Development of a pinhole gamma camera for environmental monitoring

Abstract

The collimator design for a nuclear monitoring system should be considered differently from the collimator design for medical environments because it has to be used in high-energy radiation environments. The purpose of this study was to determine the optimum pinhole design and to evaluate its performance for acquiring good-quality image in a high-energy radiation field. Simulations using the Geant4 Application for Tomographic Emission (GATE) were performed to model the pinhole gamma camera system. The gamma camera consists of a pyramid-shaped lead collimator with a tungsten pinhole insert, and a CsI(Tl) scintillation crystal with thickness of 6.0 mm and area of 50.0 mm × 50.0 mm. The acceptance angle of the pinhole collimator and the distance from pinhole to scintillator crystal were set to 45° and 60 mm, respectively. The intrinsic spatial resolution and sensitivity were simulated by changing the pinhole diameter and channel height. The point source was located 60 mm above the center of the pinhole, and the transmitted image was estimated for pinhole diameter values from 2.0 mm to 4.0 mm, while the channel heights were fixed between 2.0 mm and 6.0 mm. The optimal ranges of channel height and pinhole diameter were determined by evaluating the intrinsic resolution and sensitivity tradeoff curves. The pinhole parameters were selected based on these analyses, and we verified the simulation results through experimental tests of three types of collimators (general purpose, high sensitivity, and high resolution). The simulated and experimental results agreed, with discrepancies of 4.5% and 6.4% in the sensitivity and spatial resolution, respectively. The results demonstrate that the pinhole collimator designed in this study could be utilized to perform radiation monitoring.