Tumor specific MRI contrast agents are in development to provide better delineation and progression information for various tumors. Clinical oncology has a need for contrast agents that can identify tumors and metastases at a size of 100,000 cells rather than 1,000,000,000 cells. This level of sensitivity requires excellent tumor targeting of imaging agents and a high MRI signal.
Tumor specific agents accumulate at pathological tissues by passive or active targeting mechanisms. Passive targeting agents use e.g., the natural defense mechanisms in which phagocytic cells remove foreign particles from the body. Active targeting is based on a ligand-directed, site-specific accumulation of contrast agents. The availability of macromolecular contrast agents such as feruglose and ultrasmall superparamagnetic iron oxide (USPIO), which permit the assessment of tissue permeability, may also improve the detection of tumor grade, tumor type, and response to drugs that target angiogenesis.

See also Monoclonal Antibodies, Metalloporphyrins, Nitroxides and Ferrioxamine.