Computed Tomography
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Computed Tomography Simone Carmignato Department of Management and Engineering, University of Padua, Vicenza, Italy
Synonyms Computed axial tomography (CAT); Computeraided tomography (CAT); Computerized tomographic imaging; Computerized tomography; Computerized transverse axial scanning; X-ray computed tomography
Definition X-ray computed tomography, or simply computed tomography (CT), is an imaging method using X-ray transmission and computer algorithms to reconstruct two-dimensional (2D) images of an object, representing object’s slices, or threedimensional (3D) representations of the object’s structure, including inner geometries. In this context, the term “tomography” refers to nondestructive imaging of sections. The term derives from two Greek words: tomos, meaning “section,” and graphein, meaning “to write.” Although the term “computed tomography” is very general and could refer even to tomographic techniques not using X-rays, in practice it usually refers to the computation of tomographic images
by X-ray transmission. The term “X-ray computed tomography” is more specific.
Theory and Application Introduction Unlike conventional radiography, computed tomography goes far beyond the collection of radiographic projections. The fundamental limitation of conventional radiography is that the threedimensional volume of an object is compressed along the direction of X-ray to a two-dimensional radiographic projection, in which all the underlying object’s structures are superimposed, which results in significantly reduced visibility of the object. A recognition of this limitation led to the development of computed tomography, which allows the object’s slices and volume reconstruction from X-ray projections (Morgan 1983). Figure 1 illustrates the progression of CT data, from X-ray projections, to 3D volume reconstruction, and to surface determination. History of CT Early X-ray Tomography Techniques
The idea of determining the inside structure of an object from multiple X-ray images taken from various angulations goes back to the first decades of the twentieth century. Before the advent of computed tomography, other techniques were developed for displaying internal sections using
# CIRP 2016 The International Academy for Production Engineering et al. (eds.), CIRP Encyclopedia of Production Engineering, DOI 10.1007/978-3-642-35950-7_6681-4
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Computed Tomography
Computed Tomography, Fig. 1 CT process chain, from X-ray projections to 3D volume reconstruction and to surface determination
X-rays. These techniques are often referred to as “conventional tomography,” or “stratigraphy” or “noncomputed tomography” (Hsieh 2009). As early as 1921, one of the pioneers of conventional tomography, André Bocage, conceived a device to blur out structures above and below a section of interest (Bocage 1921). Few years later, Alessandro Vallebona developed the tomographic technique called “stratigraphy” (Vallebona 1930). Although these early tomographic techniques were somewhat successful in producing images of an object’s internal p
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