Purpose and context
Synchrotron micro-CT opens new perspectives for assessing bone metabolism. Bone remodeling is the process by which bone is sequentially resorbed and reconstructed. After reconstruction, the mineral concentration of new bone in localized regions increases progressively. At the microscopic scale, bone appears as patches of bone structural unit with different degrees of mineralization. Till now, bone mineralization was mainly investigated by two-dimensional techniques such as quantitative micro-radiography or Electronic Microscopy. |
Microradiography, G. Boivin, Inserm U403, Lyon
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Methods
We demonstrated the possibility of quantifying the degree of mineralization of bone in three-dimension from synchrotron micro-CT. This capability is related to the use of high flux monochromatic x-ray beams which makes it possible to reconstruct quantitative images of the linear attenuation in bone. A method to estimate the distribution of mineral concentrations in the bone phase was proposed. The accuracy of the method was evaluated from phantoms with known concentration of Hydroxyapatite
Results
The differences in gray levels observed in micro-CT images effectively correspond to the various stages of mineralization associated with bone remodeling. The quantitative results obtained from micro-radiography and micro-CT on matched regions are in good agreement [1].
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Images of the same slice in an iliac crest biopsy bone sample : a) computed from the 3D synchrotron micro-CT image (voxel size 10µm), b) from quantitative microradiography (from [1] |
This technique was used to study the effects of a treatment for osteoporosis with Etidronate (coll. LBTO, Inserm E366 Saint-Etienne). The analysis of biopsies taken from patients with osteoporosis before and after one or two years of treatment showed an increase in the degree of mineralization with the treatment without significant modification in the micro-architecture [Nuzzo et al, J Bone Min Res, 2002]. A more recent study was focused on the characterization of subchondral bone in patients with arthrosis and osteoporosis (below). A significant increase can be seen in the thickness of the trabeculae in the arthrosis patients, as well as a lower degree of mineralization, which could be interpreted as an increase in remodeling [Chappard et al., Osteoarthritis Cartilage, 2006].
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a) Synchrotron Radiation micro CT section of bone micro-architecture in a patient with arthrosis, and b) distribution of the degree of mineralization in patients with arthrosis and osteoporosis from [Chappard et al., Osteoarthritis Cartilage 2006]
Collaborations and acknowledgements These works were performed in collaboration with Inserm U403, Lyon, Inserm E366 Saint-Etienne, Inserm U658, Orléans, and the ESRF (Grenoble).