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The majority of current Positron Emission Tomography (PET) systems are based on block-detectors consisting of many scintillating pixels read by a smaller number of photomultipliers (PMTs). An improvement of the time resolution, using a common light readout from a cluster of PMTs, was proposed by Kuhn et al., and tested by us earlier with LSO crystals. This, triggered an idea to design a new PET detector optimized for Time of Flight (TOF) systems, based on continuous crystals. In the present u work, we report on optimization of timing with a 20 Ã 20 Ã 20 mm3 LYSO crystal coupled to a 16-channel photomultiplier -a H8711-200MOD from Hamamatsu. First, measurements were =Â¿ performed of the transit time jitter, the number of photoelectrons and the time resolution using a small 10 Ã 10 Ã 5 mm3 LSO crystal coupled to a H8711-200MOD PMT. Results were compared with data collected from fast timing photomultipliers like Photonis XP1020, XP3060, XP20D0 or Hamamatsu R9800. In the second part of the study, the time resolution measurements and the optimization of the system were made with a continuous LYSO crystal. The final results are discussed in terms of the measured photoelectron number and the requirements for the TOF-PET scanners.