Radioactive Decay

In the United States, single-photon emission computed tomography myocardial perfusion imaging (SPECT MPI) accounts for the overwhelming majority of noninvasive imaging procedures for stable ischemic heart disease.1 Most contemporary SPECT MPI is performed using blood-flow radiotracers labeled with technetium-99m (Tc-99m), which have supplanted thallium-201, an older radiotracer. Tc-99m offers several advantages including superior image quality, lower radiation exposure, and higher overall diagnostic accuracy because of greater specificity.2 Estimates suggest up to 17 million doses of Tc-99m are used annually in the United States, with the majority used in cardiac stress testing.However, 9 unplanned shutdowns at critical facilities totaling 50 months of downtime between 2008 and 2015 have made the supply chain for Tc-99m increasingly fragile.1 We and others demonstrated that these shutdowns may have had important clinical consequences by creating Tc-99m shortages that lead to increased rates of unnecessary, downstream cardiac catheterization and higher radiation exposure.3,4 Unfortunately, multiple, simultaneous challenges to the worldwide supply chain for Tc-99m may impact the care of patients and cardiologists’ decision making. In this article, we briefly review the reasons behind these trends and new solutions being proposed.Tc-99m is not found in nature and is produced as a daughter isotope of molybdenum-99 (Mo-99). Because of the short 6-hour half-life of Tc-99m and longer 2.8-day half-life of Mo-99, Tc-99m is typically eluted from generators containing Mo-99 on site in hospitals or distributed from regional radiopharmacies via a complex, worldwide supply chain (Figure). However, …