Dual-energy X-ray Absorptiometry Device Research Articles

Measures of the Forearm via a Portable Device: Ready for Prime Time?

Measurement of areal bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) is an important tool in the evaluation of bone health in children and adolescents, but available data in the pediatric population are limited, particularly in younger children. To address this issue, Hazell et al (1) present results from their study evaluating the correlation between areal BMD measures of the forearm by peripheral instantaneous X-ray imager (PIXI), a portable DXA device that affords BMD measures of the appendicular skeleton, compared with forearm measures by standard DXA in preschool-aged children. The study found that PIXI results correlated moderately well with areal BMD at the ultradistal radius as measured by DXA in boys and girls in this age group, suggesting that this tool holds promise as a skeletal assessment tool. The benefits of a portable DXA device are welldescribed, including use in field research in regions where standard DXA and peripheral quantitative computed tomography (pQCT) machines are not possible due to size and portability issues (2). The use of PIXI forearm measures in the adult population has yielded important data that might otherwise not have been feasible to obtain (3e5), and the measures have also been used in adolescent subjects (6,7). The low radiation dose associated with these devices is also noteworthy for use in a pediatric population. By applying this technology to younger children, this study provides an important foundation on which further studies can build. The ability

Technical Note: Comparison between single and multiview simulated DXA configurations for reconstructing the 3D shape and bone mineral density distribution of the proximal femur

Dual-energy x-ray absorptiometry (DXA) is used in clinical routine to provide a two-dimensional (2D) analysis of the bone mineral density (BMD). 3D reconstruction methods from 2D DXA images could improve the BMD analysis. To find the optimal configuration that should be used in clinical routine, this paper relies on a 3D reconstruction method from DXA images to compare the accuracy that can be obtained from one single-view and from multiview DXA images (two to four projections). The 3D reconstruction method uses a statistical model and a nonrigid registration technique to recover in 3D the shape and the BMD distribution of the proximal femur. The accuracy was evaluated in vivo by comparing 3D reconstructions obtained from simulated DXA images of 30 patients (using between one and four DXA views) with quantitative computed tomography reconstructions. This comparison showed that the use of one single DXA provides accurate 3D reconstructions (mean shape accuracy of 1.0 mm and BMD distribution errors of 7.0%). Among the multiview configurations, the use of two views (0° and 45°) was the best compromise, increasing the accuracy of pose (mean accuracy of 0.7°/1.2°/0.9° against 1.0°/3.5°/3.3° for the single view), reducing slightly the BMD errors (5.7%) while maintaining the same shape accuracy. The use of two views constitutes an interesting configuration when multiview DXA devices are available in clinical routine. However, the use of only one single view remains an accurate solution to recover the shape and the BMD distribution in 3D, with the advantage of a higher potential for clinical translation.

Identification of Rheumatoid Arthritis Patients With Vertebral Fractures Using Bone Mineral Density and Trabecular Bone Score

The aim of this study was to test bone mineral density (BMD), trabecular bone score (TBS), and their combination, for detection of rheumatoid arthritis (RA) patients with vertebral fractures (VFs). One hundred eighty-five women aged 56.0±13.5yr, with RA since 15.5±9.9yr were studied. Lumbar spine, total hip, and femoral neck BMD were assessed by dual-energy X-ray absorptiometry (DXA). TBS was calculated from anteroposterior image of lumbar spine BMD. VFs from T4 to L4 were evaluated using Vertebral Fracture Assessment software on DXA device. The proportions of patients with VF and T-scores ≤−2.5 were only 24.2%, 21.2%, and 33.3% at lumbar spine, total hip, and femoral neck, respectively. T-scores were significantly lower in patients with VF than in patients without VF, the largest difference being observed at femoral neck (p=0.0001). TBS was significantly lower in patients with VF vs without VF (p=0.0001). The areas under the curves were 0.621, 0.704, 0.703, 0.719, and 0.727 for lumbar spine BMD, TBS, lumbar spine BMD+TBS, total hip BMD, and femoral neck BMD, respectively. The threshold of 1.173 for TBS had the best sensitivity (63%) and specificity (74%). TBS measured at the lumbar spine has a better discrimination value than lumbar spine BMD, and similar to femoral neck BMD, for prediction of presence of VF in patients with RA. In RA subjects with osteopenia, the proportion of patients with VF was higher in the lowest tertile of TBS when compared with the highest tertile. In this population, at low risk according to BMD, TBS could help to detect patients with VF.

