Ultrasonic velocity measurements through the calcaneus: which velocity should be measured?

In Vivo Comparison of Backscatter Techniques for Ultrasonic Bone Assessment at the Femoral Neck

Ultrasonic techniques are being developed to detect changes in cancellous bone caused by osteoporosis. The goal of this study was to test the relative in vivo performance of eight backscatter parameters developed over the last several years for ultrasonic bone assessment: apparent integrated backscatter (AIB), frequency slope of apparent backscatter (FSAB), frequency intercept of apparent backscatter (FIAB), normalized mean of the backscatter difference (nMBD), normalized slope of the backscatter difference (nSBD), normalized intercept of the backscatter difference (nIBD), normalized backscatter amplitude ratio (nBAR) and backscatter amplitude decay constant (BADC). Backscatter measurements were performed on the left and right femoral necks of 80 adult volunteers (age = 25 ± 11 y) using an imaging system equipped with a convex array transducer. For comparison, additional ultrasonic measurements were performed at the left and right heel using a commercially available heel-bone ultrasonometer that measured the stiffness index. Six of the eight backscatter parameters (all but nSBD and nIBD) exhibited similar and highly significant (p < 0.000001) left-right correlations (0.51 ≤ R ≤ 0.68), indicating sensitivity to naturally occurring variations in bone tissue. Left-right correlations for the stiffness index measured at the heel (R = 0.75) were not significantly better than those produced by AIB, FSAB and FIAB. The short-term precisions of AIB, nMBD, nBAR and BADC (7.8%-11.7%) were comparable to that of the stiffness index measured with the heel-bone ultrasonometer (7.5%).

Lower bone turnover and relative bone deficits in men with metabolic syndrome: a matter of insulin sensitivity? The European Male Ageing Study

We examined cross-sectional associations of metabolic syndrome and its components with male bone turnover, density and structure. Greater bone mass in men with metabolic syndrome was related to their greater body mass, whereas hyperglycaemia, hypertriglyceridaemia or impaired insulin sensitivity were associated with lower bone turnover and relative bone mass deficits.

INTRODUCTION

Metabolic syndrome (MetS) has been associated with lower bone turnover and relative bone mass or strength deficits (i.e. not proportionate to body mass index, BMI), but the relative contributions of MetS components related to insulin sensitivity or obesity to male bone health remain unclear.

METHODS

We determined cross-sectional associations of MetS, its components and insulin sensitivity (by homeostatic model assessment-insulin sensitivity (HOMA-S)) using linear regression models adjusted for age, centre, smoking, alcohol, and BMI. Bone turnover markers and heel broadband ultrasound attenuation (BUA) were measured in 3129 men aged 40-79. Two centres measured total hip, femoral neck, and lumbar spine areal bone mineral density (_aBMD, n = 527) and performed radius peripheral quantitative computed tomography (pQCT, n = 595).

RESULTS

MetS was present in 975 men (31.2 %). Men with MetS had lower β C-terminal cross-linked telopeptide (β-CTX), N-terminal propeptide of type I procollagen (PINP) and osteocalcin (P < 0.0001) and higher total hip, femoral neck, and lumbar spine _aBMD (P ≤ 0.03). Among MetS components, only hypertriglyceridaemia and hyperglycaemia were independently associated with PINP and β-CTX. Hyperglycaemia was negatively associated with BUA, hypertriglyceridaemia with hip _aBMD and radius cross-sectional area (CSA) and stress-strain index. HOMA-S was similarly associated with PINP and β-CTX, BUA, and radius CSA in BMI-adjusted models.

CONCLUSIONS

Men with MetS have higher _aBMD in association with their greater body mass, while their lower bone turnover and relative deficits in heel BUA and radius CSA are mainly related to correlates of insulin sensitivity. Our findings support the hypothesis that underlying metabolic complications may be involved in the bone's failure to adapt to increasing bodily loads in men with MetS.

Quantitative ultrasound measurements at the heel: improvement of short- and mid-term speed of sound precision

Calcaneal quantitative ultrasound can be used to predict osteoporotic fracture risk, but its ability to monitor therapy is unclear possibly because of its limited precision. We developed a quantitative ultrasound device (foot ultrasound scanner) that measures the speed of sound at the heel with the aim of minimizing common error sources like the position and penetration angle of the ultrasound beam, as well as the soft tissue temperature. To achieve these objectives, we used a receiver array, mechanics to adjust the beam direction and a foot temperature sensor. In a group of 60 volunteers, short-term precision was evaluated for the foot ultrasound scanner and a commercial device (Achilles Insight, GE Medical, Fairfield, CT, USA‎). In a subgroup of 20 subjects, mid-term precision (1-mo follow-up) was obtained. Compared with measurement of the speed of sound with the Achilles Insight, measurement with the foot ultrasound scanner reduced precision errors by half (p < 0.05). The study indicates that improvement of the precision of calcaneal quantitative ultrasound measurements is feasible.

Discrimination of fractures by low-frequency axial transmission ultrasound in postmenopausal females

SUMMARY

In this cross-sectional study, 95 postmenopausal women, with and without fracture history, were measured by low-frequency axial transmission ultrasound. The measured ultrasound velocity discriminated the fractured subjects from the nonfractured ones equally or better than peripheral quantitative computed tomography (pQCT) and dual energy x-ray absorptiometry (DXA). These results suggest that low-frequency ultrasound is suitable for bone fragility assessment.

INTRODUCTION

Quantitative low-frequency axial transmission ultrasound is a promising modality for assessing mineral density and geometrical properties of long bones such as radius and tibia. The aim of the current study was to evaluate the ability of low-frequency axial transmission ultrasound to discriminate fractures retrospectively in postmenopausal women.

METHODS

A cross-sectional study involved 95 female subjects aged 45-88 years, whose fracture information was gathered retrospectively. The fracture group was defined as subjects with one or more low-/moderate-energy fractures. The radius and tibial shaft were measured with a custom-made ultrasonometer to assess the velocity of the low-frequency first-arriving signal (V (LF)). Site-matched pQCT was used to measure volumetric cortical and subcortical bone mineral density (sBMD), and cortical thickness (CTh). Areal BMD (aBMD) was measured using DXA for the whole body (WB), lumbar spine, and hip.

RESULTS

The majority (19/32; 59 %) of the fractures were in the upper limb. V (LF) in the radius, but not in the tibia, discriminated fractures with an age- and BMI-adjusted odds ratio (OR) of 2.06 (95 % CI 1.21-3.50, p < 0.01). In the radius, CTh and cortical BMD (CBMD) significantly discriminated fractures, as did the total, cortical, and sBMD in the tibia (adjusted OR 1.35-2.15, p < 0.05). Sensitivity and specificity were similar among all the measurements (area under the receiver operating characteristic curve 0.74-0.81, p < 0.001).

CONCLUSIONS

Low-frequency axial transmission ultrasound in the radius was able to discriminate fractured subjects from the nonfractured ones. This suggests that low-frequency axial transmission ultrasound has the potential to assess bone fragility in postmenopausal women.

Correlation of tibial low-frequency ultrasound velocity with femoral radiographic measurements and BMD in elderly women

The ultrasonic axial transmission technique has been proposed as a method for cortical bone characterization. Using a low enough center frequency, Lamb modes can be excited in long bones. Lamb waves propagate throughout the cortical bone layer, which makes them appealing for characterizing bone material and geometrical properties. In the present study, a prototype low-frequency quantitative ultrasonic axial transmission device was used on elderly women (n = 132) to investigate the relationships between upper femur geometry and bone mineral density (BMD) and tibial speed of sound. Ultrasonic velocities (V) were recorded using a two-directional measurement set-up on the midtibia and compared with dual-energy X-ray absorptiometry measurements and plain radiographs of the hip. Statistically significant, but weak, correlations were found between V and femoral shaft cortex thickness measured from radiographs (r = 0.20-0.26). V also correlated significantly with various BMD and bone mineral content parameters (r = 0.20-0.35). Femoral BMD and geometry were found to be significant independent predictors of V (R(2) = 0.07-0.16, p < 0.01). This study showed that femoral geometry and BMD affect significantly the axial ultrasound velocity measured at the tibia. In addition, the results confirmed, for the first time, a relationship between tibial ultrasound velocity and cortical bone thickness at the proximal femur.

