A study of inter-crystal scatter in small scintillator arrays designed for high resolution PET imaging

Inter-crystal scatter causes mispositioning of scintillation events, which is of particular concern in imaging detectors based on small discrete scintillators. Because it is difficult to measure the scatter and its effects on detector intrinsic spatial resolution, a Monte Carlo simulation has been used to study this effect for evaluating and optimizing the design of a high resolution animal PET detector based on a small scintillator crystal array. In this simulation, the authors quantitatively assess the mispositioning of events due to inter-crystal scatter as a function of parameters such as different scintillator materials, crystal geometry, γ-ray incident angle and energy threshold applied, etc. In analyzing the tradeoff between the detector efficiency and the position detection accuracy, the authors found that the mispositioning is not sensitive to the energy threshold, however it does change rapidly with the crystal length and the gap between crystals. The authors also evaluated different crystal positioning schemes to provide a theoretical estimation for the choice of the best scheme. To study how the inter-crystal scatter affects detector spatial resolution, the authors analyze the coincidence line spread function with and without the scatter, and found that the inter-crystal scatter has very little effect on the FWHM and FWTM of the coincidence line spread function