Comparison of physical approaches to inter-crystal scattering in a staggered-layer scintillation PET detector: a simulation study

OBJECTIVE: Inter-crystal scattering (ICS) degrades spatial resolution and contrast by causing spurious lines of response in small-pitch, staggered three-layer pixelated LSO scintillation detectors used in a high-resolution BrainPET-7T insert. This work aimed to investigate the distribution of ICS events in our BrainPET-7T detector and understand its underlying mechanisms. APPROACH: Six physical approaches for computing probabilities to identify the first interaction positions of ICS events were studied using Geant4 simulations, focusing specifically on events with two interactions, which represent the most frequent ICS occurrence. Performance was evaluated using ideal interaction positions and energies directly from simulations, ground truth crystal-center positions with ideal energies, as well as crystal-center positions and energies determined by a maximum likelihood positioning (MLP) algorithm. MAIN RESULTS: A method based on Klein-Nishina probabilities, which were computed using geometric information (KN-G) and MLP-derived crystal-center positions and energies, achieved superior accuracy, particularly when the distance between successive interactions in Compton events was shorter than 6 mm and when incident angles were below 15 • . This advantage is partly attributable to crystal-center discretization, which masks a substantial portion of backscattering events. It reached a peak accuracy of 92.2 % at a distance of 19 mm. SIGNIFICANCE: These findings demonstrate the feasibility of combining the KN-G method with the MLP algorithm to mitigate the ICS effects, with the potential to improve the image quality of the 7T BrainPET insert.