CT colonography: the next colon screening examination?

Sigmoid colon perforation at CT colonography secondary to a possible obstructive mechanism: report of a case

We report a case of colonic perforation in CT colonography, which was observed in a sigmoid colon segment contained within an inguinal hernia. At surgery, apart from the perforation, a normal large-bowel wall was found. Although rare, perforation may occur in patients with normal bowel wall, possibly resulting from a mechanical strain caused by gaseous overdistention. Radiologists performing the procedure must be aware of this possibility.

Colon polyp detection using smoothed shape operators: preliminary results

Computer-aided detection (CAD) algorithms identify locations in computed tomographic (CT) images of the colon that are most likely to contain polyps. Existing CAD methods treat the CT data as a voxelized, volume image. They estimate a curvature-based feature at the mucosal surface voxels. However, curvature is a smooth notion, while our data are discrete and noisy. As a second order differential quantity, curvature amplifies noise. In this paper, we present the smoothed shape operators method (SSO), which uses a geometry processing approach. We extract a triangle mesh representation of the colon surface, and estimate curvature on this surface using the shape operator. We then smooth the shape operators on the surface iteratively. Throughout, we use techniques explicitly designed for discrete geometry. All our computation occurs on the surface, rather than in the voxel grid. We evaluate our algorithm on patient data and provide free-response receiver-operating characteristic performance analysis over all size ranges of polyps. We also provide confidence intervals for our performance estimates. We compare our performance with the surface normal overlap (SNO) method for the same data. A preliminary evaluation of our method on 35 patients yielded the following results (polyp diameter range; sensitivity; false positives/case): (10mm; 100%; 17.5), (5-10 mm; 89.7%, 21.23), (<5 mm; 59.1%; 23.9) and (overall; 80.3%; 23.9). The evaluation of the SNO method yielded: (10 mm; 75%; 17.5), (5-10 mm; 43.1%; 21.23), (<5 mm; 15.9%; 23.9) and (overall; 38.5%; 23.9).

The evolving role of CT colonography

Colorectal cancer (CRC) screening is widely recommended as part of standard preventive care. All average risk persons over the age of 50 y are eligible. Various authorities have advocated fecal occult blood testing, flexible sigmoidoscopy, barium enema and colonoscopy at varying intervals as acceptable screening options. Despite the array of choices, CRC screening lags in frequency behind other cancer screening maneuvers like mammography or Pap smear. Of late, there is growing interest in CT colonography (CTC) as another screening option. CTC, or virtual colonoscopy, may represent an attractive, non-invasive method of CRC screening that provides images akin to traditional colonoscopy. Improvements in CTC performance, especially when coupled with declining costs, suggest that CTC's role in average risk screening will increase in the future. This review summarizes available data about the efficacy of CTC in average and high risk screening populations. Current indications as well as limitations to this technology are discussed, as are practical issues like the cost-effectiveness of CTC for widespread use.

Teniae coli-based circumferential localization system for CT colonography: feasibility study

This HIPAA-compliant study, with institutional review board approval and informed patient consent, was conducted to retrospectively develop a teniae coli-based circumferential localization method for guiding virtual colon navigation and colonic polyp registration. Colonic surfaces (n = 72) were depicted at computed tomographic (CT) colonography performed in 36 patients (26 men, 10 women; age range, 47-72 years) in the supine and prone positions. For 70 (97%) colonic surfaces, the tenia omentalis (TO), the most visible of the three teniae coli on a well-distended colonic surface, was manually extracted from the cecum to the descending colon. By virtually dissecting and flattening the colon along the TO, the authors developed a localization system involving 12 grid lines to estimate the circumferential positions of polyps. A sessile polyp would most likely (at 95% confidence level) be found within +/-1.2 grid lines (one grid line equals 1/12 the circumference) with use of the proposed method. By orienting and positioning the virtual cameras with use of the new localization system, synchronized prone and supine navigation was achieved. The teniae coli are extractable landmarks, and the teniae coli-based circumferential localization system helps guide virtual navigation and polyp registration at CT colonography.

Laboratory and diagnostic testing: a perioperative update

Perioperative nurses are challenged to stay informed about the rapidly changing field of diagnostic and laboratory testing. The brain natriuretic peptide test primarily is used to differentiate dyspnea caused by heart failure from dyspnea that results from other causes. Virtual colonoscopy is a promising new alternative for detecting colorectal polyps and cancers. The microalbumin urine test provides an early indication of the development of diabetic complications. This update of relatively new laboratory tests and diagnostic studies also provides implications for perioperative nurses.

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.

Trends in oncological CT imaging: clinical application of multidetector-row CT and 3D-CT imaging

Computed tomography (CT) plays an essential role in oncological imaging as the modality of screening for malignancies, mapping out the treatment strategy at staging, assessing response to the treatment, and following up patient outcome after the treatment. The advent of multidetector-row CT (MDCT) has brought about dramatic changes in clinical oncological imaging. The very superior temporal and spatial resolution of MDCT has transformed CT imaging from a transaxial cross-sectional technique into an isotropic volume-imaging technique. MDCT facilitates multiphasic contrast-enhanced study for a wide range of body scanning in a single examination, as well as providing flexibility of multidirectional reconstruction and high-quality three-dimensional imaging. With increases in the number of detector rows year by year, systems with 64-detector rows have become commercially available in 2006. The purpose of this article is to review the status of CT imaging in oncological imaging: (1) to outline the impact of MDCT, focusing on oncological imaging and (2) to review the clinical applications of oncological CT imaging with MDCT.

Polyps: linear and volumetric measurement at CT colonography

PURPOSE

To retrospectively determine which of several computed tomographic (CT) colonography-based polyp measurements is most compatible with the linear measurement at optical colonoscopy and which is best for assessing change in polyp size.

