Polymer-Based Compounds for Targeted Imaging

The ultimate aim of all targeted imaging is to achieve a large contrast enhancement at the diseased sites that offers not only anatomical but also functional and physicobiochemical information noninvasively. Thus, in this respect, targeted imaging is very similar to drug targeting where the goal is to treat the diseased condition without harming the host, that is, to achieve a large therapeutic index. Depending on the size of contrast agents, two distinct approaches can be envisaged: (1) the agent has low molecular weight (usually <1000 Da); (2) the agent has high molecular weight, or large size, and localization of the agent to the tumor is mediated by carriers that include particulate, liposomal, and macromolecular contrast agents. The latter approach can be further subclassified into passive targeting and active targeting.