Elsevier

Journal of Clinical Densitometry

Volume 12, Issue 1, January–March 2009, Pages 95-102
Journal of Clinical Densitometry

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

https://doi.org/10.1016/j.jocd.2008.09.004Get rights and content

Abstract

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/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.

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 (R2 = 0.85–0.99). Even so, cross-calibration equations should be used to examine data across systems to avoid erroneous conclusions.

Introduction

The accurate assessment of body composition for purposes of disease classification, disease risk, or presence (osteopenia and osteoporosis), current health status by level of fatness and fat distribution, and changes in these components after an intervention is imperative. One technique commonly used to assess body composition is dual-energy X-ray absorptiometry (DXA) which provides information on both bone mineral content (BMC) and soft tissue content of the whole-body and regions (arms, legs, and trunk). Over the past several years, a number of different DXA systems have come onto the market and into research laboratories 1, 2, 3 where the principal technology differs.

One advancement made in DXA technology has been the transition from a pencil-beam densitometer used in early systems (Lunar's DPX and DPXL) to a fan-beam densitometer used in the currently available systems (GE/Lunar's Prodigy and iDXA systems). Fan-beam systems use multiple detectors that allow for quicker scan acquisition and clearer image resolution but a higher though still minimal radiation dose (4). The results from cross-calibration studies comparing BMC, fat, and lean tissue estimates from the DPXL pencil-beam system vs the Prodigy fan-beam system in children (5) and in adults 4, 6 have shown differences across systems.

The latest densitometer for body composition and bone mineral assessment is the iDXA (GE Lunar) that employs a fan-beam technology with a greater number of detectors than earlier models. As yet it is unknown how the iDXA compares to previous DXA models. For ongoing longitudinal studies where follow-up body composition studies must be performed on a DXA system different from that on which the baseline studies were performed, it becomes essential that a cross-calibration study be performed to allow comparison of data collected on the different systems. Therefore, the use of cross-calibration equations is recommended to compare results between these systems.

The aim of this study was to compare total body fat, lean, and BMC in addition to regional fat and lean mass values for arms, legs, and trunk between a pencil-beam (Lunar DPXL) and 2 fan-beam (GE Lunar Prodigy and GE Lunar iDXA) DXA systems.

Section snippets

Subjects

The sample consisted of healthy multiethnic adults recruited to participate in a study to cross-calibrate 3 different DXA systems. Flyers placed locally in the community were used to recruit subjects. In total, 99 participants (47 males and 52 females) were tested on all 3 DXA systems. Participants ranged in age from 18 yr to 81 yr and ranged in BMI from normal to obese. The maximal weight for inclusion as a study participant was limited by the upper weight limit restriction of the DPXL and

Baseline Characteristics

The descriptive characteristics for this study cohort are presented for males and females separately in Table 1. A total of 99 subjects (47 males and 52 females) completed the study. Descriptive statistics for measurements by scanner for males and females, respectively, are presented in Table 2a, Table 2b. No differences in BMD or bone area were found in either gender. These results are summarized in Table 3a, Table 3b.

Total Body Bone Measurements

The results of the repeated measures analysis of variance are presented in

Discussion

With the advent of fan-beam technology, most DXA manufacturers are offering this technology in their newest models, although some manufacturers continue to sell pencil-beam systems. Body composition investigators who conduct longitudinal studies and those who need to merge data collected using different generation systems are encouraged to use cross-calibration equations so that the validity of merged data is maintained. This study compared total body and regional fat, lean, and BMC of a

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Supported by NIH DK42618 and P30-DK-26687.

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