MATERIALS AND METHODS

This HIPAA-compliant study had institutional review board approval; informed consent was obtained. Prone and supine CT colonography with same-day optical colonoscopy was performed in 216 patients (147 men and 69 women; age range, 46-79 years; mean age, 59.2 years) with 338 polyps detected at CT colonography. Polyp size was measured with three linear measurements and two volume measurements. One linear measurement and one volume measurement were performed by using automated segmentation; remaining measurements were performed manually. Compatibility with linear size at optical colonoscopy and measurement reproducibility were assessed three ways: variation from size measurement at optical colonoscopy, change between prone and supine scans, and variability between observers. Confidence analysis assessed the ability of each measurement to identify polyps with an optical colonoscopy measurement of 1 cm or greater.

RESULTS

Two hundred fifty-one segmentable polyps were present on both supine and prone scans. Linear polyp diameter manually measured on a three-dimensional endoluminally viewed surface (L(M3D)) indicated with 95% confidence that a polyp measured as 0.8 cm or smaller was less than 1.0 cm at optical colonoscopy. Prone and supine polyp size difference was smallest for L(M3D) and the linear diameter computed from manual and automated volume measurements, with interquartile ranges smaller than or equal to 0.3, 0.2, and 0.5 cm, respectively. Interobserver and intraobserver variability was smallest for linear polyp diameter measurements on a two-dimensional display, with a mean percentage difference of 2.8% (95% Bland-Altman limits of agreement: -17.8%, 23.4%) and 5.0% (95% Bland-Altman limits of agreement: -28.3%, 38.3%), respectively.

CONCLUSION

L(M3D) best approximated polyp size measurements at optical colonoscopy. Linear diameter calculated from automated volume measurements showed the smallest variation between supine and prone scans while avoiding observer variability and may be best for assessing polyp size changes with serial examinations.

Perceptive errors in CT colonography

Published results to date have indicated a good per patient sensitivity of computed tomographic colonography (CTC) for colorectal cancer and for polyps measuring 10 mm or more together with a very good specificity. Sensitivity and specificity for polyps in the range of 6-10 mm are moderate. These results, however, can be achieved only with meticulous attention to technique including adequate colonic distention, and acquisition of supine and prone thin-section computed tomographic (CT) images. Moreover, there is a significant learning curve involved in the interpretation of CTC studies, with performance statistics improving with operator experience. Radiologists must be comfortable in reporting directly from workstation monitors and have access to and be familiar with software for multiplanar and endoluminal reconstructions. In addition to maximize polyp detection and minimize false positive results, reporting radiologists must have a working knowledge of normal colorectal anatomy and pathology on CTC and be familiar with potential pitfalls in interpretation. Besides the description of several possible causes for perceptive errors, also a literature search of perceptive errors in CTC is included in this paper.

Massive-training artificial neural network (MTANN) for reduction of false positives in computer-aided detection of polyps: Suppression of rectal tubes

One of the limitations of the current computer-aided detection (CAD) of polyps in CT colonography (CTC) is a relatively large number of false-positive (FP) detections. Rectal tubes (RTs) are one of the typical sources of FPs because a portion of a RT, especially a portion of a bulbous tip, often exhibits a cap-like shape that closely mimics the appearance of a small polyp. Radiologists can easily recognize and dismiss RT-induced FPs; thus, they may lose their confidence in CAD as an effective tool if the CAD scheme generates such "obvious" FPs due to RTs consistently. In addition, RT-induced FPs may distract radiologists from less common true positives in the rectum. Therefore, removal RT-induced FPs as well as other types of FPs is desirable while maintaining a high sensitivity in the detection of polyps. We developed a three-dimensional (3D) massive-training artificial neural network (MTANN) for distinction between polyps and RTs in 3D CTC volumetric data. The 3D MTANN is a supervised volume-processing technique which is trained with input CTC volumes and the corresponding "teaching" volumes. The teaching volume for a polyp contains a 3D Gaussian distribution, and that for a RT contains zeros for enhancement of polyps and suppression of RTs, respectively. For distinction between polyps and nonpolyps including RTs, a 3D scoring method based on a 3D Gaussian weighting function is applied to the output of the trained 3D MTANN. Our database consisted of CTC examinations of 73 patients, scanned in both supine and prone positions (146 CTC data sets in total), with optical colonoscopy as a reference standard for the presence of polyps. Fifteen patients had 28 polyps, 15 of which were 5-9 mm and 13 were 10-25 mm in size. These CTC cases were subjected to our previously reported CAD scheme that included centerline-based segmentation of the colon, shape-based detection of polyps, and reduction of FPs by use of a Bayesian neural network based on geometric and texture features. Application of this CAD scheme yielded 96.4% (27/28) by-polyp sensitivity with 3.1 (224/73) FPs per patient, among which 20 FPs were caused by RTs. To eliminate the FPs due to RTs and possibly other normal structures, we trained a 3D MTANN with ten representative polyps and ten RTs, and applied the trained 3D MTANN to the above CAD true- and false-positive detections. In the output volumes of the 3D MTANN, polyps were represented by distributions of bright voxels, whereas RTs and other normal structures partly similar to RTs appeared as darker voxels, indicating the ability of the 3D MTANN to suppress RTs as well as other normal structures effectively. Application of the 3D MTANN to the CAD detections showed that the 3D MTANN eliminated all RT-induced 20 FPs, as well as 53 FPs due to other causes, without removal of any true positives. Overall, the 3D MTANN was able to reduce the FP rate of the CAD scheme from 3.1 to 2.1 FPs per patient (33% reduction), while the original by-polyp sensitivity of 96.4% was maintained.

The use of 3D surface fitting for robust polyp detection and classification in CT colonography

In this paper we describe the development of a computationally efficient computer-aided detection (CAD) algorithm based on the evaluation of the surface morphology that is employed for the detection of colonic polyps in computed tomography (CT) colonography. Initial polyp candidate voxels were detected using the surface normal intersection values. These candidate voxels were clustered using the normal direction, convexity test, region growing and Gaussian distribution. The local colonic surface was classified as polyp or fold using a feature normalized nearest neighborhood classifier. The main merit of this paper is the methodology applied to select the robust features derived from the colon surface that have a high discriminative power for polyp/fold classification. The devised polyp detection scheme entails a low computational overhead (typically takes 2.20min per dataset) and shows 100% sensitivity for phantom polyps greater than 5mm. It also shows 100% sensitivity for real polyps larger than 10mm and 91.67% sensitivity for polyps between 5 to 10mm with an average of 4.5 false positives per dataset. The experimental data indicates that the proposed CAD polyp detection scheme outperforms other techniques that identify the polyps using features that sample the colon surface curvature especially when applied to low-dose datasets.

