99mTc-thiomalic acid complex: a nonstannous chelate for renal scanning.

Thiomalic acid (monomercaptosuccinic acid) has been labeled with 99mTc without the use of an intermediary reducing agent. Tissue distribution studies in rats following the injection of 99mTc-tagged thiomalic acid (99mTc-TMA) showed 40-48% of the injected dose in the kidneys. Renal incorporation of this compound was influenced by various parameters such a pH, quantity of thiomalic acid, heating time, and the preparation-injection interval. Scintigrams of a midline kidney slice showed that the 99mTc activity concentrated mainly in the renal cortex. As a proposed renal-imaging agent 99mTc-TMA compared favorably with 99mTc-Sn-dimercaptosuccinate and 99mTc-penicillamine regarding the precent incorporation into the kidney and was superior in this respect to 99mTc-Sn-glucoheptonate and 99mTc-Sn-diethylenetriamine pentaacetic acid. The 99mTc-TMA was also shown to be highly stable through 24 hr. The reagent can be made available in kit form and is easily combined with 99mTc in two steps. Finally, the absence of stannous ion in the 99mTc-TMA complex should avoid the problem of interference with other procedures involving pertechnetate 99mTco4- as the imaging agent.