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Most material discrimination in security inspections is based on dual-energyx-ray imaging, which enables the determination of a material's effective atomicnumber (Zeff) as well as electron density and its consequent classification asorganic or inorganic. Recently phase-based "dark-field" x-ray imagingapproaches have emerged that are sensitive to complementary features of amaterial, namely its unresolved microstructure. It can therefore be speculatedthat their inclusion in the security-based imaging could enhance materialdiscrimination, for example of materials with similar electron densities and Zeff but different microstructures. In this paper, we present a preliminaryevaluation of the advantages that such a combination could bear. Utilising anenergy-resolved detector for a phase-based dark-field technique providesdual-energy attenuation and dark-field images simultaneously. In addition,since we use a method based on attenuating x-ray masks to generate thedark-field images, a fifth (attenuation) image at a much higher photon energyis obtained by exploiting the x-rays transmitted through the highly absorbingmask septa. In a first test, a threat material is imaged against a non-threatone, and we show how their discrimination based on maximising their relativecontrast through linear combinations of two and five imaging channels leads toan improvement in the latter case. We then present a second example to show howthe method can be extended to discrimination against more than one non-threatmaterial, obtaining similar results. Albeit admittedly preliminary, theseresults indicate that significant margins of improvement in materialdiscrimination are available by including additional x-ray contrasts in thescanning process.

physica scripta

Increased material differentiation through multi-contrast x-ray imaging:  a preliminary evaluation of potential applications to the detection of threat  materials