Biomedical subjects

P H Nicholson

Publications and source records attributed to P H Nicholson.

26 records · Page 2Linked to original sources

PubMed1997

Low-frequency ultrasonic velocity measurements in human calcaneal trabecular bone.

Ultrasonic velocities were measured in three orthogonal directions for 17 cubes (2 x 2 x 2 cm approximately) of defatted calcaneal trabecular bone using a novel pulse transmission method with 37 kHz transducers. Since the wavelength was greater than the cross-sectional dimensions of the specimens, it was assumed that bar wave propagation was occurring and this allowed Young's modulus to be derived from velocity and apparent density. Velocity varied from 1585 +/- 104 m s-1 in axis 1 (proximo-distal) to 947 +/- 131 m s-1 in axis 3 (medio-lateral). Thus, the velocities measured in axis 3 were considerably lower than those typically seen in clinical measurements of the calcaneus. The derived Young's moduli ranged from 834 +/- 248 MPa (axis 1) to 299 +/- 98 MPa (axis 3), and were comparable in magnitude to some previously published data from mechanical testing. The results suggest that velocities measured with this technique do indeed correspond to bar velocities, and consequently that low-frequency ultrasound can be used to directly predict the mechanical properties of trabecular bone specimens in vitro. On the other hand, given the marked differences in geometry, wavelengths used and the presence of fat, it raises questions about the validity of applying the bar wave equation in the context of higher-frequency velocity measurements in the intact calcaneus in vivo, despite the fact that this has been found to be useful by a number of previous workers. This may require a review of the clinical implications of high-frequency ultrasound data.

Adult↗

PubMed1997

Determinants of age-associated changes in os calcis ultrasonic indices in elderly women: potential involvement of geriatric hyposomatotropism in bone fragility.

OBJECTIVE: ultrasound measures a clinically relevant property of bone strength in addition to and distinct from bone mass. The aim of the present study was to examine the effects of healthy ageing on ultrasound measurements of the calcaneus. DESIGN: cross-sectional study. STUDY PARTICIPANTS: a sample of 177 community-dwelling healthy women aged 70-87 years. Exclusion criteria were diseases or medications known to affect the musculoskeletal system or the somatotrophic axis. MEASUREMENTS: serum levels of 1,25-dihydroxyvitamin D3 and insulin-like growth factor-I (IGF-I) were measured by radioimmunoassay, serum 25-hydroxyvitamin D3 (25(OH)D3) was determined by competitive binding assay and serum parathyroid hormone was assessed immunochemically. Isometric and isokinetic quadriceps strength were evaluated using a Cybex II system. Calcaneal ultrasound indices--broadband ultrasound attenuation (BUA) and speed of sound (SOS)--were measured with an Achilles system. RESULTS: we found a significant decrease with ageing in BUA and SOS (-0.5 and -1.3% per year, respectively), suggesting a continuing loss of bone quality. Quadriceps strength, serum IGF-I and 25(OH)D3 constituted the best predictors of BUA, while IGF-I was the only parameter found to be independently associated with SOS. CONCLUSION: these findings suggest that, among other factors, the activity of the growth hormone-IGF-I axis is of importance for skeletal integrity. Age-related bone fragility may, in part, be related to geriatric hyposomatotropism.

Aged↗

PubMed1997

Prediction of vertebral strength in vitro by spinal bone densitometry and calcaneal ultrasound.

