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This chapter provides an overviews the statistical decision theory and the associated objective image quality assessment. It focuses on the behavior of the noise propagation in computed tomography (CT) imaging systems, with and without in-line phase-contrast. The chapter analyzes the effect on noise of a widely used phase retrieval approach, based on the Transport of Intensity equation (TIE). It presents an approach, based on the noise power spectrum formalism, for quantifying noise in phase retrieved X-ray radiographs, as well as in phase-contrast computed tomography. Using this approach, in-line phase-contrast imaging in combination with a popular TIE-Hom phase retrieval algorithm has been analyzed and compared with conventional imaging in terms of the noise in the reconstructed projections and CT images. A gain factor has been introduced in order to evaluate the improvement of image quality, in terms of the variance of noise, due to phase retrieval. |
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