High resolution algolithm for fan-beam-CT system

For the improvement of spatial resolution of x-ray CT, theoretical considerations were carried out for relationship between sampling mechanism and frequency component of projection data for a fan-beam CT. Basic specifications for the third generation fanbeam x-ray CT system was proposed and its performance was examined. Examinations by a phantom and human organism were also made. By the consideration on measurement geometry of an x-ray CT system and its performance, specifications of the third generation x-ray CT system, and schematic diagram of its xenon detector was proposed. Results obtained by the examinations of factors affecting the CT system image resolution, modulation transfer function of sample aperture, correlation between projection data and sample location and related matters are shown in this paper. It was found that the nyquist frequency of total projections were practically twice to one projection by analyzing mutual relations of the data, and it was speculated that the third generation x-ray CT system contained twice of informations compared with a nyquist frequency decided by detector element width. New algorithm of high resolution was proposed to take out informations which is higher than the nyquist frequency. The proposed new algorithm was found satisfactory both by a phantom experiment and imaging experiment by human tissues or organs such as otolaryngological and spinal regions. (Takagi, S.)