A comparison of two dual-energy X-ray absorptiometry systems for spinal bone mineral measurement

Summary Two dual-energy X-ray absorptiometry (DEXA) systems—the Hologic QDR-1000 and the Norland XR-26 bone densitometers—were evaluated in terms of precision, accuracy, linearity of response, X-ray exposure, and correlation of in vivo spinal measurements. In vitro precision and accuracy studies were performed using the Hologic anthropomorphic spine phantom; linearity of response was determined with increasing thicknesses of aluminum slabs and concentrations of Tums E-X in a constant-level water bath. Both systems were comparable in precision, achieving coefficients of variation (CVs) of less than 1% in bone mineral content (BMC, g), bone area (cm²), and bone mineral density (BMD, g/cm²). Both were accurate in their determination of BMC, bone area, and BMD with reference to the Hologic spine phantom. Both systems also showed good BMC and BMD linearity of response. Measured X-ray skin surface exposures for the Hologic and the Norland systems were 3.11 and 3.02 mR, respectively. In vivo spinal measurements (n=65) on the systems were highly correlated (BMC: r=0.993, SEE=1.770 g; area: r=0.984, SEE=1.713 cm²; BMD: r=0.990, SEE=0.028 g/cm²). In conclusion, both systems are comparable in terms of precision, accuracy, linearity of response, and exposure efficiency.     

Interpretation of whole body dual energy X-ray absorptiometry measures in children: comparison with peripheral quantitative computed tomography

The assessment of bone health in children requires strategies to minimize the confounding effects of bone size on dual energy X-ray absorptiometry (DXA) areal bone mineral density (BMD) results. Cortical bone composes 80% of the total skeletal bone mass. The objective of this study was to develop analytic strategies for the assessment of whole body DXA that describe the biomechanical characteristics of cortical bone across a wide range of body sizes using peripheral quantitative computed tomography (pQCT) measures of cortical geometry, density (mg/mm³), and strength as the gold standard. Whole body DXA (Hologic QDR 4500) and pQCT (Stratec XCT-2000) of the tibia diaphysis were completed in 150 healthy children 6–21 years of age. To assess DXA and pQCT measures relative to age, body size, and bone size, gender-specific regression models were used to establish z scores for DXA bone mineral content (BMC) for age, areal BMD for age, bone area for height, bone area for lean mass, BMC for height, BMC for lean mass, and BMC for bone area; and for pQCT, bone cross-sectional area (CSA) for tibia length and bone strength (stress-strain index, SSI) for tibia length. DXA bone area for height and BMC for height were both strongly and positively associated with pQCT CSA for length and with SSI for length (all P < 0.0001), suggesting that decreases in DXA bone area for height or DXA BMC for height represent narrower bones with less resistance to bending. DXA BMC for age (P < 0.01) and areal BMD (P < 0.05) for age were moderately correlated with strength. Neither DXA bone area for lean mass nor BMC for lean mass correlated with pQCT CSA for length or SSI for length. DXA BMC for bone area was weakly associated with pQCT SSI for length, in females only. Therefore, normalizing whole body DXA bone area for height and BMC for height provided the best measures of bone dimensions and strength. DXA BMC normalized for bone area and lean mass were poor indicators of bone strength.     

Accuracy and Precision of 62 Bone Densitometers Using a European Spine Phantom

Dual-energy absorptiometry (DXA) is widely used for bone mineral density measurements. Different types of devices are available. Differences between devices from either the same manufacturer or different manufacturers can lead to difficulties in clinical practice when patients are followed on different machines. We calculated the accuracy and precision of 62 DXA devices from two manufacturers (51 Hologic, 11 Lunar) using a European Spine Phantom (ESP, semi-anthropomorphic). The ESP was measured 5 times on each device without repositioning. Accuracy was assessed by comparing bone mineral density (BMD, g/cm²) values measured on each device with the actual value of the phantom. Precision was assessed by the coefficient of variation (CVsd), using the root mean square average. The limits of agreement were estimated from the differences between each replicate measurement of BMD and the estimated true value for a particular manufacturer, according to Bland and Altman. The results confirm the difference between devices from different manufacturers (18.5%). Mean CVsd values were 0.57% and 0.64% for Hologic and Lunar respectively. The limits of agreement among devices from the same manufacturer were 0.026 g/cm² and 0.025 g/cm² for Hologic and Lunar respectively. Differences in extreme results between devices from the same manufacturer were on average 5.4% and 3.6% for Hologic and Lunar respectively. Results of different devices from the same manufacturer are highly comparable, although unpredictable differences exist that may be clinically relevant. Received: 12 June 1998 / Accepted: 20 November 1998     

