Speed of sound reflects Young's modulus as assessed by microstructural finite element analysis

Evaluation of cortical bone strength using a quantitative ultrasound measurement device in dogs

This study was performed to evaluate cortical bone strength in dogs using a quantitative ultrasound measurement device. In this study, 16 clinically healthy dogs with no lameness underwent measurement of the ultrasound propagation velocity of cortical bone (namely, speed of sound [SOS]) at the radius and tibia. Additionally, computed tomography examination with a calibration phantom was performed in 10 dogs. We calculated the bone mineral density (BMD) and Young's modulus from the computed tomography data using bone strength evaluation software. SOS, BMD, and Young's modulus were statistically compared between the radius and tibia. In addition, we examined the correlation between SOS and BMD and between SOS and Young's modulus. We also examined the correlation between SOS and age in the 13 dogs whose age was known. BMD and Young's modulus were not significantly different between the radius and tibia, but SOS was significantly different (P<0.05). Moreover, SOS and BMD showed a positive correlation in both radius and tibia. Similarly, SOS and Young's modulus showed a positive correlation. In addition, SOS and age showed a strong positive correlation (radius: r=0.77, P<0.05, tibia: r=0.83, P<0.05). Our finding that SOS of the radius and tibia cortical bone was correlated with BMD and Young's modulus indicates that quantitative ultrasound can be useful for evaluating cortical bone strength in dogs.

Skeletal Muscle Assessment Using Quantitative Ultrasound: A Narrative Review

Ultrasound (US) is an important imaging tool for skeletal muscle analysis. The advantages of US include point-of-care access, real-time imaging, cost-effectiveness, and absence of ionizing radiation. However, US can be highly dependent on the operator and/or US system, and a portion of the potentially useful information carried by raw sonographic data is discarded in image formation for routine qualitative US. Quantitative ultrasound (QUS) methods provide analysis of the raw or post-processed data, revealing additional information about normal tissue structure and disease status. There are four QUS categories that can be used on muscle and are important to review. First, quantitative data derived from B-mode images can help determine the macrostructural anatomy and microstructural morphology of muscle tissues. Second, US elastography can provide information about muscle elasticity or stiffness through strain elastography or shear wave elastography (SWE). Strain elastography measures the induced tissue strain caused either by internal or external compression by tracking tissue displacement with detectable speckle in B-mode images of the examined tissue. SWE measures the speed of induced shear waves traveling through the tissue to estimate the tissue elasticity. These shear waves may be produced using external mechanical vibrations or internal "push pulse" ultrasound stimuli. Third, raw radiofrequency signal analyses provide estimates of fundamental tissue parameters, such as the speed of sound, attenuation coefficient, and backscatter coefficient, which correspond to information about muscle tissue microstructure and composition. Lastly, envelope statistical analyses apply various probability distributions to estimate the number density of scatterers and quantify coherent to incoherent signals, thus providing information about microstructural properties of muscle tissue. This review will examine these QUS techniques, published results on QUS evaluation of skeletal muscles, and the strengths and limitations of QUS in skeletal muscle analysis.

Effect of 12 months of creatine supplementation and whole-body resistance training on measures of bone, muscle and strength in older males

BACKGROUND

The combination of creatine supplementation and resistance training (10-12 weeks) has been shown to increase bone mineral content and reduce a urinary indicator of bone resorption in older males compared with placebo. However, the longer-term effects (12 months) of creatine and resistance training on bone mineral density and bone geometric properties in older males is unknown.

AIM

To assess the effects of 12 months of creatine supplementation and supervised, whole-body resistance training on bone mineral density, bone geometric properties, muscle accretion, and strength in older males.

METHODS

Participants were randomized to supplement with creatine (n = 18, 49-69 years, 0.1 g·kg^-1·d^-1) or placebo (n = 20, 49-67 years, 0.1 g·kg^-1·d^-1) during 12 months of supervised, whole-body resistance training.

RESULTS

After 12 months of training, both groups experienced similar changes in bone mineral density and geometry, bone speed of sound, lean tissue and fat mass, muscle thickness, and muscle strength. There was a trend (p = 0.061) for creatine to increase the section modulus of the narrow part of the femoral neck, an indicator of bone bending strength, compared with placebo. Adverse events did not differ between creatine and placebo.

CONCLUSIONS

Twelve months of creatine supplementation and supervised, whole-body resistance training had no greater effect on measures of bone, muscle, or strength in older males compared with placebo.

Acoustic Cell Separation Based on Density and Mechanical Properties

Density and mechanical properties (e.g., compressibility or bulk modulus) are important cellular biophysical markers. As such, developing a method to separate cells directly based on these properties can benefit various applications including biological research, diagnosis, prognosis, and therapeutics. As a potential solution, surface acoustic wave (SAW)-based cell separation has demonstrated advantages in terms of biocompatibility and compact device size. However, most SAW-reliant cell separations are achieved using an entangled effect of density, various mechanical properties, and size. In this work, we demonstrate SAW-based separation of cells/particles based on their density and compressibility, irrespective of their sizes, by manipulating the acoustic properties of the fluidic medium. Using our platform, SAW-based separation is achieved by varying the dimensions of the microfluidic channels, the wavelengths of acoustic signals, and the properties of the fluid media. Our method was applied to separate paraformaldehyde-treated and fresh Hela cells based on differences in mechanical properties; a recovery rate of 85% for fixed cells was achieved. It was also applied to separate red blood cells (RBCs) and white blood cells (WBCs) which have different densities. A recovery rate of 80.5% for WBCs was achieved.

Influence of anisotropic bone properties on the biomechanical behavior of the acetabular cup implant: a multiscale finite element study

Although the biomechanical behavior of the acetabular cup (AC) implant is determinant for the surgical success, it remains difficult to be assessed due to the multiscale and anisotropic nature of bone tissue. The aim of the present study was to investigate the influence of the anisotropic properties of peri-implant trabecular bone tissue on the biomechanical behavior of the AC implant at the macroscopic scale. Thirteen bovine trabecular bone samples were imaged using micro-computed tomography (μCT) with a resolution of 18 μm. The anisotropic biomechanical properties of each sample were determined at the scale of the centimeter based on a dedicated method using asymptotic homogenization. The material properties obtained with this multiscale approach were used as input data in a 3D finite element model to simulate the macroscopic mechanical behavior of the AC implant under different loading conditions. The largest stress and strain magnitudes were found around the equatorial rim and in the polar area of the AC implant. All macroscopic stiffness quantities were significantly correlated (R² > 0.85, p < 6.5 e-6) with BV/TV (bone volume/total volume). Moreover, the maximum value of the von Mises stress field was significantly correlated with BV/TV (R² > 0.61, p < 1.6 e-3) and was always found at the bone-implant interface. However, the mean value of the microscopic stress (at the scale of the trabeculae) decrease as a function of BV/TV for vertical and torsional loading and do not depend on BV/TV for horizontal loading. These results highlight the importance of the anisotropic properties of bone tissue.

Effects of Creatine and Resistance Training on Bone Health in Postmenopausal Women

PURPOSE

Our primary purpose was to determine the effect of 12 months of creatine (Cr) supplementation during a supervised resistance training program on properties of bone in postmenopausal women.

