Evaluation in vitro and in vivo of two labelling techniques of different 99mTc-dextrans for lymphoscintigraphy

Five dextrans with different molecular weights and charges were labelled with 99mTc. The labelling methods presented by Henze et al. (1982a) and Ercan et al. (1985) were compared. The labelling efficiency was tested with gel column chromatography scanning (GCS), gel chromatography (GC) combined with the Anthrone test, paper chromatography (PC) and thin layer chromatography (TLC). The GCS technique always indicated a lower labelling efficiency than the PC and TLC techniques, which was due to a more optimal separation of the radioactive components. Gel chromatography in combination with the Anthrone test made it easy to identify the different radiochemical components in contrast to the other methods. Dextran solutions were injected subcutaneously bilaterally at the xiphoid processes in rabbits. The injection sites were massaged for 30 s. Uptake in the parasternal lymph nodes was registrated with a scintillation camera. The animals were killed and dissected at the end of the study. This investigation shows that the labelling method of Ercan et al. gives the highest labelling efficiency. Furthermore, the final pH (4.5) for the dextran solution makes it more useful for injection. For quality control of 99mTc-labelled dextran we recommend the Anthrone test as a complement to GC because it is a quick and simple method of determining the dextran content.