For overcoming the drawbacks of pinhole collimators, which are used to detect a wide field of view, compact diverging collimators using metal-based precision machining have recently been drawing attention in the 3D printer field. Thus, we evaluated the performances of diverging collimators among the square, circular and hexagonal holes, as well as the arrangements of the GAGG crystals. The GATE code and the STL file were used, as was a $^{99m}$Tc point source. The total area and the height of the collimator were set at 25.8 × 25.8 $mm^2$ and 15 mm respectively. While the spatial resolution for all holes was relatively constant within a low error, the sensitivity for the square holes was 37.3% better than that for circular boles and 52.2% better than that for hexagonal holes, Similar results were obtained when the source was moved to the X-axis. Also, if the arrangement of crystals matched the type of the holes in the collimator, the spatial resolution was slightly better, confirming that the higher the degree of matching the hole, the better the performance.

Keywords: Diverging collimator, GATE, Performance evaluation, 3D printer