This work is based on the optimization of quantitative analysis dedicated to the PET mouse imaging using the microPETreg FOCUS system. Five acquisition protocols were defined to improve the FOCUS sensitivity. We demonstrated that the data collection between 150-750 keV with 6 ns for coincidences windows improves the sensitivity by a factor 2 in comparison with the standard acquisition protocol (350-750 keV; 6 ns). First we showed that the inter animal variability for PET imaging using FDG, varies between 15% and 35% for liver, heart, kidney and leg muscles. These resulting values are lower than those obtained with an ex-vivo activity counting. Secondly, we demonstrated that intra animal variability is about 10% for the same organs and it is lower than the inter variability