Total body bone mineral and lean body mass by dual-photon absorptiometry

Summary A method was developed for measuring total body bone mineral (TBBM) and lean body mass in vivo using dual-photon absorptiometry. The entire body was scanned in a rectilinear raster (transverse speed of 1 cm/s and longitudinal steps of 2.5 cm) with a modified nuclear medicine scanner and conventional nuclear counting electronics. The source was¹⁵³Gd (1 Ci) with principal photopeaks at 44 and 100 keV. The scan time was about 70 min with an absorbed dose of under 1 mrem. The low dose allows measurements to be repeated at frequent intervals or used on children. Short-term (months) precision of TBBM was about 1.5% for isolated skeletons and about 2% on normal human subjects. Long-term (years) precision on skeletons was under 3%. The precision of percent fat was 0.9%, which would lead to an error of less than 1% in the TBBM. Geometry of measurements also had minimal (and correctable) influence on the accuracy of results. The accuracy (1 standard error of estimate) of TBBM on isolated skeletons (N=5) was 36 g (equivalent to about 13 g of Ca) with a correlation coefficient of 0.99; this error amounts to about 1–1.5% in normal adults, 2% in older women, and 2.5% in osteoporotic females. The dual-photon absorptiometry method could be implemented in many nuclear medicine departments to follow skeletal changes during growth and aging or to follow the course of a disease or treatment.