Removing ring artifacts in CBCT images via _L0 smoothing

Ring artifacts often appear in cone-beam computed tomography (CBCT) images due to the inconsistent response of detector pixels. How to remove ring artifacts without impairing the image quality is still a hard problem. This article proposes a novel method to remove ring artifacts from CBCT images. First, the reconstructed CBCT image is transformed from Cartesian coordinates into polar coordinates, such that ring artifacts in Cartesian coordinates are transformed as stripe artifacts in polar coordinates that are easier to be removed. Second, a minimization model based on L₀ smoothing is introduced to smooth the transformed image such that the major edges of the image are reserved while the artifacts are eliminated as special low-amplitude structures. Finally, the obtained artifacts are transformed back into Cartesian coordinates and are subtracted from the original CBCT image. Thus, the CBCT image without ring artifacts is obtained. The experiments based on different CBCT images show that the proposed method is more effective compared with other algorithms.