Body fat and fat-free mass measured by bioelectric impedance spectroscopy and dual-energy X-ray absorptiometry in obese and non-obese adults

The aim of the present study was to compare body fat mass (FM) and fat-free mass (FFM) estimates by bioelectric impedance spectroscopy (BIS), with respective estimates by dual-energy X-ray absorptiometry (DXA), in obese and non-obese subjects. Body composition was measured in ninety-three obese and non-obese men and women by BIS device, BodyScout (Fresenius Kabi, Bad Homburg, Germany) and DXA device, Lunar iDXA (GE Healthcare, Madison, WI, USA). Mean difference between the methods was analysed by t tests, and Bland-Altman plots were generated to further examine the differences between the methods. Mean difference between the estimates by DXA and BIS (ΔDXA - BIS and Bland-Altman 95 % limits of agreement) were as follows: FM 4·1 ( - 2·9, 11·2) kg and 4·5 ( - 2·9, 11·8) %, FFM - 4·1 ( - 11·2, 2·9) kg and - 4·5 ( - 11·9, 2·9) %, indicating large inter-individual variation and statistically significant underestimation of FM and overestimation of FFM by BIS, as compared to DXA. The underestimation of FMkg (FM measured in kg) and overestimation of FFMkg (FFM measured in kg) were more pronounced in men than in women, and the underestimation of FM% (FM measured in percent) and overestimation of FFM% (FFM measured in percent) were more pronounced in normal weight (BMI = 20·0-24·9 kg/m2) than in overweight and obese (BMI ≥ 25·0 kg/m2) subjects. BIS may be suitable for classification of a population into groups according to FM and FFM. However, the large inter-individual variation suggests that this BIS device with the proprietary software is insufficient for estimation of single individual body FM and FFM.

Cross Calibration of Whole Body Scans Between GE-Lunar and Hologic Systems: Bone and Body Composition

The trabecular bone score (TBS, Med-Imaps, Pessac, France) is an index of bone microarchitecture texture extracted from anteroposterior dual-energy X-ray absorptiometry images of the spine. Previous studies have documented the ability of TBS of the spine to differentiate between women with and without fractures among age- and areal bone mineral density (aBMD)-matched controls, as well as to predict future fractures. In this cross-sectional analysis of data collected from 3 geographically dispersed facilities in the United States, we investigated age-related changes in the microarchitecture of lumbar vertebrae as assessed by TBS in a cohort of non-Hispanic US white American women. All subjects were 30 yr of age and older and had an L1–L4aBMDZ-score within ±2 SD of the population mean. Individuals were excluded if they had fractures, were on any osteoporosis treatment, or had any illness that would be expected to impact bone metabolism. All data were extracted from Prodigy dual-energy X-ray absorptiometry devices (GE-Lunar, Madison, WI). Cross-calibrations between the 3 participating centers were performed for TBS and aBMD. aBMD and TBS were evaluated for spine L1–L4 but also for all other possible vertebral combinations. To validate the cohort, a comparison between the aBMD normative data of our cohort and US non-Hispanic white Lunar data provided by the manufacturer was performed. A database of 619 non-Hispanic US white women, ages 30–90 yr, was created. aBMD normative data obtained from this cohort were not statistically different from the non-Hispanic US white Lunar normative data provided by the manufacturer (p = 0.30). This outcome thereby indirectly validates our cohort. TBS values at L1–L4 were weakly inversely correlated with body mass index (r = −0.17) and weight (r = −0.16) and not correlated with height. TBS values for all lumbar vertebral combinations decreased significantly with age. There was a linear decrease of 16.0% (−2.47 T-score) in TBS at L1–L4 between 45 and 90 yr of age (vs. −2.34 for aBMD). Microarchitectural loss rate increased after age 65 by 50% (−0.004 to −0.006). Similar results were obtained for other combinations of lumbar vertebra. TBS, an index of bone microarchitectural texture, decreases with advancing age in non-Hispanic US white women. Little change in TBS is observed between ages 30 and 45. Thereafter, a progressive decrease is observed with advancing age. The changes we observed in these American women are similar to that previously reported for a French population of white women (r2 > 0.99). This reference database will facilitate the use of TBS to assess bone microarchitectural deterioration in clinical practice.

