Until recently, many studies on virtual colonoscopy (CT- or MR-colonoscopy) have shown different results [181-188]. The sensitivity is very low with lesions less than 1 cm and with flat lesions, while the specificity for adenoma varies from 69 to 99%.
Many technical factors could influence exam performances: bowel preparation, type of scan and the algorithm of rebuilt software. However, the lack of studies on general population, and the costs and discomfort of the technique  do not recommend virtual colonoscopy as a screening tool.
Normal colon cells and their DNA pass into bowel every day. Chromosomal abnormalities or DNA mutations can suggest that a colorectal polyp or cancer is present. These mutations can be detected by processing the stool. The Authors of a recent trial  comparing a panel of faecal DNA markers and Hemoccult II as screening tests for CRC in an average-risk, asymptomatic population conclude that the faecal DNA panel appears to be more sensitive than Hemoccult II for adenomas containing high-grade dysplasia and for the detection of early (TNM stage I, II) CRC.
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