Bone mass and bone resorption in postmenopausal women with type 2 diabetes mellitus

The aim of the present study was to examine the relationships between bone mass or bone resorption evaluated by urinary cross-linked N-telopeptides of type I collagen (NTx) concentration and known and potential contributors to bone mass or bone resorption such as sex hormones, age, duration of diabetes, glycemic control (hemoglobin A(1c) [HbA(1c)]), body mass index (BMI), severity of diabetic complications, smoking status, and current treatment of diabetes in postmenopausal women with type 2 diabetes mellitus (n = 196). In addition, the relationship of bone mass to pulse wave velocity, which is an earlier indicator of cardiovascular disease, was investigated in a subgroup of patients (n = 120). Bone mass was evaluated by the quantitative ultrasound method. A higher stiffness index indicates higher bone mass. Inverse correlations were found between the stiffness index and age (r = -0.374, P < .0001) and between the stiffness index and log (urinary albumin excretion) (r = -0.170, P = .0398), and a positive correlation was found between the stiffness index and serum dehydroepiandrosterone sulfate (DHEA-S) concentration (r = 0.201, P = .0136). No significant correlations were found between the stiffness index and duration of diabetes, HbA(1c), BMI, or serum estradiol concentration. No significant correlations were found between urinary NTx concentration and age, duration of diabetes, HbA(1c), BMI, serum estradiol concentration, or serum DHEA-S concentration. The stiffness index correlated inversely with urinary NTx concentration (r = -0.262, P = .0002). No significant correlation was found between the stiffness index and pulse wave velocity (r = -0.165, P = .0714). Multiple regression analysis demonstrated that serum DHEA-S concentration was an independent determinant of the stiffness index (beta = .207, P = .0428). In conclusion, serum DHEA-S concentration correlated positively with bone mass, whereas glycemic control, BMI, or duration of diabetes did not correlate with bone mass or urinary NTx concentration in postmenopausal women with type 2 diabetes mellitus.

Instrumentation for in vivo ultrasonic characterization of bone strength

Although it has been more than 20 years since the first recorded use of a quantitative ultrasound (QUS) technology to predict bone fragility, the field has not yet reached its maturity. QUS has the potential to predict fracture risk in several clinical circumstances and has the advantages of being nonionizing, inexpensive, portable, highly acceptable to patients, and repeatable. However, the wide dissemination of QUS in clinical practice is still limited and suffering from the absence of clinical consensus on how to integrate QUS technologies in bone densitometry armamentarium. Several critical issues need to be addressed to develop the role of QUS within rheumatology. These include issues of technologies adapted to measure the central skeleton, data acquisition, and signal processing procedures to reveal bone properties beyond bone mineral quantity and elucidation of the complex interaction between ultrasound and bone structure. This article reviews the state-of-the art in technological developments applied to assess bone strength in vivo. We describe generic measurement and signal processing methods implemented in clinical ultrasound devices, the devices and their practical use, and performance measures. The article also points out the present limitations, especially those related to the absence of standardization, and the lack of comprehensive theoretical models. We conclude with suggestions of future lines and trends in technology challenges and research areas such as new acquisition modes, advanced signal processing techniques, and modelization.

Frequency dependence of ultrasonic attenuation in bovine cortical bone: an in vitro study

Recent progress in quantitative ultrasonic (QUS) techniques enables the in vivo evaluation of cortical bone, which is determinant in bone fragility. However, the interaction between ultrasound and cortical bone remains poorly understood. Most ultrasonic studies have been confined to longitudinal wave speed analysis and the frequency dependence of ultrasonic wave attenuation in this complex multiscale structure has not been extensively investigated. Our objective was to evaluate in vitro the frequency dependence of attenuation in bovine femoral cortical bone samples obtained from three specimens at different anatomical locations along the diaphysis axis and around the circumference. The frequency-dependent attenuation coefficient was evaluated after correction of transmission effects using a transmission device operating at 10 MHz. Attenuation exhibits a non linear variation versus frequency. However, the quasi-linearity of attenuation on a 1 MHz restricted bandwidth around 4 MHz enables broadband ultrasonic attenuation (BUA) evaluation. Our study demonstrates the feasibility of BUA measurements in the three directions (axial, radial and tangential) with reasonable precision (standardized coefficient of variation: 10% to 12%). Significant differences in BUA are obtained according to the anatomical location. BUA values are higher in the distal and proximal parts of the bone than in the midshaft and in the posterior and lateral parts than in the medial and anterior parts. Findings are consistent with results previously obtained and may be explained primarily by scattering phenomena but also by bone viscoelasticity.

Application of a triage approach to peripheral bone densitometry reduces the requirement for central DXA but is not cost effective

A method proffered for the interpretation of measurements from peripheral dual energy X-ray absorptiometry (pDXA) is a triage approach to stratify patients into one of three risk categories; (i) high-treat, (ii) medium-refer for central DXA and (iii) low-reassure. The aim of this study was to apply the triage approach to measures from peripheral scanners and risk indices and stratify patients into one of three risk categories (i), (ii) or (iii). 207 post-menopausal women had central DXA from which they were categorised as non-osteoporotic or osteoporotic. Additional peripheral scans of the left calcaneus were performed on three scanners (GE Lunar Achilles and PIXI, McCue CubaClinical). From demographic details four risk indices were calculated and algorithms combining measures from peripheral scanners and one risk index were obtained. All peripheral measures, risk indices and combination algorithms were good at identifying women at risk of osteoporosis (ROC areas: 0.67-0.82). Each tool stratified varying numbers of osteoporotic and non-osteoporotic women into each risk category using the triage approach. One combination algorithm (PIXI & osteoporosis indices of risk (OSIRIS)) performed best by minimising misclassification (10% non-osteoporotic, 10% osteoporotic) and reducing requirement for central DXA to 36%. However the cost of implementing the triage approach for PIXI & OSIRIS was greater (263%) than central DXA (100%) scanning all women. Although the triage approach was an effective tool at identifying women at risk of osteoporosis the unnecessary treatment of non-osteoporotic women in the high risk category make it impractical. Therefore an alternative more cost-effective method has been suggested.

Absorptiometrie

This article is an introduction to dual X-ray absorptiometry (DXA), the most widely used method today for diagnosis of osteoporosis. DXA can be used to assess projective bone mineral density at the lumbar spine, the proximal hip, and the whole body as well as the skeletal periphery at the forearm, the hand, and the heel. The prominent area of application of DXA is the diagnosis and monitoring of osteoporosis and its treatment. Because of its high accuracy, precision, and ability to predict osteoporotic fracture as well as its relatively low cost, DXA has prevailed over alternative methods. This article discusses the underlying X-ray physics and technological aspects, acquisition protocols, quality characteristics, and sources of error and their relevance. It also describes the various skeletal regions accessible to measurement, details on precision, nominal results, usability to predict fracture risk, and results of influential clinical trials.

In vitro ultrasonic characterization of human cancellous femoral bone using transmission and backscatter measurements: relationships to bone mineral density

Thirty-eight slices of pure trabecular bone 1-cm thickness were extracted from human proximal femurs. A pair of 1-MHz central frequency transducers was used to measure quantitative ultrasound (QUS) parameters in transmission [normalized broadband ultrasound attenuation (nBUA), speed of sound (SOS)] and in backscatter [broadband ultrasound backscatter (BUB)]. Bone mineral density (BMD) was measured using clinical x-ray quantitative computed tomography. Site-matched identical region of interest (ROIs) of 7 x 7 mm2 were positioned on QUS and QCT images. This procedure resulted in 605 ROIs for all the specimens data pooled together. The short-term precision of the technique expressed in terms of CV was found to be 2.3% for nBUA, 0.3% for SOS and 4.5% for BUB. Significant linear correlation between QUS and BMD were found for all the 605 ROIs pooled, with r2 values of 0.73, 0.77, and 0.58 for nBUA, SOS, and BUB, respectively (all p < 0.05). For the BUB, the best regression was obtained with a polynomial fit of second order (r2 = 0.63). An analysis of measurements errors was developed. It showed that the residual variability of SOS is almost completely predicted by measurements errors, which is not the case for BUA and BUB, suggesting a role for micro-architecture in the determination of BUA and BUB.

In vitro speed of sound measurement at intact human femur specimens

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.

Which bone densitometry and which skeletal site are clinically useful for monitoring bone mass?

