Rapid X-ray energy switching for optimised K-edge subtraction imaging at narrow-band inverse Compton X-ray sources

K-edge subtraction (KES) imaging provides material-specific information exploiting the steep increase in attenuation at an absorption edge. Classically, two monochromatic images acquired with energies right above and below the K-edge are subtracted weighting one image with the approximate energy scaling of the photoelectric effect. This technique was transferred to quasi-monochromatic inverse Compton X-ray sources by implementing a filter made of the investigated material itself, yet at the cost of a reduced contrast-to-noise ratio. While switching between two spectra with a larger energy separation overcomes this issue, the X-ray energy must be changed on the timescale of seconds for this to be used in practical applications. To this end, a framework for rapid X-ray energy switching of inverse Compton X-ray sources is developed and experimentally realised. In case of a larger energy separation, the Compton contribution to the attenuation leads to artifacts using classical KES as it decreases the effective energy scaling. A theoretical model for calculating the reduced scaling factor is derived to overcome this issue. Image improvement by this optimised KES approach is experimentally demonstrated.