The comparison of neutron activation analysis and photon absorptiometry at the same part-body site.

Two non-invasive methods of bone measurement were, for the first time, compared at the dame part-body site. Bone calcium, using in vivo neutron activation analysis, and bone mineral, using photon absorptiometry, were measured in the forearm in a group of renal patients. A highly significant correlation was obtained from absolute values (r = 0.91) which was reduced after normalisation (r = 0.75). Percentage changes, over periods totalling 31.3 patient years, were also highly significantly correlated (r = 0.61, P less than 0.001). The precision of the techniques accounts for the spread of the bivariate data and the estimated line of the true relationship was not significantly different from the line described if the percentage changes measured by the two techniques were equal. The two basic techniques were shown to be equally sensitive in vivo methods for monitoring calcified bone in patients suffering from metabolic bone disease.