Determination of local density and effective atomic number by the dual-energy computerized tomography method with the 192Ir radioisotope

This paper presents the theoretical and experimental results obtained at the Research Institute for Electrical Engineering, Bucharest, Romania, in determining local density and effective atomic number by a newly developed CT method using dual-energy gamma radiation from the 192Ir radioisotope. The applied method is based on modeling total effective cross-section of gamma radiation in the natural materials in function of the atomic number (Z from 1 to 92), in terms of the photoelectric and Compton cross-sections. Also, a new parameter (composition factor k) given by the ratio of the linear attenuation coefficients from the two tomograms is introduced. We investigated 16 materials with effective atomic number Zeff between 6 and 72.2 and bulk density ranging from 2.15 to 10.51 g/cm3, using 310.5 and 469.1 keV gamma radiation. Our results show very good accuracy of the dual-energy CT method for most materials. The error in determining the effective atomic number is less than 5% for Zeff>25 and less than 10% for light materials (Zeff<15), while the error in density estimation is always smaller than 3%.