MYOCARDIAL UPTAKE AND REDISTRIBUTION OF TC-99M-N-NOET IN DOGS WITH EITHER SUSTAINED CORONARY LOW-FLOW OR TRANSIENT CORONARY-OCCLUSION - COMPARISON WITH TL-201 AND MYOCARDIAL BLOOD-FLOW

Background Tc-99m-N-NOET (NOET) is a new myocardial perfusion imaging agent that redistributes over lime. We sought to better define the red istribution kinetics of NOET using open-chest canine models of sustain ed low coronary flow (protocol 1) and transient coronary occlusion fol lowed by reflow (protocol 2). Methods and Results In protocol 1 (n=10) , NOET and Tl-201 were injected during low flow in the left anterior d escending coronary artery (LAD) that was sustained for 2 hours. Protoc ol 2 dogs (n=6) were injected with NOET during 20 minutes of LAD occlu sion followed by 2 hours of reflow. Ln both protocols, serial NOET pla nar images were acquired, and myocardial flow and 2-hour tracer activi ties were determined by gamma-well counting. Defect resolution was obs erved on images in both protocols. Initial defect count ratios, reflec ting flow disparity at injection (0.66+/-0.03 and 0.57+/-0.04, respect ively), increased over 2 hours (0.73+/-0.02 and 0.75+/-0.04, respectiv ely; P<.001 versus initial). Quantitative imaging showed that NOET red istribution resulted from greater clearance from normal areas versus l ow-flow or transiently occluded areas. In protocol 1, 2-hour NOET and Tl-201 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 tr acer redistribution. In protocol 2, NOET redistributed to an even grea ter extent (injection flow ratio, 0.27+/-0.04; 2-hour tissue activity ratio, 0.84+/-0.03, P<.001). Conclusions NOET is the first Tc-99m-labe led myocardial imaging agent with kinetics similar to Tl-201 in experi mental models, permitting redistribution imaging. NOET appears to be a promising agent for assessing patients with coronary artery disease.