Polyps Detection

Secondary prevention is aimed at preventing malignancy in a population that has already manifested an initial disease process. Secondary prevention includes procedures ranging from colonoscopic removal of precan-cerous polyps detected during screening colonoscopy to total colectomy for high-risk individuals (e.g., familial adenomatous polyposis). 

The more sensitive and convenient method of PolyP detection in situ is fluorescence microscopy using fluorochromes of the type 4/,6/-diamino-2-phenylindole.2HCl (DAPI), which is commonly used for DNA detection. At a high concentration (50 mg ml 1), it also stains PolyP granules and lipid inclusions (Allan and Miller, 1980 Tijssen et al, 1982 Streichan et al, 1990). DAPI-DNA fluorescence is blue-white, while DAPI-PolyP and DAPI-lipid fluorescence is yellow. The lipid fluorescence is weak and fades in a few seconds, while the PolyP granules appear bright yellow, thus allowing discrimination of the above types of cell inclusions (Streichan et al, 1990). 

Fig. 3.11. Reformatted sagittal CT image of a 55-year-old woman, who underwent MSCT for polyp detection of the colon...

Polyp detection in virtual colonography polyps are characterized by a mushroom-like extrusion of the colon wall, and can be detected by their shape they exhibit higher local 3D curvature" ( Gaussian curvature ) properties. These can be detected with methods from differential geometry (the theory of shapes and how to measure and characterize them), and highlighted as, e.g. colored areas as attention foci for further inspection. 

When using a primary 3D interpretation technique, navigation should be performed in both directions to maximise polyp detection unless the image is represented in such a way that the eye can observe behind obstacles (e.g. folds) as is the case with the virtual dissection or unfolded cube techniques that will be discussed in the next Chapters 19 and 20. The 3D method may be more accurate than 2D interpretation, especially for smaller lesions, but it is more time-consuming (Dachman et al. 1998 Macari et al. 2000 Rex et al. 1999). 

Lefere PA, Gryspeerdt SS, Dewyspelaere J et al (2002) Dietary fecal tagging as a cleansing method before CT colonography initial results polyp detection and patient acceptance. Radiology 224 393-403... 

Summers RM, Yao J, Pickhardt PJ et al (2005) Computed tomographic virtual colonoscopy computer-aided polyp detection in a screening population. Gatroenterology 129 1832-1844... 

Taylor SA, Halligan S, Burling D et al (2006a) Computer-Assisted Reader Software Versus Expert Reviewers for Polyp Detection on CT Colonography. AJR Am J Roentgenol 186 696-702... 

Pickhardt PJ, Taylor AJ, Gopal DV (2006) Surface visualization at 3D endoluminal CT colonography degree of coverage and implications for polyp detection. Gastroenterology 130 1582-1587... 

The longer exposure time of abnormalities may result in less perceptive errors made by the reviewer. Lee and Pickhardt compared the exposure time of 20 polyps in both an axial 2D method and a conventional endoluminal 3D method. They concluded that the opportunity of polyp detection, including both exposure time and distance of polyp visualization, is significantly greater for the 3D endoluminal display. 

In a study conducted by Vos et al. (2003) the unfolded cube display method was compared to a conventional 3D (two-directional) review approach. Two blinded trained observers reviewed a selected population of 30 patients twice, with a median interval of more than 11 weeks between the reviews. The observers first used the unfolded cube display method for polyp detection, and then, in random order, the conventional 3D method. The viewing angle in the conventional review method was set to 120° to compromise between image distortion and surface visibility. Surface visibility, evaluation time per patient, as well as sensitivity and specificity, were compared between both approach. 

Jerebko AK, Malley JD, Eranaszek M et al (2005) Support vector machines committee classification method for computer-aided polyp detection in CT coionography. Acad Radiol 12 479-486... 

Pickhardt PJ, Lee AD, McFarland EG et al (2005) Linear polyp measurement at CT colonography in vitro and in vivo comparison of two-dimensional and three-dimensional displays. Radiology 236 872-878 Pickhardt PJ, Taylor AJ, Gopal DV (2006) Surface visualization at 3D endoluminal CT colonography degree of coverage and implications for polyp detection. Gastroenterology 130 1582-1587... 

Suzuki K, Yoshida H, Nappi J et al (2006) Massive-training artificial neural network (MTANN) for reduction of false-positives in computer-aided detection of polyps suppression of rectal tubes. Medical Physics 10 3814-3824 Taylor SA, Halligan S, Burling D et al (2006a) Computer-assisted reader software versus expert reviewers for polyp detection on CT colonography. AJR Am J Roentgenol 186 696-702... 

CT colonography as a screening tool for colon cancer continues to improve and a credible alternate and non-invasive tool to evaluate the colon now exists. Initial studies in the mid- to late 1990s demonstrated sensitivities of polyp detection ranging from 50 to 90% for polyps larger than 1 cm with specificities ranging from 70 to 90% (Van Dam et al. 2004). As the technology and application of... 

Polyp detection Lower abdominal pain Toxic megacolon... 

---