Broadband Ultrasonic Attenuation Measurements Research Articles

The 25th Anniversary of BUA for the Assessment of Osteoporosis: Time for a New Paradigm?

The measurement of broadband ultrasonic attenuation (BUA) in cancellous bone at the calcaneus for the assessment of osteoporosis was first described within this journal 25 years ago. It was recognized in 2006 by Universities UK as being one of the '100 discoveries and developments in UK Universities that have changed the world' over the past 50 years. In 2008, the UK's Department of Health also recognized BUA assessment of osteoporosis in a publication highlighting 11 projects that have contributed to '60 years of NHS research benefiting patients'. The BUA technique has been extensively clinically validated and is utilized worldwide, with at least seven commercial systems currently providing calcaneal BUA measurement. However, there is still no fundamental understanding of the dependence of BUA upon the material and structural properties of cancellous bone. This review aims to provide an 'engineering in medicine' perspective and proposes a new paradigm based upon phase cancellation due to variation in propagation transit time across the receive transducer face to explain the non-linear relationship between BUA and bone volume fraction in cancellous bone.

The Measurement of Broadband Ultrasonic Attenuation in Cancellous Bone-A Review of the Science and Technology

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

Dependence of ultrasonic attenuation on bone mass and microstructure in bovine cortical bone

The development of the axial transmission technique now enables in vivo evaluation of cortical bone quality, which plays an important role in bone fragility. Cortical bone is a complex multiscale material, which may be made of different types of microstructure. The interaction between ultrasound and cortical bone remains unclear and most studies have been confined to wave speed analysis. The first aim of this study is to investigate the dependence of the frequency-dependent attenuation on the type of bone microstructure. The second goal is to determine whether broadband ultrasonic attenuation (BUA) is related to volumetric bone mineral density (vBMD) and mass density. Parallelepipedic samples of bovine cortical bone were cut from three specimens and tested in the axial, radial and tangential directions using an ultrasonic transmission device. BUA was evaluated over a 1-MHz wide bandwidth around 4 MHz. In addition, the microstructure of each sample was determined using an optical microscope. BUA values measured in porotic microstructure are significantly higher than in Haversian microstructure. The lowest BUA values are obtained for plexiform microstructure. For all structures, BUA in the axial direction is significantly smaller than in the radial and tangential directions. Moreover, BUA is correlated with both vBMD and density (determination coefficient ( R 2) equal to 0.44 and 0.65, respectively, in the axial direction). BUA variations can be explained by scattering and viscoelastic mechanisms. This study suggests that BUA measurements have the potential to discriminate among different cortical bone microstructures in addition to providing material properties.

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. (E-mail: haiat@univ-paris12.fr)

The Effect of Phase Cancellation on Estimates of Calcaneal Broadband Ultrasound Attenuation in Vivo

Broadband ultrasonic attenuation (BUA) is a clinically-accepted measurement for prediction of osteoporotic fracture risk. Typical clinical BUA measurements are performed with phase-sensitive receivers and, therefore, can be affected by phase cancellation. In order to separate the effects of conventional attenuation (absorption plus scattering) from phase cancellation, BUA was measured on phantoms with acrylic wedge phase aberrators and on 73 women using both phase sensitive (PS) and phase insensitive (PI) reception. A clinical bone sonometer with a two-dimensional (2-D) receiver array was used. PI BUA measurements on phantoms with acrylic wedge phase aberrators were found to be far more resistant to phase cancellation than PS BUA measurements. In data from 73 women, means and standard deviations for BUA measurements were 81.4 +/- 21.4 dB/MHz (PS) and 67.2 +/- 9.7 dB/MHz (PI). The magnitude of the discrepancy between PS BUA and PI BUA tended to increase with bone mineral density (BMD).

