Iterative Reconstruction of the Electron Density and Effective Atomic Number using a Non-Linear Forward Model

TL;DR

This paper introduces SIRZ-3, an iterative method that accurately estimates electron density and effective atomic number from dual-energy X-ray CT data, especially for high atomic number materials, by using a new non-linear forward model.

Contribution

SIRZ-3 extends previous methods by iteratively reconstructing rho-e and Z-e without approximations, improving accuracy for high Z-e materials through a novel non-linear forward model.

Findings

SIRZ-3 outperforms SIRZ-2 in accuracy for large Z-e materials.

The performance gap between SIRZ-3 and SIRZ-2 increases with Z-e.

SIRZ-3 effectively reconstructs material properties directly from DECT data.

Abstract

For material identification, characterization, and quantification, it is useful to estimate system-independent material properties that do not depend on the detailed specifications of the X-ray computed tomography (CT) system such as spectral response. System independent rho-e and Z-e (SIRZ) refers to a suite of methods for estimating the system independent material properties of electron density, rho-e, and effective atomic number, Z-e, of an object scanned using dual-energy X-ray CT (DECT). The current state-of-the-art approach, SIRZ-2, makes certain approximations that lead to inaccurate estimates for large atomic numbered (Z-e) materials. In this paper, we present an extension, SIRZ-3, which iteratively reconstructs the unknown rho-e and Z-e while avoiding the limiting approximations made by SIRZ-2. Unlike SIRZ-2, this allows SIRZ-3 to accurately reconstruct rho-e and Z-e even at large values of Z-e. SIRZ-3 relies on the use of a new non-linear differentiable forward measurement model that expresses the DECT measurement data as a direct analytical function of rho-e and Z-e. Leveraging this new forward model, we use an iterative optimization algorithm to reconstruct (or solve for) rho-e and Z-e directly from the DECT data. Compared to SIRZ-2, we show that the magnitude of performance improvement using SIRZ-3 increases with increasing values for Z-e.