Simulation of a pinhole-collimator insert for small animal PET using GATE

In previous work we demonstrated the feasibility to conduct SPECT imaging using a multi-pinhole collimator insert in a small animal PET scanner. A simplified analytical simulation method was used, modeling mainly geometric attributes, to optimize the multi-pinhole configuration to achieve the best trade-off between resolution and sensitivity for specific applications. To more accurately optimize the pinhole configuration more physical attributes need to be modeled, including attenuation and scatter in both the object and collimator. In this work we used GATE, a Monte Carlo simulation platform based on the well-validated Geant4 libraries, to better model our system. New simulations have been performed using the geometry of the MOSAIC (Philips) system and our simple prototype cylindrical insert (lead, 12 pinholes, pinhole diameter 1.0 mm, insert diameter 60 mm). Measurements of sensitivity (0.22%), resolution (FWHM=1.6 mm), and scatter fraction (28%) using point and capillary sources from GATE-simulated data are in good agreement with measured experimental data. Having validated this simulation environment with this baseline test, we are iteratively testing various objects, pinhole configurations, and collimator materials to design our next generation of optimal pinhole configurations for specific imaging tasks.