Design and modeling of the Hybrid Portable Gamma Camera system

The combination of a mechanically-collimated camera with an electronically-collimated camera offers both the high efficiency and good angular resolution typical in a mechanically-collimated camera for lower energies and the uncoupling of spatial resolution and efficiency provided by an electronically-collimated camera at higher energies. The application is an industrial gamma-ray imaging system with good angular resolution and efficiency over a broad energy range: 50 keV to 3 MeV. The design and performance modeling of the Hybrid Portable Gamma Camera, currently being built, is described here. The optimization of the Anger-logic first detector module in terms of spatial and energy resolution is accomplished using a Monte Carlo optical photon modeling code and Cramer-Rao lower bound calculations. Approximately 6 mm spatial resolution and 7.5% FWHM (statistical contribution only) energy resolution for a 140 keV incident energy are expected for the 100/spl times/100/spl times/10 mm/sup 3/ NaI(Tl) first detector. Analytical calculations of angular resolution components and efficiency for the Hybrid Portable Gamma Camera are compared to Monte Carlo calculations of the same quantities. The expected angular resolution performance for on-axis point sources, a central scattering angle of 30/spl deg/ and a detector separation distance of 35 cm ranges from 3-5/spl deg/ FWHM over the sensitive energy range. Intrinsic efficiency results over the same energy range are also presented.