METHODS

Participants were randomized (double-blind) into two groups: resistance training (3 d·wk) and Cr supplementation (0.1 g·kg·d) or resistance training and placebo (Pl). Our primary outcome measures were lumbar spine and femoral neck bone mineral density (BMD). Secondary outcome measures were total hip and whole-body BMD, bone geometric properties at the hip, speed of sound at the distal radius and tibia, whole-body lean tissue mass, muscle thickness, and bench press and hack squat strength. Forty-seven women (57 (SD, 6) yr; Cr, n = 23; Pl, n = 24) were randomized, with 33 analyzed after 12 months (Cr, n = 15; Pl, n = 18).

RESULTS

Cr attenuated the rate of femoral neck BMD loss (-1.2%; absolute change (95% confidence interval), -0.01 (-0.025 to 0.005) g·cm) compared with Pl (-3.9%; -0.03 (-0.044 to -0.017) g·cm; P < 0.05) and also increased femoral shaft subperiosteal width, a predictor of bone bending strength (Cr, 0.04 (-0.09 to 0.16) cm); Pl, -0.12 (-0.23 to -0.01) cm; P < 0.05). Cr increased relative bench press strength more than Pl (64% vs 34%; P < 0.05). There were no differences between groups for other outcome measures. There were no differences between groups for reports of serum liver enzyme abnormalities, and creatinine clearance was normal for Cr participants throughout the intervention.

CONCLUSIONS

Twelve months of Cr supplementation during a resistance training program preserves femoral neck BMD and increases femoral shaft superiosteal width, a predictor of bone bending strength, in postmenopausal women.

A μCT-based investigation of the influence of tissue modulus variation, anisotropy and inhomogeneity on ultrasound propagation in trabecular bone

Ultrasound propagation is widely used in the diagnosis of osteoporosis by providing information on bone mechanical quality. When it loses calcium, the tissue properties will first decrease. However, limited research about the influence of tissue properties on ultrasound propagation have been done due to the cumbersome experiment. The goal of this study was to explore the relationships between tissue modulus (Es) and speed of sound (SOS) through numerical simulations, and to study the influence of Es on the acoustical behavior in characterizing the local structural anisotropy and inhomogeneity. In this work, three-dimensional finite element (FE) simulations were performed on a cubic high-resolution (15μm) bovine trabecular bone sample (4×4×4mm(3), BV/TV=0.18) mapped from micro-computed tomography. Ultrasound excitations of 50kHz, 500kHz and 2MHz were applied in three orthogonal axes and the first arriving signal (FAS) was collected to quantify wave velocity. In this study, a strong power law relationship between Es and SOS was measured with estimated exponential index β=2.08-3.44 for proximal-distal (PD), anterior-posterior (AP) and medial-lateral (ML), respectively (all R(2)>0.95). For various Es, a positive dispersion of sound speed with respect to sound frequency was observed and the velocity dispersion magnitude (VDM) was measured. Also, with Es=15GPa in three orientations, the SOS in PD axis is 2009±120m/s, faster than that of AP (1762±106m/s) and ML (1798±132m/s) (f=2MHz) directions. Besides, the standard deviation of SOS increases with the sound frequency and the Es in all directions except for that at 50kHz. For the mechanical properties, the apparent modulus with certain Es was highest in the longitudinal direction compared with the transverse directions. It indicates that the tissue modulus combining with anisotropy and inhomogeneity has great influence on ultrasound propagation. Simulation results agree well with theoretical and experimental results.

Longitudinal assessment of bone loss using quantitative ultrasound in a blood-induced arthritis rabbit model

INTRODUCTION

Osteoporosis is common in haemophilic arthropathy. Quantitative ultrasound (QUS) can be a suitable alternative for dual-energy x-ray absorptiometry for diagnosing osteoporosis in haemophiliacs due to its lack of ionizing radiation, and ease to use.

AIM

We investigated the intra- and inter-operator reliability of QUS, its responsiveness to bone growth, its ability to differentiate bone adjacent to blood-injected vs. control joints, and the effect of soft tissues on the speed of sound (SOS) QUS values in a juvenile white New Zealand rabbit model of blood-induced arthritis.

METHODS

Eight of 16 rabbits were injected with autologous blood (0.1 mL kg(-1) ) 8 times over a 17-week period, the remaining eight rabbits served as controls. SOS was measured at baseline, weeks 8 and 17 in vivo and after the bones were excised on week 17.

RESULTS

Intra- and inter-operator coefficients of variation for QUS data were <5% and intraclass correlation coefficients were >60% for 22/27 (81.5%) of bones assessed. The level of interval increase in SOS values from baseline to week 17 was significantly different in tibiae of injected, contralateral to injected and non-injected knee groups by anova (P = 0.01). In vivo (mean ± SD, 4147.17 ± 96.27 m s(-1) ) and postmortem (4457.85 ± 104.00 m s(-1) ) measurements on week 17 differed (P < 0.01) indicating an effect of soft tissues on SOS.

CONCLUSION

In conclusion, QUS' acceptable reliability, its responsiveness to growth-related changes and its ability to discriminate injected and non-injected joints make this technique a plausible candidate as a diagnostic tool for osteoporosis in the paediatric haemophilic population if these results are confirmed upon animal-human translation.

Critical evaluation of pulse-echo ultrasonic test method for the determination of setting and mechanical properties of acrylic bone cement: influence of mixing technique

Currently there is no reliable objective method to quantify the setting properties of acrylic bone cements within an operating theatre environment. Ultrasonic technology can be used to determine the acoustic properties of the polymerising bone cement, which are linked to material properties and provide indications of the physical and chemical changes occurring within the cement. The focus of this study was the critical evaluation of pulse-echo ultrasonic test method in determining the setting and mechanical properties of three different acrylic bone cement when prepared under atmospheric and vacuum mixing conditions. Results indicated that the ultrasonic pulse-echo technique provided a highly reproducible and accurate method of monitoring the polymerisation reaction and indicating the principal setting parameters when compared to ISO 5833 standard, irrespective of the acrylic bone cement or mixing method used. However, applying the same test method to predict the final mechanical properties of acrylic bone cement did not prove a wholly accurate approach. Inhomogeneities within the cement microstructure and specimen geometry were found to have a significant influence on mechanical property predictions. Consideration of all the results suggests that the non-invasive and non-destructive pulse-echo ultrasonic test method is an effective and reliable method for following the full polymerisation reaction of acrylic bone cement in real-time and then determining the setting properties within a surgical theatre environment. However the application of similar technology for predicting the final mechanical properties of acrylic bone cement on a consistent basis may prove difficult.

Effect of exercise training combined with isoflavone supplementation on bone and lipids in postmenopausal women: a randomized clinical trial

We determined the effects of 2 years of exercise training and soy isoflavone supplementation on bone mass and lipids in postmenopausal women provided with calcium and vitamin D. Women were randomized to four groups: exercise training (Ex); isoflavone supplementation (Iso: 165 mg/d [105 mg/d aglycone equivalent]); combined Ex and Iso (ExIso); and placebo (control). Exercise included resistance training (2 days/week) and walking (4 days/week). Our primary outcomes were lumbar spine and hip bone mineral density (BMD). Secondary outcomes included hip geometry, tibia and radius speed of sound (SOS), dynamic balance (6 m backward tandem walking), blood lipids, mammography, and endometrial thickness. A total of 351 women (Ex = 86, Iso = 90, ExIso = 87, control = 88) were randomized, with 298 analyzed at 2 years (Ex = 77, Iso = 76, ExIso = 72, control = 73). There was a significant interaction for total hip BMD (p < 0.001) such that ExIso had a greater rate of decrease (absolute change [95% confidence interval] = -0.018 [-0.024, -0.012] g/cm(2) ) than either the Ex or Iso groups alone (-0.005 [-0.01, 0.001] and -0.005 [-0.011, 0.001] g/cm(2) , respectively). There were no differences between groups for changes in lumbar spine BMD and minimal significant changes in hip geometric properties and bone SOS. Exercise groups improved dynamic balance as measured by a decrease in backward tandem walking time over 6 m (p = 0.017). Isoflavone groups decreased low density lipoproteins (Iso: -0.20 [-0.37, -0.02] mmol/L; ExIso: -0.23 [-0.40, -0.06] mmol/L; p = 0.003) compared to non-isoflavone groups (Ex: 0.01 [-0.16, 0.18] mmol/L; control: -0.09 [-0.27, 0.08] mmol/L) and had lower adverse reports of menopausal symptoms (14% versus 33%; p = 0.01) compared to non-isoflavone groups. Isoflavone supplementation did not increase endometrial thickness or abnormal mammograms. We conclude exercise training and isoflavone supplementation maintain hip BMD compared to control, but these two interventions interfere with each other when combined. Isoflavone supplementation decreased LDL and adverse events related to menopausal symptoms.

