Figure 13. . The 25 is the structure of pyridazinone [¹⁸F]flurpiridaz, where further analogs have various chains attached to the phenyl ring and various positions for the ¹⁸F label; 26 is the general structure of the quinazoline series where R is an ¹⁸F labeled alkyl chain when Z and Y are H or an unlabeled alkyl chain when either Z or Y is ¹⁸F labeled.