X-ray dual-energy calibration based on estimated spectral properties of the experimental system

The authors present a calibration method for dual-energy X-ray computed tomography. Contrary to conventional methods, which derive calibration information from reference measurements of the target materials or a set of basis materials, the proposed method uses a set of gauging measurements in order to build up a spectral model of the actual acquisition system. Under the assumption of known attenuation coefficients for the gauging materials, the emitted tube spectrum and the spectral sensibility of the detection system are estimated from a set of attenuation measurements. This spectral model of the acquisition system is used to determine calibration information for any desired material combination. Besides a reduction of the number of reference measurements, this method allows quantitative measurements of substances, for which no reference samples are available. As an example, we determine the spectral model for a computed tomography (CT) system based on a conventional X-ray tube and a scintillation screen. Calibration and material separation are shown for an object of 1-cm thickness, composed of the material combination epoxy/glass.