A comparison of reflection and transmission ultrasonic techniques for measurement of cancellous bone elasticity

Prediction of trabecular bone qualitative properties using scanning quantitative ultrasound

Microgravity induced bone loss represents a critical health problem in astronauts, particularly occurred in weight-supporting skeleton, which leads to osteopenia and increase of fracture risk. Lack of suitable evaluation modality makes it difficult for monitoring skeletal status in long term space mission and increases potential risk of complication. Such disuse osteopenia and osteoporosis compromise trabecular bone density, and architectural and mechanical properties. While X-ray based imaging would not be practical in space, quantitative ultrasound may provide advantages to characterize bone density and strength through wave propagation in complex trabecular structure. This study used a scanning confocal acoustic diagnostic and navigation system (SCAN) to evaluate trabecular bone quality in 60 cubic trabecular samples harvested from adult sheep. Ultrasound image based SCAN measurements in structural and strength properties were validated by μCT and compressive mechanical testing. This result indicated a moderately strong negative correlations observed between broadband ultrasonic attenuation (BUA) and μCT-determined bone volume fraction (BV/TV, R²=0.53). Strong correlations were observed between ultrasound velocity (UV) and bone's mechanical strength and structural parameters, i.e., bulk Young's modulus (R²=0.67) and BV/TV (R²=0.85). The predictions for bone density and mechanical strength were significantly improved by using a linear combination of both BUA and UV, yielding R²=0.92 for BV/TV and R²=0.71 for bulk Young's modulus. These results imply that quantitative ultrasound can characterize trabecular structural and mechanical properties through measurements of particular ultrasound parameters, and potentially provide an excellent estimation for bone's structural integrity.

Effects of condylar elastic properties to temporomandibular joint stress

Mandibular condyle plays an important role in the growth and reconstruction of the temporomandibular joint (TMJ). We aimed to obtain orthotropic elastic parameters of the condyle using a continuous-wave ultrasonic technique and to observe the effects of condylar elastic parameters on stress distribution of the TMJ using finite element analysis (FEA). Using the ultrasonic technique, all nine elastic parameters were obtained, which showed that the mandibular condyle was orthotropic. With the condyle defined as orthotropic, the occlusal stress was transferred fluently and uniformly from the mandible to the TMJ. The stress distribution in the isotropic model showed stepped variation among different anatomical structures with higher stress values in the cartilage and condyle than in the orthotropic model. We conclude that anisotropy has subtle yet significant effects on stress distribution of the TMJ and could improve the reality of simulations.

Effects of estrogen-progestin therapy on serum levels of RANKL, osteoprotegerin, osteocalcin, leptin, and ghrelin in postmenopausal women

OBJECTIVE

The aim of this study was to evaluate the effects of estrogen-progestin therapy on serum levels of receptor-activating nuclear factor kappabeta ligand (RANKL), osteoprotegerin, osteocalcin, leptin, and ghrelin in a cross-sectional study of 99 healthy postmenopausal women conducted at the Menopause Clinic of our department.

DESIGN

In this cross-sectional, observational study, 99 participants were divided into two groups. Group A was composed of 77 postmenopausal women who had never received estrogen-progestin therapy, and group B was composed of 22 postmenopausal women who had received transdermal 17beta-estradiol at a dose of 50 microg/day in a continuous regimen for at least 24 months and nomegestrol at a dose of 5 mg/day for 12 days/month in a sequential regimen. All participants underwent blood sampling in the morning and quantitative ultrasound bone-densitometry measurement of the proximal phalanges of the dominant hand.

RESULTS

T score and amplitude-dependent speed of sound were significantly higher in group B than in group A. No significant differences in RANKL, osteoprotegerin, and osteocalcin were observed between the two groups. Serum leptin levels were significantly lower in group B than in group A, whereas ghrelin was significantly higher in group B than in group A.

