Energy dependent systematic errors in dual-energy X-ray CT

Dual-energy X-ray Computed Tomography (DECT) is a technique which is designed to allow the determination of energy-independent material properties. In this study, results of computer simulation show that energy-dependent systematic errors exist in the values of attenuation coefficient synthesized using the basis material decomposition technique with acrylic and aluminum as the basis materials, especially when iodine (e.g., from radiographic contrast media) is present in the body. The errors are reduced when acrylic and an iodine-water mixture are used as the basis materials. The authors propose a simple model for the calculation of energy-dependent systematic errors using effective energies at the lower and higher energy windows of the X-ray spectrum used in the DECT system. The calculated errors agree well with the errors observed in the simulation. These results suggest that the observed systematic errors are predominantly due to the energy dependence of the basis material coefficients.