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Medical Physics and Biomedical Engineering

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Advanced X-Ray Imaging Group (AXIm)

AXIm Research Group

Research

We are a multi-PI collaboration aiming to develop novel X-ray image formation techniques and to deploy them with the very latest developments in source and detector technology.

One of our key interests is x-ray phase contrast imaging (XPCI) – a revolutionary approach where variations in x-ray phase are exploited to generate image contrast, rather than attenuation, as has been the convention since x-ray imaging was first developed. XPCI has been shown to significantly enhance the visibility of all details in an x-ray image, and to enable the detection of features classically considered x-ray invisible – with applications in a variety of areas, from earlier detection of life-threatening diseases in medicine to improved detection of threat objects in security scans and of minute defects/blemishes in industrial inspections. Scientific applications are also wide ranging, spanning medicine, biology, energy, materials science, archeology, cultural heritage preservation and others.

As well as XPCI our research covers topics such as x-ray microscopy, novel x-ray detectors, new x-ray source technologies, methods for fast CT and micro-CT, resolution enhancement, dark-field and ultra-small angle scattering, dual and multiple-energy imaging and the development of theoretical models which underpin these techniques.

A key breakthrough – XPCI with conventional, incoherent laboratory sources

Most XPCI methods are limited to very specialized facilities called synchrotrons, of which there are approximately only 50 in the world. This is because such methods require a source of high spatial coherence (i.e., all of the x-rays originate from a very small spot) in order to work. The only alternatives to synchrotron radiation are microfocal sources, or collimated conventional sources to artificially increase the source coherence – both of which limit the available x-ray flux leading to unfeasibly long exposure times. The AXIm group has developed a method that employs uncollimated conventional sources, i.e. x-ray tubes like those found widely in clinics throughout the world, without filtering the x-ray beam in any way. This means that the full flux generated by the source is used in image formation, thus allowing clinically compatible image acquisition times. 

. More information can be found in the following links from Nature and Scientific American. A summary of our tech-transfer activities was recently provided in an EPSRC press release
    Dynamic, multi-modal imaging of additive manufacturing

    Our phase methods use apertured masks to make x-ray systems sensitive to phase effects: these are extracted by analysing the distortions in the beamlets created by the mask. If the detector resolution is smaller than the beamlets, the sample’s attenuation, phase and scatter signals can be simultaneously extracted from a single frame. However, the resolution will be limited by the spacing between the apertures. To overcome this, we have collected images while continuously scanning the mask in front of the sample. The latter was an aluminium-based powder bed, molten in real time by a high-powered laser. The method produces three complementary and automatically registered image sequences, basically attenuation, phase and scatter videos of the powder as it melts. Not only did this show that the formation of liquid droplets is detected much earlier in the phase and scatter videos than in the attenuation ones; it also allowed tracking the movement of the powder particles leading to the identification of “accumulation zones” where the droplets subsequently form. In other words, the method allows predicting melting locations before the melting actually begins. Calibration of the scatter signal also enabled estimating the local thickness of unfused powder, i.e. the extraction of a degree of 3D information from a 2D image.

    Dynamic sequence showing how the formation of liquid droplets becomes apparent
    Dynamic sequence showing how the formation of liquid droplets becomes apparent much earlier in the phase (middle row) and dark-field (bottom row) images compared to conventional x-ray attenuation (top row). Time (in milliseconds) from when the laser hits the powder bed is reported in all images.

     

    • Original paper: Massimi L, Clark SJ, Marussi S, Doherty A, Schulz J, Marathe S, Rau C, Endrizzi M, Lee PD and Olivo A “Dynamic, multi-contrast x-ray imaging method applied to additive manufacturing”, Phys. Rev. Lett. 127 (2021) 215503