Computed tomography (CT) is a
medical imaging method employing
tomography.
Digital geometry processing is used to generate a
three-dimensional image of the inside of an object from a large series of two-dimensional
X-ray images taken around a single
axis of rotation. The word "tomography" is derived from the
Greek tomos (slice) and
graphein (to write). Computed tomography was originally known as the "EMI scan" as it was developed at a research branch of
EMI, a company best known today for its music and recording business. It was later known as
computed axial tomography (CAT or CT scan) and
body section röntgenography.
CT produces a volume of data which can be manipulated, through a process known as windowing, in order to demonstrate various bodily structures based on their ability to block the X-ray/Röntgen beam. Although historically (see below) the images generated were in the axial or transverse plane (orthogonal to the long axis of the body), modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures. Although most common in medicine, CT is also used in other fields, such as nondestructive materials testing. Another example is the DigiMorph project at the University of Texas at Austin which uses a CT scanner to study biological and paleontological specimens.
In the early 1900s, the Italian radiologist Alessandro Vallebona proposed a method to represent a single slice of the body on the radiographic film. This method was known as tomography. The idea is based on simple principles of projective geometry moving synchronously and in opposite directions the X-ray tube and the film, which are connected together by a rod whose pivot point is the focus; the image created by the points on the focal plane appears sharper, while the images of the other points annihilate as noise. This is only marginally effective, as blurring occurs only in the "x" plane. There are also more complex devices which can move in more than one plane and perform more effective blurring.
Tomography had been one of the pillars of radiologic diagnostics until the late 1970s, when the availability of minicomputers and of the transverse axial scanning method, this last due to the work of Godfrey Hounsfield and South African born Allan McLeod Cormack, gradually supplanted it as the modality of CT.
