Dual X-ray absorptiometry (DXA) is the preferred technique for measuring bone mineral density (BMD). DXA has also been called dual energy X-ray absorptiometry, or DEXA.
DEXA is relatively easy to perform and the amount of radiation exposure is low. A DEXA scanner is a machine that produces two X-ray beams, each with different energy levels. One beam is high energy while the other is low energy. The amount of X-rays that pass through the bone is measured for each beam. This will vary depending on the thickness of the bone. Based on the difference between the two beams, the bone density can be measured.
At present, DEXA scanning focuses on two main areas — the hip and spine. In certain situations — if the hip or spine can’t be measured, for instance — it is measured in the forearm. Although osteoporosis involves the whole body, measurements of bone density at one site can be predictive of fractures at other sites. Scanning generally takes 10 to 20 minutes to complete and is painless and noninvasive.