Fan-beam Dual-energy X-ray Absorptiometry Research Articles

Trabecular Bone Score Vertebral Exclusions Affect Risk Classification and Treatment Recommendations: The Manitoba Bmd Registry

Lumbar spine trabecular bone score (TBS), a texture measure derived from spine dual-energy x-ray absorptiometry (DXA) images, is a bone mineral density (BMD)-independent risk factor for fracture. Lumbar vertebral levels that show structural artifact are excluded from BMD measurement. TBS is relatively unaffected by degenerative artifact, and it is uncertain whether the same exclusions should be applied to TBS reporting. To gain insight into the clinical impact of vertebral exclusion on TBS, we examined the effect of lumbar vertebral exclusions in routine clinical practice on tertile-based TBS categorization and TBS adjusted FRAX-based treatment recommendations. The study population consisted of 71,209 individuals aged 40 years and older with narrow fan-beam spine DXA examinations and retrospectively-derived TBS. During BMD reporting, 34.3% of the scans had one or more vertebral exclusions for structural artifact. When TBS was derived from the same vertebral levels used for BMD reporting, using fixed L1-L4 tertile cutoffs (1.23 and 1.31 from the McCloskey meta-analysis) reclassified 17.9% to a lower and 6.5% to a higher TBS category, with 75.6% unchanged. Reclassification was reduced from 24.4% overall to 17.2% when level-specific tertile cutoffs from the software manufacturer were used. Treatment reclassification based upon FRAX major osteoporotic fracture probability occurred in 2.9% overall, but in 9.6% of those with baseline risk ≥15%. For treatment based upon FRAX hip fracture probability, reclassification occurred in 3.4% overall, but in 10.4% in those with baseline risk ≥2%. In summary, lumbar spine TBS measurements based upon vertebral levels other than L1-L4 can alter the tertile category and treatment recommendations based upon TBS-adjusted FRAX calculation, especially for those close to or exceeding the treatment cut-off. Manufacturer level-specific tertile cut-offs should be used if vertebral exclusions are applied.

Multichannel FPGA-based Data Acquisition System for Fan-beam Dual Energy X-ray Absorptiometry

This study aimed to develop a multichannel field programmable gate array (FPGA) based data acquisition (DAQ) system that could process 8 analog signals from a 1 × 8 LYSO array coupled with a Geiger-mode avalanche photodiode (GAPD) for fan-beam dual-energy X-ray absorptiometry (DEXA) system. Each analog input signal was digitized using an 8-channel analog-to-digital converter (ADC) with a 125 MHz sampling rate and an input range of -1.0 to 1.0 V. The 14-bit digital signals were then fed into a Xilinx Virtex-6 FPGA-based evaluation board that implemented digital signal processing logic. The collected low- and high-energy events of each pixel for each input channel were stored in an on-chip block ram-based first-in-first-out (FIFO) module, and then further transmitted to a personal computer (PC) via the USB port. The intrinsic characteristics, spectral responses, and image acquisition were performed. The estimated coefficient of determination (R²) was 0.999 in voltage linearity and no considerable alterations in voltage resolution were observed. The energy resolutions of the peak 59.5 keV (Am-241) were ~28.2 %. Dual-energy peaks were isolated in the X-ray energy spectra. The synchronization between the movement part of the DEXA system and the timing control block inside the FPGA chip was well controlled in various conditions. The DEXA phantom images for each pixel were clearly resolved. This study demonstrated that FPGA with only on-chip memory resources can be used to build a multichannel DAQ system for fan-beam DEXA systems.

Contributions of Clinical and Technical Factors to Longitudinal Change in Trabecular Bone Score and Bone Density: A Registry-Based Individual-Level Analysis.

