Unlike x-ray radiography, the detectors of the CT scanner do not produce an image. In the particular case of CT, the emitter of x-rays rotates around the patient and the detector, placed on diametrically opposite sides, picks up the image of a body section (beam and detector move in synchrony). This phenomenon is represented by a single coefficient, mju.
There are two processes of absorption: the photoelectric effect and the Compton effect. Attenuation values of the x-ray beam are recorded and the data is used to build a 3D representation of the scanned object/tissue. A detector placed at the exit of the sample, measures N + ΔN photons, ΔN smaller than 0. The emitted x-rays form a beam that passes through the layer of biological material of thickness Δx. The CT x -ray tube (typically with energy levels between 20 and 150 keV), emits N photons (monochromatic) per unit of time. Using this principle, CT allows the reconstruction of the density of the body, by a two-dimensional section perpendicular to the axis of the acquisition system. Cross-sections are reconstructed from measurements of attenuation coefficients of x-ray beams passing through the volume of the object studied.ĬT is based on the fundamental principle that the density of the tissue passed by the x-ray beam can be measured from the calculation of the attenuation coefficient.
Computed tomography (CT), also known as, especially in the older literature and textbooks, computerized axial tomography (CAT), is an imaging modality that uses x -rays to build cross-sectional images ("slices") of the body.
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