An evaluation of the reproducibility and responsiveness of four 'state-of-the-art' ultrasonic heel bone measurement systems using phantoms

A European multicenter comparison of quantitative ultrasound measurement variables: the OPUS study

Quantitative ultrasound (QUS) measurement variables vary between European countries in a different way to hip bone mineral density. Standardization of data can be achieved through statistical approaches to reduce any between-center differences in QUS measurement variables. However, further validation of this method is required before it can be widely applied.

INTRODUCTION

European between-center differences in hip bone mineral density (BMD) have been shown to exist; however, little is known about the geographical heterogeneity of QUS measurement variables. We aimed to examine the differences in QUS variables between three different European countries.

METHODS

Five calcaneal and phalangeal QUS devices in Sheffield, Aberdeen (UK), Kiel and Berlin (Germany), and three devices in Paris (France) were used to measure QUS variables in younger (n = 463, 20-39 years old) and older (n = 2,399, 55-79 years old) women participating in the European multicenter Osteoporosis and Ultrasound (OPUS) study. Broadband ultrasound attenuation, speed of sound, stiffness index, amplitude-dependent speed of sound, bone transmission time, and ultrasonic bone profiler index data were collected. Between-center differences were examined using ANOVA followed by post hoc Fisher's least significant difference tests, and ANCOVA with linear contrasts. p < 0.05 indicated statistical significance.

RESULTS

Between-center differences in nonstandardized QUS measurement variables existed for younger (p = 0.0023 to p < 0.0001) and older women (p < 0.001). Anthropometric characteristics exerted a significant influence on nonstandardized data (p = 0.045 to p < 0.001). However, following statistical standardization, based on height and weight or based on measurements made in young people, geographical heterogeneity in QUS measurement variables was no longer apparent.

CONCLUSIONS

QUS measurement variables vary between European countries in a different way to those for hip BMD. Standardization of data can be achieved through statistical approaches to reduce any between-center differences in QUS measurement variables. However, further validation of this method is required before it can be widely applied.

A review of tissue substitutes for ultrasound imaging

The characterization and calibration of ultrasound imaging systems requires tissue-mimicking phantoms with known acoustic properties, dimensions and internal features. Tissue phantoms are available commercially for a range of medical applications. However, commercial phantoms may not be suitable in ultrasound system design or for evaluation of novel imaging techniques. It is often desirable to have the ability to tailor acoustic properties and phantom configurations for specific applications. A multitude of tissue-mimicking materials and phantoms are described in the literature that have been created using a variety of materials and preparation techniques and that have modeled a range of biological systems. This paper reviews ultrasound tissue-mimicking materials and phantom fabrication techniques that have been developed over the past four decades, and describes the benefits and disadvantages of the processes. Both soft tissue and hard tissue substitutes are explored.

Calcaneus ultrasound in males: normative data in the Croatian population (ECUM study)

Limited number of dual X-ray absorptiometry (DXA) devices in Croatia makes this diagnostic technique unavailable to the majority of the population. Quantitative ultrasound (QUS) of the calcaneus could be an alternative tool for assessing fracture risk. However, age-specific normative data should be obtained before using the QUS in everyday clinical practice. The aim of our Epidemiology of Calcaneus Ultrasound in Males (ECUM) study is to establish the normative QUS data in a healthy sample of Croatian males. A total of 1002 male participants, aged 20-99, recruited in different Croatian counties, were included in the study. In each subject broadband ultrasound attenuation (BUA), speed of sound (SOS) and quantitative ultrasound index (QUI) of the left calcaneus were measured using the Sahara ultrasound device (Hologic). The coefficients of variation were 2.85 for BUA, 0.37 for SOS and 2.49 for QUI. Significant declining with age was found for all three parameters, BUA (p<0.001), SOS (p<0.001) and QUI (p<0.001), with respective r values 0.14, 0.27 and 0.23. The peak SOS (1,562.8+/-28.5 m/sec) and QUI (103.6+/-16.5) values were observed in the third decade, whereas the peak BUA value (86.2+/-19.2 db/MHz) was observed in the fourth decade. A subgroup of 103 participants, aged 20-29, was used to estimate young adult mean and SD for QUI and calculate the T-scores. Using the World Health Organization diagnostic criteria the rates of osteoporosis (T-score<-2.5) in the males aged 50 and older was 5.8%. However, when we used the cut-off value of the T-score<-1.8, as previously suggested, prevalence of osteoporosis in Croatian males >50 yr was 16.2%. Although further studies might improve our understanding of the QUS role in the fracture prediction, we hope that the results presented here will improve the clinical management of osteoporosis in males.