Calcaneal ultrasound reference ranges for Australian men and women: the Geelong Osteoporosis Study

Heel ultrasound is a more portable modality for assessing fracture risk than dual-energy X-ray absorptiometry and does not use ionising radiation. Fracture risk assessment requires appropriate reference data to enable comparisons. This study reports the first heel ultrasound reference ranges for the Australian population.

INTRODUCTION

This study aimed to develop calcaneal (heel) ultrasound reference ranges for the Australian adult population using a population-based random sample.

METHODS

Men and women aged≥20 years were randomly selected from the Barwon Statistical Division in 2001-2006 and 1993-1997, respectively, using the electoral roll. Broadband ultrasound attenuation (BUA), speed of sound (SOS) and stiffness index (SI) were measured at the heel using a Lunar Achilles Ultrasonometer. Gender-specific means and standard deviations for BUA, SOS and SI were calculated for the entire sample (men 20-93 years, n=1,104; women 20-92 years, n=914) and for participants aged 20-29 years (men, n=157; women, n=151). Associations between ultrasound measures and age were examined using linear regression.

RESULTS

For men, mean±standard deviation BUA, SOS and SI were 118.7±15.8 dB/MHz, 1,577.0±43.7 m/s and 100.5±20.7, respectively; values for women were consistently lower (111.0±16.4 dB/MHz, P<0.001; 1,571.0±39.0 m/s, P=0.001; and 93.7±20.3, P<0.001, respectively). BUA was higher in young men compared with young women (124.5±14.4 vs 121.0±15.1 dB/MHz), but SOS (1,590.1±43.1 vs 1,592.5±35.0 m/s) and SI (108.0±19.9 vs 106.3±17.7) were not. The relationships between age and each ultrasound measure were linear and negative across the age range in men; associations were also negative in women but non-linear.

CONCLUSION

These data provide reference standards to facilitate the assessment of fracture risk in an Australian population using heel ultrasound.

Quantitative ultrasound and fracture risk prediction in non-osteoporotic men and women as defined by WHO criteria

This study sought to determine the association between calcaneal quantitative ultrasound (QUS) and fracture risk in individuals without osteoporosis according to the World Health Organization criteria (i.e., BMD T-score > -2.5). We found that calcaneal QUS is an independent predictor of fracture risk in women with non-osteoporotic bone mineral density (BMD).

INTRODUCTION

More than 50 % of women and 70 % of men who sustain a fragility fracture have BMD above the osteoporotic threshold (T-score > -2.5). Calcaneal QUS is associated with fracture risk. This study aimed to test the hypothesis that low calcaneal QUS is associated with increased fracture risk in individuals with non-osteoporotic BMD.

METHODS

We included 312 women and 390 men aged 62-90 years with BMD T-score > -2.5 at femoral neck. QUS was measured in broadband ultrasound attenuation (BUA) at the calcaneus using a CUBA sonometer. BMD was measured at the femoral neck (FNBMD) by dual energy X-ray absorptiometry using GE Lunar DPX-L densitometer. The incidences of any fragility fracture were ascertained by X-ray reports during the follow-up period from 1994 to 2011.

RESULTS

Of the 702 participants, 26 % of women (n = 80/312) and 14 % of men (n = 53/390) experienced at least one fragility fracture during the follow-up period. In women, after adjusting for covariates, increased risk of any fracture was significantly associated with decreased BUA (HR = 1.50; 95 % CI, 1.13-1.99). Compared with that of FNBMD, the models with BUA, in women, had greater AUC (0.71, 0.85, 0.71 for any, hip and vertebral fracture, respectively), and yielded a net reclassification improvement of 16.4 % (P = 0.009) when combined with FNBMD. In men, BUA was not significantly associated with fracture risk before and after adjustment.

CONCLUSION

These results suggest that calcaneal BUA is an independent predictor of fracture risk in women with non-osteoporotic BMD.

IN VITROACOUSTIC WAVE PROPAGATION IN HUMAN AND BOVINE CANCELLOUS BONE AS PREDICTED BY BIOT'S THEORY

Recent in vitro studies have provided evidence of the propagation of two different longitudinal wave modes at ultrasonic frequencies in cancellous bone. The genesis of these two plane waves in fluid-saturated porous media is predicted by the poroelastic approach to wave propagation originally developed by Biot. However, wave velocity is usually analyzed as a function of bone mass density only; therefore, the influence of the cancellous bone microstructure over the wave velocity is not taken into account. In the present study, a descriptor of the microstructure is considered in Biot's theory. This model is used to evaluate the large experimental variability of both fast and slow wave velocities measured on randomly oriented human and bovine cancellous bone samples. The role of the anisotropic solid structure and fluid in the behavior of fast and slow wave velocities is examined. Experimental and theoretically predicted velocities are found in close agreement when analyzed as a function of both porosity and structural index. This model has the potential to be used to determine an acoustically derived structural index in cancellous bone.

Mechanical and microarchitectural analyses of cancellous bone through experiment and computer simulation

The relationship between microarchitecture to the failure mechanism and mechanical properties can be assessed through experimental and computational methods. In this study, both methods were utilised using bovine cadavers. Twenty four samples of cancellous bone were extracted from fresh bovine and the samples were cleaned from excessive marrow. Uniaxial compression testing was performed with displacement control. After mechanical testing, each specimen was ashed in a furnace. Four of the samples were exemplarily scanned using micro-computed tomography (μCT) and three dimensional models of the cancellous bones were reconstructed for finite element simulation. The mechanical properties and the failure modes obtained from numerical simulations were then compared to the experiments. Correlations between microarchitectural parameters to the mechanical properties and failure modes were then made. The Young's modulus correlates well with the bone volume fraction with R² = 0.615 and P value 0.013. Three different types of failure modes of cancellous bone were observed: oblique fracture (21.7%), perpendicular global fracture (47.8%), and scattered localised fracture (30.4%). However, no correlations were found between the failure modes to the morphological parameters. The percentage of error between computer predictions and the actual experimental test was from 6 to 12%. These mechanical properties and information on failure modes can be used for the development of synthetic cancellous bone.

