Time resolution in scintillator based detectors for positron emission tomography

Highest time resolution in scintillator based detectors is becoming more and more important in applications for high energy physics and medical physics. In the domain of medical photon detectors L(Y)SO scintillators are commonly used for positron emission tomography (PET). The interest for time of flight (TOF) in PET is increasing since measurements have shown that new crystals like L(Y)SO coupled to state of the art photodetectors, e.g. silicon photomultipliers (SiPM), can reach coincidence time resolutions (CTRs) of far below 500ps FWHM. Several commercial whole-body TOF-PET scanners further demonstrated that already a clear improvement in image signal to noise ratio (SNR) and contrast can be achieved with time resolutions of the order of 500ps. However, CTRs smaller than 100ps FWHM are necessary to benefit of the image SNR improvement to such a level where scanning times and radiation exposure to the patient can be significantly reduced. To achieve these goals it is important to study and understand the individual processes and the associated time evolution in the whole detection chain, i.e. the high energy particle or gamma interaction in the crystal, the scintillation process itself, the light propagation in the crystal with the light transfer to the photodetector, and the electronic readout. In this work, study of time resolution measurements is reported, comparing the performance of two different readout electronics – NINO and HRFlexToT with three different configurations of silicon photomultipliers coupled to scintillating crystals.