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Development of a cone angle weighted three-dimensional image reconstruction algorithm to reduce cone-beam artefacts

¹ Department of Radiology, Shinshu University Hospital, 3-1-1, Matsumoto, Nagano, 390-8621, Japan; ² Kanazawa University, Graduate School of Medicine, 5-11-80, Kanazawa, Ishikawa, 920-0942, Japan

Received 10 July 2005; revised 19 January 2006; accepted 8 February 2006

Objectives: Image reconstruction from cone-beam projections collected along a single circular source trajectory is commonly done using the Feldkamp algorithm, which performs well only with a small cone angle. In this report, we propose an algorithm to reduce cone-beam artefacts by increasing the cone angle by several fold to achieve satisfactory image quality at the same radiation dose.

Methods: To examine the factors involved in the occurrence of cone-beam artefacts, a microspheres-phantom was arranged longitudinally at different positions and a computer simulation was performed. Due to differences in projection angle, data projected onto the detector surface were projected along trajectories shown as different periodic functions depending on the distance and position from the mid-plane position. Therefore, projection along several detector channels based on different projection data resulting from different periodic functions is considered responsible for the increase in cone-beam artefacts associated with an increase in the distance of reconstruction planes from the mid-plane position. Our recommended algorithm to reduce such artefacts features a change in weighting with respect to projection data obtained at different projection angles, three-dimensional back-projection of corrected projection data.

Results: Numerical phantom simulation and real human head origin study (a prototype cone-beam CT) showed that the effect of the reduction in cone-beam artefacts of an object located at the edges was markedly enhanced at reconstruction planes at positions further from the mid-plane position.

Conclusion: We propose a projection angle weight-based algorithm to increase the cone angle by several fold to achieve satisfactory image quality at the same radiation dose. These findings confirmed that this algorithm reduces cone-beam artefacts and generates high-quality reconstruction images.

Keywords: computed tomography;; cone-beam CT;; CT imaging;; artefacts