糖皮质激素对成年大鼠骨量的影响

目的利用双能X线吸收法(DXA)探讨成年大鼠接受糖皮质激素后骨量变化的规律。方法 21只44周龄SD雌性大鼠分别假性去卵巢+未注射糖皮质激素(SHAM组)、摘除双侧卵巢(OVX组)或注射甲基强的松龙[2.5 mg/(kg·d)](PRED组),应用扇形束DXA(QDR-4500A)每4周测定一次全身骨密度(BMD)、骨矿含量(BMC)、骨骼面积(AREA);术后12周处死,测定离体腰椎、股骨、胫骨及其兴趣区的BMD、BMC、AREA。压缩试验测定第二腰椎最大载荷和弹性模量。结果 (1)术后8周开始OVX组体重显著重于同龄SHAM组(8周时,P0.05,12周时P0.01),术后4周开始PRED组体重显著轻于同龄SHAM组(P0.05);(2)术后12周OVX组整体BMC显著高于SHAM组(P0.05),术后8、12周OVX组整体BMC显著高于PRED组(P0.05);(3)术后12周OVX组离体第5、6腰椎BMD及第6腰椎BMC显著低于SHAM组和PRED组(P0.05),PRED组离体各腰椎BMD、BMC、AREA与SHAM组无明显差异;(4)术后12周与SHAM组比较,OVX组离体股骨(-7.42%)、股骨远端(-10.85%)和近端(-6.92%)、胫骨近端(-11.40%)BMD显著降低(P0.05),其中股骨、股骨远端、胫骨近端BMC也显著降低(P0.05);(5)术后12周与SHAM组比较,PRED组离体股骨及各区BMD、BMC、AREA无显著性差异,整体胫骨及各区BMD无显著性差异;(6)术后12周与SHAM组比较,OVX组及PRED组胫骨中远端骨量增加;(7)与SHAM组比较,OVX组最大载荷和弹性模量显著降低,PRED组最大载荷显著降低。结论成熟期大鼠接受甲基强的松龙后,皮质骨和松质骨骨量没有显著变化,DXA检查难以发现其骨丢失情况;力学性能改变提示糖皮质激素更多的是引起骨质量的改变而导致了力学性能的下降及骨折的发生。     

Precision, accuracy, and reproducibility of dual X-ray absorptiometry measurements in mice in vivo.

Dual X-ray absorptiometry (DXA) has currently become a clinical standard for the assessment of bone mass and bone mineral density (BMD) at multiple sites for the diagnosis and follow-up assessment of osteoporosis in humans. The precision of DXA measurement in human studies has been well documented during the last two decades. However, there have been no systematic reports on the precision and accuracy of BMD measurements in mice using DXA, although mice have proven to be useful models for the study of osteoporosis. Accordingly, BMD of total body as well as regions of interest (ROIs) was measured twice in mice in vivo after a short (10-min) and long (16-hr) interval between scans by DXA, and scanning variations were calculated. Inter- and intra-analyzer variations from the same scans were also determined. The percent coefficients (%CVs) of short-interval scanning variation and inter- and intra-analyzer variations for total body and regional BMDs were less than 2% at sites, demonstrating high precision of in vivo BMD measurements in mice. Moreover, the BMD values comparing in vivo and ex vivo samples from the same animals were of %CV less than 10% at all sites. The correlation of bone mineral content (BMC) to bone ash was further examined, and the correlation between ROI BMC and bone ash was relatively high at all sites both in vivo and ex vivo, with the latter higher. We conclude that in vivo DXA BMD measurements in mice are very reliable with high precision and acceptable accuracy, and therefore useful for longitudinal studies of the mouse skeleton.     

