System-Independent Characterization of Materials Using Dual-Energy Computed Tomography

Abstract

We present a new decomposition approach for dual-energy computed tomography (DECT) called SIRZ that provides precise and accurate material description, independent of the scanner, over diagnostic energy ranges (30 to 200 keV). System independence is achieved by explicitly including a scanner-specific spectral description in the decomposition method, and a new X-ray-relevant feature space. The feature space consists of electron density, , and a new effective atomic number, , which is based on published X-ray cross sections. Reference materials are used in conjunction with the system spectral response so that additional beam-hardening correction is not necessary. The technique is tested against other methods on DECT data of known specimens scanned by diverse spectra and systems. Uncertainties in accuracy and precision are less than 3% and 2% respectively for the ( , ) results compared to prior methods that are inaccurate and imprecise (over 9%).

Effective atomic number and electron density determination using spectral x-ray CT

“…In their study, Azevedo et al 6 demonstrated system-independence of the method and very good accuracy and precision for a set of standard materials with Z e < 15 with well-known physical parameters.…”

“…where A(Z) is the atomic mass (g/mole) of the element Z. To approximate the atomic number of such a compound Azevedo et al 6 used the effective atomic number, Z e , defined as a non-integer atomic number that corresponds to an artificial element, for which the interactions are assumed to be modeled by the X-ray attenuation cross sections. The cross sections for the artificial element Z e are obtained by a linear interpolation between the cross section of the two adjacent elements in the periodic table:…”

“…4,5 With a DECT acquisition, the LAC of materials is probed at two different X-ray spectra (as the low-and high-energy pair in Fig. 1) and converted into the energy-independent physical parameters of electron density ρ e and effective atomic number Z e , as in the System-Independent ρ e /Z e (SIRZ) method proposed by Azevedo et al 6 and further developed by Champley et al 7 This can be technically achieved, for example with a consecutive scan with different source filtration and kilovoltage peaks, or using dual-energy sandwich detectors. 8 However, the performance of these techniques depend on the choice of the pair of spectra used for the DECT acquisitions and the estimation of their respective detector spectral responses.…”

SABER: A Systems Approach to Blur Estimation and Reduction in X-Ray Imaging

“…The ability of X-rays to penetrate deep inside a material makes it a useful tool to visualize the interior morphology of objects. X-ray imaging is very popular in applications such as industrial imaging [1]- [4], medical diagnosis [5], [6], and border security [4], [7]- [9]. A schematic representation of a typical cone-beam X-ray imaging system is shown in Fig.…”

“…µ (E, r) dr dE, (1) where µ(E, r) is the LAC of the object at X-ray energy E and spatial location r, L(i, j) is the line along which µ(E, r) is integrated, and S(E) is the X-ray spectral density such that E S(E)dE = 1 [4]. We will call the expression on the right side of the equality in equation 1as the ideal transmission functionT (i, j), i.e.,…”