Speaker
Description
X-ray Phase Contrast Imaging (XPCI) is a non-destructive imaging technique that enables imaging of weakly absorbing materials by exploiting the phase shifts introduced by the sample. One of the limitations of XPCI methods is the energy range at which they are operated, mostly below 50 keV. To image high-Z and thicker materials for industrial testing or security applications, it is essential to use high-energy X-rays due to their penetration power. However, operating at higher energies introduces challenges such as inefficiency of optical elements, decreased detector efficiency, and reduced refraction angles, which most XPCI methods measure due to their proportionality to phase shifts.
As the refraction angle scales as $\frac{1}{E^2}$, recovering sufficient signal at high energies requires optimising the experimental parameters such as increasing propagation distance between sample and detector. Increasing propagation distance requires a small focal spot to maintain low source blurring, which typically reduces flux and leads to long exposure times. Liquid Metal Jet (LMJ) sources address this by delivering an order of magnitude higher flux at high energies.
The choice of detector is critical as well. Photon counting detectors such as EIGER implement hybrid photon counting (HPC), detecting individual photons per pixel with zero readout noise and at high count rates [1]. At high energies, having low noise is essential to capture the weak phase contrast signal as all the sources of noise besides inherent Poisson noise are eliminated from the imaging process. Furthermore, CdTe sensors provide quantum efficiency above 60% up to 100 keV [2], making them well suited for high-energy applications. On the other hand, HPC detectors suffer from charge sharing, which affects the energy and spatial resolution of the detector [3]. The effect of charge sharing depends on the energy of the impinging photons, leading to loss of counts at low energies and double counting at high energies.
In this work, we present an experimental and theoretical study comparing the effects of propagation distance and energy on the contrast-to-noise ratio (CNR) and sensitivity of retrieved refraction profiles from an Edge Illumination (EI) setup, a non-interferometric XPCI method that uses highly attenuating masks to create sensitivity to phase effects [4]. We also analyse energy-binned refraction signals to evaluate detector performance across energy regimes and the energy dependence of the measured signal. Finally, by analysing the retrieved signals at various energy thresholds and comparing these with theoretical models, we assess the impact of charge sharing on the EI signal and explore potential correction strategies. Our results show that both CNR and sensitivity vary with propagation distance and energy as expected. The sensitivity of energy binned refraction signals reveals consistent detector behaviour across various energy bins, indicating that the decrease in the CNR is governed by the expected $\frac{1}{E^2}$, scaling of the refraction signal rather than detector performance degradation.
References
[1] Donath T, Trampari S, Wagner L, Jørgensen MRV, Gjørup FH, Checchia S, et al. Enhancing high-energy powder X-ray diffraction applications using a PILATUS4 CdTe detector. Journal of Synchrotron Radiation. 2025 Feb;32(Pt 2):378–384.
[2] Donath T, Sˇiˇsak Jung D, Burian M, Radicci V, Zambon P, Fitch AN, et al. EIGER2 hybrid-photon-counting X-ray detectors for advanced synchrotron diffraction experiments. Journal of Synchrotron Radiation. 2023 Jul;30(4):723–738.
[3] Fardin L, Giaccaglia C, Busca P, Bravin A. Characterization of a CdTe single-photon-counting detector for biomedical imaging applications. Physica Medica. 2023 Apr;108:102571.
[4] Olivo A, Arfelli F, Cantatore G, Longo R, Menk RH, Pani S, et al. An innovative digital imaging set-up allowing a low-dose approach to phase contrast applications in the medical field. Medical Physics. 2001 Aug;28(8):1610–1619.