Dual Energy X-ray Absorptiometry (DEXA) measures bone density and body composition, i.e. fat mass and fat-free mass, which is an important aspect of the assessment of nutritional status.
The DEXA technique has been validated for research use against gold standard methods in a number of populations (aged, pediatric, obesity) and it is widely accepted as a reference method in the research setting.
Determination of body composition by DEXA relies on the attenuation of a photon beam. After filtration, an x-ray source emits two photon energy peaks and tissues can be differentiated because of different absorption of the two photon energies. Low density material will allow more photons to pass through and high density material (ie bone) will transmit fewer photons.