CONCLUSIONS

The data gathered in this preliminary study indicate that estrogen-progestin therapy may protect against postmenopausal bone loss, but this protective effect does not seem to be exerted through action on the RANK-RANKL-osteoprotegerin system. Similarly, although several reports suggest that leptin and ghrelin are involved in bone metabolism, we could not detect any important correlation of these two hormones with bone metabolism or bone status in treated and untreated postmenopausal women. Because of the limited number of treated participants and the study design, the results of this preliminary study must be confirmed in larger, prospective, longitudinal studies.

Callus mineralization following distraction osteogenesis of the mandible monitored by scanning acoustic microscopy (SAM)

BACKGROUND

Scanning acoustic microscopy uses ultrasound to analyse histomorphology of tissues with microscopic resolution and delivers data about physical properties of the specimen.

MATERIAL AND METHODS

Bony consolidation was monitored by scanning acoustic microscopy in 12 embedded specimens of dog mandibles after distraction osteogenesis. Increasing mineralization was detected by measurements of acoustic impedance (Z).

RESULTS

There was a strong correlation between acoustic impedance and time of consolidation. Measurements of the speed of sound (v) provided specific information about non-mineralized zones of the distracted area. Distribution of density in the distracted area could be reconstructed by using the measurements of acoustic impedance and speed of sound.

CONCLUSION

The method seems suitable for studying bone remodelling qualitatively and quantitatively.

Reduction in normalized bone elasticity following long-term bisphosphonate treatment as measured by ultrasound critical angle reflectometry

Using an improved version of ultrasound critical angle reflectometry, the bone quality of cortical and trabecular bone was assessed in vivo by measuring elastic moduli (normalized for bone density) at both principal axes, referred to as the minimum and maximum normalized elasticities. The measurements were made in 30 normal premenopausal women, 30 normal postmenopausal women, 22 untreated postmenopausal women with osteoporosis, 74 postmenopausal women with osteoporosis or osteopenia on bisphosphonate treatment, and 32 patients with renal transplantation (16 women and 16 men) taking steroids. Cortical elasticity was higher than trabecular elasticity; both declined slightly and non-significantly with age in normal women. Among untreated postmenopausal women with osteoporosis, cortical maximum normalized elasticity (E(cmax)) remained within 95% prediction intervals of normal women. Among patients on bisphosphonate, E(cmax) was low in the majority of patients. E(cmax) was significantly more depressed among those taking the drug > or =3 years than <3 years (22.1% below normal premenopausal women versus 17.2%, P =0.001), and among those with incident non-spinal fractures than without (75.9 vs. 81.5%, P =0.008). E(cmax) was independent of bone mineral density at the calcaneus. Most patients with renal transplantation had low E(cmax), with a mean 20.8% below the normal premenopausal mean. Qualitatively similar findings were found with cortical minimum elasticity and with trabecular minimum and maximum elasticities. Thus, the material bone quality of cortical and trabecular bone may be impaired following bisphosphonate treatment, as in renal transplantation on steroids.

Evaluation of skeletal status by quantitative ultrasonometry in postmenopausal women without known risk factors for osteoporosis

The objective of our study was to evaluate bone density in Italian postmenopausal women without clinical risk factors for osteoporosis resident in the Naples area using quantitative ultrasonometry of bone (QUS). Subjects were 1149 Italian postmenopausal women (age: 54.9 +/- 5.0 years (mean +/- standard deviation); range: 45-74 years) resident in the Naples area. Clinical risk factors for osteoporosis resulting in exclusion from the study were family history of osteoporosis, dietary, smoking and alcohol habits, personal history of fractures and/or metabolic diseases. The following QUS parameters were calculated: amplitude-dependent speed of sound (AD-SoS), T-score and Z-score. We found significant inverse correlations between AD-SoS and age (r = - 0.23), time since menopause (r = - 0.25) and body mass index (BMI) (r = - 0.16). The same was observed for T-score. In contrast, Z-score showed a significant positive correlation with age and time since menopause, and a negative correlation with BMI. A T-score suggestive of high risk for osteoporosis (less than -3.2) was found in 1.6% of subjects, while a T-score suggestive of moderate risk for osteoporosis (between -3.2 and -2) was found in 19.3% of patients. In this group of women without clinical risk factors for osteoporosis we found a very low prevalence of QUS results suggesting a high risk for osteoporosis. However, a condition of 'moderate' risk for osteoporosis was present in a remarkable percentage of these women.

