COVID-19 and beyond: a deeper look into the lungs with dark-field X-rays

Imaging reaches its limits when it comes to looking at the lungs: Alveoli are tiny, balloon-shaped air sacs in our lungs. These tissue structures are micrometers in diameter and currently cannot be visualized directly. Meanwhile, they exhibit early changes prompted by lung diseases such as COVID-19. Dark-field X-ray images could visualize these signs in the future.

In this MEDICA-tradefair.com interview, Prof. Franz Pfeiffer explains how dark-field X-ray imaging works and how it can help diagnose different types of lung disorders.

Prof. Pfeiffer, what is dark-field X-ray technology?

Prof. Franz Pfeiffer: Dark-field X-ray imaging is a novel contrast modality to generate image signals in X-ray images. One can take light microscopy as an example. It also has different mechanisms to generate image contrast: the absorption of light waves, their scattering or phase shift. The same applies to X-rays – which are also a type of light but with a shorter wavelength. Traditional X-ray imaging utilizes the conventional absorption of X-rays by the tissue, while dark-field technology visualizes the scattering of X-rays in tissue. This gives us complementary contrasts. The images are basically dark at first. The structures appear as bright images on the dark background where the X-rays are scattered. This is where the name comes from.

You conducted a study with COVID-19 patients. How did dark-field technology benefit you in this setting?

Pfeiffer: The scattering allows us to visualize tiny structures. Compare this to tiny particles in the air, such as smoke or fog: while we do not see them directly, we see their scattering of light. This method enables us to see the alveoli, the tiny air sacs in the lungs. Lung diseases begin on the microscopic scale. This applies to COVID-19, pneumonia, and chronic obstructive pulmonary disease (or COPD). We see changes in the scattering if the alveoli change because of a disease. With COVID-19, the alveoli partially embed fluid and change their structure. This gives us information on a scale we could not visualize with conventional X-rays in the hospital.

How does this add value to the diagnostic process?

Pfeiffer: The technique has a significantly higher sensitivity for early changes, allowing us to detect COVID-19 better than we would via conventional X-ray imaging. This gives us a "high resolution" image of the tissue as it were – like a histological section you examine as a pathology slide under the microscope, except you view it inside the patient.

What prompted this development originally?

Pfeiffer: We originally discovered this contrast modality over twelve years ago and studied it for microscopic applications on tissue samples. Six or seven years ago, we developed a prototype for small animal imaging, which worked well. This prompted us to progressively lay the technical foundation to transfer the concept to humans. The University Hospital rechts der Isar ("Klinikum rechts der Isar") of the Technical University of Munich now features the first prototype that is approved for human use. We are using it to conduct the first clinical trials.

What other possible applications do you see for the technology?

Pfeiffer: The radiologists who apply it or learn about it at conferences primarily view it as a technique to diagnose different lung disorders and assist follow-up care. It is obviously a big field, starting with COVID-19 and Long COVID support and monitoring, ranging to other lung diseases such as COPD or pulmonary fibrosis. It could also facilitate the accuracy of lung cancer screening.

Needless to say, X-ray imaging applications beyond the lungs are also a conceivable option. One could use other contrast materials aside from iodine, which would protect the kidneys. However, research has not yet progressed to that point.