What is the role of dual-energy x-ray absorptiometry (DEXA) in the workup of osteoporosis?

Updated: Jan 19, 2021
  • Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Answer

Dual-energy x-ray absorptiometry (DEXA) is very much like DPA except that the radionuclide source is replaced by an x-ray source. The spectrum is heavily filtered with different filters, giving a spectrum with 2 narrow distributions of photons that simulate the spectrum from the radionuclide source. This technique eliminates the need to constantly subtract the soft-tissue thickness as in single-photon measurements; therefore, DEXA permits measurement of the spine and hip.

A deficiency of this method, in the conventional AP projection of the spine, is that the posterior elements, which consist of cortical bone, are included in the result. The mechanical strength of the vertebrae is mainly dependent on the amount of trabecular bone in the vertebral body. Despite this drawback, the low radiation dose, speed of examination, and low cost have made it popular as a clinical screen for osteoporosis.

DEXA overcomes many of the problems of DPA in that it is inexpensive and has high accuracy, precision, and resolution. DEXA has a number of advantages over DPA, including a precision of 1% or less (vs 2-5%), a radiation dose of less than 2 mrem (vs 10-20 mrem), and an examination time of less than 5 minutes (vs 20-30 min). Because of its precision, DEXA is well suited to making serial measurements to monitor the effect of treatment. At present, DEXA is the most precise method for measuring BMD.


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