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Eleven female patients (aged 18-46 y) with anorexia nervosa were measured by use of dual-photon absorptiometry for 1) bone mineral content (BMC, in g) and bone mineral density (BMD, in g/cm2) of the total skeleton and its regions, 2) BMD of the lumbar spine and the proximal femur, and 3) total body soft-tissue composition. The patients weighed 44.4 kg, approximately 15 kg less than normal peers (n = 22). The fat mass (3.35 kg) and content of soft tissue (7.8%) were four and three times lower (p less than 0.001) respectively, than those in normal women (15.1 kg and 26%, respectively). The total skeleton mineral (1921 g) was approximately 25% less than that of young normal women. The BMC as a fraction of the lean tissue mass was approximately 4.9% in the patients and 5.9% in normal women. Total body and femoral BMD averaged only 10% and 13% lower than those of normal women, respectively; however, spinal BMD was particularly reduced (approximately 25%, p less than 0.001).

Bone mineral density (BMD) and soft-tissue composition of the total body and major subregions were measured with dual-energy x-ray absorptiometry (DEXA). Total body scans were made in 12 young adults (6 male, 6 female) on five occasions at both a medium speed (20 min) and a fast speed (10 min). There were no significant differences in mean results or in precision errors between the two speeds. The precision errors (1 SD) for total body BMD, percent fat in soft tissue (% Fat), fat mass, and lean tissue mass were less than 0.01 g/cm2, 1.4%, 1.0 kg, and 0.8 kg, respectively. These results corresponded to a relative error of 0.8% for total body BMD and 1.5% for lean body mass. Regional BMD and soft-tissue values (arms, legs, trunk) were determined with slightly higher precision errors. Skeletal mineral was 5.8 +/- 0.5% of lean tissue mass (r = 0.96, p less than 0.001). DEXA provides precise composition analysis with a low radiation exposure (less than 0.1 microGy).

Dual-photon absorptiometry using 153Gd (44 and 100 keV) was used to measure the bone mineral content (BMC) of the trunk and of the total body (TBBM) in 7 volunteers with no overt bone disease. These values were compared to those obtained with partial-body neutron activation of calcium (trunk Ca). The trunk Ca seemed to represent best a 60 x 30 cm area; the correlation coefficient with the corresponding BMC in that area was 0.97 (SEE congruent to 7%). Trunk Ca was also highly correlated with TBBM (r = 0.96; SEE = 8%) and with radius BMC (r = 0.92; SEE = 11%), but the correlations with the BMC of smaller subareas of the trunk were lower (r congruent to 0.9; SEE approximately 12%). The BMC of the lumbar spine was only moderately correlated with trunk Ca, radius BMC and TBBM (r approximately 0.82; SEE approximately 18%), and only slightly more associated with trunk BMC (r approximately 0.88; SEE approximately 14%). The BMC of the combined lumbar-thoracic spine showed higher correlations with trunk Ca, radius BMC and TBBM (r approximately 0.87; SEE approximately 13%), and trunk BMC (r = 0.93; SEE approximately 10%). An accurate and sensitive measure of spinal status requires a direct measurement of that area.

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 was 153Gd (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.

Dichromatic absorptiometry (DA) is a new, non-invasive method for determining soft tissue (STC) and fluid content (FC), and their changes. The technique uses linear transmission scans made across the limbs with a congruent 125I and 241Am dual-photon source and a NaI(TI)--PMT detector. Patient measurements could be made at the bedside with the mobile system. Factors affecting the precision and accuracy were evaluated theoretically and experimentally. Repositioning and subject motion were the greatest sources of variation and limited the precision to 2--3% in normals and 3--7% in patients; instrumental variation was 0.5%. The accuracy was 4% for typical (p10%) fluid changes observed in vivo. The ease, simplicity and small errors of the technique suggest its utility in monitoring the time course and degree of fluid changes in patients.

The lean-fat composition (%FATR) of soft tissue and the mineral mass of the skeleton were determined in vivo using dual-photon (153Gd) absorptiometry (dose under 2 mrem). A rectilinear raster scan was made over the entire body in 18 subjects (14 female, 4 male). Single-photon absorptiometry (125I) measured bone mineral content on the radius. Percentage fat (%FATD) was determined in the same subjects using body density (from underwater weighing with correction for residual lung volume). Lean body mass (LBM) was determined using both %FATR and %FATD. Percentage fat from absorptiometry and from underwater density were correlated (r = 0.87). The deviation of %FATD from %FATR was due to the amount of skeletal mineral as a percentage of the LBM (r = 0.90). Therefore, skeletal variability, even in normal subjects, where mineral ranges only from 4 to 8% of the LBM, essentially precludes use of body density as a composition indicator unless skeletal mass is measured. Anthropometry (fatfolds and weight) predicted %FATR and LBM at least as well as did underwater density. The predictive error of %FATR from fatfolds was 5% while the predictive error in predicting LBM from anthropometry was 2 to 3 kg (3%).

Total body bone mineral (TBBM) was measured in vivo using dual-photon absorptiometry (DPA) in 10 subjects. The total body calcium (TBCa) was measured in the same subjects using neutron activation analysis. The correlation between the two methods was very high (r greater than 0.99) and the standard error of estimate was low. The TBCa relative to TBBM was about 39%. The two noninvasive methods provided nearly identical indications of skeletal mass, but the radiation exposure with DPA was 500 to 5000 times smaller (0.6 mrem vs 300 to 3000 mrem). The radius shaft bone mineral content was highly correlated with the TBBM (0.97) and the TBCa (0.98) and could be used to estimate the latter variables with errors (1 SEE) of 9% and 6%, respectively.