Cross-Calibration of iDXA and Prodigy on Spine and Femur Scans in Korean Adults

In this study, the authors compared bone mineral density (BMD) determined using GE Lunar iDXA and Prodigy and derived cross-calibration equations for the 2 devices in Korean adults. One hundred subjects (66 women and 34 men) participated in this study. Bone mineral density of spine and femur was measured by iDXA and Prodigy dual-energy X-ray absorptiometry (GE Lunar, Madison, WI). Subjects were divided into 3 groups. The first group (30 subjects) was scanned twice using Prodigy for precision testing and then once using iDXA. The second group (30 subjects) was scanned twice using iDXA and then once using Prodigy. Cross-calibration equations were derived using these results. The derived equations were tested in the third group (40 subjects). Predicted values from calculations based on Prodigy findings were compared with measured iDXA data. A significant difference was found between the BMD determined using the 2 devices (p < 0.001). However, linear regression analysis showed a high level of agreement between the two (r² from 0.984 to 0.994, p < 0.001). Bland-Altman analysis revealed no significant correlations between Prodigy and iDXA. Cross-calibration equations decreased systematic errors between Prodigy and iDXA by 0.4% at the spine, 0.8% at the femoral neck, and 0.1% at the total femur. A high level of agreement was found between Prodigy and iDXA in Korean adults. Cross-calibration equations proved reliable based on comparisons of measured and calculated BMD values.     

Fat Tissue Measurements by Dual-Energy X-Ray Absorptiometry: Cross-Calibration of 3 Different Fan-Beam Instruments

Analysis of total tissue composition and, particularly, body fat measurements has become progressively important in the diagnosis and follow-up of patients with different clinical conditions. Dual-energy X-ray absorptiometry (DXA) fan-beam scanners are widely used to measure body composition, but the development of translational equations to be able to compare data of different scanning systems is necessary. The aim of this study was to assess the extent of agreement for regional measurements of body composition among the following 3 fan-beam DXA scanners: (1) Hologic Discovery (Hologic, Inc., Waltham, MA), (2) Lunar iDXA (GE Healthcare, Madison, WI), and (3) Lunar Prodigy Advance (GE Healthcare, Madison, WI). The study population consisted of 91 adult healthy volunteers (40 males and 51 females; mean age 48.5 ± 14.4 yr) who underwent DXA evaluation of the lumbar spine, hip, and whole body in each machine on the same day. Agreement among the 3 scanners was evaluated according to the Bland-Altman method and Lin's concordance correlation coefficient. Results showed a better agreement and concordance for the Lunar iDXA scanner than for any of them with the Hologic scanner. Differences were higher for any tissue or region than for the whole tissue mass. Translational equations were developed to ensure comparability of body composition measurements obtained with each of these 3 scanners.     

Precision of GE Lunar iDXA for the Measurement of Total and Regional Body Composition in Nonobese Adults

Dual-energy X-ray absorptiometry (DXA) is a well-accepted technique for measuring body composition. Knowledge of measurement precision is critical for monitoring of changes in bone mineral content (BMC), and fat and lean masses. The purpose of this study was to characterize in vivo precision of total body and regional body composition parameters using the GE Lunar iDXA (GE Healthcare Lunar, Madison, WI) system in a sample of nonobese subjects. We also evaluated the difference between expert and automatic region-of-interest (ROI) analysis on body composition precision. To this end, 2 total body scans were performed on each subject with repositioning between scans. Total body precision for BMC, fat and lean mass were 0.5%, 1.0%, and 0.5% coefficient of variation (CV), respectively. Regional body composition precision error was less than 2.5% CV for all regions except arms. Precision error was higher for the arms (CV: BMC 1.5%; fat mass 2.8%; lean mass 1.6%), likely owing to the placement of arms relative to torso leading to differences in ROI. There was a significant correlation between auto ROI and expert ROI (r > 0.99). Small, but statistically significant differences were found between auto and manual ROI. Differences were small in total body, leg, trunk, and android and gynoid regions (0.004–2.8%), but larger in arm region (3.0–6.3%). Total body and regional precision for iDXA are small and it is suggested that iDXA may be useful for monitoring changes in body composition during longitudinal trials.     

