Spectrum optimization for x-ray dual-mode imager comprising radiography and coherent scatter

Abstract

Medical, industrial and security x-ray systems should give images that demonstrate material contrast for accurate identification. Acquiring images simultaneously from coherently scattered x rays plus primary is an efficient way to do so. In our projection imaging system for small biological samples, the same detector is used for both primary and scatter, necessitating attenuation of the post-object primary in order that both primary and scatter lie within the detector's dynamic range. Consideration of the cross sections shows that the peak scatter-to-primary fluence ratio is nearly independent of photon energy. At lower energies, coherent scatter produces larger diffraction rings, which give better spatial separation of primary and scatter, but there is more attenuation and multibeam information disentanglement is more difficult. Previous development work for our system used a 110 kV incident beam, with a 1.5-mm-thick post-object attenuator disk of 90% W/10% Cu alloy for each of the 15 pencil beams. In this work we investigate alternatives which are less attenuating. By reducing the kV and using K-edge filters the beam average energy is lowered to achieve greater primary image contrast. Preliminary primary beam results are shown.