Cortical thickness and medullary canal dimensions of the bone phalanx are predicted by quantitative ultrasound parameters

The aim of the study was to investigate the relationship between quantitative ultrasound (QUS) parameters extracted from the analysis of the ultrasound (US) signal and the geometric properties of the bones. One hundred and one subjects in the age range of 20-7 4yr (mean: 52+/-12 yr) have been measured by QUS at the phalanges for the evaluation of amplitude-dependent speed of sound (AD-SoS), bone transmission time (BTT), US peak amplitude (UPA), signal dynamic (SDY), slope, energy, and fast wave amplitude (FWA). Hand radiograph, lumbar spine dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT), and femoral neck DXA forearm peripheral QCT were performed on all patients. BTT is related to cortical thickness (CTh) (r=0.62, p<0.0001), and FWA is related to medullary canal thickness (r=-0.64, p<0.0001). Other parameters are related to both medullary canal thickness (AD-SoS: r=-0.21; UPA: r=-0.53; SDY: r=-0.56; slope: r=-0.64; energy: r=-0.44, p<0.05) and CTh (AD-SoS: r=0.54, p<0.0001; UPA: r=0.51; SDY: r=0.38; slope: r=0.32; energy: r=0.56, p<0.001). Linear multivariate models indicate that BTT, UPA, and energy measured at the phalanges carry independent information on CTh of the bone, whereas FWA, SDY, and slope are related only to medullary canal thickness.

Relationship between ultrasonic parameters and apparent trabecular bone elastic modulus: a numerical approach

The physical principles underlying quantitative ultrasound (QUS) measurements in trabecular bone are not fully understood. The translation of QUS results into bone strength remains elusive. However, ultrasound being mechanical waves, it is likely to assess apparent bone elasticity. The aim of this study is to derive the sensitivity of QUS parameters to variations of apparent bone elasticity, a surrogate for strength. The geometry of 34 human trabecular bone samples cut in the great trochanter was reconstructed using 3-D synchrotron micro-computed tomography. Finite-difference time-domain simulations coupled to 3-D micro-structural models were performed in the three perpendicular directions for each sample and each direction. A voxel-based micro-finite element linear analysis was employed to compute the apparent Young's modulus (E) of each sample for each direction. For the antero-posterior direction, the predictive power of speed of sound and normalized broadband ultrasonic attenuation to assess E was equal to 0.9 and 0.87, respectively, which is better than what is obtained using bone density alone or coupled with micro-architectural parameters and of the same order of what can be achieved with the fabric tensor approach. When the direction of testing is parallel to the main trabecular orientation, the predictive power of QUS parameters decreases and the fabric tensor approach always gives the best results. This decrease can be explained by the presence of two longitudinal wave modes. Our results, which were obtained using two distinct simulation tools applied on the same set of samples, highlight the potential of QUS techniques to assess bone strength.

Measurement of human trabecular bone by novel ultrasonic bone densitometry based on fast and slow waves

SUMMARY

Two longitudinal transmitted waves, fast and slow waves, were observed by employing a new quantitative ultrasound (QUS) method. The trabecular bone measurements generated by this method reflect three-dimensional structural information, and the new QUS parameters were able to identify vertebral fractures.

INTRODUCTION

The aims were to identify new quantitative ultrasound (QUS) parameters that based on new QUS method reflecting not only bone volume but also the microstructures of trabecular bone ex vivo and to observe how much they predict fracture risk in vivo.

METHODS

Ex vivo measurement: Three human femoral heads were used for the experiment. Attenuation of the slow wave, attenuation of the fast wave, speed of the slow wave, speed of the fast wave (SOFW), bone mass density of trabecular bone, and elastic modulus of the trabecular bone (EMTb) of each specimen were obtained using a new QUS method and compared with three-dimensional structural parameters measured by micro-computed tomography. In vivo measurement: Eighty-nine volunteers were enrolled, and the bone status in the distal radius was measured using a new QUS method. These parameters were compared with data evaluated by peripheral quantitative computed tomography and dual X-ray absorptiometry.

RESULTS

Ex vivo measurement: SOFW and EMTb showed correlations with the parameter of trabecular anisotropy. In vivo measurement: The new QUS parameters were able to identify vertebral fractures.

CONCLUSION

The newly developed QUS technique reflects the three-dimensional structure and is a promising method to evaluate fracture risk.

Sensitivity of qus parameters to controlled variations of bone strength assessed with a cellular model

The physical principles underlying quantitative ultrasound (QUS) measurements are not fully understood yet. Therefore, the translation of QUS results into bone strength remains elusive. In the present study, we derive the sensitivity of broadband ultrasonic attenuation (BUA) and speed of sound (SOS) to variations of bone strength. For this purpose, a mechanical cellular model is combined to a multiple regression resulting from the analysis of finite-difference time domain (FDTD) simulations. Specifically, we investigate how QUS variables respond to a variation in strength of 10%, realized either by a change in material properties or a change in bone volume fraction (BV/TV). The results show that except when BV/TV is high, the variations of BUA in response to a variation in strength realized by a pure change of BV/TV exceeds the technique imprecision and thus can be detected. When the variation of strength is realized by changes of compressive or shear stiffness, the response in QUS properties is dominated by the variation in C(11), whereas changes in C(44), remaining below the precision error, cannot be detected. The interpretation of these data, however, is not straightforward due to sparse description of elastic properties at the tissue level. To overcome the limitation of the cellular model, more realistic computational models such as micro- finite element analysis have to be considered.

Influence of density, elasticity, and structure on ultrasound transmission through trabecular bone cylinders

The aim of this in vitro study is to evaluate the potentiality of quantitative ultrasound (QUS) to separate information on density, elasticity, and structure on specimens of trabecular bone. Fifteen cylinders of spongy bone extracted from equine vertebrae were progressively demineralized and subjected to QUS, micro computed tomography (muCT), Dual energy X-ray absorptiometry (DXA) at various mineralization levels. Eventually all cylinders underwent a compression test to calculate the Young's modulus. Correlation analysis shows that speed of sound (SOS) is strictly associated to bone mineral density (BMD), Young's modulus, and all muCT parameters except for degree of anisotropy (DA). Fast wave amplitude (FWA) is directly correlated with bone surface and total volume ratio (BS/TV) and trabecular separation (Tb Sp), and inversely correlated with trabecular number (Tb N). Because muCT parameters were strictly correlated to BMD and Young's modulus data, partial correlation analysis was performed between SOS, FWA, and structural and elastic data in order to eliminate the effect of density. SOS was significantly correlated to bone volume and total volume ratio (BV/TV), BS/TV, and Young's modulus, and FWA was significantly correlated to Tb Sp only. These results show that SOS is strongly influenced by volumetric mineral bone density and elastic modulus of the specimen, and FWA is mainly affected by trabecular separation independently on density. Therefore, SOS and FWA are able to provide different and complementary information, at least on trabecular bone samples.

The measurement of broadband ultrasonic attenuation in cancellous bone--a review of the science and technology

The measurement of broadband ultrasonic attenuation (BUA) in cancellous bone at the calcaneus was first described in 1984. The assessment of osteoporosis by BUA has recently been recognized by Universities UK, within its EurekaUK book, as being one of the "100 discoveries and developments in UK Universities that have changed the world" over the past 50 years, covering the whole academic spectrum from the arts and humanities to science and technology. Indeed, BUA technique has been clinically validated and is utilized worldwide, with at least seven commercial systems providing calcaneal BUA measurement. However, a fundamental understanding of the dependence of BUA upon the material and structural properties of cancellous bone is still lacking. This review aims to provide a science- and technology-orientated perspective on the application of BUA to the medical disease of osteoporosis.

