Detection of colorectal lesions: lower-dose multi-detector row helical CT colonography compared with conventional colonoscopy

PURPOSE: To compare the performance of lower-dose multi-detector row helical computed tomographic (CT) colonography with that of conventional colonoscopy in the detection of colorectal lesions. MATERIALS AND METHODS: One hundred fifty-eight patients underwent multi-detector row helical CT colonography (beam collimation, 4 x 2.5 mm; table feed, 17.5 mm/sec; voltage, 140 kV; and effective dose, 10 mAs) followed by conventional colonoscopy. Conventional colonoscopy served as the reference standard. Two radiologists interpreted CT colonographic images to assess the presence of polyps or carcinomas. Sensitivity was calculated on both a per-polyp and a per-patient basis. In the latter, specificity and positive and negative predictive values were also calculated. Weighted CT dose index was calculated on the basis of measurements obtained in a standard body phantom. Effective dose was estimated by using commercially available software. RESULTS: CT colonography correctly depicted all 22 carcinomas (sensitivity, 100%) and 52 of 74 polyps (sensitivity, 70.3%). Sensitivity for detection was 100% in all 13 polyps 10 mm or larger in diameter, 83.3% in 20 of 24 polyps 6-9 mm, and 51.3% in 19 of 37 lesions 5 mm or smaller. With regard to the per-patient analysis, CT colonography had a sensitivity of 96.0%, a specificity of 96.6%, a positive predictive value of 94.1%, and a negative predictive value of 97.7%. The total weighted CT dose index for combined prone and supine acquisitions was 2.74 mGy. The simulated effective doses for complete CT colonography were 1.8 mSv in men and 2.4 mSv in women. CONCLUSION: Lower-dose multi-detector row helical CT colonography ensures substantial dose reduction while maintaining excellent sensitivity for detection of colorectal carcinomas and polyps larger than 6 mm in diameter.     

Colorectal polyps: detection with low-dose multi-detector row helical CT colonography versus two sequential colonoscopies

PURPOSE: To prospectively evaluate the diagnostic accuracy of low-radiation-dose computed tomographic (CT) colonography for detection of colorectal polyps by using two sequential colonoscopies, with the second colonoscopy as the reference standard. MATERIALS AND METHODS: The study was local ethics committee approved, and all patients gave written informed consent. Colonographic images were acquired by using a low-dose multi-detector row CT protocol (effective milliampere-second setting, 10 mAs). Three observers interpreted the CT colonographic data separately and independently by using a two-dimensional technique. Initial conventional colonoscopy was performed by an endoscopist unaware of the CT colonographic findings. Second colonoscopy performed within 2 weeks by a colonoscopist aware of both the CT colonographic and the initial colonoscopic findings served as the reference standard. The sensitivities of CT colonography and initial colonoscopy were calculated on a per-polyp and a per-patient basis. Specificities and positive and negative predictive values also were calculated on a per-patient basis. RESULTS: Eighty-eight patients underwent CT colonography and initial conventional colonoscopy on the same day. Per-polyp sensitivities were 62% and 83% for CT colonography and initial colonoscopy, respectively. Sensitivities for detection of polyps 6 mm in diameter or larger were 86% and 84% for CT colonography and initial colonoscopy, respectively. Initial colonoscopy failed to depict 16 polyps, six of which were correctly detected with CT colonography. For identification of patients with polyps 6 mm in diameter or larger, CT colonography and initial colonoscopy, respectively, had sensitivities of 84% and 90%, specificities of 82% and 100%, positive predictive values of 70% and 100%, and negative predictive values of 91% and 95%. CONCLUSION: Low-dose CT colonography compares favorably with colonoscopy for detection of colorectal polyps 6 mm in diameter or larger, with markedly decreased performance for detection of polyps 5 mm in diameter or smaller.     

CT colonography at different radiation dose levels: feasibility of dose reduction

PURPOSE: To investigate the sensitivity and specificity of polyp detection and the image quality of computed tomographic (CT) colonography at different radiation dose levels and to study effective doses reported in literature on CT colonography. MATERIALS AND METHODS: CT colonography and colonoscopy were performed with 100 mAs in 50 consecutive patients at high risk for colorectal cancer; 50- and 30-mAs CT colonographic examinations were simulated with controlled addition of noise to raw transmission measurements. One radiologist randomly evaluated all original and simulated images for the presence of polyps and scored image quality. Differences in image quality were assessed with the Wilcoxon rank test. Scan protocols from the literature and recent (unpublished) updates were collected. RESULTS: In nine of 10 patients with polyps 5 mm in diameter or larger (sensitivity, 90%) and in seven of 17 patients with polyps smaller than 5 mm, polyps were correctly identified with CT colonography at all dose levels. Specificity for patients without polyps 5 mm or larger was 53%-60% at all dose levels and for patients without any polyps was 26% (at 100 and 50 mAs) and 48% (at 30 mAs). Image quality decreased significantly as the dose level decreased. The median effective doses (supine and prone positions) calculated from protocols reported in the literature and updates were 7.8 and 8.8 mSv, respectively. CONCLUSION: Although image quality decreases significantly at 30 mAs (3.6 mSv), polyp detection remains unimpaired. The median dose for CT colonography at institutions that perform CT colonographic research is currently 8.8 mSv.     

