Monte Carlo simulation to evaluate factors affecting imaging performances of compact scintillation gamma camera

In recent years, a new generation of compact gamma cameras, based on monolithic scintillation crystals, has become increasingly widespread. The main advantages of small FoV gamma cameras with respect to the standard ones are high portability, low cost and low weight, allowing several clinical applications, from scintimammography to intraoperative tumor localization. In gamma cameras based on continuous scintillation crystals, intrinsic Spatial Resolution (SR) is mainly affected by two factors: scintillation light collection efficiency and overall crystal thickness. The first affects the counting statistics, the latter impacts on the light distribution width. To fully investigate the potentiality of these devices we took advantage of Monte Carlo simulations as a valuable tool to physically characterize the imaging systems and to establish a priori reference values. GEANT4 toolkit allows to completely describe the phenomenon of light emission and propagation through the media, providing control to all second-order factors existing in real systems. Results show clearly that SR is dependent on the number of photoelectrons produced and on the light spread. Furthermore, the role of refractive index has been unambiguously identified as an important factor affecting light collection and consequently SR.