Dimensionality and Background Cancellation in Energy Selective X-Ray Imaging

TL;DR

This paper investigates the use of a third basis function in energy selective X-ray imaging to improve material separation, demonstrating significant accuracy improvements in quantifying iron in tissue mixtures.

Contribution

It shows that incorporating a third basis function enhances material decomposition accuracy in energy selective X-ray imaging without contrast agents.

Findings

Including a third basis function reduces iron quantification error by orders of magnitude.

Third basis function improves separation of iron from tissue backgrounds.

Study uses simulated phantom with realistic tissue variability.

Abstract

Purpose: The set of linear attenuation coefficients that belong to materials in the human body is commonly assumed to be spanned by two basis functions in the range of clinical x-ray energies, even though there is evidence that the dimensionality of this set is greater than two. It has not yet been clear that the use of a third basis function could be beneficial in absence of contrast agents. Approach: In this work, the choice of the number of basis functions used in the basis decomposition method is studied for the task of producing an image where a third material is separated from a background of two other materials, in a case where none of the materials have a K-edge in the range of considered x-ray energies (20-140 keV). The case of separating iron from mixtures of liver and adipose tissue is studied with a simulated phantom which incorporates random and realistic tissue variability. Results: Inclusion of a third basis function improves the quantitative estimate of iron concentration by several orders of magnitude in terms of mean squared error in the resulting image. Conclusions: The inclusion of a third basis function in the basis decomposition is essential for the studied imaging task and could have potential application for quantitative estimation of iron concentration from material decomposed images.