Use of oversampling to quantify phase effects in X-ray images of straight fibers

We use oversampling techniques, similar to those applied to obtain detector MTF from slanted edges, to generate profiles of X-ray magnification images of straight fibers. We have applied this semi-automatic technique to the analysis of 0.5-0.8 mm diameter nylon fiber images acquired on a 48μm pixel pitch flat panel detector with 30 and 40 kV Mo/Mo, Mo/Nb and W/Al X-rays from a 35μm nominal focal spot size microfocus tube, under in-line magnification geometry. The oversampled profiles permit to visualize details in the image beyond what could be observed with traditional methods or visually. The edge enhancement observed in the profiles is an indication of phase effects in the interaction between radiation field and the object. Not only the interference maximum at the profile edge, but also indications of a first minimum in the fiber attenuation region, can be observed. Features of the profile agree with those predicted by Fresnel-based simulations which take into account the radiation spectral shape and the detector MTF. The inverse dependence of edge enhancement on X-ray effective energy is observed (2.8% for 30 kV Mo/Nb and 1.1% for 40 kV W/Al, at magnification 3 and source-to-detector distance 1.0 m). The systematics of the edge enhancement studied for magnifications up to 4 and source-to-detector distances up to 1 m agree with those previously reported by independent methods. This technique, that produces sampling distances many times smaller than the detector pitch, might improve the analysis of measurements designed to evaluate phase effects from fiber profiles.