NIH researchers can maintain image quality from different scanning systems while reducing or avoiding radiation exposure
When doctors want detailed images of the lungs, more often than not they turn to chest CT scans. Over the years these scans have been particularly useful in diagnosing lung diseases—so useful, in fact, that in the United States, around 80 million people get them every year.
The problem: radiation doses for CT scans can be hundreds of times higher than conventional X-rays. And that has led to debates within the scientific community about whether the diagnostic benefits outweigh the cancer-related health risks that come with high-dose radiation exposure.
Now, a pair of studies funded by the National Heart, Lung, and Blood Institute (NHLBI) have shown that it is possible to maintain good image quality when testing for certain lung diseases, while dramatically reducing radiation exposure—or, in the case of MRI, avoiding it altogether.
One of the studies was led by Marcus Chen, M.D., Assistant Clinical Investigator who leads the Cardiovascular CT Program at NHLBI. The other, using low-field MRI, was led by Adrienne Campbell-Washburn, Ph.D., a staff scientist who leads the MRI Technology Program.
Seven years ago Chen and his team developed a novel scanning technique that could dramatically reduce the use of radiation during cardiac CT scans. That development prompted a collaboration with Chen’s colleagues in the Pulmonary Branch of NHLBI’s Division of Intramural Research (DIR). Their goal: to find out if the same technique could work for people with a rare lung disease called LAM, or lymphangioleiomyomatosis.
Characterized by lung cysts that prevent air from moving freely in and out of the lungs, LAM is typically diagnosed in young women who, because of the nature of the disease, need imaging over their lifetimes, which often means long-term radiation exposure.
So Chen and his colleagues decided to clinically test the use of ultra low-dose chest CT—that’s a scan with nearly 95% less radiation than a standard low-dose scan. They scanned 105 people with LAM twice—the first using chest CT scans at a standard radiation dose, the second using an ultra-low dose.
Eight computer processors at the radiologists’ workstation worked in parallel to quickly render trillions of calculations per second needed to convert the large amounts of raw image data from the scan into visible pictures, Chen explained at a recent forum marking the Division of Lung Disease’s 50th anniversary.
“If the picture produced was not what we expected, the scanner repeated the process and the processors refined the picture again and again over time,” he said.
Once his team has the lung images, they used a “cyst score” as a way to validate the CT scans and quantify the number and volume of cysts in the lungs. When they compared ultra-low-dose scans and standard CT scans in their study, the researchers found that both techniques produced very similar scores.
The results, Chen said, were promising, as they showed that it is possible to significantly reduce radiation while retaining the ability to monitor disease progression in people with LAM.
But soon, as Campbell-Washburn of NHLBI’s MRI Technology Program has found, some patients with lung disease may be able to take advantage of radiation-free alternatives such as MRI. Her study showed how this common technology, typically used to image the brain and other structures, could prove to be a viable way to characterize the lung tissue and measure lung function.
“MRI has been difficult for imaging lung disease because the lungs would show up as a big black hole in the image,” Campbell-Washburn said. “But we can now easily see the lung structure using our high-performance, low field MRI system.”
Getting to this point was not easy. That’s because over the last 30 years MRI systems have been built with increasingly higher magnetic field strengths, mainly to get clearer images of the brain.
But higher magnetic field strengths pose problems for lung imaging. So Campbell-Washburn had an idea: revisit the low magnetic field strength (0.55 Tesla, compared to the standard clinical strengths of 1.5T and 3T) and incorporate modern hardware, advanced imaging methods, and contemporary computational power. She did just that and has produced a new configuration of high performing, low-field MRI systems.
To prove the system’s capabilities, Campbell-Washburn and her team imaged the same person with LAM using a standard MRI and again using the low-field MRI.
“We could very clearly see the tissue structure and the lung cysts,” with the low-field MRI, Campbell-Washburn said. In fact, she added, the images were much better than the ones from the standard MRI system, which “had very little signal and produced images that were blurred and distorted.”
That means with low-field MRI, it is easier to measure lung function along with lung structure, and to characterize the composition of lung tissue and pathology, Campbell-Washburn said. Her study also showed that oxygen can be used more effectively as a contrast agent with this system.
Researchers are still clinically evaluating both imaging systems—low-field MRI and ultra low-dose chest CT—with hopes of giving people with lung disease more options that lead to better treatment and outcomes.
“Ultra low-dose chest CT has the potential to increase patient safety and change the risk-benefit ratio for people with LAM, allowing more frequent follow-ups,” Chen said. “While this could be beneficial for people with LAM, the lessons learned could translate to other lung diseases like COPD and cystic fibrosis.”
Similarly, Campbell-Washburn envisions the new generation of low-field MRI being used for a variety of clinical applications, in addition to pinpointing and diagnosing lung diseases.
“This new system could allow us to do MRI-guided invasive procedures and image other parts of the body,” she said. “I’m excited to see how we can further use the system in innovative ways.”