New MRI Technology Uses Krypton Gas as Contrast Agent

While traditional MRI uses hydrogen protons in the body as molecular targets, this does not give a detailed picture of the lungs, since they are full of air. The new technique will make three dimensional (3D) imaging of the lungs possible, and could also be used with other inhaled, hyperpolarized, noble gases, such as helium and xenon-129.

The new method is made possible via catalytic hydrogen combustion, a process associated with clean energy related sciences. In the process, krypton-83 gas is mixed with molecular hydrogen as the buffer in laser spin-exchange optical pumping (SEOP). After laser pumping, the hydrogen gas is mixed with molecular oxygen, “exploding” it away in a controlled fashion via catalyzed combustion, leaving behind high-purity, hyperpolarized krypton gas. The study describing the catalytic process was published on March 9, 2016, in the Proceedings of the National Academy of Sciences of the United States of America (PNAS).

“Remarkably, the hyperpolarized state of krypton-83 ‘survives’ the combustion event. Water vapor, the sole product of the ‘clean’ hydrogen reaction, is easily removed through condensation, leaving behind the purified laser-polarized krypton-83 gas diluted only by small remaining quantities of harmless water vapor,” said senior author Prof. Thomas Meersmann, PhD, chair of translational imaging. “This development significantly improves the potential usefulness of laser-pumped krypton-83 as MRI contrast agent for clinical applications.”

The hyperpolarized state is very low spin temperature condition that is not in a thermal equilibrium with the temperature of the sample. Low spin temperature leads to high magnetization of the spin ensemble, which results in a very high nuclear magnetic resonance signal intensity. This eventually returns to the depolarized thermal equilibrium temperature. Of the quadrupolar noble gas isotopes, krypton-83 is most likely to serve as a surface sensitive MRI contrast agent, since it displays a slower relaxation compared to xenon as a result of its smaller electron cloud and its larger nuclear spin.

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