Researchers at Sir Peter Mansfield Imaging Centre in the UK have developed a process of using an inhalable contrast agent made out of the noble gas krypton for MR imaging. Krypton is a renewable resource obtained from the atmosphere, but it has previously been difficult to produce.

“There is a large variety of pulmonary disease affecting the life of patients, but also with huge impact on the economy,” Thomas Meersmann, professor and chair in translational imaging at the facility, told HCB News. “Hyperpolarized noble gas MRI will enable pulmonary disease identification, the study of disease progression and its intervention, and will be very valuable for stratified medicine by identifying patient subgroups.”

Traditional MR uses hydrogen protons in the body as molecular targets to get a picture of tissue, but it does not provide a detailed view of the lungs since they are full of air. However, the krypton gas contrast agent makes the spaces inside the lungs show up on an MR scan.
The noble gases xenon and helium can also be used for that purpose, but helium is not practical because it is too scarce for widespread hospital usage. Over the past decade, a number of clinical applications have been reported using xenon as a contrast agent for lung function and it is now moving beyond various trials and testing phases.

The researchers are interested in using both hyperpolarized krypton and xenon together for pulmonary MR.

“The MRI contrast generated with hyperpolarized krypton is very different in nature compared to the contrast generated with hyperpolarized xenon, and the two gases will provide complementary information,” said Meersmann. “The combined usage of xenon and krypton will improve the diagnosis value of the overall methodology.”

One of the issues with the noble gases was that they weren't retaining their hyperpolarized state for long enough for the gas to be inhaled, held in the lungs and scanned. But the researchers have solved that by using a technique called catalytic hydrogen combustion, which is usually used for clean energy-related sciences.

To hyperpolarize the krypton gas, they dilute it in molecular hydrogen gas and it undergoes laser treatment. The hydrogen gas is then mixed with molecular oxygen and it explodes in a safe and controlled way through a catalyzed combustion reaction.

The hyperpolarized state of krypton “survives” the combustion and water vapor, which is the sole product of the hydrogen reaction, is easily removed through condensation. So what's left behind is the purified laser-polarized krypton gas diluted by only a small amount of the water vapor.

The technique can also be used to hyperpolarize xenon as well, and may it be a cheaper and easier way to produce this contrast agent.

Since MR scanners can be found in almost all hospitals, Meersmann believes that the impact of hyperpolarized noble gas (krypton and xenon) MR on pulmonary health care will be very high. Many existing MRs can be upgraded to accommodate it.

“Like general MRI, hyperpolarized MRI won't be cheap and it will not be required for all (pulmonary) diagnostics. However, for a variety of applications it will be without alternatives and competition,” said Meersmann.

But for now, hyperpolarized noble gas MR is still mainly confined to specialized research centers. Meersmann believes that the production technology used to create the gases needs to be more widely available.

“For our methodology to become to become 'a standard in pulmonary health care and research', we need to move this method from the developmental phase toward a production phase,” he said.

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