Experimental characterization and Monte Carlo validation of a GAGG/SiPM gamma camera prototype for 111 Ag imaging

A compact gamma camera prototype has been developed within the Isotope Separation On-Line production of radioPHARMaceutical (ISOLPHARM)–Advanced Dosimetry Methods and In-vitro Radiobiology of 111Ag Labeled radiopharmaceuticals (ADMIRAL) project to enable laboratory studies and small animal imaging applications of the theranostic radionuclide 111Ag, whose main gamma emission at 342 keV is above the energy range of conventional clinical systems, optimized for 99mTc. The detector consists of a square-holes tungsten collimator facing a 23×23 pixelated GAGG(Ce) scintillator array optically coupled to an 8×8 Hamamatsu SiPM matrix and read out by a CAEN FERS (A5202) board, based on CITIROC 1A ASICs. A Geant4-based Monte Carlo application, including optical photon transport and an electronics-noise model, was developed and validated through laboratory measurements. The prototype was characterized using a 133Ba point-source-like and 111Ag extended sources. For 111Ag, an energy resolution of Δ E / E ≈ 24 % was observed at the 342 keV photopeak. Spatial resolution was assessed to be approximately 3 mm, in agreement with expectations from the Monte Carlo simulation. The efficiency of the camera on the γ-spectrum of 111Ag was measured to be 2.1 × 10-4. Finally, a preliminary mouse phantom study featuring multiple active regions confirmed the capability to qualitatively localize multiple activity regions. These results demonstrate the feasibility of a prototype modular gamma camera, built using off-the-shelf components, for high-energy imaging of 111Ag and provide an experimental platform for future optimization of collimation and reconstruction techniques.