X-ray computed tomography (CT) is a nondestructive technique that allows visualization of the internal structure of objects, determined mainly by variations in density and atomic composition. It requires the acquisition of one- or I wo-dimensional radiographs for different positions during step-wise rotation around a central axis, whereby either the source and detector or the sample are moved. This is followed by the reconstruction of two-dimensional cross-sections perpendicular to the axis of rotation.
CT images record differences in the degree of attenuation of the X-rays, which is material-and energy-dependent. The interactions that are responsible for this attenuation are mainly Comp-ton scattering and photoelectric absorption. The contribution of the photoelectric effect depends on the effective atomic number and is especially important at low energies. At high energies, the Compton effect predominates and attenuation is mainly determined by density.