Initial Characterization of Dark-Field CT on a Clinical Gantry

Abstract

X-ray computed tomography (CT) is an important non-destructive imaging technique, particularly in clinical diagnostics. Even with the latest innovations like dual-energy and photon-counting CT, the image contrast is solely generated from attenuation in the tissue. An extension -fully compatible with these novelties -is darkfield CT, which retrieves an additional, so-called dark-field contrast. Unlike the attenuation channel, the dark-field channel is sensitive to tissue microstructure and porosity below the resolution of the imaging system, which allows additional insights into the health of the lung tissue or the structure of calcifications. The potential clinical value has been demonstrated in several preclinical studies and recently also in radiography patient studies. Just recently the first dark-field CT for the human body was established at the Technical University of Munich and in this paper, we discuss the performance of this prototype. We evaluate the interferometer components and the imposed challenges that the integration into the CT gantry brings by comparing the results to simulations and measurements at a laboratory setup. The influence of the clinical X-ray source on the Talbot-Lau interferometer and the impact of vibrations, which are immanent on the clinical CT gantry, are analyzed in detail to reveal their characteristic frequencies and origin. A beam hardening correction is introduced as an important step to adapt to the poly-chromatic spectrum and make quantitative dark-field imaging possible. We close with an analysis of the image resolution and the applied patient dose, and conclude that the performance is sufficient to suggest initial patient studies using the presented dark-field CT system.

Design of a Talbot phase-contrast microscopy imaging system with a digital detector for laser-driven X-ray backlighter sources

“…To achieve a high magnification, the micro-structured sample 3 is placed close to the backlighter. The phase grating 𝐺 1 5 and the absorption grating 𝐺 2 6 , are placed downstream of the object. The X-rays are finally detected with a pixelated detector 7 .…”

“…Being sensitive to the refraction of X-ray has the potential to better discriminate low-Z elements or small density contrasts [2]. Consequently, it is being intensively investigated for medical imaging of soft tissues [3][4][5], as well as non-destructive testing [6,7]. Currently the propagation-based approach [8] and the grating-based approach [9][10][11][12][13] are investigated for high energy density (HED) experiments.…”

Advancing x-ray dark-field imaging for human-scale applications: helical CT and surview imaging

“…This, in turn, affects the accuracy of the fitting outcome. Unlike traditional laboratory setups where the necessary phase sampling is achieved through controlled steps of the gratings, our prototype operates differently as described by Viermetz: 13 In our approach, we create a spatio-temporal modulation of the fringe pattern by harnessing inherent system vibrations that move the gratings. Additionally, we fine-tune a Moiré fringe pattern on the detector, resulting in a spatial gradient in the interferometer phase.…”

Bottom-up Gold Filling of Trenches in Curved Wafers

“…11 in Ref. 22). The sensitivity and imaging quality of XGI systems are directly related to the pitch, aspect ratio and metal-fill of their gratings.…”

“…Correspondingly good performance (i.e., "visibility") of the Au-filled gratings, [5][6][7] as well as X-ray phase contrast imaging of biological samples, 5,6 demonstrated the potential for biomedical applications of these gratings, applications that have been explored previously using gratings filled by other processes. [17][18][19][20][21][22][23] Key characteristics of gratings for XGI are the grating size, which determines the field of view of the imaging system, uniformity of trench pitch and quantity of Au fill in the silicon template. Uniformity of pitch obtained through the widely used X-LIGA process is not good, which decreases the visibility in XGI, particularly for large focal spots (see for example Fig.…”