Evaluation of 99mTc-dextran as a lymphoscintigraphic agent in rabbits

Dextran (clinical grade, average mol. wt. 82,200) was labelled with 99mTc and the labelling efficiency was checked by paper and thin-layer chromatography and electrophoresis. The amount of free 99mTcO-4 was always less than 1%. The radiopharmaceutical was injected ID into the web space in hind legs of ten rabbits (200-600 microCi/0.05 ml). Scintigrams were taken at 10-min intervals up to 3 h in three rabbits. The injection site and the hind legs were massaged after injection in the other seven rabbits and scintigrams were taken at 10-min intervals up to 2 h. Blood samples were obtained at 5, 15, 30, 90 and 120 min in both groups. In addition a 180-min sample was also taken in the first group. At the end of the study the rabbits were killed and the popliteal lymph nodes and the organs were removed to be weighed and counted. Our results indicated a high concentration of radioactivity in the popliteal lymph nodes and massage at the injection site increased the average uptake of the popliteal lymph node from 1.12% +/- 0.77% to 4.28% +/- 1.57% at 3 and 2 h, respectively (P less than 0.001). In scintigrams the lymph channels and the nodes were very well visualised. The blood radioactivity levels were too low to present a background problem. With massage 30% of the injected dose was removed from the injection site in 2 h. We have shown that 99mTc-dextran is a good radiopharmaceutical for the visualisation of the lymph system and deserves further experimental and clinical studies.