The Evaluation of Consistency Between Body Composition Assessments in Pediatric Population Using Pencil Beam and Fan Beam Dual-Energy X-Ray Absorptiometers

The replacement of the old dual-energy X-ray absorptiometry system with a novel one should be preceded by a cross-calibration procedure. Therefore, the study was aimed at investigating the consistency of bone and body composition measures performed in pediatric population using pencil beam (DPX-L; GE Healthcare, GE Healthcare, Madison, WI) and fan beam (Prodigy; GE Healthcare, GE Healthcare, Madison, WI) densitometers. The study group consisted of 212 healthy children aged 4–18 yr. Total body (TB) and lumbar spine (S) (L2–L4) measurements were performed using DPX-L and Prodigy during the same visit. Bland-Altman analysis, linear regressions, and paired t-test were performed to evaluate the consistency of measurements and to establish a cross-calibration equation. The average Prodigy values for TB and lumbar spine bone mineral density (BMD) and content (BMC) were 2.7%, 2.4% and 1.6%, 1.6% higher than those of DPX-L, respectively (p < 0.0001). Prodigy-assessed bone area (BA) was lower by 1.4% for TBBA (p < 0.0001) and 1.1% for SBA (p < 0.001). Lean body mass (LBM) from Prodigy was higher by 6.9% (p < 0.0001), whereas fat mass (FM) was lower by 8.4% compared with those from DPX-L (p < 0.0001). Bland-Altman analyses revealed the effect of magnitude that was nonlinear (2nd degree polynomial) for TBBMD (r = 0.32, p = 0.001), TBBMC (r = 0.51, p < 0.0001), TBBA (r = 0.34, p < 0.0001), and LBM (r = 0.56, p < 0.0001), but not for FM (r = 0.14, not significant [n.s.]). In contrast, in lumbar spine, the magnitude dependence was linear and significant for SBMC (r = 0.46, p < 0.0001) and SBA (r = 0.34, p < 0.0001) but not for SBMD (r = 0.12, n.s.). Both skeletal and body composition variables assessed by DPX-L and Prodigy devices were highly correlated, showing R² values ranging from 0.976 for FM to 0.994 for SBMC. The results of this study document a necessity for implementation of calculated cross-calibration equations to transform DPX-L–based local pediatric references into a novel Prodigy system.     

iDXA,Prodigy, and DPXL Dual-Energy X-ray Absorptiometry Whole-Body Scans: A Cross-Calibration Study

PurposeTotal body fat, lean, and bone mineral content (BMC) in addition to regional fat and lean mass values for arms, legs, and trunk were compared across a pencil-beam (Lunar DPXL) and 2 fan-beam (GE Lunar Prodigy and GE Lunar iDXA) dual-energy X-ray absorptiometry (DXA) systems.MethodsSubjects were a multiethnic sample of 99 healthy adult males (47%) and females (mean ± SD: age, 46.3 ± 16.9 yr; weight, 73.4 ± 16.6 kg; height, 167.6 ± 9.7 cm; body mass index, 26.0 ± 5.2 kg/m²) who had whole-body scans performed within a 3-h period on the 3 systems. Repeated measures ANOVA was used to test the null hypothesis that the mean values for the 3 systems were equal. Translation equations between the methods were derived using regression techniques.ResultsBone mineral content (BMC): For both genders, total BMC by iDXA was lower (p ≤ 0.004) than the other systems. Lean: for males, iDXA was lower (p ≤ 0.03) than the other systems for total, trunk, and arms. For females, DPXL estimated higher (p < 0.001) lean mass compared with the other systems for total, trunk, and arms, but iDXA estimated greater legs lean mass. For both genders, all DPXL mean values were greater than Prodigy mean values (p < 0.001).Fat: in females, all the 3 systems were different from each other for total, trunk, and legs (p ≤ 0.04). For arms, DPXL and iDXA were higher than Prodigy (p < 0.0004). For males, DPXL was less (p < 0.001) for total body, trunk, and legs compared with the other 2 systems and greater than Prodigy only for arms (p < 0.0007). These data were used to derive translation equations between systems. For several measurements, the differences between systems were related to gender.ConclusionFor estimation of BMC and body composition, there was high agreement between all DXA systems (R² = 0.85–0.99). Even so, cross-calibration equations should be used to examine data across systems to avoid erroneous conclusions.     

