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Early Myocardial Clearance Kinetics of Technetium-99m-Teboroxime Differentiate Normal and Flow-Restricted Canine Myocardium at Rest

Saint Francis Medical Research Institute of the University of Oklahoma Health Sciences Center, Tulsa, Oklahoma

Correspondence: For reprints and correspondence contact: Gerald Johnson III, PhD, Saint Francis Medical Research Institute, 6465 South Yale, Suite 1010, Tulsa, OK 74136.

ABSTRACT

Technetium-99m-teboroxime (Cardio Tec) is a promising new myocardial perfusion imaging agent. The purposes of this study were to define teboroxime clearance kinetics in normal and flow-restricted myocardium over a 1-hr period and to determine whether teboroxime kinetics are useful in detecting myocardial hypoperfusion. Accordingly, the circumflex arteries of 23 dogs were stenosed. By using miniature cadmium-telluride radiation detectors, myocardial teboroxime activities were continuously monitored in both the control and the stenosed zones. Myocardial clearance of teboroxime was modeled and found to be biexponential over 1 hr. A significant difference in myocardial clearance between the normal and stenosed zones (t_1/2 = 4.5 ± 0.9 min versus 10.2 ± 2.6 min, respectively; p < 0.05) was observed for the first exponential phase (the first 5 min following initial uptake), but not for the second exponential phase (t_1/2 = 160.7 ± 35.9 min versus 140.4 ± 27.4 min, respectively; p = ns). One hour fractional teboroxime blood clearance was 0.95 ± 0.03, with most of the clearance occurring during the first 4 min. Gamma camera images of excellent quality demonstrated an initial defect with significant quantitative differential clearance over 1 hr. Thus, there are two phases of myocardial teboroxime clearance. During the early exponential clearance phase, teboroxime kinetics at rest may be able to differentiate between normal and hypoperfused myocardium.

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