The coincidence time resolution (CTR) becomes a key parameter of 511 keV gamma detection in time of flight positron emission tomography (TOF-PET). This is because additional information obtained through timing leads to a better noise suppression and therefore a better signal to noise ratio in the reconstructed image. In this paper we present the results of CTR measurements on two different SiPM technologies from FBK coupled to LSO:Ce codoped 0.4%Ca crystals. We compare the measurements performed at two separate test setups, i.e. at CERN and at FBK, showing that the obtained results agree within a few percent. We achieve a best CTR value of 85 ± 4 ps FWHM for 2 × 2 × 3 mm(3) LSO:Ce codoped 0.4%Ca crystals, thus breaking the 100 ps barrier with scintillators similar to LSO:Ce or LYSO:Ce. We also demonstrate that a CTR of 140 ± 5 ps can be achieved for longer 2 × 2 × 20 mm(3) crystals, which can readily be implemented in the current generation PET systems to achieve the desired increase in the signal to noise ratio.
In this paper, we show the analysis software we created for a fast and reliable automatic characterization of a silicon photomultiplier. The program can be used both in dark and under continuous low-level light illumination. It grabs Ims long waveforms, each containing many single cell pulses, from an oscilloscope connected to the PC via Ethernet. On-line data analysis is done both on the raw waveform as well as on a filtered (with DLED technique) version in order to facilitate the pulse identification and the extraction of some parameters also in cases of high count rates or cross-talk. The main outcomes of the program are: single-cell signal shape, gain, primary dark count rate, after-pulse probability, direct and delayed cross-talk probability and excess charge factor. It can be used also to determine the actual photo-detection efficiency with the proper hardware set-up.
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