Physical Principles and Measurement Accuracy of Bone Densitometry

Introduction Over the past few decades, a number of methods have been developed for the in vivo determination of bone density. The most important of these methods are based on measuring the attenuation (reduction in intensity) of a beam of either electromagnetic radiation (in the form of X-rays or gamma rays) or ultrasound when it passes through bone; in the latter case, the measurement of velocity has also been used for this purpose. There are significant differences between radiation and ultrasound as regards their interaction with bone. In general though, the nature of the measurement and its accuracy are influenced by the properties of both bone itself and the soft tissue that surrounds it.