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 × 100 μg 252Cf neutron source and two 20.3 × 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 indepdendent 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.