Xenon MRI Brings Lungs Into Focus
To millions across the country, a working knowledge of medical diagnostics comes from the TV dramas that make short work of identifying the problem with a patient and jump to devising a treatment right away. In reality, however, that first step can sometimes rely on a number of cutting-edge technologies that do not produce as clear of a picture as the clinician would like. Take lung imaging, for example; subject to a number of well-known ailments, including Covid-19, getting high-resolution pictures of this vital organ is notoriously difficult. Over two million Canadians live with the debilitating effects of Chronic Obstructive Pulmonary Disease (COPD), which increases in incidence with age. Meanwhile, patients with bronchopulmonary dysplasia, a condition affecting prematurely born infants, can suffer for their entire lives from complications and even require a lung transplant by their twenties.
One of the major complicating factors when it comes to diagnosing lung conditions is the nature of the organ itself. The lungs fill a large volume in the chest cavity, but, like a balloon, the actual tissues are extremely thin. The outer structure of the lung is only a few millimetres thick, and the complex inner membranes are up to a thousand times thinner. This means that for a diagnostic imaging device, like a standard MRI, the lungs appear as a black hole in the middle of the torso. Another commonly used device, the CT scanner, can give a static, anatomical image but cannot elucidate how well the lung is functioning. To make matters more difficult, the CT scanner gives off too much radiation to be used on the neonates and young adults who need them the most. Taken together, the diagnostic imaging repertoire for lungs is severely limited; as we develop novel treatments for these well-known conditions, clinicians need more advanced tools to ensure the best outcomes for their patients.
Developing a promising new approach to this issue is Alexei Ouriadov of the Department of Physics and Astronomy at Western University. His lab is developing a unique type of MRI imaging method using hyperpolarized xenon gas, such that lungs no longer appear as black holes. “A patient can inhale this xenon gas blend and hold their breath for ten seconds. In that time, we can take a xenon MRI image and get an incredible amount of information about the lung structure and function that was, up until recently, impossible,” explains Ouriadov. His group’s use of this naturally abundant gas gives a feasible solution to the challenge of lung MRI. “We’ve helped to set up trial programs at hospitals in London, Thunder Bay, Hamilton, and Vancouver.”
As the gas enters the patient’s lungs, it diffuses through the lung tissue, just like oxygen does when we breathe. Unlike oxygen, however, the Ouriadov group’s hyperpolarized gas shows up in the MRI image. “All of a sudden, the lung tissues are bright and sharp,” he says, “And because the xenon is visible to an MRI, we can even visualize how it moves in the blood and perfuses the organs of the body.” Xenon is an inert gas, meaning that it does not react with the body tissues; as it is used here, it allows for a dynamic series of images to be taken, which highlight the gas exchange functionality of the lungs and not just their anatomy, akin to the contrast dyes used to visualize blood vessels.
Ouriadov and his colleagues’ recent discoveries in the use of hyperpolarized xenon are also significant because of their usability. Alternative research in this area uses a rare, radioactive isotope of oxygen costing several hundred dollars per tablespoon; the average patient needs about half a cup of gas for a scan. Xenon gas occurs naturally in large amounts, meaning that costs work out to about $50 per patient. Ouriadov’s group is continuing their clinical rollout of this novel diagnostic tool to two more hospitals in Canada in the coming year. The group and their collaborators throughout Ontario are also using their xenon MRI to assess lung structure and function of Covid-19 survivors over a period of two years following initial infection. The mainstream use of hyperpolarized xenon gas MR imaging will bring a much-needed spotlight to the black box in our chests.