Long-term precision, as well as reproducibility, is important for monitoring bone mineral density (BMD) alteration in response to aging or therapy. In order to investigate which bone densitometry and which skeletal site are clinically useful for monitoring bone mass, we examined the standardized long-term precision of several bone density measurements in 83 healthy Japanese women. Annual BMD measurements were performed for 5 or 6 years using dual X-ray absorptiometry (DXA) on the lumbar spine, radius (EXP5000) and calcaneus (HeelScan); peripheral quantitative computed tomography (pQCT) on the radius (Densiscan1000); and quantitative ultrasound (QUS) on the calcaneus (Achilles+). The long-term precision error for the individual subject was given by the standard error of estimate (SEE), and the standardized long-term precision was defined as the percentage coefficient of variation (CV%) divided by the percentage ratio of the annual bone-loss rate. Based on the CV% of spinal DXA, speed of sound (SOS) and diaphyseal pQCT showed significantly higher precision than others, while radial ultradistal (UD) DXA and heel DXA showed significantly lower precision. The long-term precision errors of other measurements were statistically the same as that of the spinal DXA. The spinal DXA, the radial DXA, and pQCT at both the distal metaphysis and diaphysis showed high rates of annual bone loss. The radial trabecular BMD (pQCT) was significantly higher than that of spinal DXA. The annual rates of bone loss of QUS and of heel DXA were significantly lower than that of spinal DXA. Taken together, standardized long-term precision was obtained in the spinal DXA and radial pQCT. In conclusion, spinal DXA and radial pQCT were considered the most useful monitoring method for osteoporosis, while QUS was considered less useful.

Performance of quantitative ultrasound in the discrimination of prevalent osteoporotic fractures in a bone metabolic unit

There is a growing interest in ultrasound evaluation of bone status as an alternative to the measurement with dual X-ray absorptiometry (DXA), due to its low cost, portability, and nonionizing radiation. The aim of our study was to investigate the relation among DXA, QUS, clinical, anthropometric, and lifestyle factors, and to determine QUS cutoff values in order to discriminate fractures in patients referred to the Bone Metabolic Unit at an Endocrinology Service. We studied 300 patients (281 females and 19 males; age 58 +/- 11 years) referred for evaluation of osteoporosis. In all cases we determined basic anthropometric parameters, a clinical history including previous osteoporotic fractures and risk factors for osteoporosis, and QUS parameters in calcaneus (Hologic Sahara), and BMD in lumbar spine (LS) and femoral neck (FN), by DXA (Hologic QDR 1000). Using the WHO densitometric criteria, 37, 46.7, and 16.3% of our population were osteoporotic, osteopenic, and normal, respectively. A QUI T-score </=-1.5 SD provided a sensitivity of 68.9% and a specificity of 64.7% for osteoporotic fracture discrimination and a sensitivity of 64.9% and a specificity of 74.1% for osteoporosis defined by WHO criteria using DXA. In the logistic regression, the presence of family history of fragility fractures (OR: 3.03; CI 95%: 1.3-7.03), a DXA T-score </=-2.5 (OR: 3.58; CI 95%: 1.66-7.73), and a QUI T-score </=-1.5 (OR: 2.56; CI 95%: 1.15-5.69) were independently associated with prevalent osteoporotic fractures. In conclusion, calcaneus ultrasound appears as a useful technique for the routine clinical practice, as its performance is similar to DXA for the discrimination of subjects with osteoporotic fracture.

Discriminatory ability of quantitative ultrasound parameters and bone mineral density in a population-based sample of postmenopausal women with vertebral fractures: results of the Basel Osteoporosis Study

The discriminatory potential to classify subjects with or without vertebral fractures was tested cross-sectionally with different methods for the measurement of bone status in a population-based sample of postmenopausal women. Quantitative ultrasound (QUS) measurement at the calcaneus (Lunar Achilles, Hologic Sahara), the proximal phalanges (Igea Bone Profiler), and measurement of bone mineral density (BMD) with dual-energy X-ray absorptiometry (DXA; Lunar Expert) at several anatomic sites was performed in 500 postmenopausal women (aged 65-75 years) randomly selected from the population. In addition, 50 young female subjects (20-40 years old) had QUS measurements and served as controls to express QUS results as T-score values. Radiographs of the lumbar and thoracic spine were performed in the elderly women. Two independent radiologists reviewed the X-rays for the presence of vertebral fractures. Of 486 eligible study participants, no fracture was seen in 396 participants. Single vertebral fractures were observed in 71 subjects; 19 individuals presented multiple fractures. The overall prevalence of vertebral fractures was 18.5%. Participants without vertebral fractures were compared with subjects with vertebral fractures. Normal statistical distributions were found for all bone measurement results. Risk of vertebral fracture in subjects with no and multiple vertebral fracture was estimated using age adjusted odds ratios (ORs) for QUS and dual-energy X-ray absorptiometry (DXA) values. Each SD decrease in bone measurement increased the risk of multiple vertebral fracture by 3.0 (95% CI, 1.6-5.6) for the Achilles stiffness, by 3.8 (95% CI, 1.8-8.2) for the Sahara QUI, 2.1 (95% CI, 1.3-3.4) for the Bone Profiler amplitude-dependent speed of sound (AD-SOS), and 2.1 (95% CI, 1.2-3.9) and 2.4 (95% CI, 1.3-4.3) for DXA lumbar spine and for DXA total hip, respectively. Results of a discriminant analysis showed sensitivities between 84% and 58% and specificities between 72% and 58% for the respective DXA and QUS parameters. Optimum fracture thresholds for QUS measurements derived from this analysis were calculated also. Optimum T-score threshold values for QUS measurements tended to be higher than those for DXA measurements. However, the performance of QUS measurements is at least comparable with DXA measurements in identifying subjects with multiple vertebral fractures randomly selected from the population.

Broadband ultrasonic attenuation of children and young adults in Japan

The purpose of this study was to establish broadband ultrasonic attenuation (BUA: dB/MHz) as bone mineral density (BMD) norms for healthy young Japanese and to evaluate the standard values for an ultrasonic bone analyzer (Cuba Clinical, McCue Ultrasonics Ltd., Winchester, England), which facilitates BMD measurement without exposure to radiation. The subjects were 472 healthy young individuals with no endocrine or skeletal disorders, 197 males (mean age 16 y 5 m) and 275 females (mean age 15 y 7 m) aged from 5 to 29 years. BUA was measured at the left calcaneus. The subjects were divided into five age-stratified different age groups of five years intervals. The mean BUA values (dB/MHz) obtained were 40.6, 60.9, 78.0, 90.4 and 86.0 for males, and 41.9, 61.0, 73.4, 68.4 and 70.8 for females in the 5-9, 10-14, 15-19, 20-24 and 25-29 age groups, respectively. A significant positive correlation was observed between BUA and age in both males and females except in the male 25-29 age group and the female 20-24 and 25-29 age groups. A significantly different BUA between males and females was found in the 20-24 and 25-29 age groups (p < 0.001). The BUA values obtained in this study may serve as BMD norms for children and young adults. It might be thought that measuring BUA from childhood through early adulthood made it possible to determine peak values and peak periods of BMD, providing useful information for assessment of growth and development.

Ability of peripheral bone assessments to predict areal bone mineral density at hip in community-dwelling elderly men

We present cross-sectional data on bone mineral density (BMD) and quantitative ultrasound (QUS) indices in an ambulatory elderly male population (n = 235). Dual X-ray absorptiometry (DXA) at the proximal femur was considered the reference assessment site and was compared with DXA at the forearm and heel and to QUS at the heel and midtibia. Correlations and weighted kappa analysis indicate an only moderate concordance of absolute values between peripheral bone assessment and total hip DXA (weighted kappas: 0.31-0.45). Discrepancies are even more important when T-scores and prevalence rates of osteoporosis are considered, owing to factors related to the reference populations used. Predictive value of peripheral measurements for osteoporosis diagnosed on the basis of hip BMD by DXA, as assessed by receiver operator characteristic analysis, was moderate and comparable for all peripheral measurements (area under the curve: 0.708-0.870), with the exception of a clearly lower predictive value for QUS at the tibia. Discrimination of male subjects with a history of at least one fragility fracture was significant for DXA at the proximal femur and QUS at the heel. It is concluded that peripheral measurements cannot be used as a substitute for hip DXA. However, they might be useful to guide patient referral for central DXA.

