In this paper, our objective is to show our contribution to the development of a new Positron Emission Tomography (PET) system to reduce its impact on patients. This study was conducted as part of the RETIREX project. PET is a diagnostic system based on functional imaging that uses radioactive substances to visualize and measure the changes in different metabolic processes. There is a constant push to reduce both the radioactive dose injected into the patient and duration of the PET scan. Achieving these and providing real-time images require an innovative imaging principle. In this paper, we present our contribution to an architecture based on a new 3-photon gamma imaging PET scanner with a Liquid Xenon camera. In this project, we aim to define a new architecture for a high-throughput hardware event builder and its integration into the final PET scanner named XEMIS3 (Xenon Medical Imaging System).