ABSTRACT
As described in detail in Chapters 2 and 5, the overwhelming majority of magnetic resonance imaging is based on detecting the relaxation and local density characteristics of water protons. Since di›erent tissues have di›erent relaxation rates, they give rise to substantial contrast in a typical MR image. še native contrast between tissues can be enhanced using MRI contrast agents. In the previous chapter, contrast agents were discussed in terms of their ability to impart a direct e›ect on the surrounding bulk water, thereby providing greater water relaxation in their proximity. šis class, known as T1 contrast agents due to the enhanced longitudinal relaxation they a›ord, generally possesses a lanthanide metal chelated to a suitable targeting or biocompatible molecule. An alternative approach to increasing the contrast between two tissues is to exploit an enhancement in the transverse relaxation process, T2, through the introduction of magnetic nanoparticles.