Lumbar spine trabecular bone score (TBS), a gray-level texture measure derived from spine dual-energy X-ray absorptiometry (DXA) images, is a bone mineral density (BMD)-independent risk factor for fracture. An unresolved question is whether TBS is sufficiently responsive to change over time or in response to widely used osteoporosis therapy at the individual level to serve as a useful biomarker. Using the Manitoba DXA Registry, we identified 11,643 individuals age 40 years and older with two fan-beam DXA scans performed on the same instrument within 5 years (mean interval 3.2 years), of whom 6985 (60.0%) received antiresorptive osteoporosis medication (majority oral bisphosphonate) between the scans. We examined factors that were associated with a change in lumbar spine TBS, lumbar spine BMD, and total hip BMD exceeding the 95% least significant change (LSC). Change exceeding the LSC was identified in 23.0% (9.3% increase, 13.8% decrease) of lumbar spine TBS, 38.2% (22.1% increase, 16.1% decrease) lumbar spine BMD, and 42.5% (17.6% increase, 24.9% decrease) total hip BMD measurement pairs. From regression models, the variables most strongly associated with significant change in TBS (decreasing order) were tissue thickness change, acquisition mode change, weight change, and spine percent fat change. Consistent with the insensitivity of TBS to oral antiresorptive therapies, use of these agents showed very little effect on TBS change. In contrast, for both spine BMD change and total hip BMD change, osteoporosis medication use was the most significant variable, whereas tissue thickness change, acquisition mode change, and weight change had relatively weak effects. In summary, change in spine TBS using the present algorithm appears to be strongly affected by technical factors. This suggests a limited role, if any, for using TBS change in untreated individuals or for monitoring response to antiresorptive treatment in routine clinical practice with the current version of the TBS algorithm. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Cross-calibration of pencil-beam (DPX-NT) and fan-beam (QDR-4500C) dual-energy X-ray absorptiometry for sarcopenia.

Sarcopenia, defined as the loss of muscle mass accompanied by weakness, is an important factor leading to frailty and is a growing concern in the aging Japanese society. Muscle mass can be calculated by dual-energy X-ray absorptiometry (DXA), but results differ between devices produced by different manufactures. Thus, cross-calibration is needed to compare body composition results in multicenter trials or when scanners are replaced. The purpose of this study was to perform an in vivo calibration of total body scans between pencil-beam (DPX-NT, GE Healthcare) and fan-beam (QDR-4500C, Hologic Inc.) DXA units. A total 30 subjects (15 women, 15 men, mean age = 35 years, range 22-49 years) were recruited. The lumbar bone mineral density (BMD), femoral neck BMD, appendicular fat and lean body mass, and the appendicular skeletal muscle mass index (ASMI) were highly correlated (r = 0.979-0.993, r(2) = 0.889-0.977). The conversion formulas were as follows: lumbar BMD, Y = -0.08 + 1.16X (X = QDR-4500C, Y = DPX-NT), femoral neck BMD, Y = -0.015 + 1.11X, and ASMI Y = 0.92 + 0.90X. There is excellent comparability between the DPX-NT and the QDR-4500C DXA units. However, cross-calibration equations are required to assess muscle volume, fat, and ASMI in multicenter studies investigating sarcopenia.

Spine Trabecular Bone Score (TBS) Cross-Calibration for GE Prodigy and iDXA Scanners

Total 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.Subjects 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.Bone 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.For 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.

The accuracy and precision of DXA for assessing body composition in team sport athletes

This study determined the precision of pencil and fan beam dual-energy X-ray absorptiometry (DXA) devices for assessing body composition in professional Australian Football players. Thirty-six professional Australian Football players, in two groups (fan DXA, N = 22; pencil DXA, N = 25), underwent two consecutive DXA scans. A whole body phantom with known values for fat mass, bone mineral content and fat-free soft tissue mass was also used to validate each DXA device. Additionally, the criterion phantom was scanned 20 times by each DXA to assess reliability. Test–retest reliability of DXA anthropometric measures were derived from repeated fan and pencil DXA scans. Fat-free soft tissue mass and bone mineral content from both DXA units showed strong correlations with, and trivial differences to, the criterion phantom values. Fat mass from both DXA showed moderate correlations with criterion measures (pencil: r = 0.64; fan: r = 0.67) and moderate differences with the criterion value. The limits of agreement were similar for both fan beam DXA and pencil beam DXA (fan: fat-free soft tissue mass = −1650 ± 179 g, fat mass = −357 ± 316 g, bone mineral content = 289 ± 122 g; pencil: fat-free soft tissue mass = −1701 ± 257 g, fat mass = −359 ± 326 g, bone mineral content = 177 ± 117 g). DXA also showed excellent precision for bone mineral content (coefficient of variation (%CV) fan = 0.6%; pencil = 1.5%) and fat-free soft tissue mass (%CV fan = 0.3%; pencil = 0.5%) and acceptable reliability for fat measures (%CV fan: fat mass = 2.5%, percent body fat = 2.5%; pencil: fat mass = 5.9%, percent body fat = 5.7%). Both DXA provide precise measures of fat-free soft tissue mass and bone mineral content in lean Australian Football players. DXA-derived fat-free soft tissue mass and bone mineral content are suitable for assessing body composition in lean team sport athletes.

