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At least 19 recordsLinked to original sources
PubMed1992

Bone mass measurement by DXA: influence of analysis procedures and interunit variation.

Interunit variability among bone densitometers is due to different factors, including different calibration procedures and algorithms and variability in photon source energies and/or intensities. Other factors, such as the choice of scan parameters or the analysis procedures, can also introduce variability. The new generation of dual-energy x-ray absorptiometry (DXA) has partially improved this situation. The aim of this study was to investigate the operator-dependent analysis procedures that can affect scan results and to evaluate the phantom and in vivo interunit variation of some DXA instruments. Four DXA instruments (QDR 1000 and 1000/W, Hologic, Inc.) were used. Potential sources of variability in the analysis procedures of anteroposterior lumbar spine and hip scans were considered: in most cases these procedures significantly influenced scan results. On lumbar spine, an enlargement of the scan window of less than 3 cm was responsible for an average increase in bone mineral density (BMD) of about 3%. On the hip, lowering the scan window by about 1 cm accounted for an increase in the whole-segment BMD of about 4%. After standardization of analysis procedures, interunit and intraunit coefficients of variation and percentage differences among instruments were less than 1% for all the parameters considered (area and bone mineral content and density) with both an anatomic and a geometric phantom, and in nine subjects scanned by two different devices the percentage difference in BMD was greater than 2%. This study shows that present interunit variability allows comparisons among laboratories, but only if highly standardized analysis procedures are used.

Absorptiometry, Photon↗
PubMed1992

Measurements of bone mineral density by DXA total body absorptiometry in different skeletal sites in postmenopausal osteoporosis.

In order to evaluate the bone mineral density (BMD) of the entire skeleton and its major anatomical areas, total body DXA absorptiometry was performed in 330 postmenopausal women whose ages ranged from 42-85 years. Sixty-three of them were normal women and constituted the control group (Group 1). Two hundred sixty-seven were patients affected with postmenopausal osteoporosis: 107 osteoporotic patients had vertebral biconcavity deformities of grade 1 (Group 2), and the other 160 had vertebral wedge, biconcavity, and compression deformities of grade 2 (Group 3). Total body absorptiometry was assessed by a DXA system (Lunar DPX). Significant reduction in total body BMD values was observed in patients in Groups 2 and 3 (p less than 0.01): the bone loss was more intense in osteoporotic women of Group 3. The low values of the BMD in osteoporotic patients are, moreover, localized in the areas of spine, arms, and legs; the osteopenia was particularly enhanced in patients with grade 2 vertebral deformities. Multiple linear regression indicated that values of total BMD were significantly related to age and BMI. Receiver operating characteristic (ROC) analysis showed that total BMD provided high sensitivity: At 90% of specificity it was 78% for Group 2 and 89% for Group 3. DXA total body absorptiometry has demonstrated that, in postmenopausal osteoporotic women, the reduction in bone mass is not localized only in the spine, but also involves the appendicular skeleton.

Absorptiometry, Photon↗
PubMedDate not supplied

Evaluation of a new set of calibration standards for the measurement of fat content via DPA and DXA.

A simulation study was performed to evaluate a new set of calibration standards for estimating the fat content of the body via dual-photon absorptiometry (DPA) and dual-energy x-ray absorptiometry (DXA). The standards, proposed by Nord and Payne [presented at the 2nd meeting of The Bath Conference on Bone Mineral Measurement (1990)] consist of stearic acid (100% fat) and 0.6% NaCl in water (100% lean). They were compared with other standards consisting of average composition adipose/muscle tissues and fatty adipose/lean muscle tissues. Source and detector properties of a Gd-153 DPA system and three commercial DXA systems were modeled. For each system and calibration set, rms errors in the calculated fat contents of simulated tissues having fat mass percentages that ranged from about 4%-44% and thicknesses that ranged from 5-20 cm were determined. Beam hardening errors for the systems were evaluated as was a calibration technique employed by one of the manufacturers to correct for such errors. In general, the smallest rms errors (2% or less when the calibration standards and tissues were of equal thickness) were obtained with the average adipose/muscle standards. Equivalent results were obtained with standards consisting of stearic acid and 0.8% NaCl. The latter is a higher salt content than proposed by Nord and Payne and results from differences in the x-ray attenuation coefficients that were employed in calculating the fat equivalence of water. Other, more convenient standards, such as lucite and water may be employed by using appropriate fat equivalences (approximately 69% for lucite and approximately 10% for water). Beam hardening errors for the DXA systems are considerable, and the simulated correction technique was shown to be effective.

