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With technological advancement in x-ray photon-counting detection, the research and development in photon-counting spectral CT is gaining momentum towards clinical applications. Compared to its energy-integration counterpart, the photon-counting spectral CT is of freedom in energy binning to support three-material (or multiple-material) decomposition for spectral imaging without contrast agent, in which the selection of basis materials and energy binning (spectral channelization), including the cutting-off at low and high energy ends, the number of energy bins, the allocation of bin center and width and the adoption of spectral filtration, plays pivotal roles in determining the imaging performance. Via phantom studies carried out with a photon-counting spectral CT simulation software package, we investigate the potential performance, including contrast, noise and contrast-to-noise ratio (CNR), of three-material decomposition for spectral imaging (mainly virtual monochromatic imaging/analysis) without contrast agents and its variation as functions over base material selection and energy binning, with emphasis on soft tissue differentiation towards clinical and preclinical applications. The preliminary data show that, given identical x-ray dose, the three-material decomposition based virtual monochromatic imaging/analysis can outperform its two-material decomposition based counterpart in the best case CNR and in the scenarios while the energy goes down to approach 18 keV.
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