Spectral and phase-contrast imaging with a compact multimodal imaging system

10:50 – 11:10 BST, 17 July 2024 ‐ 20 mins

Luca Brombal

Owing to the advent of energy-sensitive detectors and phase-sensitive techniques with reduced coherence requirements, both X-ray spectral imaging (XSI) and X-ray phase-contrast imaging (XPCI) are now viable options for compact laboratory setups. 
Specifically, small-pixel (<100 µm) photon-counting detectors equipped with multiple energy thresholds and effective charge-sharing compensation mechanisms enable the acquisition of energy-binned images at high spatial resolution. By exploiting the energy dependence of the attenuation coefficient of different materials, these images are used to perform material decomposition, yielding quantitative density maps of chosen basis materials. Being based on X-ray attenuation, XSI has a limited ability to capture details featuring a poor attenuation contrast (i.e., low-Z materials). 
This limitation can be overcome by XPCI. Except for propagation-based imaging, all laboratory XPCI techniques make use of some X-ray wavefront marker or modulator. Both attenuation and (differential) phase signals are extracted based on the modification of the detected modulation pattern induced by the sample. Regardless of the employed technique, attenuation and (integrated) phase can be used, similarly to energy-binned images, as input to material decomposition algorithms. This approach is particularly suited for soft tissues and light materials, while it can be outperformed by XSI when dealing with high-Z materials with distinctive attenuation features (e.g., K-edges of contrast media). 
In this context, a joint use of spectral and phase-contrast imaging can offer quantification and visibility of both high-Z and low-Z materials. In this talk, one example of the implementation of both XSI and XPCI within a new compact multimodal X-ray imaging will be presented. The system is based on a spectral detector with a 62 µm pixel size and it integrates the edge-illumination technique. Spectral, phase-contrast, and spectral-phase contrast images of biological samples will be presented, along with demonstrations of material decomposition techniques and de-noising algorithms. The limitations of the current approach and potential future advancements will be discussed.