Reproducibility of fan-beam DXA measurements in adults and phantoms

Cross-calibration, Least Significant Change and Quality Assurance in Multiple Dual-Energy X-ray Absorptiometry Scanner Environments: 2019 ISCD Official Position

In preparation for the International Society for Clinical Densitometry Position Development Conference (PDC) 2019 in Kuala Lumpur, Malaysia, a cross-calibration and precision task force was assembled and tasked to review the literature, summarize the findings, and generate positions to answer 4 related questions provided by the PDC Steering Committee, which expand upon the current ISCD official positions on these subjects. (1) How should a provider with multiple dual-energy X-ray absorptiometry (DXA) scanners of the same make and model calculate least significant change (LSC)? (2) How should a provider with multiple DXA systems with the same manufacturer but different models calculate LSC? (3) How should a provider with multiple DXA systems from different manufacturers and models calculate LSC? (4) Are there specific phantom procedures that one can use to provide trustworthy in vitro cross calibration for same models, different models, and different makes? Based on task force deliberations and the resulting systematic literature reviews, 3 new positions were developed to address these more complex scenarios not addressed by current official positions on single scanner cross calibration and LSC. These new positions provide appropriate guidance to large multiple DXA scanner providers wishing to offer patients flexibility and convenience, and clearly define good clinical practice requirements to that end.

Ratio of trunk to leg volume as a new body shape metric for diabetes and mortality

BACKGROUND

Body shape is a known risk factor for diabetes and mortality, but the methods estimating body shape, BMI and waist circumference are crude. We determined whether a novel body shape measure, trunk to leg volume ratio, was independently associated with diabetes and mortality.

METHODS

Data from the National Health and Nutritional Examination Survey 1999-2004, a study representative of the US population, were used to generate dual-energy X-ray absorptiometry-derived trunk to leg volume ratio and determine its associations to diabetes, metabolic covariates, and mortality by BMI category, gender, and race/ethnicity group.

RESULTS

The prevalence of pre-diabetes and diabetes increased with age, BMI, triglycerides, blood pressure, and decreased HDL level. After adjusting for covariates, the corresponding fourth to first quartile trunk to leg volume ratio odds ratios (OR) were 6.8 (95% confidence interval [CI], 4.9-9.6) for diabetes, 3.9 (95% CI, 3.0-5.2) for high triglycerides, 1.8 (95% CI, 1.6-2.1) for high blood pressure, 3.0 (95% CI, 2.4-3.8) for low HDL, 3.6 (95% CI, 2.8-4.7) for metabolic syndrome, and 1.76 (95% CI, 1.20-2.60) for mortality. Additionally, trunk to leg volume ratio was the strongest independent measure associated with diabetes (P<0.001), even after adjusting for BMI and waist circumference. Even among those with normal BMI, those in the highest quartile of trunk to leg volume ratio had a higher likelihood of death (5.5%) than those in the lowest quartile (0.2%). Overall, trunk to leg volume ratio is driven by competing mechanisms of changing adiposity and lean mass.

CONCLUSIONS

A high ratio of trunk to leg volume showed a strong association to diabetes and mortality that was independent of total and regional fat distributions. This novel body shape measure provides additional information regarding central adiposity and appendicular wasting to better stratify individuals at risk for diabetes and mortality, even among those with normal BMI.

Total and regional body volumes derived from dual-energy X-ray absorptiometry output

Total body volume is an important health metric used to measure body density, shape, and multicompartmental body composition but is currently only available through underwater weighing or air displacement plethysmography (ADP). The objective of this investigation was to derive an accurate body volume from dual-energy X-ray absorptiometry (DXA)-reported measures for advanced body composition models. Volunteers received a whole body DXA scan and an ADP measure at baseline (N = 25) and 6 mo (N = 22). Baseline measures were used to calibrate body volume from the reported DXA masses of fat, lean, and bone mineral content. A second population (N = 385) from the National Health and Nutrition Examination Survey was used to estimate the test-retest precision of regional (arms, legs, head, and trunk) and total body volumes. Overall, we found that DXA-volume was highly correlated to ADP-volume (R² = 0.99). The 6-mo change in total DXA-volume was highly correlated to change in ADP-volume (R² = 0.98). The root mean square percent coefficient of variation precision of DXA-volume measures ranged from 1.1% (total) to 3.2% (head). We conclude that the DXA-volume method can measure body volume accurately and precisely, can be used in body composition models, could be an independent health indicator, and is useful as a prospective or retrospective biomarker of body composition.

