The ability to image the inside of an object is one of the driving forces of scientific progress. Applications occur in almost all areas of science and engineering, including the whole of medical imaging, non-destructive testing, geophysics and material science. In industry imaging is frequently employed for process monitoring and quality assurance. A further important application is security monitoring like for instance airport luggage screening.Medical imaging is the application which affects the general public the most. In medicine a wide range of imaging modalities is used to assist the diagnosis. Commonly used techniques include Magnetic Resonance Imaging (MRI) and X-ray Computed Tomography (CT). Unfortunately, even using state-of-the-art imaging equipment these procedures can be either very time consuming, as in the case of an MRI scan or the patient is exposed to ionising radiation which is potentially harmful, like in CT. Both procedures would greatly benefit from reducing the number of measurements, which are necessary to reconstruct the image without compromising its diagnostic value. This almost sounds like a lost cause but it turns out it is not!Think about compression algorithms such as JPEG, which allow to significantly reduce the size of an image and later are able to restore it seemingly without visual losses. We say images are compressible. Compression standards like JPEG exploit this fact by efficiently representing images with significantly fewer numbers than the number of pixels in the original image. Mathematically, this is achieved by representing the image in a basis in which most of its coefficients are so small that they can be set to zero without visibly diminishing the quality of the image. We call such a representation sparse.Would it not be great if one could directly acquire an image in this compact representation?In recent years this question has been affirmatively answered. It turns out that under certain assumptions it is indeed possible to make such compressed measurements and to subsequently recover the image almost completely. For applications like MRI and CT this means shorter scanning times and reduced radiation exposure.However, to be able to benefit from this new sensing paradigm it is necessary to modify both, the measurement procedure and the reconstructing algorithm. This fellowship addressed exactly this problem for a wide range of imaging modalities including, CT, Tomosynthesis and Optical Tomography. It develops new ways of data acquisition and new algorithms to reconstruct the image from this data. It addresses some fundamental issues concerned with the conditions on the design of the measurement and limits of what is feasible under these conditions. It explores ways of further improving the reconstruction by incorporating prior knowledge on the object. The new Sparse Way of imaging has the potential to push boundaries of what is achievable at present in terms of resolution, data acquisition time, and radiation dose. In close collaboration with experimentalists at UCL the developed methodology will be tested on real-life applications. The research will benefit from collaboration with leading experts in the field and Rapiscan Systems, manufacturer of a wide range of security monitoring equipment.Imaging is an essential technology in science and engineering. Advances in many areas depend on a steady progress of existing imaging techniques and the development of novel approaches. The research community working on sparsity-enhanced imaging has been steadily growing over the last couple of years and it has the potential to take the lead in the more general field of imaging in the future. This fellowship will be at the forefront of this exciting research area, addressing timely and relevant real-life problems. It will strengthen the expertise of the UK in image reconstruction by delivering contributions, which will have a major impact in the field.

There are many examples when taking a transmission X-ray image where correct interpretation of that image would benefit from being able to correctly identify and characterise the materials that are present. If the object is anything other than a thin sheet the ability to isolate and characterise materials in 3D space becomes important. An example where this ability could transform the use of X-ray imaging is security. We will target four areas of application: 1. Explosives and weapons - Weapons and explosives illegally imported into the UK are used in violent crime and terrorist activities. Detection and identification of these items at UK points of entry is a priority for the UK Government and is key to reducing crime and disrupting the UK based terrorist threat. 2. Illicit drugs - The use of illicit drugs costs the UK £15.4 billion per year, and has massive implications for public health due to physical harm to users, drug dependencies, and the effect on families, community and society. The UK Government implemented a new strategy in 2010 with a main aim of restricting the supply of drugs, and the Home Office CAST is very active in developing new technology for the detection of drugs and other contraband substances. 3. New psychoactive substances (NPS) - Similarly NPS or 'legal highs' can carry serious health risks. Typically the chemicals they contain are not endorsed for human consumption and the resulting effects are unknown and unpredictable. In a recent review, the UK Government outlined an action plan for dealing with the growing NPS problem. Central to the action plan was for the UK Border Agency to be able to identify shipments of NPS entering the UK so they can be seized and destroyed. 4. Counterfeit drugs - The sale of substandard and counterfeit pharmaceutical products accounts for 10% of global trade and is affecting many countries (mainly developing countries but also developed countries to a lesser extent), causing serious downstream expense, resource shortages and detriment to health. One of the main aims of the UK Medicines and Healthcare Regulatory Agency (MHRA) is preventing counterfeit drugs entering the supply chain with more responsibility being put on the wholesaler to ensure drugs are sourced from legitimate suppliers and to report any suspicious activity. The proposal is to deliver an X-ray imaging and analysis system that is capable of non-invasively identifying explosives, illicit drugs, legal highs and counterfeit pharmaceuticals within baggage, packets, boxes and other containers. The system will provide high resolution transmission images as well as the analysis and position of selected materials within a larger 3D volume (e.g. a packet of illegal drugs within a parcel containing other items). Central to this project is a novel X-ray diffraction technique developed at UCL with Home Office and Department of Homeland Security backing, which has been proven to be highly effective for this purpose. This will now be enhanced such that rapid, full 3D capability will allow larger, more complex containers, as are found in real-world applications, to be analysed.

