99mTc-pyrophosphate kinetics in man (relationship between bone uptake and mineral content)

Both the kinetics and the regional distribution of 99mTc-PPi were studied in the skeleton of healthy subjects of various ages by surface counting using a scintillation counter placed over different skeletal areas. The results were compared with bone mineral content as determined by the photonic absorption technique. Kinetic data of bone uptake were obtained by subtracting the counts measured in blood from the counts recorded over each body surface after making proportional corrections. The surface-counting patterns show a higher generalized 99mTc-PPi bone uptake in children and adolescents than in adults. The relative regional distribution of the tracer shows no difference between the two groups. The tracer accumulated more rapidly in spongy bone than in compact bone, and the fixation process was carried out during the first 30 min for both spongy and compact bone. In youths, however, higher uptake values corresponded to lower values of mineral content. The findings enable the normal surface-counting pattern to be constructed and confirm that the 99mTc-PPi uptake is related to bone metabolism; they also suggest the application of external measurements for the study of metabolic bone diseases.