Radiography is an imaging technique that uses electromagnetic radiation other than visible light, especially X-rays, to view the internal structure of a non-uniformly composed and opaque object (i.e. a non-transparent object of varying density and composition) such as the human body. To create the image, a heterogeneous beam of X-rays is produced by an X-ray generator and is projected toward the object. A certain amount of X-ray is absorbed by the object, which is dependent on the particular density and composition of that object. The X-rays that pass through the object are captured behind the object by a detector (either photographic film or a digital detector). The detector can then provide a superimposed 2D representation of all the object's internal structures.

In tomography, the X-ray source and detector move to blur out structures not in the focal plane. Conventional tomography is rarely used now having been replaced by CT. Computed tomography (CT scanning), unlike plain-film tomography, generates 3D representations used for computer-assisted reconstruction.