Hard X-ray phase tomography for brain tissue imaging

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Phase tomography based on hard X-ray double-grating interferometry (XDGI) is a well-established imaging technique for the three-dimensional visualization of soft tissues, providing tomograms with superior contrast. The experimental setup contains a beam-splitter grating and an analyzer grating. Both gratings have to be placed and oriented with high precision for an optimized functioning of the interferometer. The analyzer grating can be omitted, if the detection unit allows a direct detection of the interference pattern. Such a setup is termed hard X-ray single-grating interferometer (XSGI). XSGI profits from easier handling, as only one grating needs to be aligned, and from the related cost reduction. But, more importantly than that, for the XSGI the spatial resolution is not limited by the period of the analyzer grating, and for equal photon flux, the number of detected photons is increased by a factor of about two. In the present thesis, a peripheral human nerve was embedded in paraffin. In order to compare the performance of XSGI and XDGI for medically relevant, low-absorbing specimens, for both modalities the specimen was measured at the facility Deutsches Elektronen-Synchrotron (DESY), using synchrotron radiation. Subsequently, the acquired tomograms were superimposed using rigid registration, i.e. one dataset was translated and rotated to best fit the other one. Both techniques allow resolving anatomical features of the nerve investigated, including epineurium, perineurium, and endoneurium. Whereas the XDGI data exhibit a better contrast-to-noise ratio, the XSGI tomogram shows an improved spatial resolution by a factor close to two. Thus, it can be concluded that XSGI is the preferred approach for the visualization of paraffin-embedded soft tissues.