ABSTRACT
Provided that the bowel is carefully cleansed, virtual colonoscopy permits a safe, reliable and painfree diagnosis of the large bowel. It requires distension of the bowel with ambient air. Contraindications include pregnancy, acute inflammation of the bowel and recent surgery. Tumors and large polyps (10 mm and more) can be diagnosed with certainty, while polyps measuring 5 mm and more are detected with a high degree of sensitivity. It goes without saying that virtual colonoscopy does not allow for the taking of biopsy material or the performance of therapeutic measures, so that positive or suspicious findings must be clarified by conventional colonoscopy. In principle, virtual colonoscopy is also suitable for use as a screening procedure. Whether the radiation exposure associated with the conventional examination protocol can be considered acceptable for screening purposes is questionable. However, using mathematical means, the radiation dose can be reduced to one-tenth of the usual dose.
Subject(s)
Colonic Polyps/diagnosis , Colonoscopy , Colorectal Neoplasms/diagnosis , Imaging, Three-Dimensional , Tomography, X-Ray Computed , User-Computer Interface , Colon/pathology , Colonic Polyps/pathology , Colorectal Neoplasms/pathology , Humans , Mass Screening , Patient Acceptance of Health Care , Sensitivity and SpecificityABSTRACT
SUBJECT: Using multi-slice computed tomography (MSCT) large body areas can scanned with high spatial resolution. In this study, MSCT was employed for virtual colonoscopy in various pathologies of the colon. MATERIALS AND METHODS: For MSCT a Somatom Plus 4, Volume Zoom scanner, (Siemens, Forchheim) was employed, equipped with four parallel detector rows. Twenty-five patients were included in this trial, prior to colonoscopy or partial colon resection. After cleaning the colon, distension was achieved by insufflation of room air using a rectal tube. The parameters of acquisition and reconstruction were as follows: collimation 4 x 1 mm and 4 x 2.5 mm respectively; tube charge per slice: 140-160 mAs; pitch 5-6; i.v. contrast medium: 120 ml Ultravist 300 (Schering) with a flow rate of 3 ml/s; delay: 35 s. For 3D reconstruction we used edge-enhanced volume rendering, virtual colonoscopy and extraluminal views of volume-rendered images. RESULTS: Nine polyps and four of five colon carcinomas were detected using MSCT virtual colonoscopy. In three patients with ulcerative colitis virtual coloscopy revealed morphological alterations compatible with this disease. In two of four patients with multiple diverticula of the colon the true extent of the disorder could be assessed in virtual colonoscopy. CONCLUSION: Utilizing virtual MSCT colonoscopy polyps and cancer of the colon can be reliably detected, if proper cleaning and distension is provided. On axial images alone smaller polyps may be assessed. The high z-axis resolution of MSCT offers superior conditions for CT-based virtual colonoscopy.
