LAUSR

Hyperpolarized 15N sites have been found to be promising for generating long‐lived hyperpolarized states in solution, and present a promising approach for utilizing dissolution‐dynamic nuclear polarization (dDNP)‐driven hyperpolarized MRI for imaging in biology and medicine. Specifically, 15N sites with directly bound protons were shown to be useful when dissolved in D2O. The purpose of the current study was to further characterize and increase the visibility of such 15N sites in solutions that mimic an intravenous injection during the first cardiac pass in terms of their H2O:D2O composition. The T1 values of hyperpolarized 15N in [15N2]urea and [15N]NH4Cl demonstrated similar dependences on the H2O:D2O composition of the solution, with a T1 of about 140 s in 100% D2O, about twofold shortening in 90% and 80% D2O, and about threefold shortening in 50% D2O. [13C]urea was found to be a useful solid‐state 13C marker for qualitative monitoring of the 15N polarization process in a commercial pre‐clinical dDNP device. Adding trace amounts of Gd3+ to the polarization formulation led to higher solid‐state polarization of [13C]urea and to higher polarization levels of [15N2]urea in solution.