Imaging tests are also used to screen for and detect colorectal cancer. These tests use technologies that visualize your body organs and present them like a picture. Imaging tests are also used to determine how far the cancer has spread or how well it is responding, or has responded, to treatment. While some tests still use X-rays, newer technologies use radioactivity (in very tiny doses), ultrasound, or magnetic fields to obtain the pictures.
One imaging test for the initial detection of colorectal cancer is called CT colonography (formerly known as virtual colonoscopy).
New technology has made it possible for a computer to take CT images of the colon and reconstruct a three-dimensional model of your colon. The inside of this model can be inspected, without causing any pain to you, to search for abnormalities. The test involves enlargement or distension of the colon with air. CT colonography is sometimes used for screening the colon and detecting small polyps or asymptomatic colorectal cancers.
The main disadvantage of virtual colonoscopy is that any abnormalities have to be evaluated and treated by colonoscopy.