ABSTRACT
Imaging of the skeleton by plain radiographs has been in medical use for over 100 years. Conventional X-ray sources, however, allow only an imperfect assessment of the mineral content of a particular bone, because such sources emit X-rays of varying and unquantified energies which are variably absorbed by bone and soft tissue. The last three decades have seen major advances in our ability to quantify bone mineral non-invasively. In 1963, Cameron and Sorenson developed a method of in vivo measurement of bone mineral density called single photon absorptiometry (SPA)9. This instrument employed a sealed single energy source, but required that areas of interest be immersed in water. In 1965, dual photon absorptiometry (DPA) overcame these initial problems and enabled the measurement of bone mineral density of vertebrae (an area of interest not readily immersible). The accuracy and reproducibility of these machines was excellent but the problems associated with using a radioisotope source and diminishing source strength with time meant that widespread use of the technique was not possible. Replacement of the isotope source with an X-ray tube in 1987 overcame these problems and dual X-ray absorptiometry (DXA) became commercially viable and widely available.
