Myocardial perfusion imaging with technetium-99m-labeled agents

Thallium-201 (²⁰¹Tl) is suboptimal as a single-photon emitting agent for myocardial perfusion imaging, in view of its low-energy photons and long half-life. To circumvent these limitations, two new myocardial perfusion imaging agents labeled with technetium-99m (^99mTc) have been developed. They are Tc-sestamibi and Tc-teboroxime. Clinical trials of myocardial perfusion with both tracers have shown results similar to those obtained with ²⁰¹Tl for detection of coronary artery disease. Results to date indicate that Tc-sestamibi accurately detects and locates myocardial infarction and can accurately assess both left and right ventricular ejection fractions by the first-pass technique. In addition, research has shown that rest-stress studies can be performed on the same day and that Tc-sestamibi can be used to assess the results of thrombolytic therapy. Tc-teboroxime has excellent myocardial tracer uptake characteristics but is cleared very rapidly from the myocardium. These features make Tc-teboroxime well suited to rapid serial studies. These new technetium myocardial perfusion agents have just become available for routine clinical use and are likely to replace ²⁰¹Tl in many of its clinical applications.