Abstract
The effects of using beams of finite width and various photon energies have been examined. It is shown that the use of finite beam widths leads to 'measured' values of bone index and cortical bone density which are less than the 'true' values obtained with an infinitely narrow beam. The underestimate of the 'true' bone index or cortical bone density increases with increasing beam width and decreasing photon energy. A 'scan' of a bone section of external diameter 2.0 cm and cortex width 0.5 cm with a 0.3 cm wide beam of radiation from 125I (27.5 keV) yields an underestimate of the 'true' cortical bone density of approximately 5%.