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Technetium-99m-labeled myocardial perfusion agents: Are they better than thallium-201?
1Department of Diagnostic Radiology, Yale University School of Medicine, P.O. Box 208042, TE-2, New Haven, CT 06520-8042, USA.
Insights
Technetium-99m (99mTc) tracers offer superior imaging physics and radiation safety for myocardial perfusion imaging compared to thallium-201 (201Tl). However, 201Tl remains better for assessing myocardial viability due to its redistribution properties.
Area of Science:
- Nuclear Cardiology
- Radiopharmaceutical Imaging
- Cardiovascular Disease Diagnosis
Background:
- Thallium-201 (201Tl) and Technetium-99m (99mTc) tracers are utilized for coronary artery disease detection, myocardial viability assessment, and risk stratification.
- Comparison of 99mTc-labeled tracers with 201Tl is crucial for optimizing myocardial perfusion imaging protocols.
Purpose of the Study:
- To review the advantages and disadvantages of 99mTc-labeled perfusion tracers in comparison to 201Tl.
- To compare the myocardial kinetic properties, biodistribution, and clinical value of these radiotracers.
Main Methods:
- Comparative analysis of imaging physics, radiation safety, cost, and tracer availability.
- Evaluation of myocardial kinetic properties, biodistribution, and clinical performance of 99mTc-labeled tracers (sestamibi, tetrofosmin, and a new bis(N-ethoxy, N-ethyl dithiocarbamato) nitrido technetium(v) agent) versus 201Tl.
- Consideration of the impact of exercise and pharmacologic stressors on tracer behavior.
Main Results:
- 99mTc-labeled tracers exhibit superior imaging physics and radiation safety profiles over 201Tl.
- While cost and availability may favor 99mTc tracers, agents like sestamibi and tetrofosmin track myocardial flow less effectively than 201Tl, potentially reducing sensitivity for subcritical coronary artery disease.
- 201Tl demonstrates superior redistribution characteristics, making it more suitable for assessing myocardial viability, especially in cases of severe ischemia.
Conclusions:
- Substantial differences in uptake, clearance kinetics, and biodistribution necessitate careful consideration of each tracer's unique advantages and disadvantages for optimal clinical application in myocardial perfusion imaging.
- While 99mTc tracers offer practical benefits, 201Tl remains valuable for viability assessment, and newer 99mTc agents require further evaluation.
- The choice of tracer should be guided by the specific clinical question, whether it be acute risk assessment or long-term viability evaluation.
Abstract:
Currently, thallium-201 (201Tl)- and technetium-99m (99mTc)-labeled tracers are used interchangeably for the detection of coronary artery disease, the assessment of myocardial viability, and risk stratification. This article reviews some of the potential advantages and disadvantages of the 99mTc-labeled tracers relative to 201Tl. The basic myocardial kinetic properties and biodistribution of the commonly used 99mTc-labeled perfusion tracers are compared with those of 201Tl. The clinical value of the 99mTc-labeled perfusion tracers is then compared with that of 201Tl imaging. With regard to imaging physics and radiation safety, the 99mTc-labeled tracers are superior to 201Tl. Cost and tracer availability also may favor 99mTc-labeled perfusion tracers rather than 201Tl imaging. However, the most widely used 99mTc-labeled perfusion tracers currently approved for clinical use-99mTc-sestamibi and 99mTc-tetrofosmin-do not track myocardial flow as well as 201Tl does. This shortcoming of 99mTc-labeled perfusion tracers may reduce the sensitivity of these agents in detecting subcritical coronary artery disease. The most notable new perfusion agent is 99mTc-labeled bis(N-ethoxy, N-ethyl dithiocarbamato) nitrido technetium(v), which is considered to be the 99mTc-labeled equivalent of 201Tl. However, 99mTc-labeled bis(N-ethoxy, N-ethyl dithiocarbamato) nitrido technetium(v) is a neutral compound with kinetic properties that are very different from those of 201Tl. Myocardial perfusion imaging is often conducted in conjunction with exercise or with different pharmacologic stressors, both of which augment regional flow heterogeneity. Each of these stressors has unique effects on the coronary vasculature and influences the behavior of the radiolabeled perfusion agents. The substantial differences in myocardial uptake, clearance kinetics, and biodistribution between each of the 99mTc-labeled perfusion tracers and 201Tl should be considered in the clinical application of perfusion imaging. The myocardial retention of all of the agents is affected by myocardial viability. However, 201Tl demonstrates greater differential clearance from normal and ischemic regions (redistribution), making 201Tl a better agent for assessment of viability, particularly in patients with extremely low flow. In contrast, agents that do not redistribute, such as 99mTc-tetrofosmin, might be better for acute assessment of "risk areas" or of chest pain. Each of the available perfusion tracers has unique advantages and disadvantages that must be considered to ensure its optimal application.