Hybrid Mercuric Iodide (HgI2) - Gadolinium Orthosilicate (GSO) Detector for PET

Gadolinium orthosilicate (GSO), a high density (6.71 g/cm3), high effective Z (59) scintillation detector with faster decay time (60 ns) and higher light yield than bismuth germanate (BGO), was evaluated as a replacement for BGO for a hybrid detection system for high resolution Positron Emission Tomography (PET). The detection system consists of multiple GSO detectors attached to a single photomultiplier tube (PMT) and a HgI2 photodetector attached to each GSO crystal. The PMT signal provides coincidence timing and energy discrimination and the photodetector signal identifies the crystal of interaction. GSO light yield was 1.7 times that of BGO with energy resolution consistent with improved photon statistics (17.8 to 13.8% FWHM). Resolution of GSO coupled to a HgI2 photodetector was 13.6% FWHM. Coincidence timing was 2.3 ns FWHM. Timing between PMT and HgI2 was 136 ns FWHM.