Journal of the Acoustical Society of America, Oct 1, 2016
Guided wave propagation is at the heart of the axial transmission techniques designed to assess b... more Guided wave propagation is at the heart of the axial transmission techniques designed to assess bone health status. The method involves matching observed and predicted dispersion characteristics of guided waves. The strength of the technique is that it can infer more than one bone property from the measured ultrasonic data, such as cortical thickness, stiffness, or porosity. The suitability of the model chosen for the inversion has recently been debated and the question has been raised whether the physical model must take the soft tissue coating influence into account as well as perhaps other factors such as bone curvature. We present in this talk a series of experiments conducted on bone-mimicking phantoms (plates or tubes) with or without soft tissue-mimicking coating showing evidence 1/ that the experimental guided wave branches in the range of 0.4-1.6 MHz mainly exhibit sensitivity to the influence of the solid subsystem (bone) and 2/ that a simple non absorbing transverse isotropic free plate model provides an appropriate inverse model in all investigated cases, i.e., coated or non-coated plates and tubes. Finally, we demonstrate effectiveness of the inversion procedure in characterizing cortical bone using ex vivo and in vivo data.
Despite their desirable mechanical properties, damage propagation in carbon fiber-reinforced poly... more Despite their desirable mechanical properties, damage propagation in carbon fiber-reinforced polymers (CFRP) due to manufacturing flaws and continued use may particularly be hard to assess. In this work, damage maps are generated to identify the health state of a CFRP plate from ultrasonic signals obtained under C-Scan mode. This configuration allows us to visually inspect the effective state of the plate through the thickness. Firstly, signals are processed using an all-pole model with a sparse set of coefficients, which retains the most relevant information of each signal. Then, model coefficients are transformed to the cepstral domain in order to apply a unsupervised clustering procedure. From the resulting signal classification a visual map of the damage is generated. Five different clustering techniques are selected to this end and compared. As a result, clear and consistent maps of the damage pattern can be achieved when a underlying sparse model is exploited along with hierarchical and density-based clustering techniques.
The Journal of the Acoustical Society of America, 2022
Functional grading is a distinctive feature adopted by nature to improve the transition between t... more Functional grading is a distinctive feature adopted by nature to improve the transition between tissues that present a strong mismatch in mechanical properties, a relevant example being the tendon-to-bone attachment. Recent progress in multi-material additive manufacturing now allows for the design and fabrication of bioinspired functionally graded soft-to-hard composites. Nevertheless, this emerging technology depends on several design variables, including both material and mechanistic ingredients, that are likely to affect the mechanical performance of such composites. In this paper, a model-based approach is developed to describe the interaction of ultrasound waves with homogeneous and heterogeneous additively manufactured samples, which respectively display a variation either of the material ingredients (e.g., ratio of the elementary constituents) or of their spatial arrangement (e.g., functional gradients, damage). Measurements are performed using longitudinal bulk waves, which...
2018 IEEE International Ultrasonics Symposium (IUS), 2018
Structural decay of bone is not fully assessed by current current X-ray gold standard, i.e., Dual... more Structural decay of bone is not fully assessed by current current X-ray gold standard, i.e., Dual X-ray absorptiometry (DXA), and there is an unmet need in identifying women at risk of fracture who should receive a treatment. Recent Bi-Directional Axial Transmission (BDAT) techniques exploit the multimode waveguide response of long bones such as the radius. The objective of this ex vivo study was to evaluate the performance of a prototype BDAT device to discriminate between fractured and non-fractured specimens under realistic fall loading conditions. Thirty radii from elderly donors (79 y.o. ± 12 y.o., 15 males, 15 females) underwent AT measurements using a 1-MHz prototype (Azalée, Paris, France). Singular value decomposition-based approach, combined with a 2-D transverse isotropic free plate waveguide model, was used to estimate cortical thickness and porosity. The radius were loaded at 2 m.s−2using a servo-hydraulic testing machine to mimic impact that corresponds to a fall. Radii were measured by Dual X-Ray absorptiometry to obtain bone mineral density values (g.cm−2) at radius distal end. Among the 30 radii, 14 had a fracture after the impact, leading to two groups (fractured F and non-fractured NF). Fracture prediction was significant for the subgroup F with Ct.Th and Ct.Po odds ratios [ORs] equals to 2.27 and 2.35 and areas under the receiver operating characteristic (ROC) curve [AUCs] to 0.74 and 0.76 lower than BMD (AUC = 0.81). When adjusted on radius diameter, AUC was equal to 0.80 and 0.82 for Ct.Po and DXA respectively. These results suggest that the multimode AT has the potential to yield cortical bone parameters to predict fracture risk in postmenopausal women.
