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Biomedical subjects

C E Webber

Publications and source records attributed to C E Webber.

At least 73 records · Page 4Linked to original sources
PubMed1991

Bone mineral measurements and Tc-99m IDP retention in the dog.

The reproducibility of various procedures for the noninvasive assessment of the skeleton in dogs has been measured. In one animal, dual photon measurements of bone mineral mass were made in the whole body, the lumbar spine, and the proximal femur on 10 occasions during a 15-week period. In two other dogs, repeat measurements of Tc-99m imidodiphosphate (IDP) retention were made. For the total body and the proximal femur, the reproducibilities were 2 and 2.5%, respectively. The reproducibility of the lumbar spine was approximately 10% and was influenced by the variable fraction of the posterior spinous processes included in the measurement. The reproducibility of IDP retention measurements was not established. It was about 8% when all 10 measurements were considered but fell to 1.5% when three consecutive measurements were excluded. Dual photon measurements of the whole body and the proximal femur can be used to assess bone mass changes in the canine skeleton.

Absorptiometry, Photon↗
PubMed1991

The effect of amenorrhea on calcaneal bone density and total bone turnover in runners.

To examine in athletes the effect of long-term amenorrhea on the skeleton, measurements of calcaneal density and whole body retention of 99mTc-imidodiphosphate were made in 42 women who could be allocated to one of 3 groups defined by their level of physical activity and by menstrual status. There was no difference in bone density between eumenorrheic normoactive females and either eumenorrheic or amenorrheic athletes. However, calcaneal density was significantly greater for each group than for previously measured sedentary controls. Total body bone turnover was greater in both eumenorrheic and amenorrheic athletes than in eumenorrheic normoactive women. Sustained, intense physical activity does not significantly increase calcaneal bone density over and above the increase associated with normal levels of activity. This is despite a significant increase in the rate of total body bone mineral turnover.

Adult↗
PubMed1991

Accuracy of measurements of small changes in soft tissue mass by use of dual-photon absorptiometry.

Dual-photon absorptiometry (DPA) has recently been applied to the assessment of body composition. To evaluate the accuracy of DPA in detecting small changes in the lean soft tissue mass, we performed DPA with the use of the Norland 2600 Dichromatic densitometer on six healthy adult males before and after a 30-ml/kg transfusion of saline and before and after exercise in a warm environment, resulting in a greater than or equal to 1-kg weight loss. Absolute weight [baseline pretransfusion r2 = 0.999, standard error of estimate (SEE) = 590 g; posttransfusion r2 = 0.999, SEE = 300 g; baseline pretranspiration r2 = 0.999, SEE = 230 g; posttranspiration r2 = 0.999, SEE = 240 g] was accurately reflected in DPA total mass. Weight changes due to transfusion were poorly reflected by changes in DPA total mass (r2 = 0.417, SEE = 404 g). However, changes posttranspiration were accurately reflected in the DPA total mass (r2 = 0.886, SEE = 106 g posttranspiration). Similarly, weight changes due to transfusion were poorly measured by changes in DPA soft mass (r2 = 0.478, SEE = 365 g), but changes posttranspiration were highly correlated with DPA soft mass changes (r2 = 0.909, SEE = 92 g). Weight changes were not reflected by changes in the DPA lean soft tissue mass (r2 = 0.006, SEE = 1,737 posttransfusion, r2 = 0.094, SEE = 1,038 g posttranspiration). DPA-derived nonfat mass was highly correlated with skinfold-derived nonfat mass (r2 = 0.96, SEE = 2,400 g). Accuracy of total and soft tissue measurements implied correct mineral mass assessment.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1991

The interchangeability of radioisotope and X-ray based measurements of bone mineral density.

Lumbar spine and femoral neck bone mineral density (BMD) were measured with a Novo radioisotope based dual photon densitometer and with a Lunar X-ray densitometer in 94 subjects attending a Metabolic Bone Disease Clinic. There was a strong correlation between results obtained from each machine for the same skeletal site. The correlation coefficients for the spine and femoral neck were 0.97 and 0.88, respectively. The differences between results from each machine were normally distributed with a mean bias of 37.5% for the spine and 27.8% for the femur, which arise principally from differences in machine calibration. In each case the BMD was greater when measured by X-ray absorptiometry. The range for the bias was approximately 25-50% for the spine and 10-45% for the femoral neck. The results from these two machines are not interchangeable. When subjects who are participating in long term studies using a radioisotope densitometer are transferred to an X-ray densitometer, an individual conversion factor must be measured at each site for each subject.

Absorptiometry, Photon↗
PubMed1991

The contributions of growth and puberty to peak bone mass.

Lumbar spine bone mass was measured by dual photon absorptiometry (DPA) in 236 subjects aged between 3 and 30 years. Expected values of bone mineral density (BMD) and bone mass (BMC) for the lumbar vertebrae L2 to L4 were derived as a function of age, by non-linear regression analysis. The selected regression equation was the sum of two logistic expressions, one of which was assigned to growth at the time of puberty and the other to the slower long term component of growth. Growth during puberty contributed about 50% of peak bone mass in females, while in males this contribution was closer to 15%. No increase was found in lumbar spine bone mass in females after puberty.

