A new anisotropy index on trabecular bone radiographic images using the fast Fourier transform

BACKGROUND: The degree of anisotropy (DA) on radiographs is related to bone structure, we present a new index to assess DA. METHODS: In a region of interest from calcaneus radiographs, we applied a Fast Fourier Transform (FFT). All the FFT spectra involve the horizontal and vertical components corresponding respectively to longitudinal and transversal trabeculae. By visual inspection, we measured the spreading angles: Dispersion Longitudinal Index (DLI) and Dispersion Transverse Index (DTI) and calculated DA = 180/(DLI+DTI). To test the reliability of DA assessment, we synthesized images simulating radiological projections of periodic structures with elements more or less disoriented. RESULTS: Firstly, we tested synthetic images which comprised a large variety of structures from highly anisotropic structure to the almost isotropic, DA was ranging from 1.3 to 3.8 respectively. The analysis of the FFT spectra was performed by two observers, the Coefficients of Variation were 1.5% and 3.1 % for intra-and inter-observer reproducibility, respectively. In 22 post-menopausal women with osteoporotic fracture cases and 44 age-matched controls, DA values were respectively 1.87 ± 0.15 versus 1.72 ± 0.18 (p = 0.001). From the ROC analysis, the Area Under Curve (AUC) were respectively 0.65, 0.62, 0.64, 0.77 for lumbar spine, femoral neck, total femoral BMD and DA. CONCLUSION: The highest DA values in fracture cases suggest that the structure is more anisotropic in osteoporosis due to preferential deletion of trabeculae in some directions

Méthodes d’évaluation de la microarchitecture de l’os trabéculaire humain

La microarchitecture trabéculaire osseuse s’adapte aux contraintes mécaniques, ainsi qu’aux effets de l’âge, de la maladie ostéoporotique et des traitements. In vivo, les anomalies de la microarchitecture peuvent être évaluées à l’aide de paramètres de texture sur des radiographies haute résolution et des images en absorptiométrie biphotonique (DXA). Il est possible d’extraire des paramètres morphologiques et topologiques apparents sur les images d’IRM et 3D avec un appareil dédié appelé high resolution peripheral quantitative computed tomography (HR-pQCT) d’une résolution proche de la taille des travées. In vitro, il est possible, à partir d’échantillons, d’obtenir des analyses 2D en histomorphométrie et 3D à partir d’images de 10 µm environ obtenues par microcomputed tomography (microCT) à partir du rayonnement synchrotron ou de rayons X conventionnels

Diffraction techniques and Vibrational spectroscopy opportunities to characterise bones

International audienc

Analyse des cristaux d’hydroxyapatite dans l’os sous chondral par spectroscopie infrarouge à transformée de Fourier et diffraction neutronique sur poudres

International audienceCR_Chimie_22_HAL_Chappard_8Juin2015 1 1 Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and powder neutron diffraction methods Analyse des cristaux d'hydroxyapatite dans l'os sous chondral par spectroscopie infra-rouge à transformée de Fourier et diffraction neutronique sur poudres ABSTRACT English Fourier Transform Infrared (FTIR) spectroscopy and powder neutron diffraction (PND) were performed in human subchondral bone covered (C+) or not covered by cartilage (C-) to study hydroxyapatite. With FTIR, the carbonation rate was 30% with identical spectra in C+ and C-. With PND, the width of the diffraction peak (hkl=002) highlighted the anisotropy of nanocrystals (with needle and/or platelet-like shape) along the c-axis with average length of 50 nm and thickness of 10 nm and with no difference between C+ and C- .Des expérimentations par spectroscopie infrarouge à transformée de Fourier (FTIR) et par diffraction neutronique sur poudres (PND) ont été réalisées sur de l’os sous-chondral humain recouvert (C+) ou non recouvert par le cartilage (C) pour étudier l’hydroxyapatite (HAP).En FTIR, le taux de carbonatation est de 30% avec des spectres identiques pour C+ et C−. Avec la PND, la largeur du pic de diffraction (hkl = 002) a mis en évidence l'anisotropie des nanocristaux (en forme aiguille et/ou de plaquettes) le long de l'axe c, avec une longueur moyenne de 50 nm et une épaisseur de 10 nm, sans différence entre C+ et C−

