Optimization of signal and noise in x-ray phase and dark field imaging with a wire mesh.

Phase differences imparted by tissue are significantly larger than attenuation differences. In addition, small angle scatter from tissue microstructure can provide a dark field signal that is complementary to attenuation and phase. Unfortunately, the low spatial coherence of clinical sources reduces phase and dark field contrast. Our method structures the beam with a single low-cost wire mesh that does not need precise alignment and relaxes the coherence requirement on the source. In addition, focusing polycapillary optics, which can be permanently attached to sources, are employed to allow for the use of high-power primary sources by increasing the phase signal after the focus. However, the coarseness of the mesh reduces the phase and dark field signal-to-noise ratio (SNR) compared with grating-based techniques, so optimization of the phase and dark-field SNR is an important consideration. Here, we consider the impact on the SNR of the distances between the mesh and the source and detector, and of x-ray tube voltages, to optimize the system.