Absorptiometry, Photon↗
PubMed1990

Triple photon absorptiometry cannot correct for fat inhomogeneities in lumbar spine bone mineral measurements.

In vivo fat inhomogeneities can cause significant errors in measurements of lumbar spine mineral mass using dual photon absorptiometry. Extension to a triple photon technique to correct for the presence of fat is not possible because of the unacceptable increase of about a factor of 3,000 required in the radiation dose to yield sufficient transmitted photons for adequate precision.

Absorptiometry, Photon↗
PubMed1990

Regional bone mineral measurements.

Total body dual-photon transmission scanning was performed in 9 control persons, 15 athletes and in 5 patients with eating disorders. Total body bone mineral mass was measured, with a reproducibility of 2%; for regional bone mineral mass the reproducibility was 4%. The fraction of total bone mineral in the spines and heads of women is greater than in men. Patients with eating disorders have a smaller fraction of total body mineral in the pelvis than female controls. Weight lifters have a significantly greater mineral mass in the trunk region than other athletes and male controls. These and other differences are consistent with the conclusion that total body dual-photon absorptiometry allows quantitation of the distribution of mineral within the skeleton.

Absorptiometry, Photon↗
PubMed1990

Body composition by photon absorptiometry.

Whole-body dual photon measurements of body composition were made in 9 controls, 15 athletes and 5 patients with eating disorders. Measurements of lean body mass, mineral mass and fat mass were accurate. Lean body mass and fat mass were measured with reliabilities of about 0.8 kg while for total body bone mineral mass, the reliability was about 60 g. Women had a smaller lean body mass and a greater fat mass than men. Women with eating disorders had the same body composition as males. Measurements of body composition by dual photon absorptiometry are safe and reliable.

Absorptiometry, Photon↗
PubMed1989

The error due to fat inhomogeneity in lumbar spine bone mineral measurements.

Bone mineral mass measurements using dual photon absorptiometry rely on the assumption that fat thickness is constant within the region scanned by the photon beam. This assumption has been tested using both single and multiple slices from archived CT scans. In 26 patients, the difference in fat content between the bone and baseline measurement sites, the fat deviation, was found to vary from -2.7 to 18.7%. The median fat deviation was 4.4% which can lead to errors in measured lumbar spine bone mineral of 6 to 11%. Approximately one third of patients will have errors greater than 10%.

Adipose Tissue↗
PubMed1989

Some factors which influence the evaluation of a dual photon measurement of lumbar spine bone mineral mass.

The accuracy of a commercial dual photon densitometer was found to be within 3.0% of true values when measured using a cadaver spine. The precision, the ratio of standard deviation to mean derived from repeated measurements of a tissue-equivalent phantom spine, was 1.6%. Patient size and the age of the radioisotope source had no discernable effect upon bone mineral mass measurements. The intervention of the technologist during data analysis can influence the determination of bone mineral mass in approximately 40% of measurements. When a lumbar spine phantom was measured on six different densitometers manufactured by three different companies, within-manufacturer variations of between 4% and 7% were found. Bone mineral densities differed by up to 30% between manufacturers. Values of lumbar spine mineral mass were measured for 206 apparently normal women. The resultant normal range was similar to others documented by the manufacturer. The differences between these studies and a published study of 892 normal women can best be explained on the basis of intermanufacturer differences.

Adult↗
PubMed1987

The effect of fat on bone mineral measurements in normal subjects with recommended values of bone, muscle and fat attenuation coefficients.

Published data concerning the amount, distribution and composition of bone marrow and soft tissue fat in normal subjects are reviewed. Experimental studies of the effect of fat upon bone mineral measurement have been examined. Values of calculated and measured attenuation coefficients for bone, soft tissue and fat in the energy range of interest for bone mineral measurements have been collected and compared. For most measurement sites and in most normal subjects the thickness of fat within bone marrow is comparable with the thickness of the subcutaneous fat layer, although in obese individuals subcutaneous fat thickness can be twice the marrow fat thicknesses. In specific measurement sites there is also a contribution from deep-seated soft tissue fat which is of a similar magnitude to marrow fat. The presence of bone marrow fat alters measured values to the greatest extent in CT measurements of lumbar spine mineral, partly because the incident photon energy is higher than in single and dual photon absorptiometry but also because the fraction occupied by fat in the volume of tissue examined is larger. For scattering techniques the measured value is reduced by the volume fraction occupied by fat. The normal changes in marrow and soft tissue fat observed with aging have little influence on either scattering or transmission measurement. The values of measured and calculated linear attenuation coefficients given by previous workers show reasonable agreement despite considerable differences between measurement techniques and calculation procedures.

Adipose Tissue↗
PubMed1987

Lithium and boron in human blood.

