Quadratic relation for mass density calibration in human body using dual-energy CT data

Purpose To derive the mass density (ρ) from dual-energy computed tomography (DECT) data by calibrating electron density (ρe ) and effective atomic numbers (Zeff ) of human tissues. Methods We propose the DEEDZ-MD method, in which a single polynomial parameterization covers the entire human-tissue range to establish an empirical quadratic relation between the atomic number-to-mass ratio and Zeff . Then, we numerically evaluate the DEEDZ-MD method in reference human tissues listed in the ICRP Publication 110 and ICRU Report 46. The tissues are considered to have unknown ρ values. The attenuation coefficients of these tissues are calculated using the XCOM Photon Cross Sections Database. The DEEDZ-MD method is also applied to experimental DECT data acquired from a tissue characterization phantom and an anthropomorphic phantom at 90 kV and 150 kV/Sn. Results The numerical analysis of the DEEDZ-MD method reveals a single quadratic relation between the atomic number-to-mass ratio and Zeff in a wide range of human tissues. The simulated ρ values are in excellent agreement with the reference values over ρ values from 0.260 (lung) to 3.225 (hydroxyapatite). The relative deviations from the reference ρ remain within ±0.6% for all the reference human tissues, except for the eye lens (approximate deviation of -1.0%). The overall root-mean-square error is 0.24%. The application of the DEEDZ-MD method to experimental dual-energy CT data confirms this agreement within experimental accuracy, indicating the practical feasibility of the method. The DEEDZ-MD method enables the generation of ρ images with less image noise than the existing DECT-based conversion of ρ from ρe and with fewer beam-hardening artifacts than conventional single-energy CT images. Conclusions The DEEDZ-MD method can facilitate the generation of ρ images from dual-energy CT data without relying on the nontrivial segmentation of different tissues.