Positron Emission Tomography (PET) is a Nuclear Medicine technique that creates images that allow the study of metabolic activity and organ function using radiopharmaceuticals. Continuous improvement of scintillation detectors for radiation in PET as well as improvement in electronic detectors (e.g., SiPMs) and signal processing, makes the field of PET a fast and changing environment. If industry desires to build new systems implementing these technological improvements, it is of its interest to develop modelling strategies that can provide information on how to build them, reducing time and material costs. Bearing this in mind three different PET configurations, were simulated in Geant4, to determine which one presented the best performance according to quality parameters such as spatial resolution (SR), coincident time resolution (CTR) and acceptance value (A). This was done with three different (in size) pairs of LYSO crystals + SiPM detectors. It was found that the 2 Modules system presented worst results than the two Ring detector configurations. Between the Ring configurations the first was marginally better than the second.