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.     

Accuracy and precision of in vivo bone mineral measurements in sheep using dual-energy X-ray absorptiometry

We evaluated the precision and accuracy of in vivo measurements of spine bone mineral density (BMD) and bone mineral content (BMC) in five ewes using dual-energy X-ray absorptiometry (DXA, Lunar DPX-L). The short-term in vivo reproducibility expressed as the coefficient of variation (CV) varied from 0.9 to 1.6% for spine BMD and from 1 to 3.1% for spine BMC. The ex vivo measurements, performed in 20 cm of water to simulate soft tissue thickness, correlated closely with the in vivo measurements, yielding an r value of 0.98 and 0.97 for spine BMD and BMC, respectively. The accuracy was determined by comparing the total BMC of each vertebra measured in vivo with the corresponding ash weight. The correlation coefficient between the two measurements was r = 0.98, with an accuracy error of 5.6%. We concluded that the DXA allows a precise and accurate measurement of spine bone mineral in live ewes using the methodology designed for humans. Received: 19 March 1999 / Accepted: 26 July 1999     

Validation and application of dual-energy X-ray absorptiometry to measure bone mineral density in rabbit vertebrae.

The rabbit could be a superior animal model to use in bone physiology studies, for the rabbit does attain true skeletal maturity. However, there are neither normative bone mineral density (BMD) data on the rabbit nor are there any validation studies on the use of dual-energy X-ray absorptiometry (DXA) to measure spinal BMD in the rabbit. Therefore, our aim was twofold: first, to investigate whether DXA could be used precisely and accurately to determine the bone mineral content (BMC). bone area (BA). and BMD of the rabbit lumbar spine: Second. to evaluate the new generation fan-beam DXA (Hologic QDR-4500) with small animal software by comparing two DXA methodologies QDR-1000 and QDR-4500 with each other, as well as against volumetric bone density (VBMD) derived from Archimedes principle. As expected. there was a magnification error in the QDR-4500 (BMC, BA. and BMD increased by 52%. 38%. and 10%, respectively, when the vertebrae were positioned flat against the scanning table). With the magnification error kept constant (vertebrae positioned 10 cm above the scanning table to match the height in vivo). there were no differences among the mean BMC. BA. and BMD of the rabbit vertebrae (Ll-L7) in vivo and in vitro using the QDR-4500 (p > 0.05). BMC, BA, and BMD differed between QDR-1000 and QDR-4500 in vitro because of a magnification error when the vertebrae were flat on the table (p <0.0001). and, consequently. the machines did not correlate with one another (p > 0.05). However, the BMC, BA, and BMD of the two DXAs did significantly correlate with each other in vivo and in vitro when the magnification error was compensated for (r = 0.44 and 0.52. i2 = 0.45 and 0.63. and 12 = 0.41 and 0.60. respectively. p < 0.05-0.008). The BMC and BMD (in vivo and in vitro) of the rabbit vertebrae measured by QDR-4500 was significantly correlated with VMBD, ash weight, and mineral content (,2 = 0.67-0.90,j <0.01-0.0001). Therefore, the QDR-4500 can be used to yield precise and accurate measurements of the rabbit spine.     

Dual-energy X-ray absorptiometry,peripheral quantitative computed tomography,and micro-computed tomography techniques are discordant for bone density and geometry measurements in the guinea pig

