Design considerations of small-animal CT systems

This chapter focuses on the ability of small-animal CT to provide information about molecular species and their spatial distribution in tissues. Over the past several decades radionuclide imaging methods have been the mainstay of in vivo molecular imaging by virtue of the variety of biologically active molecules that can be labeled with a radioactive marker. CT image data has been used to provide both attenuation correction of the SPECT and PET images as well as provide the anatomic localization of the radionuclide accumulation. This important contribution of CT to molecular imaging is presented in those chapters directly addressing the radionuclide imaging approaches. Although, the presence of higher atomic weight atomic labels (e.g., iodine) of biologically active tracer molecules can be conveyed by conventional X-ray attenuation-based imaging methods (in milli-molar concentrations as compared to pico-molar concentrations by radionuclide methods), molecular species can be conveyed by non-attenuating aspects of X-ray interaction with matter by virtue of their molecular bonds that are characteristic of polymeric molecules. These non-attenuating X-ray imaging methods are now starting to emerge from the feasibility demonstrations and hence will be explored in some depth in this chapter.