Elevated C-reactive protein: a common marker for atherosclerotic cardiovascular risk and subclinical stages of pulmonary dysfunction and osteopenia in a healthy population

Atherosclerotic cardiovascular disease, osteopenia, and pulmonary dysfunction are the serious health problems, and several experimental studies have suggested that inflammation has a role in them. The present study was conducted to evaluate the usefulness of the plasma CRP is as a common marker for detecting these diseases in the general population in their subclinical stages. In a cross-sectional study, we measured the pulse wave velocity (PWV), quantitative osteo-sono-assessment index (OSI), pulmonary functions, and the plasma level of C-reactive protein (CRP) in 7283 consecutive healthy subjects (age 50+/-11 years). The PWV was higher and the OSI and pulmonary function parameters were below normal in subjects with an elevated CRP level (> or =0.2 mg/dl) than in subjects with a CRP level within the normal range. We divided the subjects into quartiles for each of these parameters and found that the first quartiles represented patients with subclinical states of the aforementioned abnormal conditions. Logistic regression analysis demonstrated that the odds ratios of an elevated CRP level were individually significant in subjects with an elevated CRP level for each abnormality in women and for abnormal PWV and pulmonary dysfunction in men. In conclusion, in addition to being a marker of elevated atherosclerotic cardiovascular risk, elevated plasma CRP seems to be a marker of the early stages of osteopenia and pulmonary dysfunction in healthy subjects.

Bone material elasticity in a murine model of osteogenesis imperfecta

To investigate the source of bone brittleness in the disease osteogenesis imperfecta (OI), biomechanical properties have been measured in the femurs from a homozygous (oim/oim) mutant mouse model of OI, its heterozygous littermates, and wild-type animals. The novel technique of ultrasound critical-angle reflectometry (UCR) was used to determine bone material elasticity matrix from measurements of the pressure and shear wave velocity at different orientations about selected points of the bone specimens. This nondestructive method is the only available means for obtaining measurements of this nature from a single surface. The ultrasound pressure wave velocity showed an increased isotropy in the homozygous compared to the wild-type specimens. This was reflected in a significant decrease in the principal elastic modulus measured along the length of the oim/oim bones (E33) while the modulus along the width (E11) did not change significantly, compared to wild-type specimens. The Poisson's ratio, v12, also had a significantly increased value in oim/oim bones. Measurements of these parameters in heterozygous animals generally fell between those from homozygous and control mice. The differences in the elasticity components in oim/oim bones indicate an altered stress distribution and a modified elastic response to loads, compared to normal bone.

Bone elasticity and ultrasound velocity are affected by subtle changes in the organic matrix

The mechanical competence of bone can be studied through the measurement of the components of its material elasticity, a property which can vary both in magnitude and in dependence upon orientation (anisotropy). While it is known that the elasticity is largely determined by the mineral constituents of the bone matrix, it is nonetheless clear that it must be also dependent upon the remaining constituents of bone material. In this work, the influence of organic components on the elasticity is explored by altering specific constituents of the bone matrix to varying degrees. This study addresses two questions: first, are the resulting changes in elasticity strongly or weakly dependent upon direction, and second, are they substantially dependent upon the nature and magnitude of the induced matrix alteration? To answer these questions, we performed different chemical manipulations of the bone matrix and measured the changes in elasticity and velocity using the technique of ultrasound critical angle reflectometry. Altering the properties of the organic matrix resulted in substantial and complex changes in the elasticity of bone. The observed changes were strongly dependent upon direction, could not be explained by changes in density alone, and varied strongly with the specific chemical treatment of the matrix. Immersion in urea selectively affected protein components of the organic matrix and resulted in reversible changes in velocity and elasticity, while removal of collagen caused anisotropic decreases and removal of all organic matter caused a collapse of all components of the elasticity. In conclusion, this study confirms that the organic matrix exerts a profound influence on the elasticity and indicates that the measurement of elastic properties at multiple directions is necessary in the assessment of bone mechanical competence.