Cross-Calibration and Comparison of Variability in 2 Bone Densitometers in a Research Setting: The Framingham Experience

New technology introduced over time results in changes in densitometers during longitudinal studies of bone mineral density (BMD). This requires that a cross-calibration process be completed to translate measurements from the old densitometer to the new one. Previously described cross-calibration methods for research settings have collected single measures on each densitometer and used linear regression to estimate cross-calibration corrections. Thus, these methods may produce corrections that have limited precision and underestimate the variability in converted BMD values. Furthermore, most of the previous studies have included small samples recruited from specialized populations. Increasing the sample size, obtaining multiple measures on each machine, and using linear mixed models to account for between- and within-subject variability may improve cross-calibration estimates. The purpose of this study was to conduct an in vivo cross-calibration of a Lunar DPX-L (Lunar Corporation, Madison, WI) with a Lunar Prodigy densitometer (GE Medical Systems Lunar, Madison, WI) using a sample of 249 healthy volunteers who were scanned twice on each densitometer, without repositioning, at both the femur and spine. Scans were analyzed using both automated and manual placement of regions of interest. Wilcoxon rank-sum tests and Bland-Altman plots were used to examine possible differences between repeat scans within and across densitometers. We used linear mixed models to determine the cross-calibration equations for the femoral neck, trochanter, total hip, and lumbar spine (L2–L4) regions. Results using automated and manual placement of the regions of interest did not differ significantly. The DPX-L densitometer exhibited larger median absolute differences in the BMD values by repeat scans of femoral neck (0.016 vs 0.012, p = 0.1) and trochanter (0.011 vs. 0.009, p = 0.06) compared with the Prodigy densitometer. The Bland-Altman plots revealed no statistically significant linear relationship between the differences in paired measures between machines and mean BMD. In our large sample of healthy volunteers, we did detect systematic differences between the DPX-L and Prodigy densitometers. Our proposed cross-calibration method, which includes acquiring multiple measures and using linear mixed models, provides researchers with a more realistic estimate of the variance of cross-calibrated BMD measures, potentially reducing the chance of making a type I error in longitudinal studies of changes in BMD.     

Cross Calibration of the GE Prodigy and iDXA for the Measurement of Total and Regional Body Composition in Adults

Dual-energy X-ray absorptiometry (DXA) body composition measurements are widely performed in both clinical and research settings, and enable the rapid and noninvasive estimation of total and regional fat and lean mass tissues. DXA upgrading can occur during longitudinal monitoring or study; therefore, cross calibration of old and new absorptiometers is required. We compared soft tissue estimations from the GE Prodigy (GE Healthcare, Madison, WI) with the more recent iDXA (GE Healthcare) and developed translational equations to enable Prodigy values to be converted to iDXA values. Eighty-three males and females aged 20.1–63.3?yr and with a body mass index range of 17.0–34.4?kg/m² were recruited for the study. Fifty-nine participants (41 females and 18 males) comprised the cross-calibration group and 24 (14 females and 10 males) comprised the validation group. Total body Prodigy and iDXA scans were performed on each subject within 24?h. Predictive equations for total and regional soft tissue parameters were derived from linear regression of the data. Measures of lean and fat tissues were highly correlated (R²?=?0.95–0.99), but significant differences and variability between machines were identified. Bland-Altman analysis revealed significant biases for most measures, particularly for arm, android, and gynoid fat mass (12.3%–22.7%). The derived translational equations reduced biases and differences for most parameters, although limits of agreement exceeded iDXA least significant change. In conclusion, variability in soft tissue estimates between the Prodigy and iDXA were detected, supporting the need for translational equations in longitudinal monitoring. The derived equations are suitable for group analysis but not individual analysis.     