Ultrasonic backscatter and transmission parameters at the os calcis in postmenopausal osteoporosis

Ultrasound technology has emerged as a new tool in the assessment of osteoporosis. Ultrasound parameters usually are measured in transmission; there is a potential for the analysis of backscattered signals to provide information on bone microarchitecture. The aim of this study was to explore a new technological development of the method, adding backscatter coefficient to transmission parameters, and to examine the appropriate thresholds to identify postmenopausal osteoporotic women. We examined 210 postmenopausal women (including 60 with osteoporotic fractures) and 30 healthy premenopausal controls. They had lumbar spine and hip bone mineral density (BMD) measurement and quantitative ultrasound (QUS) evaluation at the os calcis, measured in transmission (broadband ultrasound attenuation [BUA], speed of sound [SOS], ratio of transit time [dt] to BUA [dt/BUA], and "strength" index [STI]) and reflexion (broadband ultrasound backscattering [BUB]). The standardized CVs (sCVs) were between 2.27 % and 3.40 % for QUS measured in transmission and 4.41% for BUB. The odds ratio (OR) for fracture discrimination adjusted for age was 2.77 for hip BMD and between 1.6 and 2.9 for QUS. After adjustment for hip BMD, ORs were still highly significant for SOS, STI, and dt/BUA. According to hip BMD T score, prevalence of osteoporosis in our population was 39%. To detect the same prevalence, T scores ranged between -0.95 and -1.42 for QUS. QUS parameters have adequate ability to discriminate osteoporotic patients from controls. The World Health Organization (WHO) threshold for diagnosis of osteoporosis does not apply to this technology. The clinical utility of BUB at the os calcis, in addition to usual ultrasound parameters, is not yet proven. However, BUB evaluation, which does not require two transducers and may be implemented in conventional reflection mode systems, warrants further studies.

Reproducibility of skin characterization with backscattered spectra (12--25 MHz) in healthy subjects

Ultrasonic techniques were developed for quantitative in vivo analysis of skin composition based on measurements of apparent integrated backscatter (IBS) and its frequency dependence (n) between 12.5 and 25 MHz. Parameters were measured at five depths in healthy dermis of the midforearm of 29 volunteers (13 women, 16 men, 20 to 76 years old) on three different days. Reproducibility of measurements was evaluated (standardized coefficients of variation: 7% to 11% for IBS and 9% to 20% for n). Parameter values were significantly influenced by pressure of the ultrasonic probe on the skin, and both room and skin-surface temperatures were correlated to IBS measured in a single subject on 28 days. More precise control of these factors could further improve measurement reproducibility and sensitivity to skin composition. Significant (p < 0.05) differences of parameter values with respect to region of interest depth, age and gender of subjects were discussed in comparison with dermal composition and offer promise that these parameters could be used to characterize skin modifications.

Multisite bone ultrasound measurement on North American female reference population

The Sunlight Omnisense is a portable quantitative ultrasound device that measures speed of sound (SOS) at multiple skeletal sites and therefore has the potential to provide a more complete assessment of an individual's overall fracture risk than single-site measurements such as the calcaneus. To provide a robust normative female database, 545 healthy Caucasian women ages 20-90 were recruited at five centers across North America. SOS measurements were obtained from the distal one-third radius, proximal third phalanx, midshaft tibia, and fifth metatarsal. The results demonstrate that peak SOS occurs around the age of 40, with maximum mean values of 4161, 3928, 3786, and 4092 m/s seen at the radius, tibia, metatarsal, and phalanx, respectively. Maximal rate of decline of SOS was seen in the decade following menopause (-12.4, -9.2, -12.1, and -18.8 m/s at the radius, tibia, metatarsal, and phalanx, respectively). Reproducibility between successive measurements indicates high precision, with standardized coefficients of variance ranging between 1.5 and 4.5%. Greatest precision was seen at the metatarsal. Further work is required to clarify the biologic significance of multisite SOS measurements and their use in the assessment of fracture risk.

Evaluation of error bounds on calcaneal speed of sound caused by surrounding soft tissue

For absorptiometry measurements, soft tissue may have an impact on quantitative ultrasound (QUS) measurements. In the present study, we focused primarily on the quantification of measurement error on speed of sound (SOS) caused by surrounding soft tissue. The relevant soft tissue parameters affecting the inherent SOS inaccuracies are thickness and sound velocity. To meet our goal, SOS measurements were taken at the right heel using a QUS imaging device in 21 healthy subjects. Site-matched measurements of soft tissue thickness (STT) and bone width were performed using magnetic resonance imaging of the heel. Several bone velocities were calculated either by accounting for bone width (SOSBW) only or by taking into account the exact path lengths of all major components traversed by ultrasound &lapr;V(b)). Given that soft tissue composition is difficult to determine in vivo, we chose to estimate lower and upper error bounds on bone velocity (V(b lower) and V(b upper)) by spanning the full range of available values in the literature. The mean BW was 30.7 +/- 2.7 mm and the mean medial and external STTs were 8.8 +/- 1.7 and 8.5 +/- 1.5 mm, respectively. Accounting for true BW only resulted in no significant difference between SOS (1533 +/- 37) and SOSBW (1531 +/- 33). By contrast, accounting for both true BW and surrounding soft tissue resulted in an increase in the calculated bone velocity and statistically significant differences between SOS and V(b upper) (1568 +/- 36) and V(b lower) (1542 +/- 34). Root mean square errors between SOS and the calculated velocities were 0.34, 2. 32, and 0.70% for SOSBW, V(b upper), and V(b lower), respectively. We report here measurement errors caused by soft tissue to be 3 to 20 times higher than the SOS short-term precision (SOS coefficient of variation of 0.1%). Our results suggest that inaccuracies in SOS measurement caused by overlying soft tissue cannot be neglected. Overlying soft tissues may influence outcomes of longitudinal studies, especially if variations in tissue thickness and composition occur during the longitudinal follow-up. A practical way of minimizing the measurement error could be to perform an adequate correction for the overlying soft tissue. However, ideally, this should require knowing both the thickness and sound velocity in soft tissue. One might preferably conduct experimental investigations that directly control soft tissue thickness and composition to resolve this problem.

Monitoring skeletal changes by radiological techniques

The longitudinal sensitivity of a technique, i.e., its ability to monitor skeletal changes, is affected by two parameters: the long-term precision error (PElt) and the subject group-specific response rate (i.e., annual rates of change). Both need to be considered to avoid misinterpretation of measured changes. A new concept to aid clinical decision making for longitudinal measurements is proposed which is based on three types of measures: criteria for detecting changes-the "least significant change" (LSC) is the smallest change to be considered statistically significant, but for certain clinical questions a smaller margin, the "trend assessment margin" (TAM), can be sufficient for decision making; follow-up time intervals-for follow-up exams the patient should be called in at about the time interval specified by the (population specific) "monitoring time interval" (MTI) or, about one-third of the time earlier, after the "trend assessment interval" (TAI), depending on whether the decision can be based on the LSC or the TAM; and the standard precision error (stdPE)-the smaller stdPE, the more sensitive the technique to monitor skeletal changes. Together, these three measures yield a good characterization of a technique's ability to monitor skeletal changes. Compared with previous concepts, the proposed standardization by a response ratio instead of measures of spread or response rates makes the stdPE substantially less subject group dependent. It allows comparison of stdPE across different studies and could replace the misleading concept of expressing precision as a coefficient of variation. Application of this concept should facilitate the interpretation of measured skeletal changes.

Acoustic and ultrasonic tissue characterization--assessment of osteoporosis

Osteoporosis, often termed the 'silent epidemic', has been defined as 'a decrease in bone mass and architectural deterioration of bone tissue, leading to enhanced bone fragility and consequent increase in fracture risk'. In the United Kingdom alone, the annual health costs are in excess of 750 million Pounds, with 60,000 patients suffering a hip fracture each year. A quarter of these will die within 12 months of their fracture, half of the remainder will never regain independent living. The established procedure for assessing the risk of osteoporotic fracture is via bone mineral density (BMD) assessment using dual-energy X-ray absorptiometry (DXA). However, DXA is an expensive technique and is not widely available. Within the past 15 years, ultrasound assessment of bone has rapidly advanced in scientific understanding, technical development and clinical utility. Measurements of cancellous bone (particularly at the calcaneus) are generally performed in preference to those of cortical bone (tibial cortex). There are currently 15 commercial systems available and over 3500 systems are in use world-wide. The low cost and portability offered by ultrasound systems should enable an integrated community-based screening programme to be established in the near future. Ultrasound measurements of bone are generally obtained using transmission rather than pulse-echo techniques owing to its highly attenuating nature. Ultrasound velocity and attenuation measurements are utilized. For velocity, there are well-defined fundamental relationships describing the dependence upon the elasticity and density of bone.

