Christian M. Langton

The Measurement of Broadband Ultrasonic Attenuation in Cancellous Bone

We have carried out measurements of the frequency dependence of ultrasonic attenuation in the range 0.2–1 MHz in in vitro samples of bovine cancellous bone and in vivo os calcis heel bones. A comparison of the results allows us to infer that the in vivo measurements are dependent on the bone mineral content of the os calcis. The bone mineral content has been determined in this way for three female populations and indicates that the technique allows determination of bone loss and the study of the onset and progress of osteoporosis. The technique has the great advantage of health safety over radiographic and neutron activation analysis. It may also prove to be more sensitive to small changes in bone mineral content.

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.

A comparison of time-domain and frequency-domain approaches to ultrasonic velocity measurement in trabecular bone

Different methods for ultrasonic velocity determination using broad-band pulse transmission have been investigated in 70 human calcanae in vitro. The work took place within the context of the EC BIOMED1 concerted action Assessment of Quality of Bone in Osteoporosis. Ultrasonic velocities were determined using three different transit time definitions: first arrival (TTV1), thresholding (TTV2), and first zero crossing (TTV3). Phase velocity (PV) was determined over a range of frequencies from 200 to 800 kHz using a new phase spectral analysis technique. The different velocity measurements were compared in terms of their magnitudes and their inter-correlations. There were significant differences of up to 260 m s-1 between different transit time velocities (p < 0.0001), indicating the sensitivity of the measurement to the arrival criteria used. Phase velocities were lower than all of the transit time velocities (p < 0.0001) and decreased with increasing frequency (p < 0.005). A strong correlation (r2 = 0.968) was observed between PV at 400 kHz (PV400) and TTV3, with much weaker correlations between PV and the other transit time velocities. Reproducibility for transit time velocity measurement was optimal for TTV3 (coefficient of variation, cv = 0.41%), and for PV it was optimal at 600 kHz (cv = 0.34%). These data indicate that transit time measurements may be subject to errors due to the modification of the pulse shape during propagation through bone by attenuation and dispersion. Velocity measurement by phase spectral analysis appears to offer advantages over the transit time approach, and should be the method of choice for velocity measurement in trabecular bone. Where transit time velocity measurements are made, the first-zero-crossing criterion appears to be have some advantages over other arrival criteria. We also note that PV measurements provide new information on dispersion which could prove to be relevant to the structural and mechanical characterization of trabecular bone.

Accelerated Partial Breast Irradiation (APBI): A review of available techniques

Breast conservation therapy (BCT) is the procedure of choice for the management of the early stage breast cancer. However, its utilization has not been maximized because of logistics issues associated with the protracted treatment involved with the radiation treatment. Accelerated Partial Breast Irradiation (APBI) is an approach that treats only the lumpectomy bed plus a 1-2 cm margin, rather than the whole breast. Hence because of the small volume of irradiation a higher dose can be delivered in a shorter period of time. There has been growing interest for APBI and various approaches have been developed under phase I-III clinical studies; these include multicatheter interstitial brachytherapy, balloon catheter brachytherapy, conformal external beam radiation therapy and intra-operative radiation therapy (IORT). Balloon-based brachytherapy approaches include Mammosite, Axxent electronic brachytherapy and Contura, Hybrid brachytherapy devices include SAVI and ClearPath. This paper reviews the different techniques, identifying the weaknesses and strength of each approach and proposes a direction for future research and development. It is evident that APBI will play a role in the management of a selected group of early breast cancer. However, the relative role of the different techniques is yet to be clearly identified.

Prediction of Human Femoral Bone Strength Using Ultrasound Velocity and BMD: An In Vitro Study

Abstract: The stiffness and strength of cancellous bone are important in the management of skeletal diseases such as osteoporosis. These properties are a function not only of bone density but also of bone architecture, some measure of which can be provided by quantitative ultrasound. The ability of quantitative ultrasound and bone mineral density (BMD) to predict stiffness and strength of human femoral heads removed from live subjects during hip replacement was assessed. Stiffness and strength were measured using a uniaxial compression test. Ultrasound velocity was measured using the pulse-submersion technique (McClue CUBAResearch) and BMD using DXA (Lunar DPX-L). Ultrasound velocity (quantitative ultrasound) and stiffness varied with the three orthogonal directions, the highest significance being between the proximo-distal (PD) and antero-posterior (AP) directions (p < 0.0001) for stiffness and p = 0.0003 for velocity). Ultrasound velocity was significantly correlated with compressive bone strength (r = 0.76, p < 0.0001) and stiffness (r = 0.79–0.83, p < 0.0001). BMD was also significantly correlated with compressive strength (r = 0.82, p < 0.0001) and stiffness (r = 0.66–0.81, p < 0.001). Using multiple regression analysis both BMD and velocity were significant predictors of strength (r = 0.88, p = 0.0004 and 0.0054 respectively) and stiffness r = 0.92, p = 0.0001 and 0.0003 respectively). BMD and velocity were still independent significant predictors of both stiffness (r = 0.93, p < 0.0001 and 0.0001 respectively) and strength (r = 0.89, p < 0.0001 and 0.02) when they combined as a product (BMDn*Vm). This suggests that BMD measured using DXA, if used in conjunction with ultrasound velocity, may be able to improve osteoporosis risk assessment. The information about femur anisotropy may also be important for hip prosthesis and in vivo modelling.