Measurement of Bone Density Around the Oxford Medial Compartment Knee Replacement Using iDXA. A Precision Study

The goal of this study was to evaluate whether the Lunar iDXA densitometer can accurately measure the bone mineral density (BMD) around the tibial component of the Oxford unicompartment knee replacement (UKR). Both knees in 20 patients were measured 3 times in the supine position with repositioning between each scan. We chose 7 regions of interest to evaluate the bone density around the implant. Small but significant differences between the implant and nonimplanted knee were noticed with the nonimplanted knee having slightly higher BMD and bone mineral content (BMC) in areas 1–3 (p ≤ 0.001) and area 6 (p = 0.002). There was higher BMD in area 4 (p = 0.028). The precision for BMD in the 7 areas of interest in the implanted knee varied between 0.55% and 4.04% and BMC between 1.8% and 5.3%. There was no significant difference in the precision between the nonimplanted and implanted knees. Prospective serial measurements around the Oxford UKR using iDXA will be able to assess specific areas of stress shielding and potential implant stability, which is likely to help predict the survival of the implant.     

In vivo Precision of the GE Lunar iDXA Densitometer for the Measurement of Total-Body, Lumbar Spine, and Femoral Bone Mineral Density in Adults

Knowledge of precision is integral to the monitoring of bone mineral density (BMD) changes using dual-energy X-ray absorptiometry (DXA). We evaluated the precision for bone measurements acquired using a GE Lunar iDXA (GE Healthcare, Waukesha, WI) in self-selected men and women, with mean age of 34.8 yr (standard deviation [SD]: 8.4; range: 20.1–50.5), heterogeneous in terms of body mass index (mean: 25.8 kg/m²; SD: 5.1; range: 16.7–42.7 kg/m²). Two consecutive iDXA scans (with repositioning) of the total body, lumbar spine, and femur were conducted within 1 h, for each subject. The coefficient of variation (CV), the root-mean-square (RMS) averages of SDs of repeated measurements, and the corresponding 95% least significant change were calculated. Linear regression analyses were also undertaken. We found a high level of precision for BMD measurements, particularly for scans of the total body, lumbar spine, and total hip (RMS: 0.007, 0.004, and 0.007 g/cm²; CV: 0.63%, 0.41%, and 0.53%, respectively). Precision error for the femoral neck was higher but still represented good reproducibility (RMS: 0.014 g/cm²; CV: 1.36%). There were associations between body size and total-body BMD and total-hip BMD SD precisions (r = 0.534–0.806, p < 0.05) in male subjects. Regression parameters showed good association between consecutive measurements for all body sites (r² = 0.98–0.99). The Lunar iDXA provided excellent precision for BMD measurements of the total body, lumbar spine, femoral neck, and total hip.     

Bone Mineral Density Measured by a Portable X-ray Device Agrees With Dual-Energy X-ray Absorptiometry at Forearm in Preschool Aged Children

