An APD-based quad scintillator detector module with pulse shape discrimination coding for PET

A detector module allowing individual crystal identification without analog coding is proposed. The basic cell is made of a 2×2 array of scintillators having different decay times that can be identified by pulse shape discrimination. A 16 pixel module consisting of a 2×2 array of these quad scintillator cells coupled to a 2×2 avalanche photodiode (APD) array was assembled and tested. In this design, the signal-to-noise ratio can be optimized in two ways: (a) the electronic noise in individual APD channels is minimized by avoiding light sharing between photodetectors; (b) light collection efficiency is improved by eliminating light septa within cells to allow scintillation light propagation across crystals. All four crystals in a BGO/LSO/YSO/CsI(T1) assembly can be clearly separated and individually gated for energy. An energy resolution better than 13% can be obtained in all pixels for 511 keV gamma-rays