CT Colonography (Virtual Colonoscopy): The Present and the Future

摘要

CT colonography (CTC), also known as virtual colonoscopy, is a recent radiologic technique enabling the detection of tumoral lesions in the colon. Double contrast barium enema, has lost most of its adherents, and CTC constitutes a real opportunity for radiologists to play a preponderant role in the diagnosis and treatment of colorectal cancer and adenoma. CTC has dramatically evolved through the refinement of existing techniques as well as the introduction of new techniques such as fecal tagging, the use of carbon dioxide to inflate the colon, multi-detector row CT scanners, the use of ultra-low dose scan protocols, and computer-aided detection systems. These technical improvements have helped both the radiologists and the patients. The successful performance of CTC is dependent on several technical factors; fecal tagging, which improves patients' compliance by allowing reduced bowel preparation and facilitates the differentiation of true polyps from residual feces, resulting in the improvement of diagnostic accuracy, automated CO_2 insufflation, which is more efficient and safer in colonic distention compared to manual room air insufflation, and the performance of CTC using a thin collimation of ≤3 mm with a reconstruction increment of ≤3 mm and a low radiation dose of 30 mAs to 50 mAs. There are two strategies to interpret CTC datasets; primary 2D versus 3D interpretation. There is not any one correct method for interpretation of CTC; therefore, readers should be well-trained with both interpretation methods. Finally, radiologists should also be familiar with potential dangers in reaching a final correct diagnosis, that is, false positives and false negatives. In experienced hands, CTC seems to be ripe for prime-time colorectal cancer screening. However, it is not yet ready for widespread application of screening until several obstacles can be overcome. Therefore, considerable effort should be undertaken to take CTC to the next level, as a widely accepted screening method for colorectal cancer.