Spinal bone mineral density (BMD) measurements and calcaneal ultrasound were compared in terms of their ability to predict the strength of the third lumbar vertebral body using specimens from 62 adult cadavers (28 females, 34 males). BMD was measured using dual X-ray absorptiometry (DXA) in both vertebra and calcaneus. Quantitative computed tomography (QCT) was used to determine trabecular BMD, cortical BMD, cortical area, and total cross-sectional area (CSA) of the vertebral body. Bone velocity (BV) and broadband ultrasonic attenuation (BUA) were measured in the right calcaneus. Vertebral strength was determined by uniaxial compressive testing. Vertebral ultimate load was best correlated with DXA-determined vertebral BMD (r2 = 0.64). Of the QCT parameters, the best correlation with strength was obtained using the product of trabecular BMD and CSA (r2 = 0.61). For vertebral ultimate stress, however, the best correlation was observed with QCT-measured trabecular BMD (r2 = 0.51); the correlation with DXA-determined BMD was slightly poorer (r2 = 0.44). Calcaneal ultrasound correlated only weakly with both ultimate load and stress with correlation coefficients (r2) of 0.10-0.17, as did calcaneal BMD (r2 = 0.18). Both spinal DXA and spinal QCT were significantly (p < 0.001) better predictors of L3 ultimate load and stress than were either calcaneal ultrasound or calcaneal DXA. Multiple regression analysis revealed that calcaneal ultrasound did not significantly improve the predictive ability of either DXA or QCT for L3 ultimate load or stress. Calcaneal DXA BMD, bone velocity, and BUA correlated well with each other (r2 = 0.67-0.76), but were only modestly correlated with the DXA and QCT measurements of the vertebra. These data indicate that spinal DXA and spinal QCT provide comparable prediction of vertebral strength, but that a substantial proportion (typically 40%) of the variability in vertebral strength is unaccounted for by BMD measurements. Ultrasonic measurements at the calcaneus are poor predictors of vertebral strength in vitro, and ultrasound does not add predictive information independently of BMD. These findings contrast with emerging clinical data, suggesting that calcaneal ultrasound may be a valuable predictor of vertebral fracture risk in vivo. A possible explanation for this apparent discrepancy between in vivo and in vitro findings could be that current clinical ultrasound measurements at the calcaneus reflect factors that are related to fracture risk but not associated with bone fragility.

Absorptiometry, Photon↗

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↗

PubMed1994

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.

Adult↗

PubMed1993

Vertebral deformity, bone mineral density, back pain and height loss in unscreened women over 50 years.

Bone mineral density (BMD) was measured in the lumbar spine using dual-energy X-ray absorptiometry in 222 unscreened women (aged 50-82 years), and information on back pain and historic loss of standing height was obtained at interview. Vertebral morphometry was performed on lateral spinal radiographs. The shape of the vertebral body was quantified using appropriate vertebral shape indices (VSIs), and vertebral deformities were identified using thresholds defined in terms of the means (M) and standard deviations (SD) of these VSIs for the whole group. Severity of deformity was defined as either grade 1 (M+2SD < VSI < M+3SD), grade 2 (M+3SD < VSI < M+4SD or grade 3 (VSI > M+4SD). Subjects with grade 1 vertebral deformities were older than subjects without such deformities, but did not have a reduced age-related Z-score of BMD. Grade 2 wedge and concave deformities were associated with a reduced age-related Z-score of BMD, suggesting that the aetiology of such deformities is closest to conventional concepts of 'osteoporotic fracture'. Grade 3 deformities were associated with neither increased age nor decreased BMD. Stature decreased in these subjects with age. Subjects reporting historic height loss had a higher mean number of wedge deformities. Subjects with back pain did not have a higher incidence of vertebral deformity than subjects without, confirming that many deformities were asymptomatic. Neither back pain nor historic loss of height were found to be associated with low spinal BMD.

Absorptiometry, Photon↗

PubMed1993

Vertebral morphometry in women aged 50-81 years.

Vertebral dimensions and vertebral shape indices (VSI) were investigated in T4-L4 in 926 females aged 50-81 years. The most consistent finding was the increase of inferior antero-posterior dimension with age. Wedging and concavity also increased with age but the changes were not significant at all vertebral levels. The value of VSIs also varied with level. Thus a particular degree of VSI, considered normal at one level or at one age, would be outside the reference range at a different level or age group. The number of subjects identified as osteoporotic by skewness (5.4%) or in excess of three standard deviations from the mean (6.5%) was much lower than in recent reports from North America. The number of subjects contributing to a skewed distribution increased with age from 0.5% at 55-59 years to 10.0% at 75-79 years. Change with age in the antero-posterior dimension could increase load-bearing area in older subjects, but the decline in bone density will be increased as a declining bone mineral content occupies a larger volume.

Aged↗

PubMed1993

A computerized technique for vertebral morphometry.

A new technique for morphometric measurement of vertebral bodies has been described, in which a computerized image analysis system was used to digitize and measure standardized lateral radiographs of the thoracic and lumbar spine. The sources of error in the radiographic system and the image analysis system were assessed using vertebral phantoms and test images. Oblique projection in the radiographic image of a vertebra did not produce a significant error in the measured area. The radiographic magnification was approximately 35%. Optical non-uniformity was detected in the image analysis system, and was ascribed to the lens optics. The maximum intra-observer and inter-observer variations in vertebral area were 3.1% and 5.3% respectively for experienced observers. The technique is applicable to clinical studies of large populations, and has value in investigating vertebral deformity in the management of metabolic bone disease.

Female↗