PEPI Lab: a flexible compact multi-modal setup for X-ray phase-contrast and spectral imaging

Abstract

This paper presents a new flexible compact multi-modal imaging setup referred to as PEPI (Photon-counting Edge-illumination Phase-contrast imaging) Lab, which is based on the edge-illumination (EI) technique and a chromatic detector. The system enables both X-ray phase-contrast (XPCI) and spectral (XSI) imaging of samples on the centimeter scale. This work conceptually follows all the stages in its realization, from the design to the first imaging results. The setup can be operated in four different modes, i.e. photon-counting/conventional, spectral, double-mask EI, and single-mask EI, whereby the switch to any modality is fast, software controlled, and does not require any hardware modification or lengthy re-alignment procedures. The system specifications, ranging from the X-ray tube features to the mask material and aspect ratio, have been quantitatively studied and optimized through a dedicated Geant4 simulation platform, guiding the choice of the instrumentation. The realization of the imaging setup, both in terms of hardware and control software, is detailed and discussed with a focus on practical/experimental aspects. Flexibility and compactness (66 cm source-to-detector distance in EI) are ensured by dedicated motion stages, whereas spectral capabilities are enabled by the Pixirad-1/Pixie-III detector in combination with a tungsten anode X-ray source operating in the range 40–100 kVp. The stability of the system, when operated in EI, has been verified, and drifts leading to mask misalignment of less than 1 $$\upmu$$ μ m have been measured over a period of 54 h. The first imaging results, one for each modality, demonstrate that the system fulfills its design requirements. Specifically, XSI tomographic images of an iodine-based phantom demonstrate the system’s quantitativeness and sensibility to concentrations in the order of a few mg/ml. Planar XPCI images of a carpenter bee specimen, both in single and double-mask modes, demonstrate that refraction sensitivity (below 0.6 $$\upmu$$ μ rad in double-mask mode) is comparable with other XPCI systems based on microfocus sources. Phase CT capabilities have also been tested on a dedicated plastic phantom, where the phase channel yielded a 15-fold higher signal-to-noise ratio with respect to attenuation.

A Geant4 tool for edge-illumination X-ray phase-contrast imaging

“…The aim of the project is to combine the specific advantages of the detector, namely high efficiency, sharp response, and spectral capabilities, with the sensitivity to phase effects (i.e., refraction and ultra-small-angle scattering) enabled by EI. In order to define the optimal design of the experimental setup, a novel publicly available Geant4-based simulation platform (Geant4PEPI) has been developed [8]. Within this tool phase effects are simulated through a custom X-ray refraction process, that is not included in the available Geant4 releases, and an EI experimental setup is replicated including realistic source spatial and spectral distributions, geometry and compositions of samples and absorbing masks, and image acquisition procedures [9].…”

Edge-illumination spectral phase-contrast tomography

“…Raw projection images acquired at different positions of the illumination curve were processed via GPU-based Gaussian fitting to retrieve attenuation and differential phase signals (Przybylski et al 2017 , Brombal et al 2023a ). Integral phase projections were obtained from the differential phase via a Wiener-filter regularized phase-integration algorithm (Massimi et al 2020 ).…”

“…In this context, it is clear that the combination of spectral and phase-contrast techniques would bring both high visibility of low- Z biological tissues and effective separation of high- Z materials (contrast media). So far, due to the limited availability of phase-contrast systems equipped with spectral detectors, only a relatively small number of spectral phase contrast studies have been reported in the literature (Mechlem et al 2019 , Schaff et al 2020 , Astolfo et al 2023 , Brombal et al 2023a ). The most illustrative example is arguably the one provided by Ji et al ( 2020 ) where a GI system is coupled with a 100 μ m pixel size photon-counting detector.…”

Speckle-based imaging (SBI) applications with spectral photon counting detectors at the newly established OPTIMATO (OPTimal IMAging and TOmography) laboratory

“…As for other XPCI techniques, SBI has been first performed using coherent synchrotron sources. However, XPCI techniques can be adapted to laboratory facilities with quasi-coherent (micro-focus) sources, as reported in the literature [5][6][7]. To obtain optimal results in SBI, it is crucial to ensure the visibility of the speckles.…”