Effects of high-impact exercise on ultrasonic and biochemical indices of skeletal status: A prospective study in young male gymnasts

Physical activity has been proposed as one strategy to enhance bone mineral acquisition during growth. The aim of this study was to determine whether frequent impact loading associated with gymnastics training confers a skeletal benefit on pre- and peripubertal male gymnasts. We measured broadband ultrasonic attenuation (BUA, dB/MHz) at the calcaneus (CBUA); ultrasound velocity (m/s) at the calcaneus (CVOS), distal radius (RVOS) and phalanx (PVOS); serum osteocalcin (OC); total alkaline phosphatase (ALP) and insulin-like growth factor-I (IGF-I) every 3-4 months over an 18-month period in elite male gymnasts and matched normoactive controls (pubertal stage </=2). Ground reaction forces of common gymnastics maneuvers were determined using a force platform and loading histories of the upper and lower extremities approximated from video recordings. Ultrasound results were expressed as a standardized score (Z score) adjusted for age, height, and weight. At baseline, no differences were detected between the gymnasts (n = 31) and controls (n = 50) for CBUA, although ultrasound velocity at each site was higher in the gymnasts (0.6-1.5 SD) than the predicted mean in controls (p </= 0. 001). Over 18 months, CBUA Z scores increased significantly in the gymnasts from baseline (0.3 vs. 1.0, p < 0.05, n = 18). In contrast, ultrasound velocity did not increase in either group, although CVOS and RVOS remained significantly higher in gymnasts compared with controls (range p < 0.01 and < 0.001). No differences between groups were found for OC, ALP, or IGF-I at any time. Gymnastics training was associated with on average 102 and 217 impacts per session on the upper and lower extremities, respectively, with peak magnitudes of 3.6 and 10.4 times body weight. These results suggest that frequent high-impact, weight-bearing exercise during the pre and peripubertal period may enhance the mechanical competence of the skeleton, perhaps offering an important strategy for osteoporosis prevention if the benefits are maintained.

An evaluation of a new gel-coupled ultrasound device for the quantitative assessment of bone

Quantitative ultrasound (QUS) is now being accepted as a tool in the assessment of bone status. Most QUS devices measure broadband ultrasound attenuation (BUA) and speed of sound (SOS). A newly introduced device, the Acoustic Osteo-Screener (AOS-100), measures both SOS and an attenuation related parameter called the transmission index (TI) and provides a derived parameter called osteo sono-assessment index (OSI). The purpose of this study was to examine the reproducibility of this new device, compare the results with the UBA 575+ and evaluate the effect of using two platforms to compensate for different foot sizes on the measured values. 83 subjects aged 21-89 years, who gave informed consent, were recruited. Subjects were assigned to three different groups determined by age and health status. The short-term measurement precision (expressed as root mean square coefficient of variation) of SOS (0.13-0.16%) and TI (1.18-1.96%) was similar to and better than that obtained for the UBA 575+. Significant negative correlations were found between the differences in SOS measured with the two platforms (adaptors to adjust the position of the foot relative to the foot plate) and foot length (p < 0.0001). This implies that small feet are more influenced by the differences of measured location. All QUS parameters measured with the small platform were found to be significantly smaller than those with the large platform (p < 0.0001). The mean percentage differences were 0.6% in SOS, 2.8% in TI and 4.3% in OSI with the large foot platform giving larger value results. Proper use of the platforms resulted in more reproducible SOS and TI. This study demonstrated that the newly developed AOS-100 parameters TI and OSI were highly reproducible. This study also demonstrated that the use of an inappropriate platform can cause discrepancies in QUS readings and poor reproducibility.

Cross-calibration, precision and patient dose measurements in preparation for clinical trials using dual energy X-ray absorptiometry of the lumbar spine

Large, multicentre clinical trials using DXA to monitor bone density following intervention are now common. At the same time, several different bone densitometers and calibration phantoms are currently in use. The aim of this study was to document the technical information required on cross-calibration of equipment, reproducibility and patient dose before commencing a multicentre clinical trial. To this end, we obtained an in vitro and in vivo cross-calibration of two machines (a Hologic QDR 2000 and a Lunar DPX-L) that were not significantly different. Interobserver and intraobserver precision, and radiation dose were also measured and three commonly used phantoms assessed for their usefulness in cross-calibration and quality assurance. Measured in vitro precision on the two machines (0.3-0.7%) was better than that specified by the manufacturers. In vivo precision was worse (1.4-2.1%), as might be expected in patients with reduced bone mass. Mean entrance skin radiation doses on each machine were 280 microSv for the QDR 2000 and 38 microSv for the DPX-L. No one phantom is ideal, but the European Spine Phantom or Lunar Aluminium Spine Phantom will provide an adequate cross-calibration for a clinical trial. This study demonstrates that an adequate cross-calibration can be obtained for use in groups of patients and that the equipment used is reproducible with a low radiation output.

Does combining the results from multiple bone sites measured by a new quantitative ultrasound device improve discrimination of hip fracture?

There is a growing interest in the use of quantitative ultrasound (QUS) measurements as an alternative to current radiation-based bone densitometry techniques for the noninvasive assessment of fracture risk. While most of the commercialized ultrasound devices measure only single predefined peripheral skeletal sites, the Omnisense prototype (Sunlight Ltd., Israel) can be used on multiple bones, including the spinous processes. In this study, we examined the ability of speed of sound measured at the calcaneus, distal third and ultradistal radius, proximal third phalanx, metacarpal, capitate, patella, and the posterior process of the thoracic spine to differentiate subjects with hip fractures from normal controls. Seventy-nine postmenopausal Caucasian Israeli women who had sustained an atraumatic fracture of the proximal femur within the last 6 months were recruited from the local population (mean age 80 +/- 8.9 years). As controls, 295 postmenopausal Caucasian Israeli women without osteoporotic fractures were also included (mean age 70 +/- 8.7 years). Discrimination of hip fractures with QUS at all ultrasound sites was highly statistically significant (p < 0.01) (odds ratios [ORs] = 1.4-3.0; area under the ROC curve [AUC] 77-92%), except for the hand metacarpal. Distal radius and calcaneus measurements (ORs = 2.4 and 3.0) were the best discriminators of hip fracture patients from controls. Using a forward selective linear regression model, the discriminator values of combined assessment at two sites were investigated. There was moderate improvement in diagnostic value, but the best combination was the calcaneus with the distal radius, which improved the AUC by 3% and raised both the sensitivity and specificity to 94%. These data demonstrate the encouraging potential of improving discrimination of hip fracture by using multiple-site ultrasonic measurements.

Quantitative ultrasound in the assessment of skeletal status in uremic patients

Renal osteodystrophy (ROD) can be characterized by both high (HT) and low (LT) bone turnover states. Although bone biopsy remains the "gold standard" to diagnose ROD, noninvasive tools for the diagnosis and follow-up of such bone disease are desirable. Recently, ultrasound (US) techniques, proposed to assess skeletal status, have been shown to be correlated not only with bone density but also with bone quality. We have investigated 98 patients on chronic hemodyalisis (HD) and 98 healthy, sex- and age-matched subjects. Amplitude-dependent speed of sound (AD-SOS) and ultrasound bone profile score (UBPS) at phalanxes and speed of sound (SOS), broadband ultrasound attenuation (BUA), and a quantitative ultrasound index (QUI/stiffness) at the heel were performed in both groups. In all subjects intact parathyroid hormone (PTH), total alkaline phosphatase (T-ALP), bone isoenzyme alkaline phosphatase (B-ALP), and carboxy-terminal telopeptide of type I collagen (ICTP) were assessed. All US parameters were significantly lower in the hemodialysis group than in control subjects. Moreover, among US parameters only AD-SOS and UBPS showed a significant correlation with PTH, T-ALP, and B-ALP. Dialytic age showed a modest, but significant correlation only with US parameters at the phalanxes. On the basis of bone biochemical markers, we considered a group with high and a group with normal to low bone turnover. AD-SOS and UBPS, but not SOS, BUA, and stiffness were significantly (p < 0.01) lower in the high bone turnover than in low bone turnover group. Furthermore, in the high bone turnover group, parameters of the US phalanxes strongly correlated with B-ALP. Our results seem to demonstrate that US parameters are a useful tool in the assessment of skeletal status in patients on maintenance dialysis.

