Tc-generators - yield of 99mTc and ratio to 'inactive' 99Tc

A large amount of inactive 99Tc in some delicate labeling techniques may adversely affect the results obtained. Therefore, it is important to know the ratio Q(t) of inactive 99Tc to active 99mTc, which is dependent on the time (t) elapsed since the last elution. On the other hand, in optimizing the use of Tc-generators it is desirable to know the actual yield Y(t) at any time (t) after a preceding elution. It this paper, formulas both for Q(t) and for Y(t) are derived and numerical values are tabulated. In combination with a table of the amount of 99Mo left, M(t), all the properties of a Tc-generator and of its eluates may be derived and theoretical and practical results compared. This information will help in both optimizing the use of Tc-generators and improving quality control in radiopharmaceutical laboratories.