Effect of scintillation crystal surface finish in the light sharing TOF PET detector

Abstract

The effect of crystal surface finish on the performance of radiation detector has been studied many times mostly focused on a single isolated crystal coupled to a single photosensor. In this paper, we studied roughen crystal effect on light sharing crystal arrays using LYSO crystals of 3.95 × 5.3 × 25mm3. Four different types of crystal arrays were built: no light sharing and light sharing arrays with all polished crystals, and no light sharing and light sharing arrays with crystals of one surface lapped. ESR films were placed in between crystals to make no light sharing arrays. Each array of 2×3 crystals was coupled to a monolithic SiPM of 2×3 anodes and evaluated for light output and timing resolution. For no-light sharing, no-light sharing arrays with one surface lapped showed 14% more light output and 7% improvement in timing resolution compared to no-light sharing with polished crystals. For light sharing, lapped crystal array showed 27% more light output and 14% improvement in timing resolution than its counterpart with polished crystals. Light sharing array with polished crystals collected 16% more light output than no-light sharing array with polished crystals, however, it's increased light output did not manifest as better timing resolution. When light sharing array with lapped crystals was compared to no-light sharing array with polished crystals, it showed a surprising 47% more light output with 11% better timing resolution. In short, lapped crystals showed a big improvement in both light output and timing resolution, and more improvement was observed with light sharing array.