The Validity of Commonly Used Adipose Tissue Body Composition Equations Relative to Dual Energy X-ray Absorptiometry (DXA) in Gaelic Games Players

Dual-energy X-ray absorptiometry (DXA) and adipose tissue percentage estimates (AT%) derived from regression based skinfold equations were compared. 35 Gaelic games players [20.9 ± 1.7 years; 78.1 ± 8.6 kg; 179.5 ± 5.7 cm] underwent whole body fan beam DXA scans following a standardised protocol and assessment of skinfold thickness at 8 sites. Adipose tissue% from the sum of skinfolds and/or via body density were calculated for general and athlete specific equations (SKf-AT %). The relationship, i. e., proportional bias, fixed bias and random error (SEE) between DXA-AT % and AT % derived from the 6 skinfold equations were determined using least squares regression analysis. Skinfold AT% estimates were underestimated relative to DXA-AT % across all skinfold equations except that of Durnin and Wormersley [9] (D&W-∑(4AT %)) (16.7 ± 3.4 vs. 16.6 ± 4.0 %). All equations demonstrated 95 % prediction intervals ranges exceeding ~10 %. Each equation failed to predict AT% relative to DXA within an accepted ± 3.5 % anthropometric error rate. It is recommended that the conversion of absolute skinfold thickness to an AT % is avoided and that the skinfold equations assessed herein are not utilised in Gaelic games players. Alternate 'sum of skinfold' approaches should be considered.

Pediatric radiation dose and risk from bone density measurements using a GE Lunar Prodigy scanner

Effective radiation doses associated with bone mineral density examinations performed on children using a GE Lunar Prodigy fan-beam dual-energy X-ray absorptiometry (DXA) scanner were found to be comparable to doses from pencil-beam DXA devices, i.e., lower than 1 μSv. Cancer risks associated with acquisitions obtained in this study are negligible. No data were found in the literature on radiation doses and potential risks following pediatric DXA performed on GE Lunar DXA scanners. This study aimed to estimate effective doses and associated cancer risks involved in pediatric examinations performed on a GE Lunar Prodigy scanner. Four physical anthropomorphic phantoms representing newborn, 1-, 5-, and 10-year-old patients were employed to simulate DXA exposures. All acquisitions were carried out using the Prodigy scanner. Dose measurements were performed for spine and dual femur using the phantoms simulating the 5- and 10-year-old child. Moreover, doses associated with whole-body examinations were measured for the four phantoms used in the current study. The gender-average effective dose for spine and hip examinations were 0.65 and 0.36 μSv, respectively, for the phantom representing the 5-year-old child and 0.93 and 0.205 μSv, respectively, for the phantom representing the 10-year-old child. Effective doses for whole-body examinations were 0.25, 0.22, 0.19, and 0.15 μSv for the neonate, 1-, 5-, and 10-year old child, respectively. The estimated lifetime cancer risks were negligible, i.e., 0.02-0.25 per million, depending on the sex, age, and type of DXA examination. A formula is presented for the estimation of effective dose from examinations performed on GE Lunar Prodigy scanners installed in other institutions. The effective doses and potential cancer risks associated with pediatric DXA examinations performed on a GE Lunar Prodigy fan-beam scanner were found to be comparable to doses and risks reported from pencil-beam DXA devices.

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±14.4yr) 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.

Anthropometric equation for estimation of appendicular skeletal muscle mass in Chinese adults.