Biot theory: a review of its application to ultrasound propagation through cancellous bone

To facilitate an understanding of the dependence of ultrasound velocity and attenuation upon the material and structural properties of cancellous bone, several theoretical concepts for ultrasound propagation have been adapted or developed, including the Biot theory and several scattering theories. Biot theory considers wave propagation through an elastic porous solid interspersed with fluid, considering the separate motion of the trabecular framework and morrow, respectively. The success achieved with the Biot theory has, to date, tended to be greater for the prediction of velocity than for attenuation. This article provides a review of the relevant literature, describing the physical parameters required for the Biot theory and their experimental determination. It is suggested that future developments should consider additional attenuation mechanisms, in particular, those due to scattering, local flow in microcracks, and surface roughness of the trabeculae.

The Ability of Ultrasound Velocity to Predict the Stiffness of Cancellous Bone In Vitro

The mechanical status of bones is an important consideration in skeletal pathological conditions such as osteoporosis, which result in fracture at predominantly cancellous bone sites. Density is a good predictor of the stiffness and strength of cancellous bone. However, these mechanical properties are also dependent on the cancellous bones architecture. The objective of this work was to investigate the ability of ultrasound velocity to predict the Youngs modulus of elasticity of cancellous bone. The cancellous bone specimens were 20 mm cubes from bovine femur and 21 mm diameter mediolateral cylinders cored from human calcaneus. Ultrasound velocity (V) and Youngs modulus (E) were determined in three orthogonal directions for the bovine cubes [anteroposterior (AP), mediolateral (ML), and proximodistal (PD)], and mediolaterally in the calcaneus. Apparent density (p) was determined after the other tests. Density alone explains 87.6% of the variance of Youngs modulus in human calcaneal and bovine femoral bone tested in the PD direction only. Velocity, however, explains 95% and a combination of density and velocity 97%. Velocity and stiffness are not random with respect to the three directions in the bovine specimens. Further, for each cube we obtained the mean of the three values of E and of V, and characterized each value of E and V by their deviation from their mean. There is an extremely strong positive correlation (r = 0.80) showing that the degree of deviation is consistent for E and V, and of the same sign. These results demonstrate that the velocity of ultrasound in cubes of cancellous bone can give structure-specific information. In particular, knowledge of both density and velocity allows better predictions of stiffness than do density or ultrasound velocity on their own. Because there are noninvasive methods of measuring density that do not depend on ultrasonic measurement the combination of these two measurements promises, eventually, to give improved assessment of a bones weakness and liability to fracture.

Orthogonal relationships between ultrasonic velocity and material properties of bovine cancellous bone

Osteoporotic fractures follow a period of asymptomatic bone loss and hence bone strength, predominantly in cancellous bone. An effective management of osteoporosis requires an understanding of the mechanical behaviour of cancellous bone including the anisotropic dependence. Ultrasound velocity (V) and elasticity (Youngs modulus, E) were measured in the three orthogonal directions in 20 mm cubes of bovine cancellous bone. Student paired t-test analysis showed significant variations in velocity and elasticity for the three orthogonal directions, the highest significance being between proximal-distal (PD) and antero-posterior (AP) directions with t = 5.63 and 4.09 for velocity and elasticity respectively, the lowest significance between medio-lateral (ML) and antero-posterior directions. Elasticity followed a power law relationship with apparent density (p) as reported in the literature, the exponent (b) being direction dependent (b = 1.98 +/- 0.21 for PD, 2.42 +/- 0.24 for AP and 2.03 +/- 0.17 for ML). The adjusted R2 values between elasticity and apparent density were highly significant (79.9% for PD, 81.9% for AP and 85.7% for ML). The relationship between velocity and apparent density is less significant in terms of the amount of variance explained (48.5% for PD, 63.3% for AP and 64.4% for ML). R2 values relating elasticity and velocity were again highly significant (79.4% for PD, 82.9% for AP and 80.5% for ML) and the coefficients, determined by regression analysis, independent of direction. Analysis of velocity, elasticity and density data for a range of reference materials demonstrated that experimentally measured longitudinal wave velocity could be reliably substituted into the bar wave equation (v = square root E/p). This implies that a combination of velocity and apparent density may be an improved indicator of bone fragility than density alone.

Narrow band ultrasonic frequency attentuation bone measurement system

In the apparatus disclosed herein, a bone containing body member to be tested is placed between a pair of transducers and a predetermined sequence of tone signals having frequencies spanning a range from 200 to 600 kilohertz is transmitted through the body member, and the set of values representing the amplitudes of the corresponding received signals are stored. The set of values obtained with the body member between the transducer is normalized using a set of values obtained from the same sequence without the body member in place thereby to generate a third set of values which are compensated for the response characteristics of the transducer and related interfaces. A value corresponding to the rate of change of attenuation with respect to frequency is then calculated from the third set of values and is adjusted for the bone thickness, this adjusted value being related to characteristics of the body member. The bone thickness is determined by a broadband pulse echo measurement.

The non-linear relationship between BUA and porosity in cancellous bone

There is growing interest in assessing the clinical value of ultrasound in the prediction and management of osteoporosis. However, the mechanism of ultrasound propagation in cancellous bone is not well understood. The Biot theory is one approach to modelling the interaction of sound waves with cancellous structure, and porosity is one of its input parameters. In this paper we report the relationship between broadband ultrasonic attenuation (BUA) corrected for specimen thickness (nBUA) and porosity in a porous Perspex cancellous bone mimic, a stereolithography cancellous bone mimic and in natural human and bovine tissue. nBUA and porosity have a non-linear parabolic relationship. The maximum nBUA value (nBUAmax) occurs at approximately 30% porosity in the Perspex mimic, approximately 70% in the stereolithography mimic and approximately 75% in natural cancellous bone. We discuss the effect of structure on the form of the nBUA-porosity relationship.