Research on Conceptual Design and Image Reconstruction for 4-D Computed Tomography

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Development 4-D CT scanners which can visualize motions of human organs began very recently in a few manufactures. In particular, a scanner developed by National Institute of Radiological Sciences in conjunction with Toshiba Medical Systems has a good reputation all over the world. The current 4-D CT scanners measure projection data by rotating a cone-beam x-ray source continuously on a single circular orbit as proposed by Feldkamp. However, these methods suffers from several drawbacks such as (1)image artifacts due to incompleteness of the single circular orbit, (2)insufficient time resolution, and (3)significant increase of radiation dose. To overcome these drawbacks, this research project investigates new designs of 4-D CT scanners together with associated image reconstruction techniques. These include (1)image reconstruction algorithm to reduce the Feldkamp artifacts, (2)saddle trajectories to measure complete data, (3)design of 4-D CT scanners using multiple x-ray sources to improve time resolution, and (4)region of interest x-ray exposure techniques to reduce the radiation dose. The results have been published as 9 international journal papers and 10 international conference papers. In conclusion, we believe that several innovative basic techniques for developing future 4-D CT scanners could by obtained in this research project.