Signal optimization in mesh-based X-ray phase and dark field imaging

X-ray phase differences imparted by tissue are roughly 1000 times larger than x-ray attenuation differences. Small-angle scatter from tissue microstructure can provide an additional “dark field” signal that is complementary to attenuation and phase. Phase and dark field images can provide enhanced contrast as well as tissue specific information. However, the acquisition of these images requires highly coherent illumination or multiple precisely machined and aligned gratings, which may limit the clinical applicability of these techniques. Our method employs a single, low-cost wire mesh that does not need precise alignment and relaxes the coherence requirement on the source. However, the coarseness of the mesh reduces the strength of the phase and dark field signal compared with grating-based techniques, so it is important to design a system to optimize signal to noise ratio. We performed optimization experiments by adjusting distances between the source, mesh, phantom and detector, varying the x-ray energy and acquiring images with and without a polycapillary optic, which can improve beam coherence. We find optimal ranges for these parameters through simulation and experiment. 

This work was supported in part by the NY State Department of Health (DOH01-C33920GG-3450000).