DUAL-ENERGY X-RAY ABSORPTIOMETRY BODY-COMPOSITION MODEL - REVIEW OF PHYSICAL CONCEPTS

Although dual-energy X-ray absorptiometry (DXA) is widely used in clin ical research as a means of quantifying body composition, there remain s at present little published information that reviews the method's un derlying physical basis. Because a clear understanding of DXA physical concepts is integral to appropriate use and interpretation, we presen t 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 ph ysical concepts can lead to resolution of important methodological con cerns, such as the influence of hydration changes on DXA fat estimates . A thorough understanding of DXA physical concepts provides a basis f or appropriate interpretation of measurement results and stimulates ma ny new and important research questions.