In addition to being a powerful clinical tool, a number of imaging modalities including but not limited to CT, MRI, SPECT and PET are also used in small laboratory animal research to visualize and track certain molecular processes associated with diseases such as cancer, heart disease and neurological disorders in living small animal models of disease. In vivo small-animal imaging is playing a pivotal role in the scientific research paradigm enabling to understand human molecular biology andpathophysiology using, for instance, genetically engineered mice with spontaneous diseases that closely mimic human diseases.