99mTc-N-DBODC5, a new myocardial perfusion imaging agent with rapid liver clearance: comparison with 99mTc-sestamibi and 99mTc-tetrofosmin in rats.

Unlabelled: (99m)Tc-[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 (99m)Tc-N-DBODC5 with (99m)Tc-sestamibi and (99m)Tc-tetrofosmin.

Methods: Seventy-five anesthetized Sprague-Dawley rats were injected intravenously with 22.2-29.6 MBq (99m)Tc-N-DBODC5 (n = 25), (99m)Tc-sestamibi (n = 25), or (99m)Tc-tetrofosmin (n = 25). Rats were euthanized at either 2, 10, 20, 30, or 60 min after injection and gamma-well counting was performed on excised organ (heart, lung, and liver) and blood samples. In 3 additional rats, serial in vivo whole-body gamma-camera imaging with each tracer was performed.

Results: (99m)Tc-N-DBODC5 cleared rapidly from the blood pool. At 2 min after injection, (99m)Tc-N-DBODC5 blood activity was significantly lower than either (99m)Tc-sestamibi or (99m)Tc-tetrofosmin (P < 0.01) and remained lower over 60 min. Myocardial (99m)Tc-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 (99m)Tc-sestamibi and (99m)Tc-tetrofosmin. All 3 tracers exhibited rapid lung clearance. Importantly, (99m)Tc-N-DBODC5 cleared more rapidly from the liver than either (99m)Tc-sestamibi or (99m)Tc-tetrofosmin. As early as 30 min after injection, (99m)Tc-N-DBODC5 heart-to-liver ratio was 5.7 +/- 1.0 versus 1.6 +/- 0.1 and 2.9 +/- 0.3 for (99m)Tc-sestamibi and (99m)Tc-tetrofosmin (P < 0.05). By 60 min, (99m)Tc-N-DBODC5 heart-to-liver ratio further increased to 18.4 +/- 2.0 compared with 2.6 +/- 0.2 and 5.8 +/- 0.7 for (99m)Tc-sestamibi and (99m)Tc-tetrofosmin (P < 0.001). The rapid blood pool, lung, and liver clearance of (99m)Tc-N-DBODC5 resulted in excellent-quality myocardial images within 30 min after injection.

Conclusion: (99m)Tc-N-DBODC5 is a promising new myocardial perfusion tracer with superior biodistribution properties. The rapid (99m)Tc-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.