A phantom for quantitative ultrasound of trabecular bone

The propagation mechanisms of ultrasound in trabecular bone are poorly understood and have been the subject of extended debate; also, the reproducibility of ultrasonic measurements on bone in vivo using commercial ultrasound heel-scanning devices is such that the interpretation of the obtained data is difficult. In this paper we describe recent developments in the production of a bone-mimicking material which is well suited to the task of routine monitoring of commercial ultrasound bone scanners. The material, based on a standard epoxy resin is fabricated to a pre-determined porosity value by the inclusion of a marrow-mimicking material thereby introducing a known and controlled mean pore size. Measurements of the velocity and attenuation of the material have been performed over a range of porosity values from 10% to 80% in the frequency range 500-900 kHz; also, broadband ultrasonic attenuation (BUA) values have been obtained from commercial equipment. The material displays velocities in the range 1844-3118 m s(-1) and attenuation ranging from 7.0 to 17.7 dB cm(-1) at 500 kHz.

The dependence of ultrasonic properties on orientation in human vertebral bone

Speed of sound (SOS) and broad-band ultrasound attenuation (BUA) were measured in cubes of human trabecular bone from lumbar vertebrae, in the three major anatomical axes. There were significant differences in sos and in BUA when measured in the different axes, indicating a structural component to the ultrasonic measurement. Qualitatively different behaviour was observed in the cranio-caudal (CC) axis compared to the transverse directions: SOS was approximately 500 m s(-1) greater than in either the lateral (LT) or antero-posterior (AP) axes, and BUA was approximately 23 dB MHz(-1) cm(-1) greater. Small, but significant, differences existed between the AP and LT axes for both SOS and BUA. In the AP and LT directions, strong linear correlations existed between sos and apparent density (r = 0.90), and between BUA and apparent density (r = 0.96). In the cc axis, correlations with density were poorer. The anomalous behaviour in the cc axis was due to a transient travelling ahead of the main wavefront, and it is suggested that this represents propagation of ultrasound directly through the trabecular framework as a bar wave. This can only occur in the cc axis where the majority of trabeculae are orientated parallel to the direction of propagation. Measurements on cubes in air, as opposed to water, supported this hypothesis. Modifications to the experimental technique necessary to consistently detect this phenomenon are described.

A comparison of radial peripheral quantitative computed tomography, calcaneal ultrasound, and axial dual energy X-ray absorptiometry measurements in women aged 45-55 yr

Perimenopausal bone loss is considered to affect trabecular bone preferentially. Peripheral quantitative computed tomography (pQCT) quantifies trabecular bone mineral density (BMD) independently at the ultradistal radius. This article examines differences in pQCT BMD between late premenopausal and early postmenopausal women, comparing the differences with calcaneal ultrasound and axial dual energy X-ray absorptiometry measurements. One hundred nineteen normal perimenopausal women aged 45-55 yr who attended a randomized osteoporosis screening program were stratified by menopausal status into premenopausal (PRE: n = 79) and postmenopausal (POST: n = 40) groups. All measurements were lower in the postmenopausal group with the exception of ultrasonic velocity (PRE vs POST: 1397 +/- 53.8 vs 1421 +/- 58.5 m/s, p = 0.037). Total (391.8 +/- 52.9 vs 366.3 +/- 68.6 g/cm(3), p = 0.013) and subcortical (533.6 +/- 59.4 vs 504.3 +/- 79.8 g/cm(3) p = 0.018), but not trabecular (187.5 +/- 38.8 vs 173.2 +/- 46.6 g/cm(3), p = 0. 098) or cortical (561 +/- 53.4 vs 551.2 +/- 66 g/cm(3), p = 0.174), pQCT BMD measurements were significantly lower in the POST group, as were ultrasonic attenuation (79.4 +/- 16 vs 72.3 +/- 18.0 dB/Mz, p = 0.034), DXA spine (1.032 +/-16 vs 0.959 +/- 0.2 g/cm(2), p = 0.003), and all hip (p </= 0.001) measurements. Although body mass index (BMI) was positively and menopausal status and age negatively correlated with most bone mass measurements, adjusting for BMI did not alter the relative deficits in postmenopausal compared with premenopausal women. This study suggests that early postmenopausal bone loss at the radius preferentially affects subcortical, rather than trabecular, bone in the appendicular skeleton, which suggests preferential trabecular bone loss in the axial skeleton.

Applications of bone densitometry for osteoporosis

Over the past decade, growing awareness of the impact of osteoporosis on the elderly population and the availability of new treatments to prevent fractures have stimulated the rapid development of new radiologic techniques to assist in diagnosis. With the ability to perform high precision measurements of bone mineral density (BMD) in the spine and hip, dual X-ray absorptiometry (DXA) is well suited to meet this latter need. However, there is continuing interest in smaller, cheaper systems for assessing the peripheral skeleton that include DXA scanning of the distal forearm and a variety of devices for performing quantitative ultrasound (QUS) measurements on bone. Alongside the new equipment, new guidelines have been developed to assist in the interpretation of bone densitometry studies and, following a report by a World Health Organization working group, osteoporosis is increasingly diagnosed on the basis of the patient's T-score value (difference of BMD from young adult mean normalized to the population SD). For the future, wider provision of bone densitometry services is required to properly target the new treatments now becoming available. Since it is unlikely that conventional DXA can meet these needs, QUS is an attractive alternative, especially because this technique is now proven in its ability to predict fracture risk in the elderly and FDA approval is imminent.

Methodology for the clinical assessment of medical instrumentation: evaluating ultrasonometers

Medical instruments can be used for screening, diagnosis, prognosis, and monitoring natural history or therapeutic intervention. With the developing role of ultrasonometry it is important to assess how these instruments will effectively be used for each of these utilizations. No two types of ultrasonometers are the same: there are differences in anatomical sites, measurement variables and methodology in obtaining those variables. To determine optimal utilization the clinician has to evaluate each instrument. Eight factors have to be considered for each utilization comprising of discrimination, precision, reliability, relevance, acceptance by regulatory authorities, inexpensive, acceptability to the patient, and safety. This paper discusses these factors and presents an overview in relationship to the utilization of instruments using ultrasonometry.

Sound-tissue interaction: the physical basis of bone ultrasonometry and limitations of existing methods

Ultrasound measurements of bone are generally obtained using transmission rather than pulse-echo techniques because of its highly attenuating nature. Ultrasound velocity and attenuation measurements are utilized. For velocity, there are well-defined fundamental relationships describing the dependence on the elasticity and density of bone. However, the practical implementation and signal processing of velocity measurements has led to a significant variability in results from different commercial systems. We may measure either phase of group velocity, for the latter, adopting a range of pulse arrival definitions. We are offered bone velocity, heel velocity, time of flight, and amplitude-dependent velocity. For attenuation measurements, however, the reverse is true. We generally record the increase in attenuation with frequency (0.2-0.6 MHz), termed broadband ultrasound attenuation (BUA). Although first described in 1984, because of the complex interplay of attenuation mechanisms, there still lacks a fundamental understanding of the dependence of BUA on the material and structural properties of cancellous bone. With the increasing number of commercial systems available, there is an urgent need to understand the intrinsic (artefact free) and system estimation of ultrasound velocity and attenuation parameters that may be implemented to characterise bone and provide clinical information.

Bone densitometry: current status and future prospects

Over the past decade, growing awareness of the impact of osteoporosis on the elderly population and the consequent costs of healthcare have stimulated development of new treatments to prevent fractures, together with new imaging technologies to assist in diagnosis. With its ability to perform high-precision measurements of bone mineral density (BMD) in the spine and hip, dual X-ray absorptiometry (DXA) is well suited to meet this latter need. However, there is continuing interest in smaller, less expensive, systems for assessing the peripheral skeleton. These include peripheral DXA scanning of the distal forearm and a variety of devices for performing quantitative ultrasound (QUS) measurements of broad-band ultrasonic attenuation (BUA) and speed of sound (SOS) in bone. Pivotal to all these developments is the demonstration in prospective studies that new technologies can reliably identify patients at risk of osteoporotic fractures. Whether DXA technology can meet the anticipated need for wider provision of diagnostic services is uncertain at present. The likely alternative is bone ultrasound. Although QUS technology is substantially cheaper than DXA and has proved its ability to predict fracture risk in the elderly, it is less precise, there is a lack of appropriate phantoms for quality control and there are doubts about how to interpret results in younger women.

