Two-step iterative reconstruction of region-of-interest with truncated projection in computed tomography

Keisuke Yamakawa; Shinichi Kojima

doi:10.1117/12.2042228

Abstract

Iteratively reconstructing data only inside the region of interest (ROI) is widely used to acquire CT images in less computation time while maintaining high spatial resolution. A method that subtracts projected data outside the ROI from full-coverage measured data has been proposed. A serious problem with this method is that the accuracy of the measured data confined inside the ROI decreases according to the truncation error outside the ROI. We propose a two-step iterative method that reconstructs image inside the full-coverage in addition to a conventional iterative method inside the ROI to reduce the truncation error inside full-coverage images. Statistical information (e.g., quantum-noise distributions) acquired by detected X-ray photons is generally used in iterative methods as a photon weight to efficiently reduce image noise. Our proposed method applies one of two kinds of weights (photon or constant weights) chosen adaptively by taking into consideration the influence of truncation error. The effectiveness of the proposed method compared with that of the conventional method was evaluated in terms of simulated CT values by using elliptical phantoms and an abdomen phantom. The standard deviation of error and the average absolute error of the proposed method on the profile curve were respectively reduced from 3.4 to 0.4 [HU] and from 2.8 to 0.8 [HU] compared with that of the conventional method. As a result, applying a suitable weight on the basis of a target object made it possible to effectively reduce the errors in CT images.

Citation Download Citation

Keisuke Yamakawa, Keisuke Yamakawa, Shinichi Kojima, Shinichi Kojima, "Two-step iterative reconstruction of region-of-interest with truncated projection in computed tomography", Proc. SPIE 9033, Medical Imaging 2014: Physics of Medical Imaging, 90333B (19 March 2014); doi: 10.1117/12.2042228; https://doi.org/10.1117/12.2042228

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