Photon Absorptiometry

Abstract

Most quantitative methods for assessing bone mineral rely on the absorption of X-rays or gammarays by the relatively dense and high atomic number constituents of the skeleton. The first to be introduced was “X-ray densitometry” using continuous-spectrum X-rays with appropriate means of calibration, film as the detecting medium and an optical densitometer to measure blackening. Later came techniques using gamma-radiation and a scintillation detector. The term “densitometry” was also applied to these techniques initially, but more recently they have been characterized as “absorptiometry”, which more closely reflects the actual principles involved. Although the X-ray methods rely on many of the same principles and could be termed “radiographic absorptiometry”, there has been a tendency to retain “densitometry” to describe them.