Abstract
Material decomposition in computed tomography is a method for differentiation and quantification of materials in a sample and it utilizes the energy dependence of the linear attenuation coefficient. In this study, a post-image reconstruction material decomposition method is constructed for a low-energy micro-CT setup using a photon counting x-ray detector. The low photon energy range (4–11 keV) allows for K-edge contrast separation of naturally occurring materials in organic tissue without the need of additional contrast agents. The decomposition method was verified using a phantom and its capability to decompose biomedical samples was evaluated with paraffin embedded human atherosclerotic plaques. Commonly, the necessary dual energy data for material decomposition is obtained by manipulating the emitted x-ray spectrum from the source. With the photon counting detector, this data was obtained by acquiring two energy window images on each side of the K-edge of one material in the sample. The samples were decomposed into three materials based on attenuation values in manually selected regions. The method shows a successful decomposition of the verification phantom and a distinct distribution of iron, calcium and paraffin in the atherosclerotic plaque samples. Though the decompositions are affected by beam hardening and ring artifacts, the method shows potential for spectral evaluation of biomedical samples.
Highlights
In conventional x-ray imaging, contrast depends on material density
Decomposed images are strongly affected by ring artifacts, which are barely visible in the energy windows
The decomposition method works with the three material regions having a material fraction of 1 or close to 1 of the respective material
Summary
In conventional x-ray imaging, contrast depends on material density. While e.g. soft tissue gives good contrast against bone, materials with similar density are harder to distinguish. This can be circumvented by exploiting the energy dependence of the linear attenuation coefficient μE as proposed by [1]. The element specific absorption edges allow for material decomposition, when energy bins can be selected in the vicinity of the edge. Acquiring images with different x-ray energies will allow for separation of materials with similar density based on their specific absorption edges [2, 3]. It can be used to separate materials that are indistinguishable from another in conventional
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