A new quality of bone ultrasound research

Quantitative ultrasound (QUS) methods have strong power to predict osteoporotic fractures, but they are also very relevant for the assessment of bone quality. A representative sample of recent studies addressing these topics can be found in this special issue. Further pursuit of these methods will establish micro-QUS imaging methods as tools for measuring specific aspects of bone quality. Once this is achieved, we will be able to link such data to the clinical QUS methods used in vivo to determine which aspects of bone quality cause QUS to be a predictor of fracture risk that is independent of bone mineral density (BMD). Potentially this could lead to the development of a new generation of QUS devices for improved and expanded clinical assessment. Good quality of basic science work will thus lead to good quality of clinical patient examinations on the basis of a more detailed assessment of bone quality.

The correlation between the SOS in trabecular bone and stiffness and density studied by finite-element analysis

For the clinical assessment of osteoporosis (i.e., a degenerative bone disease associated with increased fracture risk), ultrasound has been proposed as an alternative or supplement to the dual-energy X-ray absorptiometry (DEXA) technique. However, the interaction of ultrasound waves with (trabecular) bone remains relatively poorly understood. The present study aimed to improve this understanding by simulating ultrasound wave propagation in 15 trabecular bone samples from the human lumbar spine, using microcomputed tomography-based finite-element modeling. The model included only the solid bone, without the bone marrow. Two structural parameters were calculated: the bone volume fraction (BV/TV) and the structural (apparent) elastic modulus (E(s)), and the ultrasound propagation parameter speed of sound (SOS). Relations between BV/TV and E(s) were similar to published experimental relations. At 1 MHz, correlations between SOS and the structural parameters BV/TV and Es were rather weak, but the results can be explained from the specific features of the trabecular structure and the intrinsic material elastic modulus E(i). In particular, the systematic differences between the three main directions provide information on the trabecular structure. In addition, at 1 MHz the correlation found between the simulated SOS values and those calculated from the simple bar equation was poor when the three directions are considered separately. Hence, under these conditions, the homogenization approach-including the bar equation-is not valid. However, at lower frequencies (50-300 kHz) this correlation significantly improved. It is concluded that detailed analysis of ultrasound wave propagation through the solid structure in various directions and with various frequencies, can yield much information on the structural and mechanical properties of trabecular bone.

Is discordance in bone measurements affected by body composition or anthropometry? A comparative study between peripheral and central devices

Screening of osteoporosis using peripheral bone measurements has become more common, even though diagnostic discrepancies are known to exist between peripheral dual-energy X-ray (pDXA) or quantitative ultrasound (QUS) and central DXA measurements. Values of diagnostic parameters such as bone mineral density, speed of (ultra)sound, and broadband ultrasound attenuation are affected by bone size and soft tissue composition. However, their significance for the discordance between peripheral and central techniques is unclear. In this study, bone status and total body composition of 139 women (mean age 68.3 yr [1.7 SD], mean body mass index 26.5 kg/m2 [3.6 SD]) were assessed by 3 GE Lunar devices. Heel pDXA and heel QUS were conducted using peripheral instantaneous X-ray imaging (PIXI) and Achilles, respectively, and central DXA measurements were taken at the posterior-anterior lumbar spine (L2-L4) and at the left femoral neck using Prodigy. Positive significant associations were found between body height or fat (%) and most DXA or QUS parameters. The discordance between the site-dependent DXA or QUS T-score values typically increased (p<0.05) as a function of body weight or fat (%), but not with body height. On an average, body adiposity accounted for less than 11% of the differences between the techniques; however, increase of total body fat from 20% to 45% led to a discrepancy of one T-score between DXA(HEEL) and QUS(HEEL). To avoid diagnostic bias, comparative assessment of the devices using the same population is recommended.

Effects of Thresholding Techniques on μCT-Based Finite Element Models of Trabecular Bone

Microimaging based finite element analysis is widely used to predict the mechanical properties of trabecular bone. The choice of thresholding technique, a necessary step in converting grayscale images to finite element models, can significantly influence the predicted bone volume fraction and mechanical properties. Therefore, we investigated the effects of thresholding techniques on microcomputed tomography (micro-CT) based finite element models of trabecular bone. Three types of thresholding techniques were applied to 16-bit micro-CT images of trabecular bone to create three different models per specimen. Bone volume fractions and apparent moduli were predicted and compared to experimental results. In addition, trabecular tissue mechanical parameters and morphological parameters were compared among different models. Our findings suggest that predictions of apparent mechanical properties and structural properties agree well with experimental measurements regardless of the choice of thresholding methods or the format of micro-CT images.

Unique and common genetic effects between bone mineral density and calcaneal quantitative ultrasound measures: the Fels Longitudinal Study

INTRODUCTION

Areal bone mineral density (BMD) and calcaneal quantitative ultrasound (QUS) measures are correlated, and both traits predict osteoporotic fracture risk independently. However, few studies have examined whether common genetic effects (i.e., pleiotropy) exist between these traits in extended families. In this study, we estimated the additive genetic correlation and random environmental correlation between BMD measured at various skeletal sites and calcaneal QUS measures.

METHODS

Our sample included 537 adults (251 men and 286 women) from 110 families participating in the Fels Longitudinal Study. Total hip, femoral neck, lumbar spine, and total body BMD were measured using dual energy X-ray absorptiometry. Three measures of calcaneal structure--broadband ultrasound attenuation (BUA), speed of sound (SOS), and quantitative ultrasound index (QUI)--were collected from the non-dominant heel using the Sahara sonometer. Applying a variance components-based maximum likelihood method, we estimated the heritability of each trait and estimated the genetic and environmental correlations between the different BMD and QUS measures.

RESULTS

Heritability estimates were significant for all measures of BMD and QUS ranging from 0.55 to 0.78. Significant non-zero genetic correlations were found between the different BMD and QUS measures. All genetic correlations were also significantly different from 1. Genetic correlations between total hip BMD and each of the QUS measures were 0.63 with BUA, 0.50 with SOS, and 0.56 with QUI. For femoral neck BMD, genetic correlations were similar to those between total hip BMD and QUS measures. Genetic correlations between BMD of the lumbar spine and QUS measures ranged from 0.34 to 0.38, and those between total body BMD and QUS measures, from 0.51 to 0.54. In contrast, all random environmental correlations were not significantly different from zero.

CONCLUSION

This study demonstrates that BMD and calcaneal QUS measures among healthy men and women are significantly heritable and are, in part, jointly influenced by a common set of underlying genes. Additionally, this study also provides evidence for a unique set of genes that independently influences each individual trait.

High-frequency ultrasound in the measurement of pediatric craniofacial integrity

OBJECTIVE

This study evaluates the use of high-frequency ultrasound in the measurement of the material nature of the pediatric craniofacial skeleton.

STUDY DESIGN AND SETTING

Three desiccated human skulls, aged 1 year, 5 years, and adult, underwent ultrasonic evaluation at 6 sites on each hemicranium.

RESULTS

The overall mean signal reflection coefficients for the infant, child, and adult skulls are 98.8 mV (13.75 mV SD), 172 mV (24.5 mV SD), and 230 mV (23.5 mV SD), respectively. The mean signal reflection coefficient is positively correlated with increasing chronological age. Comparison of intrasubject signal patterns suggests bone density fields, which vary as a function of growth.

CONCLUSION

High-frequency ultrasound provides accurate measurements of the osseous impedance of the craniofacial skeleton. Pattern analysis suggests increases in skull density with greater growth and age.

SIGNIFICANCE

Although further testing must be performed in vivo, high-frequency ultrasound may accurately measure the osseous impedance of the pediatric craniofacial skeleton.

EBM RATING

C.

