Before recording tomographic scans, tissue sections of 2.5⁢μ⁢m thickness were cut from the top, stained by HE (hematoxylin and eosin) and imaged with a microscope. Appendix 1—figure 1 shows the histological slice of each sample. The imaged section is just above the upper plane of the 3D PC-CT reconstruction volume, but not part of it.