Technical note: CT determination of the mineral density of dry bone specimens using the dipotassium phosphate phantom

Recent studies have demonstrated the potential application of computed tomography (CT) in research into bone density. Clinical studies of bone density using CT commonly employ a dipotassium phosphate phantom to calibrate measurements of mineral density. Designed for in vivo studies, the use of this phantom requires that bones be scanned while immersed in and permeated by fluids or soft tissues similar to water in X-ray attenuation coefficient. However, this condition may not always be met in anthropological applications, which often involve rare and fragile specimens. This study compares mineral density values calculated for a sample of bones scanned-at the same sites-in air and in water. The results indicate that, when scanned in air, the mineral density of trabecular bone is dramatically underestimated, while that of cortical bone is slightly overestimated. We present a linear regression equation to correct this error but recommend that, when possible, researchers calculate their own regressions based on their specific scanning conditions.