Journal of the Acoustical Society of America, Oct 1, 2016
Guided wave propagation is at the heart of the axial transmission techniques designed to assess b... more Guided wave propagation is at the heart of the axial transmission techniques designed to assess bone health status. The method involves matching observed and predicted dispersion characteristics of guided waves. The strength of the technique is that it can infer more than one bone property from the measured ultrasonic data, such as cortical thickness, stiffness, or porosity. The suitability of the model chosen for the inversion has recently been debated and the question has been raised whether the physical model must take the soft tissue coating influence into account as well as perhaps other factors such as bone curvature. We present in this talk a series of experiments conducted on bone-mimicking phantoms (plates or tubes) with or without soft tissue-mimicking coating showing evidence 1/ that the experimental guided wave branches in the range of 0.4-1.6 MHz mainly exhibit sensitivity to the influence of the solid subsystem (bone) and 2/ that a simple non absorbing transverse isotropic free plate model provides an appropriate inverse model in all investigated cases, i.e., coated or non-coated plates and tubes. Finally, we demonstrate effectiveness of the inversion procedure in characterizing cortical bone using ex vivo and in vivo data.
Despite their desirable mechanical properties, damage propagation in carbon fiber-reinforced poly... more Despite their desirable mechanical properties, damage propagation in carbon fiber-reinforced polymers (CFRP) due to manufacturing flaws and continued use may particularly be hard to assess. In this work, damage maps are generated to identify the health state of a CFRP plate from ultrasonic signals obtained under C-Scan mode. This configuration allows us to visually inspect the effective state of the plate through the thickness. Firstly, signals are processed using an all-pole model with a sparse set of coefficients, which retains the most relevant information of each signal. Then, model coefficients are transformed to the cepstral domain in order to apply a unsupervised clustering procedure. From the resulting signal classification a visual map of the damage is generated. Five different clustering techniques are selected to this end and compared. As a result, clear and consistent maps of the damage pattern can be achieved when a underlying sparse model is exploited along with hierarchical and density-based clustering techniques.
The Journal of the Acoustical Society of America, 2022
Functional grading is a distinctive feature adopted by nature to improve the transition between t... more Functional grading is a distinctive feature adopted by nature to improve the transition between tissues that present a strong mismatch in mechanical properties, a relevant example being the tendon-to-bone attachment. Recent progress in multi-material additive manufacturing now allows for the design and fabrication of bioinspired functionally graded soft-to-hard composites. Nevertheless, this emerging technology depends on several design variables, including both material and mechanistic ingredients, that are likely to affect the mechanical performance of such composites. In this paper, a model-based approach is developed to describe the interaction of ultrasound waves with homogeneous and heterogeneous additively manufactured samples, which respectively display a variation either of the material ingredients (e.g., ratio of the elementary constituents) or of their spatial arrangement (e.g., functional gradients, damage). Measurements are performed using longitudinal bulk waves, which...
2018 IEEE International Ultrasonics Symposium (IUS), 2018
Structural decay of bone is not fully assessed by current current X-ray gold standard, i.e., Dual... more Structural decay of bone is not fully assessed by current current X-ray gold standard, i.e., Dual X-ray absorptiometry (DXA), and there is an unmet need in identifying women at risk of fracture who should receive a treatment. Recent Bi-Directional Axial Transmission (BDAT) techniques exploit the multimode waveguide response of long bones such as the radius. The objective of this ex vivo study was to evaluate the performance of a prototype BDAT device to discriminate between fractured and non-fractured specimens under realistic fall loading conditions. Thirty radii from elderly donors (79 y.o. ± 12 y.o., 15 males, 15 females) underwent AT measurements using a 1-MHz prototype (Azalée, Paris, France). Singular value decomposition-based approach, combined with a 2-D transverse isotropic free plate waveguide model, was used to estimate cortical thickness and porosity. The radius were loaded at 2 m.s−2using a servo-hydraulic testing machine to mimic impact that corresponds to a fall. Radii were measured by Dual X-Ray absorptiometry to obtain bone mineral density values (g.cm−2) at radius distal end. Among the 30 radii, 14 had a fracture after the impact, leading to two groups (fractured F and non-fractured NF). Fracture prediction was significant for the subgroup F with Ct.Th and Ct.Po odds ratios [ORs] equals to 2.27 and 2.35 and areas under the receiver operating characteristic (ROC) curve [AUCs] to 0.74 and 0.76 lower than BMD (AUC = 0.81). When adjusted on radius diameter, AUC was equal to 0.80 and 0.82 for Ct.Po and DXA respectively. These results suggest that the multimode AT has the potential to yield cortical bone parameters to predict fracture risk in postmenopausal women.
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Papers by Nicolas Bochud