Fig. 1.

Synchrotron-based phase contrast imaging. (A) Schematic showing the detection of ASL–air interface in the lumen of an intact trachea using PCI. The synchrotron provides a sufficient amount of parallel spatial coherence X-ray to enhance the contrast between air and ASL using PCI. When X-rays pass through the preparation, the difference in refractive index between ASL and air results in a phase shift of X-rays that causes an interference pattern shown on the detector as variations in X-ray intensity. Since the ASL refractive index is very similar to that of the tissue, PCI cannot resolve the ASL–tissue interface. Thus, we use agarose beads to detect the position of the tissue with respect to the ASL–air interface. (B) Measurement of ASL height in an intact trachea as the distance between the ASL–air interface (arrow) and the edge of the agarose bead touching the surface epithelium by a researcher blinded to the experimental conditions. The agarose bead sits in the ASL layer, and the border of the agarose bead is highlighted. The distance from the bottom of the agarose bead to ASL–air interface is used to measure the height of the ASL layer. The measured height of the ASL layer in this experiment is 115 µm. (C) Frequency distribution and median (dotted line) of ASL height in control tracheas exposed to agar beads containing no bacteria for 5 min; n = 117 agarose beads obtained from tracheal preparations from 39 pigs.