Virtual histology of dried and mummified biological samples by laboratory phase-contrast tomography

Ancient remains from humans, animals and plants hold valuable information about our history. X-ray imaging methods are often, because of their non-destructive nature, used in the analysis of such samples. The classical x-ray imaging methods, radiography and computed tomography (CT), are based on absorption, which works well for radiodense structures like bone, but gives limited contrast for textiles and soft tissues, which exhibit high x-ray transmission. Destructive methods, such as classical histology, have historically been used for analysing ancient soft tissue but the extent to which it is used today is limited because of the fragility and value of many ancient samples. For detailed, non-destructive analysis of ancient biological samples, we instead propose x-ray phase-contrast CT, which like conventional CT gives volume data but with the possibility of better resolution through the detection of phase shift. Using laboratory x-ray sources, we here demonstrate the capabilities of phase-contrast tomography of dried biological samples. Virtual histological analysis of a mummified human hand from ancient Egypt is performed, revealing remains of adipose cells in situ, which would not be possible with classical histology. For higher resolution, a lab-based nano-CT arrangement based on a nanofocus transmission x-ray source is presented. With an x-ray emission spot of 300 nm the system shows potential for sub-micronresolution 3D imaging. For characterisation of the performance of phase-contrast imaging of dried samples a piece of wood is imaged. Finally, we present the first phase-contrast CT data from our nano-CT system, acquired of the dried head of a bee.