Click a button to explore the DXA
Click a button to explore the DXA
DXA Theory
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Image generated by DXA |
The term 'DXA' stands for Dual-Energy X-ray absorptiometry. X-rays are the form of radiation used, and two different energy levels of X-rays are needed to provide enough data to separate bone and non-bone areas of each scan. DXA instruments use narrow, tightly collimated X-ray beams. The X-rays are generated below the supine patient, travel upward through the patient, and are detected above by banks of electronic detectors. A computerized image is generated, which the operator uses to identify regions of interest and analyze the scan. |
DXA analysis is based on the principle that bone areas will reduce the signal (attenuate) of the higher-energy X-ray, while soft tissue areas will allow the signal to pass through. Using this information, the image generated by the scan will first be analyzed to calculate the bone threshold and identify bone and non-bone points.
The attenuation of X-rays by pure fat and non-bone lean tissue is known, and the analysis proceeds on a point by point basis. Each point is evaluated and subdivided into fractions of lean and fat. The end result is a determination of total body levels of lean, fat, and bone mass.
[DXA technique] [theory] [process] [schematic]USDA/ARS Children's Nutrition Research Center
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