CT Colonography with Computer-aided Polyp Detection: Volume and Attenuation Thresholds to Reduce False-Positive Findings Owing to the Ileocecal Valve

PURPOSE

To retrospectively identify volume and average attenuation thresholds for differentiating between ileocecal valve (ICV) and polyp at computed tomographic (CT) colonography with computer-aided detection (CAD).

MATERIALS AND METHODS

Informed consent (with consent for future retrospective research) and institutional review board (IRB) approval were obtained for the original prospective study. This retrospective study had IRB approval, as well, and was HIPAA-compliant. A total of 496 patients were selected from a larger screening population. CT colonographic images from 394 patients (227 men, 167 women; mean age, 58.0 years; range, 40-79 years) were used as a training set, and images from 102 patients (76 men, 26 women; mean age, 59.8 years; range, 46-79 years) were used as a test set. A series of 2742 volume and attenuation thresholds, for which segmented findings both larger in volume and lower in average attenuation were labeled as ICVs and remaining findings were labeled polyps, were applied to the training set to determine settings with 100% sensitivity for polyp detection and the highest specificity for ICV detection. The optimal settings were then applied to the test set. Significance was assessed with the Fisher exact test, and 95% confidence intervals (CIs) were computed for sensitivity and specificity.

RESULTS

A total of 386 ICVs and 67 adenomatous polyps from the training set and 102 ICVs and 138 adenomatous polyps from the test set could be segmented with a three-dimensional segmentation algorithm. When supine and prone images were counted individually, 746 nonunique ICVs from the training set and 191 from the test set were segmentable. In the training set, a volume of 600 mm(3) and an attenuation of 36 HU provided 100% sensitivity (67 polyps; 95% CI: 93%, 100%) and the optimal 83% specificity (618 of 746 ICVs; 95% CI: 80%, 85%). When applied to the test set, this combination provided 97% sensitivity (134 of 138 polyps; 95% CI: 92%, 99%) and 84% specificity (160 of 191 ICVs; 95% CI: 78%, 89%). Differences in sensitivity and specificity in the detection of polyps between the sets were not significant.

CONCLUSION

Volume and average CT attenuation thresholds can help differentiate most ICVs from true polyps.

A pipeline for computer aided polyp detection

We present a novel pipeline for computer-aided detection (CAD) of colonic polyps by integrating texture and shape analysis with volume rendering and conformal colon flattening. Using our automatic method, the 3D polyp detection problem is converted into a 2D pattern recognition problem. The colon surface is first segmented and extracted from the CT data set of the patient's abdomen, which is then mapped to a 2D rectangle using conformal mapping. This flattened image is rendered using a direct volume rendering technique with a translucent electronic biopsy transfer function. The polyps are detected by a 2D clustering method on the flattened image. The false positives are further reduced by analyzing the volumetric shape and texture features. Compared with shape based methods, our method is much more efficient without the need of computing curvature and other shape parameters for the whole colon surface. The final detection results are stored in the 2D image, which can be easily incorporated into a virtual colonoscopy (VC) system to highlight the polyp locations. The extracted colon surface mesh can be used to accelerate the volumetric ray casting algorithm used to generate the VC endoscopic view. The proposed automatic CAD pipeline is incorporated into an interactive VC system, with a goal of helping radiologists detect polyps faster and with higher accuracy.

Colorectal Cancer: Screening Double-Contrast Barium Enema Examination in Average-Risk Adults Older Than 50 Years

PURPOSE

To retrospectively determine the diagnostic yield of double-contrast barium enema examinations performed for colorectal cancer screening of neoplasms 1 cm or larger or advanced neoplastic lesions of any size in average-risk adults older than 50 years.

MATERIALS AND METHODS

The Institutional Review Board at the affiliated Veterans Affairs Medical Center approved this HIPAA-compliant study protocol and did not require informed consent from patients. Computerized databases revealed 276 double-contrast barium enema examinations performed for colorectal cancer screening in average-risk adults older than 50 years. Radiographic and pathologic reports were reviewed to determine the number of patients who had polypoid lesions 1 cm or larger, polyps smaller than 1 cm, or advanced neoplastic lesions of any size. Forty-five (16.3%) of the 276 patients underwent follow-up sigmoidoscopy or colonoscopy. Medical, endoscopic, and pathologic records were reviewed and compared with radiographic findings.

RESULTS

The results of double-contrast barium enema examination revealed 74 (26.8%) of 276 patients with 104 polypoid lesions in the colon, including 32 patients (11.6%) with 41 polypoid lesions 1 cm or larger, 15 patients (5.4%) with 19 polyps 6-9 mm, and 27 patients (9.8%) with 44 polyps 5 mm or smaller. Endoscopy was performed in 24 (75%) of 32 patients, the results of which confirmed 23 (72%) of 32 radiographically diagnosed lesions 1 cm or larger in 16 (67%) of 24 patients. In two of these individuals, the polyps were hyperplastic. The remaining 14 patients had a total of 21 neoplastic lesions 1 cm or larger, including 11 tubular adenomas, seven tubulovillous adenomas, one villous adenoma with marked dysplasia, and two cancers. The diagnostic yield of screening double-contrast barium enema examination was 5.1% (14 of 276 patients) for neoplastic lesions 1 cm or larger and 6.2% (17 of 276 patients) for advanced neoplastic lesions of any size.

