Controls: The imaging workflow was also applied to hydrated and/or healthy lung tissue as a control. First, overview scans covering the entire samples were recorded. Then, hydrated 1 mm biopsy punches (two for CTRLI, one for CTRLII and CTRLIII, where CTRLII and CTRLIII are from the same patient) were recorded in (1 - parallel beam) configuration. Biopsy punches from CTRLII and CTRLIII were also examined in (2 - cone beam) mode. Appendix 3—figure 1 presents (a) the rendering of the hydrated control, and (b,c) virtual slices through the reconstruction volume, showing the lung parenchymal architecture in healthy control tissue. UA-stained samples: For all Covid-19 patients, autopsies were also treated by UA-staining in order to increase the contrast. Stitched overview scans in (1 - parallel beam) configuration were recorded, similar to Figure 3. From the UA-labeled tissue blocks of patients I, III, IV and V, 1 mm, biopsy punches were than scanned in the same configuration (Figure 4). Using the (2 - cone beam) setup, these samples from I, III and IV were imaged at 8.0⁢keV x-rays, while V was examined at 13.8⁢keV, as shown for Figure 5. Variation of propagation distance: Scans of the unstained tissue block from patient II were recorded at different propagation distances (z12=50, 100 and 125keV) and different x-ray energies (13.3, 13.8, 14.3 and 14.8 keV). In cone-beam configuration, the unstained biopsy punch from patient I was scanned at 13.8⁢keV x-rays. Compact μCT scans: Prior to the synchrotron experiment, some of the samples have been examined with a laboratory phase-contrast μCT-setup in large mm2-sized FOV-configuration (Liquid metal jet source, Kα=9.5keV, pxeff=5μm, z12=1.7m, 1200 projections of 1 s exposure time with a flat panel CMOS detector with 150⁢μ⁢m Gadox-scintillator, PerkinElmer, USA) (Bartels et al., 2013). Metal-staining (here UA) of the lung tissue helped to achieve sufficient contrast, similar to previous μCT-studies of other biological tissues (Müller et al., 2017; Busse et al., 2018; De Clercq et al., 2019). The resulting overview scans could also be correlated well with histological sections.