ABSTRACT
Among many possible radiopharmaceutical (RP) agents, contemporary molecular imaging and therapy studies have been involved with liposomes, antibodies, segments of RNA and DNA, selective high-affinity ligands (SHALs), and a variety of nanoparticles. The number of reports has now grown to thousands of published articles on these targeting structures. The entries are not mutually exclusive as combinations are possible. More generic types will certainly be developed, so the question of which agent is best for a given role is unclear today. Historically, figures of merit based on ratios of uptake or of ratios of areas under the curve (AUCs) have been generated as an ad hoc quality indicator for imaging and therapy, respectively. As has been shown, such historical figures of merit (FOMs) are not acceptable as true descriptors because of their ratio formulations. Ratios lead to a cancellation of absolute factors, so the actual amount in the lesion or target site is lost in the analysis. In other words, whereas the ratio may be large, the numerator may still be so miniscule as to make imaging or therapy impossible in any finite time or with any realistic amount of activity, respectively.