Patterns of Bone Mineral Accretion and Sex Differences in Healthy Term Vitamin D Replete and Breastfed Infants From Montreal,Canada: Bone Mass Reference Data

Infancy is a period of rapid bone growth and mineral accretion; nonetheless, reference data remain scarce for this age group. The purpose of this report is to generate reference data for bone mass in breastfed vitamin D replete infants and investigate patterns of bone mineral accretion and sex differences. This is a secondary analysis from a double-blinded randomized controlled trial (NCT00381914). Healthy term breastfed (exclusively or mixed) infants were randomized to different doses of oral vitamin D supplementation (400-1600 IU/d) and followed prospectively from 1 to 12 mo. Plasma 25-hydroxyvitamin D (LC-MS/MS), bone mineral content (BMC; whole body (WB) and lumbar spine (LS)) and bone mineral density (BMD; LS) were measured at 1, 3, 6, 9, and 12 mo by dual-energy x-ray absorptiometry (Hologic Discovery 4500A) with no effect of supplementation on bone outcomes. For the purpose of this analysis, 63 infants with adequate plasma 25-hydroxyvitamin D ≥ 50 nmol/L at baseline, were included. Differences over time and between sexes were tested using mixed model repeated measures ANOVA. Infants (31 males, 32 females) were 39.5 ± 1.1 wk gestational age at birth and appropriate for gestational age. WB BMC, LS BMC, and LS BMD increased by 143.2%, 116.8%, and 31.1% respectively across infancy. WB BMC was higher (4.2% - 9.4%; p = 0.03) in males than in females across the study. After adjusting WB BMC for weight, length or head BMC, sex differences were not evident. LS BMC and LS BMD did not vary by sex. LS BMD growth charts for both sexes combined, were generated using LMS chartmaker. WB BMC more than doubles during the first year of life confirming the importance of skeletal growth and the need for age-specific reference data in infancy. Sex differences in BMC, if any, are mostly driven by differences in body size.     

Anomalies in the Measurement of Changes in Bone Mineral Density of the Spine by Dual-Energy X-ray Absorptiometry

Dual-energy X-ray absorptiometry (DXA) is frequently used for longitudinal studies of bone mineral status because of the high precision obtained, but evidence is emerging that the accuracy of measurements of changes may be a limitation because of artefacts of the analysis procedure, in particular, a dependence of the measured bone area (BA) on the bone mineral content (BMC). Results of spine bone mineral measurements taken at intervals with two DXA scanners, a Hologic QDR 1000W, and a Norland XR 26 HS, were examined. There was a consistent correlation between changes in BA and in BMC, with a slope of approximately 0.25 when expressed as percentages. A real change of BA of the magnitude observed is not feasible. There were no differences among the correlations for different instruments, genders, ages, or weight changes. There would appear to be an underestimation of changes in bone mineral density (BMD), but there is a possibility that some of the anomaly is manifested as an overestimation of a change in BMC. Phantom measurements were undertaken with the DXA scanners mentioned above and with a Lunar DPX. The phantoms consisted of simulations of the spine cut from aluminium sheet, so that the effective BMD could be varied. The dependence of the measured BA on BMC varied with the phantom outline, particularly the thickness of the transverse processes. Evidence was obtained of both an underestimate of BMD changes and an overestimate of BMC changes. There are errors in measuring spine changes, but these do not seem to be as serious as a previous report suggests for the Hologic scanner and are not likely to lead to misinterpretation of results. Received: 17 June 1997 / Accepted: 23 January 1998     

A multinational study to develop universal standardization of whole-body bone density and composition using GE Healthcare Lunar and Hologic DXA systems

Dual‐energy x‐ray absorptiometry (DXA) is used to assess bone mineral density (BMD) and body composition, but measurements vary among instruments from different manufacturers. We sought to develop cross‐calibration equations for whole‐body bone density and composition derived using GE Healthcare Lunar and Hologic DXA systems. This multinational study recruited 199 adult and pediatric participants from a site in the US (n = 40, ages 6 through 16 years) and one in China (n = 159, ages 5 through 81 years). The mean age of the participants was 44.2 years. Each participant was scanned on both GE Healthcare Lunar and Hologic Discovery or Delphi DXA systems on the same day (US) or within 1 week (China) and all scans were centrally analyzed by a single technologist using GE Healthcare Lunar Encore version 14.0 and Hologic Apex version 3.0. Paired t‐tests were used to test the results differences between the systems. Multiple regression and Deming regressions were used to derive the cross‐conversion equations between the GE Healthcare Lunar and Hologic whole‐body scans. Bone and soft tissue measures were highly correlated between the GE Healthcare Lunar and Hologic and systems, with r ranging from 0.96 percent fat [PFAT] to 0.98 (BMC). Significant differences were found between the two systems, with average absolute differences for PFAT, BMC, and BMD of 1.4%, 176.8 g and 0.013 g/cm², respectively. After cross‐calibration, no significant differences remained between GE Healthcare Lunar measured results and the results converted from Hologic. The equations we derived reduce differences between BMD and body composition as determined by GE Healthcare Lunar and Hologic systems and will facilitate combining study results in clinical or epidemiological studies. © 2012 American Society for Bone and Mineral Research.     

