Characteristics of Lu1.8Gd0.2SiO5:Ce (LGSO) for APD-based PET detector

Since its discovery in 1993, LGSO has been foreseen as a promising scintillator for positron emission tomography (PET) imaging. Recently, new high Lutetium content Lu1.8Gd0.2SiO5:Ce (LGSO-90%Lu) has been produced with Ce concentration varying from 0.025 to 0.75 mol% Ce, yielding decay times in the range of 34.2 to 44.8 ns. These scintillators could potentially be used as phoswich detectors in PET for improving spatial resolution. To validate this assumption, light output, energy resolution, temperature dependence, timing resolution and pulse shape discrimination performance were assessed. The light output of these LGSO scintillators is 3.5 to 4.8 times higher than BGO with avalanche photodiode readout (7.5 to 8 times with PMT) and increases with Ce concentration. Light output variation for temperature ranging from 10°C to 50°C is lower than 0.22%/°C. Energy resolution at 662 keV is about 11% (l0%) with APD (PMT) readout. Timing resolution with APD is ∼1.65 ns for all samples relative to a fast PMT-plastic detector. Pulse shape discrimination of LGSO-90% Lu with 0.025 mol% Ce (τ = 34.2 ns) and 0.75 mol% Ce (τ = 44.8 ns) was successfully achieved in a phoswich assembly, making this new high Lutetium content LGSO with adjustable decay times a strong candidate for high resolution DOI detector intended for PET imaging.