Experimental assessments of the timing performances of detectors constructed with LaBr3, CeBr3, LFS, LSO, LYSO, GAGG scintillators

The purpose of this study is to compare the timing performances of popular scintillators for time-of-flight (TOF) PET. Six types of scintillators, including LaBr3, CeBr3, LFS, LSO, LYSO (Ca doped) and GAGG, are fabricated in different shapes and different surface finishes, and constructed into detectors. The coincidence time resolution (CRT) of those detectors are measured. Findings and collusions in the studies are (1) We have measured a 67.6ps FWHM CTR with a pair of detector constructed with 6 mm LaBr3 cubes; (2) We have measured 88.1ps FWHM CTR with a pair of detector constructed with 4 mm LYSO: Ce, Ca pyramids; (3) The two SiPMs from SensL and AdvanSiD have no significant differences in the timing performances; (4) the crystals with rough surfaces have a better timing than those with polished surfaces; (5) LYSO: Ce, Ca from different venders and LSO from Siemens have similar performances; (6) 0.2%Ca co-doped LYSOs have a better CTR than 0.1% co-doped LYSO; (7) LYSO: Ce, Ca has a better timing performance than LFS; (8) The CRT measurements are related to the size of the crystals. 2 mm crystals has a better timing than 4 mm crystals. 4 mm crystals has a better timing than 6 mm crystals. (8) Timing performance can be improved by using a geometry such as a pyramid shape which can improve the light transportation in the crystals. (9) The CRT of 2 mm GAGG cubes is 193 ps. But note that the SensL's SiPM has a much lower photo detection efficiency (PDE) @ 520nm compared to that @ 420nm. Thus, the measured light yield from GAGG is 47% lower than that of LYSO. The CTR of the 2mm GAGG cubes improves to 117ps, if the effect of the low PDE @ 520nm is compensated.