Collimators for Gamma Dual Energy CT Arch-Detector: A Simulation Study

The image resolution of computed tomography (CT) scan system can be affected by numbers of factors such as collimator material, collimator design, stopping power of detector and scatter photons rejection and/or correction technique. The scatter photons are one of the major sources of background noise that can immensely degrade the image quality of the CT system. The image quality, in turn, affects the discrimination and identification performance of the system especially in the case of dual-energy CT systems for material decomposition. Therefore, for material identification, acquisition of raw data with minimal noise is of immense importance. In this simulation study, the performance of two types of collimators was evaluated to come up with a better collimator design for background noise compression. Both collimators were made of tungsten with similar length of 30 mm but with different hole shapes (fan and parallel). In both cases, results suggest that there is a clear improvement in terms of spatial resolution. In a comparison of grids structure, fan grid performed slightly better than parallel for most of the cases. The peak-to-valley (PV) ratio for 122 keV gamma radiation source improved on average ∼0.16 (16%) and ∼0.23 (23%) for fan collimator and parallel collimator respectively. For 60 keV gamma source, the improvements were ∼0.14 (14%) and ∼0.17 (17%) respectively. Thus, from the results, it can be concluded that fan grid collimator can provide superior performance compared to parallel grid collimator.