CT Colonography: Experiments And Clinical Application

Computerd tomographic colonography(CTC) represents a novel noninvasive technique for examining the colon. It combines a volumetric data set created by means of helical CT with modern computer software used to generate two- and three-dimensional images of the colon. The authors of some resent studies have estimated the sensitivity of current methods of CT colonography for the detection of colorectal polyps and have suggested that the technique will be competitive with other full structural colonic screening examinations. Before large clinical trials are conducted in screenig population, the methods for CT colonography must be optimized and standardized to maximize its ability to help detect colonic neoplasia. The purpose of this study was to find out optimal scanning parameters, accumulate postprocessing experience and evaluate the detectability of colon neoplasia with CT colonography.Ten 25-cm-long segments of pig colon and eight colectomy specimens with simulated polyps underwent volum scanning at different parameters. The images were downloaded to AdvantageWindows 3.1 workstation for postprocessing .The effect of different scanning parameters and postprocessing methods on image quality and sensitivity for detecting simulated polyps were compared and analysized. We also evaluated the effect of positive contrast media of different concentration on sensitivity for detecting simulated polyps .29 patients with colon neoplasia underwent volume scanning in supine and prone positions. 58 data sets with colon cancer or polyps were obtained from thin-section helical CT of the abdomen and pelvis and then downloaded to Advantage Windows 3.1 workstation for postprocessing. CTVC(CT Virtual Colonoscopy), MPR (Mulitiplanar Reformation) +Axial ,SSD (Shaded Surface Display) + Raysum images were generated by using different software in workstation. The results were compared with the findings of electrical colonoscopy or/and surgery and correlated with pathologic outcome. Furthermore, we postprocessed six volumetric data sets on Advantage Windows 4.1 workstation to compare the capability of colon dissected panoramic technique and CTVC of diaplaying colon neoplasia .The results indicated that the image quality of CT colonography and the sensitivity for detecting simulated polyps improved with the decrease of collimation and pitch. The optimal angle of the colon lumen to the gantry was 90 . CT colonography was superior to other imaging methods in displaying the asymmetry folds and the lesion surface and had higher sensitivity than that of other imaging methods. But the combination of CTVC with other imaging methods couldimprove the sensitivity. In addition, the image quality of colon with gas was better than that of positive contrast media.The correct rate of identifying pathologic patterns of colon carcinoma with MPR + Axial,CTVC and SSD + Raysum were 71.74%, 89.13% and 58.70% respectively. The accuracy of showing the circumferential extension of colon carcinoma were 100%, 82.61% and 73.91% respectively. The accuracy of measuring the sizes of colon carcinoma were 80.43%, 60.87% and 100% respectively. The sensitivity for detecting colon polyps were 53.03%, 77.27% and 46.97%. CTVC helped identify all 18 occlusive carcinoma and demonstrated two cancers and two polyps in the proximal colon. Panoramic technique displayed colon cancer and colon polyps more directly and rapidly. The interpretation time of panoramic technique reduced remarkably.In conclusion, the performance of CTC had a close relationship with the scanning parameter. For single slice spiral CT, considering clinical application, the optimal scanning parameter was 5mm collimation, 1.5 pitch and the colon filled gas. MPR + Axial was superior to other postprosessing methods in showing the circumferential extension of colon carcinoma, CTVC most correct in identifying the tumor patterns and providing information of the proximal colon in occlusive colon carcinoma, and SSD + Raysum most suitable to measure the tumor sizes. The panoramic technique...