Accuracy and precision of bone mineral density and bone mineral content in excised rat humeri using fan beam dual-energy X-ray absorptiometry.

The aim of this study was the evaluation of fan beam dual-energy X-ray absorptiometry (DXA) for measuring bone mineral density (BMD) and bone mineral content (BMC) of isolated rat humeri. Defleshed rat humeri from male Lewis rats were examined with a Hologic QDR 4500 A (Hologic, Inc., Bedford, MA) high-resolution densitometer both in water and 0.9% saline solution. The small animal scan protocol with the regional high-resolution mode was used. BMC measured by DXA was compared with bone dry weight, ash weight, and bone calcium content. Furthermore, DXA BMD and BMC precision were determined. We also evaluated the effect of salinity of the water bath in which the bones were measured. Correlations (r(2)) of BMC, as determined by DXA with dry weight, ash weight, and bone calcium content, were 0.978, 0.988, and 0.890, respectively. DXA overestimated ash weight by 5%-9%. Precision errors for BMC (BMD) were 0.90% (0.76%) without and 1.3 (0.86) with repositioning. Changes in the salinity of the water bath had a significant influence on the DXA results: At the 0.9% physiological level, BMC (-4.4%) and area (-4.1%), but not BMD, values were significantly lower (p < 0.005) compared with measurements in tap water. Fan beam DXA is a highly accurate and precise technique for measuring BMC and BMD in excised small animal bones. A physiological saline concentration in the water bath had a significant impact on BMC and area, but not on BMD, and should therefore be strictly controlled to avoid an underestimation of BMC.     

Whole body bone mass and body composition in a girl with achondroplasia, at ages 9 through 12.

A 9-yr-old white female with achondroplasia was one of a group of 773 children who were recruited for a study of the accumulation of whole body skeletal mass during four annual measurements. Measurements of bone, fat, and lean mass were obtained with a Hologic 1000W instrument. The following variables are used to compare the subject with the 130 healthy white girls who participated in the study: bone mineral content (BMC), bone mineral density (BMD), and bone mineral apparent density (BMAD). Ratios of BMC to weight or BMC to height, and BMD to weight or height, were also calculated. We found that the BMC of the subject was lower when compared to the reference group, but the ratios of BMC to weight or BMC to height were similar in both. BMD was also lower in the patient, but, when expressed in relation to height and weight, the ratios were similar or slightly higher in the case. BMAD was higher in the subject with achondroplasia at all ages. The subject had a lower percentage fat and higher percentage lean mass than the reference children. We conclude that the accumulation of bone mass in this subject with achondroplasia is appropriate for her reduced body size.     

Bone mineral density of proximal femur and spine in Korean children between 2 and 18 years of age

Ethnic factors affect bone mass acquisition during childhood. The aim of our study was to establish normative data for bone mineral content (BMC) and bone mineral density (BMD) in healthy Korean children and adolescents, using 446 lumbar spine scans (224 males and 222 females) and 364 proximal femur scans (181 males and 183 females) of healthy children between ages 2 and 18 years measured by dual-energy X-ray absorptiometry using Hologic QDR Discovery A 2004. There was an increase in both BMC and BMD during early childhood, acceleration during the adolescence spurt, and a slower increase later. Until 11 years of age, both male and female BMC and BMD were not statistically different. There was a rapid increase in both BMC and BMD in females earlier than in males, and later males caught up with the females and overshot the female values. When compared with Canadian children, BMD and BMC of total proximal femur was found to be more and BMD and BMC of total lumbar spine to be less at some ages. Tanner's stage was significantly associated with BMD and BMC of spine and proximal femur in males and BMC of spine in females in the first three Tanner's stages. Height, body weight, fat content, and body mass index influenced BMC and BMD at different sites by variable amount. Hence, the values presented in this study should be used as reference values in Korean children and adolescents.     