Dual-energy X-ray absorptiometry-based body volume measurement for 4-compartment body composition

BACKGROUND

Total body volume (TBV), with the exclusion of internal air voids, is necessary to quantify body composition in Lohman's 4-compartment (4C) model.

OBJECTIVE

This investigation sought to derive a novel, TBV measure with the use of only dual-energy X-ray absorptiometry (DXA) attenuation values for use in Lohman's 4C body composition model.

DESIGN

Pixel-specific masses and volumes were calculated from low- and high-energy attenuation values with the use of first principle conversions of mass attenuation coefficients. Pixel masses and volumes were summed to derive body mass and total body volume. As proof of concept, 11 participants were recruited to have 4C measures taken: DXA, air-displacement plethysmography (ADP), and total body water (TBW). TBV measures with the use of only DXA (DXA-volume) and ADP-volume measures were compared for each participant. To see how body composition estimates were affected by these 2 methods, we used Lohman's 4C model to quantify percentage fat measures for each participant and compared them with conventional DXA measures.

RESULTS

DXA-volume and ADP-volume measures were highly correlated (R(2) = 0.99) and showed no statistically significant bias. Percentage fat by DXA volume was highly correlated with ADP-volume percentage fat measures and DXA software-reported percentage fat measures (R(2) = 0.96 and R(2) = 0.98, respectively) but were slightly biased.

CONCLUSIONS

A novel method to calculate TBV with the use of a clinical DXA system was developed, compared against ADP as proof of principle, and used in Lohman's 4C body composition model. The DXA-volume approach eliminates many of the inherent inaccuracies associated with displacement measures for volume and, if validated in larger groups of participants, would simplify the acquisition of 4C body composition to a single DXA scan and TBW measure.

Cross calibration of Hologic QDR2000 and GE lunar prodigy for whole body bone mineral density and body composition measurements

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

Soy isoflavone supplementation and bone mineral density in menopausal women: a 2-y multicenter clinical trial

BACKGROUND

Isoflavones are naturally occurring plant estrogens that are abundant in soy. Although purported to protect against bone loss, the efficacy of soy isoflavone supplementation in the prevention of osteoporosis in postmenopausal women remains controversial.

OBJECTIVE

Our aim was to test the effect of soy isoflavone supplementation on bone health.

DESIGN

A multicenter, randomized, double-blind, placebo-controlled 24-mo trial was conducted to assess the effects of daily supplementation with 80 or 120 mg of soy hypocotyl aglycone isoflavones plus calcium and vitamin D on bone changes in 403 postmenopausal women. Study subjects were tested annually and changes in whole-body and regional bone mineral density (BMD), bone mineral content (BMC), and T scores were assessed. Changes in serum biochemical markers of bone metabolism were also assessed.

RESULTS

After study site, soy intake, and pretreatment values were controlled for, subjects receiving a daily supplement with 120 mg soy isoflavones had a statistically significant smaller reduction in whole-body BMD than did the placebo group both at 1 y (P < 0.03) and at 2 y (P < 0.05) of treatment. Smaller decreases in whole-body BMD T score were observed among this group of women at 1 y (P < 0.03) but not at 2 y of treatment. When compared with the placebo, soy isoflavone supplementation had no effect on changes in regional BMD, BMC, T scores, or biochemical markers of bone metabolism.

CONCLUSION

Daily supplementation with 120 mg soy hypocotyl isoflavones reduces whole-body bone loss but does not slow bone loss at common fracture sites in healthy postmenopausal women. This trial was registered at clinicaltrials.gov as NCT00665860.

Training requirements for DXA technologists in the United States

The purposes of this study were to determine, by state, the requirements for dual-energy X-ray absorptiometry(DXA) operators' training, knowledge of these state requirements, and factors that predicted state and International Society of Clinical Densitometry (ISCD) certification of DXA technologists. Seventeen states required registered technologist (RT) certification or authorized/licensed limited certification for DXA operators, 16 had no certification requirements, 12 required RT certification, and 5 had state-specific requirements. There were 9745 surveys mailed toDXA users including 50% Hologic Inc., 50% GE Lunar, and 100% Norland; 3148 surveys are included in this analysis. Among responders who indicated that their state did not have any certification requirements (n=1673), 1095(65.5%) were incorrect; there were requirements. Possession of state and ISCD certification was significantly correlated with the number of patients scanned per week (p<or=0.05), the number of technologists employed within a center (p<0.01), and the subspecialty of the practitioner (p<or=0.02). Our study uncovered a lack of uniformity amongstates with respect to central DXA operator training requirements. Additionally, in those states with requirements, DXA operators were often unaware of these requirements. Uniform national training requirements for central DXA operators to ensure adequate DXA scan quality are urgently needed.