RESUMO
The paper deals with the estimation of thyroidal uptake of 131I in living rats. The animals are fixed in a specially marked glass tube. This tube is discontinuously moved over a scintillation counter within a lead collimator. Counts of 131I are estimated segmentically. The highest counts ratio with the geometrical factor of the appropriate segment is used to calculate the thyroidal radioiodine uptake. Similar results, obtained with an 131I-source placed in various segments of the top side of glass tube, indicate that the uptake values obtained in this manner exact. Thyroidal uptake values, which were received on living rats with this method (in vivo) and compared with values obtained with the prepared and plated thyroid of the same rats (in vitro) show a very high correlation (r = 0,99; p greater than 0,001). In repeated estimations of the thyroidal 131I-uptake on one animal a variation coefficient of 1.5% (n = 13) was obtained. The advantage of this in vivo method is the possibility to determine the thyroidal activity at various times after 131I-application (2 phase test) and by repeated 131I-applications under different conditions (diet, age, for instance).
