In this paper, a Feldkamp-type approximate algorithm is proposed for helical multislice Computed Tomography (CT) image reconstruction. For a planar transversal reconstruction slice under consideration, the algorithm adopts a set of scanning data samples such that all points of the planar plane satisfy Tuy's exact reconstruction condition and, therefore, have potential to be exactly reconstructed. This can provide a practically feasible compromise between image quality and computation efficiency in the reconstruction. Simulation results can show advantages of this algorithm in reduction of artifacts and improvement of computational efficiency in comparison with the existing algorithms.
FDK algorithm has been known to be a popular 3D approximate computed tomography (CT) reconstruction algorithm. However, it may not provide satisfactory image quality for large cone angle. Recently, it has been improved by performing ramp filtering along the direction tangent to the helix, so to provide improved image quality for large cone angle. In this paper, we present a FDK type approximate reconstruction algorithm for gantry-tilted CT imaging. The proposed method improves FDK algorithm by filtering the projection data along a proper direction. Its filtering direction is determined by CT parameters and gantry-tilted angle. As a result, the proposed gantry-tilted reconstruction algorithm can provide more scanning flexibilities in clinical CT scanning and is efficient in computation. The performance of the proposed algorithm is evaluated with Turbell Clock phantom and Thorax phantom compared with gantry tilted FDK algorithm and a popular 2D approximate algorithm. The results show that our new algorithm can achieve better image quality than FDK algorithm and the 2D approximate algorithm for gantry-tilted CT image reconstruction.