X-ray images have played a crucial role in medical diagnostics for more than a century, especially now as they are used as a first-line tool to diagnose or screen for COVID-19. Researchers at the Technical University of Munich (TUM), led by Franz Pfeiffer, Professor for Biomedical Physics and Director of TUM’s Munich School of BioEngnieering, first presented a dark-field x-ray method in 2008 and after extensive research and development, they are now able to present a device, which is suitable for examining patients.
The difference between conventional x-ray imaging and the new method is that the conventional method shows the attenuation of x-rays on their way through tissue, while the dark-field method focuses on the small share of the x-ray light which is scattered, i.e. diverted from its straight path.
The new method thus uses the physical phenomenon of scattering in a way similar to long-established dark-field microscopy technologies using visible light. They make it possible to clearly visualize objects which are for the most part transparent and which appear in the darkfield microscope as clear structures in front of a dark background, giving dark-field microscopy its name.
A total of three gratings are used in dark-field imaging with x-rays. The x-rays are produced by a conventional x-ray tube, pass through the three gratings and are then registered by a detector. The detector replaces the x-ray film of the classic x-ray image and works in a manner similar to the chip in a digital camera. Because of the short wavelength of the x-rays, the lines of the gratings are only a few micrometers (thousandths of a millimeter) wide. During an examination, the patient is located between the second and third grating. The x-ray detector then receives a conventional x-ray image which is overlaid with a pattern of fringes having a width of several millimeters. The scattering weakens this additional pattern so that it is weaker in the parts of the image which visualize areas of the body where much light is diverted by scattering.
Additionally, the new method is designed to clearly identify abnormalities typical of the illness and involves a significantly lower radiation dose than the computed tomography methods currently in use. This is because the new technology requires only a single image per patient, while computed tomography requires a large number of individual images taken from various angles.
With the coronavirus still being present in our environment, it is safe to assume that the demand for cost-effective, reliable and low-impact Covid-19 diagnostics will only increase. For that reason, the Federal Office for Radiation Protection (Bundesamt für Strahlenschutz) has issued its approval on the device and testing is set to begin within the next weeks.