Absorptiometry, Photon↗
PubMed1991

Bone mass in healthy children: measurement with quantitative DXA.

Dual-energy x-ray bone densitometry was used to study the lumbar vertebral bone mass in 218 healthy children (134 girls and 84 boys) aged 1-19 years. Vertebral bone mass increased with weight, age, and pubertal Tanner stage. Results of multiple regression analyses showed that Tanner stage and weight were the best predictive indicators of bone mass and bone mineral density. The influences of age, sex, race, physical activity, and diet were not significant when Tanner stage and weight were controlled. Two tables of predictive intervals for lumbar vertebral bone mineral density in healthy children (one based on Tanner stage and weight; the other, on age and weight) are presented. With normative data now available for use with this precise technique, clinicians can better detect abnormal bone mineral density in children and evaluate changes in mineralization over time.

Absorptiometry, Photon↗
PubMed1991

Effect of 2-hydroxypropyl-beta-cyclodextrin on the ocular absorption of dexamethasone and dexamethasone acetate.

Complexation of dexamethasone (DX) and dexamethasone acetate (DXA) with 2-hydroxypropyl-beta-cyclodextrin (HPCD) was investigated with an ultimate goal of formulating a topical ophthalmic solution of DXA. Aqueous solubility of DX and DXA was markedly increased due to formation of soluble inclusion complexes with HPCD. Based on characterization of complex formation by phase solubility and UV-spectroscopy methods, a stoichiometry of 1:1 and 1:1, 1:2 was assumed for DX-HPCD and DXA-HPCD complexes, respectively. The stability constants for complex formation estimated by phase solubility and UV-spectroscopy methods, respectively, were as follows: for DX-HPCD complex, K1:1 = 2193 and 2221 M-1; and for DXA-HPCD complex, K1:1 = 2240 and 2445 M-1 and K1:2 = 3 and 17 M-1. K1:1 of 2266 M-1 and K1:2 of 20 M-1 were also estimated for the DXA-HPCD complex by kinetics. The kinetics of DXA degradation in pH 7 phosphate buffer at 25 degrees C followed pseudo first order. The addition of HPCD decreased the rate but the order of reaction remained unchanged. Free DXA degraded at a faster rate than complexed DXA. Ocular bioavailability in conjunctiva, cornea, iris, and aqueous humor postadministration of a 25-microliters dose of formulations containing an equivalent of 0.1% (w/v) DX followed a rank-order of DXA-HPCD solution greater than DXA suspension greater than DX-HPCD solution greater than DX suspension.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1992

An evaluation of dual-energy X-ray absorptiometry and comparison with dual-photon absorptiometry.

Dual-photon absorptiometry (DPA) is a well-established procedure for measuring bone mineral density (BMD). Recently, dual-energy X-ray absorptiometry (DXA) has become available, which has the ability to measure BMD both regionally and in the total body (TB). We have evaluated the in vivo and in vitro precision of a DXA instrument and compared it with a DPA instrument with similar software characteristics. The short-term precision of BMD measurements using DXA was assessed in 65 postmenopausal women who had duplicate scans performed, with repositioning between scans. Precision was 0.9% in the lumbar spine and 1.4% in the femoral neck. The midterm precision of DXA was compared with DPA by scanning 10 volunteers a mean of four times over 24 weeks, on both instruments. The precision of the bone mineral content (BMC) and area measurements was significantly better (P less than 0.05) with DXA than with DPA. Long-term in vitro precision was assessed by scanning an aluminium spine phantom over 42 weeks, and a cadaveric sample over 52 weeks, on both instruments. Precision was similar using the aluminium phantom, but was significantly improved (P less than 0.001) when using DXA for scanning the cadaveric sample. Highly significant correlations (all P less than 0.001) of BMD, BMC and area measurements were observed when 70 volunteers were scanned on both instruments. However, there was a systematic difference in BMD values between the instruments. The precision of TB composition measurements assessed in 16 volunteers, over a 16-week period, were TB BMD 0.65%, TB lean tissue 1.47%, and TB fat tissue 2.73%.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1991