This study aims to examine agreement among bone mineral content (BMC) and density (BMD) estimates obtained using dual-energy X-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), and micro-computed tomography (μCT) against high-resolution μCT and bone ash of the guinea pig femur. Middle-aged (n = 40, 86 weeks) male guinea pigs underwent in vivo followed by ex vivo DXA (Hologic QDR 4500A) scanning for intact and excised femur BMC and areal density. To assess bone architecture and strength, excised femurs were scanned on pQCT (Stratec XCT 2000L) as well as on two μCT scanners (LaTheta LCT-200; Skyscan 1174), followed by three-point bending test. Reproducibility was determined using triplicate scans; and agreement assessed using Bland–Altman plots with reference methods being high-resolution μCT (Skyscan) for BMD and bone ashing for BMC. All techniques showed satisfactory ex vivo precision (CV 0.05–4.3 %). However, bias compared to the reference method was highest (207.5 %) in trabecular bone volume fraction (BV/TV) measured by LaTheta, and unacceptable in most total femur and cortical bone measurements. Volumetric BMD (vBMD) and BV/TV derived by LaTheta and pQCT at the distal metaphysis were biased from the Skyscan by an average of 49.3 and 207.5 %, respectively. Variability of vBMD, BV/TV and cross-sectional area at the diaphysis ranged from ?5.5 to 30.8 %. LaTheta best quantified total femur BMC with an upper bias of 3.3 %. The observed differences among imaging techniques can be attributable to inherent dissimilarity in construction design, calibration, segmentation and scanning resolution used. These bone imaging tools are precise but are not comparable, at least when assessing guinea pig bones.     

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.     

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.     

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.     

Fundamental evaluation of dual x-ray absorptiometry (DXA) for measurement of bone mineral density in rats

This study was designed to assess the precision and accuracy of newly developed ultra high resolution mode (rat mode) in DXA (Hologic, QDR-1000), determine how body thickness affects measured BMD values and to derive a formula by which BMDs in animals with varying degrees of body thickness can be compared. The long term reproducibility on two phantoms (BMD: 170 and 300 mg/cm²) were under CV 1.0%. The repeated precision in vivo and in vitro lumbar spines and phantoms were within CV 1.5%. Accuracy was evaluated by determining the correlation coefficient between ash weight and tibial BMC. The correlation was excellent (r=0.999, p<0.001) over the ash range of 250–600 mg. Using single regression equations, QDR-1000 BMC values were compared with those obtained by conventional methods. There was a close linear correlation with both SPA (Norland Co., r=0.997) and DCS-600 (Aloka Co., r=0.996) measurements. The effects of body thickness were assessed by immersing phantoms at various water depths. There was a significant linear decrease in BMD, as measured by QDR-1000, with increasing water depth. BMDs in vivo with varying body thickness can be compared with each other by using the following correcting formula: BMD₁=(BMD₂+5.5w+7.6) × 10³/(977-4.8w), where BMD₁=expected BMD of extracted bone (mg/cm²), BMD₂=BMD in vivo (mg/cm²), w=body thickness (cm). There was a significant positive correlation (r=0.996, p<0.001) between calculated BMDs from this equation and the values actually obtained. These results confirm that QDR-1000 rat mode yields data useful for assessing BMD and BMC in small animal bones.     

Comparison of Pencil-, Fan-, and Cone-Beam Dual X-ray Absorptiometers for Evaluation of Bone Mineral Content in Excised Rat Bone

The aim of the present study was to assess the reproducibility and accuracy of measurements done on excised rat bone with three different generations of densitometers: Hologic QDR2000 pencil beam, Hologic QDR4500 fan beam, and Lunar PIXImus cone beam. The coefficients of variation for repeated measurements of bone mineral content (BMC) were 0.62 and 0.85% for pencil beam, 1.73 and 3.59% for fan beam, and 0.70 and 1.52% for cone beam for femur and tibia, respectively. BMC and ash weight were linearly correlated: 0.998 for pencil, 0.984 for fan, and 0.995 for cone beam. However, the three densitometers overestimated BMC by 10.9, 12.6, and 3.1%, respectively, and the overestimation was found to be dependent on the net BMC. The highest coefficient of correlation was found between BMC measurements from pencil and cone beam (r = 0.995). Data from cone-beam DXA were, respectively, 8.8 and 9.2% lower than those from penciland fan-beam DXA. We conclude that the three DXA instruments precisely and accurately measure BMC in excised rat bone; however, DXA overestimates BMC with a dependence on the bone ash weight. This dependence was less pronounced with the cone-beam technology.     

Simulated change in body fatness affects Hologic QDR 4500A whole body and central DXA bone measures.

