Detection and correction of stripes in the sinogram for suppression of ring artifacts in CT imaging

Abstract

the reconstructed images. This thesis has two thrust: the ¯rst goal is to detect the ring generating stripes in the sinogram, which encompasses the detection of both isolated and contiguous stripes generated due to dysfunctional and defunct detector elements. The second goal is to correct those erroneous detectors' responses in the sinogram domain. As ring artifacts are manifested as edge creating stripes, single or contiguous, in the sinogram, they are detected based on the absolute sum of the second derivative of the sinogram and a self adaptive threshold computed from its ¯rst derivative using its statistical properties. The wide band contiguous stripes are detected using the mean curve and multilevel polyphase decomposition of the given sinogram. For the correction of ring artifacts, variable window moving average (VWMA) and weighted moving average (WMA) ¯lters are proposed in this work. The robustness of the proposed method is then checked by producing images reconstructed from both fan beam and cone beam reconstruction algorithms. All diverse data and di®erent patterns of artifacts like isolated or band rings, artifacts from defunct and mis-calibrated detectors are observed in this thesis. Experimental results show that the proposed method can detect ring artifacts with high accuracy and thus remove them more e®ectively without imparting noticeable distortion in the image as compared to other reported techniques.