High-energy X-ray phase-contrast CT of an adult human chest phantom

TL;DR

This study assesses the feasibility of high-energy propagation-based X-ray phase-contrast CT for adult-scale lung imaging using the LungMan phantom at the Australian Synchrotron IMBL. By comparing a photon-counting detector (Eiger) and an integrating detector (Xineos) across 50–80 keV and propagation distances up to 7.5 m, the authors demonstrate detectable phase contrast with Eiger, even at high energies and relatively large pixel sizes. Phase-characterization confirms soft-tissue–equivalent LungMan materials match reference $\delta$ values, validating the phantom for PBI, while energy and distance optimization identifies $E\approx70$ keV and $\Delta\approx7.5\ \mathrm{m}$ as favorable conditions for adult lung imaging, albeit with practical constraints such as penumbral blur. These results constitute a first step toward clinical adult lung PBI at IMBL, informing detector choice, geometry, and dose considerations for future in vivo studies.

Abstract

Propagation-based phase-contrast X-ray imaging is a promising technique for in~vivo medical imaging, offering lower radiation doses than traditional attenuation-based imaging. Previous studies have focused on X-ray energies below 50 keV for small-animal imaging and mammography. Here, we investigate the feasibility of high-energy propagation-based computed tomography for human adult-scale lung imaging at the Australian Synchrotron's Imaging and Medical Beamline. This facility is uniquely positioned for human lung imaging, offering a large field of view, high X-ray energies, and supporting clinical infrastructure. We imaged an anthropomorphic chest phantom (LungMan) between 50 keV and 80 keV across the range of possible sample-to-detector distances, with a photon-counting and an integrating detector. Strong phase-contrast fringes were observed with the photon-counting detector, even at high X-ray energies and a large pixel size relative to previous work, whereas the integrating detector with lower spatial resolution showed no clear phase effects. Measured X-ray phase-shifting properties of LungMan aligned well with reference soft tissue values, validating the phantom for phase-contrast studies. Imaging quality assessments suggest an optimal configuration at approximately 70 keV and the longest available propagation distance of 7.5 m, indicating potential benefit in positioning the patient in an upstream hutch. This study represents the first step towards clinical adult lung imaging at the Australian Synchrotron.

Figures (9)

• Figure 1: Experimental setup in hutch 3B of the Imaging and Medical Beamline (IMBL). The CT stage can be moved along the beam path (shown in red). As Eiger is set back by 50 on the detector table, the propagation distances for Eiger datasets were always 50 more than for Xineos datasets. The inset images show (\ref{['fig:setup-tree']}) the tree insert, composed of a mediastinum with attached pulmonary vessels, and (\ref{['fig:setup-foam']}) the foam insert, while the inset diagram (\ref{['fig:setup-beampos']}) shows the approximate size and position of the beam on LungMan.
• Figure 2: Incident air kerma to local absorbed dose conversion coefficients for (\ref{['fig:dosedist-bone']}) cortical bone and (\ref{['fig:dosedist-st']}) soft tissue at 70.
• Figure 3: Incident air kerma to mean absorbed dose (MAD) conversion coefficients ($C_\text{CB}$ and $C_\text{ST}$) from Monte Carlo simulation.
• Figure 4: The fileswell algorithm for semi-automated line profiling. (\ref{['fig:fw-im']}) The input image and region of interest. (\ref{['fig:fw-threshold']}) Binary thresholding. (\ref{['fig:fw-holefill']}) Hole filling. (\ref{['fig:fw-selectregion']}) Selection of the largest region within the field of view. (\ref{['fig:fw-edges']}) Edge detection using the Canny algorithm. (\ref{['fig:fw-order']}) Ordering of the edge points using the travelling salesman algorithm. (\ref{['fig:fw-spline']}) Spline interpolation of the ordered edge points. (\ref{['fig:fw-differentiate']}) Differentiation of the spline to get the local gradients. (\ref{['fig:fw-profiles']}) Taking line profiles, that fit within the ROI, across the interface. (\ref{['fig:fw-lp']}) All line profiles across the interface. (\ref{['fig:fw-lp_aligned']}) Aligning the line profiles. (\ref{['fig:fw-lp_mean']}) Averaging to get the mean profile and the standard deviation of the points within that profile.
• Figure 5: Comparing features in flat-field corrected and stitched projections of LungMan taken with Eiger and Xineos. In the central image, Eiger contains the tree insert. It is a composite image, with each quadrant showing a whole-lung stitched projection with a respective detector and propagation distance. In addition, we show a small region of interest from images taken of Eiger containing the foam insert (the approximate position of the ROI is shown on the composite image). While phase fringes and speckle patterns clearly develop in the Eiger images taken at the longer propagation distance, they cannot be seen with the Xineos detector. Note that the images are stitched from approximately 35 tall projections in which the flat-field illumination strongly varied. In addition, the Eiger projections were taken with an exposure time three times longer than the Xineos projections. Therefore, the dose cannot be directly compared between the different images in this figure; the figure is included to show the qualitative features that were present. The reader is referred to \ref{['fig:eigerxineos-Q']} for a dose-matched and quantitative comparison of the two detectors.