Study of optical reflectors used in scintillation detectors that achieve 100 ps coincidence time resolution for TOF-PET

Incorporating 511 keV photon time-of-flight (TOF) information in PET enables a significant boost in reconstructed image signal-to-noise ratio (SNR). This SNR boost depends on the 511 keV photon pair coincidence time resolution (CTR) of the PET system, which is determined by several factors including properties of the scintillation crystal and photodetector, crystal-to-sensor coupling configurations, and reflective materials. The goal of the present work is to achieve 100 picoseconds (ps) CTR for > 2-fold additional improvement in reconstructed image SNR compared to state-of-the-art PET systems that currently have 250–400 ps CTR. A critical parameter to optimize in achieving this goal is the optical reflector's influence on light collection and transit time to the photodetector. For the experimental set-up, we made use of PET detector elements based on both 3×3×10 and 3×3×20 mm3 LGSO crystals coupled to an array of SiPMs by using a novel “side-readout” configuration. We have tested the CTR performance by applying four different reflector materials to the crystal surfaces namely: Enhanced Specular Reflector (ESR), Teflon, BaSO4 paint and TiO2 paint. In addition, we have also evaluated the influence of the scintillation crystal length on the CTR performance by testing 3×3×10mm3 and 3×3×20mm3 LGSO crystals.