Reflection ultrasound velocities and histomorphometric and connectivity analyses: correlations and effect of slow-release sodium fluoride

To better understand how structural and functional bone properties contribute to the changes in bone biomechanical properties revealed by ultrasound critical angle reflectometry (UCR) analysis, we measured both UCR velocities and histomorphometric properties in bone biopsy specimens from 33 osteoporotic patients before and following intermittent slow-release sodium fluoride (SRNaF) and continuous calcium citrate administration. Mean skeletal fluoride exposure was 17 months, and mean skeletal fluoride content was 0.203 +/- 0.088 SD% bone ash. Intermittent SRNaF and continuous calcium citrate promoted significant increases in trabecular thickness (122 +/- 18 SD microm to 131 +/- 20, p = 0.020), mineral apposition rate (0.79 +/- 0.26 to 1.05 +/- 0.40 microm/day, p = 0.014), and a significant decline in eroded surface (3.9 +/- 1.6 to 2.8 +/- 1.4%, p = 0.002). There were also significant increases in node number (0.193 +/- 0.100 to 0.368 +/- 0.245, p < 0.01) and node-to-node strut length (0.076 +/- 0.087 to 0.191 +/- 0.173, p < 0.01) relative to total cancellous area. Cortical UCR velocity did not change but cancellous velocity significantly increased by 97 m/s following therapy (p = 0.0005). When compared against the significant changes in bone histomorphometry and connectivity, the sum of both cancellous and cortical ultrasound velocities was significantly correlated with node number/area (R2 = 0.305, p < 0.0001) and node-to-node strut length/area (R2 = 0.372, p < 0.0001) and to a lesser extent with mineral apposition rate (R2 = 0.106, p = 0.032). Multiple regression analysis demonstrated that 40% of the variance in the sum of the UCR velocities can be accounted for by the variability in these histomorphometric and connectivity parameters. There were no significant correlations between the sum of cortical and cancellous ultrasound velocities and cancellous bone volume (R2 = 0.014, p = 0533), trabecular thickness (R2 = 0.012, p = 0.47), or bone mineral density (R2 = 0.003, p = 0.80). These observations indicate that velocity measurements with the UCR methodology show an improvement in bone elasticity associated, in part, with an improvement in the rate of bone mineralization and an improvement in bone quality at the structural level as shown by microarchitecture.

Ultrasound critical-angle reflectometry (UCR): a new modality for functional elastometric imaging

This paper discusses the measurement of velocity in a solid based on the analysis of the amplitude and phase of ultrasound waves reflected by a solid, a technique called ultrasound critical-angle reflectometry (UCR). To this end, the complete formulation of ultrasound wave reflection and refraction from a liquid-solid interface is described. Differences between this formulation and previously published ones are briefly discussed. Based on this analysis it is in particular possible to measure by this technique not only pressure but also, for the first time in such studies, shear wave velocities, an experimentally confirmed result. The measurement of the complete stiffness matrix of a transversely isotropic solid, specifically cortical bone, by applying UCR elastometry to any point on the solid's surface is demonstrated. Finally this method is extended to functional elastometric imaging. The techniques presented in this paper offer new opportunities for applications of UCR imaging to the assessment of bone metabolism, formation and disease and also the analysis of composite materials in general.

Measurement of shear-wave velocity by ultrasound critical-angle reflectometry (UCR)

There exists a growing body of research that relates the measurement of pressure-wave velocity in bone to different physiological conditions and treatment modalities. The shear-wave velocity has been less studied, although it is necessary for a more complete understanding of the mechanical properties of bone. Ultrasound critical-angle reflectometry (UCR) is a noninvasive and nondestructive technique previously used to measure pressure-wave velocities both in vitro and in vivo. This note describes its application to the measurement of shear-wave velocity in bone, whether directly accessible or covered by soft tissue.