In Vitro Ultrasound Measurement at the Human Femur

Measurements of broadband ultrasonic attenuation (BUA) represent an established means of skeletal status assessment in osteoporosis. Today, the skeletal site that is the most widely used clinically is the calcaneus (heel bone). However, we hypothesized that fracture risk predictions could be improved if ultrasound measurements were performed directly at the main site of fracture, e.g., the proximal femur. The goal of this paper is to demonstrate in vitro the feasibility of quantitative ultra sound (QUS) imaging at the upper part of fee femur, and to investigate the relationships of BUA to bone mineral density (BMD). Forty-four excise human femurs were measured in transmission with a pair of focused 0.5-MHz central frequency transducers. Two-dimensional scans were performed, and the radio frequency (rf) signals were recorded at each measurement point. A data acceptance criterion for region of interest (ROI) selection was established based on the linearity of the frequency-dependent attenuation. Five measurements with repositioning were performed on each sample to determine the reproducibility. Dual energy x-ray absorptiometry (DXA) scans have been performed on the samples for BMD measurements: Three ROIs were selected in the specimens: greater, trochanter intertrochanteric, and femoral neck regions. Coefficient of variations were in the range 1.6% to 2.5%. The determination coefficients (r(2)) between BUA and BMD in site-matched ROIs were 0.81, 0.78, and 0.73, respectively, for the greater trochanteric, intertrochanteric, and femoral neck regions. Our results are consistent with data previously shown at the calcaneus and demonstrate the feasibility of QUS measurements at the femur in vitro, with reasonable reproducibility.

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.

Reference data for ultrasonic bone measurement: variation with age in 2087 Caucasian women aged 16-93 years.

Data from the measurement of broadband ultrasonic attenuation (BUA) and speed of sound (SOS), using the Lunar Achilles ultrasonic densitometer, were collected for Caucasian women from five centres in the United Kingdom (Leeds, London, Nottingham, Lincoln and Sheffield). After correcting for machine variability at each site, the data were combined into a central reference database comprising 2087 women aged 16-93 years. The data are presented in 5-year bands and show a mean fall of 0.36% per year for BUA and 0.08% per year for SOS in the 60 years following the attainment of peak bone mass. This fall in BUA compares with that observed using dual energy X-ray absorptiometry studies of the lumbar spine and femoral neck of 0.32% per year and 0.44% per year, respectively, for the age range 25-65 years.

Calcaneal ultrasound attenuation in older African-American and Caucasian-American women.

The lower fracture rates among African-American women relative to Caucasian women may reflect their higher bone mass. However, bone mass is not the only determinant of bone strength: the quality and microarchitecture of the bone are also important. Quantitative ultrasound is believed to measure properties of bone strength that are independent of bone mass. To test the hypothesis that there are racial differences in quantitative ultrasound measures of bone, we recruited 154 African-American women age > or = 65 years. A random sample of 300 Caucasian women participating in the Study of Osteoporotic Fractures in Pittsburgh, Pennsylvania, was chosen for comparison. The Walker Sonix UBA 575+ was used to measure calcaneal broadband ultrasonic attenuation (BUA). Duplicate BUA measurements were obtained with a reproducibility of 5%. We measured bone mineral density (BMD) of the hip and calcaneus using single (calcaneus) or dual (hip) energy X-ray absorptiometry. The correlation between BUA and calcaneal BMD was similar in Caucasians (r = 0.66, p < 0.001) and African-Americans (r = 0.58, p < 0.001). Age-adjusted BUA (dB/MHz) was higher among the African-American women than Caucasian women (69.1 and 66.2, respectively), but these differences were not statistically significant, (p = 0.12). Adjustment for calcaneal BMD completely attenuated the racial differences in BUA. BMD at the femoral neck and calcaneus was higher among the African-American women, even after adjusting for age, height and weight. In conclusion, our results suggest that racial differences in rates of fracture cannot be explained by differences in bone quality as assessed by ultrasound attenuation.

An investigation of the measurement of broadband ultrasonic attenuation in trabecular bone.

Commercial devices for the ultrasonic characterisation of bone normally report the broadband ultrasonic attenuation (BUA). This is the slope of the attenuation against frequency in some part of the frequency range 200-1000 kHz. The assumption is that the relationship is linear and hence independent of the frequency range selected. In this study the ultrasonic attenuation in the frequency range 200 to 800 kHz was measured with a variety of transducers in ten trabecular heel bone samples from elderly cadavers, assumed to be osteoporotic. The results indicate that the attenuation fits better to a second order polynomial function of frequency, than to the linear fit. The use of a straight line fit is only satisfactory in the higher frequency ranges (above 400 kHz). The use of lower frequencies results in a significant measurement error caused by the combination of a poor signal to noise ratio and the departure from linearity and this is greatest for samples with low attenuation. In the worst cases this can amount to a 30% discrepancy between the BUA values measured over different frequency ranges.

