SIMIND Based Pinhole Imaging Development and Validation

Abstract: The Monte Carlo method has become increasingly used to simulate imaging systems like the scintillation camera and SPECT systems. In order to investigate intrinsic properties of SPECT systems the Monte Carlo based application SIMIND (Simulating Medical Imaging Nuclear Detectors) has been developed. Up to now, it has not been able to simulate a pinhole-imaging device with SIMND. The aim of this work was therefore to develop such an application. The application has been developed for pinhole-imaging devices that consist of a knife-edge- shaped pinhole insert and a conical shielding device.The pinhole collimator routine, developed in FORTRAN, tracks the path of each photon through the pinhole collimator during a simulation session. As a photon moves through the pinhole collimator, the routine registers if the photon passes through the aperture, penetrates trough the edge of the aperture or if the photon scatters in the pinhole collimator. This makes it possible to calculate fractions of geometrical, penetrating and scattered photons that contribute to an image generated by the simulation application, which is impossible in the real case. Results from the constructed pinhole collimator routine were validated by comparing results from simulations with results obtained from experimental studies on a SPECT system with a pinhole collimator. Comparisons were also conducted with results from previously published characteristics of pinhole-imaging devices. The comparisons showed good agreement but with some differences in the values of the fraction of geometrical, penetrating and scattered photons compared to previously reported results.