Timing measurements of lutetium based scintillators combined with silicon photomultipliers for TOF-PET system

As time-of-flight PET (TOF-PET) gains popularity in clinical diagnostic, the coincidence timing resolution of PET systems becomes more crucial. The most common scintillators for commercial TOF-PET systems are Lu-based ones such as LSO or LYSO for their high light output, high density and fast decay time. Recently, LGSO with 0.025% Ce (LGSO-fast) was developed which has faster decay time than LGSO with Ce concentration of 0.1 mol% (LGSO-standard). Using the LGSO-fast in conjunction with silicon photomultiplier (Si-PM) may improve the timing performance for the development of TOF-PET systems. Consequently, we tested the basic performance of LGSO-fast and coupled them with Si-PMs to measure the coincidence timing resolution using a high bandwidth digital oscilloscope. The performance was also evaluated for LGSO-standard and other Lu-based scintillators such as lutetium fine silicate (LFS) and two types of LYSOs from other manufacturers. The light output was largest for one of the LYSO from one manufacture and smallest for the LYSO from other manufacture. Decay time was fastest for LGSO-fast (33.8 ns) and slowest for one of the LYSO (39.9 ns). Coincidence timing resolution for 2.9 mm long Lu-based scintillators, LGSO-fast was the best (156.5 ps) and one of the LYSO showed the worst (235.1 ps). For the 20 mm long scintillators, coincidence timing resolution was also best for LGSO-fast (273.2 ps) and worst for one of the LYSO (481.8 ps). We conclude that LGSO-fast combined with Si-PM showed best timing performance among measured Lu-based scintillators. Also within the same Lu-based scintillators such as LYSOs, we found that the performance differences were sometimes significant and quality control of the Lu-based scintillator is essential to achieve good performance in PET systems.