Bone Mineral Density Reference of 10-20 year-old Korean Children and Adolescents - Based on Hologic DXA from the Korean National Health and Nutrition Examination Surveys -

Purpose: To obtain normative data on bone mineral density of each region of interest (ROI) measured by Hologic model dual-energy x-ray absorptiometry (DXA) of children and adolescents. Methods: Cross sectional results from 723 healthy Korean children and adolescents (10-20 years of age) in the Korean National Health and Nutrition Examination Surveys were analyzed. We used age- and sex-specific reference data for bone mineral density (BMD) of the lumbar spine, femur neck, and total body except head from Hologic DXA device as recommended by the International Society for Clinical Densitometry. Results: The bone mineral density of each ROI increased with age in both boys and girls. Maximal increase in the lumbar BMD occurred between ages 11 and 12 in girls and between ages 12 and 14 in boys. However, the increases of BMD in each ROI were different. The plateaus of the lumbar spine and whole body except head BMD in girls occurred at ages 15 and 17, respectively. The plateaus of BMD in each ROI occurred at age 17 in boys. Conclusion: Most of the skeletal mass, including lumbar spine and total body except head, is reached before the end of the second decade. This study provides reference values for bone density of each ROI measured with DXA for children and adolescents. (J Korean Soc Pediatr Endocrinol 2011;16:92-99)

The effect of bone strontium on BMD is different for different manufacturers' DXA Systems

Osteoporotic patients treated with strontium ranelate show relatively large increases in bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) due to the replacement of some of the calcium atoms in bone by strontium. A study published by Pors Nielsen and colleagues reported that replacement of 1% of calcium atoms by strontium causes a 10% increase in BMD. We refer to the ratio of the percentage increase in BMD to the molar percentage of strontium in bone as the strontium ratio. Theoretically it is expected that the strontium ratio should vary between different manufacturers' DXA equipment depending on the effective photon energy of the device, an effect that arises because of the proximity of the X-ray energies produced by lower energy devices to the strontium K-edge at 16 keV. In this study we report theoretical estimates of the strontium ratio for two axial DXA systems and two peripheral DXA devices based on their broad spectrum X-ray emission. The theoretical figures were verified in an experimental study in which the strontium ratio for each device was measured using phantoms containing mixtures of hydroxyapatite and strontium hydrogen-phosphate. The theoretical values of the strontium ratio were 11.0 for the Hologic Discovery, 9.9 for the GE-Lunar Prodigy, 9.1 for the Demetech Calscan, and 8.5 for the Osteometer Dexacare G4. Experimental results were 11.2 for the Discovery, 9.9 for the Prodigy, 8.6 for the Calscan and 6.3 for the Dexacare G4. The results confirm both theoretically and experimentally that the effect of bone strontium on BMD measurements is different for different DXA systems. In the future it might be possible to exploit this effect to make a non-invasive estimate of average bone strontium content in groups of patients receiving strontium medication for osteoporosis.

Dual-Energy X-ray Absorptiometry With Serum Ferritin Predicts Liver Iron Concentration and Changes in Concentration Better Than Ferritin Alone

Accurate assessment of liver iron concentration (LIC) is critical for optimal monitoring of iron toxicity in multitransfused patients. Serum ferritin is the most widely used although its association to LIC is only modest. We studied if a liver-specific measure using dual-energy X-ray absorptiometry (DXA) systems could improve LIC estimates over ferritin alone in Thalassemia (Thal) patients. Thirty-seven patients with Thal (19.2 ± 9.0 yr, 20 male) were studied and 10 had multiple visits. Height, weight, ferritin, whole-body DXA, and hepatic superconducting quantum interference device (SQUID) were measured within 5 wk. DXA hepatic density was measured using right rib, whole liver, and multiple subliver regions. The best agreement to SQUID LIC was found using a combination of ferritin, weight, DXA subliver region 3 bone mineral content (BMC), and right rib BMC. DXA with ferritin improved the ferritin alone correlation from R 2 = 0.35 to R 2 = 0.62. Serial LIC changes using DXA were associated with serial SQUID changes ( r = 0.73, p = 0.02). Changes in ferritin alone were not significant ( p = 0.06). We conclude that the addition of whole-body DXA measures and body weight substantially increased the accuracy of LIC and change in LIC estimates over the use of ferritin alone and could be useful when magnetic resonance imaging or SQUID is not available.

