Abstract
Time of flight (TOF) in positron emission tomography (PET) has experienced a revival of interest after its first introduction in the eighties. This is due to a significant progress in solid state photodetectors (SiPMs) and newly developed scintillators (LSO and its derivatives). Latest developments at Fondazione Bruno Kessler (FBK) lead to the NUV-HD SiPM with a very high photon detection efficiency of around 55%. Despite the large area of 4×4 mm2 it achieves a good single photon time resolution (SPTR) of 180±5ps FWHM. Coincidence time resolution (CTR) measurements using LSO:Ce codoped with Ca scintillators yield best values of 73±2ps FWHM for 2×2×3 mm3 and 117±3ps for 2×2×20 mm3 crystal sizes. Increasing the crystal cross-section from 2×2 mm2 to 3×3 mm2 a non negligible CTR deterioration of approximately 7ps FWHM is observed. Measurements with LSO:Ce codoped Ca and LYSO:Ce scintillators with various cross-sections (1×1 mm2 - 4×4 mm2) and lengths (3mm - 30mm) will be a basis for discussing on how the crystal geometry affects timing in TOF-PET. Special attention is given to SiPM parameters, e.g. SPTR and optical crosstalk, and their measured dependency on the crystal cross-section. Additionally, CTR measurements with LuAG:Ce, LuAG:Pr and GGAG:Ce samples are presented and the results are interpreted in terms of their scintillation properties, e.g. rise time, decay time, light yield and emission spectra.
Highlights
State of the art timing in Time of flight (TOF)-positron emission tomography (PET) detectors with LuAG, GAGG and L(Y)SO scintillators of various sizes coupled to Fondazione Bruno Kessler (FBK)-SiPMs
The Coincidence time resolution (CTR) versus the bias overvoltage and NINO threshold voltage is shown for 2 × 2 × 3 mm3 LSO:Ce:0.4%Ca crystals coupled to the NUV-HD SiPM
A best CTR value of 73±2ps full width at half maximum (FWHM) is achieved at an overvoltage of 12.5V and a NINO threshold voltage of ∼120mV, which corresponds to 1 SiPM single cell signal amplitude (SPAD signal amplitude)
Summary
State of the art timing in TOF-PET detectors with LuAG, GAGG and L(Y)SO scintillators of various sizes coupled to FBK-SiPMs. Lecoq et al Timing measurements of lutetium based scintillators combined with silicon photomultipliers for TOF-PET system S. : Time of flight (TOF) in positron emission tomography (PET) has experienced a revival of interest after its first introduction in the eighties. This is due to a significant progress in solid state photodetectors (SiPMs) and newly developed scintillators (LSO and its derivatives). Increasing the crystal crosssection from 2 × 2 mm to 3 × 3 mm a non negligible CTR deterioration of approximately 7ps
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