MAXPCI · Maximizing sensitivity and resolution in edge illumination - based X-ray phase-contrast imaging methods

Maximizing sensitivity and resolution in edge illumination - based X-ray phase-contrast imaging methods

X-ray phase-contrast imaging (XPCi) techniques have attracted considerable research interest in recent years, thanks to their ability to provide greatly increased image contrast compared to conventional X-ray methods. Being based on measuring the phase/refraction of the X-rays instead of their absorption within the sample, they can produce very high image contrast even when absorption differences are tiny. However, widespread use of XPCi has been so far hampered by the beam coherence requirements of such techniques, preventing efficient application outside of synchrotrons, and by the large doses and long exposure time needed when these are translated to conventional X-ray sources. Edge illumination (EI) XPCi, developed at University College London (UCL), can potentially remove most of these roadblocks, thanks to a simple setup applicable to conventional laboratory X-ray sources. The aim of this Grant was twofold: 1) to further develop the EI technique, both theoretically and experimentally, to obtain significant improvements in the achievable phase sensitivity and spatial resolution; 2) to apply these advances in both synchrotron and laboratory setups for specific applications in the biomedical, materials science and industrial fields. The research carried out during this 4-year Grant lead to several important results. A quantitative phase retrieval method was developed for synchrotron setups (Diemoz et al., Phys. Rev. Lett. 110, 138105, 2013) and then extended to laboratory setups based on X-ray tubes (Diemoz et al., Appl. Phys. Lett. 103, 244104, 2013). In its synchrotron implementation, in particular, this method enabled the achievement of unprecedented angular resolutions down to few nanoradians. Moreover, several studies on the spatial resolution and sensitivity of the EI technique were carried out (among the various publications, we can mention Diemoz et al., Phil. Trans. R. Soc. A 372, 20130128, 2014, Diemoz et al., Opt. Express 22, 15514, 2014, Diemoz et al., Opt. Express 22, 28199, 2014, Diemoz et al., Opt. Express 24, 11250, 2016). These studies provide a deep insight into the technique and enable optimizing sensitivity and spatial resolution when designing new setups for specific applications. A single-shot phase retrieval method, based on extracting the sample phase information from a single input image, was developed initially for use with synchrotron radiation (Diemoz et al., J Synchrotron Radiat. 22, 1072, 2015, Diemoz et al., Physica Medica 32, 1759, 2016). The need of only a single input image significantly simplifies the acquisition procedure and provides a way to reduce both acquisition time and radiation dose to the sample. This is particularly useful for biomedical applications, as well as in computed tomography (CT), where several projection images around the sample need to be acquired typically leading to long acquisition times and high doses. This method was very recently extended to laboratory setups, leading to unprecedented times of few minutes to perform a full XPCi CT (Diemoz et al., Phys. Rev. Appl. 7, 044029, 2017), compared to previous times of tens of minutes or hours. Finally, a breakthrough in medical imaging was achieved thanks to the methods developed by the Fellow, where reduction of radiation doses by a factor of 10 compared to clinical practice was demonstrated (Diemoz et al., Phys. Med. Biol. 61, 8750, 2016). This result was achieved by exploiting the nanoradian sensitivity synchrotron setup mentioned and the single-shot retrieval method, and might have profound impact on clinical diagnostics should its translation to laboratory sources be successful.

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