Biomedical subjects

Colin E Webber

Publications and source records attributed to Colin E Webber.

15 recordsLinked to original sources

PubMed2006

Radiation exposure for 'caregivers' during high-dose outpatient radioiodine therapy.

On 27 occasions, radiation doses were measured for a family member designated as the 'caregiver' for a patient receiving high-dose radioiodine outpatient therapy for differentiated thyroid carcinoma. For 25 of the administrations, patients received 3.7 GBq of (131)I. Radiation doses for the designated caregivers were monitored on an hourly basis for 1 week using electronic personal dosemeters. The average penetrating dose was 98 +/- 64 microSv. The maximum penetrating dose was 283 microSv. Measured dose rate profiles showed that, on average, one-third of the caregiver dose was received during the journey home from hospital. The mean dose rate profile showed rapid clearance of (131)I with three distinct phases. The corresponding clearance half-times were <1 h, 21 h and approximately 8 d. These components were associated, respectively, with the drive home, the clearance of radioiodine from an athyreotic patient and small quantities of (131)I contaminating the home.

Caregivers↗

PubMed2006

Photon absorptiometry, bone densitometry and the challenge of osteoporosis.

During the lifetime of Physics in Medicine and Biology, osteoporosis has been recognized as the cause of a major health burden for societies, particularly within developed countries. The health detriment is associated with the consequences of bone fractures and the subsequent increases in morbidity and mortality. Much of the credit for the current availability of means for identifying groups of subjects at risk of fracture and the provision of means for the effective treatment of excessive bone loss can be attributed to the technique of dual photon absorptiometry. In this review, the history of the development of techniques based on the interactions of x- and gamma-rays with bone is considered and the ultimate dominance of x-ray based absorptiometry is described. The advantages and disadvantages of current absorptiometric techniques are presented and the likely future path for bone measurement is outlined.

Absorptiometry, Photon↗

PubMed2006

Can body weight supported treadmill training increase bone mass and reverse muscle atrophy in individuals with chronic incomplete spinal cord injury?

This study evaluates the impact of 12 months of body weight supported treadmill training (BWSTT) on muscle and bone in individuals with spinal cord injury (SCI). Fourteen individuals who sustained an incomplete SCI at least 12 months before the study were recruited to participate in BWSTT 3 times/week for a total of 144 sessions. Thirteen individuals completed the study. The average age of subjects was 29 y, average time post-injury was 7.70 y (range: 1-24 y). Areal bone densities of the proximal and distal femur, proximal tibia, spine, and whole body were measured using dual-energy X-ray absorptiometry. Muscle cross-sectional area (CSA), volumetric bone density, and bone geometry at mid-femur and proximal tibia were measured using computed tomography. Serum osteocalcin and urinary deoxypyridinoline were measured at baseline and after 6 and 12 months of training. All other measures were made before and after training. Participants experienced significant increases in whole-body lean mass, from 45.9 +/- 8.7 kg to 47.8 +/- 8.9 kg (mean +/- SD; p < 0.003). Muscle CSAs increased by an average of 4.9% and 8.2% at the thigh and lower leg sites, respectively. No significant changes occurred in bone density or bone geometry at any site, or in bone biochemical markers. Whole-body bone density exhibited a small but statistically significant decrease (p < 0.006). BWSTT may therefore be a promising intervention for increasing muscle mass. Although 12 months of BWSTT did not increase bone density in individuals with chronic incomplete SCI, it did not appear to decrease bone density at fracture-prone sites.

Adult↗

PubMed2006

Dual X-ray absorptiometry model for characterizing water in the human forearm using multiple frequency bioimpedance analysis.