Border security is a high priority. The detection of contraband, narcotics, firearms etc. requires improved technical solutions to improve the identification of these materials at entry points and elsewhere. In this proposal we will investigate the use of backscattered x-rays to produce a three dimensional image of the materials inside cargo that is being carried in vehicles or containers. Using a pulsed x-ray source the time of flight of the backscattered x-rays will be measured with an array of scintillation detectors in order to obtain data that can be used to create a three dimensional image. Preliminary experiments at the VELA facility at Daresbury using a single detector have shown a relationship between the time of flight and the position and composition of an object. As the time of flight is a few nanoseconds it is necessary to develop a fast digital data acquisition system for the detector array. This data acquisition development and the use of the system in two sets of experiments are the focus of this proposal. The array of up to eight scintillation detectors and the data acquisition system will be used at the VELA facility at Daresbury to collect data that will be later analysed to show its potential for producing three dimensional images. The system will then be used a Rapiscan's facility at Stoke where the pulsed x-ray beam is more like those that could be widely deployed. These experiments will investigate improving the response of the system and the algorithms developed in the first part of the work.

X-ray screening is high priority for securing borders from the influx of firearms, narcotics, and contraband. The ability of an x-ray screening system to detect photons attenuated by dense cargo directly affects the radiographic image quality that an operator uses to identify such illicit material. When screening cargo and vehicles, high-energy high-dose pulsed linear accelerators are used to generate the x rays. The detection package integrates the signal over the duration of a single pulse and this forms the basis of each pixel value in the image. However, with no means to reject low-energy photons scattered into the detectors or electronic dark current, the signals include a large degree of noise that distorts the final radiographic images. The technological advances in recent years and the exploitation of spectroscopic techniques present an opportunity to utilise novel detector material and off-the-shelf fast electronic components to identify individual photons. This will vastly improve the performance of screening systems and increase image quality, particularly in areas of high attenuation. To this end, this project seeks to investigate new detector material, design, construct and test a prototype detection system capable of photon counting in such high x-ray flux environments. Detector characterisation and design will be carried out at the University of Manchester. Experimental investigations will require the use of the new Compact Linac facility at Daresbury laboratory, capable of producing low-dose x-ray pulses so that algorithms to control the detection package can be developed and the limitations obtained. The detection package will then be used at Rapiscan Systems facility at Stoke using a field-ready linac to prove its capabilities.

X-ray screening is high priority for securing borders from the influx of firearms, narcotics, and contraband. The ability of an x-ray screening system to detect photons attenuated by dense cargo directly affects the radiographic image quality that an operator uses to identify such illicit material. When screening cargo and vehicles, high-energy high-dose pulsed linear accelerators are used to generate the x rays. The detection package integrates the signal over the duration of a single pulse and this forms the basis of each pixel value in the image. However, with no means to reject low-energy photons scattered into the detectors or electronic dark current, the signals include a large degree of noise that distorts the final radiographic images. The technological advances in recent years and the exploitation of spectroscopic techniques present an opportunity to utilise novel detector material and off-the-shelf fast electronic components to identify individual photons. This will vastly improve the performance of screening systems and increase image quality, particularly in areas of high attenuation. To this end, this project seeks to investigate new detector material, design, construct and test a prototype detection system capable of photon counting in such high x-ray flux environments. Detector characterisation and design will be carried out at the University of Manchester. Experimental investigations will require the use of the new Compact Linac facility at Daresbury laboratory, capable of producing low-dose x-ray pulses so that algorithms to control the detection package can be developed and the limitations obtained. The detection package will then be used at Rapiscan Systems facility at Stoke using a field-ready linac to prove its capabilities.