Design of a high resolution phoswich PET detector

Phoswich technique is used in PET detector development to improve spatial resolution by obtaining the depth of interaction (DOI) information or reduce the number of electronic channels. In this work, a new design scheme is proposed to reduce event´s mispositioning in the transverse direction. A 6×6 detector block is assembled with two types of crystals, LYSO and YSO in an interleaved placed pattern in the transverse direction and then couple to four PMTs with quadrant-sharing technique. The block was exposed to a flood source of Cs137. The signals were recorded digitally by an oscilloscope (LeCroy waveRunner 204MXi-A) under the sequence mode. By linearly fitting the waveforms, the decay time constant of the two crystal materials were experimentally determined, which is τ_LYSO = 44.2.8±5.8 ns and τ_YSO = 72.8±13.2 ns. In the phoswich, a triple-Gaussian model was used to fit the distribution of the decay time constants for considering of the cross-talk. When the cut is set as 56.2 ns, the crystal discrimination rate is between 75.7% and 91.6%. Separated 2-dimension maps (2Dmap) can be generated for each kind of crystal. Compared to the 6×6 2Dmap, the two 3×6 2Dmaps has minimal overlap in the interleave direction. The design is capable of reduce event´s mispositioning and improving the spatial resolution of the detector.