RESUMEN
Optimising plant nitrogen (N) usage and inhibiting N leaching loss in the soil-crop system is crucial to maintaining crop yield and reducing environmental pollution. This study aimed at identifying quantitative trait loci (QTLs) and differentially expressed genes (DEGs) between two N treatments in order to list candidate genes related to nitrogen-related contrasting traits in tomato varieties. We characterised a genetic diversity core-collection (CC) and a multi-parental advanced generation intercross (MAGIC) tomato population grown in greenhouse under two nitrogen levels and assessed several N-related traits and mapped QTLs. Transcriptome response under the two N conditions was also investigated through RNA sequencing of fruit and leaves in four parents of the MAGIC population. Significant differences in response to N input reduction were observed at the phenotypic level for biomass and N-related traits. Twenty-seven (27) QTLs were detected for three target traits (Leaf N content, leaf Nitrogen Balance Index and petiole NO3- content), ten and six at low and high N condition, respectively; while 19 QTLs were identified for plasticity traits. At the transcriptome level, 4,752 and 2,405 DEGs were detected between the two N conditions in leaves and fruits, respectively, among which 3,628 (50.6%) in leaves and 1,717 (71.4%) in fruit were genotype specific. When considering all the genotypes, 1,677 DEGs were shared between organs or tissues. Finally, we integrated DEGs and QTLs analyses to identify the most promising candidate genes. The results highlighted a complex genetic architecture of N homeostasis in tomato and novel putative genes useful for breeding tomato varieties requiring less N input.
RESUMEN
Anisotropy of wave velocity and attenuation induced by a dynamic uniaxial strain is investigated by dynamic acoustoelastic testing in limestone. Nonlinear resonance spectroscopy is performed simultaneously for comparison. A compressional resonance of the sample at 6.8 kHz is excited to produce a dynamic strain with an amplitude varied from 10(-7) to 10(-5). A sequence of ultrasound pulses tracks variations in ultrasonic velocity and attenuation. Variations measured when the ultrasound pulses propagate in the direction of the uniaxial strain are 10 times larger than when the ultrasound propagation occurs perpendicularly. Variations consist of a "fast" variation at 6.8 kHz and an offset. Acoustically induced conditioning is found to reduce wave velocity and enhance attenuation (offset). It also modifies "fast" nonlinear elastodynamics, i.e., wave amplitude dependencies of ultrasonic velocity and attenuation. At the onset of conditioning and beyond, different excitation amplitudes bring the material to non-equilibrium states. After conversion of velocity-strain dynamic relations into elastic modulus-strain dynamic relations and integration with respect to strain, the dynamic stress-strain relation is obtained. Analysis of stress-strain hysteresis shows that hysteretic nonlinear elasticity is not a significant source of the amplitude-dependent dissipation measured by nonlinear resonance spectroscopy. Mechanisms causing conditioning are likely producing amplitude-dependent dissipation as well.
RESUMEN
Dynamic acoustoelastic testing provides a more complete insight into the acoustic nonlinearity exhibited by micro-inhomogeneous media like granular and cracked materials. This method consists of measuring time of flight and energy modulations of pulsed ultrasonic waves induced by a low-frequency standing wave. Here pulsed ultrasonic head waves were employed to assess elastic and dissipative nonlinearities in a region near the surface of a solid. Synchronization of the ultrasound pulse sequence with the low-frequency excitation provided instantaneous variations in the elastic modulus and the attenuation as functions of the instantaneous low-frequency strain. Weak quadratic elastic nonlinearity and no dissipative nonlinearity were detected in duralumin. In limestone, distinction between tensile and compressive behaviors revealed an asymmetry in the acoustic nonlinearity and hysteresis in both the elastic modulus and the attenuation variations. Measured nonlinear acoustical parameters are in good agreement with values obtained by different techniques. Reversible acoustically induced conditioning modified the acoustic nonlinearity both quantitatively and qualitatively. It reduced tension-compression asymmetry, suggesting a nonequilibrium modification of the sources of acoustic nonlinearity. Additionally to the metrology of the acoustic nonlinearity, head wave based dynamic acoustoelastic testing may be a useful tool to monitor changes in the microstructure or the accumulation of damage in solids.