The risk of Colles' fracture is associated with the collagen I alpha1 Sp1 polymorphism and ultrasound transmission velocity in the calcaneus only in heavier postmenopausal women

To compare the ability of the bone mineral density (BMD) at the distal forearm, collagen I alpha 1 (COLIA1) polymorphism, and ultrasound stiffness to identify individuals with increased risk of wrist fracture, we studied 183 postmenopausal Czech women with a wrist fracture and 178 postmenopausal controls, ages 45-70 years. The genotypes "Ss" and "ss" were significantly overrepresented among fracture cases. The BMD measurements at the femoral neck, total femur, and distal forearm as well as ultrasound stiffness of the heel, broadband ultrasound attenuation (BUA), and speed of sound (SOS) were significantly lower in the fracture cohort. BMD of the distal forearm was the main determinant of susceptibility to the wrist fracture. Weight, the COLIA1 genotype, and ultrasound SOS further strengthened the predictive value of BMD. However, we found interaction between weight and both the COLIA1 Sp1 polymorphism and ultrasound parameters. Presence of the "s" allele as well as low SOS acted as significant predictors of wrist fracture only in heavier women, (> or =62 kg) but not in women with a body weight of less than 62 kg. In heavier women, both the COLIA1 Sp1 polymorphism and ultrasound parameters acted as independent markers that contributed to BMD to enhance fracture prediction. However, the COLIA1 enabled a higher specificity (specificity 72.4%, sensitivity 44.2%), whereas SOS enabled a higher sensitivity (sensitivity 73.9%, specificity, 45.7%). We conclude that BMD at total forearm, the COLIA1 polymorphism, and ultrasound SOS are independent predictors of wrist fracture in postmenopausal women. The effect of the COLIA1 Sp1 polymorphism and SOS on wrist fracture risk is more pronounced in patients with a higher body weight.

Effect of trabecular orientation on mechanical resistance and ultrasound propagation in specimens of equine vertebrae

Osteoporosis involves alterations, not only in density, but also in the architectural organisation of the bone; in particular, trabecular orientation, following the skeletal load directions, lends a high degree of stiffness to the whole bone. We investigated the relationship between trabecular orientation, density, stiffness and ultrasound (US) propagation in two orthogonal directions (par. = parallel to, and ort. = orthogonal to the main orientation of the trabeculae) in cylindrical equine bone specimens (thoracic vertebrae) where a preferential orientation is present. A total of 15 cylinders were progressively decalcified with 0.2 mol/L ethylenediaminetetraacetic acid (EDTA). At different levels of decalcification, we measured the apparent density (g/cm(3)), bone mineral density or BMD (g/cm(2)), stiffness coefficient (MPa) and various US parameters. Before decalcification, stiffness values were the same in all directions. As the decalcification proceeded, the stiffness declined and, at low BMD values, it was significantly different in the two directions, being the highest in the par. one. Different behaviours of US parameters were observed in the two directions: SoS (speed of sound) was closely related to apparent density, BMD and stiffness in the par. direction (r = 0.88, 0.92 and 0.88, respectively, p < 0.0001). In the ort. direction, no significant association has been found between SoS and apparent density, BMD or stiffness. In the same experimental setup, US fast wave amplitude (FWA) was related to apparent density and BMD in the par. direction (r = 0.72 and 0.67, respectively, p < 0.0001) and in the ort. direction (r = 0.83 and r = 0.84 respectively, p < 0.0001). FWA was also correlated to stiffness in both directions (r = 0.61 par.; 0.81 ort., p < 0.0001). These results show that trabecular orientation strongly influences both mechanical properties of bone and US propagation. Furthermore, we found that US parameters can be predictors of mechanical properties of the bone independent of bone density.

In vitro acoustic waves propagation in human and bovine cancellous bone

The acoustic behavior of cancellous bone with regard to its complex poroelastic nature has been investigated. The existence of two longitudinal modes of propagation is demonstrated in both bovine and human cancellous bone. Failure to take into account the presence of these two waves may result in inaccurate material characterization.

INTRODUCTION

Acoustic wave propagation is now a commonly used nondestructive method for cancellous bone characterization. However, wave propagation in this material may be affected by fluid-solid interactions inherent to its poroelastic nature, resulting in two different longitudinal waves. This phenomenon has been demonstrated in previous studies and is in agreement with Biot's theory. The purpose of this paper is to extend these findings to human trabecular bone and to thoroughly investigate these two waves.

MATERIALS AND METHODS

Sixty human and 14 bovine cancellous bone cubic specimens were tested in vitro in three different directions using an immersion acoustic transmission method. Original procedures were developed to quantify both velocity and attenuation characteristics of each wave. In term of attenuation, a modified broadband ultrasound attenuation (BUA), describing the rate of change of the frequency-dependent attenuation, was defined for each wave (FDUA).

RESULTS

Both waves were identified in most of the specimens. The fast wave velocities demonstrated a negative linear correlation with porosity (1500-2300 m/s, R2 = 0.44, p < 10(-3)), whereas the slow wave velocities exhibited two different behaviors: (1) a first set of data clearly dependent on porosity showing a positive linear correlation (1150-1450 m/s, R2 = 0.26, p < 10(-3)) and (2) a second group independent on porosity. The fast wave FDUA (20-140 dB/cmMHz) showed a parabolic behavior and reached a maximum for 75% porosity (second degree relationship R2 = 0.41,p < 10(-3)), whereas a positive linear behavior was observed for the slow wave FDUA (15-40 dB/cmMHz; R2 = 0.15, p < 10(-2)).

CONCLUSIONS

Existence of two wave propagation modes were demonstrated in human cancellous bone. Our data suggest that, in some cases, the amplitude of the slow wave is much larger than the amplitude of the fast wave. For this reason, care should be taken when using measurement systems that incorporate simple threshold detection because the fast wave could remain undetected. Moreover, failure to consider the presence of these two waves could result in an inaccurate quantification of cancellous bone physical properties.

Speed of sound measurements of the third metacarpal bone in young exercising thoroughbred racehorses

The purpose of this longitudinal in-field study was to evaluate the influence of exercise, age, and gender on superficial cortical bone of the third metacarpal bone (MC III) in young Thoroughbreds by measuring speed of sound (SOS) values with an axial transmission technique (Omnisense, Sunlight Ltd, Israel). Both MC III of 75 racehorses, 2 to 4 years old, were monitored with SOS measurements in 5- to 7-week intervals during a 9- month physical exercise period. Medical data and training programs (slow gallop, canter, and high-speed work) of each horse were recorded. SOS measurements began before 2-year-old horses started high-speed training. SOS values of the dorsal aspect of MC III were significantly lower in comparison with values obtained at the lateral and the medial aspect of MC III, and SOS values were inversely correlated with measurement cycles. Significant limb-associated differences in dorsal MC III SOS values were observed at measurement cycles 2, 3, and 4. SOS values obtained at the lateral and medial aspect of MC III increased with age. SOS values obtained at the dorsal aspect of MC III, decreased with age. Mares had significantly higher SOS values at the dorsal aspect of MC III, when compared with corresponding values in stallions. In 2-year-old Thoroughbreds SOS values of the dorsal MC III were significantly different between cycles 1 and 2, between cycles 3 and 4, and between cycles 4 and 5. Three-year-old horses showed significant differences between SOS values of the dorsal MC III obtained at cycles 3 and 4. Training intensities did not significantly influence SOS values. The results indicate that young exercising Thoroughbred racehorses have age-, gender-, and measurement-cycle-dependent variations in SOS values of MC III, which probably reflect adaptive variations in superficial cortical bone properties of MC III.