Identification and characterisation of materials by broadband ultrasonic attenuation analysis

Ultrasound attenuation analysis has been demonstrated as a cheap, reliable method of identifying and characterising polymeric materials and components, which can assist in the separation and reclamation of thermoplastics from polymer waste streams. Material/Component broadband ultrasonic attenuation measurement, and the measurement of the time of flight of an ultrasonic pulse, in either pulse echo or pulse through transmission mode, can be combined to attain a signature of the material under investigation. The HL (Hull/Langton) signature is independent of component dimensions, and hence, is a powerful tool for the identification of components of complex shape where access to all surfaces may be restricted. The results presented demonstrate the ability of the technique to identify a range of different polymers, including reinforced materials. The approach adopted is not confined solely to polymers, but can also be used to identify the levels of porosity in ceramic pottery, including both open and closed cell pores.

Broadband ultrasonic attenuation: are current measurement techniques inherently inaccurate?

Measurements of broadband ultrasonic attenuation (BUA) are currently made using large aperture, piezoelectric transducers. The use of such a receiver is known to lead to the possibility of an overestimate of ultrasonic attenuation due to phase cancellation and it is shown theoretically that this same effect can also lead to an overestimate of BUA. Using a new scanning approach, BUA was measured using two methods, one sensitive to the phase of the acoustic wave, the other not. The phase sensitive BUA measurements were found to be of significantly higher value (p < 0.0001) than the phase insensitive measurements with a mean difference of 31.2 dB MHz-1. These findings are compatible with the hypothesis that BUA measurement systems with large aperture, piezo-electric receivers are inherently inaccurate.

Identification and characterization of reclaimed and recycled polymers by ultrasound attenuation

Ultrasound attenuation analysis has been demonstrated as a cheap, reliable method of identifying and characterizing polymeric materials and components, which can assist in the separation and reclamation of thermoplastics from polymer waste streams. Material-component broad band ultrasonic attenuation measurement and the measurement of the time of flight of an ultrasonic pulse, in either pulse echo or pulse through-transmission mode, can be combined to attain a signature of the material under investigation. The HL (Hull-Langton) signature is independent of component dimensions and hence is a powerful tool for the identification of components of complex shape where access to all surfaces may be restricted. The results presented demonstrate the ability of the technique to identify a range of different polymers, including reinforced materials.

The ultrasonic assessment of osteopenia as defined by dual X-ray absorptiometry

Dual X-ray absorptiometry (DXA) studies of bone mineral density (BMD) of the lumbar spine and femoral neck were compared with measurements of broadband ultrasonic attenuation (BUA) and velocity of ultrasound (VOS) in the calcaneus in 300 pre- and postmenopausal women (mean age 53 years). The women were referred for evaluation of possible osteopenia as defined by DXA. The ability of ultrasound measurements to predict osteopenia in women was compared with the ability of lumbar spine and femoral neck DXA scans to predict osteopenia in the hip and spine. A new ultrasound parameter obtained by combining BUA and VOS (combined attenuation and velocity (CAV)) was also evaluated. Linear regression analysis of the three ultrasound parameters and lumbar spine and femoral neck BMD gave weak but statistically significant correlations (r = 0.45-0.54). The correlation between spine and femoral neck BMD was statistically significantly better (r = 0.72). Receiver-operating characteristic (ROC) analysis was used to investigate the sensitivity and specificity of ultrasound measurements in predicting patients with osteopenia. The areas under the ROC curves ranged from 0.64 to 0.75 and ultrasound parameters were shown to be poor at predicting osteopenia as defined by DXA. The ability of lumbar spine and femoral neck DXA measurement to predict osteopenia in the hip and spine, respectively, was statistically significantly better than any of the ultrasound parameters. Ultrasound measurements in the calcaneus did not appear to identify accurately patients with osteopenia defined by DXA measurements of bone density in the axial and appendicular skeleton.

Variation between os calces as measured by broadband ultrasound attenuation

We compared broadband ultrasonic attenuation (BUA) values of right with left os calcis in 65 women. All subjects were right handed, and they were divided into two groups: Group 1 consisted of 32 normal volunteers and Group 2 of 33 osteoporotic subjects. Both groups had mean absolute differences in BUA between the two os calces greater than the coefficient of variation (p < 0.001). This difference is not related to stated handedness of the individuals. Osteoporosis affects both os calces similarly. BUA measurements should always be performed in the same site in longitudinal studies, otherwise false comparisons will result.

