High-resolution quantitative phase-contrast x-ray imaging for biomedical samples at PETRA III

Abstract

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.