[Effect of Matrix Size on Lesion Detectability in CT Colonography].

OBJECTIVES: While computed tomography colonography (CTC) has become a non-invasive alternative to traditional colonoscopy, superficial lesions tend to be harder to detect, with reports of lesions <2 mm in height being missed. Therefore, for the evaluation of lesion detectability using CTC, optimizing scan parameters becomes important. In this study, we investigate the effect of the reconstructed matrix size from CTC on the lesion conspicuity. METHODS: A CTC phantom was scanned, and images were reconstructed with 512, 768 and 1024 matrix sizes with the same raw data. The image data in each matrix size were compared in terms of physical assessment of the task-transfer function (TTF) and the noise power spectrum (NPS), and of visual assessment using Scheffé's paired comparison. RESULTS: Comparing 768 and 1024 matrix sizes with that of 512, NPS was higher in high-frequency components. On the other hand, TTF was improved using these larger matrix sizes along with significant statistical differences in the visual assessment. CONCLUSION: Larger matrix sizes (768 and 1024) improve the lesion conspicuity, thereby helping to detect superficial and small lesions (size<2 mm) in CTC.

Efficacy of Barium-Based Fecal Tagging for CT Colonography: a Comparison between the Use of High and Low Density Barium Suspensions in a Korean Population - a Preliminary Study

OBJECTIVE: This preliminarily study was designed to determine and to compare the efficacy of two commercially available barium-based fecal tagging agents for CT colonography (CTC) (high-density [40% w/v] and low-density [4.6% w/v] barium suspensions) in a population in Korea. MATERIALS AND METHODS: In a population with an identified with an average-risk for colorectal cancer, 15 adults were administered three doses of 20 ml 40% w/v barium for fecal tagging (group I) and 15 adults were administered three doses of 200 ml 4.6% w/v barium (group II) for fecal tagging. Excluding five patients in group I and one patient in group II that left the study, ten patients in group I and 14 patients in group II were finally included in the analysis. Two experienced readers evaluated the CTC images in consensus regarding the degree of tagging of stool pieces 6 mm or larger. Stool pieces were confirmed with the use of standardized CTC criteria or the absence of matched lesions as seen on colonoscopy. The rates of complete fecal tagging were analyzed on a per-lesion and a per-segment basis and were compared between the patients in the two groups. RESULTS: Per-lesion rates of complete fecal tagging were 52% (22 of 42; 95% CI, 37.7-66.6%) in group I and 78% (28 of 36; 95% CI, 61.7-88.5%) in group II. The difference between the two groups did not reach statistical significance (p = 0.285). The per-segment rates of complete tagging were 33% (6 of 18; 95% CI, 16.1%-56.4%) in group I and 60% (9 of 15; 95% CI, 35.7%-80.3%) in group II; again, the difference between the two groups did not reach statistical significance (p = 0.171). CONCLUSION: Barium-based fecal tagging using both the 40% w/v and the 4.6% w/v barium suspensions showed moderate tagging efficacy. The preliminary comparison did not demonstrate a statistically significant difference in the tagging efficacy between the use of the two tagging agents, despite the tendency toward better tagging with the use of the 4.6% w/v barium suspension.

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.

Efficacy of CT Colonography in the Detection of Colorectal Polypoid Lesions

PURPOSE: We wished to compare CT colonography with conventional colonoscopy for the detection of colorectal polypoid lesions, and we wanted to evaluate the role of IV contrast-enhanced CT colonography for the differentiation between benign polypoid lesions and malignant polypoid lesions. MATERIALS AND METHODS: Thirty-four consecutive patients underwent CT colonography prior to conventional colonoscopy. Precontrast prone-position CT images and postcontrast supine position CT images were obtained and the virtual colonoscopic images were reconstructed. Axial, sagittal and coronal images with virtual colonoscopic images were prospectively interpreted for the presence, size and morphologic features of colorectal polypoid lesions, and then these findings were compared with the colonoscopic findings. The degree of enhancement of colorectal polypoid lesions was measured by subtracting the attenuation values obtained with precontrast and postcontrast CT images for the differentiation of benignity and malignancy of the colorectal polypoid lesions. RESULTS: Among 75 colorectal polypoid lesions identified on conventional colonoscopy, 49 neoplasms were found on CT colonography, and the overall detection rate was 65.3%. Detection rate of lesions smaller than 10 mm was 52.1% (24/46), and the detection rate for lesions equal to or larger than 10 mm was 86.2% (25/29). Morphologic features of the sessile type lesions on CT colonography were well correlated with those noted on colonoscopy, but the stalks were not identified in 6 of 13 polyps on CT colonography. There was no statistical correlation between benignity and malignancy and the degree of contrast enhancement on CT colonography. CONCLUSION: CT colonography is a useful modality for the detection of colorectal polypoid lesions equal to or larger than 10mm, and it well demonstrates the morphologic features, except for the stalk of pedunculated polyps. However, CT colonography cannot differentiate benignity from malignancy.