Although the diagnosis of osteoporosis is mainly based on dual x-ray absorptiometry, it has been shown that trabecular bone micro-architecture is also an important factor in regard to fracture risk. In vivo, techniques based on high-resolution x-rayradiography associated to texture analysis have been proposed to investigate bone micro-architecture, but their relevance for giving pertinent 3D information is unclear. Thirty-three calcaneus and femoral neck bone samples including the cortical shells (diameter: , height: ) were imaged using 3D-synchrotron x-ray micro-CT at the ESRF. The 3D reconstructed images with a cubic voxel size of were further used for two purposes: (1) quantification of three-dimensional trabecular bone micro-architecture, (2) simulation of realistic x-rayradiographs under different acquisition conditions. The simulated x-rayradiographs were then analyzed using a large variety of texture analysis methods (co-occurrence, spectral density, fractal, morphology, etc.). The range of micro-architecture parameters was in agreement with previous studies and rather large, suggesting that the population was representative. More than 350 texture parameters were tested. A small number of them were selected based on their correlation to micro-architectural morphometric parameters. Using this subset of texture parameters, multiple regression allowed one to predict up to 93% of the variance of micro-architecture parameters using three texture features. 2D texture features predicting 3D micro-architecture parameters other than BV/TV were identified. The methodology proposed for evaluating the relationships between 3D micro-architecture and 2D texture parameters may also be used for optimizing the conditions for radiographicimaging. Further work will include the application of the method to physical radiographs. In the future, this approach could be used in combination with DXA to refine osteoporosis diagnosis.
The authors thank the ID19 ESRF group for help during tomographic data acquisition. This work was done in the context of the French GDR STIC Santé (CNRS 2647-INSERM) and supported by the French Ministry of Research in the framework of a RNTS project.
II. MATERIAL AND METHODS
II.A. Bone samples
II.B. 3D image acquisition
II.C. 3D image processing
II.C.1. Stacking the different scans
II.C.2. Extraction of trabecular bone volume of interest (VOI)
II.C.3. Quantification of 3D bone micro-architecture
II.D. Radiographic texture analysis
II.D.1. Simulation of radiographicimages
II.D.2. Preprocessing of 2D radiographicimages
II.D.3. Texture analysis
II.E. Statistical analysis
III.A. Results on 3D micro-architecture
III.B. Results on texture analysis
III.B.1. Identification of relevant 2D texture parameters
III.B.2. Incidence of the x-ray beam orientation
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