NEW MAGNETIC-RESONANCE-IMAGING TECHNIQUES FOR THE DETECTION OF BREAST-CANCER

The importance of contrast agents in enhancing diagnoses from magnetic resonance images has been established in numerous cases. However, the development of a potent tissue-specific contrast agent, as a sensitiv e probe for early detection and investigation of the physiological cha racteristics of a tumor, has not yet been realized in MR imaging (MRI) . In nuclear scintigraphy the technique has been demonstrated; however , the poor spacial resolution inherent to the modality and the substan tial dose of radioactivity administered to the patient has hindered it s widespread use. This article will review the different classes of co ntrast agents in MRI, with special focus on the strategies involved in the development of targeted tissue-specific MRI contrast agents for t he early detection of breast cancer. The features of a new class of co ntrast agents for targeted MR imaging will be described. Gadolinium-co ntaining melanin polymers (GMP's) have been synthesized as MR contrast agents in our laboratory. These GMP's demonstrate significantly highe r relaxivities than any other paramagnetic contrast agents reported; c onsequently, they are extremely effective contrast enhancing, imaging agents by themselves. The successful coupling of these potent GMP's to a monoclonal antibody specific for breast carcinoma, the 323/A3 monoc lonal antibody, suggests that in vivo tissue-specific MR imaging, at t he receptor level, will become feasible in the near future.