Measurements of postmenopausal bone loss with a new contact ultrasound system

Measurements of broadband ultrasonic attenuation (BUA) and velocity of ultrasound through the heel (heel velocity, HV) were performed with a Contact Ultrasonic Bone Analyzer (CUBA-Research model) in 229 women. The subjects consisted of 16 healthy young volunteers (Group 1, mean age 26 years), 170 healthy pre- and postmenopausal women (Group 2, mean age 53 years), and 43 osteoporotic women with radiographically defined vertebral crush fracture (Group 3, mean age 66 years). Subjects in Group 1 had 10 repeated measurements in a study of short-term precision. Women in Groups 2 and 3 also had dual X-ray absorptiometry (DXA) scans to measure lumbar spine and femoral neck bone mineral density (BMD). The BUA and HV measurements for all 229 women showed a significant correlation (r = 0.75, P < 0.001). The precision study on the subjects in Group 1 gave a root mean square coefficient of variation of 6.3% for BUA and 1.04% for HV. Linear regression analysis gave the following relationship between BUA and age for the 170 normal women in Group 2: BUA = 83.6-0.86 (age 40) dB/MHz (r = -0.31, P < 0.001, SEE = 16.3 dB/MHz). The relationship between HV and age was as follows: HV = 1614-2:3 (age 40) m/s (r = -0.33, P < 0.001, SEE = 42 m/s). Multivariate regression analysis showed that in addition to age, years since the menopause was also a significant factor in determining both BUA and HV.(ABSTRACT TRUNCATED AT 250 WORDS)

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

The assessment of skeletal integrity by the measurement of ultrasonic velocity through the calcaneus has only recently become widely available and is usually made in conjunction with the measurement of broadband ultrasonic attenuation. Using data obtained with a contact ultrasonic bone analyser (CUBA) system, this report examines whether ultrasonic studies of the heel require the measurement of true velocity of sound in the calcaneus (Vbone), or whether heel velocity (Vheel, defined as the mean velocity through bone and soft tissue) or time of flight velocity (Vtof, defined as the mean velocity between the two transducers) are adequate surrogates. The populations selected for study were 15 healthy young women (group 1, mean age 26 years), 231 healthy peri- and postmenopausal women (group 2, mean age 52 years) and 33 osteoporotic women with confirmed vertebral fracture (group 3, mean age 66 years). Precision was studied by performing 10 repeated scans on the subjects in group 1 and duplicate scans on 144 women randomly selected in groups 2 and 3. Precision was expressed as the percentage coefficient of variation (CV). Both precision studies yielded similar results. The precisions (and 5% to 95% ranges) for all groups combined were: Vbone 2.71% (1465-1809 m/s); Vheel, 1.10% (1511-1646 m/s): Vtof, 0.70% (1349-1425 m/s). Although the precision data suggest Vtof should be preferred, when the range of clinical values is taken into account the smaller CV is exactly cancelled by the narrower range.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurements of broadband ultrasonic attenuation in the calcaneus in premenopausal and postmenopausal women.

We report a study of broadband ultrasonic attenuation (BUA) in the calcaneus in 248 women. Measurements were performed with a Walker-Sonix UBA-575 ultrasonic bone analyser. The populations studied were 15 healthy young volunteers (group 1, mean age 26 years), 200 healthy pre- and postmenopausal women (group 2, mean age 53 years) and 33 osteoporotic women with vertebral crush fractures (group 3, mean age 66 years). Subjects in group 1 each had 10 repeated measurements of their right heel. Duplicate BUA measurements in the right heel were performed in 96 subjects and bilateral scans in a further 87 women in group 2. The remaining 17 subjects in group 2 and those in group 3 had a single scan of the right heel. All women in groups 2 and 3 had dual X-ray absorptiometry (DXA) scans of the lumbar spine and femoral neck. The precision study on the women in group 1 gave a root mean square (RMS) coefficient of variation (CV) of 4.2%. Individual CV results showed statistically significant differences (range 1.3%-7.6%). Duplicate scans in subjects in group 2 gave a RMS CV of 4.6% while the bilateral measurements showed no significant difference between the two heels. Linear regression analysis gave the following relationship between BUA and age: BUA = 87.1 - 0.76 (Age - 40) dB/MHz (r = -0.31, p less than 0.001, SEE = 14.0 dB/MHz). Multivariate regression analysis showed that, in addition to age, years since the menopause was also a significant factor in predicting BUA.(ABSTRACT TRUNCATED AT 250 WORDS)