Optical Simulation of Dual-Ended Readout of Axially-Oriented 100 mm Long LYSO Crystals for Use in a Compact PET System

Monte Carlo simulations of optical photon transport were performed using DETECT2000 for detectors using dual-ended readout of axially-oriented 100 mm long LYSO crystals. In order to modulate the light transport in the crystals and improve the axial-positioning resolution, systematic etched band patterns were simulated on the long surfaces of the crystals. Roughed surface bands with a width of 1 mm and inter-band spacing of 5 mm over the central 8 cm of the crystal were simulated on the long surfaces of initially polished 3 mm×2 mm×100 mm and 2 mm×2 mm×100 mm crystals. This band pattern was simulated for cases of bands on one surface, bands on two opposite surfaces, and bands on all four surfaces. Each crystal was modeled as Teflon-wrapped and read out at both ends using position sensitive photomultiplier tubes (PSPMTs). Optical photons were simulated as originating at nine central-axis locations, separated by 10 mm, along the crystal length. The ratio of two PMT signals was used to determine the axial-positioning resolution while their sum was used to determine the energy resolution. The DETECT2000 simulation parameters required to give good agreement with measured data were determined in order to benchmark the simulation for this detector geometry. These simulation parameters were then used to examine the effects of alternative banding pattern designs. The best axial-positioning resolution obtained in this work was 3.5 mm FWHM for the case of etched bands along the central 8 cm of the crystal with band size of 4 mm and inter-band-spacing of 20 mm on two opposite surfaces.