Phase Imaging Using Focused Polycapillary Optics

Conventional radiographic techniques depend on attenuation, which provides low contrast between soft tissues. However, X rays can accumulate large differential phase delays even in weakly absorbing materials. This can produce significantly higher contrast. One technique for taking advantage of phase effects, propagation-based phase imaging, can yield marked edge enhancement but requires spatially coherent intense sources. Microfocus sources have sizes on the order of tens of microns but necessarily are low power and hence require long exposures. In this project, X-ray optical and computational techniques were explored to develop both edge-enhancement and phase imaging using a large spot conventional source. A polycapillary optic was employed to create a small secondary source from a large spot rotating anode X-ray generator. The secondary spot created by the focusing polycapillary optic was 114 µm ± 50 µm. Images of a 1.6 mm polyethylene rod were taken at varying distances from the optic. Edge enhancement was observed with a maximum edge-enhancement-to-noise ratio of 6.5. Insect images were also acquired and analyzed. Phase reconstructions were computed using two different approaches, weak attenuation and phase attenuation duality. Pure phase images were successfully reconstructed from the phase contrast images by employing the weak attenuation model.