Advancing Positron Imaging with Alginate-Based Tracers: Design, Synthesis, and Radiolabelling Methods.

Nuclear imaging plays a vital role in both medical diagnostics and the flow visualisation of engineering systems. Among these techniques, Positron Emission Particle Tracking (PEPT) and Positron Emission Tomography (PET) are renowned for their ability to provide high-resolution tracking of radioactive materials in industrial and biological environments. The success of these methods relies on the effective radiolabelling of materials with suitable radioisotopes, ensuring high activation efficiency and optimal tracer properties. However, the radiolabelling of solid particulates, which is essential for PEPT and increasingly relevant for PET, remains technically challenging. To overcome these limitations, this work presents a methods for the formulation, fabrication, and radiolabelling of "designer" tracer particles, utilizing a porous alginate-based hydrogel matrix combined with an evaporative radiolabelling technique. This approach enables the production of small, mechanically robust tracers exhibiting high single-particle activity and radiochemical stability. This document details the synthesis, characterisation, and radiolabelling methodologies developed to produce these tracers, along with a simple extrusion dripping process that allows customisation of tracer properties through controlled formulation and operating parameters. The key components of this method are: • The synthesis of alginate hydrogels through extrusion dripping. • The characterisation of tracer particles. • The radio-labelling procedure to obtain particle tracers.