CONCLUSION

Double-contrast barium enema examinations performed in average-risk adults older than 50 years have a diagnostic yield of 5.1% for neoplastic lesions 1 cm or larger and 6.2% for advanced neoplastic lesions, regardless of size.

Assessment of cardiovascular risk status at CT colonography

PURPOSE

To retrospectively determine whether calcium scores of the abdominal aorta obtained during computed tomographic (CT) colonography relate to Framingham risk factors and clinical cardiac events.

MATERIALS AND METHODS

The institutional review board approved the current HIPAA-compliant retrospective study and waived informed consent. Between 1995 and 1998, 480 patients underwent CT colonography; 467 patients were available for assessment. Calcium scores with a threshold attenuation value of 130 HU or greater were recorded for abdominal aorta (suprarenal, infrarenal, and aortic bifurcation regions and total). Patient histories were abstracted for established cardiac risk factors and subsequent cardiac events. Associations between calcium measurements and binary risk factors were assessed with Wilcoxon rank sum test; those with continuous risk factors, with Spearman rank correlation coefficient; and those with combined end points, with Cox proportional hazards model.

RESULTS

Follow-up data were available for 467 patients with median age of 65 years (range, 34-83 years); 59% (275 of 467) were men. Nine patients had cardiac events subsequent to CT colonography. Results of proportional hazards regression analysis revealed a significant association between myocardial infarction or cardiac event-related death and calcium scores of the aortic bifurcation that exceeded 895, the value for the 75th percentile for this calcium variable (P < .01). Associations with established cardiac risk factors for all four calcium scores were significant (P < .05). Spearman rank correlation coefficients for associations between total calcium score and patient characteristics of age, number of pack-years of smoking, and systolic blood pressure were 0.51, 0.43, and 0.29, respectively (P < .001 for all).

CONCLUSION

Aortic calcification scores at CT colonography are significantly associated with established cardiac risk factors and cardiac-related events. This screening information can be obtained without additional scanning or risk to the patient.

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.

Effective screening for bowel cancer: a United kingdom perspective

Bowel cancer is a major cause of morbidity and death and is a high cost to health care systems. Screening currently offers the best chance of improving outcomes from bowel cancer. When introducing screening, the problems encountered in other cancers need to be avoided to maximize benefits and minimize harms.

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.

Oral Contrast Adherence to Polyps on CT Colonography

Although oral contrast agents are known to improve the accuracy of CT colonography (CTC) by tagging fluid and stool, it is not well recognized that oral contrast also adheres to the surface of polyps. The authors' objective was to quantitate the frequency of contrast adhering to polyps. Three hundred thirty-eight optical colonoscopy-proven polyps were identified on CTC of all of the 216 patients with polyps in a larger cohort of screening patients. CT scans of polyps were analyzed for adherent contrast (ie, a thin coat/adherent drops) in at least one view (prone/supine). Forty-six percent of the 312 polyps not touching a contrast pool had adherent contrast. Polyps with villous histology were significantly more likely to have adherent contrast (77% [20/26] vs. 43% [124/286], P<0.001). Oral contrast agents often tag polyp surfaces in a pattern that is distinct from internal tagging of adherent stool, which must be recognized during CTC interpretation. Polyps with villous histology show a higher rate of contrast adherence than nonvillous polyps.

Colonic perforation after computed tomographic colonography in a patient with fibrostenosing Crohn's disease

Computed tomographic colonography (CTC) offers great promise in the management of patients with disorders of the colon. Few complications have been reported with its use thus far. We describe herein a case of colonic perforation during CTC in a patient with active stenosing ileocolonic Crohn's disease. To our knowledge, this is the first reported case of CTC-related perforation in the setting of Crohn's disease, and the third reported perforation overall. Perforation likely occurred in this case due to barotrauma in the setting of colonic strictures and an inflamed, weakened colonic wall. Physician awareness of the increased risk of perforation with CTC in the setting of inflammatory and/or obstructive disease of the colon will allow for improved clinical decision-making in the care of these patients.

Multi-detector CT-colonography in inflammatory bowel disease: prospective analysis of CT-findings to high-resolution video colonoscopy

AIM

Prospective analysis of multi-detector CT-colonography (MDCTC) in patients with inflammatory bowel disease (IBD) compared to high-resolution video-endoscopy (HRVC).

MATERIALS AND METHODS

Twenty-one patients (mean age 49.6 years) with Crohn's disease or ulcerative colitis underwent MDCTC (Somatom Volume Zoom, Siemens, Erlangen; 1mm collimation, Pitch 8, 100 mAs, 120 kVp). HRVC was performed within 2 h after MDCTC. MDCTC was analyzed by two blinded readers. MDCTC-findings including bowel wall alterations and extraintestinal changes were compared to results of HRVC.

RESULTS

Over-all-sensitivity was 100% for endoluminal lesions with correct diagnosis of two cancers. Acute and chronic IBD were correctly identified by MDCTC in 63.6%, and 100%, respectively, with a specificity of 75%, and 100%. Sensitivity, specificity, positive and negative predictive values of MDCTC for diagnosis of acute and chronic disease were best for chronic disease. Sensitivity was worst for acute ulcerative colitis and specificity was worst for acute Crohn's disease. Haustral loss was seen only in ulcerative colitis. Pseudopolyps and fistulae were findings exclusive to Crohn's disease. Particularly extraintestinal findings as increased vascularization and local lymphadenopathy correlated well with endoscopic definition of acute disease. Because of the possibly more vulnerable colonic wall in acute inflammatory bowel disease, the air inflation for MDCTC should be performed most carefully to avoid any risk of colonic perforation.

CONCLUSION

MDCTC may help to distinguish between patients with acute and chronic IBD. Especially extraintestinal complications, tumorous as well as pseudo-tumorous lesions can be detected with high sensitivity and specificity.

Screening of patients after colectomy: virtual colonography

BACKGROUND

Virtual colonography is a powerful new method of imaging the entire colon and is useful to assess polyps and diagnose colon cancer. We evaluated virtual colonography in the postoperative screening of patients who had colon cancer.