Assessment of bone quality by quantitative ultrasound of proximal phalanges of the hand and fracture rate in children and adolescents with bone and mineral disorders

Bone quality by quantitative ultrasound and fracture rate were assessed in 135 (64 males) children and adolescents aged 3-21 y with bone and mineral disorders such as chronic anticonvulsants or glucocorticoids treatment, juvenile rheumatoid arthritis, celiac disease, paucity of intrahepatic bile ducts, autoimmune hepatitis, genetic diseases, idiopathic juvenile osteoporosis, disuse osteoporosis, beta-thalassemia major, survivors of acute lymphoblastic leukemia, liver transplantation, calcium deficiency, and nutritional or X-linked hypophosphatemic rickets. Amplitude-dependent speed of sound through the distal end of the first phalangeal diaphysis of the last four fingers of the hand was measured by an ultrasound device. In the majority of patients cortical area to total area ratio by metacarpal radiogrammetry (n = 120) and lumbar bone mineral density (BMD) by dual-energy x-ray absorptiometry (n = 99) were also assessed. In patients with X-linked hypophosphatemic rickets radial BMD by single-photon absorptiometry instead of lumbar BMD was measured. Mean values of amplitude-dependent speed of sound, cortical area to total area ratio, lumbar BMDarea, or lumbar BMD corrected for bone sizes estimated by a mathematical model (BMDvolume), as well as mean values of radial BMD in patients with X-linked hypophosphatemic rickets, expressed as z score, were significantly reduced (p < 0.0001) in comparison with their reference values (-1.7 +/- 1.0, -2.0 +/- 0.9, -3.0 +/- 1.3, -1.9 +/- 1.0, -2.7 +/- 0.7, respectively). A positive relationship was found between amplitude-dependent speed of sound and cortical area to total area ratio (r = 0.90, p < 0.0001), lumbar BMDarea (r = 0.62, p < 0.0001), or lumbar BMDvolume (r = 0.66, p < 0.0001). Fifty-two patients (38.5%) had suffered fractures in the 6 mo preceding the bone measurements, the radial distal metaphysis being the most frequent fracture site (28.8%). Mean values of amplitude-dependent speed of sound, cortical area to total area ratio, lumbar BMDarea, or lumbar BMDvolume, expressed as z score, of fractured patients were significantly lower (p < 0.0001) than those of fracture-free patients (-2.2 +/- 1.0 and -1.4 +/- 0.8, -2.6 +/- 0.9 and -1.7 +/- 0.7, -3.5 +/- 1.2 and -2.5 +/- 1.0, -2.5 +/- 1.0 and -1.3 +/- 0.7, respectively). Phalangeal quantitative ultrasound may be a useful method to assess bone quality and fracture risk in children and adolescents with bone and mineral disorders.

Normal bone mineral density and lean body mass, but increased fat mass, in young adult patients with congenital adrenal hyperplasia

Patients with congenital adrenal hyperplasia attributable to 21-hydroxylase deficiency are treated with glucocorticoids. Glucocorticoid administration, even in substitution doses, may cause decreased bone mineral density (BMD) and obesity. The purpose of this study was to determine BMD, lean mass, and fat mass in young adult male (M, n = 15) and female (F, n = 15) patients with 21-hydroxylase deficiency, who had been treated with currently recommended low doses of glucocorticoids. Measurements were performed with dual-x-ray absorptiometry. In addition, calcaneal ultrasound measurements were performed (broadband ultrasound attenuation and speed of sound). Results were compared with those in age- and sex-matched controls; to adjust for height, lean and fat mass were divided by (height)(2). M and F patients [M, 21.7 +/- 2.4; F, 20.6 +/- 2.9 yr old (mean +/- SD)] were shorter than the controls (M, P < 0.001; F, P < 0.003) and their body mass indices were higher [M patients (25.0 +/- 3.6) vs. controls (22.3 +/- 1.9 kg/m(2)) (P < 0.02); F patients (25.5 +/- 4.5) vs. controls (21.9 +/- 2.3 kg/m(2)) (P < 0.02)]. BMD values (lumbar spine L1-L4, femoral neck, and total body) were not different from controls. Calcaneal ultrasound measurements showed that M patients had higher speed of sound values [M patients (1564 +/- 38) vs. controls (1529 +/- 29 m/sec) (P < 0.01)]. Lean mass in M and F patients was not different from controls when adjusted for height. Fat mass was higher in M and F patients when adjusted for height [M patients 5.6 +/- 2.9 vs. controls 2.7 median (1.7-7.0 min-max) kg/m(2) (P < 0.04); F patients 8.7 +/- 2.8 vs. controls 5.8 (4.3-10.7) kg/m(2) (P < 0.02)]. Relative fat mass (fat mass as a percentage of the total body mass) was higher in patients, compared with controls [M patients 22.0 +/- 9.1 vs. controls 12.8 (8.5-27.0)% (P < 0.04); F patients 34.1 +/- 5.0 vs. controls 29.0 +/- 5.1% (P < 0.02)]; this resulted from increased fat mass, not from decreased lean mass. Fat distribution over the body was not different in patients and controls. No significant correlations were found between cumulative glucocorticoid doses in the last 0.5, 2, or 5 yr or mean salivary morning levels of 17-hydroxyprogesterone and androstenedione in the last 5 yr on one hand and bone parameters, lean mass, or fat mass on the other hand. We conclude that, at prevailing low-dose glucocorticoid regimens, young adult patients with 21-hydroxylase deficiency have normal BMD. Their lean mass is in accordance with height, but fat mass is increased, with a normal distribution over the body. This results in a higher fat percentage of the total body and a higher body mass index than in healthy peers. Because overweight and increased fat mass are associated with the metabolic syndrome and increased cardiovascular risk, weight management should have appropriate attention in the follow-up of congenital adrenal hyperplasia patients, to prevent overweight-associated morbidity.

Equine third metacarpal bone assessment by quantitative ultrasound and dual energy X-ray absorptiometry: an ex vivo study

The purpose of this ex vivo study was to analyse two commonly established methods of mechanical bone property assessment for application in horses: Quantitative ultrasound (QUS), which depends on the bone's density and Young's modulus, and dual energy X-ray absorptiometry (DXA), which depends on the areal bone mineral density (BMD). The third metacarpal bone (MC III) of horses was selected as examination region for practical reasons. An interrelationship between QUS- and DXA-values was examined. Both MC III of eleven randomly selected equine cadavers were divided in nine regions of interest (ROI). A multi-site QUS device was used for axial transmission speed of sound (SOS) measurements and a DXA device was used for BMD evaluation. Full cortical thickness BMD (FcBMD), overall aspect BMD and 4 mm cortical border slice BMD (4 mmBMD) were evaluated. In addition, each ROI of one MC III was measured 10 times to determine QUS- and DXA-measurement precision. SOS values and BMD values obtained at different aspects of MC III were different (P < 0.001). FcBMD and overall BMD obtained at different levels were different (P < 0.001). SOS data correlated with FcBMD-, overall BMD- and 4 mmBMD-data at various ROI. FcBMD-, overall BMD- and 4 mmBMD-data were strongly correlated. The intra-operator coefficient of variation was 1.3% for SOS-measurements and ranged between 1.94 and 10.3% for BMD-measurements. Multi-site axial transmission QUS as well as DXA can be used to precisely measure bone characteristics of MC III in horses. However, both techniques do not measure the same bone properties. It is therefore concluded, that QUS and DXA techniques are complementary for application in horses.

