ABSTRACT
Compounds labeled with isotopes have played an important role in chemistry, biology, and medicine since they were ™rst used as tracers by Hevesey.1,2 Both stable3-5 and radioactive6,7 isotopes were utilized in early investigations, but the situation changed dramatically with the invention of the cyclotron by Lawrence in 1930 and the construction of the nuclear reactor by Fermi in 1942 that enabled access to radioisotopes on a regular basis. Radioisotope use in medicine was also accelerated by advances in radiation-detection techniques.8,9 The development of single-photon emission computerized tomography (SPECT)10,11 and positron emission tomography (PET)12-14 revolutionized diagnostic medical imaging by facilitating noninvasive, in vivo, three-dimensional imaging of living systems after administration of appropriate compounds labeled with short-lived nuclides.15,16 PET and SPECT techniques complement the traditional x-ray CAT scan and are responsible for the tremendous upsurge in the use of radiopharmaceuticals in hospitals today.
