A simple semi-empirical model for positron annihilation non-collinearity based on quadHIDAC measurements

Positron annihilation non-collinearity is one physical factor that constraints the achievable spatial resolution in PET. The quadHIDAC is a high resolution small animal PET scanner with a unique detection principle, relying on multi-wire proportional chamber detectors. In a comparison of simulation and measurement of a 22Na point source, slight discrepancies are observed, which are addressed to an inappropriateness of the used non-collinearity model. Hence, a new simple model for non-collinearity is developed and adjusted to the observed data. It will be presented that the exclusive properties of the quadHIDAC, i.e., high 3D spatial resolution for single photon interactions measured on large radial offsets, offer a perfect environment to separate positron range and detector resolution influences from the measurements and simulations. This allows the investigation of the pure spatial resolution degradation induced by the annihilation non-collinearity of positron emitting sources. Furthermore, simulations, including the proposed non-collinearity implementation, for a possible improved HIDAC setup on an illustrative zebrafish emission model are performed, where associated reconstructed images for the different setups are compared.