Magnetic resonance imaging of hyperpolarized long-lived proton singlet states originated from para-hydrogen induced polarization in symmetrical molecules

MANUEL BRAUN; DIRK GRAAFEN; MARÍA BELÉN FRANZONI; BARBARA PIECHALSKA; HANS W. SPIESS; KERSTIN MÜNNEMANN

Congreso; Euromar 2014; 2014

  The problem of low sensitivity in nuclear magnetic resonance (NMR), which affects in particular magnetic resonanceimaging (MRI), can be addressed by various hyperpolarization techniques.  In the case of para- hydrogen inducedpolarization (PHIP) a hyperpolarized spin state is created by catalytic hydrogenation of a double or triple bond withpara-hydrogen.However, applications like MRI are limited due to the short lifetime of the hyperpolarized state, which is usuallyrelaxing to thermal equilibrium with the spin- lattice relaxation time T 1 .  This can be addressed by storing thehyperpolarization in singlet states, which are slowly relaxing with the storage time T S .  Protons in symmetricalmolecules hyperpolarized by PHIP are well suited for this strategy because they naturally possess a long-lived singletstate. In the molecule dimethyl maleate for example the hyperpolarized proton singlet state can be stored at 7 T for4 min without using radiofrequency (RF) pulses [1].The conversion of the NMR silent singlet state to measurable magnetization is achieved by making use of singlet-triplet level anticrossings [2]. For this purpose a low-power RF pulse sequence is applied allowing multiple successivesinglet-triplet conversions [3].  We combine this approach with MR imaging and demonstrate its feasibility in astandard clinical 1 H-MR scanner. Our results might pioneer unexplored opportunities in metabolic imaging.