Generator systems for PET radionuclides

Unlike single photon emitters, the practice of PET has not revolved around the development of a single dominant generator system. In fact, generator systems have had little impact on the field to data. Two systems are commercially available, the Ge-68/Ga-68 system and the Sr-82/Rb-82 system. Rubidium-82 is useful for cardiac imaging. Gallium-68 is the subject of some work on conjugation chemistry since the pharmacology of ionic gallium in vivo requires a longer half life than Ga-68's one hour. There have been attempts at developing other generator systems for use in PET, but few have been utilized extensively in the clinic. Among the most promising are the Zn-62/Cu-62, Te-118/Sb-118, Se-72/As-72 and the Ti-44/Sc-44 systems. Other systems have been reported include Fe-52/Mn-52m, Xe-122/I-122, Ba-128/Cs-128 and Ce-134/La-134. In general, the problems surrounding these systems have included short parent half life, large β+ energy or long daughter half life resulting in high radiation dose to the patient, high abundance and/or high energy gamma rays resulting in radiation hazards to the patient and personnel working in the clinic; and difficult production, separation from target or separation from the parent. For these reasons, and the inherent advantages of using positron emitting isotopes of C,N,O, and F for labeling, radionuclides from generators make up a small percentage of studies done in the clinic