Investigation of Lu1.8Gd0.2SiO5:Ce (LGSO) scintillators with APD readout for medical imaging applications

New high lutetium content Lu_1.8Gd_0.2SiO₅:Ce (LGSO) scintillators with promising physical properties for PET, but also for SPECT and X-ray counting CT applications, have recently been developed. The new crystals have a high density (7.3 g/cc), high light output (>90% of NaI(Tl)), suitable emission wavelength for APD readout (420, 480 nm), and fast decay time that can be adjusted from 34 to 45 ns by varying Ce-doping concentration. Three different LGSO species with 0.025 mol% Ce (34.2 ± 0.3 ns), 0.15 mol% Ce (38.3 ± 0.3 ns) and 0.75 mol% Ce (44.8 ± 0.3 ns) were investigated. Photoelectron yields measured with a high performance UV-enhanced APD readout were respectively 12380 ± 570, 14250 ± 570 and 17690 ± 760 phe/MeV. Energy spectra of ⁶⁸Ge (511 keV, PET), ^99mTc (140 keV, SPECT) and ²⁴¹Am (60 keV, CT) sources were obtained with the crystals coupled to the APD. FWHM energy resolutions at 511, 140 and 60 keV reached 10.5%, 17.6% and 32.2%, respectively. Timing resolution was measured in reference to a fast PMT-plastic detector and yielded 1.3-1.5 ns. It is concluded that APD-based detectors using these new high lutetium content LGSO scintillators are very promising candidates for multimodality medical imaging applications.