A YSO/LSO phoswich array detector for single and coincidence photon imaging

The performance of a phoswich array detector module for possible use in a combined single and coincidence photon imaging system has been evaluated. The detector consist of a linear array of discrete 4×4×15 mm³ YSO elements coupled to a combined detector array/light guide of LSO, 10 mm thick. Since the scintillation light decay time is different in YSO and LSO (70 and 40 ns, respectively), events originating from the two detector materials can be separated by pulse shape discrimination. The front layer of YSO could then be used for detection of low energy, single photon events and the LSO layer for coincidence detection of annihilation radiation. The light collection of the PMTs coupled to the detector was found to be adequate to accurately identify each detector element in the array using the same positioning logic used in conventional EGO block detectors. The average energy resolution of the YSO elements at 140 keV for the block detector was found to be 14.5% FWHM, ranging from 13.8 to 15.4%. Spatial resolution of the detector block in single photon mode, using a high resolution collimator (geometric resolution 6.5 mm at 10 cm) was measured by scanning a ^99mTc line source. The resolution at 5 and 10 cm from the collimator face was found to be 5.9 and 8.5 mm FWHM, respectively