RESUMEN
SUMMARY: A quantitative ultrasound (QUS) device for measurements at the proximal femur was developed and tested in vivo (Femur Ultrasound Scanner, FemUS). Hip fracture discrimination was as good as for DXA, and a high correlation with hip BMD was achieved. Our results show promise for enhanced QUS-based assessment of osteoporosis. INTRODUCTION: Dual X-ray absorptiometry (DXA) at the femur is the best predictor of hip fractures, better than DXA measurements at other sites. Calcaneal quantitative ultrasound (QUS) can be used to estimate the general osteoporotic fracture risk, but no femoral QUS measurement has been introduced yet. We developed a QUS scanner for measurements at the femur (Femur Ultrasound Scanner, FemUS) and tested its in vivo performance. METHODS: Using the FemUS device, we obtained femoral QUS and DXA on 32 women with recent hip fractures and 30 controls. Fracture discrimination and the correlation with femur bone mineral density (BMD) were assessed. RESULTS: Hip fracture discrimination using the FemUS device was at least as good as with hip DXA and calcaneal QUS. Significant correlations with total hip bone mineral density were found with a correlation coefficient R (2) up to 0.72 and a residual error of about one half of a T-score in BMD. CONCLUSIONS: QUS measurements at the proximal femur are feasible and show a good performance for hip fracture discrimination. Given the promising results, this laboratory prototype should be reengineered to a clinical applicable instrument. Our results show promise for further enhancement of QUS-based assessment of osteoporosis.
Asunto(s)
Densidad Ósea/fisiología , Fémur/diagnóstico por imagen , Fracturas de Cadera/diagnóstico por imagen , Fracturas Osteoporóticas/diagnóstico por imagen , Absorciometría de Fotón/métodos , Anciano , Anciano de 80 o más Años , Estudios de Casos y Controles , Estudios de Factibilidad , Femenino , Fémur/fisiopatología , Fracturas de Cadera/etiología , Fracturas de Cadera/fisiopatología , Humanos , Persona de Mediana Edad , Osteoporosis Posmenopáusica/complicaciones , Osteoporosis Posmenopáusica/diagnóstico por imagen , Osteoporosis Posmenopáusica/fisiopatología , Fracturas Osteoporóticas/fisiopatología , UltrasonografíaRESUMEN
Recent ultrasound (US) axial transmission techniques exploit the multimode waveguide response of long bones to yield estimates of cortical bone structure characteristics. This pilot cross-sectional study aimed to evaluate the performance at the one-third distal radius of a bidirectional axial transmission technique (BDAT) to discriminate between fractured and nonfractured postmenopausal women. Cortical thickness (Ct.Th) and porosity (Ct.Po) estimates were obtained for 201 postmenopausal women: 109 were nonfractured (62.6 ± 7.8 years), 92 with one or more nontraumatic fractures (68.8 ± 9.2 years), 17 with hip fractures (66.1 ± 10.3 years), 32 with vertebral fractures (72.4 ± 7.9 years), and 17 with wrist fractures (67.8 ± 9.6 years). The areal bone mineral density (aBMD) was obtained using DXA at the femur and spine. Femoral aBMD correlated weakly, but significantly with Ct.Th (R = 0.23, p < 0.001) and Ct.Po (R = -0.15, p < 0.05). Femoral aBMD and both US parameters were significantly different between the subgroup of all nontraumatic fractures combined and the control group (p < 0.05). The main findings were that (1) Ct.Po was discriminant for all nontraumatic fractures combined (OR = 1.39; area under the receiver operating characteristic curve [AUC] equal to 0.71), for vertebral (OR = 1.96; AUC = 0.84) and wrist fractures (OR = 1.80; AUC = 0.71), whereas Ct.Th was discriminant for hip fractures only (OR = 2.01; AUC = 0.72); there was a significant association (2) between increased Ct.Po and vertebral and wrist fractures when these fractures were not associated with any measured aBMD variables; (3) between increased Ct.Po and all nontraumatic fractures combined independently of aBMD neck; and (4) between decreased Ct.Th and hip fractures independently of aBMD femur. BDAT variables showed comparable performance to that of aBMD neck with all types of fractures (OR = 1.48; AUC = 0.72) and that of aBMD femur with hip fractures (OR = 2.21; AUC = 0.70). If these results are confirmed in prospective studies, cortical BDAT measurements may be considered useful for assessing fracture risk in postmenopausal women. © 2019 American Society for Bone and Mineral Research.
