University of Texas at Arlington researcher Michael Nelson doesn't recall the specifics of the presentation, but he remembers the photo. It showed astronauts floating in space, wearing unusual gear called lower body negative-pressure pants, which simulate gravity's pull on the human body.
The image sparked an "aha" moment for Dr. Nelson: What if the same concept could be used to improve heart testing in an MRI?
During an exercise stress test inside an MRI machine, patients normally lie flat. That position causes more blood to return to the heart from the lower body, since gravity is no longer pulling it downward. This increases stroke volume—the amount of blood the heart pumps with each beat—which can make the heart appear to function more effectively, even in people with heart disease.
As a result, it becomes harder for doctors to detect real differences in heart performance between healthy and unhealthy patients.
Nelson and his team use the negative-pressure pants to solve that problem. By mimicking the effects of standing up, the pants reveal how the heart truly functions under stress. This patent-pending technology marks a major advancement in heart imaging, and UT Arlington is one of just a few places in the world exploring it.
"We've completely transformed the way we look at exercise cardiac MRI," Nelson said. "In my opinion, the recent developments we've made should become the new standard. You shouldn't be doing exercise cardiac MRI without lower body negative-pressure pants."
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The lower body negative-pressure pants are just one of several innovations Nelson and his team are developing to advance exercise-based MRI testing. In November 2024, UTA opened its $6.2 million Clinical Imaging Research Center (CIRC), which features a 3-Tesla MRI machine with a 70-centimeter bore that provides enough space for exercise studies. In another recent study, published in the American Journal of Physiology, the researchers showed that MRI can be used to measure venous oxygen levels—important indicators of how well the body is extracting oxygen from the blood—without inserting an invasive catheter.
Previously, doctors had to insert a catheter into the inferior vena cava, the body's largest vein, to get this kind of data. The new MRI technique avoids that invasive step—reducing risk for patients while still providing the same level of accuracy and reliability, said Richard Thompson, a professor at the University of Alberta and senior author of the study.
Why does that matter? By combining this venous oxygen data with cardiac output—how much blood the heart pumps per minute—Nelson's team can now calculate how much oxygen a person's body is actually using during exercise—a significant measure that can be used to predict the likelihood of future illness or risk of death.
Taken together, these advancements provide the foundation for a new generation of heart testing that's completely noninvasive, highly repeatable and powered entirely by MRI. In the past, researchers had to rely on patients using a stationary bike while wearing an oxygen mask attached to a metabolic cart and separate scans to image and evaluate the heart.
"Our initial proof-of-concept data clearly highlights the strength and promise of this approach," said Brandon Hathorn, a Ph.D. student in Nelson's Applied Physiology and Advanced Imaging Laboratory and lead author of a recently published article on the topic in the European Heart Journal.
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The negative-pressure pants, combined with the new noninvasive blood oxygenation method, represent groundbreaking developments in advancing MRI exercise-based heart testing.
"What's great about MRI is that it's completely safe—we could do one of these MRI stress tests every day, or every month," said Mark Haykowsky, a former UTA professor who is now at the University of Alberta and is a senior investigator on the project. "We've eliminated a lot of the risks since it's noninvasive and there's no ionizing radiation."
Ultimately, the research is critical to understanding why some people struggle with physical activity. Poor exercise capacity is not only a predictor of disease and death—it also impacts daily life, Nelson said, making even basic tasks like walking to the mailbox or vacuuming feel difficult. By identifying the specific causes of exercise intolerance, doctors can develop more targeted therapies to help improve it.
"Imagine feeling like you're working at your absolute maximum most of the day?" Nelson said. "Being able to noninvasively identify specific mechanisms limiting someone's capacity, whether it is the heart, the muscles, or both, will allow for targeted treatments to improve quality of life and longevity."
About The University of Texas at Arlington (UTA)
Celebrating its 130th anniversary in 2025, The University of Texas at Arlington is a growing public research university in the heart of the thriving Dallas-Fort Worth metroplex. With a student body of over 41,000, UTA is the second-largest institution in the University of Texas System, offering more than 180 undergraduate and graduate degree programs. Recognized as a Carnegie R-1 university, UTA stands among the nation's top 5% of institutions for research activity. UTA and its 280,000 alumni generate an annual economic impact of $28.8 billion for the state. The University has received the Innovation and Economic Prosperity designation from the Association of Public and Land Grant Universities and has earned recognition for its focus on student access and success, considered key drivers to economic growth and social progress for North Texas and beyond.
