X-ray phase-contrast tomography can significantly increase the contrast-resolution of conventional\nattenuation-contrast imaging, especially for soft-tissue structures that have very\nsimilar attenuation. Just as in attenuation-based tomography, phase contrast tomography\nrequires a linear dependence of aggregate beam direction on the incremental direction\nalteration caused by individual voxels along the path of the X-ray beam. Dense objects\nsuch as calcifications in biological specimens violate this condition. There are extensive\nbeam deflection artefacts in the vicinity of such structures because they result in large distortion\nof wave front due to the large difference of refractive index; for such large changes in\nbeam direction, the transmittance of the silicon analyzer crystal saturates and is no longer\nlinearly dependent on the angle of refraction. This paper describes a method by which\nthese effects can be overcome and excellent soft-tissue contrast of phase tomography can\nbe preserved in the vicinity of such artefact-producing structures.
Loading....