Optimization of pinhole collimator for small animal SPECT using Monte Carlo simulation

The aim of this study is to design an optimized pinhole collimator using Monte Carlo simulation for the development of an ultra high-resolution SPECT using a position sensitive photo-multiplier tube. Simulations using Monte Carlo N-Particle Transport code, version 4c were performed to model the pinhole SPECT system. The simulation geometries consist of a cone-shaped pinhole collimator with tungsten aperture and a NaI(Tl) scintillation crystal with 6 mm thickness and 120 mm diameter. Spatial resolution, sensitivity, edge penetration and scatter fraction were simulated by changing pinhole diameter and channel height. The optimal ranges of pinhole diameter and channel height were determined from trade-off curves and from sensitivity, penetration and scatter fraction. Trade-off curves of sensitivity and resolution allowed to determine that the optimal range of pinhole diameter was from 1 mm to 1.5 mm. The penetration and scatter fraction curve indicated that the channeled aperture is preferable over knife-edge. The optimal range of channel height was from 0.3 mm to 0.6 mm. The results demonstrate that the pinhole collimator designed in this study could be utilized to perform ultra high-resolution small animal imaging.