Storage of hydrogen spin polarization in long-lived 13C2 singlet order and implications for hyperpolarized magnetic resonance imaging.

Hyperpolarized magnetic resonance imaging (MRI) is a powerful technique enabling real-time monitoring of metabolites at concentration levels not accessible by standard MRI techniques. A considerable challenge this technique faces is the T1 decay of the hyperpolarization upon injection into the system under study. Here we show that A(n)A'(n)XX' spin systems such as (13)C2-1,2-diphenylacetylene ((13)C2-DPA) sustain long-lived polarization for both (13)C and (1)H spins with decay constants of almost 4.5 min at high magnetic fields of up to 16.44 T without spin-locking; the T1 of proton polarization is only 3.8 s. Therefore, storage of the proton polarization in a (13)C2-singlet state causes a 69-fold extension of the spin lifetime. Notably, this extension is demonstrated with proton-only pulse sequences, which can be readily implemented on standard clinical scanners.