Changes in body fatness may impact the accuracy of dual energy X-ray absorptiometry (DXA) measures of bone mineral content (BMC) and bone mineral density (BMD). The aim of this study was to determine if DXA can accurately assess BMC and BMD with changes in exogenous fat (lard) placed to simulate weight change. Whole body (WB), lumbar spine (LS), and proximal femur (PF) DXA scans (Hologic QDR 4500A) were performed on 30 elderly (52-83 yr) and 60 young (18-40 yr) individuals (i.e., 45 females and 45 males) of varying body mass index (mean+/-standard deviation: 26.1+/-4.9 kg/m2). When scans were repeated with lard packets (2.54 cm thick, 25.4x17.8 cm, 1 kg), WB BMD decreased 1.1% and 1.6% after chest and thigh packet placement, respectively (p=0.001), PF BMD increased 0.7% (p=0.02) and LS BMD decreased 1.6% (p=0.001) primarily due to a 2.2% reduction in LS BMC (p<0.001). Initial LS BMC and trunk mass were related to error in LS BMC measures due to lard-loading (r=0.64 and 0.45, respectively, p<0.001). We conclude that on average simulated weight change minimally impacts PF bone measures and moderately impacts WB and LS bone measures; however, individual variability in measurement error was noteworthy and may be impacted by body thickness.     

DXA estimates of vertebral volumetric bone mineral density in children: potential advantages of paired posteroanterior and lateral scans.

Dual-energy X-ray absorptiometry (DXA) estimates of areal bone mineral density (BMD) are confounded by bone size in children. Two strategies have been proposed to estimate vertebral volumetric BMD: (1) bone mineral apparent density (BMAD) is based on the posteroanterior (PA) spine scan; (2) width-adjusted bone mineral density (WABMD) is based on paired PA lateral scans. The objective of this study was to compare DXA estimates of vertebral bone mineral content (BMC), volume and volumetric BMD obtained from Hologic PA scans (Hologic, Inc., Bedford, MA) alone, and paired PA lateral scans in 124 healthy children, ages 4 to 20 yr. The PA scans were used to estimate bone volume (PA Volume) as (PA Area)1.5 and BMAD as [(PA BMC)/(PA Volume)]. Paired PA lateral scans were used to estimate width-adjusted bone volume (WA Volume) as [(pi/4)(PA width)(lateral depth)(vertebral height)] and WABMD as [(lateral BMC)/(WA Volume)]. Generalized estimating equations were used to compare the relationship between scan type (PA vs. paired PA lateral) and bone outcomes, and the effects of height and maturation on this relationship. The estimates of BMC and volume derived from PA scans and paired PA lateral scans were highly correlated (r>0.97); WABMD and BMAD were less correlated (r=0.81). The increases in BMC, volume, and volumetric BMD with greater height and maturation were significantly larger (all p<0.001) when estimated from paired PA lateral scans, compared with PA scans alone. The proportion of spine BMC contained within the vertebral body, versus the cortical spinous processes, increased significantly with age (p<0.001) from 28% to 69%. The smaller increases in bone measures on PA scans may have been due to magnification error by the fan beam as posterior tissue thickness increased in taller, more mature subjects, and the distance of the vertebrae from the X-ray source increased. In conclusion, paired Hologic PA lateral scans may increase sensitivity to growth-related increases in trabecular BMC and density in the spine, with less bias due to magnification error.     

容积性定量CT测量股骨近端骨密度准确性研究

目的通过分别对比容积性定量CT(vQCT)、双能X射线吸收法(DXA)与灰化法测量股骨近端骨密度结果,确定并对比相关性,进行指导临床骨质疏松诊断及治疗。方法选取20个尸体股骨近端标本,先使用DXA骨密度仪扫描,测得骨矿含量(BMC)及骨密度(BMD)。再对标本相同部位行64层螺旋CT扫描,数据导入OsteoCAD软件自动分析得出骨密度值。应用灰化法得出标本灰质量密度。所有资料进行统计分析分别确定并对比vQCT及DXA测量的骨密度值与灰密度之间的相关性。结果vQCT测量股骨颈骨密度与灰质量密度线性相关性较好(r=0.852,P0.01),DXA与灰质量密度的相关性略差(r=0.807,P0.01)。结论vQCT测得的骨密度较DXA与灰质量密度线性相关性更好,可靠性高,对于诊断骨质疏松,预测骨质疏松性骨折,评价、指导骨质疏松骨折手术更有应用价值。     

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.     

