Quantitation of a spin polarization-induced nuclear Overhauser effect (SPINOE) between a hyperpolarized (13) C-labeled cell metabolite and water protons

Abstract

The spin polarization-induced nuclear Overhauser effect (SPINOE) describes the enhancement of spin polarization of solvent nuclei by the hyperpolarized spins of a solute. In this communication we demonstrate that SPINOEs can be observed between [1,4-(13) C2 ]fumarate, hyperpolarized using the dissolution dynamic nuclear polarization technique, and solvent water protons. We derive a theoretical expression for the expected enhancement and demonstrate that this fits well with experimental measurements. Although the magnitude of the effect is relatively small (around 2% measured here), the SPINOE increases at lower field strengths, so that at clinically relevant magnetic fields (1.5-3 T) it may be possible to track the passage through the circulation of a bolus containing a hyperpolarized (13) C-labeled substrate through the increase in solvent water (1) H signal.

Keywords: SPINOE; cross-relaxation; signal enhancement; spin-lattice relaxation.

Figure 1

Simulation of the SPINOE enhancement of the ¹H signal with ¹³C polarized to 50%, calculated using eqn 20. The parameters used in the simulation were T_1,I = 1/ρ_I = 2.8 s, N_I = 4.01 × 10²³, N_S = 1.44 × 10²⁰, P(t_max) = 0.5, B₀ = 9.4 T, T = 293 K, and different T_1,S = 1/ρ_S as shown.

Figure 2

Measured SPINOE effect curve for solvent protons (water) at 9.4 T following the addition of 20 mm [1,4-¹³C₂]fumarate that had been hyperpolarized to 36% at the time of injection (n = 2). Error bars are the standard deviation on the mean. η^a(t) was calculated using eqn 20 and the experimental values shown in Table 1 (dashed line). η^b(t) is the best fit to the experimental data (solid line).