Introduction and historical overview

Dual-energy X-ray absorptiometry (DXA) is a rapid, non-invasive technique that allows for the measurement of total and regional bone mineral (TBBM, g), total bone mineral density (TBMD, g/cm2), fat mass (FM, g) and bone-free lean tissue mass (LM, g) in vivo in animals ranging in size from man to mouse. Since its introduction slightly more than a decade ago (Cullum et al., 1989; Mazess et al., 1989; Blake & Fogelman, 1997), DXA has become the most widely used technology for measuring TBBM and TBMD in humans, and its use for determining FM and LM mass is widespread. The use of DXA in animal research is also increasing (Grier et al., 1996). Recent advances in both hardware and software now allow for the determination of body composition in mouse-sized animals (Hunter & Nagy, 1999; Nagy & Wharton, 1999; Nagy et al., 1999a,b; Nagy & Clair, 2000).

Historically, the use of absorptiometry or densitometry for the measurement of TBBM and TBMD began with the advent of single-photon absorptiometry (SPA) in the 1960s (Cameron & Sorenson, 1963; Cameron et al., 1968). Although this technique proved useful, its applicability was limited to measuring bones that could be immersed in water or other soft tissue-like materials (Grier et al., 1996; Blake & Fogelman, 1997). The development of dual-photon absorptiometry (DPA) overcame the limitations of SPA and allowed for the determination of TBBM and TBMD in areas that were not surrounded by homogeneous soft tissue. In addition, the use of a second energy level allowed for the determination of two tissue types simultaneously (Gotfredsen et al., 1986; Heymsfield et al., 1989; Mazess et al., 1990).