Unlike conventional X-ray imaging, which is based on absorption (attenuation) of X-rays as they pass through tissue, dark-field imaging visualizes X-ray scattering. This scattering occurs, for example, at interfaces between air and tissue. For this reason, the dark-field image is ideally suited for imaging of the lung: the basic structure of the lung is made up of many small air sacs (alveoli), where gas exchange between blood and breath is taking place. Thus, countless air-tissue interfaces exist within the lung. When passing through a healthy lung, X-ray radiation is therefore scattered in all directions, creating a strong dark-field signal.
During disease progression of pulmonary emphysema, the alveoli are gradually destroyed and the number of the air-tissue interfaces is reduced. X-rays passing through a lung that is affected by pulmonary emphysema are therefore scattered less. In animal studies, a significant signal decrease in the dark-field X-ray image of the lung was consequently noted. The signal strength of the dark-field image shows excellent correlation with the lung tissue's condition (see figure).
Thus, dark-field imaging can safely diagnose early pulmonary emphysema and allows classification into different levels of severity of the disease. This is not possible in conventional transmission imaging due to the low density of pulmonary tissue. In conventional radiography, the diagnosis "emphysema" usually cannot be made until a very advanced stage, when the lung is significantly overinflated leading to, for example, changed proportions of the bony chest wall, or a flattened diaphragm.
It is assumed that approximately 1,000,000 people in Germany suffer from emphysema, which mainly affects smokers over the age of 50. The destruction of alveoli leads to a reduced lung surface and blood oxygen levels decrease. As a result, patients suffer from shortness of breath, cough, blue-colored lips and fingernails and a barrel-shaped inflated chest. Emphysema cannot be cured, but optimal therapy can slow the progression of the disease significantly. An earlier diagnosis by dark-field imaging could lead to early and appropriate treatments, improving the quality of life and life expectancy of those affected.
Dark-field X-ray imaging may further result in additional, completely new applications in lung imaging. For example, it could be used in screening studies, follow-up examinations, or therapy monitoring - without the help of computed tomography, which is requires significantly more radiation.
The new X-ray technology is not yet applicable in clinical practice. So far, the superiority of the method for the diagnosis of pulmonary emphysema was only shown in living mice. A transfer of the results into a clinical application is the main goal of the current research activities.
This research is funded by the DFG Cluster of Excellence "Munich Center for Advanced Photonics" (MAP). Involved institutions include the Hospital of the University of Munich, Department of Clinical Radiology (Katharina Hellbach, Felix Meinel, Tobias Saam, Maximilian F. Reiser), the Technical University of Munich, Department of Physics (Andre Yaroshenko, Astrid Velroyen, Mark Mueller, Franz Pfeiffer), and the Helmholtz Zentrum Munich, Comprehensive Pneumology Center (Ali Önder Yildirim, Oliver Eickelberg).
original publication:
K. Hellbach, A. Yaroshenko, F. G. Meinel, A. Ö. Yildirim, T. M. Conlon, M. Bech, M. Müller, A. Velroyen, M. Notohamiprodjo, F. Bamberg, S. Auweter, M. Reiser, O. Eickelberg, and F. Pfeiffer
In Vivo Dark-Field Radiography for Early Diagnosis and Staging of Pulmonary Emphysema
Invest Radiol. (2015)