Unparalleled contribution of technetium-99m to medicine over 5 decades.

Since the first tracer study by George C. de Hevesy in 1923, in which he used the tracer principle to study the absorption and translocation of lead nitrate with Pb-212 (1), radionuclides have been used both in vitro and in vivo to trace various biologic processes. The radioisotopes of iodine in particular have played an important role in the early development of nuclear medicine since their use in thyroid metabolism studies (I-131) and radioimmunoassay (I-125). Although I-131 did not have ideal nuclear properties for external imaging with the Anger camera, it was used extensively because of its ready availability and easy conversion to the appropriate chemical form. A long list of I-131–labeled radiotracers illustrates its importance in the postwar period (2). However, the rapid succession of discoveries of the element technetium (Tc), the molybdenum-99 (Mo-99)/Tc-99m generator (Fig. 1) and the “instant” kit (Fig. 2) concept led to unparalleled growth in nuclear medicine (3). Tc-99m radiopharmaceutical imaging is a key diagnostic in 85% of nuclear medicine procedures. There are about 40 million procedures performed worldwide per year, which includes 20 million procedures in North America. The early history of technetium and technetium radiopharmaceuticals is best characterized by the quote from Louis Pasteur: “In the fields of observation, chance favors only the prepared mind” (4). In the mid-1930s,