The purpose of this study was to develop a method for measuring intracellular (ICW) and extracellular water (ECW) in the human forearm using multiple frequency bioimpedance analysis (MFBIA). The approach was (i) to measure whole-body and forearm fat-free mass using dual X-ray absorptiometry (DXA); (ii) to use these measurements to estimate the fat-free mass (FFM) resistivity in both the forearm and in the whole body; and (iii) to use the ratio of these FFM resistivities to estimate the resistivity in the ICW and ECW compartments of the forearm. To first demonstrate the accuracy of the DXA software in differentiating lean body mass from fat and bone within a volume of tissue, ex-vivo bovine muscle tissue samples (n = 3) were used to approximate the physical properties of the human forearm. It was found that although the human whole-body software overestimates FFM, it was slightly underestimated by the small animal software. Using this technique, DXA measures of FFM were obtained from human volunteers (n = 11; age = 20 +/- 5 years; height = 170 +/- 12 cm; mass = 64 +/- 16 kg). These measures were used in conjunction with MFBIA measures of impedance of the whole body and of the forearm to determine the resistivities of the ICW and ECW compartments of the forearm, namely 375.8 +/- 25.2 ohms cm and 55.6 +/- 3.7 ohms cm, respectively. These were used in MFBIA equations to calculate the ICW, ECW, and total arm water (TAW) volumes of the human forearm. The calculated TAW and the ECW (+/- SD) volume fraction (667.29 +/- 200.15 mL and 0.169 +/- 0.039 mL, respectively) were in agreement with literature values. MFBIA results were compared with those obtained using nuclear magnetic resonance relaxometry (NMRR). MFBIA was performed on 15 subjects before and after an intense maximal handgrip exercise to estimate changes in water volume in muscle. Following exercise, the total and intracellular water of the forearm increased on average by 8% +/- 3% and 10% +/- 4% (mean +/- SD), respectively. In 5 healthy volunteers, MFBIA and NMRR were performed before and after a similar exercise of the forearm muscle. The changes with exercise of intracellular and total arm water volumes as measured by MFBIA were estimated. The percent increases in total water were found to be 9.4% +/- 4.2% and 9.4% +/- 2.6% and in intracellular water were found to be 10.6% +/- 4.6% and 12.0% +/- 2.8% (mean +/- SD) for NMRR and MFBIA, respectively. The results show that the exercise-induced changes in ICW and TAW determined with the MFBIA model are consistent with those observed with NMRR and radiotracer literature.

Absorptiometry, Photon↗

PubMed2005

The study of age influence on human bone lead metabolism by using a simplified model and X-ray fluorescence data.

Long term lead metabolism in the human body has never been fully understood due to the lack of human data in this area. The technological improvement of bone lead measurement systems has made bone lead data of substantial populations available. In this study, a set of X-ray fluorescence bone lead data was used to test Leggett's lead metabolism model (R. W. Leggett, Environ. Health Perspect., 1993a, 101, 598-616), especially the model of metabolism in bone. The data set includes the bone lead concentration of 539 occupationally exposed workers, of whom 327 were measured twice in five years. The bone lead concentrations of both cortical bone (tibia) and trabecular bone (calcaneus) were obtained by Cd-109 gamma-ray induced XRF measurement. The histories of blood lead concentration for these workers were used to regulate the input file of the model. The results show that the bone lead concentrations predicted by Leggett's model greatly underestimate the measured values, especially for older workers. This data set was then organized into five age groups. A new simplified model was applied to estimate the lead transfer rates between blood and lead compartments for these age groups. The original transfer rates and the new transfer rates are compared, and the differences are discussed. When the transfer rates derived from measured bone lead data were put into the input file of the model to replace the existing parameters, the predicted values were much closer to the measured values for both cortical bone and trabecular bone.

Adult↗

PubMed2005

Grid search: an innovative method for the estimation of the rates of lead exchange between body compartments.

This paper describes a new metabolic model for lead in humans and a numerical method to solve the differential equations governing the transfer of lead between body compartments. The model includes 3 compartments-cortical bone, trabecular bone and blood-and accounts for absorption from external sources and release through excreta. Estimation of the lead kinetics parameters was performed using the grid search method. Grid search is a simple procedure that allows the fit of an arbitrary function to data. When applied to data from occupationally exposed populations, the method demonstrated the exposure dependence of the rate of lead uptake and release by the compartments in the model. The results confirm and refine previous observations of the significant decrease of the transfer rate of lead from cortical bone to blood with increasing exposure, as expressed by half-lives of (in years): 6.5 +/- 0.7, 13.6 +/- 1.0 and 47.5 +/- 2.3, in subgroups of low, intermediate and high long-term lead exposure. A similar trend was observed for the transfer rate from trabecular bone, which could be statistically supported for the first time. Reduction by a factor of 7 to 10 in the default values assigned to the fractional removal of lead from cortical bone to plasma in existing metabolic models was also predicted. These results can be used in the review of current metabolic models for lead, which are still based on the assumption of a constant rate of lead removal from bone, independently of the level of exposure.

