The Influence of Crystal Size and Material on Intercrystal Scattering and Parallax in PET Block Detectors: A Monte Carlo Study

In this study, we utilized the MCNP4C Monte Carlo code to quantitatively evaluate the influence of crystal size and material on intercrystal scatter and parallax effects. For each of the 5 selected crystals (BGO, LSO, LYSO, LuAP, GSO), transport of 511 keV photons originating from a point source and incident on the central crystal of a block detector consisting of a 13 × 13 array of 4 mm × 4 mm × 20 mm crystals was simulated. Functions such as position detection accuracy (PDA) and point spread function (PSF) in different crystals were considered by changing the parameters such as crystal thickness, crystal pixel size and gamma ray angle of incidence. The code was validated against the simulated data published by Shao et al. The results of the simulations and their analysis showed that increasing the crystal pixel size increased the PDA and decreased the ICS but increasing the crystal thickness decreased the PDA and increased the ICS.Discussion and By considering the attenuation properties of 511 keV photons, we conclude that BGO is the most appropriate crystal for reducing the intercrystal scattering phenomenon. However, the higher light yield and lower decay time of LSO and LYSO makes them the most appropriate crystals for use in PET systems. The obtained functions for intercrystal scattering can be used for recovering spatial resolution and improving image quality in the image reconstruction process.