Caloric Restriction Decreases Cortical Bone Mass but Spares Trabecular Bone in the Mouse Skeleton: Implications for the Regulation of Bone Mass by Body Weight

Introduction: Body weight is positively correlated with bone mass and density, and both muscle mass and body fat are thought to play a role in regulating bone metabolism. We examined bone metabolism in calorically restricted mice to determine how alterations in soft tissue mass affect bone mass, density, and strength. Materials and Methods: Caloric restriction (CR) was initiated in male mice at 14 wk of age at 10% restriction, increased to 25% restriction at 15 wk, and then increased to 40% restriction at 16 wk, where it was maintained until 24 wk of age when the study was terminated. Control mice were fed ad libitum (AL). Body composition, BMD, and BMC were measured by DXA, BMD and BMC in the femoral metaphysis were measured by pQCT, femora were tested in three‐point bending, serum leptin and IGF‐1 were measured using immunoassay, and osteoblast and osteoclast numbers were determined using histomorphometry. Results: Body weight, lean mass, fat mass, percent body fat, serum leptin, and serum IGF‐1 were all significantly lower in CR mice than AL mice. Whole body BMC and BMD did not differ significantly between the two groups. Femur BMC, BMD, cortical thickness, and fracture strength decreased significantly in CR mice, but trabecular bone volume fraction in the femur did not change with food restriction. Vertebral cortical thickness also decreased with caloric restriction, whereas spine BMC, BMD, and trabecular bone volume fraction were significantly increased with caloric restriction. Conclusions: Caloric restriction and its related weight reduction are associated with marked decreases in lean mass, fat mass, serum leptin and IGF‐1, and cortical bone mass. Consistent with the opposite effects of leptin on cortical and cancellous bone, trabecular bone mass is spared during food restriction.     

Mineral content of upper tibia assessed by dual photon densitometry

Bone mineral content (BMC, g/cm) and bone mineral density (BMD, g/cm²) of the proximal tibia were determined by dual photon absorptiometry (DPA). Measurements just distal to the subchondral plates of the tibia condyles, where the bone structure is predominantly trabecular, proved to give the most consistent results. The precision of BMC measurements in this region, expressed as the coefficient of variation, was 1.1 per cent and of BMD measurements 2.5 per cent.

In a cross-sectional study on 63 normal women and men, BMC and BMD showed a decrease with age at a rate of about 8 and 9 per cent per decade, respectively, in women, but not in men. In normal women, BMC of proximal tibia was correlated with BMC of lumbar spine, femoral neck, and femoral shaft, as well as with body weight and height. DPA may be useful in the study of bone reactions, such as in patients undergoing arthroplasty of the knee.     

Mineral content of upper tibia assessed by dual photon densitometry

Bone mineral content (BMC, g/cm) and bone mineral density (BMD, g/cm2) of the proximal tibia were determined by dual photon absorptiometry (DPA). Measurements just distal to the subchondral plates of the tibia condyles, where the bone structure is predominantly trabecular, proved to give the most consistent results. The precision of BMC measurements in this region, expressed as the coefficient of variation, was 1.1 per cent and of BMD measurements 2.5 per cent. In a cross-sectional study on 63 normal women and men, BMC and BMD showed a decrease with age at a rate of about 8 and 9 per cent per decade, respectively, in women, but not in men. In normal women, BMC of proximal tibia was correlated with BMC of lumbar spine, femoral neck, and femoral shaft, as well as with body weight and height. DPA may be useful in the study of bone reactions, such as in patients undergoing arthroplasty of the knee.     

Validation of peripheral dual-energy X-ray absorptiometry for the measurement of bone mineral in intact and excised long bones of rats.

We evaluated the precision and accuracy of peripheral dual-energy X-ray absorptiometry (DXA) for the measurement of bone mineral density (BMD) and bone mineral content (BMC) in intact and excised femurs and tibias from rats. Thirty-one Sprague-Dawley rats (18F/13M; 114-360 g) were used in the study. Precision and accuracy were determined in 23 rats and prediction equations were evaluated in an independent sample of 8 animals. Precision was determined by measuring the right hindquarter three times with repositioning between scans. The femur and tibia were then excised, cleaned, and scanned in triplicate, with repositioning. CVs ranged from 0.66 to 2.24%. Accuracy of BMC was determined by comparison to bone ash values. BMC values for the intact and excised femur significantly overestimated bone ash (p < 0.001) by 33% and 5.5%, respectively. BMC for the intact tibia overestimated ash by 37% (p < 0.001), whereas BMC for the excised tibia underestimated ash by 1% (p < 0.05). However, BMC and bone ash were highly related for both bones, whether BMC was measured in the intact animal or after excision (r2 > 0.99). Cross-validation of prediction equations in an independent sample showed that there were no significant differences between predicted ash (based on BMC from DXA) and measured bone ash. These results suggest the peripheral DXA is a useful tool for measuring intact and excised rat leg bones.     