Adult↗

PubMed2005

Impact of occupational exposure on lead levels in women.

In 1994, 207 women participated in a study designed to examine the effects of occupational exposure and various lifestyle factors on bone and blood lead levels. In vivo measurements of Pb concentrations in tibia were performed by X-ray fluorescence. All 108 former smelter employees and 99 referents provided blood samples and answered a questionnaire on lifestyle characteristics and the relevant medical history. Lead concentrations in tibia and blood were significantly higher in the exposed group. The difference in mean bone Pb concentrations of the two groups is markedly greater than the difference in the mean blood Pb concentrations, supporting the view that bone Pb measurements are a more reliable determinant of Pb body burden. Chronic exposure did not result in any statistically significant differences in adverse pregnancy outcomes. A significantly lower age at the onset of menopause in occupationally exposed women may suggest that Pb causes adverse changes in the pattern of estrus and menses. The exposed women had lower bone Pb concentrations than those found in most studies on predominantly male workers. Blood Pb concentrations remain increased in women long after the cessation of occupational exposure, reflecting the importance of the endogenous exposure. The endogenous exposure relation found for postmenopausal exposed women is consistent with data on male smelter workers, whereas the relation found for premenopausal women is significantly lower. This suggests that sex plays an important role in the metabolism of lead, and current models of exposure extrapolated from male data may be inappropriate for use on women.

Adult↗

PubMed2005

Musculoskeletal changes in women with spinal cord injury: a twin study.

Bone mineral density (BMD), bone geometry, and muscle cross-sectional area (CSA) were investigated in two sets of monozygotic female twins, where one of each pair had sustained a spinal cord injury (SCI). Twin pair 1 (TP1) and twin pair 2 (TP2) were 32 and 47 yr old and were 7 and greater than 20 yr postinjury, respectively. BMD was measured using dual-energy X-ray absorptiometry. Computed tomography was used to measure volumetric BMD, bone geometry, and muscle CSA of the thigh and calf. For the SCI twin of TP1, BMDs of hip, distal femur, proximal tibia, and spine were 59.5, 46.6, 53.1, and 93.3%, respectively, of values of the noninjured twin. For TP2, corresponding values in the SCI twin were 36.2, 35.9, 39.2, and 62.2%, respectively, of the non-SCI twin. Average muscle CSAs of the SCI twins were 31.2+/-2.3% and 31.0+/-6.1% of the values for their non-SCI twin, indicating that muscle CSAs were reduced by 70%. Among the SCI twins, volumetric BMDs were 83.4+/-2.4% and 87.0+/-3.45% of the non-SCI twins' values. Moments of inertia in the SCI twins ranged from 62.4 to 97.9% of the non-SCI twins' values at mid-femur and calf. This study reveals that in addition to the declines in muscle CSA and BMD, important changes in bone geometry occur in women after SCI.

Absorptiometry, Photon↗

PubMed2003

Predicting the failure load of the distal radius.

The distal radius is an important site for the early detection of patients at risk for fracture. Since measuring bone strength in vivo is not possible, we evaluated which bone assessment method of the forearm would best predict failure load of the distal radius and computed a factor of risk for wrist fracture (Phi wrist). Thirty-eight cadaveric forearm specimens were measured by five different techniques to assess bone density, bone mineral content, geometry and trabecular structure at the distal forearm. The bone assessment techniques included dual-energy X-ray absorptiometry (DXA) of the radius, peripheral quantitative computed tomography (pQCT) of the 4% and 20% distal sites of the radius, DXA of the phalanges, digital X-ray radiogrammetry of the forearm (DXR-BMD), and quantitative ultrasound of the radius. The failure load of each excised radius was determined by simulating a fall on an outstretched hand. The pQCT measurements of polar stress-strain index and cortical content explained the greatest portion of variance in failure load (r2=0.82-0.85). Bone mineral content measures were generally better predictors of failure load (r2=0.53-0.85) than the corresponding volumetric or areal bone mineral density values (r2=0.22-0.69) measured by either pQCT or DXA. Multiple regression analysis showed that the addition of a bone geometry measure improved the ability of a bone density measure alone to predict failure load. There was high variability in the ability of different techniques and different variables within a given technique to predict failure load. Estimates of the factor of risk for wrist fracture (Phi wrist) revealed that the women in this study would have been likely to fracture their distal radius upon falling from a standing height (Phi wrist= 1.04), whereas the men would have likely withstood the impact without fracturing their wrist (Phi wrist= 0.79).

