Hyperpolarized MR imaging: Neurologic applications of hyperpolarized metabolism

Hyperpolarization is the general term for a method of enhancing the spin-polarization difference of populations of nuclei in a magnetic field. No less than 5 distinct techniques (dynamic nuclear polarization [DNP]; parahydrogen-induced polarization-parahydrogen and synthesis allow dramatically enhanced nuclear alignment [PHIP-PASADENA]; xenon/helium polarization transfer; Brute Force; ¹H hyperpolarized water) are currently under exhaustive investigation as means of amplifying the intrinsically (a few parts per million) weak signal intensity used in conventional MR neuroimaging and spectroscopy. HD-MR imaging in vivo is a metabolic imaging tool causing much of the interest in HD-MR imaging. The most successful to date has been DNP, in which carbon-13 (¹³C) pyruvic acid has shown many. PHIP-PASADENA with ¹³C succinate has shown HD-MR metabolism in vivo in tumorbearing mice of several types, entering the Krebs-tricarboxylic acid cycle for ultrafast detection with ¹³C MR imaging, MR spectroscopy, and chemical shift imaging. We will discuss 5 promising preclinical studies: ¹³C succinate PHIP in brain tumor; ¹³C ethylpyruvate DNP and ¹³C acetate; DNP in rodent brain; ¹³C succinate PHIP versus gadolinium imaging of stroke; and ¹H hyperpolarized imaging. Recent developments in clinical ¹³C neurospectroscopy encourage us to overcome the remaining barriers to clinical HD-MR imaging.