Kinetic characterization of a novel cationic ^99mTc(I)- tricarbonyl complex, ^99mTc-15C5-PNP, for myocardial perfusion imaging

Background: Intense liver uptake of ^99mTc-sestamibi (MIBI) often interferes with visualization of myocardial perfusion in the inferior wall of the left ventricle. To develop improved myocardial perfusion agents, crown ether-containing dithiocarbamates and bisphosphines have been introduced in recent years. This study was designed to investigate the myocardial imaging properties and in vivo kinetics of a cationic ^99mTc(I)-tricarbonyl complex, ^99mTc-15C5-PNP, in comparison with MIBI. Methods: Dynamic cardiac images were acquired for 60 minutes after intravenous tracer injection using a small-animal SPECT system in healthy control rats and rats with myocardial infarcts. Myocardial and liver time-activity curves were generated for radiopharmaceutical kinetic analysis. Results: Good visualization of the left ventricular wall and perfusion defects could be achieved 20 minutes after ^99mTc-15C5-PNP administration. ^99mTc-15C5-PNP images in all hearts with infarcts showed perfusion defects, which were comparable to MIBI images. The kinetic curves plotted from 1 to 60 minutes demonstrated that ^99mTc-15C5-PNP has a shorter washout half-life (6.4 ± 3.2 vs 124 ± 30.5 minutes, P < .01) in the liver, lower residual liver activity (14.5 ± 10.2% vs 36.5 ± 28.9%, P < .01), and higher heart/liver ratio than MIBI. Conclusions: ^99mTc-15C5-PNP has potential for rapid myocardial perfusion imaging with low liver uptake.