This work is based on the use of an implemented PET simulation system dedicated for small animal PET imaging using. GATE, a Monte Carlo simulation platform based on the Geant4 libraries, is well suited for modeling the microPET® FOCUS system and to implement realistic phantoms, as the MOBY phantom and imaging maps of real exams. The use of the microPET® FOCUS model with GATE was validated for spatial resolution, counting rates performances, imaging contrast recovery and quantitative analysis. Results of realistic simulations for static and dynamic studies are presented. These simulations include realistic injected doses in the animal and realistic time framing.