Bone Disorders in Patients With Chronic Liver Disease Awaiting Liver Transplantation

Background An important complication of chronic liver disease is osteodystrophy, which includes osteoporosis and the much rarer osteomalacia. Both conditions are associated with significant morbidity through fractures resulting in pain, deformity, and immobility. Liver transplantation may further deteriorate bone metabolism. The aim of the present study was to investigate the frequency and severity of hepatic osteodystrophy among patients with liver cirrhosis who were referred for liver transplantation. We also evaluated modifications in bone metabolism after liver transplantation. Materials and methods We recruited 35 consecutive patients with chronic liver disease who were undergoing assessment for transplantation over a 1-year period. Bone mass in the total skeleton and proximal hip was evaluated using a dual-energy X-ray absorptiometry device (Lunar Prodigy Advance, GE Healthcare, USA). According to World Health Organization recommendations, osteoporosis was defined as a T score < −2.5 and osteopenia as T score between −1 and −2.5. Results We enrolled in the study 35 patients, including 8 females and 27 males of overall mean age of 57 ± 7, who showed a viral etiology (57%) or alcohol etiology (28%), Child-Pugh 8.7 ± 2.3. The overall prevalence of osteodystrophy was 40% (26% osteopenia and 14% osteoporosis). No difference was evident according to gender, severity of liver disease (Child-Pugh, Model for End-stage Liver Disease), or origin of liver disease. A subgroup of 10 transplanted patients reached 3-month follow-up, showing total body T score with a significant decrease after 3 months while femoral T scores tended to decrease insignificantly. Conclusions This study revealed a high prevalence of low bone mineral density among cirrhotic patients before liver transplantation. We suggest that both bone mineral density and biochemical examinations should be considered to be routine tests to identify the status of bone mass and bone metabolism among recipients prior to liver transplantation.

Age-Related Changes in Hip Geometic Parameters in the Japanese Female Population: Cross-Sectional and Longitudinal Data from JPOS Cohort Study

For patients undergoing screening computed tomography colonography (CTC), an opportunity exists for bone mineral density (BMD) screening without additional radiation exposure using quantitative computed tomography (QCT). This study investigated the use of dual-energy X-ray absorptiometry (DXA)–equivalent QCT Computed Tomography X-Ray Absorptiometry (CTXA) analysis at the hip obtained using CTC examinations using a retrospective asynchronous calibration of patient scans. A cohort of 33 women, age 61.3 (10.6) yr (mean [standard deviation]), had routine CTC using various GE LightSpeed CT scanner models followed after 0–9 mo by a DXA hip BMD examination using a GE Lunar Prodigy machine. Areal bone mineral density (aBMD) and T-scores of the proximal femur were measured from either prone or supine CTC examinations using Mindways QCT Pro software following standard workflow except that the CT scanners were asynchronously calibrated by phantoms scanned retrospectively of the CTC examination without the subject present. CTXA and DXA aBMD were highly correlated (R2 = 0.907) with a linear relationship of DXA_BMD = 1.297*CTXA_BMD + 0.048. The standard error of estimate (SEE) on the linear fit was 0.053 g/cm2. CTXA and DXA T-scores showed a linear relationship of DXA_T-score = 1.034*CTXA_T-score + 0.3 and an SEE of 0.379 T-scores. CTXA and DXA aBMD and T-score measurements showed good correlation despite asynchronous scan acquisition and retrospective QCT calibration. The SEE of 0.053 g/cm2 is on par with the literature comparing Hologic and Lunar DXA devices. The observed relationship between CTXA and Lunar DXA aBMD matches predictions from published cross-calibrations relating CTXA to DXA aBMD measurement. Thus, opportunistic use of CTXA T-scores obtained at the time of CTC could enhance osteoporosis screening.

