Hyperpolarization allows one to increase the NMR sensitivity by several orders of magnitude. The main drivers behind the development of hyperpolarization techniques are their biomedical applications. For example, the inhalation of hyperpolarized noble gases, such as 129Xe and 3He, enables functional imaging of lung diseases. However, highly specialized 129Xe and 3He MR equipment and software is required which is not available on conventional clinical MRI scanners. Therefore, 1H-hyperpolarized gases, e.g. propane, represent a promising alternative. Hyperpolarization of propane can be accomplished by pairwise addition of parahydrogen to propylene over heterogeneous catalyst.
Here, we present our recent results on hyperpolarization of propane gas. We developed propane polarizer that enables production of hyperpolarized propane on a clinical scale (production rate >0.3 L just in 2 s, that is more than an order of magnitude greater than that demonstrated previously). Importantly, high polarization levels (~1%) can be retained despite the increase in production rate, allowing stopped-flow slice-selective high-resolution 2D MRI visualization. It was demonstrated that at ~0.05 T magnetic field hyperpolarized propane occurs as a long-lived spin state, which lifetime TLLS is ~3 times greater than T1. The use of buffering gases leads to the increase of propane polarization despite slight TLLS decrease. Cryocollection of hyperpolarized propane, which can be employed for buffering gas separation, increases TLLS up to 14.7 s in the liquid state, which is higher than that of gaseous hyperpolarized propane at any pressure studied. We also explored feasibility of propane hyperpolarization via hydrogenation of cyclopropane with parahydrogen. 1H polarization up to 2.4% was obtained, that is several times greater than that obtained with propylene as a precursor. The resulting NMR signal enhancement was sufficient for 2D MRI despite relatively low chemical conversion of cyclopropane substrate.
This work was supported by Russian Science Foundation (grant #17-73-20030) and DOD CDMRP W81XWH-15-1-0271.