Characteristics of Lu$_{1.8}$Gd$_{0.2}$SiO$_{5}$:Ce (LGSO) for APD-Based PET Detector

Abstract

Since its discovery in 1993, LGSO has been seen as a promising scintillator for positron emission tomography (PET) imaging. Recently, new high lutetium content Lu 1 8 Gd 0 2 SiO 5 :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 photomultiplier tube (PMT)] and increases with Ce concentration. The variation of light output for temperature ranging from 10 to 50 C is less than 18% with PMT readout. Energy resolution at 662 keV is about 11% (l0%) with avalanche photodiode (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 ( = 34 2 ns) and 0.75 mol% Ce ( = 44 8 ns) was successfully achieved in a phoswich assembly, making this new high lutetium content LGSO with adjustable decay time constants a strong candidate for a high-resolution depth-of-interaction detector intended for PET imaging.

Structure–Property Correlations in a Ce-Doped (Lu,Gd)2SiO5:Ce Scintillator

“…12 The reported scintillation characteristics of LGSO:Ce with 90% Lu are almost the same as those in LSO. 14 LGSO:Ce crystals with Lu concentration in the medium concentration range (30−60%) were proposed by us in ref 15. They demonstrated light output around 400% relative to BGO, energy resolution 6.9−7.3%, and afterglow level 0.02− 0.1% after 5 ms (by 2−3 orders lower compared to LSO:Ce).…”

“…Low light yield, similar to that of GSO:Ce, is inherent to LGSO:Ce at Lu concentration < 20%; 14 for example, LGSO (20% Lu) possesses the light yield approximately 15000 phot/ MeV and a high afterglow level up to several percent in the microsecond range. 12 The reported scintillation characteristics of LGSO:Ce with 90% Lu are almost the same as those in LSO.…”

“…Lu 2 x Gd 2–2 x SiO 5 :Ce (0 < x < 1) crystals form lattices of two types of monoclinic space symmetry. − A structure transition is observed near x = 0.2. At 0 < x < 0.2 the monoclinic P 2 1 / c is observed, and at 0.2 < x < 1 the monoclinic C 2/ c .…”

“…[16,17] and from 6 to 6.8 eV in LSO [18][19][20]. Since the conductance band edge in all the range of Lu 2x Gd 2-2x SiO 5 :Ce (0 < x < 1) crystals is formed by 5d wave functions of Lu 3+ and Gd 3+ and the valence band is formed by 2pO wave functions, one may assume an insignificant bangap change Low light yield, similar to GSO:Ce, is inherent to LGSO:Ce at Lu concentration <20 %, [14], for ex.…”

Performance comparison of high quantum efficiency and normal quantum efficiency photomultiplier tubes and position sensitive photomultiplier tubes for high resolution PET and SPECT detectors

“…New promising scintillators with larger light output have been developed to improve the PET and SPECT detectors. 8,9 Another method to improve the performance of PET and SPECT detectors is using new photodetectors with higher performance. Silicon-photomultipliers (Si-PMs) are promising candidates for new photodetectors 10,11 and some PET systems have been developed.…”