X-ray grating interferometry (XGI) is a phase-contrast imaging technique that allows for a quantitative measurementof the refractive index with high density resolution in a model-independent manner|i.e. without a prioriknowledge of the specimen composition. However, the retrieval of the X-ray wavefront phase shift relies on theaccurate measurement of the interference pattern phase shift, making XGI vulnerable to phase wrapping whenthe interference pattern phase shift, related to the derivative of the wavefront phase shift, is large. Standardprocedure for avoiding phase wrapping involves submerging the specimen in a water bath to reduce the mismatchof the index of refraction at the boundaries, but this requires a top-down rotation stage and is susceptible togas bubble formation inside the water bath. Our team has presented an algorithm to remove phase wrappingartifacts for cylindrically shaped specimens that is applied to the phase-retrieved sinogram. This algorithmmodels and replaces phase-wrapped data to prevent the spread of cupping" artifacts due to the integration ofthe di erential phase during reconstruction. We give a criterion for selecting the modeling parameters so thatthe resulting measurement of the index of refraction matches the results of measurements without phase wrapping.We also apply this technique to cases where phase wrapping occurs at multiple interfaces. This algorithmallows for XGI measurements without a water bath and top-down rotation stage at synchrotron and laboratoryfacilities, especially as sensitivity increases.
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