Asunto(s)
Hueso Cortical/diagnóstico por imagen , Fracturas Óseas/diagnóstico por imagen , Fracturas Óseas/patología , Posmenopausia/fisiología , Ultrasonografía , Anciano , Femenino , Humanos , Persona de Mediana Edad , Oportunidad Relativa , Porosidad , Curva ROC , Reproducibilidad de los Resultados , Estadísticas no ParamétricasRESUMEN
We used quantitative scanning acoustic microscopy (SAM) to assess tissue acoustic impedance and microstructure of cortical bone of human radii with the aim to provide data on regional distribution of acoustic impedance along the circumferential and across the radial directions in the entire cross-section of the radius diaphysis as well as to determine the range of impedance values in transverse (perpendicular to bone axis) and longitudinal (parallel to bone axis) cross-sections. Several microstructural features related to cortical porosity were analyzed in order to determine whether these features differ in different parts of the cortex and to assess the relationship between the microstructure and tissue acoustic impedance. Fifteen fresh bone specimens (human radius) were investigated using a SAM (center frequency of 50 MHz and -6 dB lateral resolution of approximately 23 microm). The sample acoustic impedance was obtained by means of a calibration curve correlating the reflected signal amplitude of reference materials with their corresponding well-known acoustic impedance. Tissue acoustic impedance and microstructural features were derived from the morphometric analysis of the segmented impedance images. A higher porosity was found in the inner cortical layer (mean+/-SD=8.9+/-2.3%) compared to the peripheral layer (2.7+/-1.5%) (paired t-test, p<10(-5)). ANOVA showed that most of the variance can be explained by the regional effect across the radial direction with a minor contribution due to between-sample variability. Similar to porosity, the number and diameter of pores were greater in the inner layer. In contrast to porosity, ANOVA showed that impedance variability can mostly be explained by between-specimen variability. Two-way ANOVA revealed that after compensation for the between-sample variability the variation in acoustic impedance across the radial direction was much larger than that along the circumferential direction. In addition to the significant difference between the inner cortical layer (8.25+/-0.4 Mrayl) and peripheral layer (8.0+/-0.5 Mrayl) (unilateral paired t-test, p<10(-4)), the values in the anterior region (8.2+/-0.5 Mrayl) were found to be significantly higher than those of the posterior region (7.9+/-0.6 Mrayl). Impedance mean value of longitudinal sections was lower than mean value measured in transverse cross-sections, resulting in an impedance acoustic anisotropy ratio of 1.17+/-0.03 in the inner cortical layer and 1.19+/-0.02 in the peripheral layer. SAM is a valuable tool to provide data on the spatial distribution of microstructural and microelastic bone properties that is useful to improve our understanding of the impact of bone microstructure on tissue material properties.
Asunto(s)
Huesos/diagnóstico por imagen , Huesos/ultraestructura , Microscopía Acústica/métodos , Anciano , Anciano de 80 o más Años , Análisis de Varianza , Anisotropía , Femenino , Humanos , Masculino , Porosidad , Reproducibilidad de los ResultadosRESUMEN
The present study was designed to assess the relationships between QUS parameters and bone density or microarchitecture on samples of human femoral trabecular bone. The normalized slope of the frequency-dependent attenuation (nBUA), the speed of sound (SOS) and the broadband ultrasound backscatter coefficient (BUB) were measured on 37 specimens of pure trabecular bones removed from upper parts of fresh human femurs. Bone mineral density (BMD) was assessed using a clinical scanner. Finally, 8 mm diameter cylindrical cores were extracted from the specimens and their microarchitecture was reconstructed after synchrotron radiation microtomography experiments (isotropic resolution of 10 microm). A large number of microarchitectural parameters were computed, describing morphology, connectivity and geometry of the specimens. BMD correlated with all the microarchitectural parameters and the number of significant correlations was found among the architectural parameters themselves. All QUS parameters were significantly correlated to BMD (R=0.83 for nBUA, R=0.81 for SOS and R=0.69 for BUB) and to microarchitectural parameters (R=-0.79 between nBUA and Tb.Sp, R=-0.81 between SOS and Tb.Sp, R=-0.65 between BUB and BS/BV). Using multivariate model, it was found that microstructural parameters adds 10%, 19%, and 4% to the respective BMD alone contribution for the three variables BUA, SOS and BUB. Moreover, the RMSE was reduced by up to 50% for SOS, by up to 21% for nBUA and up to 11% when adding structural variables to BMD in explaining QUS results. Given the sample, which is not osteoporosis-enriched, the added contribution is quite substantial. The variability of SOS was indeed completely explained by a multivariate model including BMD and independent structural parameters (R(2)=0.94). The inverse problem on the data presented here has been addressed using simple and multiple linear regressions. It was shown that the predictions (in terms of R(2) or RMSE) of microarchitectural parameters was not enhanced when combining 2 or 3 QUS in multiple linear regressions compared to the prediction obtained with one QUS parameter alone. The best model was found for the prediction of Tb.Th() from BUA (R(2)=0.58, RMSE=17 microm). Given the high values of RMSE, these linear models appear of limited clinical value, suggesting that appropriate models have to be derived in order to solve the inverse problem. In this regard, a very interesting multivariate model was found for nBUA and BUB with Tb.Th and Tb.N, in agreement with single scattering theories by random medium. However, the source of residual variability of nBUA and BUB (15% and 45% respectively) remained unexplained.
