**11.8 Second antibody**

The background counts can be reduced by removing radioactivity from the circulation. This can be achieved by the use of a second antibody active against the RIS antibody. In this technique, after the binding time of original antibody to tumor tissue, the second antibody administers to the patient (Sergides et al., 1999). The second antibody binds to the radioactive antibody that remains in the blood stream. The reticuloendothelial system uptakes antibody-antibody complex and leads to concentrate radioactivity in liver and spleen. This technique leads to increase in T/B ratio without adverse effects. The only disadvantage of this method is limitation in the detection of metastases at liver and spleen (Sergides et al., 1999).
