Dark-Field Chest X-rays Could Improve Diagnosis, Early Detection

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by Marta Figueiredo PhD |

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Dark-field chest X-ray imaging provides greater detail of lung microstructure than standard chest X-rays, and allows for the accurate diagnosis of chronic obstructive pulmonary disease (COPD), a study shows.

“In the future dark-field X-rays could help improve early detection of COPD and other respiratory ailments,” Alexander Fingerle, MD, of the Technical University of Munich (TUM)’s university hospital Klinikum rechts der Isar, in Germany, and the study’s co-first author, said in a press release.

“Given the close connection between the alveolar structure and the functional condition of the lung, this ability [to provide additional information on lung microstructure] is of great significance for pulmonary medicine,” Fingerle said.

Importantly, Fingerle and the research team noted, the new technique uses 50 times less radiation than thorax CT scans, supporting its broad use as an effective screening and follow-up tool.

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Until now, CT scans provided the most relevant lung information for a COPD diagnosis, but were not globally recommended due to their associated high radiation exposure.

These findings suggest that dark-field chest X-rays offer “a chance to significantly improve the early detection of lung diseases and at the same time to implement [such X-rays] on a wider basis than before,” said Franz Pfeiffer, PhD, the study’s senior author and director of TUM’s Munich Institute of Biomedical Engineering.

The study, “X-ray dark-field chest imaging for detection and quantification of emphysema in patients with chronic obstructive pulmonary disease: a diagnostic accuracy study,” was published in The Lancet Digital Health.

COPD is characterized by excessive and sustained airway inflammation and lung tissue remodeling, often resulting in the progressive destruction of alveoli and the formation of air-filled cavities or spaces, two hallmark features of emphysema. Alveoli are the tiny air sacs that are responsible for exchanging oxygen and carbon dioxide in the lungs.

While chest X-rays are typically the first diagnostic tool for lung diseases, they lack sensitivity to detect emphysema. CT imaging, which collects several images from different directions to generate 3D images, is a validated technique to assess the presence, extent, and pattern of emphysema.

However, it is not widely used for the diagnosis and management of mild to moderate COPD due to its high radiation exposure.

As such, “a low-dose, fast, and inexpensive option for early detection of respiratory diseases and follow-ups is still lacking,” the researchers wrote, adding that “the novel method of x-ray dark-field chest imaging might fill this gap.”

In contrast to conventional X-ray imaging, which measures the attenuation of X-rays as they go through tissues, dark-field imaging harnesses the wave properties of X-rays. Specifically, the new system detects the signal of ultrasmall-angle scattering that takes place in water-to-air transitions in the alveolar structure of the lungs.

In the resulting image, the lungs’ microstructure appears bright in a dark background — hence the name dark-field — as the space around the lungs has no matter to scatter X-rays.

“The X-ray dark-field signal is particularly strong for interfaces between air and tissue,” Pfeiffer said.

“This makes it possible for a dark-field X-ray image of the lung to clearly distinguish between intact alveoli, i.e. those filled with air, and regions in which less intact alveoli exist,” Pfeiffer said.

In addition, given its single exposure (similar to conventional X-rays), the new method is expected to reduce radiation exposure “by a factor of fifty” relative to chest CT, Pfeiffer noted.

By “enabling the assessment of microstructural changes in lung [tissue], this technique presents a more sensitive alternative to conventional chest x-rays, and yet requires only a fraction of the dose applied in CT,” the researchers wrote.

However, its diagnostic performance in a clinical setting had not been tested before.

To address this, Pfeiffer and his team compared the diagnostic performance of dark-field chest X-rays against conventional chest CT scans at assessing emphysema in 77 adults who had undergone a medically indicated chest CT. All were white, 71% (47) were male, and their average age was 64.9.

The participants — enrolled between October 2018 and December 2019 — underwent CT, lung function testing, and dark-field examination, most commonly on the same day.

Dark-field examination was conducted through a new system conceived and built by the researchers, which allows healthcare professionals to get both dark-field and attenuation x-ray images of the thorax.

Results from the CT images showed that 45% of the patients had no signs of emphysema and 25% showed trace emphysema. Further, 12% had mild emphysema, 9% exhibited moderate emphysema, 8% had confluent emphysema, and one (1%) had advanced destructive emphysema.

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Emphysema assessment based on dark-field chest x-ray yielded consistent conclusions with those based on CT scans and showed greater diagnostic performance than conventional clinical tests of emphysema.

Notably, the dark-field signal also yielded a stronger, significant association with lung diffusion capacity, compared with CT-based parameters. Lung diffusion capacity refers to how well oxygen and carbon dioxide are transferred to the bloodstream and is strongly dependent on alveolar surface area.

The study demonstrated that “dark-field chest radiography can technically and physically be translated to an application in humans using readily available x-ray imaging hardware and acceptable exposure doses,” the researchers wrote.

“Providing detailed information on lung micromorphology, dark-field chest radiography could serve as a low-dose imaging tool enabling periodic examinations to help resolve the prevalent condition of underdiagnosed COPD,” they wrote.

Given their preliminary nature, these findings must be confirmed in a larger, multi-ethnic group of patients, the team emphasized. Pfeiffer hopes these early results will accelerate the launch of additional clinical studies and the development of marketable devices that use this method.

The team believes that the dark-field chest X-ray system can be produced and used at a large scale, as it requires standard X-ray imaging components and is operated similarly to conventional X-ray systems.

Since this method does not provide information exclusive to emphysema, it also may be useful to diagnose and monitor other lung conditions, such as fibrosis, cancer, collapsed lung, called pneumothorax, or pneumonia, including COVID-19-related pneumonia.

Still, researchers noted the system requires patients to hold their breath for seven seconds during acquisition, which might be challenging for those with poorer lung function and therefore, represents a limitation that requires further development.