Effect of treadmill exercise on vertebral and tibial bone mineral content and bone mineral density in the aged adult rat: Determined by dual energy X-ray absorptiometry

Summary Dual energy X-ray absorptiometry (DXA; Hologic QDR-1000W) in an ultrahigh-resolution mode, was used to examine the changes in tibial/fibula and vertebral L4 +L5 bone mineral content (BMC) and bone mineral density (BMD) in each 14-month-old female rat at 0, 9, and 16 weeks of study. Twenty rats were randomized by a stratified weight method into two groups, control and exercised. Exercise consisted of running on a flat-bed treadmill, 17 m/minute, 1 hour/day and 5 days/week. As compared with the control group, a significant increase in tibia/fibula BMC and vertebral BMD was apparent at 9 weeks after exercise training (P=0.014 by 2-way analysis of variance). The slope of the gain of the tibia/fibula BMC and BMD by 16 weeks of training was ninefold and fivefold higher than that of the control group (P<0.01 and P<0.05, respectively, by Mann-Whitney test). The correlation coefficient (r) between the final dry weight of excised bone and the final BMC of the intact rat was 0.843 and 0.71 for tibia/fibula and vertebrae, respectively. In summary, we found that in the aged rat, by 9 weeks, exercise increases BMC and BMD in the tibia, whereas in the vertebrae, only increases in the BMD were found. This study demonstrates that this precise and accurate DXA technique is useful in a longitudinal study of in vivo bone mineral changes in the rat over time by taking into account the individual variation between animals as well as changes between groups.     

Precision and Accuracy of a Transportable Dual-Energy X-ray Absorptiometry Unit for Bone Mineral Measurements in Guinea Pigs

Dual energy X-ray absorptiometry (DXA) is a valuable tool for measuring bone mineral content (BMC) and bone mineral density (BMD) in small-animal research. The present study was devised to establish guidelines and to define sites for bone mineral measurements in guinea pigs and to evaluate the accuracy of a new transportable research DXA unit. Repeated scans were performed on 30 guinea pig hindlimbs (in situ) as well as the isolated bones from these limbs (ex situ). Nine exactly specified regions of interest (ROIs) were analyzed twice for BMC and BMD by three different observers. Additionally, the BMC of whole bones and bone segments as measured by DXA was correlated to ash weights of bone in a subset of five animals to determine the accuracy of the DXA measurements. On ex situ scans, intra-observer variability for BMD ranged from 0.09% to 2.33% and inter-observer variability from 0.23% to 5.86% depending on the site studied, with smaller ROIs exhibiting more variability. Coefficients of variance (CV) for BMC measurements were slightly higher than for BMD. However, BMC offered a better correlation between in situ and ex situ values than BMD. On in situ scans, observer variability for BMD and BMC for comparable sites was higher than the ex situ variability. The results of this study indicate that DXA provides an accurate measurement of BMC even in small specimens. The precision of BMC and BMD measurements in situ can be improved considerably by using specific, well-defined ROIs and by careful placement of the bones to be scanned in close proximity to the scanning surface.     

Precision and accuracy of in vivo bone mineral measurement in rats using dual-energy X-ray absorptiometry