Validation of DXA Body Composition Estimates in Obese Men and Women

The aim of this study was to determine the accuracy of dual-energy X-ray absorptiometry (DXA)-derived percentage fat estimates in obese adults by using four-compartment (4C) values as criterion measures. Differences between methods were also investigated in relation to the influence of fat-free mass (FFM) hydration and various anthropometric measurements. Six women and eight men (age 22-54 years, BMI 28.7-39.9 kg/m(2), 4C percent body fat (%BF) 31.3-52.6%) had relative body fat (%BF) determined via DXA and a 4C method that incorporated measures of body density (BD), total body water (TBW), and bone mineral mass (BMM) via underwater weighing, deuterium dilution, and DXA, respectively. Anthropometric measurements were also undertaken: height, waist and gluteal girth, and anterior-posterior (A-P) chest depth. Values for both methods were significantly correlated (r(2) = 0.894) and no significant difference (P = 0.57) was detected between the means (DXA = 41.1%BF, 4C = 41.5%BF). The slope and intercept for the regression line were not significantly different (P > 0.05) from 1 and 0, respectively. Although both methods were significantly correlated, intraindividual differences between the methods were sizable (4C-DXA, range = -3.04 to 4.01%BF) and significantly correlated with tissue thickness (chest depth) or most surrogates of tissue thickness (body mass, BMI, waist girth) but not FFM hydration and gluteal girth. DXA provided cross-sectional %BF data for obese adults without bias. However, individual data are associated with large prediction errors (+/-4.2%BF). This error appears to be associated with tissue thickness indicating that the DXA device used may not be able to accurately account for beam hardening in obese cohorts.

Exceptional bone density DXA values of the rostrum of a deep-diving marine mammal: a new technical insight in the adaptation of bone to aquatic life

The use of dual energy X-ray absorptiometry (DXA) to measure bone mineral density (BMD) has been applied to several animal species to examine bone and body composition in longitudinal studies. Although the rat is the most frequently used mammal in DXA-based investigations, the BMD of several species of larger-sized nonhuman mammals has already been reported [1]. Studies on a single specific bone or total body BMD have been performed on nonhuman primates [2, 3], sheep [4], bovine calves [5, 6], horses [7], pigs [8], dogs [9, 10], cats [11], and striped [12] and bottlenose dolphins [13]. All BMD values (expressed as g/cm) obtained from the species listed above ranged between 0.463 (canine III metacarpal bone) and 2.12 (pig skull). Other values to consider for reference are 1.1 (dolphin arm) and 1.85 (equine III metacarpal bone). In terrestrial mammals, the most important intraspecific factors affecting BMD are body weight and age, whereas in aquatic mammals, the arm and forearm BMD correlated to body dimensions and age of the animal [10–13]. For the first time, we radiographed the whole skull and scanned by means of a DXA device (Hologic QDR1000, Hologic Inc., Waltham, MA, USA) the rostrum of a male Blainville’s beaked whale Mesoplodon densirostris (Blainville, 1817). This specimen was found stranded by Lamberto Loria in Papua New Guinea (ex British New Guinea) at the end of nineteenth century and is now preserved at the “G. Doria” Civic Museum of Natural History in Genova (Italy) with the number MSNG 16. The rostrum of M. densirostris is made up by maxillary and premaxillary bones, pterygoids, palatines, and vomer and in mature animals is supported axially by ossification of the mesorostral canal. In adult males, the mesorostral ossification is due to the gradual replacement of mesethoid cartilage with secondary bone [14]. The rostrum consists of dense Haversian tissue, the secondary osteons of which are oriented longitudinally, themselves constituted by hypermineralized parallel-fibered osseous tissue [15]. The ultrastructure of the walls of the secondary osteons is characterized by a strong volumetric reduction of the collagenous network, composed by very thin fibrils oriented longitudinally. The biomechanical behavior of the rostrum is that of an exceptionally rigid, hard but also apparently fragile material [15]. The BMD values of this bone (2.612 to 2.686 g/cm) obtained by simple measurements based on Archimedes’s principle have been reported as the highest values hitherto observed for mammalian bone and the rostral mineralization has been quantified up to 22% above that of “normal” adult mammalian bone [15]. We divided the scan of our specimen into three regions of interest (RoI) because the length of the bone exceeded the DEXA-arm motion track (approximately 70 cm). The proximal (pRoI), medium (mRoI), and distal RoI (dRoI) were then scanned in a dorsoventral projection starting from infraorbital foramina toward the foremost extremity of Skeletal Radiol (2009) 38:1123–1125 DOI 10.1007/s00256-009-0647-4

Self-Reported Physical Activity Improves Prediction of Body Fatness in Young Adults

