3D Synchrotron Imaging of Bone Tissue : from micro to cellular scale

International audienceThe osteocyte system located within the lacuno-canalicular network (LCN) is playing a key role in the mechanobiology of bone. Synchrotron Radiation (SR) micro-CT was recently used in a number of studies to characterize osteocyte lacunae. Nevertheless, few works are reporting three-dimensional properties of both osteocyte lacunae and canaliculi. Here, we show that SR nano-CT can be used either for a global assessment of the LCN in entire osteons or a detailed analysis around a few cells.We used SR parallel-beam micro-CT at beamline ID19 at the European Synchrotron Radiation Facility (ESRF) to image the LCN [1]. With a nominal voxel size of 280nm, this technique provides images of the LCN within a cubic FOV of side 600μm, including over hundreds of cells in one or several osteons. We developed a framework to extract statistical information about the lacunae and on the number of canaliculi issued from each lacuna. Due to the limited spatial resolution of the image compared to the canaliculi diameter, the segmentation of the LCN is the most challenging part of the analysis and new solutions were investigated. This method was applied to the analysis of human femoral cortical bone samples. The mean and standard deviation of lacunar volume was 216.44 ± 84.7 μm3 and their average lengths were respectively 15.2, 7.8 and 4.0, with a length ratio about 4:2:1. The average distance between lacunae was found to be 23.2 μm. The average number of canaliculi per lacuna was found to increase between 36.9 and 108.6 with the distance from the lacunae. The mean of the average length of the primary canaliculi was about 6.4 μm.SR magnified phase CT at the nano scale (voxel size : 60 nm) was used to image the LCN on more restricted FOV (side ~ 120 μm) at beamline ID22, ESRF [2]. This technique provides a detailed rendering of the LCN architecture including the organization of canaliculi around the lacunae, an assessment of the local degree of mineralization of bone, as well as information about the 3D organization of the collagen fibers.The imaging techniques developed here are likely to provide a better understanding of the role of the 3D geometry of the LCN on biomechanical strain and stress at the nano scale level.[1] Pacureanu A, Langer M, Boller E, Tafforeau P, Peyrin F. Med Phys 2012;39:2229.[2] Langer M, Pacureanu A, Suhonen H, Grimal Q, Cloetens P, Peyrin F. PLoS ONE 2012;7:e35691