Hyperpolarized agents for advanced MRI investigations.

The strong signal enhancement attainable by hyperpolarization methods has allowed the detection of heteronuclei in magnetic resonance imaging (MRI), allowing to obtain high quality images with very high signal to noise ratios in few seconds. The four methods to produce hyperpolarized molecules, i.e. the "brute force" approach, optical pumping of noble gases, parahydrogen induced polarization (PHIP) and dynamic nuclear polarization (DNP), are reported. The applications of hyperpolarized probes to MRI range from vascular imaging to interventional imaging and perfusion studies, up to the emerging and challenging field of molecular/metabolic imaging. In fact, the high signal intensities achievable by using hyperpolarized molecules make it possible to detect and image the metabolic products formed upon the administration of the hyperpolarized agent. The most striking examples are surveyed, including the use of hyperpolarized 13C-pyruvate in tumor diagnosis and stadiation, and in myocardium perfusion and activity studies, as well as the recently reported proposal of using 13C-bicarbonate as agent for pH-mapping in vivo.