| Περίληψη: | The current thesis concerns Dual Energy Computed Tomography and specifically the physical
principles and methods it is based on. Dual Energy CT offers the potential of not only
anatomical, but also functional information from Computed Tomography (CT) exams. This is
achieved by utilizing the energy dependence of X-rays’ attenuation within matter. In this way,
materials are divided into those that are characterized by energy-dependent attenuation
(strong spectral behavior), due to strong photoelectric effect contribution to total attenuation,
and those that do not exhibit important photoelectric attenuation at radiological energies and
therefore they attenuate X-rays in a much less energy dependent way. This information is
useful for the identification of materials that, despite the fact that they are completely different
as far as their chemical composition is concerned, they have the same or similar CT number
values at a particular kVp level.
The energy dependence of attenuation leads to the determination of a polychromatic linear
attenuation coefficient. This coefficient may be approximated either by considering an
equivalent monoenergetic attenuation coefficient that is characterized by the same half value
layer as the the polyenergetic beam, or by a local linear attenuation coefficient that is
determined by knowledge of the local x-ray spectrum. The energy dependence of attenuation
is the cause of beam hardening effects.
The basic fields where dual energy CT has become feasible and its current clinical
applications are described in the thesis. The utility of DECT ranges from artifact elimination
(beam hardening, metal artifacts) to tissue discrimination, material selective images and
“conventional CT acquisition” equivalent images. The implementations of dual energy CT are
also presented in the thesis and include consecutive scans at two different kVp values, fast
kV-switching, dual source CT and dual layer CT.
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