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 scintillator elements. 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 inter-crystal scatter effects for evaluating and optimizing the design of a high resolution animal PET detector based on an array of small scintillator crystals. 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 applied energy threshold. 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 compared four different crystal positioning algorithms to provide a theoretical estimate of positioning accuracy and to determine the best algorithm to use. To study how inter-crystal scatter affects detector spatial resolution, the authors analyzed the coincidence line spread function with and without inter-crystal scatter and found that the inter-crystal scatter had very little effect on the FWHM and FWTM of the coincidence line spread function