A multicenter comparison of dual-energy X-ray absorptiometers: In vivo and in vitro measurements of bone mineral content and density (original) (raw)
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European Journal of Clinical Nutrition, 1997
Objective: To assess intra-and inter-site soft tissue variability by dual energy X-ray absorptiometry (DXA). Design: Cross-sectional trial. Setting: Three medical research institutions. Subjects: Five humans (in vivo) and four phantoms (in vitro), con®gured from two whole body phantoms with arti®cial skeletons and thickness overlays. Interventions: Duplicate total-body DXA scans were performed on all subjects at each institution within a 15 d period. Results: All intra-site coef®cients of variation (CV) were`0.5% for total tissue mass, but in vitro and in vivo Cvs were 7.2% and 2.3% for fat mass (FM) and 2.5% and 0.9% for lean mass (LM), respectively. Several totalbody and regional FM and LM measurements were signi®cantly different between sites (P`0.05), with percent differences between sites ranging from 2.6±13.3% for FM and from 1.6±13.6% for LM. Site 2 was consistently lower for FM and Site 3 was consistently lower for LM. Conclusions: These results stress the need for both rigorous and standardized cross-calibration procedures for soft tissue measurement by DXA.
Journal of Nuclear Medicine
Dual energy x-ray absorptiometry (DEXA) has been shown to be a precise method for measuring bone mineral density (BMD) and content (BMC) in lumbar spine and proximal femur, but it has not been widely used in other skeletal sites. The in vivo day-to-day precision of DEXA (Norland XR-26) for seven anatomic sites in the upper extremities was evaluated by twice measuring both the right and left sides in ten subjects. For consistently defined regions-of-interest, the following precision values (coefficient of variation) were obtained for BMD and BMC: 0.8% and 1.0% (proximal humerus); 0.5% and 0.5% (humeral shaft); 0.7% and 0.5% (radial shaft); 1.3% and 1.1% (ulnar shaft); 0.7% and 1.0% (distal radius); 0.7% and 1.2% (distal ulna); 0.4% and 0.6% (hand). The initially observed relative side-to-side differences did not change significantly in the repeated measurements. Our results indicate that DEXA is a precise method for assessment of BMD and BMC also in the upper extremities.
Soft tissue composition and bone mineral status: evaluation by dual-energy X-ray absorptiometry
The Journal of nutrition, 1993
Dual-energy X-ray absorptiometry (DXA) is a new method for assessing whole-body and regional bone, fat and fat-free mineral-free soft tissue masses. X-rays at two discrete energy levels are collimated and directed into the body. The attenuation of the X-rays by the various chemical components in the body permits determination of important compositional variables. The precision and accuracy of the DXA measurements of bone mineral content and density are 99% and < 1% error, respectively. The reproducibility of the determinations of soft tissue composition is approximately 99%. Because the radiation dose associated with the X-ray exposure is low, DXA is a safe method for routine use in humans. Various applications are described, including an assessment of bone mineral status and body composition in adults and infants. This method is appealing for nutritional studies because it directly determines the composition of bone and of the body.
Calibration of dual-energy X-ray absorptiometry for bone density
Journal of Bone and Mineral Research, 2009
Bone mineral content (BMC, g) using DEXA (Lunar DPX) was measured on known hydroxyapatite samples in a water bath in the presence of uniform and nonuniform coverings of fat-equivalent materials. Selective placement of paraffin over bone had a greater effect than lard in reducing apparent BMC, and polycarbonate plastic had a lesser effect. Measured BMC was 100.1 f 1.1% of actual hydroxyapatite weight when (1) fat over bone was about twice the mass of hydroxyapatite, and (2) the surrounding soft tissue was 15-30% fat. There was a linear relationship between observed and expected BMC, area (cm2), and bone mineral density (BMD, g/cm2) measured on an aluminum phantom using either the Lunar DPX or the Hologic QDR-1OOO. The measured area with the two densitometers was identical, but BMC differed. For both an anthropomorphic phantom and human subjects, use of a constant-threshold (0.2 g/cm2) edge-detection algorithm excluded less low-density bone from the transverse processes than the standard DPX edge-detection algorithm. Differences in edge detection could influence the results obtained with phantoms and in vivo and make system intercomparison difficult.
Journal of Bone and Mineral Research, 1991
A total of 81 subjects (41 males and 40 females) were scanned by dual-photon absorptiometry by 153Gd source (DPA; Lunar DP4) and by dual-energy x-ray absorptiometry (DEXA; Lunar-DPX) within a 24 h period. Total-body bone mineral density (TBMD), calcium content (Ca), and soft tissue mass (ST) were determined with a precision of about 1–1.5% using DPA and 0.5–1.0% using DEXA. Measurements of TBMD, Ca, ST, bone area (area), percentage fat, and regional bone mineral densities (BMD) were compared. Paired t-tests showed small but significant differences between all measurements. Correlations (r) for TBMD, Ca, area, ST, percentage fat, arm BMD, leg BMD, and trunk BMD were 0.99, 0.99, 0.97, 0.99, 0.97, 0.99, 0.99, and 0.98. There were small systematic differences for TBMD (<1%), calcium (3%), bone area (3%), soft tissue mass (7%), and percentage fat (9%) between the two approaches. Regression equations are given relating these measurements.