Absorptiometry, Photon↗

PubMed2003

Hormone replacement therapy improves distal radius bone structure by endocortical mineral deposition.

Hormone replacement therapy (HRT) produces a small increase in bone mineral density (BMD) when measured by dual energy X-ray absorptiometry (DXA). The corresponding decrease in fracture risk is more impressive, implying that other factors that contribute to bone strength are favourably modified by HRT. We investigated, using peripheral quantitated computed tomography (pQCT), the changes produced by HRT in both the distribution of mineral between cortical and trabecular bone and the changes produced by HRT in the apparent structure of trabecular bone, expressed as average hole area and apparent connectivity. Twenty-one postmenopausal women starting HRT and 32 control women were followed for 2 years, with distal radius pQCT measurements every 6 months. HRT prevented the loss of total bone mass seen in controls (p < 0.02). HRT also produced an apparent rapid loss of trabecular bone mass within the first 6 months of the study (p < 0.02), with an associated rapid loss in the apparent connectivity (p = 0.034). Average hole area also increased but not to a statistically significant extent. Exogenous estrogen apparently fills small marrow pores close to the endocortical surface, such that the pQCT-defined boundary between trabecular and cortical bone is shifted in favour of cortical bone. Trabecular bone structure indices are adversely affected, as the central, poorly interconnected trabecular bone with greater than average marrow spaces constitutes a greater fraction of the remaining trabecular bone. This study suggests that the improvements in fracture risk resulting from HRT are explained by a reversal of net endocortical resorption of bone.

Absorptiometry, Photon↗

PubMed2003

In vivo measurement of apparent trabecular bone structure of the radius in women with low bone density discriminates patients with recent wrist fracture from those without fracture.

The purpose of this cross-sectional case-control study was to determine whether indices of bone structure at the 4% site of the radius discriminate women who have sustained a recent low-energy fracture of the contralateral distal radius (n = 21) from women with similar bone density and no history of fracture (n = 21). Images of the distal forearm were acquired using peripheral quantitative computed tomography (pQCT) and were analyzed using in-house-developed software to determine indices of trabecular bone structure (average hole size [H(A)], maximum hole size, and connectivity index). The same images were analyzed using commercial software to determine bone density, mass, geometry, and torsional strength. The fracture group had significantly larger H(A) (p = 0.03). No other bone variable differed between groups. Individual H(A) values were compared to the mean value for young adult women (n = 42). The odds ratio (95% confidence interval) associated with an H(A) >2 SDs above the young adult mean was 5.4 (1.2-24.3). Thus, estimation of in vivo trabecular bone porosity by measuring the average diameter of the pQCT-imaged marrow spaces in the ultradistal radius identifies individuals with low bone mass most at risk for osteoporotic fracture.

Bone Density↗

PubMed2003

A 6-mo home-based exercise program may slow vertebral height loss.

Twenty-one of 46 postmenopausal women were assigned to a home-based exercise program consisting of 60 min of exercise, 3 d/wk. The 25 nonexercisers continued usual daily activities. Each woman had at least one prevalent vertebral fracture and suffered from osteoporosis as defined by the application of WHO criteria to lumbar spine bone mineral density. Vertebral heights were measured using bone densitometry at baseline and 12 mo later. Vertebrae T9 to L4 were all identified for each of the 46 subjects in both the baseline and end-of-study lateral scans. The change in mean vertebral height over the course of the study was -0.3 mm anteriorly, -0.7 mm at the mid-location, and -0.4 mm posteriorly for the nonexercisers. For the exercisers, the corresponding changes were +0.1 mm anteriorly, -0.3 mm at the mid-location, and +0.2 mm posteriorly. The benefit of exercise in preserving vertebral morphometry in patients with osteoporosis deserves further investigation.

