Lifetime of Para hydrogen in Aqueous Solutions and Human Blood

Molecular hydrogen has unique nuclear spin properties. Its nuclear spin isomer, para hydrogen ( p H 2 ), was instrumental in the early days of quantum mechanics and allows to boost the NMR signal by several orders of magnitude. p H 2‐ induced polarization (PHIP) is based on the survival of p H 2 spin order in solution, yet its lifetime has not been investigated in aqueous or biological media required for in vivo applications. Herein, we report longitudinal relaxation times ( T 1 ) and lifetimes of p H 2 ( τ P O C ) in methanol and water, with or without O 2 , NaCl, rhodium‐catalyst or human blood. Furthermore, we present a relaxation model that uses T 1 and τ P O Cfor more precise theoretical predictions of the H 2 spin state in PHIP experiments. All measured T 1 values were in the range of 1.4–2 s and τ P O Cvalues were of the order of 10–300 minutes. These relatively long lifetimes hold great promise for emerging in vivo implementations and applications of PHIP.