Assessment of the 3D spatial distribution of the Calcium/Phosphorus ratio in bone

The purpose of this study was the development of a technique for the non-invasive assessment of the 3D spatial distribution of the Ca/P ratio in bone, which can be applied in a conventional computed-tomography (CT) system, to investigate the variation of Ca/P ratio in healthy and osteoporotic bone, and to potentially enhance osteoporosis understanding and diagnosis. Three-material mass-fraction decomposition CT dual energy analysis (CT-DEA) was developed and optimised for the assessment of Ca/P ratio. As part of this process, density values are provided as a bi-product. The technique was optimised and experimentally applied through a microCT system. The target of the optimisation was to achieve a precision of better than 0.09 in the Ca/P ratio, in order to be able to distinguish between all healthy and osteoporotic regions. Electron dispersive X-ray spectroscopy (EDX) was used to evaluate the performance of CT-DEA on bone apatite. Ca/P ratio measurements were made on the same healthy and inflammation mediated osteoporotic (IMO) rabbit cortical bone surfaces, using CT-DEA and EDX. The mean di fference in the Ca/P ratio between the two techniques was 0.11± 0.08 (8 6%) and the correlation was R²=0.69, suggesting su cient con dence in the experimental capabilities of the CT-DEA technique. Healthy and IMO rabbit, both collagen-free and intact, cortical bone samples were assessed by CT-DEA. Qualitative analysis of the results involved the production of Ca/P ratio and density distribution maps. Quantitative analysis involved the quanti cation of the Ca/P ratio and density across the whole sample and in volumes of interest, as well as the low Ca/P ratio proportion in each sample. Furthermore, a 3D region growing technique was used to study the uniformity of Ca/P ratio in the samples. Results showed di erences in both density and Ca/P ratio between healthy and IMO bone samples, supporting their use as possible osteoporosis indicators and the use of the developed technique for further studies.