The new 99mTc myocardial perfusion imaging agents: 99mTc-sestamibi and 99mTc-teboroxime

The two new 99m (^99mTc) labeled myocardial perfusion agents, ^99mTc-Sestamibi and ^99mTc-Teboroxime, are now available for routine clinical application. Both agents allow assessment of ejection fraction by the first-pass technique at rest or during exercise, thus providing additional information not available with thallium-201. ^99mTc-Sestamibi has long myocardial residence time, as well as adequate myocardial extraction, providing images of higher count density and superior quality compared with thallium-201. ^99mTc-Teboroxime has excellent myocardial uptake characteristics but is cleared very rapidly from the myocardium. Both tracers have shown results similar to those obtained with thallium-201 for detection of coronary artery disease and the assessment of defect reversibility. ^99mTc-Sestamibi studies using the rest/stress imaging sequence can be accomplished in approximately 5 hours; studies using dual-isotope imaging (rest thallium-201 and stress ^99mTc-Sestamibi injection) can be completed in 1 to 2 hours. Gated stress images can be performed with ^99mTc-Sestamibi, providing simultaneous information of myocardial perfusion at stress and resting wall motion or thickening and allowing rapid differentiation of ischemic from infarcted tissue. Because of its slow myocardial clearance and absence of redistribution, ^99mTc-Sestamibi allows uncoupling of the time of injection from the time of imaging and thus can be valuable in the evaluation of acute myocardial infarction and outcome of thrombolytic therapy. With ^99mTc-Teboroxime, rapid serial studies are feasible. Pharmacologic stress and rest studies with ^99mTc-Teboroxime single photon emission computed tomography potentially can be completed in under 30 minutes. Because of its linear myocardial uptake even at very high coronary flow levels, ^99mTc-Teboroxime with pharmacologic stress may be particularly well suited to the detection of early coronary disease.