Asunto(s)
Densidad Ósea , Fémur , Ultrasonido , Anciano , Anciano de 80 o más Años , Femenino , Fémur/anatomía & histología , Fémur/diagnóstico por imagen , Humanos , Procesamiento de Imagen Asistido por Computador , Imagenología Tridimensional , Masculino , Persona de Mediana Edad , Análisis de Regresión , UltrasonografíaRESUMEN
Bone micro-damage is commonly accepted as a relevant parameter for fracture risk assessment, but there is no available technique for its non-invasive characterization. The objective of this work is to study the potential of nonlinear ultrasound for damage detection in human bone. Ultrasound is particularly desirable due to its non-invasive and non-ionizing characteristics. We show results illustrating the correlation of progressive fatigue of human bone samples to their nonlinear dynamical response. In our experiments, damage was induced in 30 samples of diaphyseal human femur using fatigue cycling. At intervals in the cycling, the nonlinear response of the samples was assessed applying Nonlinear Resonant Ultrasound Spectroscopy (NRUS). The nonlinear parameter alpha, which in other materials correlates with the quantity of damage, dramatically increased with the number of mechanical testing cycles. We find a large spread in alpha in the pristine samples and infer that the spread is due to damage differences in the sample population. As damage accumulates during cycling, we find that alpha is much more sensitive to damage than other quantities measured, including the slope and hysteresis of the load/displacement curve, and the dynamic wavespeed. To our knowledge, this study represents the first application of the concept of nonlinear dynamic elasticity to human bone. The results are promising, suggesting the value of further work on this topic. Ultimately, the approach may have merit for in vivo bone damage characterization.
Asunto(s)
Fémur/diagnóstico por imagen , Fémur/lesiones , Anciano , Anciano de 80 o más Años , Femenino , Humanos , Masculino , Persona de Mediana Edad , Dinámicas no Lineales , Estrés Mecánico , UltrasonografíaRESUMEN
The objective was to compare the prediction of bone mechanical properties provided by axial transmission to that provided by peripheral quantitative computed tomography (pQCT) at the distal radius. The distal radius is the location for Colles' fractures, a common osteoporosis related trauma situation. Measurements of the radial speed of sound were performed using three axial transmission devices: a commercial device (Sunlight Omnisense, 1.25 MHz), a bi-directional axial transmission prototype (1 MHz), both measuring the velocity of the first arriving signal (FAS), and a low frequency (200 kHz) device, measuring the velocity of a slower wave. Co-localized pQCT measurements of bone mineral density and cortical thickness were performed. Ultrasound and pQCT parameters were compared to mechanical parameters such as failure load and Young's modulus, obtained using quasistatic compressive mechanical testing and finite elements modelling (FEM). Correlations of the ultrasound and pQCT parameters to mechanical parameters were comparable. The best predictor of failure load was the pQCT measured cortical thickness. The best predictor of Young's modulus was the bi-directional SOS. The low frequency device significantly correlated to cortical thickness and failure load. The results suggest that different axial transmission approaches give access to different bone mechanical parameters. The association of different axial transmission techniques should be able to provide a good prediction of bone mechanical parameters, and should therefore be helpful for fracture risk prediction.