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.     

CT colonography: single- versus multi-detector row imaging

PURPOSE: To compare respiratory artifacts, colonic distention, and polyp detection at computed tomographic (CT) colonography by using single- and multi-detector row helical CT systems. MATERIALS AND METHODS: A total of 237 consecutive patients received subcutaneously administered glucagon and underwent prone and supine CT colonography with single-detector row CT (n = 77) and multi-detector row CT (n = 160), followed by colonoscopy. Examination results were graded for colonic distention, respiratory artifacts, and polyp depiction by two radiologists working independently. RESULTS: Suboptimal colonic distention was significantly more common with single-detector row CT and was present in at least one segment in 52% (40 of 77 patients) of examinations versus only 19% (30 of 160 patients) with multi-detector row CT (P <.001). Mild respiratory artifacts were present in 61% (47 of 77 patients) of single-detector row CT examinations versus only 16% (26 of 160 patients) of multi-detector row CT examinations (P <.001). Depiction of polyps larger than 10 mm was 89% (eight of nine polyps) for single-detector row CT and 80% (eight of 10 polyps) for multi-detector row CT (P >.05). CONCLUSION: CT colonography performed with multi-detector row CT significantly improved the demonstration of colonic distention and depicted fewer respiratory artifacts compared with single-detector row CT. No significant differences in the depiction of polyps larger than 10 mm were demonstrated between single- and multi-detector row CT for a small number of polyps. Studies with a larger prevalence of clinically important polyps are needed for further evaluation of differences in polyp detection.     

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

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

Feasibility of ultra-low-dose multislice CT colonography for the detection of colorectal lesions: preliminary experience

Our objective was to evaluate the feasibility of ultra-low-dose scanning for multislice CT colonography in the detection of colorectal lesions. Twenty-seven patients (14 men, 13 women) with clinical indication for conventional colonoscopy were recruited. Multislice spiral CT (Somatom Plus 4 Volume Zoom, Siemens, Germany) examinations were performed after standard oral colonoscopic preparation and colonic distension with room air. Images were acquired using 2.5-mm collimation, 3.0-mm slice thickness, standard reconstruction kernel, 140 kVp, and 10 mAs. Supine and prone acquisitions were obtained in all patients. Images were analyzed on a workstation by two gastrointestinal radiologists. Conventional colonoscopy was performed on the same day in all patients and represented the standard of reference. Total radiation exposure was also calculated. All colorectal cancers were correctly identified at CT colonography (9 of 9, sensitivity 100%). The CT colonography also detected 10 of 12 polyps (overall sensitivity 83.3%). Based on polyp diameter, the sensitivity for the detection of polyps 10 mm or larger was 100% (3 of 3); between 6 and 9 mm, 100% (3 of 3); and 5 mm or smaller, 66.6% (4 of 6). Total radiation exposure for prone and supine acquisitions combined was 1.7 mSv (for men) and 2.3 mSv (for women). Although preliminary, our experience suggests that ultra-low-dose scanning for multislice CT colonography is feasible. This technique provides a sensitivity comparable to that of previous experiences with CT colonography but with a 40–70% reduction of the radiation dose delivered to patients. Electronic Publication     

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.     

Colorectal cancer: role of CT colonography in preoperative evaluation after incomplete colonoscopy

