  Dark-field images are formed by small-angle scattering of x-ray photons. The
small-angle scattering signal is particularly sensitive to structural
variations and density fluctuation on a length scale of several ten to hundred
nanometers, offering a new contrast mechanism to reveal subtle structural
variation of object. In this paper, we derive a novel physical model to
describe x-ray absorption and small-angle scattering, and use the proposed
model to reconstruct the volumetric small-angle scattering images. The
numerical experiments and test experiments demonstrate that the reconstructed
scattering images reveal unique features with a high contrast resolution. The
proposed approach has great potential in biomedical imaging, nondestructive
detections, and other applications.
