In conventional radiology, anatomy is depicted in only two dimensions. The depth or thickness of structures cannot be measured on projection images. For a comprehensive evaluation of morphology of a structure, data related to the third dimension are essential. For nearly three quarters of a century, multiple, different angle views were used in routine radiography to gain three-dimensional perception of structures through triangulation. In a continuing quest for methods to access data in the third dimension, techniques such as stereoscopic pair image acquisition and tomography were developed. Although they were highly valuable technical advancements, they still could not provide accurate quantitative information in all three dimensions of a volume structure. Projection images were subject to optical distortions such as those caused by geometric magnification and penumbra (Yune,1993, p. 613). The mathematical concept behind computed tomography (CT) was first described in 1917 by the mathematician Radon who showed that a two-dimensional or three dimensional object could be reconstructed from the infinite set of all its projections. About 40 years later, this concept was proposed for use in radiology. In 1969, Godfrey Hounsfield, a researcher working for EMI Limited in England, developed a prototype scanner based on the principle of image reconstruction, for which he and Allen Cormack received a Nobel Prize in 1979. The first clinical CT scanner was installed in a hospital in 1971. Since then, there have been constant improvements in scanner design, which have led to higher quality images made in ever shorter periods of time.
Computed tomography is a radiographic technique that blends the concepts of thin-layer radiology with computer synthesis of the image. X-ray beam attenuation measurements are made in a 360-degree circle around the part of the patient=s body being scanned. These measurements are then fed into a computer, which co...