Evaluation of 99mTc-labelled vitamin K4 as an agent for testicular imaging

Vitamin K4 was labelled with 99mTc with an efficiency higher than 97%. The compound was stable up to 24 h at room temperature, and its biodistribution in NMRI mice indicated its in vivo stability. Blood radioactivity levels were high over a wide range. 10% of the injected activity remained in blood after 24 h. Excretion was mostly via kidneys. Only the liver and kidneys concentrated appreciable amounts of radioactivity. Testis/soft tissue ratios were 1.4 and 1.57 at 6 and 24 h, respectively. Testis/blood ratios were lower than 1. In vitro studies with mouse blood indicated that 33.9 +/- 9.6% of the radioactivity was associated with RBCs; it was washed out almost completely with saline. Protein binding was 28.7 +/- 6.3% as determined by TCA precipitation. Blood clearance of 99mTc-K4 in normal subjects showed a slow decrease of radioactivity, reaching a plateau after 16 h at 20% of the injected activity. In scintigraphic images in men the testes could be well visualized. The right/left testis ratio was 1.08 +/- 0.13. Testis/soft tissue and testis/blood activity ratios were highest at 3 h. These ratios were higher than those obtained with pertechnetate at 20 min post injection. 99mTc-K4 appears to be a promising radiopharmaceutical for the scintigraphic visualization of testes.