  We propose an imaging system and methodology for mapping soft-tissue samples
in three dimensions, with micron-scale and isotropic spatial resolution, with
low-concentrations as well as in the absence of heavy metal staining. We used
hard X-ray phase-contrast imaging for the X-ray ability to non-destructively
probe the internal structure of opaque specimens and for enhanced contrast
obtained by exploiting phase effects, even in cases with reduced or absent
staining agents. To demonstrate its applicability to soft-tissue specimens, we
built a compact system that is easily deployable in a laboratory setting. The
imaging system is based on a conventional rotating anode X-ray tube and a
state-of-the-art custom-made radiation detector. The system's performance is
quantitatively assessed on a calibration standard. Its potential for
soft-tissue microscopy is demonstrated on two biological specimens and
benchmarked against gold-standard synchrotron data. We believe that the
approach proposed here can be valuable as a bridging imaging modality for
intravital correlative light electron microscopy and be applied across
disciplines where the three-dimensional morphology of pristine-condition soft
tissues is a key element of the investigation.
