On the applicability of x-ray strain imaging using the edge illumination technique in biomedical applications.

Strain imaging using conventional x-ray tomography is a widely established technique for investigating the mechanical deformation of materials, including cement and batteries. However, its biomedical applications are primarily restricted to bone tissue due to the low contrast of soft tissues. X-ray phase contrast imaging, offering superior contrast-to-noise ratios in soft tissues, can in principle overcome this limitation. This study explores the feasibility of x-ray strain imaging for soft tissues using edge illumination (EI), a laboratory-based x-ray phase contrast technique. A phantom mimicking the mechanical properties of healthy and tumorous soft tissues, with a stiff inclusion invisible to conventional x-ray imaging, was tested alongside chicken soft tissue fixed in ethanol. While our study confirmed that EI phase contrast imaging provides improved contrast for such samples compared to absorption imaging, it also revealed a reduction in strain retrieval precision. Artefacts caused by absorbing bridges in the mask design and errors arising from differential phase signal integration, which vary spatially between scans, were identified as key limiting factors. Consequently, EI phase contrast strain imaging was unable to locate phantom inclusions based on mechanical contrast. However, EI's capability to increase spatial sampling frequency without compromising the field of view improved strain retrieval precision using its absorption contrast beyond that achieved with conventional x-ray strain imaging. These findings highlight the potential and challenges of applying EI to strain analysis in soft tissues, providing insights into its limitations and opportunities for further improvement.