Measurement of spinal bone mineral density on a Hologic Discovery DXA scanner with and without leg elevation.

Although it is generally recommended that patients keep their hips flexed by 90 degrees during the measurement of spinal bone mineral density (BMD), there is no uniform agreement among the manufacturers of dual-energy X-ray absorptiometry (DXA) scanners regarding the positioning of legs while scanning the spine. We measured spinal BMD in 54 postmenopausal women, from L1 to L4 in posterior-anterior projection, using a Hologic Discovery scanner, first with their legs elevated as recommended by the manufacturer and then with their legs flat on the scanning table. Differences of bone mineral content (BMC), area of the region of interest (ROI), BMD, and T-score of the total spine between the 2 scans were compared. The mean (SD) age of the women was 54.3 yr (15 yr). Between the 2 scans, BMC, area of the ROI, BMD, and T-scores showed high correlations (r=0.98, 0.94, 0.99, and 0.99, respectively). BMC and the area of the ROI changed significantly between the 2 scans, but the changes of BMD and T-scores were not significant. The percentage changes of BMC and the area of the ROI were similar (2.6% and 2.4%, respectively), whereas T-scores showed no change and change of BMD was only 0.6%. The absolute difference in BMD between the 2 scans was only 0.005 (p=0.09). When spinal BMD was measured with their legs elevated, 31 women were found to have osteoporosis and further 13 were found to have osteopenia. When spinal BMD was measured with their legs flat, 32 women were found to have osteoporosis and further 12 were found to have osteopenia. In conclusion, no clinically or statistically significant difference in the total spinal BMD was found when the BMD in a group of women was measured on a Hologic Discovery DXA scanner with their legs positioned flat.     

Birth weight is an independent determinant of whole body bone mineral content and bone mineral density in a group of Lebanese adolescent girls

The aim of this study was to explore the relation between birth weight and bone mass in a group of adolescent girls. This study included 40 post-menarchal adolescent (aged 13–20 years) girls. Anthropometric characteristics (height and weight) were measured and birth weights were obtained from the obstetric records. Body composition, bone mineral content (BMC) and bone mineral density (BMD) of the whole body (WB) were assessed by dual-energy X-ray absorptiometry (DXA). Calculations of the ratio BMC/height and of the bone mineral apparent density (BMAD) were completed for the WB. Birth weight was positively correlated to BMC and to the ratio BMC/height even after adjusting for weight and maturation index (years since menarche). Finally, birth weight was correlated to BMD even after adjusting for weight. In conclusion, this study suggests that birth weight is an independent determinant of whole body BMC and BMD in adolescent girls.     

Gene polymorphisms,bone mineral density and bone mineral content in young children:the Iowa bone development study

We examined the association of candidate gene polymorphisms with bone mineral density (BMD) and bone mineral content (BMC) in a cohort of 428 healthy non-Hispanic white children participating in the Iowa Bone Development Study, a longitudinal study of determinants of bone accrual in childhood. BMD and BMC measurements of the hip, spine and whole body were made using a Hologic 2000 Plus densitometer in 228 girls and 200 boys ages 4.5–6.5 years. Genotypes at 14 loci representing eight candidate genes [type I collagen genes (COL1A1 and COL1A2), osteocalcin, osteonectin, osteopontin, vitamin D receptor (VDR), estrogen receptor (ER), androgen receptor (AR)] were determined. Gender-specific and gender-combined prediction models for bone measures that included age, weight, height (and gender) were developed using multiple linear regression analysis. COL1A2 and osteocalcin genotypes were identified as having the strongest and most consistent association with BMD/BMC measures. Osteonectin, osteopontin and VDR translation initiation site polymorphisms were associated with some individual bone measures, but none of the associations was as consistent as those identified for the COL1A2 and osteocalcin genes. No association was identified with COL1A1 (RsaI and Sp1), VDR (BsmI) and ER polymorphisms (PvuII, XbaI, TA) and BMD/BMC. However, we identified significant gene-by-gene interaction effects involving the ER and both VDR and osteocalcin, which were associated with BMD/BMC. Our data suggest that genetic variation at multiple genetic loci is important in bone accrual in children. Moreover, the combination of genotypes as several loci may be as important as a single genotype for determining BMD and BMC.     

