The Return of Thallium-201 for American Patients: History, Radiopharmaceutical Features, and Current Applications.

purpose of reviewAfter years of declining use of thallous chloride-201 (thallium) for myocardial perfusion imaging (MPI), commercial production in the U.S ceased in 2022. Recognizing unique patient-care roles that thallium can serve, it was reintroduced in July 2026. A new generation of cardiologists has no or little familiarity with this radiopharmaceutical, and even many experienced nuclear cardiology practitioners are unfamiliar with its role to improve accuracy of cardiac amyloid radionuclide imaging with bone-avid tracers, gaps which this review aims to address. RECENT

findingsClaims data indicate that while thallium use progressively declined, during the last few years of its availability this appears to have plateaued, with approximately 5% of SPECT MPI studies in 2021 performed using thallium, reflecting a persistent albeit limited role. Updated radiation dosimetric modeling reveals the radiation effective dose of a thallium stress test, while higher than that of a technetium-99m study, to be less than previously appreciated, e.g. 3 mCi of thallium has an effective dose of 11.3 mSv, vs. 24.4 mSv using older dosimetry. For its novel application to amyloid diagnosis, dual isotope thallium localization/technetium-99m pyrophosphate amyloid imaging demonstrated improved diagnostic performance and interobserver reproducibility for detection of transthyretin cardiac amyloidosis compared to single-isotope amyloid imaging. Here we address thallium's history, from its 1975 introduction as a superior analog to potassium-43 and rubidium-81 for myocardial perfusion imaging, to its growth and then decline caused by radiation and image-quality concerns. We address thallium's distinguishing physical, chemical, pharmacological, and manufacturing features, and six use cases: viability testing where PET or MRI is not feasible or a poor option, simultaneous dual-isotope cardiac amyloid radionuclide imaging to improve diagnostic accuracy of SPECT, stress testing during technetium-99m shortages and in patients with poor-quality technetium-99m imaging due to subdiaphragmatic activity, rapid stress testing in patients with low radiation risk, such as the elderly and those with significant comorbidities, and potentially for SPECT stress myocardial blood-flow quantification. While the extent of thallium's readoption remains uncertain, its renewed availability diversifies diagnostic options for cardiac patients.