Indium labeled particles for lung imaging: Homogeneous and heterogeneous phase reactions

Abstract

AbstractThe labeling of microspheres with In, intended as potential lung and capillary‐bed imaging agents, was studied using an EDTA‐exochelator to specifically bind indium. Incubation of the azo‐phenyl‐EDTA‐microsphere with indium, resulted in an unstable preparation which primarily localized in the liver and spleen. When, however, 111In was reacted with the diazo‐phenyl‐EDTA in solution, and this complex then coupled to the microspheres, excellent binding resulted. Similarly, complexing of In to azo‐phenyl‐EDTA‐albumin in solution followed by aggregation, also yielded radiolabeled particles which were resistant to washing and localized over 90% in the lung, immediately upon injection to rats. These results have been rationalized by proposing a mechanism where the kinetics of homogeneous and heterogeneous phase reactions account for the nature of the different products formed. The present study, while it leads to better indium microspheres and aggregates than recorded in the literature, above all points out to the need of a better understanding of reaction kinetics in the preparaation of such radiopharmaceuticals.