Phase contrast imaging with a laboratory-based microfocus X-ray source

Abstract

This project looks at the design of an in-line X-ray phase contrast imaging system, based around the Bede Microsource®, on a suitable scale for imaging small pathological samples. The system is applied to two test objects to assess feasibility of its use in practice. The system comprises: microfocus X-ray source, copper and rhodium targets, phase object and detector. By altering sample position, phase contrast is seen to vary proportionally with propagation distance. By increasing source size, phase contrast is seen to degrade with increasing source dimensions. It is furthermore determined that transverse coherence in the direction perpendicular to a sample boundary dominates the result. Using different operating voltages with an image manipulation approach, the importance of monochromaticity is investigated. It is determined that less polychromatic X-rays provide better phase contrast. However, applying a filter method of monochromation reduces phase contrast due to beam hardening, so this method is unsuitable for phase imaging with this system. By increasing sample thickness, phase contrast is seen to plateau at a certain thickness, dependant on X-ray energy, revealing a practical limitation of the system. Introduction of water and glass to the system is seen to be detrimental to phase contrast, due to beam hardening. However phase contrast is not destroyed by the presence of water. When imaging a mammographic test object comprising low-contrast details and breast tissue morphology, the system detects all low-contrast details extremely well. Furthermore, using a phase object together with breast tissue morphology, with the harder rhodium X-rays, the system detects an anomaly of -500J.!m through the noise of simulated breast tissue. Finally, we see the difference in two scorpion sting images: an absorption image taken at the beginning of the project and a phase image taken after the system has been improved.