New Classes of MRI Contrast Agents

Abstract

A very high spatial resolution and a so far unsurpassed ability in distinguishing soft tissues characterize magnetic resonance imaging (MRI). This imaging technique has therefore become one of the most important diagnosis tools available in medicine. Insufficient contrast is nevertheless a drawback of the technique in many instances, hence the need for contrast agents. A number of such substances have been developed and enjoy widespread use in hospitals around the globe. However, there remains a need for new and more selective contrast media that would allow a better delineation of diseases thus helping the radiologist in giving a more precise diagnosis. This chapter is devoted to these new types of contrast agents and provides an overview of new ideas and their applications as they appear in the recent literature. Examples are given of new blood-pool agents mostly based on macromolecular derivatives. Linking contrast agents to antibodies or other biologically relevant macromolecules may provide a way of highlighting regions of interest. Such compounds are also discussed. Very recent examples of in vitro and in vivo contrast agents for imaging gene expression will also be presented, as this appears to be of utmost importance for assessing gene delivery and gene expression in gene therapy applications and for studying developmental stages in embryology. Finally, MRI contrast agents are presented that react to variables in their environment. Temperature, pH, ions, enzymes are just a few of the parameters that may influence the response of these so-called smart contrast agents.