Search PubMed⌕ Search

Biomedical subjects

C M Langton

Publications and source records attributed to C M Langton.

At least 37 records · Page 2Linked to original sources
PubMed1997

Prediction of human femoral bone strength using ultrasound velocity and BMD: an in vitro study.

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 (McCue 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 were 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.

Absorptiometry, Photon↗
PubMed1997

Development of a cancellous bone structural model by stereolithography for ultrasound characterisation of the calcaneus.

A novel method for the development of a user-defined structural model simulating cancellous bone of the human calcaneus is described using stereolithography (SL). The digital image of a cancellous bone section was modified by skeletonisation and dilation to produce a structural model of uniform wall thickness, determined by the resolution of the stereolithography system. Six SL models were produced using the same data file. The SL models were assessed using the McCue CUBAclinical ultrasound bone densitometer. The broadband ultrasound attenuation (BUA) and velocity (VOS) values obtained were commensurate with the commercial phantom provided with the CUBAclinical system. The intra- and inter-sample variability for the six SL models were similar at 5% for BUA and 2.5% for VOS. Stereolithography offers the potential to firstly, simulate perforation and thinning of cancellous bone associated with osteoporosis, and secondly, to evaluate the dependence of ultrasonic and mechanical parameters upon cancellous bone structure.

Anisotropy↗
PubMed1997

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 bone's architecture. The objective of this work was to investigate the ability of ultrasound velocity to predict the Young's 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 Young's 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 Young's 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 bone's weakness and liability to fracture.

Analysis of Variance↗
PubMed1997

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.

Age Factors↗
PubMed1997

A phantom for evaluating bone mineral density of the hand by dual-energy x-ray absorptiometry.

Dual-energy x-ray absorptiometry (DXA) is a precise, widely used method for measuring bone mineral density (BMD), usually of the lumbar spine and femoral neck. Recent developments, such as a lower x-ray tube current and pixel by pixel analysis, enable smaller bones and thinner tissues volumes, as in the hand, to be measured. Measurements of hand bone mineral content (BMC) and BMD could be useful in assessing disease severity in early rheumatoid arthritis and in monitoring disease progression and response to therapeutic intervention. A phantom is required for evaluating the software, measuring long-term precision and comparing with other DXA methods. This note describes the design and evaluation of a hand phantom for use on a Lunar DPX-L dual-energy x-ray absorptiometer. The phantom consists of three sections representing the metacarpals, and proximal and distal phalanges, using aluminum and Perspex as the bone and lean tissue equivalents respectively. The BMD of the three sections is approximately 1.0, 0.6 and 0.3 g cm-2. The phantom demonstrates limitations in the potential accuracy of BMD determination at low densities using the Small Animal Software on the Lunar DPX-L. Improved recognition of low-density regions was obtained with the Lunar EXPERT with precision values of 0.9, 1.1 and 2.0% for the three sections of the phantom respectively.

Absorptiometry, Photon↗
PubMed1997

Assessment of bone status using the contact ultrasound bone analyser.

Broadband ultrasound attenuation (BUA) was measured at the calcaneum in 367 healthy white schoolchildren (193 girls and 174 boys) aged 6-15 years. The mean calcaneal BUA increased with age and was significantly related to age, height, and weight. Measurement of calcaneal BUA may be helpful in the radiation free assessment of childhood disorders associated with increased fracture risk.

Adolescent↗
PubMed1997

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.

Aged↗
PubMed1997

Male and female normative data for ultrasound measurement of the calcaneus within the UK adult population.

The establishment of accurate normative data for specific populations is required before ultrasound bone densitometry may be considered for routine clinical application. A single general practice was utilized, representing both rural and urban populations, to recruit 169 male and 210 female subjects in the age range 20-80 years. Measurements of broadband ultrasound attenuation (BUA) and velocity (VOS) of the left calcaneus were undertaken using the McCue CUBAClinical II system. Two descriptive statistical models were used, mean and 95th percentile, and regression analysis. The female data for both BUA and VOS illustrated peak values in the 30-39 years age group, falling steadily thereafter. For male BUA and VOS data there was less evidence of an age related dependence. Upon analysis of previous normative studies and current data it is evident that there is considerable variability. In addition to different commercial systems being utilized, there is a lack of consistency in study design and method of subject recruitment. The need for accurate calibration and cross-calibration methods for commercial ultrasound bone densitometers is therefore of paramount importance to enable clinical interpretation of ultrasound measurements to be performed.