Graph Structuring of Skeleton Object for Its High-Level Exploitation

International audienceSkeletonization is a morphological operation that summarizes an object by its median lines while preserving the initial image topology. It provides features used in biometric for the matching process, as well as medical imaging for quantification of the bone microarchitec-ture. We develop a solution for the extraction of structural and morpho-metric features useful in biometric, character recognition and medical imaging. It aims at storing object descriptors in a re-usable and hierarchical format. We propose graph data structures to identify skeleton nodes and branches, link them and store their corresponding features. This graph structure allows us to generate CSV files for high level analysis and to propose a pruning method that removes spurious branches regarding their length and mean gray level. We illustrate manipulations of the skeleton graph structure on medical image dedicated to bone mi-croarchitecture characterization

Semi-automatic Compartment Extraction to Assess 3D Bone Mineral Density and Morphometric Parameters of the Subchondral Bone in the Tibial Knee

International audienceWe present a new semi-automatic method to extract the bone mineral density (BMD) and bone proportion (BV/TV) with the aim to analyze subchondral bone changes due to knee osteoarthritis in clinically relevant compartments (medial versus lateral) and (anterior versus posterior). This method based on convex hull is developed initially on high resolution peripheral computed tomography but can potentially be applied in clinical CT with sufficient resolution

Combined estimation of thickness and velocities using ultrasound guided waves: a pioneering study on in vitro cortical bone samples

International audienceIn this paper, the issue of the determination of both thickness and elastic characteristics from the propagation of multiple Lamb waves on ex-vivo human long cortical bones is addressed. Prior to the measurements on bone, the method is validated on cortical bone-mimicking phantoms. The experimental setup was previously developed for clinical measurement and the multi-Lamb mode response is analyzed using the singular value decomposition signal processing method recently introduced in the field. The repeatability and the trueness of the estimated parameters on bone-mimicking phantoms were found around a few percent. Estimation of cortical thickness on bone samples was in good agreement with cortical thickness derived from high-resolution peripheral quantitative computed tomography data analysis of the samples

In Vivo Characterization of Cortical Bone Using Guided Waves Measured by Axial Transmission

International audienceCortical bone loss is not fully assessed by current X-ray methods, and there is an unmet need in identifying women at risk of osteoporotic fracture who should receive a treatment. The last decade has seen the emergence of ultrasound axial transmission techniques to assess cortical bone. Recent axial transmission techniques exploit the multimode waveguide response of long bones such as the radius. A recent ex vivo study by our group evidenced that a multimode axial transmission approach can yield simultaneous estimates of cortical thickness and stiffness. The aim of the present work is to move one step forward to evaluate the feasibility of measuring multimode guided waves in vivo and to infer from it cortical thickness. Measurements were taken on the forearm of 14 healthy subjects with the goal to test the accuracy of the estimated thickness using the bidirectional axial transmission method implemented on a dedicated 1-MHz linear ultrasound array. This setup allows determining in vivo the dispersion curves of guided waves transmitted in the cortical layer of the radius. An inverse procedure based on the comparison between measured and modeled dispersion curves predicted by a two-dimensional transverse isotropic free plate waveguide model allowed an estimation of cortical thickness, despite the presence of soft tissue. The cortical thickness values were validated by comparison with site-matched estimates derived from X-ray high-resolution peripheral quantitative computed tomography. Results showed a significant correlation between both measurements (r 2 = 0.7, p < 0.05, RM SE = 0.21 mm). This pilot study demonstrates the potential of bidirectional axial transmission for the in vivo assessment of cortical thickness, a bone strength-related factor