Technetium-99m and indium-111 double labelling of granulocytes for kinetic and clinical studies

A new technique of labelling granulocytes with both technetium-99m and indium-111 in a single protocol was developed. 14 patients were included in this prospective study. Granulocytes were labelled with both 111In-tropolonate and 99mTc-HMPAO. The comparative kinetics of 111In and 99mTc in the blood, liver, spleen, and bone marrow were studied by blood sampling and dual radionuclide imaging early (1 h) and late (24 h) after injection. The functional integrity of the double-labelled granulocytes and the feasibility of the technique were investigated in 14 patients with a painful prosthetic hip due to causes other than infection. The efficiency of double labelling was 63% (SD 14%) for 111In and 39% (SD 12%) for 99mTc-HMPAO. In vitro granulocyte activation and ex vivo recovery values were comparable to those from single radionuclide labelling. No artefactual granulocyte sequestration was seen in the lungs or liver. The radioactivity was distributed between the liver, spleen and bone marrow and, to a lesser extent, the lung. Early 99mTc counts were significantly higher than 111In counts while the reverse was seen in late images. Furthermore, circulating ''free'' 99mTc was significantly higher than free 111In at 24 h. Organ 99mTc counts decreased in the spleen, increased in the liver and remained unchanged in bone marrow, whereas 111In counts increased in the bone marrow and liver, and decreased in tfe spleen. By favourably exploiting their kinetics for early and late imaging, double-labelled granulocytes may be useful in several clinical and investigative situations. (orig.)