Removing ring artefacts in CT images via unidirectional relative variation model

CT images often have some ring artefacts caused by the inconsistent response of detector pixels and other factors. Removing ring artefacts effectively without impairing the image quality is still a hard problem although some methods have been proposed. Given that total variation minimisation is widely used for image denoising, a unidirectional relative variation model is proposed and performs it on the reconstructed images transformed into polar coordinates to reduce the artefacts. The proposed method is tested on both simulated data and real CT images, and the qualitative and quantitative results show that it is effective.