Adult↗
PubMed1997

The in vitro measurement of ultrasound in cancellous bone.

This paper describes our recent findings on the relationships between ultrasonic measurements (velocity and broadband ultrasonic attenuation) and some physical properties of human and bovine cancellous bone (density, trabecular orientation and Young's modulus of elasticity). We have found velocity to be an extremely effective measure of Young's modulus (R2 approximately 95%). When velocity is combined with a measure of apparent density R2 improves to approximately 97%. We demonstrate that this is due to the ability of ultrasound velocity to measure structural anisotropy in the tissue. The findings for broadband ultrasonic attenuation (BUA) are more complex. In the same specimens BUA is not as good as velocity at predicting Young's modulus (R2 approximately 62%). We demonstrate that this is due to a non-linear relationship between BUA and tissue density (porosity). However there is a strong indication that BUA is also affected by variation in cancellous structure.

Aged↗
PubMed1997

Maximising the cost effectiveness of BMD referral for DXA using ultrasound as a selective population pre-screen.

Bone mineral density (BMD) referral for dual energy X-ray absorptiometry (DXA) is generally based upon agreed clinical referral criteria (CRC). The aim of this study was to determine whether ultrasound measurements of Broadband UI-trasound Attenuation (BUA) and velocity (VOS) provide a superior selective pre-screen referral method for BMD assessment by DXA. 107 women aged 60-69 years (64.2 +/- 2.8) had BMD measurements at lumbar spine and right femoral neck along with ultrasound BUA and VOS measurements of the left calcaneus. Each subject completed an extensive clinical and social questionnaire to ascertain those who would have met one or more of the five general clinical referral criteria adopted by our Centre. Each subject was classified by DXA using the WHO criteria as normal, osteopenic or osteoporotic at lumbar spine or femoral neck. The cost per osteoporotic subject correctly identified was calculated. As a reference, based upon DXA measurements alone on all 107 subjects, the cost per osteoporotic subject identified would be Ponds 185. If subjects had been referred using the clinical referral criteria the cost is Ponds 171. For assessment of referral by BUA or VOS, an additional charge for ultrasound measurement of all subjects was incorporated. At a BUA of 60 dB MHz-1 the cost per osteoporotic subject is Ponds 107. Ultrasound velocity or a combination of BUA or VOS with clinical referral criteria did not provide a significantly reduced cost than the current clinical referral criteria alone. This study has demonstrated that BUA provides an improved referral procedure to that currently achieved with clinical referral criteria and supports the concept of BUA being used as a selective pre-screen for DXA in 7th decade subjects.

Absorptiometry, Photon↗
PubMed1996

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 (Young's 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.

Animals↗
PubMed1996

Prediction of mechanical properties of the human calcaneus by broadband ultrasonic attenuation.

Broadband ultrasonic attenuation (dB MHz cm-1, nBUA) was determined for specimens from 20 human calcanei, along with apparent density, elasticity (Young's modulus), and compressive strength. The calcanei were modified to provide "whole" (only soft tissue removed), "core" (mediolateral cores corresponding to in vivo measurement region), "can" (cortical end plates removed from core), and "def" (core defatted) samples. The nBUA values for the various modifications were highly correlated. The presence of the cortical endplates creates a significant nBUA, probably due to complex phase interactions. nBUAcan was a good predictor of elasticity (R2 = 75.7%) and strength (R2 = 73.6%). Apparent density was a better predictor of the mechanical variables than nBUA, with R2 values of 88.5% for elasticity and 87.6% for strength. The morphological anisotropy defined by "fabric" for the specimens was extremely uniform. The coefficient of variation in nBUA (40.5%) and compressive strength (64.4%) was significantly greater than for apparent density (23.5%) and fabric (6.7%). It is well known that a power law relationship exists between apparent density and elasticity or strength in cancellous bone. An interesting finding in this work is that there also appears to be a power law relationship between nBUA and apparent density, with an exponent of approximately 2, which, in the light of clinical implications, warrants further investigation.

Aged↗
PubMed1996

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.

Animals↗
PubMed1996

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.

Adult↗