Simulation and validation of point spread functions in pinhole imaging

Modeling and assessment of point spread functions (PSF) of pinhole collimators is essential for the design of small animal SPECT imaging systems. PSFs also can be used in resolution recovery methods implemented into reconstruction algorithms. Therefore, we have developed and validated a ray tracing approach to simulate PSFs. The PSFs were calculated for user defined pinhole and source geometries with multiple rays to account for collimator penetration. For validation we compared our simulations to analytical. models, Monte Carlo simulations from literature, and experiments with Tc-99m sources using a variety of pinhole geometries including knife and keel edges. We find that shape and magnitude of the simulated PSFs are in very good agreement with analytical and experimental results. In particular, we find that the detection efficiency of a keel-edge pinhole decreases significantly faster with angle away from the central ray than for a knife-edge pinhole. The simulated projection data for a Tc-99m-flood source demonstrated a detection efficiency of about 30% higher than its measured value; however, an overestimation of the detection efficiency is expected since our simulation omits scatter and attenuation in the object. In conclusion, we developed a simulation program which calculates the PSFs and detection efficiencies for different pinhole and source geometries fast and reliably.