Quantification strategies for MRI

Quantification strategies have been a long-standing challenge since the early days of magnetic resonance molecular and cellular imaging. Quantitative imaging is desirable in the framework of comparative or follow-up studies in order to establish objective evidences of a specific target expression pertaining to a specific disease. Numerous strategies of increasing complexity have been proposed to address this need. In this chapter, common strategies related to quantitative molecular imaging for MRI are briefly reviewed and their respective outcomes are discussed. The focus is on relaxation contrast agents (CAs) that generate magnetic resonance contrast by affecting the proton relaxation times, and which are the most common kind of CAs used in MRI. Particular attention is paid to cutting-edge applications that enable local CA quantification as well as distinction of the bound/activated subpopulation of the CA.