Asunto(s)
Huesos/fisiología , Radio (Anatomía)/diagnóstico por imagen , Anciano , Anciano de 80 o más Años , Fenómenos Biomecánicos , Huesos/diagnóstico por imagen , Elasticidad , Femenino , Humanos , Imagenología Tridimensional , Técnicas In Vitro , Masculino , Persona de Mediana Edad , Radio (Anatomía)/fisiología , Tomografía Computarizada por Rayos X , UltrasonografíaRESUMEN
Our goal is to assess the potential of computational methods as an alternative to analytical models to predict the two longitudinal wave modes observed in cancellous bone and predicted by the Biot theory. A three-dimensional (3D) finite-difference time-domain method is coupled with 34 human femoral trabecular microstructures measured using microcomputed tomography. The main trabecular alignment (MTA) and the degree of anisotropy (DA) were assessed for all samples. DA values were comprised between 1.02 and 1.9. The influence of bone volume fraction (BV/TV) between 5% and 25% on the properties of the fast and slow waves was studied using a dedicated image processing algorithm to modify the initial 3D microstructures. A heuristic method was devised to determine when both wave modes are time separated. The simulations (performed in three perpendicular directions) predicted that both waves generally overlap in time for a direction of propagation perpendicular to the MTA. When these directions are parallel, both waves are separated in time for samples with high DA and BV/TV values. A relationship was found between the least bone volume fraction required for the observation of nonoverlapping waves and the degree of anisotropy: The higher the DA, the lower the least BV/TV.
Asunto(s)
Anisotropía , Fémur/diagnóstico por imagen , Porosidad , Tomografía Computarizada por Rayos X , Ultrasonido , Algoritmos , Elasticidad , Humanos , MicrocomputadoresRESUMEN
Speed of sound measurements are widely used clinically to assess bone strength. Trabecular bone is an attenuating composite material in which negative values of velocity dispersion have been measured, this behavior remaining poorly explained physically. The aim of this work is to describe the ultrasonic propagation in trabecular bone modeled by infinite cylinders immersed in a saturating matrix, and to derive the physical determinants of velocity dispersion. A homogenization model accounting for the coupling of multiple scattering and absorption phenomena allows the computation of phase velocity and of dispersion while varying bone properties. The present model is adapted from the generalized self-consistent method developed in the work of Yang and Mal [(1994). "Multiple-scattering of elastic waves in a fiber-reinforced composite," J. Mech. Phys. Solids 42, 1945-1968]. It predicts negative values of velocity dispersion, in agreement with experimental results obtained in phantoms mimicking trabecular bone. In trabecular bone, mostly negative and also positive values of velocity dispersion are predicted by the model, which span within the range of values measured experimentally. Scattering effects are responsible for the negative values of dispersion, whereas the frequency dependence of the absorption coefficient in bone marrow and/or in the trabeculae results in an increase in dispersion, which may then become positive.
Asunto(s)
Huesos/diagnóstico por imagen , Modelos Biológicos , Fantasmas de Imagen , Ultrasonografía/instrumentación , Absorción , Médula Ósea/diagnóstico por imagen , Simulación por Computador , Humanos , Reología , Sustancias Viscoelásticas , AguaRESUMEN
Several studies showed the ability of the cortex of long bones such as the radius and tibia to guide mechanical waves. Such experimental evidence has given rise to the emergence of a category of quantitative ultrasound techniques, referred to as the axial transmission, specifically developed to measure the propagation of ultrasound guided waves in the cortical shell along the axis of long bones. An ultrasound axial transmission technique, with an automated approach to quantify cortical thickness and porosity is described. The guided modes propagating in the cortex are recorded with a 1-MHz custom made linear transducer array. Measurement of the dispersion curves is achieved using a two-dimensional spatio-temporal Fourier transform combined with singular value decomposition. Automatic parameters identification is obtained through the solution of an inverse problem in which the dispersion curves are predicted with a two-dimensional transverse isotropic free plate model. Thirty-one radii and fifteen tibiae harvested from human cadavers underwent axial transmission measurements. Estimates of cortical thickness and porosity were obtained on 40 samples out of 46. The reproducibility, given by the root mean square error of the standard deviation of estimates, was 0.11â¯mm for thickness and 1.9% for porosity. To assess accuracy, site-matched micro-computed tomography images of the bone specimens imaged at 9 µm voxel size served as the gold standard. Agreement between micro-computed tomography and axial transmission for quantification of thickness and porosity at the radius and tibia ranged from R2=0.63 for porosity (root mean square error RMSE=1.8%) to 0.89 for thickness (RMSE=0.3â¯mm). Despite an overall good agreement for porosity, the method performs less well for porosities lower than 10%. The heterogeneity and general complexity of cortical bone structure, which are not fully accounted for by our model, are suspected to weaken the model approximation. This study presents the first validation study for assessing cortical thickness and porosity using the axial transmission technique. The automatic signal processing minimizes operator-dependent errors for parameters determination. Recovering the waveguide characteristics, that is to say cortical thickness and porosity, could provide reliable information about skeletal status and future fracture risk.
