(Circulation. 1997;96:2325-2331.)
© 1997 American Heart Association, Inc.
Articles |
Myocardial Uptake and Redistribution of 99mTc-N-NOET in Dogs With Either Sustained Coronary Low Flow or Transient Coronary Occlusion
Comparison With 201Tl and Myocardial Blood Flow
From the Experimental Cardiology Laboratory, University of Virginia, Charlottesville, and CIS-Bio International, Gif sur Yvette, France (R.P.).
Background 99mTc-N-NOET (NOET) is a new myocardial perfusion imaging agent that redistributes over time. We sought to better define the redistribution kinetics of NOET using open-chest canine models of sustained low coronary flow (protocol 1) and transient coronary occlusion followed by reflow (protocol 2).
Methods and Results In protocol 1 (n=10), NOET and 201Tl were injected during low flow in the left anterior descending coronary artery (LAD) that was sustained for 2 hours. Protocol 2 dogs (n=6) were injected with NOET during 20 minutes of LAD occlusion followed by 2 hours of reflow. In both protocols, serial NOET planar images were acquired, and myocardial flow and 2-hour tracer activities were determined by gamma-well counting. Defect resolution was observed on images in both protocols. Initial defect count ratios, reflecting flow disparity at injection (0.66±0.03 and 0.57±0.04, respectively), increased over 2 hours (0.73±0.02 and 0.75±0.04, respectively; P<.001 versus initial). Quantitative imaging showed that NOET redistribution resulted from greater clearance from normal areas versus low-flow or transiently occluded areas. In protocol 1, 2-hour NOET and 201Tl stenotic-to-normal tissue activity ratios were similar (0.76±0.06 versus 0.73±0.04, P=NS) and higher than injection flow ratios (0.52±0.06 and 0.56±0.07, respectively, P<.001), consistent with tracer redistribution. In protocol 2, NOET redistributed to an even greater extent (injection flow ratio, 0.27±0.04; 2-hour tissue activity ratio, 0.84±0.03, P<.001).
Conclusions NOET is the first 99mTc-labeled myocardial imaging agent with kinetics similar to 201Tl in experimental models, permitting redistribution imaging. NOET appears to be a promising agent for assessing patients with coronary artery disease.
Key Words: radioisotopes • ischemia • thallium • technetium
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