PURPOSE: To evaluate computed tomographic (CT) colonography in patients with clinical suspicion of colorectal cancer and in whom colonoscopy was incomplete. MATERIALS AND METHODS: After incomplete colonoscopy, 34 patients underwent CT colonography before and after intravenous injection of iodinated contrast agent, in supine and prone positions. Twenty patients with no evidence of colon cancer after complete colonoscopy were included as a control group. Sensitivity and specificity of CT colonography were determined for detection of cancers, polyps, and metastases to liver. RESULTS: In 29 patients, surgery revealed 30 colorectal cancers (three synchronous cancers) and two ischemic lesions of the descending colon. Colonoscopy missed 10 colorectal cancers and three synchronous cancers; all were detected with CT colonography. Sensitivity and specificity for detection of colorectal cancer were 56% and 92%, respectively, for incomplete colonoscopy and 100% and 96%, respectively, for CT colonography (P <.01). Sensitivity and specificity of CT colonography in detection of polyps were 86% and 70%, respectively, for diameters of 5 mm or less; 100% and 80%, respectively, for 5-10-mm diameters; and 100% for diameters greater than 10 mm. Spiral CT of the liver revealed four metastases (2-5 cm); sensitivity and specificity were 100% and 43% for nonenhanced scans and 100% for contrast-enhanced scans (P <.01). CONCLUSION: In this selected group of patients, CT colonography provided complete information to properly address surgery of colorectal cancer and treatment of liver metastases.     

CT colonography using 16-MDCT in the evaluation of colorectal cancer

OBJECTIVE: This study evaluated CT colonography as a method to stage colorectal cancer and detect polyps and cancers in patients with the disease. SUBJECTS AND METHODS: Fifty-one consecutive patients thought to have colorectal cancer underwent CT colonography, following a colonoscopy, in both the prone and supine positions. The transverse CT images, multiplanar reconstruction, volume rendered, and virtual colonoscopy images, were independently interpreted by two radiologists. Disagreements were resolved by consensus. The diagnostic accuracy of TNM staging was calculated, and the sensitivity of CT colonography for the detection of cancers and polyps, compared with that of colonoscopy, was calculated using repeated colonoscopic and surgical findings as reference standards. The technical result for distention was also graded. RESULTS: In the 51 patients, surgery and follow-up colonoscopy revealed 21 colorectal cancers (one synchronous cancer) and 41 polyps. The diagnostic accuracies of CT colonography for TNM staging were 95%, 85%, and 100% for tumor, node, and metastasis, respectively. The sensitivity of both CT colonography and initial colonoscopy for cancer detection was 100%. The overall sensitivities of CT colonography and initial colonoscopy for polyp detection were 90% and 78%, respectively (p = 0.001). The sensitivities of CT colonography for detecting polyps of 5 mm or smaller, of 6-9 mm, and of 10 mm or larger were 84%, 94%, and 100%, respectively. The mean overall technical results for the supine and prone positions were ranked as 2.80 (SD, +/- 0.4) and 2.78 (+/- 0.4), respectively, but were without statistical significance (p = 0.781). CONCLUSION: Our preliminary data suggest that for patients with clinical suspicion of colorectal cancer, CT colonoscopy is valuable in staging the tumor and in detecting additional polyps or cancers in areas not evaluated by conventional colonoscopy.     

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.     

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

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

Colorectal polyps: detection with dark-lumen MR colonography versus conventional colonoscopy

PURPOSE: To prospectively compare dark-lumen magnetic resonance (MR) colonography with conventional colonoscopy in the detection of colorectal polyps. MATERIALS AND METHODS: Local ethical committee approval and informed consent were obtained. One hundred consecutive patients (56 men, 44 women; mean age +/- standard deviation, 67.7 years +/- 14.7; range, 25-82 years) who were referred for conventional colonoscopy from January 2003 to January 2004 underwent MR colonography and conventional colonoscopy after standard precolonoscopic bowel cleansing. Colonoscopy was performed immediately after MR colonography. For MR colonography, the colon was filled with approximately 2000 mL of tap water. Imaging was performed with a 1.5-T MR unit with patients in the prone position. A T1-weighted three-dimensional volumetric interpolated breath-hold sequence was performed before and 75 seconds after intravenous administration of 0.2 mmol gadobenate dimeglumine per kilogram of body weight. Results of MR colonography were analyzed on a per-polyp and per-patient basis. Findings at colonoscopy were used as the reference for determining accuracy, sensitivity, specificity, and positive and negative predictive values of MR colonography. RESULTS: Of 100 patients recruited for study, 92 (52 men, 40 women; mean age, 61.5 years +/- 14.5; range, 25-82 years) underwent complete MR and conventional colonoscopy examinations. Forty-three of the 92 patients (47%) had normal findings at conventional colonoscopy. In the other 49 patients (53%), conventional colonoscopy depicted 107 polyps (82 adenomas, 25 hyperplastic polyps) and seven carcinomas. At per-polyp analysis, sensitivity of MR colonography in the detection of adenomatous polyps was 100% for polyps at least 10 mm in diameter and 84.2% for polyps 6-9 mm in diameter. At per-patient analysis, the accuracy of MR colonography was 93.1% (sensitivity, 89%; specificity, 96%) if detection of adenomatous polyps of all sizes was considered. CONCLUSION: Dark-lumen MR colonography is a promising modality with high accuracy for detecting colorectal polyps larger than 5 mm in diameter.     

