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Dual-energy x-ray absorptiometry (DXA)

Introduction

Dual-energy x-ray absorptiometry (DXA) measures the amount of bone, or calcium, usually in the vertebral bodies or hip, but also in other bones. It may also be used to estimate the proportion of body fat. Doses are low, ranging from 10 to 300 µGy, depending on the equipment and procedure.

Important Principles

A dual-energy x-ray source is used to scan the patient producing images from which actual bone mineral content can be calculated and compared to normative data. Scan times are relatively long, typically minutes.
For the data to be clinically valuable it is essential that a standard phantom be scanned frequently to assure consistent measurements from the system. This also assures that the measured results are comparable from one scanner to another.

Introduction to References

The references on this topic are relatively limited. The CRCPD white paper provides an excellent, basic tutorial. Faulkner discusses quality control for multicenter trails. The ISCD provides guidance regarding quality control for clinical and precision assessment. The Australia and New Zealand Bone Mineral Society provides the capability for monitoring results as part of a quality control program.