Final answer:
CT colonography's main disadvantage compared to conventional endoscopy is that it does not allow for the biopsy or removal of polyps, requiring a follow-up colonoscopy if abnormalities are found.
Step-by-step explanation:
The chief disadvantage of CT colonography over conventional endoscopy is that it can't biopsy or remove polyps. CT colonography, also known as virtual colonoscopy, uses detailed cross-sectional images to detect cancers or polyps in the rectum and colon. However, if polyps or potentially cancerous lesions are detected, a follow-up colonoscopy is required to biopsy or remove these lesions. In contrast, conventional colonoscopy is both diagnostic and therapeutic, as it allows for the identification and removal of precancerous polyps during the same procedure.