Related to the demand for fast and efficient tomographic reconstruction methods, the interest for Direct Fourier (DF) methods, which have a reduced computational complexity, has been growing. In this paper we present a new NUFFT-based DF reconstruction method which can be directly applied to fan-beam CT data sets avoiding the interpolation in Radon space as well as the interpolation in Fourier space. The performance of the new algorithm, in ideal and noisy conditions, is compared to those of other well known reconstruction methods, revealing an excellent behavior, specially in noisy conditions.
We've developed a Multi-slice Spiral CT Simulator modeling the acquisition process of a real tomograph over a 4-dimensional phantom (4D MCAT) of the human thorax. The simulator allows us to visually characterize artifacts due to insufficient temporal sampling and a priori evaluate the quality of the images obtained in cardio-pulmonary studies (both with single-/multi-slice and ECG gated acquisition processes). The simulating environment allows both for conventional and spiral scanning modes and includes a model of noise in the acquisition process. In case of spiral scanning, reconstruction facilities include longitudinal interpolation methods (360LI and 180LI both for single and multi-slice). Then, the reconstruction of the section is performed through FBP. The reconstructed images/volumes are affected by distortion due to insufficient temporal sampling of the moving object. The developed simulating environment allows us to investigate the nature of the distortion characterizing it qualitatively and quantitatively (using, for example, Herman's measures). Much of our work is focused on the determination of adequate temporal sampling and sinogram regularization techniques. At the moment, the simulator model is limited to the case of multi-slice tomograph, being planned as a next step of development the extension to cone beam or area detectors.