Cardiac motion correction based on partial angle reconstructed images in X-ray CT

Abstract

X-ray CT has been widely used in medical diagnosis for its high spatiotemporal resolution. Since the gantry rotation speed is not fast enough compared with the heart motion, however, cardiac X-ray CT imaging is still challenging due to the cardiac motion during CT scanning, which leads to the presence of motion artifacts in the reconstructed image. To obtain a heart image with less motion artifacts, many algorithms have been developed to compensate motion artifacts by estimating the motion using projection data or reconstructed images. However, these algorithms have some limits in motion correction performance. In this dissertation, we propose a novel motion estimation (ME) and compensation (MC) algorithm based on partial angle reconstructed (PAR) images. We first estimate an initial 4D motion vector field (MVF) by using conjugate PAR images, and then refine the MVF by maximizing the information potential of a motion-compensated image. Finally, motion-compensated image reconstruction is performed by using the determined MVF. The experimental results show that the proposed algorithm can noticeably improve the image quality by reducing motion artifacts throughout the image. Another issue in cardiac imaging is that the length of the heart along the z-axis is usually greater than a nominal beam width in conventional CT systems. Thereby, the step-and-shoot or the low-pitch helical scan mode over several cardiac cycles is usually used with ECG-gating to obtain a whole heart image, which causes misalignment artifacts to the reconstructed image due to beat-to-beat variability. In this dissertation, we extend the proposed PAR-based ME/MC algorithm to a non-gated helical scan with an ordinary pitch of around 1.0. We thereby provide a motion-compensated whole heart image without misalignment artifacts while reducing the scan time dramatically. The experimental results show that the proposed algorithm significantly improves the image quality by alleviating motion artifacts.