To examine self-reported physical activity levels from the International Physical Activity Questionnaire (IPAQ) as an independent predictor of dual-energy x-ray absorptiometry (DXA)-measured percent body fat (%BF) from body mass index (BMI), gender, and race. Two hundred and seventy-eight students, aged 18-24 yr, volunteered to participate. There were 133 males (85 white and 48 black) and 145 females (77 white and 68 black). Total activity levels were quantified in MET hours per week (MET h wk(-1)) using the IPAQ short form. Height and weight were measured, and BMI values were calculated (kg m(-2)). %BF was assessed using DXA. Linear regression analysis was used to develop and compare a body fat prediction equation with (full) and without (reduced) the variable MET-h.wk. Both models included BMI, gender, and race as predictor variables. The prediction sum of squares (PRESS) statistic was used to cross-validate both models, and the individual predictive accuracy was compared using modified Bland-Altman plots. Mean +/- SD values were as follows: BMI = 24.4 +/- 4.1 kg m(-2), %BF = 24.5 +/- 9.3%, and MET h wk(-1) = 37.4 +/- 21.9. Gender, BMI, and race explained 81% of the variance in %BF, with a root mean square error (RMSE) of 4.07. The full model with MET-h.wk improved the prediction of %BF by 2% (R2 = 0.83, RMSE = 3.87). When cross-validated, the corresponding PRESS statistics for the reduced and full model were 4.10 and 3.90, respectively. Bland-Altman limits of agreement were greater for the reduced model compared with the full model (-8.09, 8.10 vs -7.67, 7.68). These results suggest that %BF can be predicted with greater precision and accuracy in a young adult population when MET-h.wk are included in addition to BMI, gender, and race.

Effects of lean and fat mass on bone mineral density and arterial stiffness in elderly men

The role of body composition on arterial stiffness and osteoporosis remains unclear, especially in the elderly male population. Our results indicate that elderly men with high lean mass and low fat mass exhibit the best arterial and bone profile with the lowest arterial stiffness and the highest bone mineral density. The aim of this study was to evaluate the influence of fat and lean mass on both arterial stiffness and bone mass density (BMD) in elderly men. This study was performed in 169 French males over 60 years old. Aortic stiffness was assessed by carotid/femoral pulse wave velocity (PWV). BMD and body composition were determined with a dual-energy X-ray absorptiometry device in the lumbar spine L1-L4, femoral neck, and total body. Lean mass was positively correlated with the three T scores accounting for 11.6%, 26.6%, and 12.2% of the variability in the lumbar spine L1-L4, femoral neck, and total body BMD T scores, respectively. Fat mass had no effect on BMD. However, fat mass was positively correlated with aortic PWV, accounting for 9.8% of its variability. Lean mass was not a determinant of PWV. Hypertension, diabetes, and dyslipidemia were associated with higher PWV but had no effect on BMD. In males from a general population over 60 years of age, bone and arterial aging are differently influenced by lean and fat mass. Our results indicate that elderly men with high lean mass and low fat mass exhibit the best arterial and bone profile with the lowest arterial stiffness and the highest BMD.

Well-nourished cystic fibrosis patients have normal mineral density, but reduced cortical thickness at the forearm

Our goal was to assess mineral density and geometry of the cortex at the level of the forearm in adolescents and young adults with cystic fibrosis, using peripheral quantitative computed tomography. We found that density was normal, but cortical thickness significantly reduced, as well in males as in females. Our goal was to measure bone mineral density as a volumetric density, as well as total cross-sectional area, cortical area and cortical thickness, using peripheral quantitative computed tomography (pQCT) at the forearm in adolescents and young adults with cystic fibrosis. We evaluated relationships between forearm bone measurements and body composition assessed using dual energy X-ray absorptiometry (DXA). An XCT 2000 pQCT (Stratec, Pforzheim, Germany) and a QDR 4500 A-upgraded to Discovery DXA device (Hologic, Waltham, MA, USA) were used. Forty-eight patients (31 males,17 females, mean+/-SD 20+/5 years) were studied. Anthropometric features were: height 169+/- 10 cm, SDS 0.05+/-0.12, body mass index 19.8+/- 2.5 kg/m(2), SDS -0.56+/-0.14. Bone mineral density and total cross-sectional area of the forearm and body composition were normal, whereas cortical thickness was significantly reduced in males (mean Z-score - 1.22, p < 0.05), and in females (mean Z-score - 1.61, p < 0.05). Total body lean mass correlated more strongly with cortical thickness (r = 0.72, p < 0.001) than with total bone mineral density at the proximal radius (r = 0.39, p < 0.05). Adolescents and young adults with cystic fibrosis, presenting with only a slight degree of underweight, have at the radius a preserved bone mineral density but a reduced cortical thickness.

