Three‐dimensional helical‐scan computed tomography using cone‐beam projections

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Abstract
In this paper, we propose an image reconstruction method and computed tomography (CT) equipment with high resolving power that generates three‐dimensional CT images at a high speed. In the proposed method, an X‐ray source that irradiates conical X‐rays and a two‐dimensional detector which consists of fan‐beam detector arrays stacked in the direction of the object's axis rotate continuously at the same time the bed carrying the object translates in the visual field. This method is called a helical scan because the object is fixed and the X‐rays move on a helix and the same measurement data are obtained. We have previously proposed a scanning method in which the X‐ray source moves on a helix [4, 6]. However, the physical implementation of the previous proposal was difficult because it was assumed that the X‐ray beam completely covers the object. In this paper, in order to solve this problem, the implementation of a helical scan is based on a practical model that combines continuous rotation of an X‐ray source and a two‐dimensional detector and translation of the object. We derive an approximate reconstruction method based on the convolution/back‐projection method for fan‐beam projections. We also perform simulation tests based on a model of the human head and demonstrate the effectiveness of the proposed method.

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