Extracting atomic numbers and electron densities from a dual source dual energy CT scanner: Experiments and a simulation model

Background and purpose: Dual energy CT (DECT) imaging can provide both the electron density rho(e) and effective atomic number Z(eff), thus facilitating tissue type identification. This paper investigates the accuracy of a dual source DECT scanner by means of measurements and simulations. Previous simulation work suggested improved Monte Carlo dose calculation accuracy when compared to single energy CT for low energy photon brachytherapy, but lacked validation. As such, we aim to validate our DECT simulation model in this work. Materials and methods: A cylindrical phantom containing tissue mimicking inserts was scanned with a second generation dual source scanner (SOMATOM Definition FLASH) to obtain Z(eff) and rho(e). A model of the scanner was designed in ImaSim, a CT simulation program, and was used to simulate the experiment. Results: Accuracy of measured Z(eff) (labelled Z) was found to vary from -10% to 10% from low to high Z tissue substitutes while the accuracy on rho(e) from DECT was about 2.5%. Our simulation reproduced the experiments within +/- 5% for both Z and rho(e). Conclusions: A clinical DECT scanner was able to extract Z and rho(e) of tissue substitutes. Our simulation tool replicates the experiments within a reasonable accuracy.