A DXA unit consists of a whole-body scanner frame, an x-ray source and detector, and a control computer. The subject is positioned on top of the scanner frame, in a supine position. The scanner moves above and below the subject, along the scanner frame.
The method is based on measurements of the attenuation coefficients of different radiation energies through a medium consisting primarily of two materials, bone and soft tissue. The dual energy method employs both high and low energy x-ray beams. By comparing the absorption of the low and high energy x-rays, the contribution of soft tissue can be identified, and eliminated for bone measurements. This allows for accurate measurements of bone mineral content (BMC) and bone mineral density (BMD) even in areas where the amount of soft tissue can be large and variable, such as the hip or spine.