Accuracy and precision of lumbar bone mineral content by dual-energy X-ray absorptiometry in live female monkeys.

Dual-energy X-ray absorptiometry (DXA) was used to determine the in vivo bone mineral content (BMC) of lumbar vertebrae in 20 feral adult female cynomolgus macaques (Macaca fascicularis). The ash weight of the third lumbar vertebra (L3) was compared to the measured L3BMC of the in vivo DXA analyses. Correlation between the estimated L3BMC by DXA and the actual ash weight was significant (r = 0.965, P less than 0.01); however, DXA methodology underestimated ash weight on the average of 6.2%. Correlation was significant between two sequential in vivo DXA scans (r = 0.988, P less than 0.001). Noninvasive in vivo DXA was a fast, precise, and effective method for measuring the lumbar BMC in female cynomolgus macaques.

Absorptiometry, Photon↗
PubMed1992

Comparison of single-photon and dual-energy x-ray absorptiometry of the radius.

We compared dual-energy x-ray absorptiometry (DXA) for measurement of the radius with the conventional single-photon absorptiometry (SPA) method. To evaluate reproducibility, 34 healthy male and female subjects were measured twice each by both methods. While the instruments measured bone mineral content (BMC) similarly, projected area was consistently lower by SPA and therefore bone mineral density (BMD) was higher by an average of 10%. We report similar coefficients of variation for the two methods, which are 0.8% (SPA) and 0.7% (DXA) for BMC (P = 0.71) and 0.8% (SPA) and 1.4% (DXA) for BMD (P = 0.02). We also evaluated the relationship between the methods with data from 196 clinic patients who were measured once each on both instruments. The BMD measurements from the two instruments were highly correlated (r = 0.97) in these patients, which permits the conversion of databases from SPA to DXA-equivalents. We conclude that DXA can replace SPA for radial bone densitometry.

Absorptiometry, Photon↗
PubMed1992

Assessment of whole-body composition with dual-energy x-ray absorptiometry.

Dual-energy x-ray absorptiometry (DXA) allows noninvasive direct measurement of the three major components of body composition: lean body mass (LBM), fat body mass (FBM), and bone mineral body mass (BBM). To study the accuracy and short-term and long-term precision of body composition measurements, the authors measured body composition with DXA in 60 healthy young adults. Independent measurement of LBM (LBMK-40), obtained from the determination of the whole-body content of potassium-40 with a whole-body scintillation detector, was highly correlated with LBM determined with DXA (LBMDXA) (LBMK-40 = 1.069.LBMDXA,R2 = .996). Assessment of body composition in 10 patients with acquired immunodeficiency syndrome (AIDS) and 10 patients with cystic fibrosis was performed with DXA. The AIDS patients showed a marked decrease in LBM, while in patients with cystic fibrosis, LBM and BBM were decreased. DXA measurements of body composition appeared accurate and precise enough to be of clinical relevance in detecting specific alterations of body composition.

Absorptiometry, Photon↗
PubMed1992

Determination of bone mineral density by dual x-ray absorptiometry in patients with uncemented total hip arthroplasty.

