In vivo labelling of RBC with 99mTc for blood pool imaging using different stannous radiopharmaceuticals

The in vivo ^99mTc-RBC labelling efficiency and stability of labelling was assessed after pretinning with a high-stannous content DTPA kit (Sn DTPA) in comparison with Sn-pyrophosphate (Sn PPi) and a low-stannous DTPA kit (DTPA). The distribution in Sprague Dawley rats showed that similar fractions of administered ^99mTc remained within the blood pool after pretinning with Sn DTPA and Sn PPi when equal quantities of stannous ions (15 g/kg) and equal time intervals (30 min) between successive IV injections of pretinning agent and ^99mTc-pertechnetate were used. Significantly lower fractions were found when DTPA (1.9 g Sn²⁺/kg) was used for pretinning. The rate of ^99mTc elution emphasises the importance of the Sn²⁺ concentration used, not only for labelling efficiency but also for stability of the labelling. Satisfactory intravascular activity, exceeding 80% during the first hour post-injection, was demonstrated in three volunteers after ^99mTc injection, when Sn DTPA was used for pretinning. Left ventricular ejection fractions (LVEF) measured by equilibrium radionuclide angiography angiography after pretinning with Sn DTPA in 24 patients correlated well (r=0.98) with those obtained by contrast angiographies over a broad spectrum of values (0.14–0.72). Four repeated LVEF measurements at 45-min intervals in six additional patients at rest showed excellent reproducibility in each patient: maximum variation was less than 6%.