The purpose of this study was to develop and cross-validate anthropometric equations for the estimation of appendicular skeletal muscle mass (ASM) in Chinese adults. A total of 763 adults aged 18-69 years (345 men and 418 women) were recruited from residents living in four regions (Jinan, Guangzhou, Xi'an and Chengdu) in China. ASM were measured by fan-beam dual energy x-ray absorptiometry. Participants' body weight, height, limb circumferences (upper arm, thigh, and calf), waist circumference, and skinfold thicknesses (triceps, thigh, and calf) were measured by trained testers. The participants were randomly assigned to two groups: a model-development group (MD group) and a cross-validation group (CV group). Prediction models were established using the data from the MD group, and cross-validated with the data of the CV group. The results suggested that the developed equations had satisfactory prediction qualities, and could be applied as a practical method of quantifying ASM in Chinese adults.

Ethnic variation in body composition assessment in a sample of adolescent girls

To compare body composition assessment by bioelectrical impedance analysis (BIA) and dual-energy X-ray absorptiometry (DXA) in a multiethnic sample of adolescent girls. Data were from a physical activity intervention study among 254 14-20-year-old sedentary American girls, including 69 whites, 74 blacks, 42 Hispanics, and 69 Asians. Height and weight were objectively measured. Body composition was assessed using a foot-to-foot BIA and a fan-beam DXA. We calculated ethnic-specific estimates of percentage body fat (BF%), fat mass (FM), fat mass index (FMI), fat-free mass (FFM), and fat-free mass index (FFMI) from BIA and DXA. We used Bland-Altman plots to examine ethnic-specific agreement between BIA and DXA, and used linear regression to test whether the BIA-DXA difference varied across the mean. Compared to DXA, BIA estimates of fat measures (BF%, FM, and FMI) were lower and lean tissue measures (FFM and FFMI) higher. For example, the BIA-estimated BF% was lower than the DXA estimate by between 4.9% (95% CI: -5.9, -3.9) in blacks and 8.7% (-7.0, -5.0) in Asians, with large limits of agreement (-15.4 to -5.4 in blacks and -16.8 to -0.4 in Asians). Regression analysis showed that BIA-DXA differences were not constant across means for any body composition measure among Asians or for any measure except BF% among whites. Compared to DXA, BIA yielded lower estimates of adiposity in a multiethnic adolescent sample. BIA-DXA differences varied by ethnicity, and across mean body composition values for some ethnicities.

Regional versus total body bone mass and body composition during infancy

Summary Background & aims Total body dual energy X-ray absorptiometry (DXA) is a useful non-invasive technique in the assessment for bone and soft tissue growth and development in infants although the role of regional DXA measurements is not well defined. Methods Regional measurements including extremities, trunk and head were obtained by software delineation from a database of infant whole body DXA scans based on pencil beam (PB) and fan beam (FB) DXA techniques. Results Data from fan beam or pencil beam were similar. All regional DXA measurements were correlated and predictive of total body measurements. The relationship to total body measurements was better for larger regions such as the trunk and lower extremities, and for lean, fat, bone mineral content, fat and fat percent (adjusted r 2 0.78 to 0.98 for FB and 0.82 to 1.00 for PB). At the head region, bone mineral density was best related to total body measurements with adjusted r 2 > 0.92 for both DXA techniques. DXA measurements from left and right extremities were correlated but the agreement varied among different DXA parameters. Weight was the best predictor for regional as well as total body bone and soft tissue measurements although other physiologic predictors including length, age, gender and race could be forced into prediction equation. Conclusions Regional DXA measurements may be considered as a screening tool to monitor changes in bone and soft tissue composition during infancy but they should not be used as a surrogate replacing total body measurements.

