Clinical dark-field chest radiography. Patient exposure and application for COVID-19-pneumonia

Chest radiography is commonly used in clinical routine for the initial assessment of the lung. However, its diagnostic sensitivity for the detection of pulmonary disorders such as pulmonary emphysema or fibrosis is rather low, especially in early stages of disease. Contrast formation is based on the attenuation of X-rays alone, while the air-filled lung itself is overlayed by surrounding tissue and bones. Dark-field radiography is a novel and promising interferometric X-ray imaging technique that provides additional contrast information in comparison to the conventional attenuation signal. Due to small-angle scattering of X-rays, the otherwise unresolvable microstructure of the imaged specimen can be visualized. Various animal models showed that the lung's alveolar structure can be well assessed with dark-field radiography, allowing for facilitated diagnosis of numerous pulmonary diseases. Recently, a clinical prototype system for dark-field chest radiography was commenced in operation and applied to human subjects for the first time. In this PhD project, the benefits and risks associated with dark-field chest radiography for patients were evaluated. An extensive risk analysis concerning the effective radiation dose a subject is exposed to, along with a comparison to regulatory dose levels, was conducted. As a central result, we found that the effective dose at the clinical dark-field radiography system is within the range of reported standard dose values for chest radiography, enabling further research on this method's potential in humans. Also, different exposure control methods were developed, validated with an anthropomorphic phantom, and evaluated for patient examinations. We have successfully implemented exposure control approaches that deliver images of diagnostic quality. After ensuring the safe application of dark-field radiography for patients, its benefits for the assessment of COVID-19-pneumonia were evaluated in comparison to conventional attenuation-based chest radiography. We found that dark-field imaging has a higher sensitivity for COVID-19-pneumonia than attenuation-based imaging. Moreover, the simultaneous display of both modalities is superior to dark-field imaging alone. Based on the results of the risk analysis and first imaging results concerning lung diseases within the range of this thesis, we are fully convinced that dark-field chest radiography complements and improves conventional radiography for the assessment of pulmonary disorders in a dose-compatible manner.