Comparison of BMD precision for Prodigy and Delphi spine and femur scans

Precision error in bone mineral density (BMD) measurement can be affected by patient positioning, variations in scan analysis, automation of software, and both short- and long-term fluctuations of the densitometry equipment. Minimization and characterization of these errors is essential for reliable assessment of BMD change over time. We compared the short-term precision error of two dual-energy X-ray absorptiometry (DXA) devices: the Lunar Prodigy (GE Healthcare) and the Delphi (Hologic). Both are fan-beam DXA devices predominantly used to measure BMD of the spine and proximal femur. In this study, 87 women (mean age 61.6+/-8.9 years) were measured in duplicate, with repositioning, on both systems, at one of three clinical centers. The technologists were International Society for Clinical Densitometry (ISCD) certified and followed manufacturer-recommended procedures. All scans were acquired using 30-s scan modes. Precision error was calculated as the root-mean-square standard deviation (RMS-SD) and coefficient of variation (RMS-%CV) for the repeated measurements. Right and left femora were evaluated individually and as a combined dual femur precision. Precision error of Prodigy and Delphi measurements at each measurement region was compared using an F test to determine significance of any observed differences. While precision errors for both systems were low, Prodigy precision errors were significantly lower than Delphi at L1-L4 spine (1.0% vs 1.2%), total femur (0.9% vs 1.3%), femoral neck (1.5% vs 1.9%), and dual total femur (0.6% vs 0.9%). Dual femur modes decreased precision errors by approximately 25% compared with single femur results. This study suggests that short-term BMD precision errors are skeletal-site and manufacturer specific. In clinical practice, precision should be considered when determining: (a) the minimum time interval between baseline and follow-up scans and (b) whether a statistically significant change in the patient's BMD has occurred.

Fracture Risk Assessment in African American Women Using Quantitative Ultrasound of the Os Calcis

Osteoporosis is a disease characterized by reduced bone mass and quality with increased risk for fracture. While dual-energy X-ray absorptiometry (DXA) is typically used to assess bone density (BMD), the technique of quantitative ultrasound (QUS) allows for the assessment of bone quality or stiffness index (SI). PURPOSE: To examine bone quality and risk for osteoporotic fracture in African American women using quantitative ultrasound of the os calcis. METHODS: This investigation included two separate studies. First, T-score risk for fracture was compared between quantitative ultrasound (QUS) of the os calcis and dual-energy X-ray absorptiometry (DXA) of the dual femur and spine in a group of African American women forty years of age and older (n = 20). The definitions of low bone mass proposed by the world health organization were used to classify the women (T-score ≤ −1.0 = osteopenia and T-score ≤ −2.5 = osteoporosis). The QUS apparatus was an Achilles Insight (GE Medical Systems, Madison, WI) and the DXA device was a Prodigy Pro (GE Medical Systems, Madison, WI). Secondly, QUS measurement of the os calcis was used to screen for osteoporotic fracture in ambulatory African American women attending local community health fairs. RESULTS: In the first study, mean descriptives were: age = 55.2 ± 11.0 yrs, dual femur BMD = 1.000 ±0.181 g-cm-2, spine BMD = 1.180 ± 0.214 g-cm-2, os calcis SI = 97.4 ±21.6. The correlation between QUS SI and DXA BMD was greater with the dual femur (r = 0.78, p = 0.00) than with the spine BMD (r = 0.65, p = 0.00). The sensitivity in identifying risk for fracture (T-score <-1.0) was 100% between the QUS and DXA dual femur assessment and 80% compared to the DXA spine assessment. The specificity between the two machines was 87% with the dual femur and 86% with the spine assessment. In the second study, one hundred and nineteen women, 40 to 94 years of age (mean age = 64.3 ± 10.5 years) were measured. Mean SI value was 92 ± 21.9. Forty-two percent of the women were classified by SI T-score as having low bone quality with 5% in the osteoporotic fracture range. CONCLUSIONS: In a small group of African American women QUS and DXA assessments of bone quality appear to be very similar. Community screening using QUS suggests that a large percentage of African American women have reduced bone quality and may be at risk for future osteoporotic fracture.

