X-ray energy spectrum plays an essential role in computed tomography (CT)imaging and related tasks. Due to the high photon flux of clinical CT scanners,most of spectrum estimation methods are indirect and usually suffered fromvarious limitations. In this study, we aim to provide a segmentation-freeindirect transmission measurement-based energy spectrum estimation method usingdual-energy material decomposition. The general principle of the method is tominimize the quadratic error between the polychromatic forward projection andthe raw projection to calibrate a set of unknown weights which are used toexpress the unknown spectrum together with a set of model spectra. Thepolychromatic forward projection is performed using material-specific imageswhich are obtained using dual-energy material decomposition. The algorithm hasbeen evaluated using numerical simulations, experimental phantom data as wellas realistic patient data. The results show the estimated spectrum matches thereference spectrum quite well and the method is robust. Extensive studiessuggest the method provides accurate estimate of the CT spectrum withoutdedicated physical phantom and prolonged work flow. This paper may beattractive for CT dose calculations, artifacts reduction, polychromatic imagereconstruction and other spectrum-involved CT applications.
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