Comparison of Body Composition by Bioelectrical Impedance Analysis and Dual‐Energy X‐Ray Absorptiometry in Hispanic Diabetics

The purpose of this study was to compare Tanita tetrapolar foot‐to‐foot bioelectrical impedance analysis (Model TBF‐310, Tanita Corporation of America, Arlington Heights, IL; Tanita‐BIA) and fan beam dual‐energy X‐ray absorptiometry (Hologic Discovery A v12.6, Waltham, MA; DXA). Seventy Hispanic diabetic participants (23 male, 47 female; mean age: 53.03 ± 10.32 yrs; mean weight: 81.45 ± 17.65 kg; and mean body mass index: 31.40 ± 6.80 kg/m^2) participated in a three‐month diabetes education follow‐up study. Fat mass (FM), percent fat mass (%FM), and fat free mass (FFM) were compared using both relative and absolute measures of agreement. Relative measures included Pearson's and Spearman's rank correlation coefficients while absolute agreement was assessed using Bland‐Altman analyses and concordance correlation with 95% confidence intervals calculated using a bootstrap resampling of the data. Pearson's (FM: 0.96, %FM: 0.91, and FFM: 0.82), and Spearman's rank (FM: 0.94, %FM: 0.91, and FFM: 0.92) correlation coefficients showed high measures of association. Bland‐Altman and concordance analyses also demonstrated good agreement [FM: 0.93 (95% CI: 0.89, 0.96)], [%FM: 0.86 (95% CI: 0.79, 0.90)], and [FFM: 0.93 (95% CI: 0.89, 0.96)]. Tanita‐BIA may provide valid measures of FM, %FM and FFM in Hispanic diabetics, and could be a convenient and practical approach for assessment in community‐based research. This study was supported in part by grants 03‐00335 from the Centers for Medicare and Medicaid Services and 5P20MD001632 from the National Institutes of Health.

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

Purpose Total 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. Methods Subjects 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/m 2) 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. Results Bone 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. Conclusion For estimation of BMC and body composition, there was high agreement between all DXA systems ( R 2 = 0.85–0.99). Even so, cross-calibration equations should be used to examine data across systems to avoid erroneous conclusions.

Measurement of lower-leg volume change by quantitative computed tomography

Lower-leg edema is a common symptom in many diseases. A precise method with low variability for measurement of edema is warranted in order to obtain optimal conditions for investigation of treatment effects. To evaluate computed tomography for precise measurement of lower-leg muscle and adipose tissue volumes using a very low level of effective radiation dose. Eleven volunteers were examined three times during 1 day, either as two consecutive examinations in the morning and one single examination in the afternoon, or as one examination in the morning and two in the afternoon. Eleven scans with computed tomography were made at each examination, and lower-leg volumes were calculated from automatically measured scan areas and interscan distances. Volumes for muscle, adipose tissue, and bone were calculated separately. Minimal radiation dose was used. Mean difference between the repeated examinations was -0.1 ml for total volume, -1.4 ml for muscle, and 1.6 ml for adipose tissue volume. The corresponding 95% confidence intervals were -6.5 to 6.0 ml, -3.5 to 6.5 ml, and -7.0 to 4.0 ml, respectively. The resulting effective dose was 0.5 microSv to one leg. Computed tomography can be used as a precise quantitative method to measure small volume changes of the lower leg as a whole, and separately for muscle and adipose tissue. The results were obtained with a negligible effective dose, lower than that delivered by modern fan-beam dual-energy X-ray absorptiometry whole-body examinations and equal to a few hours of background radiation.

Enhanced Fracture Detection With IDXA; Effect On Mild Fracture Identification

Total 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.Subjects 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.Bone 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.For 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.

Estimating Segment Inertial Parameters Using Fan-Beam DXA

Body segment inertial parameters are required as input parameters when the kinetics of human motion is to be analyzed. However, owing to interindividual differences in body composition, noninvasive inertial estimates are problematic. Dual-energy x-ray absorptiometry (DXA) is a relatively new imaging approach that can provide cost- and time-effective means for estimating these parameters with minimal exposure to radiation. With the introduction of a new generation of DXA machines, utilizing a fan-beam configuration, this study examined their accuracy as well as a new interpolative data-reduction process for estimating inertial parameters. Specifically, the inertial estimates of two objects (an ultra-high molecular density plastic rod and an animal specimen) and 50 participants were obtained. Results showed that the fan-beam DXA, along with the new interpolative data-reduction process, provided highly accurate estimates (0.10-0.39%). A greater variance was observed in the center of mass location and moment of inertia estimates, likely as a result of the course end-point location (1.31 cm). However, using a midpoint interpolation of the end-point locations, errors in the estimates were greatly reduced for the center of mass location (0.64-0.92%) and moments of inertia (-0.23 to -0.48%).