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

Summary Dual-energy X-ray absorptiometry (DXA) was used to determine thein 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 thein vivo DXA analyses. Correlation between the estimated L3BMC by DXA and the actual ash weight was significant (r=0.965,P<0.01); however, DXA methodology underestimated ash weight on the average of 6.2%. Correlation was significant between two sequentialin vivo DXA scans (r=0.988,P<0.001). Noninvasivein vivo DXA was a fast, precise, and effective method for measuring the lumbar BMC in female cynomolgus macaques.     

The effect of swimming on bone modeling and composition in young adult rats

Summary The purpose of this study was to investigate the adaptability of long bones of young adult rats to the stress of chronic aquatic exercise. Twenty-eight female Sabra rats (12 weeks old) were randomly assigned to two groups and treatments: exercise (14 rats) and sedentary control (14 rats) matched for age and weight. Exercised animals were trained to swim in a water bath (35°±1°C, 1 hour daily 5 times a week) for 12 weeks loaded with lead weights on their tails (2% of their body weight) (BW). At the end of the training period following blood sampling for alkaline phosphatase, all rats were sacrificed and the humeri and tibiae bones were removed for the following measurements: bone morphometry, bone water compartmentalization, bone density (BD), bone mineral content (BMC), and bone ions content (Ca, Pi, Mg, Zn). The results indicate that exercise did not significantly affect the animals' body weight, bone volume, or length and diameters. However, bone hydration properties, BD, bone mass, and mineralization revealed significant differences between swim-trained rats and controls (P<0.05). Longitudinal (R₁) measurement was higher by 43% for both humerus and tibia, and Transverse (R₂) relaxation rates of hydrogen proton were higher by 117 and 76% for humerus and tibia, respectively; fraction of bound water was higher by 36 and 46% for humerus and tibia, respectively. BD, bone weight, and ash were higher by 13%. BMC and bone ions content were higher by 10%, and alkaline phosphatase was higher by 67%. These results indicate that long bones of young adult rats after the age of rapid growth can adapt positively to nonweight-bearing aquatic exercise. This adaptation is evident by an increase in bone mass, density, mineralization, and hydration properties.     

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.     

Long-term unilateral loading and bone mineral density and content in female squash players

We examined 19 female Finnish national level squash players and 19 healthy female controls with a dual energy x-ray absorptiometric (DXA) scanner for the determination of the association between long-term unilateral activity and bone mineral density (BMD) and content (BMC) of the upper extremities. In players, the BMDs and the BMCs were significantly higher in each bone site of the playing extremity. The side-to-side difference was largest in the proximal humerus (BMD 15.6%, BMC 17.8%) and smallest in the ulnar shaft (BMD 5.6%, BMC 7.3%). In sex-, age-, weight-, and height-matched controls, the side-to-side differences were significantly smaller, ranging from 1.6% to 4.1%. The number of training years and elbow flexion strength correlated positively with the relative BMD and BMC in the humerus of the playing arm (r=0.632–0.685). The starting age training in turn correlated negatively (r=-0.483 to-0.577) with these bone parameters. Significantly larger side-to-side differences (average 22%) were found in players who had started their career before or during menarche than in those who had begun the training 1 year or more after the menarche (9%). These findings suggest that the bones of the playing extremity clearly benefit from active squash playing. The benefit is largest in humerus and smaller in the bone of the forearm. The benefit of playing is stronger if the athlete has started the training at or before menarche than after it. Thus, physical activity seems to best enhance bone mineralization at childhood and puberty, the time when the natural rapid increase in bone mass also occurs.