A new method for determination of lithium and boron in biologic material has been developed. It uses neutron irradiation and subsequent measurements of helium 3 and helium 4 in a static mass spectrometer. Concentrations of lithium and boron in blood from seven apparently healthy donors were in rather narrow ranges (Li = 2.64 +/- 0.94 ng/gm dry weight, B = 97 +/- 22 ng/gm dry weight), and these concentrations also appeared to be correlated at the 0.05 level of significance.

Boron↗
PubMed1987

Calcaneal bone density reduction in patients with restricted mobility.

This cross-sectional study revealed a prevalence of reduced calcaneal bone density in a population of 49 chronic continuing care patients with restricted mobility. Calcaneal bone density was measured using the Compton gamma ray scattering technique, which permits examination of trabecular bone. Predicted densities were determined from the ages and weights of the subjects. Descriptive factors such as gender, diagnosis, duration of the condition, and muscle tone were correlated with bone density. Twenty-eight patients (57%) had indications of reduced calcaneal bone density. None of the descriptive factors was associated with the variability in bone density ratio (forward stepwise regression analysis, p = NS). The reduced calcaneal density found in these patients with restricted mobility is probably a result of their not bearing weight and the inevitable severe reduction in their physical activity.

Absorptiometry, Photon↗
PubMed1985

The precision and accuracy of noninvasive measurements of total body calcium in the rat.

It has been proposed that the adult castrated male rat may be used as a model of human postmenopausal osteoporosis. If such a model is valid then the total body calcium of castrated rats should progressively decrease compared with normal rats. To search for this age-related difference, it will be necessary to use a measurement technique with a precision which is small compared with the magnitude of the change to be detected. From measurements of total body calcium by neutron activation and by whole body ashing of eight dead rats, it has been shown that total body calcium can be measured with an accuracy and precision which should allow distinction between the expected lifetime changes in normal and castrated rats.

Animals↗
PubMed1984

Determining causation--a case study: adrenocorticosteroids and osteoporosis. Should the fear of inducing clinically important osteoporosis influence the decision to prescribe adrenocorticosteroids?

It is generally accepted that exogenous adrenocorticosteroids cause clinically important osteoporosis. We have reviewed the evidence regarding causation in two stages: an examination of the strength of the methods used, and an application of five "diagnostic tests" for causation. The methods that have been used to investigate the association are weak: there have been no randomized clinical trials or prospective cohort studies. The measures of bone density used to quantify osteoporosis do not bear a close relation to clinically important outcomes. Nine analytic surveys and two before-after studies have examined the relation between steroids and osteoporosis. Although some have shown a strong relation, this finding has not been consistent. Evidence regarding temporality , dose-response gradient, and underlying mechanisms are conflicting. The available evidence does not substantiate a causal role of exogenous adrenocorticosteroids in producing clinically important osteoporosis, and does not support withholding steroid therapy on the basis of fears of osteoporosis induced pain and disability.

Adrenal Cortex Hormones↗
PubMed1984

Photon scattering measurements of calcaneal bone density: results of in vivo longitudinal studies.

Sequential measurements of the density of calcaneal trabecular bone were made in normal postmenopausal women and in patients treated for osteoporosis. Cross-sectional measurements of density were made in previously normal patients who had been without ovarian function for a known length of time of at least one year. There was a significant reduction in calcaneal density associated with aging in normal postmenopausal women. Estrogen lack was also associated with density reductions and the reduction was related to the length of time of estrogen deprivation. When osteoporotic patients were treated with combination therapy, density rose in females while in males the expected age dependent reduction was prevented. It is concluded that photon scattering measurements of calcaneal density can be used to monitor changes in the mineral status of the skeleton.

Adolescent↗
PubMed1984

Measurement of pulmonary clearance of radioaerosol using a portable sodium iodide probe.

To determine whether a portable sodium iodide (NaI) probe could provide a valid measure of the pulmonary half-life (T1/2) of aerosolized technetium-99m-diethylenetriaminepentaacetate (99mTc-DTPA, mol wt = 492) in small chests, we measured pulmonary clearance in rabbits using a gamma-scintillation camera and the portable probe. In 10 experiments the lungs of New Zealand White rabbits were insufflated with aerosolized 99mTc-DTPA (0.6 mum aerodynamic mass median diameter) and then simultaneously imaged with the gamma-camera and the probe positioned over the upper right lung. In an additional 12 experiments, alveolar-capillary membrane permeability was increased by either intratracheal instillation of 0.1 N hydrochloric acid (HCl) or intravenous injection of 100 mg/kg of oleic acid. All animals tolerated the procedure. There was a significant decrease in pulmonary T1/2 in both the HCl group (53.4 +/- 10.4 min, mean +/- SE) and the oleic acid group (14.7 +/- 2.3 min) when compared with control (127.5 +/- 18.1 min). When we compared the T 1/2 of the right lung determined by the gamma-camera with that measured by the probe, the correlation coefficient was 0.95. Potential nonpulmonary contributions to thoracic radioactivity were not significant. We conclude that a portable NaI probe is a valid means of determining T 1/2 of 99mTc-DTPA in small chests when compared with a gamma-camera and can detect increases in the permeability of the alveolar-capillary membrane to small solutes.

Aerosols↗