Scintillation crystal design features for a miniature gamma ray camera

We are developing a miniature scintillation camera with a 5 cm × 5 cm field-of-view (FOV) to aid in surgical staging of cancer. In this paper we report on certain interesting design aspects of the scintillation crystal array. We investigated different types of crystal materials through simulations and measurements. Lutetium oxyorthosilicate (LSO) which is ordinarily used in PET, has appealing properties for detecting 140 keV photons, such as requiring only 3 mm of thickness for 95% detection efficiency at 140 keV. This small thickness is appealing for high light collection efficiency, narrow light distribution, and minimizing the LSO volume in order to reduce intrinsic background events produced by ¹⁷⁶Lu (2.6% abundance). We studied both discrete and sheet crystals and determined that discrete crystal arrays have the advantage of increased spatial linearity and dynamic range compared to crystal sheets. For optimizing sensitivity and spatial resolution, we investigated several crystal array parameters including ground crystal pixels packed tightly together without internal reflectors and without optical coupling grease. This design focuses the light, but also allows adequate light sharing for positioning with the position sensitive photomultiplier tube (PSPMT) that we are using.