Radio Frequency Sweeps at uT Fields for Parahydrogen Induced Polarization of Biomolecules

Magnetic resonance imaging of the metabolic processes within the human body opens up new methods of studying cancers. It is accomplished through the monitoring of the 13C NMR signal of a metabolite, which has an inherently low signal strength. Hyperpolarization, where parahydrogen is chemically added to an unsaturated precursor molecule, generating an entangled spin state in the product molecule, offers a solution. The spin-order of the hyperpolarized protons is converted into observable 13C magnetization using magnetic field sweeps. However, when using deuterated precursor molecules, the efficiency is severely reduced. We demonstrate that using a radio-frequency sweep, a 50% stronger signal can be measured compared to the protonated molecule. We demonstrate that the technique is robust and works for a large variety of molecules. Furthermore, we show that using optimal control can enhance the speed of polarization transfer, while avoiding transfer to fast relaxing spins.