a new method for computer-aided detection of polyps in computed tomography (CT) colonography (virtual colonoscopy), a technique in which polyps are imaged along the wall of the air-inflated, cleansed colon with X-ray CT. Initial work with computer aided detection has shown high sensitivity, but at a cost of too many false positives. We present a statistical approach that uses support vector machines to distinguish the differentiating characteristics of polyps and healthy tissue, and uses this information for the classification of the new cases. One of the main contributions of the paper is the new three-dimensional pattern processing approach, called random orthogonal shape sections method, which combines the information from many random images to generate reliable signatures of shape. The input to the proposed system is a collection of volume data from candidate polyps obtained by a high-sensitivity, low-specificity system that we developed previously. The results of our ten-fold cross-validation experiments show that, on the average, the system increases the specificity from 0.19 (0.35) to 0.69 (0.74) at a sensitivity level of 1.0 (0.95).

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.

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.