METHODS

Fifty-three patients were examined with virtual colonography 12 to 48 months postoperatively. Forty-four patients had received segmental colectomy with restoration of the gastrointestinal tract, and nine patients underwent abdominoperineal resection and permanent colostomy. After proper cleaning of the colon and distention with air, spiral computed tomographic examination of the abdomen with a slice thickness of 5 mm (table speed [TS] 10 mm, reconstruction interval [RI] 2.5 mm) was performed in the supine and prone positions (including intravenous contrast medium infusion). Images were transferred to a separate workstation (Philips Easy Vision) for postprocessing, three-dimensional rendering, and endoluminal viewing.

RESULTS

Eleven recurrences (16.41%) were identified in 10 patients by virtual colonography, but one recurrence was missed. Conventional colonoscopy was incomplete in six cases, and two patients with colostomy refused colonoscopy. In these eight cases (15%), virtual colonoscopy was completed without problems. A second tumor in one patient who had received abdominoperineal resection was demonstrated by virtual colonography, but conventional colonoscopy failed to demonstrate the lesion. Liver metastases were identified in only one patient.

CONCLUSIONS

Virtual colonography seems to provide a good alternative in the follow-up of patients after colectomy. The technique is effective in the diagnosis of locoregional recurrences and distant metastases and is well accepted by patients, and results are equal to those of the conventional colonoscopy.

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.

Elevated gastric lesions: virtual gastroscopy

With the development of multidetector computed tomography and the improvement in the capabilities of workstations, the use of high-quality three-dimensional reconstructions and virtual images can be applied to organs other than the colon such as the stomach. As a noninvasive technique, virtual gastroscopy represents an alternative to conventional endoscopy for the detection of elevated lesions. Findings of this technique are illustrated.

An intelligent system for automatic detection of gastrointestinal adenomas in video endoscopy

Today 95% of all gastrointestinal carcinomas are believed to arise from adenomas. The early detection of adenomas could prevent their evolution to cancer. A novel system for the support of the detection of adenomas in gastrointestinal video endoscopy is presented. Unlike other systems, it accepts standard low-resolution video input thus requiring less computational resources and facilitating both portability and the potential to be used in telemedicine applications. It combines intelligent processing techniques of SVMs and color-texture analysis methodologies into a sound pattern recognition framework. Concerning the system's accuracy this was measured using ROC analysis and found to exceed 94%.

Centerline-based colon segmentation for CT colonography

We have developed a fully automated algorithm for colon segmentation, centerline-based segmentation (CBS), which is faster than any of the previously presented segmentation algorithms, but also has high sensitivity as well as high specificity. The algorithm first thresholds a set of unprocessed CT slices. Outer air is removed, after which a bounding box is computed. A centerline is computed for all remaining regions in the thresholded volume, disregarding segments related to extracolonic structures. Centerline segments are connected, after which the anatomy-based removal of segments representing extracolonic structures occurs. Segments related to the remaining centerline are locally region grown, and the colonic wall is found by dilation. Shape-based interpolation provides an isotropic mask. For 38 CT datasets, CBS was compared with the knowledge-guided segmentation (KGS) algorithm for sensitivity and specificity. With use of a 1.5 GHz AMD Athlon-based PC, the average computation time for the segmentation was 14.8 s. The sensitivity was, on average, 96%, and the specificity was 99%. A total of 21% of the voxels segmented by KGS, of which 96% represented extracolonic structures and 4% represented the colon, were removed.

Computer-aided detection for virtual colonoscopy

Colon cancer is one of the leading causes of cancer deaths in the developed countries. Most colon cancers can be prevented if precursor colon polyps are detected and removed. Virtual colonoscopy, or CT colonography, has shown promise to be the future screening tool for polyp detection, with a number of studies performed at academic institutions showing high sensitivity and specificity. Two main factors limiting CT colonography in general use are its excessive interpretation time and the variable sensitivity among readers. This article discusses the potential of computer-aided detection to address these problems. We also review the current state of research in this field and the future roles and challenges of CAD for CT colonography.

State-of-the-art computed tomographic and magnetic resonance imaging of the gastrointestinal system

Among the major innovations in radiology of the gastrointestinal (GI) system are the replacement of classic invasive diagnostic methods with noninvasive ones and the improvement in lesion characterization and staging of pancreatobiliary malignancies. Developments in imaging technology have led to many improvements in the field of diagnostic GI radiology. With its fast and thin-section scanning abilities, multidetector-row CT (MDCT) strengthens the place of CT as the most efficient tool to diagnose, characterize, and preoperatively stage pancreatic neoplasms. MR cholangiopancreatography has widely replaced endoscopic retrograde cholangiopancreatography in the diagnosis and staging of pancreatobiliary malignancies. MR imaging, using phased-array or endorectal coils, demonstrates local tumor invasion accurately in rectal cancers and thus allows an improved surgical planning. Virtual colonoscopy with MDCTs is an efficient screening method for colon cancer, and MDCT enterography is becoming the standard imaging technique for many small bowel disorders. The continuing developments in CT and MR technology will most probably further improve the accuracy of these and other imaging applications in the near future.

CAD techniques, challenges, and controversies in computed tomographic colonography

Computer-aided diagnosis (CAD) for computed tomographic colonography (CTC) automatically detects the locations of suspicious polyps and masses on CTC and provides radiologists with a second opinion. CAD has the potential to increase radiologists' diagnostic performance in the detection of polyps and masses and to decrease variability of the diagnostic accuracy among readers without significantly increasing the reading time. Technical developments have advanced CAD substantially during the past several years, and a fundamental scheme for the detection of polyps has been established. The most recent CAD systems based on this scheme produce a clinically acceptable high sensitivity and a low false-positive rate. However, CAD for CTC is still under active development, and the technology needs to be improved further. This report describes the expected benefits, the current fundamental scheme, the key techniques used for detection of polyps and masses on CTC, the current detection performance, as well as the pitfalls, challenges, controversies, and the future of CAD.

