A novel approach for the localization of X-ray stains in individual cells with ptychographic computed tomography was recently demonstrated. With a basis material decomposition in the image domain the quantitative stain concentration can be retrieved with nanoscopic resolution. So far, the approach was demonstrated for two different staining elements, but it has the potential to be easily applied to other contrast agents. The noise in the resulting basis materials depends on the one hand on the noise in the original data, and is furthermore given by the basis materials and specifically their attenuation properties and electron density. In this work, we theoretically predict the standard deviation in basis material images for several heavy elements. This is done by applying the material decomposition algorithm to an experimental data set. It was found that for more electron dense materials the decomposition should have lower noise in the basis material image of the stain. Furthermore, the energy used for the measurement impacts the standard deviation in the basis material images especially for materials with low atomic number, for which therefore lower X-ray energy should be used for data acquisition.
Phase-contrast imaging is one of the standard X-ray imaging methods at synchrotron beamlines and has already proven to be beneficial for soft-tissue visualization. However, most implementations use single-distance inline phase-contrast techniques, and are thus not able to provide quantitative information. To access these, grating-based imaging (GBI) setups or, rather recently, speckle-based imaging (SBI) methods can be used. We built a new grating-based setup at the beamline P05 operated by HZG at the storage ring PETRA III / DESY. This new setup overcomes the previously reported limitations in spatial resolution compared to inline phase-contrast imaging. Furthermore, it allows for accurate quantitative phase contrast micro computed tomography of biological soft tissue. We replaced the typically used sandpaper by a 2D phase-grating as a wavefront marker, which increased the visibility and allowed for using fewer phase steps. Combined with an existing SBI phase-retrieval algorithm, the so-called Unified Modulated Pattern Analysis (UMPA) and an optimized scan protocol, we reached a resolution below 4 microns in scan times less than two hours. We investigated stained and unstained tissue samples, to quantify the staining process of different tissue types and were able to observe an increase in electron density, dependent on the stain and tissue type. By this, we could show the successful operation of our setup to quantitatively investigate samples on a micro meter scale at the beamline P05.
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