Aged↗

PubMed2003

Effects of metal implants on whole-body dual-energy x-ray absorptiometry measurements of bone mineral content and body composition.

OBJECTIVE: The purpose of this study was to evaluate the influence of metal implants on measurements of bone mineral content and body composition by x-ray-based dual-photon absorptiometry. METHODS: Four whole-body dual-photon absorptiometry scans were performed on 13 participants with metal rods either present or absent during the scans. The influence of the amount of metal (50 g, 100 g and 150 g), the proximity of the metal rod to the x-ray source and the reproducibility of any metal-induced effects were evaluated by altering the position or the size of the metal rod used, or both. RESULTS: The presence of metal rods weighing 100 g or 150 g significantly increased reported total body mass and bone mineral content (p < 0.034). Soft-tissue mass was increased when the scan included the 100-g rod (p < 0.003). The proximity of the metal to the x-ray source did not have a significant influence on the body composition changes induced by the metal. The effects of the metal rods on body composition variables were reproducible. CONCLUSION: The presence of metal rods inflated body composition variables measured by dual-photon absorptiometry; however, the effects are reproducible during repeat scans of an individual patient. Metal had the largest impact on whole-body bone mineral content, causing errors of 1.5%-3%.

Absorptiometry, Photon↗

PubMed2002

Evaluation of a novel structural model to describe the endogenous release of lead from bone.

The aim of this paper was to assess the endogenous release of lead from bone to blood, in 204 exposed subjects. resuming their duties after a 10-month strike in a primary lead smelter in 1991. In vivo 109Cd K X-ray Fluorescence (109Cd K XRF) was used to measure the bone lead concentration in tibia and calcaneus in the smelter, in 1994 and five years later. The 1994 data were used to derive the post-strike bone lead concentrations retrospectively from the significant association between bone lead and the cumulative blood lead index (CBLI). When a linear model was used to predict the current blood lead upon the level of lead in bone, structural analysis of the data produced slopes for tibia (2.0, 95% CI 1.66-2.54) and calcaneus (0.19, 95% CI 0.16-0.23) that were significantly higher than those predicted by the commonly used simple linear regression method, for tibia (0.73, 95%, CI 0.58-0.88) and calcaneus (0.08, 95% CI 0.06-0.09). This suggests that more lead than previously predicted by regression is released from bone to blood. Furthermore, the structural analysis of the data produced an estimation of the contribution of the bone lead stores to the bloodstream that was more consistent with the 1999 epidemiological data than did the regression estimation. Moreover, a non-linear relationship between tibia lead and blood lead was suggested from the assumption checking procedures for regression. When a non-linear regression model was fit to the data, the method produced estimates of important parameters in human lead kinetics, namely the blood lead saturation constant, showing a good agreement with current knowledge of lead metabolism. Finally, the likelihood of a non-linear bone lead release seems to be supported by the recently described dependence of the half-life of lead in bone on age and intensity of occupational exposure.

Adult↗

PubMed2002

North American male reference population for speed of sound in bone at multiple skeletal sites.

Alternatives to dual-energy X-ray absorptiometry (DXA) have been sought to increase access to low-cost osteoporosis risk assessment. Early quantitative ultrasound (QUS) systems measured speed of sound (SOS) and broadband ultrasound attenuation (BUA) at the calcaneus, and these were demonstrated to be good predictors of hip fracture risk. Recent studies have demonstrated the usefulness of other peripheral sites to assess bone status. The Sunlight Omnisense (Sunlight Medical, Rehovot, Israel) is a portable, inexpensive QUS device capable of multiple-site SOS measurement. To provide a robust male reference database, 588 healthy Caucasian males aged 20-90 yr were recruited from 6 centers across North America. SOS measurements were taken at the distal 1/3 radius, proximal third phalanx, midshaft tibia, and fifth metatarsal. A female reference database has previously been collected at North American sites. The results indicate that SOS in males exhibits an age-related decline beginning in the fifth decade at the radius, phalanx, and metatarsal, whereas the tibial SOS remains nearly constant until the ninth decade. Although females reach a higher-peak SOS than males at most sites, SOS is higher in males at all sites after the sixth decade, as a result of a more gradual decline in SOS. Longitudinal monitoring of healthy men should be performed to confirm these cross-sectional results.

Adult↗