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.

Vascular Virtual Endoluminal Visualization of Invasive Colorectal Cancer on MDCT Colonography

OBJECTIVE

The purpose of this study was to assess the utility of vascular views for visualization of invasive colorectal cancers on contrast-enhanced MDCT colonography.

CONCLUSION

By means of Hounsfield-transparency settings, we obtained virtual endoluminal images that show vascular structures and delineate invasive cancers of the colorectal wall, and we call these images "vascular views." Using this technique for contrast-enhanced MDCT colonography, we found that the increase in flow and pooling of blood related to angiogenesis of cancerous lesions is easy to identify and that this finding is useful in the detection of invasive colorectal cancers.

Virtual Endoscopic Visualization of the Colon by Shape–Scale Signatures

We developed a new visualization method for virtual endoscopic examination of computed tomographic (CT) colonographic data by use of shape-scale analysis. The method provides each colonic structure of interest with a unique color, thereby facilitating rapid diagnosis of the colon. Two shape features, called the local shape index and curvedness, are used for defining the shape-scale spectrum. When we map the shape index and curvedness values within CT colonographic data to the shape-scale spectrum, specific types of colonic structures are represented by unique characteristic signatures in the spectrum. The characteristic signatures of specific types of lesions can be determined by use of computer-simulated lesions or by use of clinical data sets subjected to a computerized detection scheme. The signatures are used for defining a two-dimensional color map by assignment of a unique color to each signature region. The method was evaluated visually by use of computer-simulated lesions and clinical CT colonographic data sets, as well as by an evaluation of the human observer performance in the detection of polyps without and with the use of the color maps. The results indicate that the coloring of the colon yielded by the shape-scale color maps can be used for differentiating among the chosen colonic structures. Moreover, the results indicate that the use of the shape-scale color maps can improve the performance of radiologists in the detection of polyps in CT colonography.

CT colonography with fecal tagging after incomplete colonoscopy

The objective of this study was to evaluate dietary fecal tagging (FT) as a cleansing method prior to CT colonography (CTC) in patients with incomplete conventional colonoscopy (CC). After written informed consent was obtained, 24 patients had standard colonoscopic preparation (ScCl), and 25 patients had FT as cleansing method. Segmental distention, fluid levels, fecal residues, tagged appearance of fluid levels, and residual stool were evaluated. Mann-Whitney U test was used to test for significant differences between FT and ScCl groups. Compared with ScCl, FT improved distention (p=0.001), reduced the amount of fluid (p=0.043), but suffered from residual stool (p=0.046). A clear correlation was found between distention and fluid. No differences were found in stool size between FT and ScCl. FT showed a good labeling of fecal residues, and acceptable labeling of fluid levels. Compared with ScCl, FT reduces fluid, favors distention, but suffers from fecal residues. The tagged nature of these residues, however, allows differentiation from polyps.

Full-Body Cardiovascular and Tumor MRI for Early Detection of Disease: Feasibility and Initial Experience in 298 Subjects

OBJECTIVE

High diagnostic accuracy, emerging whole-body concepts, and lack of side effects combine to render MRI a natural candidate for screening purposes. The aim of this study was to evaluate the technical feasibility of a comprehensive multiorgan-targeting MRI examination and determine the frequency of findings in subjects without a history of serious disease.

SUBJECTS AND METHODS

The study group was composed of 331 subjects. The MRI protocol (mean examination time, 63 min) encompassed the target organs: the brain, arterial system, heart, and colon. Diagnoses were deemed relevant if the physician had to inform the subject about the findings. Subjects with a history of serious illnesses were excluded from subsequent analysis (n=33). All analyses were performed for the resulting subgroup of 298 subjects (247 men, 51 women; mean age, 49.7 years).

RESULTS

All 298 examinations were diagnostic excluding eight MR colonography components in which remaining stool hampered reliable diagnosis. Follow-up or radiologic confirmation could be obtained in 75% of all cases with relevant findings (128/169); only one false-positive result was encountered. Of the study group, 21% exhibited signs of atherosclerotic disease. Two cerebral infarctions and one myocardial infarction, previously unknown, were encountered; 12% had peripheral vascular disease. Twelve colonic polyps and nine pulmonary lesions were correctly detected. Of all MRI examinations, 29% revealed relevant additional findings in nontargeted organs. Only one minor allergoid reaction was encountered.

CONCLUSION

The presented data point toward an increased use of MRI for screening in the future, but to date screening MRI should not be performed outside a research setting because the cost-benefit relation is unclear.

The emerging role of virtual colonoscopy

A review of the current status of virtual colonoscopy is germane and topical. Clinicians need to be knowledgeable about this rapidly evolving and clinically relevant technology to understand the test benefits and limitations and to refer patients for this test appropriately. A critical review of the exponentially expanding literature on this subject is important. This article describes the imaging meth-ods, adjunctive techniques, and radiologic interpretation of CT colonography, and comprehensively and critically reviews the clinical data to help the clinician evaluate the current and potential applications of this technology.

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.

