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Dual-energy X-ray Absorptiometry

written by: Jason C. Chavis•edited by: Paul Arnold•updated: 7/5/2011

As a means for the medical industry to measure the density of bone material in patients, the dual-energy X-ray absorptiometry machine is an advanced piece of machinery that essentially takes pictures of a person's bones.

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    How does It Work?

    Bone density scanner 

    The way dual-energy X-ray absorptiometry works is by utilizing traditional scanning techniques and modern computerized technology to find the density of bones and other tissues. Basically, the machine sends two X-ray beams through a patient in the region of concern. X-rays are partially absorbed by the biological tissue and the machine measures the remaining energy level. By finding the amount of absorbed energy, one can ascertain the density of the bones or tissue.

     To ensure the accuracy of the test, relative measurements are taken using two beams, one of high intensity and one of low intensity. This allows technicians to determine the level of absorption from each beam, giving them an accurate comparison. Essentially, the beam with higher intensity should be absorbed at the same rate as the lower intensity one. The presence of soft tissue is then deducted from the equation, leaving a close approximation of bone density.

    Above right: Bone Density Scanner. (Supplied by Kevin Vrrrreeeeeeeeeee.... at Wikimedia Commons; Cretive Commons Attribution; http://upload.wikimedia.org/wikipedia/commons/3/3a/Bone_density_scanner.jpg)

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    Radiation and Problems with the Procedure

    The amount of radiation used in the process is relatively small compared to other devices used in scanning the body, such as CT technology or even standard chest X-rays. It would take approximately 800 separate dual-energy X-ray absorptiometry scans to equal the radiation exposure of traditional X-rays. Despite the low levels of radiation, the technology is reserved for patients at greatest risk for potential problems. This is mainly due to the cost of each scan, which totals relatively high compared to other technology scans.

    Another challenge that dual-energy X-ray absorptiometry is the fact that the device calculates bone mass density using an arial equation. This means that the relative mass is divided by volume, giving a general idea of the density rather than a completely accurate analysis. Namely, the machine cannot make adjustments to the level of absorption caused by different sizes of bones. For example, the technology cannot distinguish accurately between the absorption caused by a larger bone such as a femur versus a smaller one, such as a phalange.

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    Testing Bone Mineral Density and Other Uses

    Dual-energy X-ray absorptiometry is most widely used by physicians testing for bone mineral density. This helps diagnose diseases such as osteoporosis and osteopenia. It can also determine certain diseases impacting the metabolic balance in bones in the process of healing from fractures, tumors or infections. Other uses for dual-energy X-ray absorptiometry approved by the FDA is for the measurement of body fat or total body composition. However, using the dual-energy X-ray absorptiometry machine for these scans is usually conducted in conjunction with other types of measurement.

    Notably, the technology is used heavily in the field of athletics, providing a way for physicians to maintain proper body mass and bone density in people playing sports. When an athlete is injured or simply attempting to increase a facet of his or her body, the dual-energy X-ray absorptiometry machine is an essential, if costly option.

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    Resources

    "Dual-energy X-ray Absorptiometry" Healthline: http://www.healthline.com/hlbook/nut-dual-energy-x-ray-absorptiometry-dexa

    "DEXA" University of Vermont: http://nutrition.uvm.edu/bodycomp/dexa/dexa-toc.html