Asunto(s)
Hueso Cortical/diagnóstico por imagen , Ultrasonografía , Anciano , Anciano de 80 o más Años , Femenino , Humanos , Procesamiento de Imagen Asistido por Computador , Masculino , Persona de Mediana Edad , Porosidad , Reproducibilidad de los ResultadosRESUMEN
Quantitative ultrasound (QUS) measurements at peripheral sites can be used to estimate osteoporotic fracture risk. However, measurements at these sites are less suitable to predict bone mineral density (BMD) or fracture risk at the central skeleton. We investigated whether direct QUS measurements at the femur would allow to estimate dual X-ray absorptiometry (DXA) BMD of the total proximal femur with errors comparable to established DXA accuracy errors. Two independent sets of femora were measured in Kiel (6 f, 4 m, age: 55-90) and Paris (19 f, 20 m age: 45-95) using different benchtop systems in the two laboratories. The femora were scanned in transverse transmission mode using focused US transducers of 500 kHz center frequency. The QUS values were averaged over a region similar to the total hip region of dual X-ray absorptiometry (DXA) measurements. BMD was measured using DXA. SOS and BMD correlated significantly (p<0.0001) in both data sets (R2=0.81-0.93). Correlations between BUA and BMD were also significant at p<0.001, but correlation coefficients were lower (R2=0.61-0.75). Residual errors for the estimation of BMD were 8%-10% for SOS as predictor, and 14%-16% for BUA as predictor. The residual error of 8 to 10% for the estimation of BMD from SOS is comparable to variabilities among different DXA femur subregions and accuracy errors of femoral DXA measurements caused by the impact of soft tissue. It is substantially smaller than the errors of 13% for the estimation of total femur BMD from spine BMD, 14% for the estimation of total femur BMD from calcaneus SOS or 16% for the estimation of ash weight from DXA. The results of the study show that SOS is able to predict total BMD with adequate accuracy. If femoral BMD could be obtained in vivo with comparable accuracy, femoral QUS would be suited for the assessment of bone status at one of the main osteoporotic fracture sites.
Asunto(s)
Densidad Ósea , Fémur/diagnóstico por imagen , Ultrasonografía/normas , Absorciometría de Fotón , Cadáver , Femenino , Humanos , UltrasonidoRESUMEN
The ability to assess the elastic and failure properties of cortical bone at the radial diaphysis has a clinical importance. A new generation of quantitative ultrasound (QUS) devices and peripheral quantitative computed tomography (p-QCT) has been developed to assess non-invasively bone material and structural properties at the distal radius. This anatomical site is characterized by a thin cortical thickness that complicates traditional mechanical testing methods on specimens. Until now, mechanical properties of cortical bone at distal radius (e.g., elastic modulus, yield stress and strain) remain rarely studied probably due to experimental difficulties. The present study introduces an inverse finite-element method strategy to measure the elastic modulus and yield properties of human cortical specimens of the radial diaphysis. Twenty millimeter-thick portions of diaphysis were cut from 40 human radii (ages 45-90) for biomechanical test. Subsequently the same portion was modeled in order to obtain a specimen-specific three dimensional finite-element model (3D-FEM). Longitudinal elastic constants at the apparent level and stress characterizations were performed by coupling mechanical parameters with isotropic linear-elastic simulations. The results indicated that the mean apparent Young's modulus for radial cortical bone was 16 GPa (SD 1.8) and the yield stress was 153 MPa (SD 33). Breaking load was 12,946 N (SD 3644), cortical thickness 2.9 mm (SD 0.6), structural effective strain at the yield (epsilon(y)=0.0097) and failure (epsilon(u)=0.0154) load were also calculated. The 3D-FEM strategy described here may help to investigate bone mechanical properties when some difficulties arise from machining mechanical sample.
