Fig 1.
Human X-ray dark-field prototype chest scanner.
(A) The X-ray chest scanner combines a three-grating arrangement (with an oblong active area) with a continuous line-scanning approach, with the purpose of imaging an entire human thorax. By scanning the active area over the field of view, every pixel is sampled at various phases of the Moiré pattern, allowing retrieval of attenuation, differential-phase, and dark-field information. In order to simulate in-vivo conditions and demonstrate clinical relevance of the presented results, tracheal intubation was performed on the deceased body and the lungs were inflated at 23 mbar during measurement. (B) X-ray dark-field contrast is generated by ultra small-angle scattering for instance at air-tissue interfaces of lung alveoli. Scattering causes blurring (red) of the initially well-delimited (black) intensity pattern generated by G1 resulting in a reduction of the measured visibility. Note that several slit sources contribute to the intensity value at any specific location in front of G2. For sake of simplicity, only a few rays passing trough one G1 slot are shown for illustrational purposes.
Fig 2.
Complementarity of X-ray attenuation and dark-field radiography.
X-ray attenuation (A) and dark-field (B) signal of dry (upper) and water drenched (lower) open cell melamine sponges. Similar to the human lung, a fine-pored melamine sponge comprises thousands of air-tissue interfaces and causes strong ultra small-angle X-ray scattering and therefore exhibits a distinct dark-field signal. At the same time, comprising porous structures, both lung and sponge yield small overall densities and appear radiolucent in the attenuation channel. When drenching the foam, air is displaced by water resulting in a high contrast in the attenuation channel due to stronger attenuation in comparison to air. Simultaneously, the interfaces become neutralized, explaining an inversion of both contrast modalities. The image acquisition protocol except for the tube current was similar to the one of the dead body scan (70 kVp, 100mA, 20 ms exposure time per pulse, 12 Hz pulse frequency, 3x3 pixel binning).
Fig 3.
Dark-field and conventional human chest radiography images of a deceased body.
Anteroposterior (AP) X-ray dark-field (A) and absorption (B) contrast images acquired with the scanner described in the materials and methods section. We measured a slight decrease in the dark-field signal intensity in the regions highlighted by the marker, indicating an edema (consistent with the findings in the autopsy and CT investigation, see Fig 3). This behaviour illustrates the signal formation mechanism, because the water in the lung reduces the contrast between the air-tissue interfaces, and subsequently reduces the ultra small-angle scattering (dark-field) signal.
Fig 4.
Computed tomography (CT) human chest images of a deceased body showing pulmonary edema due to cardiac failure.
Coronal CT image (A) at a level dorsal to the tracheal bifurcation and axial CT image (B) of the lower lobes. The pulmonary edema indicated by the markers presents as diffuse ground-glass opacities with a predominant perihilar distribution. Both images: 3 mm slice thickness, window level -600 HU, window width 1700 HU.