The aim of this study was to evaluate the precision and accuracy of dual-energy X-ray absorptiometry (DXA) for measuring bone mineral content at different sites of the skeleton in rats. In vitro the reproducibility error was very small (<1%), but in vivo the intra-observer variability ranged from 0.9% to 6.0%. Several factors have been shown to affect in vivo reproducibility: the reproducibility was better when the results were expressed as bone mineral density (BMD) rather than bone mineral content (BMC), intra-observer variability was better than the inter-observer variability, and a higher error was observed for the tibia compared with that for vertebrae and femur. The accuracy of measurement at the femur and tibia was assessed by comparing the values with ash weight and with biochemically determined calcium content. The correlation coefficients (R) between the in vitro BMC and the dry weight or the calcium content were higher than 0.99 for both the femur and the tibia. SEE ranged between 0.0 g (ash weight) and 2.0 mg (Ca content). Using in vitro BMC, ash weight could be estimated with an accuracy error close to 0 and calcium content with an error ranging between 0.82% and 6.80%. TheR values obtained between the in vivo and in vitro BMC were 0.98 and 0.97 respectively for femur and tibia, with SEE of 0.04 and 0.02 g respectively. In conclusion, the in vivo precision of the technique was found to be too low. To be of practical use it is important in the design of experimentation to try to reduce the measurement error. This can be achieved by performing measurements in the same position, by repeating measurements several times and by using the mean values of several BMD calculations performed by the same observer on each BMD measurement. Furthermore, better reproducibility can be obtained on the vertebra or the femur than on the tibia.     

Ultrasound velocity and dual-energy X-ray absorptiometry in normal and pagetic bone

Bone affected by Paget's disease is known to be dense but more prone to fractures. It is proposed that dual-energy X-ray absorptiometry (DXA) and quantitative ultrasound (QUS) assess different aspects of the skeletal status. In this study, we used Paget's disease of the tibia as a model to explore this. Ten patients with Paget's disease affecting a single tibia were investigated with the normal side acting as the control within each individual. Tibial speed of sound (SOS) was measured at the midpoint of the affected and control tibiae using a Soundscan 2000 (Myriad Ultrasound System, Rehovot, Israel) device. Bone mineral density (BMD) of the tibia was measured at a level corresponding to the site of the tibial ultrasound using a QDR-2000+ (Hologic, Inc., Waltham, MA). The mean bone area and estimated volume in the pagetic tibia was greater than that in the normal tibia (bone area: 25.10 +/- 8.00 vs. 20.23 +/- 5.43 cm(2), p = 0.017; estimated bone volume: 68.79 +/- 41.99 vs. 43.62 +/- 22.56 cm(3), p = 0.02), reflecting the bone expansion characteristic of Paget's disease. The bone mineral content (BMC) was more markedly increased in the pagetic tibia (27.38 +/- 12.98 vs. 14.39 +/- 6.14 g, p = 0.003) and, consequently, areal bone mineral density (BMD) was also markedly increased in the pagetic bone (1.09 +/- 0.38 vs. 0.77 +/- 0.44 g/cm(2), p = 0.018). There was no significant difference in the estimated volumetric BMD between the pagetic and the normal tibia (0.48 +/- 0.24 vs. 0.47 +/- 0.51 g/cm(3), p = 0.96). In contrast, the mean tibial SOS in the leg affected by Paget's disease was significantly lower than in the unaffected leg (3228 +/- 234 vs. 3840 +/- 164 m/sec, p < 0.001). When expressed as a z score using the normal limb as reference, areal BMD was 0.72 SD higher in the affected limb, whereas tibial SOS was 3.72 SD lower. We conclude that tibial SOS detects important changes in bone quality in Paget's disease of bone, which are unrelated to calcium content.     

Cross Calibration of Hologic QDR2000 and GE Lunar Prodigy for Whole Body Bone Mineral Density and Body Composition Measurements

The objective of this study was to undertake an in vivo cross calibration of body composition, whole body bone mineral content (BMC) and bone mineral density (BMD) between a Hologic QDR2000 and a GE Healthcare Lunar Prodigy. Twenty-one subjects attending for routine bone densitometry were recruited to the study (19 female and 2 male, aged 30–79 yr). Phantom cross calibrations were carried out using the Bio-Imaging Variable Composition Phantom (VCP) for percentage fat (%fat) and the Bona Fide Phantom (BFP) for BMD. There was no significant difference in whole body lean body mass between the QDR2000 and the Prodigy. Fat mass (FM) and %fat were significantly higher on the QDR2000. BMC and whole body BMD were significantly higher on Prodigy. As the BMC increased, so did the difference between the 2 instruments. The VCP did not provide an adequate cross calibration of %fat compared with in vivo. The BFP provided a good cross calibration of whole body BMD compared with in vivo. The results suggest that the partitioning of the soft tissue component between lean and fat in the 2 instruments is systematically different. The variation between instruments from the same and different manufacturers reported in the literature varies widely, as does the comparison with criterion methods. This makes it difficult to generalize the results of this study to other centers and it is recommended that each center would have to cross calibrate when changing equipment.