The DXL Calscan heel densitometer: evaluation and diagnostic thresholds

The DXL Calscan (Demetech AB) is a new dual energy X-ray absorptiometry device for determining heel bone mineral density (BMD). The system is based on the standard technique of dual energy X-ray absorptiometry (DXA), using a fan beam configuration, but introduces an additional laser measurement of heel thickness intended to improve accuracy. We have examined the utility, in vitro and in vivo performance of the DXL Calscan and established triage thresholds based on the UK's National Osteoporosis Society guidelines on peripheral densitometry. The Calscan proved convenient, easy to use and was stable over time and within a range of operating temperatures. Short-term in vitro precision as %CV, with phantom repositioning, was 0.75% and long term precision 0.73%. Precision in vivo, determined from duplicate right heel scans of 67 subjects, was 1.19%. Effective radiation dose to the patient was <0.1 microSv per scan. 140 white females (70 osteoporotic and 70 non-osteoporotic), aged 55-70 years underwent scans of both heels. Subjects were defined as osteoporotic or non-osteoporotic on the basis of axial DXA (spine L2-L4 and total hip). Triage thresholds for reassurance-referral or referral-treatment were 0.391 g cm(-2) and 0.306 g cm(-2) for non-dominant and 0.395 g cm(-2), 0.294 g cm(-2) for dominant heel, respectively. The non-dominant heel proved slightly superior to the dominant for triage purposes. Of the seven non-osteoporotic subjects misclassified as osteoporotic by Calscan of either heel, six had severe axial osteopenia. If operated by trained personnel and used in appropriate populations exhibiting risk factors, the Calscan is well suited for use in the management of post-menopausal osteoporosis.

Between-centre variability versus variability over time in DXA whole body measurements evaluated using a whole body phantom

This study aimed to compare the variability of whole body measurements, using dual energy X-ray absorptiometry (DXA), among geographically distinct centres versus that over time in a given centre. A Hologic-designed 28 kg modular whole body phantom was used, including high density polyethylene, gray polyvinylchloride and aluminium. It was scanned on seven Hologic QDR 4500 DXA devices, located in seven centres and was also repeatedly ( n = 18) scanned in the reference centre, over a time span of 5 months. The mean between-centre coefficient of variation (CV) ranged from 2.0 (lean mass) to 5.6% (fat mass) while the mean within-centre CV ranged from 0.3 (total mass) to 4.7% (total area). Between-centre variability compared well with within-centre variability for total area, bone mineral content and bone mineral density, but was significantly higher for fat ( p < 0.001), lean ( p < 0.005) and total mass ( p < 0.001). Our results suggest that, even when using the same device, the between-centre variability remains a matter of concern, particularly where body composition is concerned.

Comparison of body weight and composition measured by two different dual energy X-ray absorptiometry devices and three acquisition modes in obese women

Weight measured by dual-energy X-ray (DXA) was shown to be increasingly underestimated in subjects over 75 kg compared to an electronic scale. This study compares body weight and composition measured by balance beam scale and three DXA acquisition modes in obese subjects. In 39 obese, body weight was measured by balance beam scale, and body weight and composition by DXA Hologic QDR4500A in normal (NPM) and high power mode (HPM) (Enhanced v8.26 and v8.26* software) and DXA GE-Lunar Prodigy (v6.5 software). To ensure linearity of body weight and composition measured by the different DXA acquisitions, we also measured 13 women with a body mass index (BMI) of 25-30 kg/m(2). While QDR4500A HPM overestimates scale weight by about 2 kg over the whole BMI spectrum, QDR4500A NPM underestimates scale weight as a weight-dependent response (-1.7+/-1.8 kg overall, -4.1+/-1.6 kg in morbidly obese women). These results suggest switching from one mode to the other at a specific threshold, i.e. in our study a weight of 90 kg or a BMI of 34 kg/m(2). Prodigy gives weight about similar to scale (+0.5+/-0.8 kg). Both Hologic acquisition modes underestimate fat mass but overestimate lean body mass compared to Prodigy. The QDR4500A NPM is inappropriate in women over 90 kg. Unfortunately, the QDR4500A HPM overestimates body weight in the range of 90-150 kg. The difference between scale and Prodigy weight remains stable throughout weight ranges. To better assess their accuracies in terms of body composition, QDR4500A NPM, HPM and Prodigy should be tested against phantoms or in vivo multi-compartment models.