Dual-energy X-ray analysis using synchrotron computed tomography at 35 and 60keV for the estimation of photon interaction coefficients describing attenuation and energy absorption

A novel method for dual-energy X-ray analysis (DEXA) is tested using measurements of the X-ray linear attenuation coefficient ?. The key is a mathematical model that describes elemental cross sections using a polynomial in atomic number. The model is combined with the mixture rule to describe ? for materials, using the same polynomial coefficients. Materials are characterized by their electron density N e and statistical moments Rk describing their distribution of elements, analogous to the concept of effective atomic number. In an experiment with materials of known density and composition, measurements of ? are written as a system of linear simultaneous equations, which is solved for the polynomial coefficients. DEXA itself involves computed tomography (CT) scans at two energies to provide a system of non-linear simultaneous equations that are solved for N e and the fourth statistical moment R 4. Results are presented for phantoms containing dilute salt solutions and for a biological specimen. The experiment identifies 1 systematic errors in the CT measurements, arising from third-harmonic radiation, and 20-30 noise, which is reduced to 3-5 by pre-processing with the median filter and careful choice of reconstruction parameters. DEXA accuracy is quantified for the phantom as the mean absolute differences for N e and R 4: 0.8 and 1.0 for soft tissue and 1.2 and 0.8 for bone-like samples, respectively. The DEXA results for the biological specimen are combined with model coefficients obtained from the tabulations to predict ? and the mass energy absorption coefficient at energies of 10keV to 20MeV.