Clarification of aspects in in-line phase-sensitive x-ray imaging.

In this report we clarify two aspects for in-line phase-sensitive x-ray imaging, which includes phase-contrast imaging and phase imaging. First, we point out that there is confusion in the literature about the lateral coherence length, which is widely adopted as the coherence criteria for implementing phase-sensitive imaging. The confusion exaggerates the coherence requirement for clinical implementation of in-line phase-sensitive imaging. Instead we show that the ratio of the phase-space shearing length to lateral coherence length is a good measure for gauging the partial coherence realized in a specific image setting. Second, based on the general intensity equation for in-line phase-sensitive imaging, we discuss the differences between the phase-contrast imaging and phase imaging in terms of the physics mechanism, image acquisition approaches, computation algorithm development, and the potentials for tissue quantitative characterization.