Technetium-94m-teboroxime: synthesis, dosimetry and initial PET imaging studies.

Technetium-94m (T1/2 = 53 min) allows the in vivo study of technetium radiopharmaceuticals with positron emission tomography (PET). PET provides a quantitative assay of radioactivity with excellent temporal and spatial resolution, revealing biodistributions that were previously available only through in vitro assay methods. Technetium-94m, produced by the proton irradiation of natural molybdenum on an 11 MeV cyclotron, was extracted with an electrochemical etching technique. Technetium-94m-pertechnetate was prepared to make the myocardial perfusion agent teboroxime in an identical manner as 99mTcO4-. The increased absorbed radiation dose requires a sevenfold reduction in administered activity compared to 99mTc-teboroxime. Eleven clinical PET studies were performed and visually compared to 13N-ammonia. The clearance half-time for 94mTc-teboroxime was approximately 8 min, with a peak myocardial extraction of approximately 3% of the injected dose into a 400-g heart. These results confirm the potential of 94mTc PET for quantitatively studying the pharmacokinetics of new, and old, technetium agents in man.