Methods to Improve Light Transport Efficiency in LYSO Crystals Based on Characteristics of Optical Reflectance

Abstract

It is important to optimize the flight path of scintillating photons in crystals for positron emission tomography detectors because the flight path is directly linked to the coincidence timing resolution (CTR). In this study, we tracked the scintillating photons and recorded the flight path, energy, and time information. First, the specular and diffuse reflections for light transport were compared via simulation, and their regularity was summarized. Two methods were proposed to reduce the randomness and exploit the advantages of diffuse reflection. The first method involves studying nine combinations of diffuse and specular reflection, each of which always shows a better light output and transport efficiency. The second method employs a light guide of low reflectivity between the scintillators and the diffuse reflectors on the side surfaces of the crystal. Three types of media with different refractive indexes were simulated. The optimum result predicts a relative increase of up to 58.8% of the light output for 3 mm $\times3$ mm $\times20$ mm crystals coupled with a 6.13 mm $\times6.13$ mm silicon photomultiplier with optical glue.