Fast and robust computation of colon centerline in CT colonography

Although several methods for generating the centerline of a colon from CT colonographic scans have been proposed, in general they are time-consuming and do not take into account that the images of the colon may be of nonoptimal quality, with collapsed regions, and stool within the colon. Furthermore, the colonic lumen or wall, which is often used as a basis for computation of a centerline, is not always precisely segmented. In this study, we have developed an algorithm for computation of a colon centerline that is fast compared to the centerline algorithms presented in the reviewed literature, and that relies little on a complete colon segments identification. The proposed algorithm first extracts local maxima in a distance map of a segmented colonic lumen. The maxima are considered to be nodes in a set of graphs, and are iteratively linked together, based on a set of connection criteria, giving a minimum distance spanning tree. The connection criteria are computed from the distance from object boundary, the Euclidean distance between nodes and the voxel values on the pathway between pairs of nodes. After the last iteration, redundant branches are removed and end segments are recovered for each remaining graph. A subset of the initial maxima is used for distinguishing between the colon and noncolonic centerline segments among the set of graphs, giving the final centerline representation. A phantom study showed that, with respect to phantom variations, the algorithm achieved nearly constant computation time (2.3-2.9 s) except for the most extreme setting (20.2 s). The algorithm successfully found all, or most of, the centerline (93% - 100%). Displacement from optimum varied with colon diameter (1.2-6.6 mm). By use of 40 CT colonographic scans, the computer-generated centerlines were compared with the centerlines generated by three radiologists. The similarity was measured based on percent coverage and average displacement. The computer-generated centerlines, when compared with human-generated centerlines, had approximately the same displacement as when the human-generated centerlines were compared among each other (3.8 mm versus 4.0 mm). The coverage of the computer-generated centerlines was slightly less than that of the human-generated centerlines (92% versus 94%). The 40 centerlines were, on average, computed in 10.5 seconds, including computation time for the distance transform, with an Intel Pentium-based 800 MHz computer, as compared with 12-17 seconds or more (excluding computation time for the distance transform needed) per centerline as reported in other studies.

Computer-Aided diagnosis for CT colonography

CT colonography, or virtual colonoscopy, is a promising alternative screening tool for colon cancer. Computer-aided diagnosis (CAD) for CT colonography has the potential to increase radiologists' diagnostic performance in the detection of polyps and to reduce variability of the diagnostic accuracy among readers. Technical developments have advanced CAD for CT colonography substantially during the last several years. This paper describes the key techniques used for CAD for detection of polyps and masses in CT colonography, the current detection performance, and challenges and the future of CAD.

Significance of missed polyps at CT colonography

OBJECTIVE

Our purpose was to determine the clinical significance of polyps missed on CT colonography using histologic analysis and the natural history of colorectal polyps and to propose guidelines for follow-up colon surveillance based on CT colonographic findings. SUBJECTS AND METHODS. One hundred eighty-six men (age range, 40-87 years; mean, 62.3 years) underwent CT colonography immediately before conventional colonoscopy. All polyps detected on CT colonography were measured and imaged, and their segmental location was documented. All polyps detected on colonoscopy were measured, photographed, biopsied, and histologically analyzed. Results of CT colonography and conventional colonoscopy were compared with the final pathology reports. Conventional colonoscopy was used as the gold standard unless CT colonography showed a lesion measuring 10 mm or more that was not detected on conventional colonoscopy and had characteristics of a polyp. In these cases, follow-up conventional colonoscopy was offered.

RESULTS

One hundred ninety-one polyps were detected on conventional colonoscopy. CT colonography prospectively detected 53 polyps. Histologic analysis of the polyps not detected on CT colonography showed that of those 5 mm or smaller, 58.1% were not adenomas, and of those measuring 6-9 mm, 42.8% were not adenomas. Both missed polyps at CT colonography of 10 mm or more were adenomas. Of the 22 polyps measuring 10 mm or more, three were not detected on conventional colonoscopy. Of these three, CT colonography showed a lesion having characteristics of a polyp, follow-up endoscopy confirmed the presence of the lesion, and histologic analysis showed a villous adenoma, a tubulovillous adenoma, and a tubular adenoma.

CONCLUSION

If CT colonography shows no abnormality, follow-up screening in 5 years is recommended. If CT colonography detects a lesion smaller than 5 mm, follow-up imaging in 3-5 years is recommended. If CT colonography detects a lesion measuring 6 mm or more, endoscopy and polypectomy should be offered unless contraindicated.

CT colonography in cancer detection: methods and results

Colon cancer is the second leading cause of cancer-related death in the Western world. Approximately 80–90% of colon cancers develop in adenomas after mutations. The risk of encountering malignancy increases with the size of the adenomatous polyp. It is approximately 1% in adenomas <1 cm, and increases to 10% for adenomas 1–2 cm, and 20–53% for adenomas >2 cm. CT colonography (CTC) is a new technique, which allows, after bowel preparation and distension of the cleansed colon, to generate a volumetric display of the colon. Multi-detector CTC has a sensitivity of 93–100% and 70–83% for detection of polyps sized \documentclass[12pt]{minimal} \usepackage{wasysym} \usepackage[substack]{amsmath} \usepackage{amsfonts,amssymb,amsbsy} \usepackage[mathscr]{eucal} \usepackage{mathrsfs} \DeclareFontFamily{T1}{linotext}{} \DeclareFontShape{T1}{linotext}{m}{n}{<-> linotext}{} \DeclareSymbolFont{linotext}{T1}{linotext}{m}{n} \DeclareSymbolFontAlphabet{\mathLINOTEXT}{linotext} \begin{document} ${\ge }$ \end{document} 10 mm and 6–9 mm, respectively. For detection of colo-rectal cancer, CTC has a sensitivity of 83–100%. CTC is especially of value in patients with incomplete colonoscopy due to stenosis or colon elongation. It reliably detects synchronous cancers proximal to occlusive colon cancers, when colonoscopy fails to evaluate the entire colon. First results of a colon cancer screening study have shown that CTC is equal or even slightly superior to conventional colonoscopy in detection of adenomatous polyps \documentclass[12pt]{minimal} \usepackage{wasysym} \usepackage[substack]{amsmath} \usepackage{amsfonts,amssymb,amsbsy} \usepackage[mathscr]{eucal} \usepackage{mathrsfs} \DeclareFontFamily{T1}{linotext}{} \DeclareFontShape{T1}{linotext}{m}{n}{<-> linotext}{} \DeclareSymbolFont{linotext}{T1}{linotext}{m}{n} \DeclareSymbolFontAlphabet{\mathLINOTEXT}{linotext} \begin{document} ${\ge }$ \end{document} 8 mm. Moreover, CTC detects clinically significant extracolonic abnormalities not shown by colonoscopy. To increase the patient acceptance for wide-spread application of CTC cancer screening the issue of patient discomfort by bowel preparation and radiation exposure needs to be addressed further.

