  Low dose, high contrast x-ray imaging is of general interest in medical
diagnostic applications. X-ray Mach-Zehnder interferometers using collimated
synchrotron beams demonstrate the highest levels of phase contrast under a
given exposure dose. However, common x-ray sources emit divergent cone beams.
Here, we developed a spherical-wave inline Mach-Zehnder interferometer for
phase contrast imaging over an extended area with a broadband and divergent
source. The first tabletop system was tested in imaging experiments of a
mammographic accreditation phantom and various biological specimens. The noise
level of the phase contrast images at a clinical radiation dose corresponded to
a 6 nano radian bending of the x-ray wavefront. Un-resolved structures with
conventional radiography and near-field interferometer techniques became
visible at a fraction of the radiation dose.
