Technetium-99m-Teboroxime: A New Agent for Myocardial Perfusion Imaging

The assessment of myocardial perfusion by nuclear scintigraphy is an important diagnostic tool for the evaluation of patients with ischemic heart disease. Although a variety of radiopharmaceuticals have been used to assess coronary blood flow, thallium-201 ( 01 Tl) has become the most commonly used imaging agent since its introduction for clinical use by Lebowitz eta!. in 1973 (J). Thallium-20 1 does, however, demonstrate several drawbacks that makes it less than ideal for imaging. Cyclotron production limits its availability and increases its cost. The physical properties of ~ TI are not ideal for Anger camera scintigraphy. It has a low-energy photopeak (68-80 keV mercury-20 I X-ray) which results in soft tissue attenuation artifacts. Its relatively long half-life (73 hr) limits the activity amount that may be administered, which results in a low photon flux. The low administered activity also results in prolonged imaging times. Myocardial perfusion imaging currently relies on redistribution after a single stress injection to assess resting perfusion. However, recent studies suggest that a second rest injection may be needed to obtain a true resting perfusion image (2). Technetium-99m C~mTc) has physical properties that are ideal for Anger camera imaging. It is readily available from an on-site generator, is inexpensive, has a short half-life (6 hr), and emits a photopeak (140 keV) with an optimal energy for imaging. Due to its favorable radiation dosimetry, higher activity amounts of ~mTc can be administered, which may allow for a significant reduction in the time necessary for data acquisition. For reasons such as these, many researchers have worked toward the development of a new ~~mTc-labeled myocardial