ABSTRACT
This chapter discusses available groups of MR CAs, the general mechanisms of contrast enhancement in Magnetic resonance imaging (MRI) targeting strategies, and some applications of targeted MRI in preclinical model systems. MRI produces highest spatial resolution and strongest endogenous soft tissue contrast among all other available medical imaging modalities. There are multiple parameters that determine the amplitude of the measured MR signals such as concentration of resonating nuclei (protons), their relaxation times, diffusion parameters, flow effects, and water exchange. Paramagnetic MR CAs are the most important class of MR CAs that are based on the transition metal, gadolinium (Gd). Gd has nine electron coordination sites, and up to eight of them can be used to form stable biologically inert complexes with linear and cyclic chelates such as diethylenetriaminepentaacetic acid (DTPA) and tetraazacyclododecanetetraacetic acid (DOTA). Superparamagnetic iron oxide (SPIO) nanoparticles were introduced as highly efficient MR CAs.