Dual-energy X-ray absorptiometry (DXA) measures of bone mineral density (BMD) are generally not feasible in fieldwork. The present study determined the agreement between BMD measured by DXA and portable peripheral DXA in preschool aged children. Fifty-seven children (4.2 ± 1.0 yr) had their nondominant distal forearm scanned using a peripheral DXA scanner (PIXI; GE Medical Systems Lunar, Madison, WI) at their daycare and a DXA (4500A Discovery Series; Hologic Inc., Bedford, MA) at our research clinic. Correlation analysis, one-way analysis of variance, and Bland-Altman plots were performed to examine the agreement between measurements. Data were also divided into tertiles for cross-classification analysis and calculation of kappa coefficients. Distal forearm BMD measured by PIXI was significantly correlated with DXA measures of total forearm BMD (r > 0.51; p < 0.001), proximal 1/3 BMD (r > 0.41; p < 0.001), mid-BMD (r > 0.37; p < 0.001), and ultradistal (UD) BMD (r > 0.57; p < 0.001). Cross-classification in the same or adjacent tertile between measures (UD forearm: 96.5%; UD radius: 94.4%; total forearm: 87.7%; total radius: 84.2%) resulted in weighted kappa coefficients of 0.46, 0.58, 0.42, and 0.43, respectively. Bland-Altman plots further clarified these agreements as all had low bias (UD forearm: bias = 0.003 ± 0.002; UD radius: ?0.015 ± 0.021; total forearm: ?0.062 ± 0.027; total radius: ?0.077 ± 0.026). These results demonstrate that portable DXA measures of forearm BMD agree moderately with DXA.     

Effect of Female Database Use for T-score Derivation in Men

Whether to use male or female databases to obtain T-scores in men remains controversial. This study evaluated the impact of deriving male T-scores using female databases in 350 men aged 22.8–93.5 (mean 67.5 ± 12.2) yr who were referred for clinically indicated dual-energy X-ray absorptiometry exams. Spine, femur, and nondominant radius scans were obtained in routine clinical manner using a GE Healthcare Lunar Prodigy densitometer. Analyses were performed using software version 9.30. Initially, the GE Healthcare Lunar male normative database was used to calculate T-scores. Subsequently, scans were reanalyzed using female databases; GE for the spine and radius, and NHANES III for the femur. Using the manufacturer's male database, T-scores (mean [range]) of the L1–4 spine, femur neck, total femur, and .3 radius were 0.0 [−4.6 to +8.5], −1.6 [−4.3 to +2.3], −1.1 [−4.0 to +3.3], and −0.7 [−5.3 to +2.9], respectively. On reanalysis with female databases, T-scores “improved” (p < 0.0001) with a positive bias of 0.34, 0.33, 0.58, and 1.20, respectively at the above 4 sites. Using female databases, the proportion of men classified as having normal bone mass increased from 22% to 33% and those identified as osteoporotic decreased from 29% to 17%. If pharmacologic treatment were prescribed at a T-score <−2.0, use of the female databases would reduce those treated for low bone mass from 46% to 32%. In conclusion, using female databases to derive male T-scores results in “improvement” of diagnostic classification for a substantial number of men with fewer being classified as having low bone mass.     

Effect of Precision on Longitudinal Follow-Up of Bone Mineral Density Measurements in Elderly Women and Men

Precision error of dual-energy X-ray absorptiometry exceeds the expected annual rate of bone loss in the elderly. The capacity to detect changes in areal bone mineral density (aBMD; g/cm²) over a 5-yr period was assessed. Six hundred ninety-one women, 75.2 (0.1) yr, from the Malmö OPRA-study, were measured using Lunar DPX-L (GE Lunar, Madison, WI), and 211 men, 74.7 (3.2) yr, from the Malmö Mr Os-study, were measured using Lunar Prodigy (GE Lunar) with follow-up 5 yr later. Precision error was determined with 30 degrees of freedom. Least significant change (LSC, i.e., 2.77 × precision error) was calculated. Women's precision errors (g/cm²) for DPX-L were 0.028 (total hip [TH]) and 0.016 (lumbar spine [LS]), and for Prodigy, they were 0.009 (TH) and 0.039 (LS). In men, corresponding results for Prodigy were 0.014 and 0.031. In women, 41% and in men, 39% had aBMD changes exceeding the LSC at TH. Follow-up intervals (i.e., LSC/median rate of aBMD change) for both women and men were 8 yr (TH) and 13 yr (LS). Based on Prodigy precision data, follow-up intervals for women were 3 and 32 yr at TH and LS. In summary, several years were needed to detect change. Only when a high rate of bone loss is suspected, a short follow-up time is possible, in elderly persons.     

