Measurement system of body radioactivity

A system for in vivo radioactivity measurement - Canberra Accuscan Model 2260 Whole Body Counter was investigated in this work. A parallel slit collimator for NaI(Tl) detector was designed to enable better localization of radioactivity in the human body and measurement of higher source activities, simultaneously with NaI(Tl) and Ge detector. Various characteristics of the measurements system were analyzed with and without the collimator (spatial resolution, detection efficiency, energy resolution, background, geometric uniformity, energy window width). Gamma reference point, mixed and I-131 sources were measured in air or anthropomorphic phantoms. A collimator opening was varied from 1 to 10 cm. In vivo studies of patients after oral administration of I-131 were also performed. Use of collimator improves spatial resolution up to 20 times, decreases detection efficiency up to 200 times and background index up to 2 times. It has been enabled to measure radioactivity levels in the total range of 1 million. Analytical expression of point spread function was found, as the sum of straight line, Gaussian and Lorentzian distribution(s). Using collimator no significant changes of geometric uniformity have been indicated. Variation of number of counts depends greatly on radioactivity distribution and energy window setting. At the basis of the achieved results, necessary and additional preconditions for wide use of the whole body counter in diagnostic and therapeutic procedures in nuclear medicine have been realized, as well as for the approach to internal dosimetry problems in radiation medicine and radiation protection. (author). 26 figs., 13 tabs., 99 refs