Effect of Unmatched System Models on Iterative Reconstruction in Computed Tomography: A Phantom Study

System models used for iterative reconstruction affect the quality of computed tomography (CT) images. The imaging performance of the system models depends on the projectors, which implements forward- and back-projection. The system model based on a single projector is limited to improve image quality because each projector has both benefits and drawbacks. In this study, the effect of unmatched system models on iterative reconstruction was investigated by evaluating the image quality of reconstructed images. The unmatched system models composed of different projectors were used to perform iterative reconstruction. The image quality was evaluated in order to investigate the effect of the unmatched system models, and the imaging performance of the unmatched system models was compared with that of the matched system models by simulations and experiments with digital and anthropomorphic head phantoms. The results showed that the characteristics of CT images depended on the combinations of forward- and back-projectors, and the unmatched system models are able to improve the quality of the images obtained by using iterative reconstruction. The unmatched system models can be potentially used to improve the imaging performance of iterative reconstruction in CT systems.