Dual-Energy X-ray Absorptiometry Diagnostic Discordance Between Z-Scores and T-Scores in Young Adults

Diagnostic criteria for postmenopausal osteoporosis using central dual-energy X-ray absorptiometry (DXA) T-scores have been widely accepted. The validity of these criteria for other populations, including premenopausal women and young men, has not been established. The International Society for Clinical Densitometry (ISCD) recommends using DXA Z-scores, not T-scores, for diagnosis in premenopausal women and men aged 20–49 yr, though studies supporting this position have not been published. We examined diagnostic agreement between DXA-generated T-scores and Z-scores in a cohort of men and women aged 20–49 yr, using 1994 World Health Organization and 2005 ISCD DXA criteria. Four thousand two hundred and seventy-five unique subjects were available for analysis. The agreement between DXA T-scores and Z-scores was moderate (Cohen's kappa: 0.53–0.75). The use of Z-scores resulted in significantly fewer (McNemar's p < 0.001) subjects diagnosed with “osteopenia,” “low bone mass for age,” or “osteoporosis.” Thirty-nine percent of Hologic (Hologic, Inc., Bedford, MA) subjects and 30% of Lunar (GE Lunar, GE Madison, WI) subjects diagnosed with “osteoporosis” by T-score were reclassified as either “normal” or “osteopenia” when their Z-score was used. Substitution of DXA Z-scores for T-scores results in significant diagnostic disagreement and significantly fewer persons being diagnosed with low bone mineral density.     

The Effect of 99mTc on Dual-Energy X-Ray Absorptiometry Measurement of Body Composition and Bone Mineral Density

Whether the γ-emission by radioisotopes influences the outcome of dual-energy X-ray absorptiometry (DXA) measurements is not fully elucidated. The aim of this study was to evaluate the effect of antecedent administration of ^99mTc on DXA measurements regarding body composition and bone mineral density (BMD) using a K-edge filter scanner. The phantom measurements were performed by placing a urinary bladder phantom containing 40 mL of radioisotope solution on the pelvic region of a whole-body phantom. Twenty-seven patients attending our department for a routine examination involving the administration of a tracer marked with ^99mTc were included. The patients underwent a whole-body DXA scan before and within 2 h after tracer injection using a GE/Lunar Prodigy scanner. Control scans were performed on 40 volunteers, who had not received any radioactive tracer. In both phantom and patient measurements, we found a significant dose-related decrease in fat mass and BMD and a corresponding increase in fat-free mass (p < 0.001). Based on the linear regression analysis, we suggest upper dose limits for the measurement of BMD at 0.77 μSv/h and body composition at 0.21 μSv/h (dose rate measured at a distance of 1 m from the patient). Caution should be taken when interpreting the results of DXA scans performed in close temporal proximity to procedures involving the administration of ^99mTc.     

Precision Errors,Least Significant Change,and Monitoring Time Interval in Pediatric Measurements of Bone Mineral Density,Body Composition,and Mechanostat Parameters by GE Lunar Prodigy

Dual-energy X-ray absorptiometry (DXA) method is widely used in pediatrics in the study of bone density and body composition. However, there is a limit to how precise DXA can estimate bone and body composition measures in children. The study was aimed to (1) evaluate precision errors for bone mineral density, bone mass and bone area, body composition, and mechanostat parameters, (2) assess the relationships between precision errors and anthropometric parameters, and (3) calculate a “least significant change” and “monitoring time interval” values for DXA measures in children of wide age range (5–18 yr) using GE Lunar Prodigy densitometer. It is observed that absolute precision error values were different for thin and standard technical modes of DXA measures and depended on age, body weight, and height. In contrast, relative precision error values expressed in percentages were similar for thin and standard modes (except total body bone mineral density [TBBMD]) and were not related to anthropometric variables (except TBBMD). Concluding, due to stability of percentage coefficient of variation values in wide range of age, the use of precision error expressed in percentages, instead of absolute error, appeared as convenient in pediatric population.     

