Micro-CT is a complement, collaborator and competitor of radionuclide-based micro-tomographic imaging methods. It complements in that it provides high spatial resolution micro-anatomic information which cannot be provided by radionuclide tomographic imaging methods, it collaborates in that it provides anatomic location of the radionuclide accumulation provided by the radionuclide image as well as enabling attenuation correction of the radiation emitted by the radionuclide and it is a competitor in that vascular transport (especially perfusion) can be imaged by both modalities. For these multi-modality strengths to be maximally synergistic the different images must be accurately registered in both space and time. While this chapter focuses on the strengths of micro-CT, its intent is to highlight their relationship to radionuclide imaging as applied to the cardiovascular system.