Effect of temperature on the longitudinal variability of quantitative ultrasound variables

It is unclear whether longitudinal change in phantom measurements bears any relation to the long-term in vivo instrument performance of quantitative ultrasound devices. Longitudinal quantitative ultrasound phantom data were obtained by measuring the manufacturer-provided phantom at ambient temperature and two different sets of Leeds phantoms at either ambient temperature or following a phantom temperature-control protocol. Measurements were performed using the Achilles Plus bone densitometer. Changes in longitudinal phantom data were compared to in vivo quantitative ultrasound data obtained from seven healthy, young volunteers. A cosinor model with linear trend and Hotelling's T2-test were used to quantify seasonal rhythms and long-term drift in quantitative ultrasound variables. Temperature effects and marked seasonal rhythms on quantitative ultrasound phantom measurements were evident but were far less apparent in vivo. Longitudinal precision of quantitative ultrasound variables was poorer for the manufacturer-provided phantom than for phantoms that were subjected to a temperature-control protocol or for healthy volunteers. This study has shown that longitudinal precision and longitudinal change differs between in vivo and phantom data. Longitudinal quantitative ultrasound measurements for monitoring change in skeletal status cannot, as yet, be properly controlled.

Discrimination of osteoporotic patients with quantitative ultrasound using imaging or non-imaging device

OBJECTIVES

Quantitative ultrasound (QUS) has emerged as a new tool in the assessment of fracture risk. The aim of this study was to compare the clinical utility of QUS parameters measured using imaging and non-imaging devices in the discrimination of osteoporotic patients.

METHODS

QUS (Broadband Ultrasound Attenuation, BUA dB/MHz, and Speed of Sound, SOS m/s) were measured and then statistical analyses were performed.

RESULTS

The 106 women included were 65 +/- 8 years aged. Using DXA, T score was < or = -2.5 at either lumbar spine or hip in 59% of patients, and 25% had osteoporotic fractures. QUS results were different among devices, and these differences were highly dependent on the measured value. There was a similar effect of age and duration of menopause for all parameters. To obtain 90% of sensitivity for the diagnosis of osteoporosis, the thresholds were 50.80 and 71.70 dB/MHz for BUA and 1544.80 and 1551.50 m/s for SOS, using imaging and non-imaging devices, respectively. Belonging to the highest tertile of QUS had a negative predictive value for osteoporosis ranging from 59% to 65%. In the lowest tertile of QUS, the proportion of osteoporotic women was between 73% and 80%. All QUS parameters, except BUA measured with the non-imaging device, were able to discriminate post-menopausal women with fractures after adjustment for age and hip BMD.

CONCLUSIONS

Our data suggest that an imaging system improves the utility of BUA measurement, but not SOS, for post-menopausal osteoporosis assessment.

Quantitative assessment of osteoporosis from the tibia shaft by ultrasound techniques

Bone mineral density (BMD) is used as a clinical estimate of the risk of fracture. Ultrasound provides an alternative or complement to X-ray based methods of bone densitometry for determining BMD. Among ultrasonic characteristics, the speed of sound (SOS) is a useful tool for assessment of osteoporosis because, as recently reported, it represents a combination of density and compressibility of bone tissue. Thus, it might provide better information on bone quality to estimate the fracture risk. In this paper, a dual-transducer ultrasound technique was employed to measure the mean ultrasound propagation speed of the cortical layer as well as the cancellous layer at the tibia shaft. Encouraging results from 18 outpatients showed a high correlation (r = 0.93) between measurements of BMD and those from dual energy X-ray absorptiometry (DEXA).

Reproducibility and concordance in quantitative ultrasound measurements between densitometers: a comparative study

