The present application discloses compositions and methods of synthesis and use of F-18 labeled molecules of use, for example, in PET imaging techniques. The labeled molecules may be peptides or proteins, although other types of molecules may be labeled by the described methods. Preferably, the F-18 may be conjugated to a targeting molecule by formation of a metal complex and binding of the F-18-metal complex to a chelating moiety. Alternatively, the metal may first be conjugated to the chelating group and subsequently the F-18 bound to the metal. In other embodiments, the F-18 labeled moiety may comprise a targetable construct used in combination with a bispecific or multispecific antibody to target F-18 to a disease-associated antigen, such as a tumor-associated antigen. The F-18 labeled targetable construct peptides are stable in serum at 37° C. for a sufficient time to perform PET imaging analysis.