Dual-energy X-ray absorptiometry body composition model: review of physical concepts

Abstract

Although dual-energy X-ray absorptiometry (DXA) is widely used in clinical research as a means of quantifying body composition, there remains at present little published information that reviews the method's underlying physical basis. Because a clear understanding of DXA physical concepts is integral to appropriate use and interpretation, we present here a three-section review that includes both relevant in vitro and in vivo experimental demonstrations. In the first section we describe the main physical principles on which DXA is based. The section that follows presents a step-by-step analysis of the DXA two-component soft tissue model. In the final section we demonstrate how knowledge of physical concepts can lead to resolution of important methodological concerns, such as the influence of hydration changes on DXA fat estimates. A thorough understanding of DXA physical concepts provides a basis for appropriate interpretation of measurement results and stimulates many new and important research questions.

Validity of the leg-to-leg bioimpedance to estimate changes in body fat during weight loss and regain in overweight women: a comparison with multi-compartment models

“…30 The technical limitations of the DXA may preclude the valid assessment of mineral content during short-term weight change as a consequence of changes in the hydration of FFM, fat distribution, thickness of subcutaneous fat layers and positioning of the patient. 25,30 There is stronger evidence of the short-term stability of mineral mass during weight loss [30][31][32] and we have therefore used the 3-C model as reference method for comparison with other methods to avoid any confounding owing to imprecision in the measurement of the mineral mass.…”

“…This allows partitioning between bone vs soft tissue and fat vs lean tissue in pixels of the body where there is no overlaying calcified tissue. 25 SFTs SFTs were measured at four sites (triceps, biceps, subscapula and suprailiac crest) on the non-dominant side of the body using Harpenden calipers. Predicted body density was calculated using the age-and sex-specific prediction equations of Durnin and Womersley, 9 based on the sum of the SFTs at each site.…”

Body fat measurement in adolescents: comparison of skinfold thickness equations with dual-energy X-ray absorptiometry

“…A DXA scanner (Lunar DPX-L scanner; Lunar Corporation, Madison, WI, USA) with DPX-L software (Lunar Corporation) was used to estimate %FM. All DXA scans, which were completed with the same device and software, were performed by the same technician who had been fully trained in the operation of the scanner, the positioning of subjects, and the analysis of results, according to manufacturer's guidelines and adhering to accepted methodology (Lunar, 1993;Pietrobelli et al, 1996). Parameters used by the machine were a tube voltage of 76 kV, collimation size for the X-ray beam of 1.68 mm, a pixel size of 4.8 Â 9.6 mm, and a sample interval of 1/16 s for each sample point (Lunar, 1993).…”

Comparison of anthropometry to DXA: a new prediction equation for men

“…Dual energy X-ray absorptiometry (DXA) is a technically sophisticated method of body composition that simultaneously measures fat mass, lean mass, and bone (three components) without having to make assumptions about their densities (Pietrobelli et al, 1996). DXA is safe, requires minimal subject cooperation, and is very quick (6-20 min).…”