Although calcaneal quantitative ultrasound (QUS) is an independent predictor of osteoporotic fracture, its role in monitoring changes in bone status remains limited because of its relatively poor precision compared to the rate of bone loss. Recently, imaging QUS has been developed that can standardize the region of interest in the calcaneus with the potential of improving precision. We assessed the concordance and precision of an imaging QUS scanner (UBIS 5000) and a nonimaging scanner (LUNAR Achilles+) in 52 subjects aged between 27 and 79 yr. Each subject had duplicate measurements on each scanner on the same day. The measurements were broad-band ultrasound attenuation (BUA), speed of sound (SOS), and stiffness index, which was derived from BUA and SOS. Precision was evaluated by the standard error of measurement (SEM) and within-subject coefficient of variation (CV). There was significant correlation between the two scanners in all QUS measurements (r > 0.8; p < 0.001); however, BUA and SOS measurements by the UBIS were significantly lower than by the Achilles+. The SEM of BUA (0.6 dB/MHz) and SOS (2.7 m/s) in the UBIS were significantly lower (p < 0.001) than the Achilles+ (1.4 dB/MHz for BUA and 6.3 m/s for SOS). When the SEM was expressed as the percentage of the mean, there were no significant differences in CVs between UBIS (0.9% for BUA and 0.2% for SOS) and Achilles+ (1.2% for BUA and 0.4% for SOS) scanners. The SEM of stiffness index derived by UBIS was not significantly different from that derived by the Achilles+. These data suggest that although there are systematic differences between the UBIS and Achilles+ scanners in QUS measurements, the precision of the two instruments is equivalent.

Quality controls for two heel bone ultrasounds used in the Swiss Evaluation of the Methods of Measurement of Osteoporotic Fracture Risk Study

Because of the important morbidity and mortality associated with osteoporosis, it is essential to detect subjects at risk by screening methods, such as bone quantitative ultrasounds (QUSs). Several studies showed that QUS could predict fractures. None, however, compared prospectively different QUS devices, and few data of quality controls (QCs) have been published. The Swiss Evaluation of the Methods of Measurement of Osteoporotic Fracture Risk is a prospective multicenter study that compared three QUSs for the assessment of hip fracture risk in a population of 7609 women age >/=70 yr. Because the inclusion phase lasted 20 mo, and because 10 centers participated in this study, QC became a major issue. We therefore developed a QC procedure to assess the stability and precision of the devices, and for their cross-calibration. Our study focuses on the two heel QUSs. The water bath system (Achilles+) had a higher precision than the dry system (Sahara). The QC results were highly dependent on temperature. QUS stability was acceptable, but Sahara must be calibrated regularly. A sufficient homogeneity among all the Sahara devices could be demonstrated, whereas significant differences were found among the Achilles+ devices. For speed of sound, 52% of the differences among the Achilles+ was explained by the water s temperature. However, for broadband ultrasound attenuation, a maximal difference of 23% persisted after adjustment for temperature. Because such differences could influence measurements in vivo, it is crucial to develop standardized phantoms to be used in prospective multicenter studies.

Quantitative heel ultrasound in assessment of bone structure in renal transplant recipients

Many patients with advanced renal disease have osteopenia or even osteoporosis by the definition of the World Health Organization based on bone mineral density (BMD). Dual-energy X-ray absorptiometry (DXA), the standard method to assess BMD, is not always available. Quantitative heel ultrasound (QUS) is an inexpensive, mobile, and radiation-free diagnostic alternative, yet few data address this method's usefulness in patients with renal disease. The present study assessed the value of QUS in detecting changes in bone structure in renal transplant recipients compared with DXA. In a cross-sectional analysis, 50 patients (29 women) with a mean age of 50 +/- 13 years, mean time since transplantation of 60 months (range, 1 to 205 months), and stable renal allograft function were studied. BMD was quantified by DXA of the hip and spine. QUS of the left heel measured broadband ultrasound attenuation (BUA) and speed of sound (SOS). Stiffness index (SI) was calculated as SI = (0.67 * BUA + 0.28 * SOS) - 420. DXA measurements established the diagnoses of osteopenia and osteoporosis in 49% and 22% of the patients, respectively. Femoral neck BMD and QUS parameters showed good correlation (r = 0.638; P < 0.001). Sensitivities of BUA, SOS, and SI for diagnosing osteoporosis were 100%, and specificities were 73%, 76%, and 78%, respectively. Positive predictive values were 50%, 53%, and 56%, and negative predictive values were 100%. QUS can be recommended for screening patients who do not have osteoporosis. Those suspected of osteopenic bone structure should be examined by additional DXA measurement for quantification before initiation of therapy.

Quantitative ultrasound in postmenopausal osteoporosis

Ultrasound has been proposed as a low-cost, radiation-free method for osteoporosis assessment in postmenopausal women. Large prospective studies have shown that ultrasound parameters can be used for fracture risk estimate in this population, providing that adequate quality control is performed. The places of both ultrasound and the current gold standard method for bone assessment, dual energy x-ray absorptiometry, are still to be determined. Further studies are needed on the diagnosis of osteoporosis using ultrasound, because current diagnostic thresholds, designed by the World Health Organization, do not apply to this-new technology. Monitoring of skeletal changes and treatment effects by ultrasound cannot be recommended.