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Division of Cardiology, Department of Internal Medicine; Division of Nuclear Medicine, Department of Radiology; Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine; Cincinnati, Ohio
Correspondence: For correspondence or reprints contact: Anthony J. McGoron, PhD, E. L. Saenger Radioisotope Laboratory, Division of Nuclear Medicine, Department of Radiology, University of Cincinnati, P.O. Box 670577, Cincinnati, OH 45267-0577.
ABSTRACT
We investigated the myocardial flow kinetics of six putative radioperfusion agents (99mTc-Q3, 99mTc-Q4, 99mTc-Q12, 99mTc-sestamibi, 99mTc-tetrofosmin and 99mTcN-NOET)and 201TI in a canine model of myocardial ischemia with pharmacologie coronary artery vasodilation. Methods: In 31 open-chest dogs with acute coronary occlusion, dipyridamole (
0.56 mg/kg) was infused intravenously, followed by a perfusion tracer injection and radioactive microspheres for myocardial blood flow (MBF) measurement. The paired data were normalized using three techniques; average, normal or maximum myocardial tracer activity and MBF. Results: The upper limit of MBF obtained for the group of tracers ranged from 4.2 ml/min/g to 8.2 ml/min/g. There was a statistically significant (p < 0.0001) linear correlation (r = 0.87–0.98) between the normalized myocardial activity and the normalized MBF values of each of the tracers. The slope of the curve normalized by average for 201TI (0.83) was greater than those for the 99mTc tracers, and the intercept (0.07) was lower than those for the 99mTc tracers. Slopes and intercepts for the 99mTc agents were as follows: 99mTc-QS, 0.81 and 0.18; 99mTc-Q4, 0.61 and 0.41; 99mTc-Q12, 0.63 and 0.39; 99mTc-sestamibi, 0.62 and 0.34; 99mTc-tetrofosmin, 0.68 and 0.32; and 99mTcN-NOET, 0.71 and 0.29, respectively. Conclusion: In an anesthetized open-chest canine model of regional myocardial ischemia with dipyridamole induced hyperemia, 201TI shows a more ideal relationship between tracer uptake and MBF than do the 99mTc-based agents. Of the various 99mTc-based imaging agents studied, the myocardial flow kinetics of 99mTc-Q3 appear to be closest to ideal. This relationship is maintained regardless of the normalization technique used. This may, in theory, imply a higher sensitivity in discerning ischemic from normal myocardium and a role in diagnostic nuclear imaging for 99mTc-Q3.
Key Words: myocardium • ischemia • perfusion imaging • microspheres • technetium-99m
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