Extending the Lifetime of Hyperpolarized Propane Gas through Reversible Dissolution

Abstract

Hyperpolarized (HP) propane produced by the parahydrogen-induced polarization (PHIP) technique has been recently introduced as a promising contrast agent for functional lung magnetic resonance (MR) imaging. However, its short lifetime due to a spin-lattice relaxation time T₁ of less than 1 s in the gas phase is a significant translational challenge for its potential biomedical applications. The previously demonstrated approach for extending the lifetime of the HP propane state through long-lived spin states allows the HP propane lifetime to be increased by a factor of ∼3. Here, we demonstrate that a remarkable increase in the propane hyperpolarization decay time at high magnetic field (7.1 T) can be achieved by its dissolution in deuterated organic solvents (acetone-d₆ or methanol-d₄). The approximate values of the HP decay time for propane dissolved in acetone-d₆ are 35.1 and 28.6 s for the CH₂ group and the CH₃ group, respectively (similar values were obtained for propane dissolved in methanol-d₄), which are ∼50 times larger than the gaseous propane T₁ value. Furthermore, we show that it is possible to retrieve HP propane from solution to the gas phase with the preservation of hyperpolarization.

Figure 1

(a) Scheme of the experimental setup for HP propane production. (b) Reaction scheme of propene hydrogenation. (c) ALTADENA single-scan ¹H NMR spectrum acquired during gas-phase hydrogenation of propene with parahydrogen over 1 wt % Rh/TiO₂ catalyst.

Figure 2

(a) Scheme showing the production of dissolved HP propane. (b) Single-scan ¹H NMR spectrum of dissolved HP propane produced by hydrogenation of propene with parahydrogen over 1 wt % Rh/TiO₂ catalyst and subsequent dissolution of HP propane in acetone-d₆. The signal enhancement was ∼17-fold. (c) Corresponding ¹H NMR spectrum of the same solution as in panel b acquired after complete relaxation of hyperpolarization. (d) T_HP measurements for HP propane dissolved in acetone-d₆ through the use of 10° rf pulses. (e) T₁ measurements for thermally polarized propane dissolved in acetone-d₆ by the inversion–recovery sequence.

Figure 3

(a) MR image of a 10-mm NMR tube filled with solution of HP propane in acetone-d₆ in axial orientation. SNR = 17.2. (b) Corresponding MR image of fully relaxed solution shown in panel a. The field of view (FOV) was 5 × 5 cm, with a 64 × 64 matrix size and a slice thickness equal to the diameter of the NMR tube. The total acquisition time was 1.7 s.

Figure 4

(a) Scheme showing the production of dissolved HP propane. (b) T_HP measurements for HP propane dissolved in methanol-d₄ through the use of 10° rf pulses. (c) T₁ measurements for thermally polarized propane dissolved in methanol-d₄ by the inversion–recovery sequence.