Myocardial Uptake and Redistribution of 99m Tc-N-NOET in Dogs With Either Sustained Coronary Low Flow or Transient Coronary Occlusion

Background 99m Tc-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 201 Tl 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 201 Tl 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 99m Tc-labeled myocardial imaging agent with kinetics similar to 201 Tl in experimental models, permitting redistribution imaging. NOET appears to be a promising agent for assessing patients with coronary artery disease.