What is the x-ray technology

New X-ray technologyRecognize lung diseases better

"With the doctors, they were actually always incredibly open and supportive. It was more like the work of convincing medical physics colleagues. At the beginning it was always said: 'It never works with a moving lung or a mouse and such a rotating, unsprung setup '. But you have to have a certain stubbornness. No blind stubbornness. Instead, you have to think ten times whether it works so physically. And if it does, then you have to stick with it. "

When Franz Pfeiffer began developing dark field x-rays for medical diagnostics in 2009 and 2010, he had to listen to a lot. The criticism was not by chance: since the 1980s there had been repeated attempts to use the advantages of phase contrast X-ray, which has long been used in materials research with synchrotron radiation, for medical imaging, explains the professor of biomedical physics at the Technical University of Munich. But many well-known X-ray machine manufacturers had failed. Franz Pfeiffer has shown that it can be done. The world's first dark field x-ray machine was approved for patients a year ago.

"The trick is that you have a completely new contrast modality that shows you the ability of scattering in every pixel. And that in turn is linked to microporosity. So if you have a lot of small fibers, a lot of small holes, a lot of porous structures - think You to a foam, to a lung, to bone structures - then there is a dark field signal. And in the end, information about the microstructure has been obtained, to which you have practically no access in normal absorption. "

Do not measure the absorption, but the scatter

Normal X-ray machines measure the absorption of X-rays as they pass through the body. Because different types of tissue swallow different amounts of X-ray light, X-rays are created as we know them - white structures on a milky background. With dark-field X-ray it is more complex to generate an image, because here it is not measured how strongly tissue absorbs the X-rays, but how strongly it takes them off course - because of the scattering at the interfaces between air and tissue. To do this, the smallest deflections have to be detected - so small that they change the position of the X-ray beam by just one millimeter after one kilometer.

"Ultimately, we do this by using lattice structures that are micrometers apart. So these are essentially pinholes or strip diaphragms that are placed one behind the other in the beam. From the 3 or 4 images we take, we can while we shift these grids slightly against each other by only a few nanometers, analyze exactly how an object has expanded this beam at a point. And this scattering is then the dark field signal. "

For imaging in the dark field, the X-ray light passes a total of three grids, each of which has different permeability, as well as the object that is to be examined. The X-ray detector then shows white structures on a dark background. Diseased tissue appears as shadowing because the number of air-tissue interfaces decreases and the X-rays are less scattered.

Well suited for lung tissue

Franz Pfeiffer and his colleague Christian David from the Paul Scherrer Institute in Villigen, Switzerland, realized early on that this grid-based structure could work in principle. The first studies with small tissue samples in the Munich laboratory provided the proof and in 2011 brought Franz Pfeiffer the Leibniz Prize of the German Research Foundation, endowed with 2.5 million euros. Around 2013, 2014 - after the scientist had obtained funding from the European Research Council - he started the first experiments on living mice. In the meantime, he and colleagues had developed and built the first small dark field X-ray machine for this purpose.

"This suddenly enabled us to look at many disease models in the mouse, for emphysema, for pulmonary fibrosis, for pneumonia, for lung cancer. And that has resulted in a medically important publication that has added value for the diagnosis of diseases that have just been listed. And that was an important milestone after the demonstration that it works in the laboratory. "

That ultimately won over the critics in the medical physics community. The physicist had cleared the decisive hurdle: he introduced a grille directly behind the X-ray tube. This means that the dark field works with a conventional, i.e. rather weak, radiation source. And a sophisticated algorithm corrects measurement errors that can arise from environmental influences. In 2015, Franz Pfeiffer was ready for an industrial partner to take over the further development. However, he decided to scale the system up even for clinical applications. Today the world's first prototype is at the Klinikum rechts der Isar. A first clinical study is currently underway.

The first corona patients were also examined

"We started with a study on chronic obstructive pulmonary disease, COPD for example, which is caused by air pollution, for example. And we see that we are getting a very good signal and are in the process of publishing these first results. Corona then came in between and we put the COPD study on hold for safety reasons. We then started with corona patients, a total of five or six. But that's not enough for reliable statistics. "

It is difficult to say when the dark field x-ray will really make an impact in everyday hospital life. The first collaborations with X-ray machine manufacturers have started. Franz Pfeiffer believes that this could happen in university hospitals in the next one to three years. The advantages are obvious: Because the images are "sharper" than conventional X-rays, serious lung diseases, perhaps at some point lung cancer, could be diagnosed much earlier. In addition, the radiation dose is around 100 times lower than with computed tomography.

"And then of course the next stage of development would be to build a dark-field CT. I think that in five, six, seven years we will be as far as we are now with classic 2-D X-rays."