Near Field ptychography with a laboratory x-ray source: a new tool for brain tissue studies and beyond

This project aims to develop a new, laboratory-based, x-ray quantitative phase contrast imaging (QPI) technique, namely near-field ptychography (NFPty), ideal for multi-scale imaging of weakly absorbing hierarchical samples, such as biological tissues. NFPty offers resolution bridging that available through other lab-based QPI techniques, and the high resolution of coherent diffraction imaging methods.
X-ray imaging (XI) is a powerful tool for investigating matter non-destructively, with applications encompassing the life and physical sciences. Synchrotrons are the best instruments for performing XI; however, their small number makes access competitive, it enables fundamental science studies but not everyday applications. To serve a larger community, from academia to industry, it is essential to translate the x-ray imaging techniques born at synchrotrons to laboratory sources, by developing ways to work around the degraded quality of the x-ray beam. X-ray phase contrast imaging (XPCI) is a subset of x-ray imaging that allows imaging weakly absorbing specimens and differentiating materials with similar absorption properties. Different implementations exist: from the simplest in-line holography to edge illumination, grating interferometry, near and far-field ptychography. These imaging tools are available at synchrotron facilities and some of them, e.g. edge illumination, grating interferometry, have been successfully adapted to laboratory sources. NFPty has not yet been exported to laboratory but it is a promising candidate: NFPty requires a simple setup, has relaxed x-ray beam quality requirements, and benefits from robust reconstruction algorithms.
This project will translate NFPty into the lab-environment to make it available to a large user community. The project uses simulations and experiments to adapt the method to the lower flux and x-ray quality of the laboratory sources and develop a dedicated instrument. The project will be based at UCL, within the Advanced X-ray Imaging Group whose activity is focused on developing new x-ray imaging techniques for laboratory sources. At UCL different x-ray sources (from standard rotating anode to the novel Liquid Metal Jet) will be available for the experiments.
To maximise the impact of the project, the research will be driven by a case study in brain imaging, with the ultimate aim of demonstrating the technique's potential in that important area. By working closely with experts in the field (Dr Palombo from Cardiff University, Prof Parker from UCL and, Dr Fratini from CNR-Nanotec Rome), the lab-based NFPty will be applied to image brain tissue and brain phantoms and use the acquired data to validate diffusion Magnetic Resonance Imaging (dMRI). dMRI is a key tool for brain study and diagnosis. However, the interpretation of dMRI signal and the validation of the analysis are challenging because of the multiscale nature of the task. The validation relies on data from ex-vivo samples, software phantoms or physical phantom. Physical phantoms have the advantage of being realistic and controllable while preventing animal sacrifice. Nevertheless, the creation of useful brain biomimetic phantoms requires accurate characterization of the phantom structure at micrometric resolution and specific contrast for cellular structures. This information can be directly obtained by using multiscale high-resolution XPCI at synchrotrons, but the limited access to these facilities limits the available statistics. This project will make it possible to acquire these data in a standard laboratory by using NFPty. The programme will produce a new instrument with adjustable field of view from 100s of microns to millimetres (scale of the neuron's arrangements and typical MRI voxel), with sub-micron resolution (scale of the cellular/sub-cellular structures). The acquired data will be instrumental in understanding brain structure, guiding the development of better phantoms, and driving the validation of dMRI.