CORRECTION OF ENERGY-DEPENDENT SYSTEMATIC-ERRORS IN DUAL-ENERGY X-RAYCT USING A BASIS MATERIAL COEFFICIENTS TRANSFORMATION METHOD

Computer simulation results from our previous studies showed that ener gy dependent systematic errors exist in the values of attenuation coef ficient synthesized using the Basis material decomposition technique w ith acrylic and aluminum as the basis materials, especially when a hig h atomic number element (e.g., iodine from radiographic contrast media ) was present in the body. The errors were reduced when a basis set wa s chosen from materials mimicking those found in the phantom. In the p resent study, we employed a basis material coefficients transformation method to correct for the energy dependent systematic errors. In this method, the basis material coefficients were first reconstructed usin g the conventional basis materials (acrylic and aluminum) as the calib ration basis set. The coefficients were then numerically transformed t o those for a more desirable set of basis materials. The transformatio n was done at the effective energies of the low and high energy window s of the x-ray spectrum. With this correction method using acrylic and an iodine-water mixture as our desired basis set, computer simulation results showed that accuracy of better than 2% could be achieved even when iodine was present in the body at a concentration as high as 10% by mass. Simulation work had also been carried out on a more inhomoge neous 2D thorax phantom of the 3D MCAT phantom. The results of the acc uracy of quantitation were presented here.