Use of multisite quantitative ultrasonography for noninvasive assessment of bone in horses

OBJECTIVE

To evaluate the usefulness of multisite quantitative ultrasonography for noninvasive assessment of bone in horses.

SAMPLE POPULATION

12 healthy horses and both forelimbs from 8 clinically normal horses.

PROCEDURE

For in vivo measurements, various regions of interest (ROI) were examined on the third metacarpal bone, radius, and tibia. Precision error for speed of sound (SOS) measurements was obtained by measuring each ROI of 4 horses 10 times with probe repositioning. Additionally, 3 operators measured each aspect of the third metacarpal bone of 6 horses 5 times each. For ex vivo measurements, third metacarpal bones were examined at 9 ROI, and SOS measurements were performed before and after soft tissue removal. One ROI of a single forelimb was subjected to 96 ex vivo measurements with 3 different contact media.

RESULTS

The lateral aspect of the third metacarpal bone had significantly higher SOS values than the dorsal and medial aspect of the third metacarpal bone. No difference was obtained between SOS values of the lateral and medial aspect of the radius. The tibia had significantly higher SOS values than the lateral aspect of the radius and the dorsal and medial aspect of the third metacarpal bone. Intraoperator coefficients of variation ranged from 0.62 to 3.15%, and interoperator coefficients of variation ranged from 0.78 to 2.70%. Values of SOS were highest when silicone oil was used as the contact medium.

CONCLUSIONS AND CLINICAL RELEVANCE

Speed of sound measurements obtained by quantitative ultrasonography in axial transmission mode can be used to precisely measure superficial cortical bone properties of third metacarpal bone, radius, and tibia in horses.

The use of ultrasound in the assessment of bone status

The assessment of skeletal status has wide clinical applications, especially in the management of osteoporosis. Osteoporosis, once thought of as an unpreventable and untreatable aging process, has revealed many of its secrets over the last decade, and the advent of successful drug therapy has changed our perception of the disease. Non-invasive techniques play a fundamental role in the diagnosis of osteoporosis and in the assessment of the efficacy of drug treatments. The primary technique used in osteoporosis is dual X-ray absorptiometry (DXA), that has been established as a reliable means of measuring bone density. Quantitative ultrasound (QUS), because of the relative portability of the equipment, ease of use, lack of ionizing radiation and low cost, has great potential for widespread use. Five devices for QUS assessment have recently been approved by the Food and Drug Administration and many more applications are in progress. QUS is a relatively new technology, at least in its application to bone fragility. Nevertheless, QUS has demonstrated that it is able to detect bone fragility as well as DXA. However, diagnosis of osteoporosis by QUS remains contentious, but the problems are due more to the limitations of the present T-scores rather than to the technique. A better option for QUS would be to report results in terms of remaining lifetime fracture risk, keeping in mind that a risk estimate needs not only the QUS or DXA measurement, but also the specific data, such as age, weight, gender, hormonal status and fracture history of the patient.

North American male reference population for speed of sound in bone at multiple skeletal sites

Alternatives to dual-energy X-ray absorptiometry (DXA) have been sought to increase access to low-cost osteoporosis risk assessment. Early quantitative ultrasound (QUS) systems measured speed of sound (SOS) and broadband ultrasound attenuation (BUA) at the calcaneus, and these were demonstrated to be good predictors of hip fracture risk. Recent studies have demonstrated the usefulness of other peripheral sites to assess bone status. The Sunlight Omnisense (Sunlight Medical, Rehovot, Israel) is a portable, inexpensive QUS device capable of multiple-site SOS measurement. To provide a robust male reference database, 588 healthy Caucasian males aged 20-90 yr were recruited from 6 centers across North America. SOS measurements were taken at the distal 1/3 radius, proximal third phalanx, midshaft tibia, and fifth metatarsal. A female reference database has previously been collected at North American sites. The results indicate that SOS in males exhibits an age-related decline beginning in the fifth decade at the radius, phalanx, and metatarsal, whereas the tibial SOS remains nearly constant until the ninth decade. Although females reach a higher-peak SOS than males at most sites, SOS is higher in males at all sites after the sixth decade, as a result of a more gradual decline in SOS. Longitudinal monitoring of healthy men should be performed to confirm these cross-sectional results.

The prospects of estimating trabecular bone tissue properties from the combination of ultrasound, dual-energy X-ray absorptiometry, microcomputed tomography, and microfinite element analysis

Osteoporosis commonly is assessed by bone quantity, using bone mineral density (BMD) measurements from dual-energy X-ray absorptiometry (DXA). However, such a measure gives neither information about the integrity of the trabecular architecture nor about the mechanical properties of the constituting trabeculae. We investigated the feasibility of deriving the elastic modulus of the trabeculae (the tissue modulus) from computer simulation of mechanical testing by microfinite element analysis (muFEA) in combination with measurements of ultrasound speed of sound (SOS) and BMD measurements. This approach was tested on 15 postmortem bovine bone cubes. The apparent elastic modulus of the specimens was estimated from SOS measurements in combination with BMD. Then the trabecular morphology was reconstructed using microcomputed tomography (muCT). From the reconstruction a mesh for muFEA was derived, used to simulate mechanical testing. The tissue modulus was found by correlating the apparent moduli of the specimens as assessed by ultrasound with the ones as determined with muFEA. A mean tissue modulus of 4.5 GPa (SD, 0.69) was found. When adjusting the muFEA-determined elastic moduli of the entire specimens with their calculated tissue modulus, an overall correlation of R2 = 96% with ultrasound-predicted values was obtained. We conclude that the apparent elastic stiffness characteristics as determined from ultrasound correlate linearly with those from muFEA. From both methods in combination, the elastic stiffness of the mineralized tissue can be determined as an estimator for mechanical tissue quality. This method can already be used for biopsy specimens, and potentially could be applicable in vivo as well, when clinical CT or magnetic resonance imaging (MRI) tools with adequate resolution reach the market. In this way, mechanical bone quality could be estimated more accurately in clinical practice.

Tibial quantitative ultrasound versus whole-body and lumbar spine DXA in a Dutch pediatric and adolescent population

RATIONALE AND OBJECTIVES

To understand normal bone development, studies in healthy children and adolescents are important. To assess the applicability of tibial quantitative ultrasound measurements (QUS) in children, we performed a study that compared dual-energy x-ray absorptiometry (DXA) of the lumbar spine and whole body with tibial QUS.

METHODS

For this study we recruited 146 Dutch children and adolescents, 58 boys (median age, 14.1 years; range, 7.6-23.4 years) and 88 girls (median age, 18.0 years; range, 7.6-23.5 years). Tanner stage, weight, and height were assessed for all participants. Bone mineral density (BMD; g x cm(-2)) of the whole body and lumbar spine (L2-L4) and bone mineral apparent density (BMAD) of the lumbar spine (g x cm(-3)) were assessed by using the Lunar DPXL. For tibial QUS, the Soundscan compact system was used.

RESULTS

Both lumbar as well as whole-body BMD showed a strong, significant correlation with tibial QUS in boys and girls: rtotal body boys = 0.81, rtotal body girls = 0.77, rlumbar spine boys = 0.79, and rlumbar spine girls = 0.72. Lumbar spine BMAD also showed significant correlations with tibial QUS: rboys= 0.63 and rgirls = 0.63 (for all correlations, P < 0.001).

CONCLUSIONS

Our study showing strong, significant correlations between DXA and tibial QUS measurements suggests that tibial QUS is a technique that may be applicable in children and adolescents.