Nuclear medicine imaging offers the possibility to study in vivo different aspects of inflammatory process by the use of radio-labeled molecules that bind to specific receptor targets on cells and tissues. This noninvasive technique, combined with pathogens engineered to express luciferase, allows quantification in the same animal of the spatial and temporal progression of the infection and identification of animal-to-animal variations in pathogen replication and dissemination. One strategy to use optical imaging in living animals is the use of luciferase reporter genes as internal sources of light called bioluminescence imaging (BLI). This enables real-time noninvasive imaging of infections and gene expression in living organisms. Nuclear medicine imaging is characterized by the use of radio pharmaceuticals (radiolabeled probes) that, administered in pico- and nanomolar amounts. These probes can also be used for early diagnosis of diseases, in susceptible subjects, for detection of disease relapse and radio-guided surgery.