Signal enhancement of hyperpolarized 15 N sites in solution-increase in solid-state polarization at 3.35 T and prolongation of relaxation in deuterated water mixtures

Hyperpolarized N 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, N sites with directly bound protons were shown to be useful when dissolved in D O. The purpose of the current study was to further characterize and increase the visibility of such N sites in solutions that mimic an intravenous injection during the first cardiac pass in terms of their H O:D O composition. The T values of hyperpolarized N in [ N ]urea and [ N]NH Cl demonstrated similar dependences on the H O:D O composition of the solution, with a T of about 140 s in 100% D O, about twofold shortening in 90% and 80% D O, and about threefold shortening in 50% D O. [ C]urea was found to be a useful solid-state C marker for qualitative monitoring of the N polarization process in a commercial pre-clinical dDNP device. Adding trace amounts of Gd to the polarization formulation led to higher solid-state polarization of [ C]urea and to higher polarization levels of [ N ]urea in solution.