Precision of dual energy x-ray absorptiometry in the upper extremities
Bone and mineral, 1993
Dual energy x-ray absorptiometry (DEXA) has been shown to be a precise method for measuring bone mineral density (BMD) and content (BMC) in lumbar spine and proximal femur, but it has not been widely used in other skeletal sites. The in vivo day-to-day precision of DEXA (Norland XR-26) for seven anatomic sites in the upper extremities was evaluated by twice measuring both the right and left sides in ten subjects. For consistently defined regions-of-interest, the following precision values (coefficient of variation) were obtained for BMD and BMC: 0.8% and 1.0% (proximal humerus); 0.5% and 0.5% (humeral shaft); 0.7% and 0.5% (radial shaft); 1.3% and 1.1% (ulnar shaft); 0.7% and 1.0% (distal radius); 0.7% and 1.2% (distal ulna); 0.4% and 0.6% (hand). The initially observed relative side-to-side differences did not change significantly in the repeated measurements. Our results indicate that DEXA is a precise method for assessment of BMD and BMC also in the upper extremities.
Monitoring of Dual-Energy X-ray Absorptiometry Measurement in Clinical Practice
Journal of Clinical Densitometry, 2006
Bone densitometry has become the ''gold standard'' in osteoporosis diagnosis and treatment evaluation. It has also become more and more common to perform a second dual-energy X-ray absorptiometry (DXA) measurement to monitor bone mineral density (BMD) status or the effect of therapeutic intervention. When a second measurement is performed on a patient, the clinician needs to distinguish between a true change in BMD and a random fluctuation related to variability in the measurement procedure. The reproducibility of DXA measurements is claimed to be good. Such variability is due to multiple causes, such as device errors, technician variability, patients' movements, and variation due to other unpredictable sources. The precision error is usually expressed as the coefficient of variation (CV). However, several other statistics to express reproducibility exist such as the smallest detectable difference (SDD) or the least significant change (LSC). The SDD represents a cut-off that can be measured in an individual and is usually considered more useful than the CV in clinical practice. Indeed, the use of the SDD is preferable to the use of the CV and LSC because of its independence from BMD level and its expression in absolute units (g/cm 2 ). At each measurement center, the SDD must be calculated from in vivo reproducibility data. The choice of the optimum time and site for performing follow-up scans depends on the ratio of the expected BMD treatment effect to the precision of the measurements.
Influence of fat on bone measurements with dual-energy absorptiometry
1990
In order to investigate the influence of fat on bone in dual-energy absoqniome~ry measuremenu, we evaluated a rpecinl pbsnmm on the tbrec sc~nnew Lunar DW, Lunar DPX and HoI& QDR-ImO. The phantom employed bydroxyaparite blocks of various thicknesses to simulate bone, water 10 rim"late muscle and Lucite to simulate fat. The Lucite plates were arranged in one and WO layerr in ,hree different configurations: over the whole measurement area. over the hydroxya@te mocks only and at bath sidesofthe hydroxyapatite blocks. For all scanners. no influence of fat could be demonstrated if it was homogeneously distributed wm the whole measurement axa. However. changes in area bone-densiry were ~bseww if fa, wa distrib uted inhomogeneausly over the measurement area. Fat ~"er only the bone area reduced ,hc measured hone values by 0.051 g!cm' per cm fat layer. Far over only the rofr-,irrue axa inneaxd the nvawrred bane "aIues by the same amount. These results apply IO the Lunar DPX acanner. The resut,s br ,hc Lunar DP-3 scanner are similar: those for Ihe Hologic OUR-,W show a skghlly smaller ial dspndencs of 0.044 gkm2percm fat layer. The la, influencer are na, dependent on rhe amoun,ofbmwandonly minimally on thesoft-tissue thicknsss. A change of 50% in the fat c~n,en, of the bone marrow will chanp the measured area bone-density of an awn&d sized vertebra by 5-6% depending on scanner model. Inhomogeneous far distribution in soft &UC, rerulling in a difference of 2 cm fat layer hcfween soft-,issue area and bone area, will infhtence the measured area hone-denshy by 9-10%. Key wardsz Dual-photon absolpriamerry; Dual-energy X-ray absorptiomctry; Bone meawremenl; Fat influence; Osteoporosis Since the commercialization of dual-photon absorptiometry, the accuracy of the method under various conditions has been a major topic of discussion. One factor
Journal of Bone and Mineral Research, 2009
Pencil-beam dual-energy X-ray absorptiometers (DXA) are being replaced with instruments that rely solely on fan-beam technology. However, information has been lacking regarding the translation of bone mineral and body composition data between the two devices. We have compared total body scans using pencil-beam (Hologic QDR-2000W) and fan-beam (Hologic QDR-4500A) instruments for 33 children (ages 3-18 years) and 14 adults. Bone mineral content (BMC), bone mineral density (BMD), fat, lean, and body fatness (%fat) values were highly correlated (r 2 ؍ 0.984 -0.998) between the two DXA instruments. The mean differences between the paired measurements were: ⌬BMC ؍ 7.5 ؎ 73.6 g, ⌬BMD ؍ 0.0074 ؎ 0.0252 g/cm 2 , ⌬lean ؍ 1.05 ؎ 1.8 kg, ⌬fat ؍ ؊0.77 ؎ 1.7 kg, and ⌬%fat ؍ ؊0.94% ؎ 2.5%. The BMC and BMD values were not statistically different, whereas the differences for the body composition values were significant ( p < 0.02-0.005). Regression equations are provided for conversion of bone and body composition data between pencil-beam and fan-beam values for the whole body. To test the performance of these equations for a second group (23 subjects), predicted values were compared with the measured data obtained using the fan-beam instrument. The mean differences were ؊1.0% to 1.4%, except for body fat mass, where the difference was 6.4%. For cross-sectional studies, the two DXA technologies can be considered equivalent after using the translational equations provided. For longitudinal studies in which small changes in body composition for the individual are to be detected, we recommend that the same DXA instrument be used whenever possible. For example, transition from a pencil-beam to a fan-beam instrument could, in extreme cases, result in differences as large as 19% for the estimate of body fat mass. (J Bone Miner Res 1998;13:1613-1618) *This work is a publication of the USDA/ARS Children's