Abstract : A prototype of a high resolution small animal PET scanner with continuous LYSO crystals coupled to SiPMs matrices has been developed. First tomographic images of point-like sources in different positions have been reconstructed, demonstrating the feasibility of the system. In order to improve the scanner performance, work in three different approaches is being performed: improved data analysis for noise reduction, improvement of the detector performance, and simulations to have a better understanding of the detector response and to predict its performance in different conditions. Innovative detector geometries such as the use of tapered crystals are being considered for a further enhancement of the detector sensitivity and reduction of the gaps between the detectors. Also, the placement of the photodetector in the inner part of the crystal is expected to improve the performance. The possible benefits of these innovations are being investigated. Simulations bring a powerful tool to test different geometries and their impact in the detector behavior in an easy way. They also help to understand complex physical processes that take place inside the scintillator crystal or in the crystal-detector interface. A GEANT4 simulation of the prototype, including the optical properties of the detectors, has been carried out. The results have been compared to real data in terms of light distribution in the crystal, number of SiPMs elements illuminated, energy resolution and reconstructed interaction position. Preliminary results show good agreement between simulated and real data. Besides, the simulation is being adapted to new crystal geometries and system configurations to study potential improvements.