Principles behind Computed Tomography (CT)

The use of Computed tomography (CT) for anatomical information in a combination with the SPECT system has in many ways added substantial information to many nuclear medicine imaging procedures. The information from the CT system can provide information on the location of lesions and can be used for attenuation correction. Modern SPECT/CT and PET/CT today have CT scanners that provide diagnostic quality. This chapter provides the principles behind the X-ray imaging and in particular CT. It describes scanner configurations and components for a typical CT system and how data are acquired. Also, a short description of dual-energy systems that provide additional information is included. Iterative reconstruction of image, and the definition of the Hounsfield unit is discussed together with how different factors affect the image quality. A part of the chapter also discusses CT dosimetry and how the absorbed doses can be measured, quantified, and possibly be reduced. A section also discusses different types of artefacts in the images caused by, for example, metals, respiratory movements, and beam hardening