Diamonds May Hold the Future for MR Technologies

Researchers at Lawrence Berkeley National Laboratory (LBL; Berkeley, CA, USA) and the University of California (UC; Berkeley, USA) succeeded in demonstrating NMR hyperpolarization of carbon-13 nitrogen vacancy (NV) centers in diamond nuclei in arbitrary magnetic fields and crystal orientations, all at room-temperature. The signal of the hyperpolarized carbon-13 spins showed an enhancement of NMR/MRI signal sensitivity by many orders of magnitude above what is ordinarily possible with conventional NMR/MRI magnets at the same temperatures.

The researchers observed a bulk nuclear spin polarization of six-percent, which represents an NMR signal enhancement of approximately 170,000 times over the thermal equilibrium. The signal of the hyperpolarized spins was detected in situ, with a standard NMR probe, and without the need for sample shuttling or precise crystal orientation. Furthermore, the hyperpolarization was achieved with microwaves, rather than relying on precise magnetic fields for hyperpolarization transfer.

In earlier studies, the researchers demonstrated that a low-strength magnetic field could be used to transfer NV center electron spin polarization to nearby carbon-13 nuclei, resulting in hyperpolarized nuclei. This spin transference process—called dynamic nuclear polarization—had been used before to enhance NMR signals, but always in the presence of high-strength magnetic fields and cryogenic temperatures. These requirements have been eliminated by placing a permanent magnet near the diamond. The study describing the development process was published on December 7, 2015, in Nature Communications.

“In our new study we're using microwaves to match the energy between electrons and carbon-13 nuclei rather than a magnetic field, which removes some difficult restrictions on the strength and alignment of the magnetic field and makes our technique more easy to use,” said lead author Jonathan King, PhD, of LBL. “By eliminating the need for even a weak magnetic field, we're now able to make direct measurements of the bulk sample with NMR.”

The authors believe that the new diamond hyperpolarization technique based on optically polarized NV centers is far more robust and efficient than current methods, and should enable orders of magnitude sensitivity enhancement for NMR studies of solids and liquids, and especially biological systems that must be maintained at near ambient conditions.

Related Links:
US Lawrence Berkeley National Laboratory
University of California