For the first time, the accuracies of two radiologic methods for determining bone mineral content were compared under the same test conditions. Direct photon absorptiometry at the University of Wisconsin uses a monoenergetic radionuclide source (125I at 27.4 kev) with a scintillation detector/pulse-height analyzer system. The source and detector are passed across the bone and changes in beam intensity are proportional to the mineral content. Radiographic photodensiometry at Fels Research Institute uses optical density measurements of the bone image on a standard radiograph. A microdensitometer/computer system is used for these radiographic measurements, while the radiograph itself is made with an ordinary x-ray machine. The error in predicting ash weight using Wisconsin absorptiometry was 3% while the error using the Fels method of photodensitometry was 6%. The accuracy of the Fels method was superior to that reported by other workers who do not correct for background film, density.
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Colbert et al. (1970) studied this question.