The Influence of Inter-Crystal Scattering on Detection Efficiency of Dedicated Breast Gamma Camera: A Monte Carlo Study

Abstract

Dedicated gamma cameras based on Photodiodes coupled to pixellated small size scintillators, is suitable for high resolution imaging such as small animal and breast cancer imaging. It is well known that inter-crystal scattering (ICS) is of the major resolution degradation factors in the system with small crystal size. The aim of this study is to quantitatively calculate the ICS events in different types of crystal material (CsI, NaI and LaBr3) and size (0.5×0.5, 1×1, 1.5×1.5 and 3×3 mm2) using Monte Carlo simulation. The simulations were designed to optimize camera design particularly for crystal pixel size and scintillation material. Three types of scintillation crystal were exposed by 140 keV photons of a point source as a pencil beam in orthogonal and oblique incidences. In oblique incidence, detected events in central pixel of crystal array decreased in small angles slowly and then decreased rapidly by increasing of incidence angle. In orthogonal incidence in four different pixel sizes, the percentage of photons encounters the ICS event in CsI crystal was 1.82%, 3.76%, 4.94% and 6.49% events for 3×3, 1.5×1.5, 1×1 and 0.5×0.5 mm2 crystal pixel size respectively, that were less than NaI and LaBr3 crystals. Also in the oblique incidence, in all pixel sizes of CsI crystal the photons encountered ICS events were less than NaI and LaBr3. According to our results, The CsI crystal from the point of view of higher detection efficiency and position detection accuracy (PDA) and lower ICS is preferable. However, the optimal crystal material and size for high resolution breast imaging are still open questions which require further research and development efforts.