CT colonography (also called virtual colonoscopy or CT pneumocolon) is an alternative way to visualize and assess the colon for abnormal lesions such as polyps or strictures with the use spiral CT to produce high-resolution 3D views of the large bowel. It is less invasive than traditional colonoscopy, but to achieve good-quality images the patient needs to take bowel preparations to ensure bowel cleansing, and the colon needs to be insufflated with CO2. If a tumor is present (Fig. 4.77), both CT and MRI are used to assess regional disease (MRI), abnormal lymph nodes (MRI, CT), and distant metastases (CT).