Asunto(s)
Análisis de Elementos Finitos , Modelos Biológicos , Radio (Anatomía)/fisiología , Anciano , Anciano de 80 o más Años , Fenómenos Biomecánicos , Fuerza Compresiva , Femenino , Humanos , Masculino , Persona de Mediana Edad , Estrés MecánicoRESUMEN
Elasticity assessment based on bulk wave velocity (BWV) measurements is the most popular technique to characterize the anisotropic stiffness tensor in cortical bone. Typically, a cuboid bone specimen is cut with its sides along the different anatomical directions. Then, the velocity of shear and longitudinal waves propagating along different directions are assessed, from which stiffness coefficients are calculated. Despite the importance of obtaining accurate elasticity values for bone research, there is no generally accepted protocol to measure BWV and the precision of the technique has been seldom investigated. The purpose of this work is to critically assess the method to measure BWV on cuboid specimens in terms of ultrasound frequency, specimen size and signal processing technique. In this study, we measured polycarbonate specimens of different dimensions and 55 human bone specimens with different transducers using frequencies ranging from 2.25 to 10MHz and 1-5MHz for longitudinal and shear waves, respectively. We compared four signal processing methods to detect the wave arrival time. The main results are that, (1) the measurement of shear waves is more complex than that of longitudinal wave, being less precise and more sensitive to sample size; (2) the estimated stiffness depends on the signal processing technique used (up to 10% variation for shear coefficients of bone); and (3) bone stiffness assessed from BWV using the first arrival of the signal to determine the time-of-flight is not different from stiffness assessed using resonant ultrasound spectroscopy (RUS). These results evidence that the measurement method can have an effect on the stiffness values estimates and hence, a well-defined protocol is needed to accurately measure bone stiffness coefficients based on BWV.
Asunto(s)
Hueso Cortical/diagnóstico por imagen , Diagnóstico por Imagen de Elasticidad/métodos , Fémur/diagnóstico por imagen , Anciano , Femenino , Humanos , Técnicas In Vitro , Masculino , Fantasmas de Imagen , Procesamiento de Señales Asistido por Computador , TransductoresRESUMEN
The material properties of the trabeculae (tissue-level properties), together with the trabecular architecture and the bone volume fraction determine the apparent millimetre-scale bone mechanical properties. We present a novel method to measure trabecular tissue elastic modulus Et using resonant ultrasound spectroscopy (RUS). The first mechanical resonance frequency fe of a freestanding cuboid specimen is measured and used to back-calculate Et. The steps of the back-calculation are (1) the apparent stiffness tensors C(EtË) is computed using micro-finite elements for a set of trial values of tissue Young's modulus EtË based on the computed tomography image of the specimen; (2) the modeled free-vibration resonance frequencies fm(EtË) of the specimen is calculated with the Rayleigh-Ritz method using C(EtË); (3) finally, Et is obtained by interpolation using fe and fm(EtË). Four bovine bone specimens were tested (nominal size 5×6 ×6mm3). Average (standard deviation) of Et was 13.12 (1.06)GPa. The measurement of a single resonance frequency enabled an estimation of tissue elasticity in line with available data. RUS is a non destructive technique relatively easy to implement compared to traditional mechanical testing. The novel method could contribute to a better documentation of bone tissue elasticity which is an important parameter of micro-finite element analyses for the clinical assessment of bone strength.
Asunto(s)
Hueso Esponjoso/fisiología , Animales , Bovinos , Módulo de Elasticidad , Análisis de Elementos Finitos , Modelos Biológicos , Análisis Espectral , UltrasonografíaRESUMEN
In the study of mechanical properties of human bone, specimens may be defatted before experiments to prevent contamination and the risk of infections. High energy synchrotron radiation micro-computed tomography (SR-µCT) is a popular technique to study bone microstructure. However, little is known about the effects of defatting or irradiation during SR-µCT imaging on different elastic coefficients including shear and longitudinal moduli in different anatomical directions. In this work, these effects are evaluated on a set of 24 samples using resonant ultrasound spectroscopy (RUS), which allows one to accurately measure the complete set of elastic coefficients of cortical bone non destructively. The results show that defatting with diethylether and methanol and irradiation up to 2.5kGy has no detectable effect on any of the elastic coefficients of human cortical bone.