PET/CT colonography in patients with colorectal polyps: a feasibility study

PURPOSE: To examine: (1) the feasibility of PET/CT colonography (PET/CTc) in patients with colorectal polyps; (2) the impact of metabolic information on CTc interpretation and, conversely, the impact of morphological information on PET characterisation of focal colorectal uptake. METHODS: Ten patients with colorectal polyps underwent PET/CTc, followed within 3 h by therapeutic conventional colonoscopy (CC). A radiologist and a nuclear medicine physician analysed the PET/CTc images. The agreement of morphological and metabolic information in the colon and rectum was evaluated. The sensitivity and specificity of PET, CT and PET/CT were calculated for colorectal polyps. RESULTS: Seventeen polypoid lesions were identified at CC: six< or =5 mm, six between 6 and 9 mm, and five > or =10 mm (four hyperplastic polyps, 11 tubular adenomas, one adenocarcinoma and one submucosal lipoma). A total of 20 scans (supine and prone) were performed in the ten patients: the agreement of morphological and metabolic information was excellent in 17 scans, good in two and moderate in one. PET/CTc showed a sensitivity of 91% for lesions > or =6 mm and a specificity of 100%. The metabolic information did not disclose any further polyps missed on CTc. The morphological information permitted correct classification of all eight instances of focal radiotracer uptake. CONCLUSION: PET/CTc is a feasible study. Adding a colonographic protocol to PET/CT images seems to allow correct characterisation of all cases of colorectal focal radiotracer uptake. The metabolic information does not seem to increase the accuracy of CTc.     

Automated polyp detection at CT colonography: feasibility assessment in a human population

PURPOSE: To test the feasibility of and improve a computer algorithm to automatically detect colonic polyps in real human computed tomographic (CT) colonographic data sets. MATERIALS AND METHODS: Twenty patients with known polyps underwent CT colonography in the supine position. CT colonographic data were processed by using a shape-based algorithm that depicts masses that protrude into the lumen. We studied nine shape criteria and three isosurface threshold settings. Results were compared with those of conventional colonoscopy performed the same day. RESULTS: There were 50 polyps (28 were > or =10 mm in size; 12, 5-9 mm; 10, <5 mm). The sensitivity with optimal settings for detecting polyps 10 mm or greater was 64% (18 of 28). Sensitivity improved to 71% (10 of 14) for polyps 10 mm or greater in well-distended colonic segments. Performance decreased for polyps less than 10 mm, poorly distended colonic segments, and other shape algorithms. There was a mean of six false-positive lesion sites per colon. These sites were reduced 39% to 3.5 per colon by sampling CT attenuation at the lesion site and discarding sites having attenuation less than a threshold. CONCLUSION: Automated detection of colonic polyps, especially clinically important large polyps, is feasible. Colonic distention is an important determinant of sensitivity. Further increases in sensitivity may be achieved by adding prone CT colonography.     

Optimization of CT colonography technique: prospective trial in 180 patients

PURPOSE: To assess the added benefits of prone positioning in addition to supine positioning and oral iodinated contrast medium for help in the detection of colonic polyps at computed tomographic (CT) colonography. MATERIALS AND METHODS: CT colonography was performed in prone and supine positions in 180 patients with polyps or risk factors for colonic neoplasia. Patients were randomly assigned to receive a standard bowel preparation or a standard preparation plus oral iodinated contrast medium. One radiologist interpreted supine images alone, and another analyzed supine and prone images. All patients subsequently underwent colonoscopy. RESULTS: At colonoscopy, 121 large (> or =1-cm-diameter) polyps and 142 smaller (0.5-0.9-cm) polyps were identified. Prone positioning resulted in increased sensitivity for identification of patients with large (> or =1-cm) polyps (increase from 70% to 85%, P: =.004) and of patients with polyps 0.5 cm or larger (increase from 75% to 88%, P: <.005), with no change in specificity. Use of oral contrast medium did not significantly improve polyp detection even in the subset of patients in whom colonic fluid attenuation was markedly increased. CONCLUSION: Acquisition and review of supine and prone CT colonographic images significantly improves the ability to identify patients with polyps 0.5 cm in diameter or larger. Administration of oral iodinated contrast medium does not significantly improve polyp detection.     

