A collimator is a key component of gamma cameras, which affects imaging performance significantly. Recently, pixelated scintillator arrays are widely applied in the development of highresolution gamma cameras, instead of monolithic scintillator blocks. Therefore, combining the collimator and the pixelated scintillator has been a crucial factor in achieving good imaging performance. In this study, we investigated the effects of the shape and position of a collimator hole on the image resolution of a gamma camera with a pixelated scintillator. We designed a pixel-matched collimator and a low-energy high-resolution (LEHR) collimator with hexagonal shaped holes that have the same collimator geometrical efficiency. Simulation experiments were performed with a Monte Carlo simulation package (GATE v7.0). For both types of collimator, camera sensitivity was measured for validating the collimator efficiency, and planar images were obtained to measure spatial resolution, with changing the line profile angle based on the septa direction. Camera sensitivities for both collimators were equivalent (difference = 1.76 ± 0.51%). In contrast to the case of the pixel-matched collimator, in the case of the LEHR collimator, as the angle of the line profile varied, the spatial resolution showed a difference at each profile angle. In the case when two collimator holes symmetrically matched with one scintillator pixel, the spatial resolution showed a 64.87% difference in its maximum and a position distortion of 26.06% from the original source position, according to the profile angle, compared to the other unmatched cases. These results showed that using a pixel-matched collimator in gamma camera systems employing a pixelated scintillator is essential for the exact delineation of small regions using high resolution gamma camera imaging
