Atomic number measurement precision of spectral decomposition methods for CT

We have investigated the classical attenuation decomposition and base material decomposition CT algorithms invented by Alvarez and Macovski in 1976 for their ability to provide quantitative atomic number Z of a given attenuator. For this purpose we have generated attenuation functions of the elements from Z = 1 to Z = 20 from measured attenuation data. We have fitted these functions to two sets of base functions: 1. the photoelectric absorption + Klein-Nishina scattering model and 2. the effective bone and water attenuator model. The results indicate model mismatches in the range of DeltaZ = plusmn0.5 for the base material decomposition and DeltaZ = plusmn0.7 for the attenuation decomposition