A Safe, Accurate, Flexible, and Efficient Computed Tomographic System: SAFE-CT

摘要

The X-ray computed tomography (CT) has been widely utilized as a nondestructive diagnostic means to visualize internal structures of human body. However, high radiation exposure in X-ray CT has been an important issue as it will increase the risk of cancer. Unfortunately, CT data acquired at low radiation doses adversely affects the quality of the reconstructions, impeding their readability. Therefore, this thesis focuses on developing a SAFE (Safe, Accurate, Flexible, and Efficient) X-ray CT system to handle reduced X-ray dose levels without compromising image quality.;Firstly, a statistical iterative reconstruction (SIR) algorithm has showing improved image quality in low-dose levels in contrast to the conventional reconstruction methods like filtered back-projection (FBP). However, such improvement requires accurate CT system modeling as well as dramatically increased computation time that arises from the sequential update scheme. In this thesis, we introduce a multi-voxel update scheme that brings out two speedups of two orders of magnitude. In addition, for more realistic, accurate CT system model, this thesis presents the Lookup Table-based Ray Integration (LTRI) method. Secondly, the external knowledge that already exists in the domain of reconstructed high-quality CT scans can be utilized to restore low-quality CT scans suffering from harsh noise and streak artifacts. In this thesis, we incorporate this knowledge by creating a database of high-quality CT scans to assist in the restoration process since after all this is what radiologists do when they examine these low-quality CT images. The external knowledge is also utilized to remove metal artifacts captured during image-guided surgery for the spinal region.;Lastly, we have developed a general-purpose X-ray imaging system using two commercial six-joint robot arms. Unlike the existing CT system, the proposed robotic X-ray imaging system has more freedom in the imaging trajectories and in the imaging modalities. This thesis reports on a first phantom study using the proposed system within a standard circular trajectory. We used the acquired data in a 3D reconstruction framework and achieved promising results. Overall, in this thesis, we build the SAFE CT system that provides the safety of patients by reducing X-ray exposure while keeping highly accurate image quality in efficient and flexible manner. The performance of the proposed CT system is evaluated on simulated and clinical CT data.