Asunto(s)
Hueso Cortical/fisiología , Elasticidad , Humanos , Análisis Espectral , Sincrotrones , Microtomografía por Rayos X , Rayos XRESUMEN
200 MHz scanning acoustic microscopy (SAM) and synchrotron radiation muCT (SR-muCT) were used to assess microstructural parameters and tissue properties in site-matched regions of interest in cortical bone. Anterior and postero-lateral regions of ten cross sections from human cortical radius were explored. Structural parameters, including diameter and number of Haversian canals per cortical area (Ca.Dm, N.Ca/Ar) and porosity Po were assessed with both methods using a custom-developed image fusion and analysis software. Acoustic impedance Z and degree of mineralization of bone DMB were extracted separately for osteonal and interstitial tissues from the fused images. Structural parameter estimations obtained from radiographic and acoustic images were almost identical. DMB and impedance values were in the range between 0.77 and 1.28 g cm(-3) and 5.13 and 12.1 Mrayl, respectively. Interindividual and regional variations were observed, whereas the strongest difference was found between osteonal and interstitial tissues (Z: 7.2 +/- 1.1 Mrayl versus 9.3 +/- 1.0 Mrayl, DMB: 1.06 +/- 0.07 g cm(-3) versus 1.16 +/- 0.05 g cm(-3), paired t-test, p < 0.05). Weak, but significant correlations between DMB and Z were obtained for the osteonal (R(2) = 0.174, p < 10(-4)) and for the pooled (osteonal and interstitial) data. The regression of the pooled osteonal and interstitial tissue data follows a second-order polynomial (R(2) = 0.39, p < 10(-4)). Both modalities fulfil the requirement for a simultaneous evaluation of cortical bone microstructure and material properties at the tissue level. While SAM inspection is limited to the evaluation of carefully prepared sample surfaces, SR-muCT provides volumetric information on the tissue without substantial preparation requirements. However, SAM provides a quantitative estimate of elastic properties at the tissue level that cannot be captured by SR-muCT.
Asunto(s)
Huesos/patología , Microscopía Acústica/métodos , Tomografía Computarizada por Rayos X/métodos , Anciano , Anciano de 80 o más Años , Densidad Ósea , Huesos/diagnóstico por imagen , Calibración , Femenino , Humanos , Procesamiento de Imagen Asistido por Computador , Masculino , Microscopía , Microscopía Confocal , Modelos Estadísticos , Radiografía/métodos , Programas Informáticos , Distribución TisularRESUMEN
Recent progress in quantitative ultrasound has exploited the multimode waveguide response of long bones. Measurements of the guided modes, along with suitable waveguide modeling, have the potential to infer strength-related factors such as stiffness (mainly determined by cortical porosity) and cortical thickness. However, the development of such model-based approaches is challenging, in particular because of the multiparametric nature of the inverse problem. Current estimation methods in the bone field rely on a number of assumptions for pairing the incomplete experimental data with the theoretical guided modes (e.g. semi-automatic selection and classification of the data). The availability of an alternative inversion scheme that is user-independent is highly desirable. Thus, this paper introduces an efficient inversion method based on genetic algorithms using multimode guided waves, in which the mode-order is kept blind. Prior to its evaluation on bone, our proposal is validated using laboratory-controlled measurements on isotropic plates and bone-mimicking phantoms. The results show that the model parameters (i.e. cortical thickness and porosity) estimated from measurements on a few ex vivo human radii are in good agreement with the reference values derived from x-ray micro-computed tomography. Further, the cortical thickness estimated from in vivo measurements at the third from the distal end of the radius is in good agreement with the values delivered by site-matched high-resolution x-ray peripheral computed tomography.
Asunto(s)
Algoritmos , Hueso Cortical/diagnóstico por imagen , Modelos Teóricos , Fantasmas de Imagen , Ultrasonografía/métodos , Microtomografía por Rayos X/métodos , Humanos , Valores de ReferenciaRESUMEN
Quantitative ultrasound has been recognized as a useful tool for fracture risk prediction. Current measurement techniques are limited to peripheral skeletal sites. Our objective was to demonstrate the in vitro feasibility of ultrasonic velocity measurements on human proximal femur and to investigate the relationship between velocity and bone mineral density (BMD). Sound velocity images were computed from 2-D scans performed on 38 excised human femurs in transmission at 0.5 MHz. Different regions-of-interest were investigated. Dual x-ray absorptiometry scans have been achieved for BMD measurements in site-matched regions. Our study demonstrates the feasibility of ultrasonic velocity measurements at the hip with reasonable precision (coefficient of variation of 0.3%). The best prediction of BMD was reached in the intertrochanter region (r(2) = 0.91, p < 10(-4)), with a residual error of 0.06 g/cm(2) (10%). Because BMD measured at the femur is the best predictor of hip fracture risk, the highly significant correlation and small residual error found in this study suggest that speed of sound measurement at the femur might be a good candidate for hip fracture risk prediction.