99mTc-Tetrofosmin in Rats

99mTc-[bis (dimethoxypropylphosphinoethyl)-ethoxyethylamine (PNP5)]-[bis (N-ethoxyethyl)-dithiocarbamato (DBODC)] nitride (N-PNP5-DBODC or N-DBODC5) is a new monocationic myocardial perfusion tracer. We sought to compare the myocardial uptake and clearance kinetics and organ biodistribution of 99mTc-N-DBODC5 with 99mTc-sestamibi and 99mTc-tetrofosmin. Methods: Seventy-five anesthetized Sprague–Dawley rats were injected intravenously with 22.2–29.6 MBq 99mTc-N-DBODC5 (n 25), 99mTc-sestamibi (n 25), or 99mTc-tetrofosmin (n 25). Rats were euthanized at either 2, 10, 20, 30, or 60 min after injection and -well counting was performed on excised organ (heart, lung, and liver) and blood samples. In 3 additional rats, serial in vivo whole-body -camera imaging with each tracer was performed. Results: 99mTc-N-DBODC5 cleared rapidly from the blood pool. At 2 min after injection, 99mTc-N-DBODC5 blood activity was significantly lower than either 99mTc-sestamibi or 99mTc-tetrofosmin (P 0.01) and remained lower over 60 min. Myocardial 99mTc-N-DBODC5 uptake was rapid (2.9% 0.1% injected dose/g at 2 min), and there was no significant clearance over 60 min, similar to 99mTc-sestamibi and 99mTc-tetrofosmin. All 3 tracers exhibited rapid lung clearance. Importantly, 99mTcN-DBODC5 cleared more rapidly from the liver than either 99mTc-sestamibi or 99mTc-tetrofosmin. As early as 30 min after injection, 99mTc-N-DBODC5 heart-to-liver ratio was 5.7 1.0 versus 1.6 0.1 and 2.9 0.3 for 99mTc-sestamibi and 99mTctetrofosmin (P 0.05). By 60 min, 99mTc-N-DBODC5 heart-toliver ratio further increased to 18.4 2.0 compared with 2.6 0.2 and 5.8 0.7 for 99mTc-sestamibi and 99mTc-tetrofosmin (P 0.001). The rapid blood pool, lung, and liver clearance of 99mTc-N-DBODC5 resulted in excellent-quality myocardial images within 30 min after injection. Conclusion: 99mTc-NDBODC5 is a promising new myocardial perfusion tracer with superior biodistribution properties. The rapid 99mTc-N-DBODC5 liver clearance may shorten the duration of imaging protocols by allowing earlier image acquisition and may markedly reduce the problem of photon scatter from the liver into the inferoapical wall on myocardial images.