Diagnostic Imaging - CT scan

A computed tomography scan (also called a CT scan or a CAT scan) also uses X-rays to create images of the body. However a radiograph and a CT scan show different types of information. Although an experienced radiologist can get a sense for the approximate three-dimensional location of a tumor from a radiograph, in general, a plain radiograph is two-dimensional.

An arm or chest radiograph looks all the way through a body without being able to tell how deep anything is. A CT scan is three-dimensional. By imaging and looking at several three-dimensional slices of a body (like slices of bread) a doctor could not only tell if a tumor is present, but how deep it is in the body.

A CT scan can be three dimensional because the information about how much of the X-rays are passing through a body is collected not just on a flat piece of film, but on a computer. The data from a CT scan can then be computer-enhanced to be more sensitive than a plain radiograph. With both plain radiographs and CT scans the patient can be given a contrast agent in a drink and/or by injection to more clearly show the boundaries between organs or between organs and tumors.

Source: National Cancer Institute