Empirical multiple energy calibration (EMEC) for material-selective CT

Multiple energy CT may become widely available due to the technological advances of photon-counting energy-selective x-ray detectors. Dual energy imaging allows to provide images of the photo effect and the Compton effect or linear combinations therefrom (basismaterials). With photon-counting energy-selective x-ray detectors the number of energy bins can be increased and one may want to additionally image one or more contrast agent with K-edges. We propose the empirical multiple energy calibration method (EMEC). It determines all spectral properties necessary for material-selective CT imaging from a single measurement of a calibration phantom. In the special cases of only one material and of two materials the calibration process reduces to the well-known empirical cupping correction (ECC) method and the empirical dual energy calibration (EDEC) method, respectively. If more than two energy bins are measured, EMEC is a generalization of the EDEC idea. Results of simulations with four and five energy bins and four basis materials show the high image quality achieved with EMEC and prove the ability of EMEC to quantify the decomposition quality of the imaging system for each basis material.