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

This paper presents the theoretical and experimental results obtained at th e Research Institute for Electrical Engineering, Bucharest, Romania, in det ermining local density and effective atomic number by a newly developed CT method using dual-energy gamma radiation from the Ir-192 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 att enuation coefficients from the two tomograms is introduced. We investigated 16 materials with effective atomic number Z(eff) between 6 and 72.2 and bu lk density ranging from 2.15 to 10.51 g/cm(3), using 310.5 and 469.1 keV ga mma radiation. Our results show very good accuracy of the dual-energy CT me thod for most materials. The error in determining the effective atomic numb er is less than 5% for Z(eff) > 25 and less than 10% for light materials (Z (eff) < 15), while the error in density estimation is always smaller than 3 %. (C) 2001 Elsevier Science B.V. All rights reserved.