A time of arrival estimator based on multiple timestamps for digital PET detectors

Recent fully digital CMOS detectors suggested for PET can feature multiple on-chip TDCs. In these detectors, the timestamps of up to virtually all detected scintillation photons can be stored for later processing. However, the improvement in timing resolution that these multiple timestamps can provide strongly depends on the estimator (i.e. the post-processing algorithm) used. In this work, we propose an estimator that utilizes the timestamps of the first few photons to obtain a single time of arrival for the gamma event. The estimator is to be implemented in an FPGA for real-time coincidence detection, and thus aims at low computational complexity. The estimator performance was evaluated through Monte Carlo simulations of a scintillation with double exponential pulse shape and a photodetector with Gaussian jitter. The results of a LYSO scintillator coupled to a 250 ps jitter FWHM detector with 1000 detected photons per scintillation show that our estimator provides around 10% improvement over a single photon estimator.