Hyperpolarized 1H NMR Employing Low γ Nucleus for Spin Polarization Storage
Eduard Y. Chekmenev, Valerie A. Norton, Daniel P. Weitekamp and Pratip Bhattacharya
Here, we demonstrate the utility of low gamma nuclei for spin storage of hyperpolarization followed by proton detection, which theoretically can provide up to (gamma[1H]/gamma[X])2 gain in sensitivity in hyperpolarized biomedical MR. This is exemplified by hyperpolarized 1-13C sites of 2,2,3,3-tetrafluoropropyl 1-13C-propionate-d3 (TFPP), 13C T1 = 67 s in D2O, and 1-13C-succinate-d2, 13C T1 = 105 s in D2O, pH 11, using PASADENA. In a representative example, the spin polarization was stored on 13C for 24 and 70 s, respectively, while the samples were transferred from a low magnetic field polarizer operating at 1.76 mT to a 4.7 T animal MR scanner. Following sample delivery, the refocused INEPT pulse sequence was used to transfer spin polarization from 13C to protons with an efficiency of 50% for TFPP and 41% for 1-13C-succinate-d2 increasing the overall NMR sensitivity by a factor of 7.9 and 6.5, respectively. The low gamma nuclei exemplified here by 13C with a T1 of tens of seconds acts as an efficient spin polarization storage, while J-coupled protons are better for NMR detection.