Bone remodeling is an expected sequela with total hip arthroplasty (THA). Although there are several methods of estimating bone response in THA patients from radiographs, there are no accurate and generally accepted methods for quantitative determinations in vivo. In this study, we describe an application of dual x-ray absorptiometry (DXA) for measuring bone mineral content and bone mineral density in the proximal femur following THA. DXA is a noninvasive technique with minimal radiation exposure (< 5 mrem). Various aspects of measurement error (accuracy and reliability) of this application of DXA were determined in a series of studies reported here. Accuracy error (how similar are the measured and actual values) was < 1% determined in bone phantoms of four densities. Precision error (how reproducible are the measurements) was also < 1% at all four densities in the phantoms and was only slightly elevated (0.9-1.5%) in repeated measurements of implanted cadaver femora. Precision error in vivo, determined both from multiple replicates on five patients and from duplicate scans on 30 patients, was further elevated but remained < 5%. Contributions to precision error, rotation of the leg, and interoperator variability were assessed; none was found to elevate precision error appreciably. We suggest that DXA is a feasible method for quantifying bone response following THA, and will allow discrimination of small changes (> 5%) not previously measurable.

Absorptiometry, Photon↗
PubMed1992

Comparative assessment of bone mineral density of the forearm using single photon and dual X-ray absorptiometry.

Forearm bone mineral density (BMD) was measured at proximal and distal sites by 125I single photon absorptiometry (SPA) and by dual energy X-ray absorptiometry (DXA) in 67 consecutive subjects, aged 18-75 years. Correlations and regression equations between these two techniques were determined. All forearm measurements were significantly correlated with each other (r = 0.599-0.926; P < or = 0.0001). Although SPA and DXA correct for fat in different ways, we found similar correlation and regression equations in women with body mass index measurements above and below the mean. In addition, forearm measurements by both techniques were moderately correlated with vertebral spine and hip BMD. We conclude that overall, SPA forearm measurements in a population can be calibrated to DXA measurements if necessary, and that DXA forearm measurements are as predictive of the remainder of the skeleton as SPA measurements.

Absorptiometry, Photon↗
PubMed1991

Comparison of dual photon and dual energy X-ray bone densitometers in a clinic setting.

In clinical practice, decisions must be made about whether and how to convert to newer technologies. To address this issue, two separate studies were conducted. We evaluated the relationships between results of lumbar spine measurements using two dual photon absorptiometry (DPA1 and DPA2) instruments and one dual energy X-ray (DXA) instrument with the same subjects (49 volunteers), and also in 65 patients who were measured on the DPA1 and DXA machines. Second, we measured the lumbar spine and the proximal femur in three groups of 12 female volunteers three times on one instrument within 1 week. We purposely simulated a busy clinic setting with different technologists, older radioactive sources, and a heterogeneous patient group. The comparison study indicated a significant difference between the mean bone density values reported by the machines, but the results were highly correlated (R2 = 0.89-0.96). The short-term precision errors (coefficients of variation) differed among the instruments, ranging from 1.3% (DXA of the spine) to 5.1% (DPA1 of the spine), and in the femoral neck, 2.3% and 2.4% (DXA and DPA1, respectively) versus 3.5% by DPA2. This study emphasizes the differences between instruments, the potential for greater error in busy clinic environments, and the apparent superiority of dual energy X-ray absorptiometry under these less than ideal conditions.

Absorptiometry, Photon↗
PubMed1992

Successful use of the sperm motility enhancer 2-deoxyadenosine in previously failed human in vitro fertilization.

The outcome of in vitro fertilization treatment in male-factor infertility is generally poor, due mainly to poor fertilization rate and hence fewer available embryos for replacement. This study was carried out to assess the value of asthenospermic sperm exposure to a motility enhancing agent, 2-deoxyadenosine (2-DXA), on our in vitro fertilization program in couples undergoing repeat treatment after previous failed fertilization. Following sperm wash and incubation in 2-DXA-supplemented medium, marked significant improvements were observed in the sperm motility pattern and the number of recoverable sperms as compared to control unexposed samples. There was also a significantly better fertilization rate and higher number of replaceable embryos available following sperm wash in 2-DXA as compared to those washed without it. Following embryo transfer, pregnancy rate was comparable to the generally reported pregnancy rates for routine in vitro fertilization and embryo transfer treatment. Three normal babies were born. Our results indicate that 2-DXA enhances fertilization rate in some asthenospermic patients and that it has no adverse effect on embryonic development.

Adult↗