Synchrotron Imaging Assessment of Bone Quality

Abstract

Bone is a complex hierarchical structure, and its principal function is to resist mechanical forces and fracture. Bone strength depends not only on the quantity of bone tissue but also on the shape and hierarchical structure. The hierarchical levels are interrelated, especially the micro-architecture, collagen and mineral components; hence, analysis of their specific roles in bone strength and stiffness is difficult. Synchrotron imaging technologies including micro-CT and small/wide angle X-ray scattering/diffraction are becoming increasingly popular for studying bone because the images can resolve deformations in the micro-architecture and collagen–mineral matrix under in situ mechanical loading. Synchrotron cannot be directly applied in vivo due to the high radiation dose but will allow researchers to carry out systematic multifaceted studies of bone ex vivo. Identifying characteristics of aging and disease will underpin future efforts to generate novel devices and interventional therapies for assessing and promoting healthy aging. With our own research work as examples, this paper introduces how synchrotron imaging technology can be used with in situ testing in bone research.

Measuring bone stiffness using spherical indentation

“…In a study in which nanoindentation elastic modulus data were combined with high-resolution Synchrotron computed tomography (CT) calculations of bone porosity the prediction of the elastic modulus of cortical bone at the millimetre-scale (apparent level) was very good [ 20 ]. Synchrotron CT imaging is not feasible in vivo , though, due to the extremely high radiation dose [ 57 ]. Nanoindentation-derived mechanical properties do not always correlate well with mechanical properties of the whole bone [ 58 ] and this is likely due to it only sampling the tissue-level mechanical properties in a small area, without taking into account changes in porosity or other features in the hierarchical structure of bone [ 58 ].…”

The effect of long-term bisphosphonate therapy on trabecular bone strength and microcrack density

“…To avoid scanning bone tissue damaged during the coring process, the SR micro-CT volume of interest was imaged at the centre of the bone core away from the cut edges (following). 22 Several studies have reported that SR micro-CT is an accurate technique for quantifying bone microstructure in 3D. 23 - 25 A comparison between 2D histology, 3D micro-CT and 3D SR micro-CT reported that the structural parameters were highly correlated (r 2 = 0.84), 26 hence it is unlikely that the preparation of SR micro-CT affected microstructure.…”

Effect of SR-microCT radiation on the mechanical integrity of trabecular bone using in situ mechanical testing and digital volume correlation

“…A deep understanding of bone mechanics at different dimensional scales is of fundamental importance since musculoskeletal pathologies such as osteoporosis or bone metastasis are associated with alterations in the bone structure [1]. Thus, advances in mechanical characterisation of bone at the micro-and nanoscale [2][3][4] would ultimately improve the assessment of the effect of treatments and interventions in pathological conditions [5,6].…”

“…Particularly, in [16,17] deformation and fracture of human cortical bone were evaluated following irradiations up to 630 kGrays (kGy) to simulate typical scan time for a tomographic data set. It was shown how plastic deformation was suppressed after 70 kGy of radiation, due to the reduction of strain carried by the collagen fibrils from ~80% (unirradiated) to ~40% of the applied tissue strain, and apparent strain decreased by a factor of five after tripling the radiation dose; ultimately, suggesting that in situ SR-microCT testing, typically requiring multiple sequential tomograms of the same sample over time, may result in accumulation of significantly large radiation doses that affect mechanical properties [6]. However, despite an ideal safety value in the region of 35 kGy (and below) was suggested, corresponding to the typical dose used to sterilize bone allografts [18], uncertainties still remain on what is the effect of X-ray SR radiation on the genesis and development of bone microdamage with different accumulated dose.…”