DXA

DXA, or dual-energy X-ray absorptiometry, is an imaging technique that uses low-dose X-rays at two different energy levels to assess bone mineral and estimate body composition. As the X-rays pass through the body, bone and soft tissues attenuate, or weaken, the beams by different amounts. Measuring these differences allows the system to estimate the composition of the scanned region .^1,2

For bone assessment, DXA measures bone mineral content and calculates areal bone mineral density (BMD), usually expressed in grams per square centimeter. This is an important distinction because DXA BMD is a two-dimensional, area-based measurement rather than a direct measurement of bone mineral per unit of three-dimensional volume .^2,3

Whole-body DXA can also estimate fat mass and lean soft tissue mass, both for the body as a whole and for selected regions. Bone mineral content is assessed separately. Lean soft tissue should not be interpreted as a direct measurement of skeletal muscle because it includes water, protein, and other nonfat soft-tissue components in addition to muscle tissue .^1,2

DXA provides projection-based body-composition estimates rather than the cross-sectional tissue images produced by methods such as computed tomography or magnetic resonance imaging. Its body-composition values are derived from X-ray attenuation and mathematical models. Results can be influenced by factors including positioning, hydration, tissue thickness, scanner hardware and software, and analysis procedures, making standardized measurement methods important when comparing scans over time .^1,2