Optimum neutron source to subject distance (ONSSD) and the influence of air-gap on body irradiation in activation analysis.

An optimum neutron source to subject distance (ONSSD) for body irradiation with a 238Pu-Be neutron source is described. Results are presented which show that the influence of air gaps on the results of neutron activation analysis (NAA) is unimportant when irradiation is performed at the ONSSD. In addition, for subjects having similar bone volumes, differences in the thickness of the surrounding soft tissue may not significantly influence the NAA results. The ONSSD is dependent on the medium surrounding the sources. For 238Pu-Be sources in water, surrounding an air-filled or water-filled sample chamber of radius 6 cm, the ONSSD is about 12 cm from the centre of the chamber. A configuration such as described above will be suitable for in vivo studies of the human extremities in the course of investigation of metabolic bone diseases and also for whole body in vivo studies of small animal models in clinical situations. The technique can easily be extended to other neutron sources.

In vivo analysis of bone fluoride content via NMR.

In vivo free induction decay signals have been detected from the fluoride ion (F) content of human finger bones by a 27 MHz pulsed single-coil nuclear magnetic resonance (NMR) spectrometer. The intensity of these dipolar-broadened NMR signals can be used to estimate the F content of the middle phalanx of the index finger. This NMR procedure is the first non-invasive method capable of monitoring bone F contents. The preliminary results we report were obtained from patients known by previous biopsies to have relatively high bone F concentrations in their pelvis. This new monitoring technique does not yet have adequate sensitivity or accuracy for routine clinical use. As a research technique, it has applications to the diagnosis of fluorosis (both industrial and endemic) as well as renal osteodystrophy, and to the establishment of optimal NaF does for the treatment of osteoporosis.

A system for in vivo measurement of bone calcium by local neutron activation of the hand.

A 252Cf neutron-irradiation facility designed specifically for clinical in vivo measurement of calcium in the hand is described. Results of preliminary measurements are presented. Hand phantoms were exposed to the neutron beam for 10 min and the induced 49Ca activities were counted for 10 min after an elapsed time of 2 min. The results indicate that with a 2 X 100 micrograms 252Cf neutron source and two 20.3 X 12.7 cm NaI crystals, the counts per gram of bone mineral mass changes by about 4% for each 100 cm3 change in the overall volume (soft tissue plus bone) of the hand. For hands of equal volumes the counts per gram are expected to be almost independent of the bone volume. With an absorbed dose equivalent of 150 mSv (15 rem), the sensitivity is about 200 counts per 10 min per gram Ca. The statistical reproducibility of the results is better than 3% for the average value of 11 g Ca in the normal hand.