  Phase-contrast imaging is an emerging technology that may increase the
signal-difference-to-noise ratio in medical imaging. One of the most promising
phase-contrast techniques is Talbot interferometry, which, combined with
energy-sensitive photon-counting detectors, enables spectral differential
phase-contrast mammography. We have evaluated a realistic system based on this
technique by cascaded-systems analysis and with a task-dependent ideal-observer
detectability index as a figure-of-merit. Beam-propagation simulations were
used for validation and illustration of the analytical framework. Differential
phase contrast improved detectability compared to absorption contrast, in
particular for fine tumor structures. This result was supported by images of
human mastectomy samples that were acquired with a conventional detector. The
optimal incident energy was higher in differential phase contrast than in
absorption contrast when disregarding the setup design energy. Further, optimal
weighting of the transmitted spectrum was found to have a weaker energy
dependence than for absorption contrast. Taking the design energy into account
yielded a superimposed maximum on both detectability as a function of incident
energy, and on optimal weighting. Spectral material decomposition was not
facilitated by phase contrast, but phase information may be used instead of
spectral information.
