The influence of X-ray source focal spot size on the sensitivity of grating-based X-ray interferometer

In this paper, a geometric optics based method was established to simulate the propagation-based X-ray phase-contrast imaging (pbXPCI) and calculate the refraction angle of X-ray after passing through an object, the result proved that geometric optics could also deal with the interaction between the object and X-rays in the pbXPCI , thus unifying the theoretical description of the interaction between the object and X-rays in the pbXPCI and the grating-based X-ray interferometer (gbXI). In the region where the refractive index changed quickly, the refraction angle obtained by using wave optics was divergent, while the refraction angle obtained by using geometrical optics was finite. Finally, refraction angles calculated using geometrical optics indicated that smaller focal spot size of X-ray source would produce larger refraction angles. Consequently, smaller focal spot size of X-ray source would produce stronger phase-contrast signal in the pbXPCI and the gbXI, and it is suggested that the maximum detectable refraction angle could be used as a complementary measure of system sensitivity.