Technetium-99m (99mTc) is used in two-thirds of all diagnostic nuclear medicine procedures in the United States.
This amounts to 13 million procedures per year at a cost of $130 million for the material alone. In 2009, NIST scientists have produced a new 99mTc radioactivity standard, and demonstrated its equivalence to the reference value maintained in France by the Bureau International de Poids et Mesures (BIPM). The short half-life of many medical radionuclides, such as 99mTc (6 hours), had previously prohibited such a long-distance comparison. The present work was made possible by a new transfer-instrument program, developed in part by the NIST team. In this inaugural comparison for the program, the standardization was carried out by NIST scientists using the 4peX-g anticoincidencemethod. This determination was a particular challenge due not only to the short half-life of 99mTc, but also to the low-energy (below 2 keV) of the electrons emitted in its decay. After producing the standard, NIST scientists were joined by their BIPM counterpart in using the standard to calibrate the new BIPM transfer instrument.
The NIST standard was found to be in excellent agreement with the BIPM reference value, having a difference of 0.2 percent with a combined standard uncertainty of 0.4 percent. This result provides a foundation for comparative imaging and functionality studies encompassing treatment centers whose internal calibrations are based on primary standards from other countries. The radioactivity metrology community was demonstratively encouraged by the recent report of this first intercontinental comparison of 99mTc and plans to continue with comparisons in Asia and Africa.
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