1. A phase-contrast computed tomography scanner for providing phase-contrast, x-ray computed tomography images of a sample, comprising: a polychromatic x-ray source; a power supply source coupled to the polychromatic x-ray source to power the polychromatic x-ray source; a first translation stage coupled to the power supply source; a rotational stage in spaced relation with the translation stage and configured to hold and rotate the sample; wherein the polychromatic x-ray source is spaced sufficiently far from the rotational stage so that x-rays reaching the rotational stage are substantially coherent; a detector in spaced relation with the rotational stage and configured to collect phase-contrast x-ray data from the sample; a second translation stage coupled to the detector; and a computer coupled to the detector and configured to form a computed tomography image of the sample using the phase-contrast x-ray data.