Multi-detector row CT colonography: effect of collimation, pitch, and orientation on polyp detection in a human colectomy specimen

PURPOSE: To investigate the effects of orientation, collimation, pitch, and tube current setting on polyp detection at multi-detector row computed tomographic (CT) colonography and to determine the optimal combination of scanning parameters for screening. MATERIALS AND METHODS: A colectomy specimen containing 117 polyps of different sizes was insufflated and imaged with a multi-detector row CT scanner at various collimation (1.25 and 2.5 mm), pitch (3 and 6), and tube current (50, 100, and 150 mA) settings. Two-dimensional multiplanar reformatted images and three-dimensional endoluminal surface renderings from the 12 resultant data sets were examined by one observer for the presence and conspicuity of polyps. The results were analyzed with Poisson regression and logistic regression to determine the effects of scanning parameters and of specimen orientation on polyp detection. RESULTS: The percentage of polyps that were detected significantly increased when collimation (P =.008) and table feed (P =.03) were decreased. Increased tube current resulted in improved detection only of polyps with a diameter of less than 5 mm. Polyps of less than 5 mm were optimally depicted with a collimation of 1.25 mm, a pitch of 3, and a tube current setting of 150 mA; polyps with a diameter greater than 5 mm were adequately depicted with 1.25-mm collimation and with either pitch setting and any of the three tube current settings. Small polyps in the transverse segment (positioned at a 90 degrees angle to the z axis of scanning) were significantly less visible than those in parallel or oblique orientations (P <.001). The effective radiation dose, calculated with a Monte Carlo simulation, was 1.4-10.0 mSv. CONCLUSION: Detection of small polyps (<5 mm) with multi-detector row CT is highly dependent on collimation, pitch, and, to a lesser extent, tube current. Collimation of 1.25 mm, combined with pitch of 6 and tube current of 50 mA, provides for reliable detection of polyps 5 mm or larger while limiting the effective radiation dose. Polyps smaller than 5 mm, however, may be poorly depicted with use of these settings in the transverse colon.     

Use of multidetector-row CT colonography for detection of colorectal neoplasia in patients referred via the Department of Health "2-Week-wait" initiative

AIM: Patients referred under the Department of Health 2-week wait initiative with symptoms of colorectal cancer frequently undergo whole-colon examination. We investigated the use of computed tomography (CT) colonography as an alternative to colonoscopy in this scenario. MATERIALS AND METHODS: Fifty-four consecutive patients, referred via the 2-week wait initiative and scheduled for colonoscopy, consented to undergo multidetector CT colonography immediately before endoscopy. The site and morphology of any polyp or cancer detected by CT was noted and comparison made with subsequent colonoscopy. RESULTS: Colonoscopy detected polyps or cancer in 29 patients (53.7%). CT colonography prospectively detected 18 of 41 (44%) polyps of 1-5 mm, three of four (75%) polyps of 6-9 mm, four of four (100%) polyps 10 mm or larger, and five of six (83%) cancers. The missed cancer occurred early in the series and was a perceptive error. The overall sensitivity, specificity, positive predictive value and negative predictive value of CT colonography for cancer and polyps 10 mm or greater on a per patient basis were 90, 100, 100 and 98%, respectively. CT detected one renal cancer and one colonic cancer, initially missed due to incomplete colonoscopy. CONCLUSION: CT colonography is a robust technique for investigation of symptomatic patients. The learning curve must be overcome for optimal performance.     

Feasibility study of computed tomography colonography using limited bowel preparation at normal and low-dose levels study

The purpose was to evaluate low-dose CT colonography without cathartic cleansing in terms of image quality, polyp visualization and patient acceptance. Sixty-one patients scheduled for colonoscopy started a low-fiber diet, lactulose and amidotrizoic-acid for fecal tagging 2 days prior to the CT scan (standard dose, 5.8–8.2 mSv). The original raw data of 51 patients were modified and reconstructed at simulated 2.3 and 0.7 mSv levels. Two observers evaluated the standard dose scan regarding image quality and polyps. A third evaluated the presence of polyps at all three mSv levels in a blinded prospective way. All observers were blinded to the reference standard: colonoscopy. At three times patients were given questionnaires relating to their experiences and preference. Image quality was sufficient in all patients, but significantly lower in the cecum, sigmoid and rectum. The two observers correctly identified respectively 10/15 (67%) and 9/15 (60%) polyps ≥10 mm, with 5 and 8 false-positive lesions (standard dose scan). Dose reduction down to 0.7 mSv was not associated with significant changes in diagnostic value (polyps ≥10 mm). Eighty percent of patients preferred CT colonography and 13% preferred colonoscopy (P<0.001). CT colonography without cleansing is preferred to colonoscopy and shows sufficient image quality and moderate sensitivity, without impaired diagnostic value at dose-levels as low as 0.7 mSv.     

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

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