MR contrast agents

Abstract

This chapter is devoted to survey the major classes of MRI contrast agent (CA), their modes of action, and some of the most significative applications. The two more established classes of MRI CA are represented by paramagnetic metal complexes (i.e., Gd(III) and Mn(II)) and iron oxide particles, acting on T1 and T2* of the water protons signals, respectively. Along the years, many efforts have been devoted to endow these relaxation enhancement agents with improved sensitivity, targeting, and responsive properties that have markedly broadened the range of applications in respect to the clinically used systems. CEST agents represent innovative frequency-encoding probes that yield negative contrast in the MR images upon transfer of saturated magnetization from the agent to the bulk water signal. Interesting developments have been attained that markedly increase the number and typology of systems with CEST properties. Currently, much attention is devoted to hyperpolarized molecules that display a sensitivity enhancement sufficient for their direct exploitation for the formation of the MR image. A real breakthrough is provided by the use of molecules (such as pyruvate) that report about the cellular metabolism thanks to the maintainment of the hyperpolarization in the derived species. Finally, 19F-containing molecules have been considered as the improved sensitivity of the new MRI scanner generation makes it possible to acquire images based on this heteronucleous. © 2011 Springer-Verlag Berlin Heidelberg.