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