Precision and discriminatory ability of calcaneal bone assessment technologies

To determine if measuring skeletal status at the calcaneus is a potentially valuable technique for diagnosing osteoporosis, we examined five calcaneal assessment techniques in 53 young normal women and 108 postmenopausal women with osteoporosis and compared these measurements to dual-energy X-ray absorptiometry (DEXA) at the calcaneus, hip, and spine. The five instruments, including single-energy X-ray absorptiometry (SEXA) and four quantitative ultrasound (QUS) instruments, were evaluated for precision, ability to discriminate osteoporotic from young normal subjects, and correlation to the other instruments. The coefficient of variation (%CV) for instrument, positioning, interobserver, and short-term precision of the five calcaneal instruments ranged from 1.34-7.76%, 1.63-7.00%, 1.84-9.44%, and 1.99-7.04%, respectively. The %CVs for positioning, interobserver, and short-term precision were similar for calcaneal DEXA, calcaneal SEXA, and stiffness (as measured by Achilles). The %CVs for instruments precision were similar between calcaneal DEXA and SEXA. The ability of the five calcaneal instruments to discriminate osteoporotic from young normal subjects was similar based on the analysis of area under the receiver operating characteristic curves (range 0.88-0.93) and equivalent to DEXA of the calcaneus and hip (0.88-0.93). The correlations between the measurements of five calcaneal instruments were strong (0.80 < or = r < or = 0.91, p < 0.001). These data suggest that although the precision is variable, the calcaneal QUS and SEXA instruments can discriminate between osteoporotic patients and young normal controls and appear to be a useful technique for assessment of osteoporosis.

Quantitative ultrasound techniques for the assessment of osteoporosis: expert agreement on current status. The International Quantitative Ultrasound Consensus Group

Quantitative ultrasound (QUS) methods have been introduced in recent years for the assessment of skeletal status in osteoporosis. The performance of QUS techniques has been evaluated in a large number of studies. Reviewing existing knowledge, an international expert panel formulated the following consensus regarding the current status of this technology. To date, evidence supports the use of QUS techniques for the assessment of fracture risk in elderly women. This has been best established for water-based calcaneal QUS systems. Future studies should include the predictive validity of other QUS systems. Additional clinical applications of QUS, specifically the assessment of rates of change for monitoring disease progression or response to treatment, require further investigation. Its low cost and portability make QUS an attractive technology for assessing risk of fractures in larger populations than may be suitable or feasible for bone densitometry. Additional investigations that assess innovative QUS techniques in well defined research settings are important to determine and utilize the full potential of this technology for the benefit of early detection and monitoring of osteoporosis.

How can we measure bone quality?

Osteoporosis is a systematic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue. This leads to diminished biomechanical competence of the skeleton and is associated with low-trauma or atraumatic fractures. In the past decade, considerable progress has been made in the development of methods for assessing the skeleton non-invasively, so that osteoporosis can be better managed. While dual X-ray absorptiometry (DXA) is still the preferred methodology, several limitations will be addressed. Another densitometric technique which is widely accepted for diagnosis of spinal osteoporosis is single energy QCT. Measurements of vertebral trabecular bone mineral density (BMD) demonstrate larger percentage decrements between vertebrally-fractured subjects and normal controls, and confer higher relative risks for vertebral fracture than either anteroposterior or lateral DXA measurements. As an emerging alternative to photon absorptiometry techniques, there is a growing interest in the use of quantitative ultrasound (QUS) measurements for the non-invasive assessment of osteoporotic fracture risk in the management of osteoporosis. The attractiveness of QUS lies in the fact that indirect and in vitro experience has suggested that ultrasound may give information not only about BMD but also about architecture and elasticity. Whether or not combining QUS and DXA improve fracture prediction is still unclear and needs further analysis. Due to the growing evidence supporting the use of QUS in osteoporosis and the large number of QUS devices already on the market, a general clinical consensus on the application of QUS is urgently needed. Other techniques that are less widely used for the management of osteoporosis. For example, peripheral quantitative computed tomography, quantitative magnetic resonance (QMR) and magnetic resonance microscopy are promising tools for the evaluation of the skeleton. For example, the ability of QMR and high resolution magnetic resonance imaging has been explored and shows promise as a technique for assessing trabecular bone structure in osteoporosis.

Peripheral measurement techniques for the assessment of osteoporosis

Peripheral measurement techniques have been the first to be developed for the assessment of osteoporosis, and they remain useful. Besides traditional approaches such as radiographic absorptiometry (RA), radiogrammetry, and single-photon absorptiometry (SPA), new peripheral approaches have been developed that offer powerful ways to assess skeletal status in osteoporosis. These include single x-ray absorptiometry (SXA), peripheral dual x-ray absorptiometry (pDXA), peripheral quantitative computed tomography (pQCT), quantitative ultrasound (QUS) techniques, and magnetic resonance imaging (MRI) approaches. This review describes the current role of peripheral imaging techniques vis-à-vis their central imaging counterparts. Peripheral measurement techniques are attractive because equipment cost is substantially lower, radiation exposure is small, and the devices require less space and sometimes are even portable. Additionally, QUS and MRI offer the potential to measure aspects of bone status beyond the limits of bone densitometry. Peripheral techniques represent important diagnostic methods for the assessment of osteoporosis.

Technical principles of dual energy x-ray absorptiometry

Since its introduction nearly ten years ago, dual-energy x-ray absorptiometry (DXA) has become the single most widely used technique for performing bone densitometry studies. One reason for its popularity is the ability of DXA systems to measure bone mineral density (BMD) in the spine and proximal femur, the two most common sites for osteoporotic fractures. Other advantages of DXA include the exceptionally low radiation dose to patients, short scan times, high resolution images, good precision and inherent stability of calibration. For these reasons DXA scans are widely used to diagnose osteoporosis, assist making decisions in treatment, and as a follow-up response to therapy. Another important application has been the use of DXA in many clinical trials of new treatments for osteoporosis. Since the first generation pencil beam DXA systems became available, the most significant technical innovation has been the introduction of fan beam systems with shorter scan times, increased patient throughput, and improved image quality. New clinical applications include the measurement of lateral spine and total body BMD, body composition, and vertebral morphometry. Despite these advances, posteroanterior (PA) spine and proximal femur scans remain the most widely used application because of their utility in treatment decisions and monitoring response to therapy.

The effect of cortical endplates on ultrasound velocity through the calcaneus: an in vitro study

Ultrasound velocity has been reported as a good predictor of bone strength measured in vitro using standard mechanical testing techniques. Such mechanical investigation of bone strength cannot be carried out in vivo, because of the invasive nature of the testing. Therefore to be able to extrapolate the in vitro findings to the clinical situation, the effect of cortex on ultrasound transmission velocity through the calcaneus is required. This was investigated in vitro by measuring ultrasound velocity through samples of different modification using a CUBAResearch ultrasound machine. The different sample modifications were: "whole" (soft tissue removed), "core" (cylindrical sample), "can" (cancellous sample without the cortex) and "def" (defatted cancellous sample). Ultrasound transmission velocity for the various sample modification were highly correlated with each other (r = 0.80-0.97). Coring resulted in a 0.77% increase in the mean velocity. Substituting bone marrow (defatting) with water at room temperature had no measurable effect on the ultrasound velocity. The velocity in the whole samples and the cancellous samples were statistically different with the cortex introducing only a 2% increase in the ultrasound velocity. Therefore the in vivo ultrasound velocity measured at the calcaneus is determined mainly by the cancellous bone component which is more sensitive to osteoporotic changes. Hence the reported ability of ultrasound velocity in vitro to predict bone strength could be expected in vivo.

ZSD: a universal parameter for precision in the ultrasonic assessment of osteoporosis

There are now several commercial systems available for the ultrasonic assessment of osteoporosis, differing in anatomical location (calcaneus, tibia and phalanges), measurement parameters (broadband ultrasonic attenuation, BUA, and velocity) and their respective calculation algorithms. Comparison of system performance to date has centred upon precision (reproducibility) defined as coefficient of variation (CV%). It has been shown by both theoretical and in vivo studies that the computational algorithm implemented in the calculation of BUA of the calcaneus may have a significant effect upon CV%. The CV% for BUA is inherently inferior to the CV% for velocity by a factor of approximately seven since no allowance is made for population dynamic range. This note proposes and validates a novel parameter for precision, the standard deviation of the Z-score (ZSD). The precision of ultrasound velocity, even when expressed as ZSD, is superior to BUA by a factor of approximately two in the calcaneus. Since precision defined as ZSD is automatically sealed for both mean value and population dynamic range, and is dimensionless, it may be applied to all densitometric technologies. There is a broad range of precision values within the population and future work should investigate the causes of the variability.

