Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition.
A heterogeneous beam of X-rays is produced by an X-ray generator and is projected toward an object. According to the density and composition of the different areas of the object a proportion of X-rays are absorbed by the object. The X-rays that pass through are then captured behind the object by a detector (film sensitive to X-rays or a digital detector) which gives a 2D representation of all the structures superimposed on each other. In tomography, the X-ray source and detector move to blur out structures not in the focal plane. Computed tomography (CT scanning) is different to plain film tomography in that computer assisted reconstruction is used to generate a 3D representation of the scanned object/patient.
Read more about Radiography: Medical and Industrial Radiography, History of Radiography, Theory of X-ray Attenuation, Obsolete Terminology