Calcium supplementation and bone mineral accretion in adolescent girls: an 18-mo randomized controlled trial with 2-y follow-up

Background:A recent meta-analysis raised doubt as to whether calcium supplementation in children benefits spine and hip bone mineral density (BMD). Objective:We used state-of-the-art measures of bone (fan-beam dual-energy X-ray absorptiometry and 4 bone turnover markers) to determine whether girls with low habitual calcium intake benefited from supplementation with a soluble form of calcium (calcium citrate malate dissolved in a fruit drink). Design:The trial was an 18-mo randomized trial of calcium supplementation (792 mg/d) with follow-up 2 y after supplement withdrawal. Subjects were 96 girls (mean age: 12 y) with low calcium intakes (mean: 636 mg/d). The main outcome measure was change in total-body, lumbar spine, and total hip bone mineral content (BMC) during supplementation and 2 y after supplement withdrawal. Changes in BMD and bone turnover markers were secondary outcome measures. Results:The mean additional calcium intake in the supplemented group was 555 mg/d. Compared with the control group, the supplemented group showed significantly (P < 0.05) greater gains in BMC (except at the total hip site) over the 18-mo study. BMD change was significantly (P < 0.05) greater for all skeletal sites, and concentrations of bone resorption markers and parathyroid hormone were significantly (P < 0.01) lower in the supplemented group than in the control group after 18 mo. After 42 mo, gains in BMC and BMD and differences in bone resorption were no longer evident. Conclusions:Calcium supplementation enhances bone mineral accrual in teenage girls, but the effect is short-lived. The likely mechanism for the effect of the calcium is suppression of bone turnover, which is reversed upon supplement withdrawal.

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

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

Vertebral Morphometry by DXA: A Comparison of Supine Lateral and Decubitus Lateral Densitometers

Identification of vertebral fracture has become increasingly important in the diagnosis and management of osteoporosis. This study compares the morphometric techniques on a fan beam dual-energy X-ray absorptiometry (DXA) GE-Lunar Expert system (Expert) using a supine lateral position and a narrow fan beam GE-Lunar Prodigy system (Prodigy; GE Lunar, Madison, WI) that requires lateral decubitus positioning. Patient acceptability, image quality, observer, and equipment variability were determined. Study subjects were recruited from clinical referrals sent for a routine DXA study that included vertebral morphometry. Twenty-five patients underwent lateral vertebral assessment on both machines and completed a questionnaire on comfort and tolerability. Analysis was undertaken by two trained observers. Vertebral height, anterior/posterior height (A/P) and mid/posterior height (M/P) ratios, image quality, and prevalent fractures were assessed. There were no significant differences in patient comfort or image quality scores. More upper thoracic vertebrae could be assessed on the Expert, and good radiographic positioning was easier to achieve on the Expert. Inter-observer coefficients of variance percentage (CV%) of vertebral height was lower on the Prodigy (3.5% in the lumbar spine rising to 12.8% in the thoracic spine) than the Expert (4.2% to 16.9%). Inter-observer CV% for A/P and M/P ratios varied from 2.5% to 10.5% on the Prodigy compared with 3.5% to 12.3% on the Expert, depending on vertebral level. The variation between instruments was similar to the inter-observer CV% (anterior height: -0.11+/-1.65 mm; mid height: 0.54+/-1.51 mm; posterior height: 0.43+/-1.46 mm). There was good agreement between observers and between the Expert and Prodigy in identifying severe fractures, but lack of agreement in identifying moderate fractures. In conclusion, there was no clinically significant difference in patient comfort and image quality between the Expert and the Prodigy. The inter-observer variations in vertebral height and A/P and M/P ratios are similar to the variations between instruments. In making the change from the supine lateral to the decubitus lateral positioning, measurements of vertebral height are reproducible and patient comfort is not compromised.