Correlative study of liquid in human bone by 3D neutron microscopy and lab-based X-ray μCT

Liquid plays an important role in bone that has a complex 3D hierarchical pore structure. However, liquid (water) is difficult to discern from e.g. an organic matrix by X-ray imaging. Therefore, we use a correlative approach using both high resolution X-ray and neutron imaging. Human femoral bone with liquid adsorbed into some of the pores was imaged with both the Neutron Microscope at the ICON beamline, SINQ at PSI, and by lab-based μCT using 2.7 μm voxel size. Segmentation of the two datasets showed that, even though the liquid was clearly distinguishable in the neutron data and not in the X-ray data, it remained challenging to segment it from bone due to overlaps of peaks in the gray level histograms. In consequence, segmentations from X-ray and neutron data varied significantly. To address this issue, the segmented X-ray porosities was overlaid on the neutron data, making it possible to localize the liquid in the vascular porosities of the bone sample and use the neutron attenuation to identify it as H₂O. The contrast in the neutron images was lowered slightly between the bone and the liquid compared to the bone and the air. This correlative study shows that the complementary use of X-rays and neutrons is very favorable, since H₂O is very distinct in the neutron data, while D₂O, H₂O, and organic matter can barely be distinguished from air in the X-ray data.