A clinical instrument for multi-element in vivo analysis by prompt, delayed and cyclic neutron activation using 252Cf

The design and construction of a versatile clinical instrument for multi-element in vivo neutron activation analysis of major and minor body elements is described. A 200 micrograms (4 GBq) 252Cf neutron source is stored below ground level and pneumatically propelled to one of two irradiation ports. These deliver collimated beams of fast neutrons either to a localised volume such as the liver or kidney, or across the width of a patient for a head-to-toe scanning whole-body measurement. The source control system allows selection of either a continuous or cyclic mode of activation. The instrument is intended primarily for measurement, by the prompt-gamma technique, of total and partial body calcium, total body nitrogen and partial body cadmium. The potential of the instrument for determination of these three elements has been established. Phantom results suggest that total body calcium can be measured with a precision of +/- 2.6% (CV) for an average whole-body skin dose equivalent of 6.4 mSv; total body nitrogen with a precision of +/- 2.0% for an average whole-body skin dose equivalent of less than 0.4 mSv; and a detection limit (2 SD of the background) of 2.4 mg of cadmium in the kidney has been obtained for a radiation dose equivalent to the skin of 3 mSv (QF = 10). The suitability of this instrument for the measurement of other elements is also discussed.