Beyond Anatomy

Technical advances in software and hardware make MR imaging competitive with CAT scanning as an anatomic imaging tool. Although anatomic relationships remain important, increased understanding of cell structure and function is rapidly moving us toward diagnosis and treatment at the cellular level. By virtue of its reliance on nuclear magnetic spin moment, MR imaging is responsive to real time physico-chemical characteristics of cells and tissues being imaged. This intrinsic advantage of MR imaging is being rapidly developed through the use of targeted imaging agents and magnetic resonance spectroscopy. Imaging agents that target specific cell populations have been prepared by using monoclonal antibodies, liposomes, and short peptides bound to chelates containing paramagnetic atoms. Using magnetic resonance spectroscopy, the chemical composition of tumors can be analyzed and compared with normal tissues in vivo and in vitro. Areas of possible clinical usefulness for magnetic spectral analysis include: (1) in vitro or in vivo characterization of lesions as benign or malignant, (2) differentiation between in situ and invasive carcinomas, (3) determination of responsiveness to specific chemotherapeutic regimens before their institution, (4) study of in vivo drug metabolism by neoplasms, and (5) assessment of response to therapy and of residual disease at the completion of therapy. Early experiences in these parallel fields show great promise, with widespread clinical applications expected in the near future.