A novel high resolution PET scanner dedicated to imaging small volumes (small animals or positron mammography) has been developed. The system utilises a novel SiPM detector array coupled to a pixelated LYSO scintillator and placed in an edge-on formation around the ring. The unique design provides a more accurate placement of the Lines of Response (LoR) by measuring the Depth of Interaction (DoI) which results in a uniform spatial resolution across the whole field of view (FoV). Analytical modelling of the effect of parallax error on spatial resolution is presented. A full prototype of the system is simulated using GATE/GEANT4 with Ge-68 point sources placed at various positions within the FoV. The simulation results are compared to experimental measurements on the prototype system, and the effectiveness of the proposed approach to determining the DoI is demonstrated. The effectiveness of the DoI estimation in achieving a uniform spatial resolution across the entire FoV is demonstrated where a 30% improvement in spatial resolution close to the outer edge of the gantry ring is obtained. Preliminary images of a micro-Defrise phantom filled with F-18 obtained using the prototype system are presented and compared with a simulation of the same configuration.