Estimation of changes in bone calcium content by radiographic densitometry.

Abstract

A point of conflict often arises when investigators of calcium mobility (as determined by metabolic balance studies) meet with investigators of radiographic bone densitometry (1–6). This is the apparent inability to explain the magnitude of change sometimes observed by densitometry with that thought physiologically possible by proponents of metabolic balance technics. The opinion has often been expressed that changes detectable by quantitative x-ray densitometry are unexplainable on the basis of metabolic balance studies in which a daily negative calcium balance on the order of 500 mg is considered to be high while 500 mg of calcium represents only 0.03 per cent of the entire skeleton. How then can reported changes in radiographic density on the order of 5 to 10 per cent within a single bone (7) be explained on the basis of metabolic balance studies? The described investigation was carried out in an attempt to reconcile the apparent discrepancies between the two methods of measuring bone turnover rate. Th...