Development of a Two-layer Staggered GAGG Scatter Detector for Whole Gamma Imaging

Silicon photomultiplier (SiPM) based scintillation detectors are widely used for positron emission tomography (PET), but their application to Compton cameras should be further explored. Whole gamma imaging (WGI) is a combination of PET and a Compton camera realized by inserting a scatter detector ring into a PET ring. In a previous study, we developed a WGI prototype in which the scatter detector consists of Gd3Al2Ga3O12:Ce (GAGG) scintillators coupled with SiPM for a proof-of-concept. However, its Compton imaging performance was not as good as its PET imaging performance. In this paper, we developed a two-layer staggered GAGG scatter detector which was optimized for WGI. GAGG crystals 1.45×1.45×4.5 mm3 in size were arranged into a 13×13 array for the 1st layer and a 14×14 array for the 2nd layer with a staggered arrangement. The two-layer crystal block was optically coupled to an 8×8 SiPM array (3 mm pixel). Using radioactive sources with different energies, we investigated the energy resolution performance experimentally. Almost all crystals were clearly separated in the flood histogram at multiple energies. The developed detector showed energy resolutions of 7.7% to 8.5% at 511 keV, which was better than that of the detector of the current WGI prototype. The next generation WGI system was modeled in simulations using the obtained energy resolution data. The simulation results showed that the WGI with the developed detector had 1.2 times better sensitivity and better angular resolution in the peripheral region than the current WGI prototype.