Early experiences with computed axial tomography colonography

BACKGROUND

Computed axial tomography (CT) colonography is the latest radiologic technique to be used to image the large bowel. We studied its role as a diagnostic tool in colorectal practice.

METHODS

One hundred and three patients suspected of having colorectal pathology underwent CT colonography.

RESULTS

CT colonography suggested a diagnosis of colonic carcinoma in 18 patients, and 17 of these underwent surgery. A colorectal neoplasm was not found in only 1 patient who had extrinsic colonic compression by an ovarian cyst. Twenty-one patients had suspected colonic polyps on scanning. Subsequent endoscopy in 19 of these patients confirmed the presence of polyps in only 10. CT colonography also revealed valuable extracolonic pathology: 8 occult noncolonic neoplasms and 163 other incidental findings.

CONCLUSIONS

CT colonography has good patient compliance and is a useful diagnostic modality in detecting colorectal neoplasms. Its main advantage over other such investigative tools is its ability to detect extracolonic pathology.

Extracolonic and Incidental Findings on CT Colonography (Virtual Colonoscopy)

OBJECTIVE

The objective of our study was to prospectively determine the frequency and clinical importance of extracolonic findings on CT colonography in symptomatic patients. SUBJECTS AND METHODS. One hundred eleven symptomatic patients referred for colonoscopy underwent CT colonography before colonoscopy. Helical CT from the diaphragm to the symphysis was performed with the patient in the supine and prone positions after rectal air insufflation. Image interpretation was done on a digital workstation. Extracolonic findings were classified as minor, moderate, or major according to potential clinical importance. Patient records, with a follow-up time of about 3 years, were reviewed to determine final diagnoses.

RESULTS

Twenty-six (23%) of the patients had CT findings of major importance such as lymphadenopathy (n = 7), aortic aneurysm (n = 6), suspected solid hepatic masses (n = 5), and suspected solid renal masses (n = 4). Fifty-eight patients (52%) had findings of moderate importance such as gallstones (n = 16), indeterminate renal masses (n = 9), adrenal masses with benign appearance (n = 8), and hiatal hernia (n = 7). Forty-six patients (41%) had no or only minor findings, such as renal cysts (n = 34), renal calcifications (n = 19), and hepatic cysts (n = 14). Review of patient records showed that CT colonography contributed to the detection of major, previously unknown extracolonic disorders in 14 (13%) of the 111 patients.

CONCLUSION

Potentially important extracolonic findings were revealed in 23% of the patients, leading to additional diagnostic or therapeutic considerations. Some of these findings were clinically important, whereas others were previously known or led to unnecessary workup. This finding must be taken into account when CT colonography is considered for routine diagnostic workup or screening.

Preoperative T and N staging of colorectal cancer: accuracy of contrast-enhanced multi-detector row CT colonography--initial experience

PURPOSE

To evaluate the accuracy of contrast material-enhanced multi-detector row computed tomographic (CT) colonography for preoperative staging of colorectal cancer.

MATERIALS AND METHODS

Forty-one patients with colorectal carcinoma underwent preoperative contrast-enhanced multi-detector row CT colonography. Images were obtained in the arterial (start delay of 35 seconds) and portal venous (start delay of 70 seconds) phases. The arterial phase was focused on the suspected region of neoplasm, whereas the venous phase included the whole abdomen and pelvis. Two radiologists independently evaluated the depth of tumor invasion into the colorectal wall (T) and regional lymph node involvement (N) on transverse CT images alone and in combination with multiplanar reformations (MPRs). Disagreements were resolved by means of consensus. CT findings were compared with pathologic results, which served as the reference standard. Sensitivity, specificity, accuracy, positive predictive value, and negative predictive value were assessed. Differences in accuracy for T and N staging were assessed by using the McNemar test.

RESULTS

In T staging, overall accuracy was 73% when transverse images were evaluated alone and 83% when they were evaluated in combination with MPRs. This difference was not significant. N staging was associated with an overall accuracy of 59% with transverse images alone and 80% with combined transverse and MPR images (P <.01).

CONCLUSION

Contrast-enhanced multi-detector row CT colonography is an accurate technique for preoperative local staging of colorectal tumors.

Colorectal polyps and cancers in asymptomatic average-risk patients: evaluation with CT colonography

PURPOSE

To compare thin-section multi-detector row computed tomographic (CT) colonography with conventional colonoscopy in the evaluation of colorectal polyps and cancer in asymptomatic average-risk patients.

MATERIALS AND METHODS

Sixty-eight asymptomatic men (age > 50 years) scheduled to undergo screening colonoscopy were enrolled in this study. CT colonography was followed by conventional colonoscopy, performed on the same day. Supine and prone CT colonography were performed after colonic insufflation with room air. A gastroenterologist measured all polyps, which were categorized as 1-5, 6-9, or over 10 mm. Biopsy and histologic evaluation were performed of all polyps. CT colonography and colonoscopy results were compared for location, size, and morphology of detected lesions. Point estimates and 95% CIs were provided for specificity and sensitivity of CT by using results at conventional colonoscopy as the reference standard.

RESULTS

At colonoscopy, 98 polyps were identified in 39 patients; 21 (21.4%) of 98 were detected at CT colonography. Sensitivity was 11.5% (nine of 78) for polyps 1-5 mm, 52.9% (nine of 17) for polyps 6-9 mm, and 100% (three of three) for polyps over 10 mm. Results at colonoscopy were normal in 29 (42.6%) of 68 patients; at CT colonography, results were correctly identified as normal in 26 of these 29 patients. In one of these patients, a lesion larger than 10 mm was detected at CT colonography. The per-patient specificity of CT was 89.7% (26 of 29; 95% CI: 72.7%, 97.8%). The mean time for CT image interpretation was 9 minutes.

CONCLUSION

In patients at average risk for colorectal cancer, CT colonography is a sensitive and specific screening test for detecting polyps 10 mm or larger; the sensitivity for detecting smaller polyps is decreased. Examination findings can be interpreted in a clinically feasible amount of time.