A new method of bone tissue measurement based upon light scattering

In recent years, time-resolved spectroscopy systems using near infrared pulsed laser have been applied to develop optical computed tomography. We applied this technique to measure the optical properties of osseous tissues. First, we gradually demineralized 10 mm blocks of bovine trabecular bone with EDTA, maintaining the absorption characteristics and structure but varying the hydroxyapatite content, thus creating specimens differing only in light scattering properties. We used computer densitograms to assess light penetration, and analyzed the correlation with bone mineral density (BMD) as with dual-energy X-ray absorptiometry scans. The light penetration increased with decreasing BMD. Second, using the above-mentioned pulsed laser time-resolved spectroscopy system, we investigated the correlation between the BMD and the time response waveforms of 10-mm blocks of bovine cortical bone, trabecular bone, and surrounding tissue as well as human trabecular bone. The human lumbar vertebral bone also displayed an inverse correlation between BMD and maximum light penetration and a positive correlation between BMD and peak time delay. This is the first demonstration of a correlation between BMD and light scattering properties showing that BMD can indeed be measured with light. Our results show the possibility of obtaining information on internal bone structure and composition in vivo through assessment of the waveforms obtained by a time-resolution system in the near infrared region.

Ultrasound bone densitometry of os calcis in elderly Japanese women with hip fracture

We evaluated 138 elderly patients (mean age 79 years) within 2 weeks after hip fracture (67 cervical and 71 trochanteric) using an Achilles ultrasound bone densitometer (Lunar Corporation, Madison, WI). The ultrasound variables of speed of sound (SOS in m/second), broadband ultrasound attenuation (BUA in dB/MHz), and stiffness (%) index were measured on the os calcis. Ultrasound densitometry also was done on 563 normal postmenopausal women to assess normal age changes. An elderly subgroup (n = 138) served as age-matched controls for the hip fracture group. Further subgroups of 33 patients and 33 controls were compared for lumbar spine and femoral neck BMD. There were no statistically significant differences between the hip fracture group and age-matched controls in height and weight, but each ultrasound variable was significantly lower for the hip fracture group (P < 0.0001). For the hip fracture group, SOS was 1470 +/- 19 m/second, BUA was 84.3 +/- 8.4 dB/MHz, and the stiffness index was 47.8 +/- 9.2%, whereas for the age-matched controls, SOS was 1486 +/- 27 m/second, BUA was 94.0 +/- 11.4 dB/MHz, and the stiffness index was 59.1 +/- 12.5%. There were no significant differences between cervical and trochanteric hip fracture groups. Logistic regression analysis showed that a change of the ultrasound values by 1 standard deviation (SD) changed the odds ratio for SOS, BUA, and stiffness index by 2.51, 3.24, and 3.60, respectively. Ultrasound variables, particularly stiffness, were good indicators of hip fracture risk.

Quantitative ultrasound imaging at the calcaneus using an automatic region of interest

A new approach to measuring bone properties at the calcaneus using ultrasound parametric imaging has recently emerged. However, an additional source of observer-related error is the substantial regional variations in the pattern of ultrasound parameters. The contribution of intra-observer and inter-observer variability to the coefficient of variation can be eliminated using an algorithm which selects the region of interest (ROI) completely automatically. The objective of the present study was the clinical assessment of an automatic ROI for both broadband ultrasonic attenuation (BUA) and speed of sound (SOS) measurement using ultrasound parametric imaging. The automatic ROI was defined as the circular region of lowest attenuation in the posterior tuberosity of the calcaneus. We have tested this algorithm using clinical images of the calcaneus from 265 women. Mean coefficients of variation were 1.6% (95% confidence interval 1.4%-1.9%) and 0.26% (95% confidence interval 0.23%-0.32%) for BUA and SOS respectively (standardized CV was 2.1% for BUA and 2.6% for SOS). Z-scores in an osteoporotic group were -0.61 and -0.52 for BUA and SOS respectively. In healthy women, the age-related decline was -0.50 dB/ MHz per year (0.7%/year) for BUA and -1.2 m/s per year (0.08%/year) for SOS. In the subgroup of healthy postmenopausal women, using stepwise multiple regression, we found that BUA was predicted best by years since menopause (YSM) and weight, with overall model r2 = 0.28; SOS was predicted best by YSM only (r2 = 0.21). Neither the range of biological variation of ultrasound parameters nor the clinical value were affected by the choice of the region of lowest attenuation for measurement. The automatic procedure was totally independent of operator interaction, therefore excluding loss of precision due to intra- or inter-observer variability. The results showed the high precision and robustness of the procedure. These factors make this approach viable for routine clinical use.

Longitudinal changes in ultrasound parameters of the calcaneus

We examined with a median follow-up of 1.4 years (range 1.0-2.0 years) the rates of change per year in ultrasound parameters of the calcaneus. Speed of sound (SOS), Broadband ultrasound attenuation (BUA) and Stiffness were measured twice in 543 subjects (224 men) participating in the Rotterdam Study. SOS fell by -2.5 m/s per year in both sexes (95% CI -4.0 to -1.1 m/s per year in men and -3.6 to -1.4 m/s per year in women). Stiffness decreased by -0.62 (-1.33 to 0.09) per year in men and -0.66 (-1.24 to -0.08) per year in women. In men the rate of change in SOS and Stiffness tended to increase with age. BUA did not change significantly during follow-up in either sex. The prospectively assessed rates of loss differed considerably from those observed cross-sectionally, especially for SOS in men (cross-sectional -0.7 m/s per year, longitudinal -2.5 m/s per year). There was substantial variation between individuals both in changes per year in SOS and in changes per year in BUA. With a median follow-up time of 1.4 years, approximately 27% of the variation in the rate of change for SOS could be explained by measurement error while for BUA this was approximately 9% and for Stiffness 11%. Only a small percentage of subjects had changes larger than could be accounted for by measurement error (SOS: men 26.8%, women 21.6%; BUA: men 28.5%, women: 38.8%; Stiffness: men 32.6%, women 35.1%). The latter may limit the use of ultrasound measurements as a follow-up tool in individuals rather than in populations.

The role of ultrasound in the assessment of osteoporosis: a review

Osteoporosis is now being recognized as a "silent epidemic" and there is an increasing need to improve its diagnosis and management. Quantitative ultrasound (QUS) measurement [broadband ultrasound attenuation (BUA) and velocity] is emerging as an alternative to photon absorptiometry techniques in the assessment of osteoporosis. The fundamental principles governing ultrasound measurements are discussed, and some of the commercially available clinical systems are reviewed, particularly in relation to data acquisition methods. A review of the published in vivo and in vitro data is presented. The general consensus is that ultrasound seems to provide structural information in addition to density. The diagnostic sensitivity of ultrasound measurement of the calcaneus in the prediction of hip fracture has been shown by recent large prospective studies to be similar to hip bone mineral density (BMD) measured with dual-energy X-ray absorptiometry (DXA) and superior to spine BMD. Ultrasound has also been shown to correlate better with the type of hip fracture (intertrochanteric or cervical) than BMD and to provide comparable diagnostic sensitivity to spine BMD in vertebral fractures. It has also been observed that combining the results of both ultrasound and DXA BMD significantly improved hip fracture prediction. Areas where further research is required are identified.

The effect of ankle oedema on bone ultrasound assessment at the heel

Relatively inexpensive, portable bone ultrasound systems are of particular relevance to disabled or elderly subjects, who may have problems with access to other forms of densitometry. The effects of local soft tissues on ultrasound measurements are poorly understood and, as ankle oedema is common in such subjects, we examined its consequences for bone ultrasound readings at the heel. Eleven elderly subjects (mean age 81 years) with below-knee pitting oedema were assessed using a direct-contact bone ultrasound system (CUBA Clinical). We made a total of 16 series of readings, 6 unilateral and 5 bilateral. In each series an initial reading was followed by repeated pressure over the measurement site to disperse oedema; subsequent readings were thus subject to a progressively lessening degree of local oedema, until a steady state was eventually reached in which no further oedema could be displaced. Heel width fell by a mean of 6.3 mm between initial and steady-state readings; consistent with the clinical appearance of moderate oedema, pitting to a mean depth of only 3.15 mm. Measurements in the presence of oedema were compared with those after its elimination, and oedema was shown to cause a mean reduction of 23.9 m/s in velocity of sound (VOS) and of 5.5 dB/MHz in broadband ultrasound attenuation (BUA). Both changes were equivalent to a fall by a quarter of one standard deviation of the reference range, and were significant at p < 0.05 on paired t-test. As the severity of oedema will vary through the day, and from day to day, measurement protocols for bone ultrasound should pay attention to the confounding effects of oedema.