In Vivo Precision of the GE Lunar iDXA for the Assessment of Lumbar Spine,Total Hip,Femoral Neck,and Total Body Bone Mineral Density in Severely Obese Patients

No study has evaluated the precision of the GE Lunar iDXATM (GE Healthcare) in measuring bone mineral density (BMD) among severely obese patients. The purpose of the study was to evaluate the precision of the GE Lunar iDXATM for assessing BMD, including the lumbar spine L1–L4, L2–L4, the total hip, femoral neck, and total body in a severely obese population (body mass index [BMI] > 40 kg/m²). Sixty-four severely obese participants with a mean age of 46 ± 11 yr, BMI of 49 ± 6 kg/m², and a mean body mass of 136.8 ± 20.4 kg took part in this investigation. Two consecutive iDXA scans (with repositioning) of the total body (total body BMD [TBBMD]), lumbar spine (L1–L4 and L2–L4), total hip (total hip BMD [THBMD]), and femoral neck (femoral neck BMD [FNBMD]) were conducted for each participant. The coefficient of variation (CV), the root mean square (RMS) averages of standard deviations of repeated measurements, the corresponding 95% least significant change, and intraclass correlations (ICCs) were calculated. In addition, analysis of bias and coefficients of repeatability were calculated. The results showed a high level of precision for total body (TBBMD), lumbar spine (L1–L4), and total hip (THBMD) with values of RMS: 0.013, 0.014, and 0.011 g/cm²; CV: 0.97%, 1.05%, and 0.99%, respectively. Precision error for the femoral neck was 2.34% (RMS: 0.025 g/cm²) but still represented high reproducibility. ICCs in all dual-energy X-ray absorptiometry measurements were 0.99 with FNBMD having the lowest at 0.98. Coefficients of repeatability for THBMD, FNBMD, L1–L4, L2–L4, and TBBMD were 0.0312, 0.0688, 0.0383, 0.0493, and 0.0312 g/cm², respectively. The Lunar iDXA demonstrated excellent precision for BMD measurements and is the first study to assess reproducibility of the GE Lunar iDXA with severely obese adults.     

Systematic vertebral fracture assessment in asymptomatic postmenopausal women

IntroductionRecognition of vertebral fractures (VFs) changes the patient's diagnostic classification, estimation of fracture risk, and threshold for pharmacological intervention. Vertebral fracture assessment (VFA) enables the detection of VFs in the same session as bone mineral density (BMD) testing.ObjectiveTo study prevalence and risk factors of VFs using VFA in asymptomatic women and measure its effect on treatment recommendations.MethodsWe enrolled 908 postmenopausal women (mean age, weight and BMI of 60.9 ± 7.7 (50–91) years, 73.2 ± 13.2 (35–150) kg and 29.8 ± 5.3 (14.5–50.8) kg/m², respectively. Lateral VFA images and scans of the lumbar spine and proximal femur were obtained using a GE Healthcare Lunar Prodigy densitometer. VFs were defined using a combination of Genant semiquantitative (SQ) approach and morphometry.ResultsVFs were identified in 382 patients (42.0%): 203 (22.3%) had grade 1 and 179 (19.7%) had grade 2 or 3. The prevalence of VFA-detected fractures globally increased significantly with age and as BMI and BMD declined. A fracture was identified on VFA in 63 (28.3%) women with normal BMD (8.5% had grade 2/3 VFs) and in 145 (38.5%) with osteopenia (15.7% had grade 2/3 VFs). Stepwise regression analysis showed that presence of VFs was independently related to age, BMI, number of parity, history of peripheral fracture and lumbar spine BMD.ConclusionA high proportion of women with asymptomatic VFs would not receive treatment if screening were based only on BMD evaluation. Our results support the recommendation to enlarge the indications of VFA in the presence of risk factors such as age over 60, multiparity, history of peripheral traumatic fractures and low BMI.     

Does the Precision of Dual-Energy X-ray Absorptiometry for Bone Mineral Density Differ by Sex?

Given larger bone size in men, bone mineral density (BMD) precision might differ between sexes. This study compared dual-energy X-ray absorptiometry BMD precision of 3 International Society for Clinical Densitometry-certified technologists in older men and women. Each technologist scanned a cohort of 30 men and 30 women (total n = 180) by using a Lunar iDXA densitometer (GE Healthcare, Madison, WI). Each volunteer had 2 lumbar spine and bilateral hip scans with repositioning between examinations. BMD least significant change was calculated. Age and body mass index did not differ between men and women. Mean height and weight were greater in men, 174.6 cm ± 6.9 and 81.6 kg ± 11.1 respectively, (p < 0.0001) than in women, 161.5 cm ± 5.9/69.1 kg ± 14.2, respectively. Bone area was greater in men (p < 0.0001) at all sites. BMD least significant change was statistically better (p < 0.05) in women at the mean total femur (0.014 vs 0.018 g/cm²) and left femoral neck (0.025 vs 0.038 g/cm²), but not different at either total femur, the right femoral neck, or lumbar spine (all p > 0.05). In conclusion, statistically significant male/female differences in BMD precision were observed at the mean total femur and left femoral neck. Given the small magnitude of difference in g/cm² and inconsistent pattern, that is, no right femoral neck difference, there is virtually no clinical difference in BMD precision between sexes. These data do not support a need for sex-specific precision analyses.     

Cross-calibration of a GE iDXA and Prodigy for Total and Regional Body Bone Parameters: The Importance of Using Cross-calibration Equations for Longitudinal Monitoring After a System Upgrade

We aimed to determine if cross-calibration equations could be applied to convert GE Lunar Prodigy total and regional bone measurements to the GE iDXA model to support longitudinal monitoring of subjects. The cross-calibration group comprised 63 adults (age 45.1 [12.8] yr; body mass index: 25.6 [3.7] kg/m²) and the validation group comprised 25 adults (age 40.5 [11.5] yr; body mass index: 25.7 [3.5] kg/m²). The parameters reported were total and regional bone mineral density (BMD), bone mineral content, and bone area. There were significant differences between densitometers for all anatomical regions and reported bone parameters (p < 0.0001); iDXA reported lower BMD than the Prodigy apart from the ribs. Linear regression indicated good agreement for all measurements. Bland-Altman analyses indicated significant bias for all measurements and that cross-calibration equations were required. The derived cross-calibration equations were effective in reducing differences between predicted and measured results for each parameter and at each region apart from leg BMD, where the difference remained significant (0.013 g/cm²; p < 0.05). Our results indicate that cross-calibration is important to maintain comparability of total body-derived regional bone measurements between the Lunar Prodigy and iDXA.     

BMD measurement and precision: a comparison of GE Lunar Prodigy and iDXA densitometers

This study assessed bone mineral density (BMD) comparability and precision using Lunar Prodigy and iDXA densitometers (GE Healthcare, Madison, WI) in adults. Additionally, the utility of supine forearm measurement with iDXA was investigated. Lumbar spine and bilateral proximal femur measurements were obtained in routine clinical manner in 345 volunteers, 202 women and 143 men of mean age 52.5 (range: 20.1-91.6)yr. Seated and supine distal forearm scans were obtained in a subset (n=50). Lumbar spine and proximal femur precision assessments were performed on each instrument following International Society for Clinical Densitometry recommendations in 30 postmenopausal women. BMD at the L1-L4 spine, total proximal femur, and femoral neck was very highly correlated (r(2)≥0.98) between densitometers, as was the one-third radius site (r(2)=0.96). Bland-Altman analyses demonstrated no clinically significant bias at all evaluated sites. BMD precision was similar between instruments at the L1-L4 spine, mean total proximal femur, and femoral neck. Finally, one-third radius BMD measurements in the supine vs seated position on the iDXA were highly correlated (r(2)=0.96). In conclusion, there is excellent BMD correlation between iDXA and Prodigy densitometers. Similarly, BMD precision is comparable with these two instruments.